the water vascular system and functional morphology of paleozoic asteroids

The water vascular system and functional morphology of Paleozoic asteroids DANIEL B. BLAKE AND THOMAS E. GUENSBURG

Blake, Daniel B. & Guensburg, Thomas E. 1988 07 15: The water vascular system and functional morphology of Paleozoic asteroids. Lethaia, Vol. 21, pp. 189-206. Oslo. ISSN 00241164.

Asteroids of all geologic ages share a single basic body form, surlicial skeletal arrangement, and aspects of water vascular construction. In almost all described Paleozoic species, however, either podial pores to the interior of the arm were lacking, or they are directed laterally, above the adambulacrals. They are internal and above the ambulacrals in known post-Paleozoic species and the Pennsylvanian Calliasterellu. Certain features of the ambulacral skeletal arrangement also differ. Calliasterella is the closest known Paleozoic relative of post-Paleozoic asteroids. Classifications of asteroids that stress only overall form and surticial skeletal arrangement erroneously include Paleozoic and Holocene species in common ordinal or even lower level groupings. Taxonomic revision is premature: however, most known Paleozoic asteroids represent primitive lineages. Transitional forms allow reconstruction of events leading to the modern arrangement. Ampullar and skeletal arrangements of post-Paleozoic asteroids appear to offer some functional advantages over those of their precursors, but as early as the Ordovician, diverse feeding habits had evolved and ecological roles paralleled those of Holocene species. 0 Asteroidea, Echinodermata, functional morphology, phylogeny, Paleozoic.

Daniel B. Blake, Department of Geology, University of Illinois, Urbana, Illinok 61801, U.S.A.; Thomas E. Guensburg, Department of Earth Science and Geography, Southern Illinois University, Edwardsuille, Illinois 62026, U.S.A.; 30th June, 1987.

LETHAIA

Paleozoic asteroids are rare fossils, and few specimens are preserved well enough to show many basic morphological details clearly. As a result, although many important observations have been made through the years, classifications, phy- logenies and functional interpretations are generally unsatisfactory. Asteroids are significant today in many communities (e.g., Menge 1982) and they are likely to have been similarly important in the past; it is therefore desirable to deter- mine as much of their history as is possible.

It is the purpose of this paper to evaluate aspects of the functional, taxonomic and phylogenetic significance of some particularly well preserved Paleozoic asteroids. The water vascular system. is critical; aspects of it and associated ambulacral column ossicles differ from those of post-Paleozoic asteroids. The oral frame is important but not stressed here because of difficulties in obtaining adequate materials. Diskussion of Holocene asteroids provides background before continuing with evaluation of selected fossils; certain taxonomic implications are noted but taxonomic revision is considered premature.

Arrangement and function in post- Paleozoic asteroids Morphological arrangement of the water vascular and associated ossicular systems in contemporary asteroids has been described by a number of authors (e.g., Hyman 1955), and only need be summarized here.

The radial canal of the water vascular system extends along the midline of the arm below the ambulacrals (Fig. 1D). One lateral canal extends abradially between and below each two successive ambulacrals, and joins a tube foot. Ampullae are large single or double internal structures above the ambulacrals. Each tube foot connects to its ampullae via a short canal extending between successive ambulacrals at the narrowed mid- ossicular waists.

Ambulacral column articular structures are complex but uniform among Holocene asteroids (Fig. 1A-D). Ambulacral ossicles are paired across the furrow, and each ambulacral abuts two adambulacrals laterally. Ambulacrals articulate across the furrow axis by means of interlocking ridges and grooves, and associated cross-furrow connective tissues. Near the axis on each side of

190 D. B. Blake and T. E. Guensburg LETHAIA 21 (1988)

Fig. 1 . Morphology of modern asteroids. 0 A, B. Pkmm ochracerrs (Asteriidae), aboral (A) and oral (B) views of right side of ambulacral column, note plate-like ambulacrals with quadriserial podial pores (arrow); ambulacrals offset on adambulacrals, well- developed dentition visible in B only, x6. 0 C, D. Asrerodkcides wuncarrrs (Asterodiscididae), aboral (C) and cross-sectional views of arm; ambulacral ossicles stouter than those of Pkmrer, podial pores biserial (arrow), base of ambulacral abuts two successive adambulacrals; strong arch of ambulacrals encloses protective cavity for withdrawn tube feet, furrow closed by adambulacrals, spines; articular structures well developed, x6.

LETHAIA 21 (1988) Paleozoic asteroids 191

the arm, successive ambulacrals are articulated and imbricated proximally. Ambulacrals articulate with adambulacrals by means of small facets and muscles. Muscles below (ventral to) the ambulacral/adambulacral contact area connect successive adambulacrals. Tissues also link adambulacrals, superambulacrals (if present), and lateral ossicles (i.e., actinals or marginals).

Functional significance of the anatomical array is less well understood. Nichols (1972) treated operation of water vascular systems in various classes, and Spencer (1914), Fell (1963), Heddle (1967), Branstrator (1975) and Blake (1981) described movement in various Paleozoic and younger asteroids. Eylers (1976) published a quantitative analysis of the operation of tissues and the skeleton of the extant Asterias forbesi. Because musculature and articular facets are well developed in Holocene asteroids, authors have stressed the importance of ambulacral systems as active contributors to arm movement including raising, lowering and twisting.

A number of authors have noted the ability of asteroids to move and then lock arms in different orientations (e.g., Eylers 1976; Christensen 1970 on use in feeding; Schmid & Schaerer 1981, on possible use in defense). A likely mechanism is what Motokawa (1985:69) termed ‘catch connective tissue’. These are collagenous tissues with or without muscle fibers that are found in the supportive systems of diverse echinoderms, and perhaps asteroids. The tissues are capable of rapid (seconds or minutes) changes in mechanical properties in response to stimulation. Mechanical changes are largely of viscosity rather than elas- ticity, and viscosity is controlled by nerves through the ionic environment of the tissue. Motokawa attributed the ability to change stiff- ness in asteroids to these tissues, but at present their occurrence has only been demonstrated with the spines of Acanthaster (Motokawa 1986). In any event, the tissue has been confirmed in other echinoderms; assuming catch connective tissue is the locking mechanisms for Holocene asteroids, it is also likely to have been present in Paleozoic representatives.

Wainwright (1982) separated arm movement from locking mechanisms. He suggested that local longitudinal arm muscles (not interossicular muscles) bend the arm, with each ossicular junc- tion taking up a tiny amount of the total deformation. Then, at any shape, ambulacral system muscles are contracted and connective liga-

ments made rigid. Ossicles are pulled together so that they meet over large bearing surfaces, and lock the arm. According to this view, interossicular tissues of the ambulacra are used to lock rather than move the arm and therefore the interpretation limits the active contribution of ambulacral column ossicular musculature.

Life modes of Holocene sea stars. - Asteroids today inhabit broad ranges of water temperature and depths, and substrate types. They are largely epifaunal; however, some spend part or most of their time at very shallow infaunal depths. Most of the latter move down vertically during burial, although lateral movement is known. Certain authors have suggested some asteroids are capable of infaunal burrowing, but to our knowl- edge this has not been confirmed. Agassiz (1869) implied some might float; none is known to swim.

Many asteroids have broad feeding habits, see Sloan (1980) and Jangoux (1982). Some are her- bivores or small particle feeders, the latter usually collecting food from the substratum, but sus- pension feeding is known. Sessile colonial organisms - coelenterates, sponges and bryozoans - are also taken.

Others are predators on solitary prey. Pax- illosidans (e.g., Astropecten, Luidia) are intraoral feeders, feeding by pushing food into the mouth using tube feet; particles larger than the disc diameter are sometimes swallowed (Christensen 1970, Fig. 5; Blake 1982, PI. 22). Tube feet are pointed in this order (i.e., a suckered disc is lacking), but they are sticky and handle food items effectively.

Jangoux (1982) recognized two categories of extraoral feeders. A first group, limited to the asteriids, are predators on large, well-protected shell-bearing molluscs. Asteriids exploit natural gaps between prey valves, or they can force valves to partially open. Once a small gap is developed, digestion leads to further opening of the valves.

A second extraoral feeding group exploits relatively unprotected rock-encrusting organisms, as well as coelenterates and echinoderms. Prey either can be seized using pedicellariae and arms, or it is engulfed by the disc and everted stomach. Both intraoral and extraoral feeders use chemo- reception or contact in locating prey, and they move relatively rapidly once potential prey is located.


Morphology of the Pa asteroids studied here

.leozoic

Morphology of the fossils studied here is summarized in Table 1 and illustrated in Figs. 2 to 6. Summary information is in the Appendix.

Morphology of the water vascular system. - The distribution of radial and lateral canals in all of the Paleozoic specimens available to us was the same as that of Holocene asteroids. A reentrant for an axial radial canal is visible in Devonaster, and space for this structure is large in specimens of Petraster, Salteraster, Promopalaeaster dyeri

and P. magnificus. Wherever exposed, podial basins are commodious.

All post-Paleozoic asteroids have internal ampullae above the ambulacra, and internal ampullae above adambulacra seemingly were present in Devonaster. Arnpullar function in Holocene asteroids might be largely respiratory, although they could also be involved in tube foot operation. Nichols (1972) discussed devices other than ampullae available for filling and evacuating tube feet in echinoderms. Holocene asteroids have both radial and lateral water vascular canals equipped with a valve system that permits main- tenance of a hydrostatic head. In addition,

Table I . Ambulacral column morphology in selected Paleozoic.asteroids.

Features Salteraster grandis Promopalaeaster wilroni Petraster speciosus

Adambulacral form Broadly suggestive of modem astropectinids, solasterids; ossicles large, scalloped, overlapping distally(?), not significantly wider than amb articulation surface

Interadambulacral articulation

Ambulacral form

Crosrfurrow interambulacral articulation

Longitudinal interambulacral articulation

Ambulacral/ adambulacral relationships

Side faces with transverse articular ridge overlying large muscle depression

Short, stout, upright in furrow, with strong adoral keel defining podial basin

Contact surfaces apparently large; dentition, if present, not exposed; cross furrow muscle surfaces well developed

Ambulacral side faces closely fitted, undulatory, prominent facets lacking

Ossicles paired, abut on short, wide transverse ridge; adamb facets not apparent

Stout, upright, not significantly overlapping, broader than amb articulation surface so as to support lateral and form arm margin

Side faces with transverse articular ridge overlying large muscle depression

Stout, upright in furrow. somewhat spool-shaped, low prominences separate subsequent podial basins

Arm poorly exposed, contact surfaces probably fairly large

Only aboral part of row exposed; ridges well defined, side face depressions large, concave

Ossicles paired, abut on short, wide articular surface; adamb facets not developed

Upright, not overlapping, transversely elongate, aboral outline hourglass- shaped

Side faces with transverse abradial bar, prominent contact point adradial to bar; large depression

Aboral outline nearly square, ambs closely fitted

Surfaces large, somewhat rounded, closely abutted, with dentition, cross- furrow muscle depressions

Closely fitted, overlapping, with sinuous contact surfaces; small reentrants for longitudinal musculature near adradial margins

Ossicles paired, abut small(?) prominence at adradial end of adamb; muscle facets unclear, possible flange present near adradial aboral margin of adamb


Nichols (1972) reported alternate filling of tube feet in holothuroids, and use of a head bulb in ophiuroids.

Internal ampullae were absent from known Ordovician species because ambulacral ossicles form a solid floor to the ambulacral furrow (Fig. 3A, B, D-F, H-L); ampullar respiration therefore was impossible. Radial channels for radial water canals are large in several Paleozoic fossils, suggesting involvement in tube foot operation; alternatively, any of the other three mechanisms cited by Nichols (1972) might have been employed. Ampullar presence thus seems neither functionally nor morphologically necessary in

Ordovician asteroids; nevertheless, because podial basins are large, discussion here assumes occurrence of either ampullae or their precursor. If external ampullae were present, function presumably was locomotory. A respiratory function would have arisen in conjunction with ampullar migration to an internal position. Internal respiratory ampullae then could have permitted large animal sizes seen in post-Paleozoic asteroids, and extended the range of life habits found in the class.

In Salteraster and Promopalaeaster wilsoni, a lateral pocket adjacent to the podial basin (beneath the ambulacral) is formed by the tapered

Table 1. (continued)

Features Promopalaeaster dyeri Deuonaster eucharis Calliasterella americana

Adambulacral form Upright, not overlapping, Upright, overlap limited or Overlapping proximally, relatively short, high, absent; large, stout, adradial large. scalloped, short, width about width of edge truncated forming lateral, oral arm amb articulation surface margins

lnteradambulacral articulation

Ambulacral form

Cross-furrow interambulacral articulation

Longitudinal interambulacral articulation

Ambulacral/ adambulacral relationships

Side faces with vertical ridges and grooves

Proximal ossicles upright, slab-like, wide, short; distal ossicles similar to those of Salteraster

Proximal ossicles with prominent dentition, large cross-furrow tissue depressions

Ossicles closely fitted, side faces rounded; articular facets not evident

Ossicles paired, abut on transverse ridge extending full width of adamb; no obvious tissue facets

Side faces with transverse articular ridge interlocking along S-contact overlying large muscle depression

Relatively small, stout, upright in furrow

Surfaces bulbous, with two longitudinally aligned medial prominences; dentition, facets not obvious

Side faces closely fitted across ossicular breadth; surfaces broadly imbricated, facets lacking

Ossicles paired, abut on broad, fairly long articular surface; articular facets not developed

Side faces with subtle contact facets above large muscle depression

Relatively small, stout, triangular

Articular surface broad, planar, with distinct transverse ridges and grooves, subtle notching for tissues

Small lateral contact facets, muscle grooves near adradial aboral corner

Ossicles staggered, articular facets rather small, inclined so that ossicles shingled rather than abutted; ambs with large lateral muscle facets


aboral margins of the adambulacrals and the abradial adoral margins of the ambulacrals. The pocket extends essentially the full breadth of the adambulacral and it is bounded abradially by these four ossicles. An arm cross-section of Sal- teraster sp. cf. S. grandis (Figs. 4G, 5A) shows the pocket to be continuous with the space of the ambulacral furrow.

No pores to the interior were developed in Salteraster sp. cf. S. grandis, Promopalaeaster wilsoni, nor Petraster speciosis; ampullae, if present, apparently were restricted to the pockets above the adambulacrals and the furrows. The arrangement of the water vascular system in the precursor of these species is unknown, but if restricted to the exposed part of the furrow, extension over the adambulacrals in at least S. sp. cf. S. grandis required no significant geometric changes.

Petraster speciosus proved particularly difficult to interpret. Ossicles of the commonly illustrated MCZ 557 have been somewhat displaced relative to one another, and they are deeply corroded. In ambulacrals of this specimen, and unlike those of S. sp. cf. S. grandis, notching is not present for lateral pockets, but the adradial edges of the adambulacrals are incised (Fig. 61, J) suggesting possible pores. Specimens of P. speciosus USNM 418218,418219 are incomplete but otherwise less disturbed; they show no indication of pores (Fig. 6E, F). We therefore concluded that the apparent pores in MCZ 557 were produced by ossicular offset and corrosion; Blake & Guensburg (1986) were incorrect in their earlier interpretation of this fossil.

Available Devonaster specimens are preserved without significant damage or distortion, and they are free of matrix. The ambulacral furrow is narrow and as in S. sp. cf. S. grandis, pockets extend laterally above the adambulacrals. The pockets are not closed abradially in Devonaster as they are in S. sp. cf. S. grandis, but instead they open into chambers above the adambulacrals; walls of

these internal chambers are formed by concavities in the surfaces of the adambulacrals and lateral ossicles (Figs. 4B, E, F, J, 5B). Walls of the large connective pores are smooth; there are no flanges to serve as muscle pads, as there are in post- Paleozoic asteroids (Fig. 2A). The pores are too large and well defined to be simple gaps between ossicles for flexure, and they are not oriented as to enhance movement. A number of features suggest the pores enclosed part of the water vascular system. The internal chambers would have provided space for ampullae, the pores are aligned with both internal chambers and podial basins in the furrow, and they are large enough to house a part of the tube foot; little space is available for a withdrawn tube foot in the furrow alone. Finally, no other organ system or function seems appropriate for the pores.

Promopalaeaster dyeri, P. magnificus and Cal- liasterella americana are specialized in different ways. Proximal intervals of arms of P. dyeri and P. magnificus are suggestive of modem asteriids and zoroasterids in that podial basins are arranged in offset quadriserial rows (Figs. 3A, D, E, H, L, 5C); sinuous ridges separate the alternate podial basins. Also, as in the modern asteroids, ambulacrals are foreshortened. Distally, tube feet are biserial and ossicular shape is suggestive of that of P. wilsoni or Salteraster.

Offset podial basins lead to different morphologies between ambulacrals and adambulacrals. Lateral to adradial podial basins, large contact processes mark the adradial aboral cor- ners of adambulacrals (Fig. 3G, L); these are abutted in subsequent ossicles, clearly marking the limits of the furrow space. No pore to the interior was present. Abradial to the facet, however, is a large chamber, defined by the adambulacrals, ambulacrals and laterals (Figs. 3G, 5C). In contrast, lateral to the abradial podial basins there is an abradial pocket that opens to the furrow. This pocket is separated by a low saddle

Fig. 2. Ossicular structure of fossil and modern asteroids. 0 A, approx. x9; 0 B, approx. x6. Anrhenea acum in oblique distal, adoral views. Note podial pores, ambulacrals and adambulacrals are offset, articular structures are strong, compare with Figure 1B. 0 C, approx. x8; 0 D, approx. x6. Prornopalaeaster sp., furrow left, note quadriserial podial basins, strong cross furrow articulation; D based on 3C. 0 E. Devonaster eucharis, cross furrow articulation edentate, large podial pores extend laterally; pores occupy positions housing articular tissues in modem asteroids, see 2A, B, pores presumably accommodated both articular tissues and canals to internal ampullar chambers; adambulacral faces are truncated for furrow closure, compare with Figs. 4C, F; approx. ~ 1 6 . 0 F. Calliasterella amricana, based on specimen of Fig. 6H, approx. X8. Key: ADAMBS, adambulacral ossicles; AMBS, ambulacral ossicles; abb, abradial podial basin; adb, adradial podial basin; af, articularflange, ambulacral to adambulacral; arf, articular flange, ambulacral to ambulacral; as, articular surface, ambulacral to adambulacral; d, cross-furrow dentition; ic, internal chamber; im, inferior cross-furrow muscle surface; mf, muscle flange, ambulacral to adambulacral; mp, muscle pad, adambulacral to adambulacral; pp. podial pore; sm, superior cross-furrow muscle surface.

1% D. B. Blake and T. E. Guensburg LETHAL4 21 (1988)


from an internal chamber similar to that lateral to the adradial podial basin (Figs. 2D, 3C, 5C). No enclosure of the ampulla is possible in the first type, above. An internal ampulla is minimally possible in the chamber associated with the second type because the space over the saddle could be interpreted as a canal. Because Sal- teraster grandis and Promopalaeaster wilsoni lack chambers it is possible that P. magnificus and P. dyeri represent an intermediate stage, with internal ampullae evolving, first on abradial tube feet, or it is possible that quadriserial podial rows precluded an internal ampullae for the adradial basins, and absence reflects loss. Although incom- pletely exposed, no podial pores can be seen in distal arm fragments (where podial rows are biserial) of P. magnificus, USNM 40883 (see Schuchert 1915, PIS. 21, 22) and therefore loss seems unlikely. Finally, and most probably, internal chambers could have functioned as sites for ambulacral column articular tissues (instead of ampullar chambers); analogous musculature occurs between ambulacrals and adambulacrals in Holocene asteroids (Fig. 2A).

Calliasterella americana (Fig. 6A) is unique among described Paleozoic asteroids in that its ambulacrals are similar to those of Holocene asteroids, although other specimens apparently are similar, e.g., Gale 1987. A concavity on the proximal side face of the ambulacral ossicles (Fig. 6B, C), is the passageway for the tube foot leading to the ampullar chamber above the ambulacral, as in Holocene species (Figs. 2A, B, F, 5D). Also as in Holocene asteroids, flanges on both adambulacrals and especially ambulacrals suggest articular tissues extending between the two ossicular types; these tissues occupy the space filled by the ampullar pocket in the other Paleozoic taxa discussed here. Saddle-shaped aboral surfaces of ambulacrals provided space for ampullae. As in many other Paleozoic asteroids, the adambulacrals are relatively wide, and arm pro- portions, as well as the large size of the ampullae

in Holocene asteroids, suggest that ampullae extended over the adambulacrals in Calliasterella americana.

Phylogenetic and taxonomic significance of the ambulacra. - Overall body forms and skeletal development of many Paleozoic asteroids are similar to those of post-Paleozoic representatives; classifications emphasizing these similarities tend to include asteroids of all ages in the same ordinal groups (e.g., Spencer & Wright 1966). Changes in the ambulacral column, possibly including the oral frame, are the only known major evolutionary modifications in asteroids since the Ordovician origins of the class (ignoring the prob- lematic Somasteroidea). Ambulacral arrangements thus provide the best available criteria for phylogenetic reconstruction of early events and development of classifications.

Ambulacral structure is well known for few Paleozoic asteroids; however, no podial pores are present in Ordovician specimens available to the writers, nor in our view have they been satis- factorily demonstrated in other species of this age (as has been suggested, e.g., Branstrator 1975; Gale 1987). They are present, however, in Devonaster, and essentially the Holocene arrangement occurs in Calliasterella; this development was first noted by Schondorf (1909a, b). The stratigraphic sequence suggests evolution of ampullar position in asteroid water vascular systems began with ampullar restriction to an external furrow position, then extension laterally over the adambulacrals, and finally, internally above the ambulacrals.

Operation of the water vascular system in Paleo- zoic and younger asteroids. - Both Paleozoic and younger asteroids committed much space to the water vascular system. Tube feet would seem to be most effective, and probably least vulnerable, if large, firmly anchored, and with a minimum of connective tubing (e.g., lateral canals) between

Fig. 3. 0 A-D, G-J. Prornopdueusrer sp., UI X-6461; (C, G , x8, others, ~ 6 ) . 0 A, D, H. Adoral views of proximal ambulacra, note double row of podial basins on each side of arm axis, compare with Fig. lA, 1C; dentition (arrows) well developed. 0 B, J. Lateral views of inverted ambulacra, rounded surfaces suggest some relative motion although ossicles were closely spaced in life; arrows show half of podial basins. 0 C, G. Lateral views of adambulacrals behind abradial (C) and adradial (G) podial basins, arrows point to chambers for articular (?) tissues, see text for further explanation. 0 I. Aboral view of two proximal ambulacras. 0 E, F. Promopulocasrer dyen', FMNH 10989, E, part of central disc, general ambulacral arrangement (x1.5); F, ambulacrals showing dentition, surfaces for probable cross-furrow tissues and lateral water canals (arrow), x4. OK. Promopalaccrsrer mugnijicus, central portion of disc; as in modem predatory asteriids, the skeleton is of smaU ossicles, the mouth is recessed and orals are small, adambulacrals abut (arrow), and podial pores are quadriserial, FMNH 10981, x 2 . 0 L. Promopaloeastermug~cw, deep quadriserial podial basins, well-developed cross-furrow articular surfaces, USNM 40883A, X4.


the axial radial canal, ampullae (assuming they were present, see above), and the tube feet. This is effectively accomplished in modem asteroids, with large ampullae firmly anchored to the interior medial portions of the ambulacrals (Fig. 1F). Most early Paleozoic species had keel-like or flattened ambulacrals lacking pores extending aboral to the orals (Figs. 3,4D, 6F); these shapes provided large podial basins as well as space for well-developed water vascular canals. These basins appear to have ample space for ampullae; however, as noted above, ampullae may have been absent from early true asteroids. Tube foot function would be similar in both groups. The plate-like form of Paleozoic species seems to reflect demands for space for the external water vascular system rather than any major intrinsic strength limitations of the ambulacral column ossicles and their associated soft tissues.

Ambulacrals of Holocene asteroids are more or less strongly imbricate, and provided with interossicular adradial muscles and contact facets (Figs. 1, 2A, B). Articular surfaces also extend across ambulacra of Paleozoic genera (Figs. 2C-F, 3-6); although of low relief, their size would seem to provide effective articulation. In Calliasterella and post-Paleozoic species, displacement of the ampulla between and above ambulacrals offset all connective tissues adradially, restricting these tissues to the ends of the ossicles. Such offset could inhibit strength as well as the ability to raise and lower the arm in the vertical plane. Musculature in post-Paleozoic asteroids between ambulacrals and adambulacrals might in part be replacement for these lost connections.

External placement of ampullae and large radial canals in early Paleozoic species exposed tissues to predation. Small predators or exoparasites have not been identified from the fossil record, but crustacean exoparasites are known

today (Rottger et al. 1972) and presumably they were present in the Paleozoic. The truncated facets on furrow margins of Deuonaster adambulacrals (Figs. 2E, 4E) reflect an ability to pull furrows together; this protective capability suggests presence of a threat.

Displacement of ampullae to the interior saves space along the length of the arm; the greater the area filled by external ampullae, the less is available for tube feet. The rounded pores (Figs. 2E, 4E, F) in Deuonaster are too large for connective tubing only; the tube feet apparently were capable of partial withdrawal, thus providing protection for tube feet, and reduction of the breadth and exposure of the ambulacral furrow by mini- mizing furrow storage space for water vascular structures.

Lateral chambers for the ampullae, as in Deuonaster, are disadvantageous in that they require a greater length of connective tubing (i.e., lateral canals) between the radial canals, ampullae and tube feet; reduction of the breadth of the furrow reduced the length of connective tubing. There is a loss of potential in narrow ambulacral furrows, however. Blake (1983) argued that Holo- cene asteroid predators on solitary invertebrates have broad ambulacral furrows, providing ample space for many large tube feet, whereas asteroids with narrow furrows feed on colonial prey, or small particles; narrow furrows thus seemingly restrict predatory abilities. In this vein, it is important to note that Promopalaeaster dyeri and P. magnificus, which had largely external podial structures and the broadest furrows among species considered here, also had a variety of other characters typical of modem predatory asteriids (see below). In Calliasterella, ampullae were internal, and

the podia extended between the ambulacrals. This arrangement minimizes connective tubing, and protects and provides sturdy attachment for the

Fig. 4. 0 A, H. Hudsonasrer incomphcs. Although among the most stoutly constructed of Paleozoic asteroids, large concave depressions between marginals (arrows) suggest extensive tissues and arm flexibility. FMNH 8830 (X3, X6). 0 B, E, F, I, J . Deuonasrer eucharis. 0 B. Adambulacrals and laterals form adoral surfaces of arms, oral portion of disc missing, ~ 2 . 5 . 0 E, F. Adradial views of inverted furrows, note large adambulacrals with broad gaps for interadambulacral muscles, truncated adradial facets (arrow); podial pores each enclosed by two adambulacrals and two ambulacrals, subsequent ambulacrals weakly imbricated suggesting relative movement; adradial surfaces of ambulacrals edentate but their rounded nature suggests extensive cross furrow connective tissues; abactinals at bottom of E; X8, X6. 0 I. Dense stereom of ambulacral for water vascular system connective tissues, ~ 3 0 4 ; 0 J. Interior of aboral surface of arms showing concave inferred ampullar basins (arrow) between lateral aborals and marginals, x6. 0 J, USNM 385018, others USNM 385017. 0 C, D, G. Salrerasfer sp. cf. S. grandis, UI X-5775. 0 C, D. Overall form, contorted orientation, small imbricated ossicles, large interadambulacral muscle depressions all reflect arms capable of complex movement in a Middle Ordovician species; podial basins between ambulacrals are large, ambulacrals and adambulacrals paired, compare with Figs. 1A-C. x l , x6. 0 G. Cross section of distal part of arm; arrow shows ridge enclosing part of external ampullar pocket, x 10.

200 D. B. Bloke and T. E. Gunsburg LETHAIA 21 (1988)

Fig. 5. Reconstruction of the water vascular system in Paleozoic asteroids, in cross sectional views of a m , much enlarged; ossicles in bold outline, water vascular tissues are stippled. 0 A. Sakeraster sp. cf. S. grandis, ampullae are partially lateral but confined to external pockets. 0 B. Deoonasrereuchark, ampullae are lateral and internal. 0 C. Promopalaeasrer. abradial ampullae (coarse stipple) are in deeply recessed but external podial basins; chamber between adambulacral and lateral probably housed articular tissues; complex arrangement of abactinals not shown. 0 D. Calliaslerella americana with essentially the modern arrangement, ampullae are shown relatively large, compare with Fig. 1F.

soft tissues. Changes required are offset of the water vascular system, and development of pores between successive ambulacrals. These events require rather small evolutionary steps and all intermediates are functionally plausible.

A second major change between most Paleo- zoic and post-Paleozoic species is in position of the ambulacrals relative to adambulacrals, which are paired in most Paleozoic species, but offset

and articulating with two adambulacrals in Calliasterella and postPaleozoic species. Func- tionally, the alternate (zippered) Holocene arrangement is both relatively sturdy, and allows for more effective muscle placement (Figs. 1,2A, B). Offset of ossicles as an evolutionary sequence seems relatively straightforward and continuously functional, but musculature offers more subtle problems of phylogenetic reconstruction.

Fig. 6. 0 A-D, H. Calliasterclla umericana. 0 A. Overall appearance, tendency to enroll arms, x2, ISGS 42p2. 0 B. Oblique adoral view of articulated ambulacral pair showing podial pore, well-developed ambulacral/adambulacral articular structures, including large apparent muscle flange (arrow), ~ 1 8 . 0 C. Oblique aboral view showing podial pore (arrow), x 12. 0 D. Adradial view of broad, flat adradial face, dentition, X l S . 0 H. Somewhat disrupted ambulacral column ossicles in aboral view. relatively large adambulacrals, interadambulacral muscle gaps, podial pores (arrow), x6. 0 E D , H, ISGS 42P180. 0 E-G, I, J. Perrasrer speciosur. 0 E. Aboral view of row of ambulacrals (left), adambulacrals (right, largely obscured by abactinals), podial pores are lacking, x6, USNM 418218. 0 F. Oral view of ambulacrals in well-preserved arm fragment, some displaced to show articular structures (arrows); relatively wide spinose adambulacrals are paired with ambulacrals, podial pores are lacking; x6, USNM 418219.0 G, I, J, MCZ554.0 G. Overall view shows general appearance suggestive of certain modem species such as Ctenodiscus crispurus, Fig. 1E; distally deflected ambulacrals at mouth frame (arrow) suggest feeding by sediment ingestion, ~ 1 . 5 . 0 I, J. Displaced corroded adambulacrals suggest podial pores (arrows) but better preserved material in Figure E shows these are absent, X6.

LETHAIA 21 (1988) Paleozoic asteroidr 201


In Holocene species, wing-like flanges bear powerful muscles linking ambulacrals to adambulacrals, but these muscles occupy the space filled by lateral portions of the water vascular structures of the Paleozoic species. Facets for such muscles are absent from Paleozoic species, although a flange on a distal ambulacral of Sal- teraster sp. cf. S. grandis (Fig. 4G) is suggestive of muscle flanges on Holocene species (Fig. 2A).

Ampullae in Holocene species are anchored by tissues, and they probably were in the Paleozoic species as well. Walls in the large podial pores in Devonaster, for example (Figs. 2E, 4E, F), are large enough and of correct configuration to have housed tissues for both articulation and anchoring water vascular structures; the fine stereom also suggests anchoring tissues (Fig. 41).

The only described Paleozoic genus with offset ambulacrals, Calliasterella, is also the only one with ampullae above the ambulacrals. Presence of water vascular tissues above the adambulacrals would have obstructed ambulacral/adambulacral ossicular offset, but there are at least three advantages to shifting the water vascular system above the ambulacra. First, offset reduces the dimensions of the water vascular system; sec- ondly it permits offset and strengthening of the ambulacral-adambulacral linkage, and finally, it allows development of a more effective ambulacral-adambulacral tissue linkage.

Modes of life of Paleozoic asteroids It is the writers’ view that as early as the middle and late Ordovician, modes of life of asteroids broadly paralleled those seen today. Gale (1987) was of a different opinion. This author considered ossicles of many Ordovician and Silurian asteroids to have been firmly abutted and weakly articulated. These relationships, he suggested, reflect generally passive habits: ‘All known lower Paleo- zoic asteroids lacked musculature between the ambulacral groove ossicles, and thus were rather inflexible animals, incapable of complex arm movements. They lived on muds and sands by ingestion of the substrate, probably shoveling sediment into the open peristome with the proximal tube feet . . .’ (Gale 1987:129). Our con- tradictory interpretation of diverse life habits is based on the following arguments.

Despite the ambulacral differences discussed

above, Paleozoic and Holocene asteroids share a common structural plan amenable to adaptation to a variety of habits and habitats. All asteroids, as far as is known, were and remain mobile organisms with unfused skeletons consisting of pro- portionately small more or less imbricate ossicles imbedded in more or less extensive muscles and connective tissues; the ‘system is inherently flexible. Holocene asteroids make use of flexibility provided by this arrangement in conforming to the substrate, in manipulating food, and in righting following inversion. Paleozoic asteroids were subject to demands comparable to those encountered by Holocene species; course clasts would have rendered their substrates irregular for example, and subjected them to potential inversion by water movement or passing organisms. Because of the common body plan, potential behavioral range is judged by us to have been similar.

Holocene asteroids are behaviorly diverse. For example, asteriids and solasterids generally are large and active predators, whereas many others feed on much smaller particles. Morphologies of Paleozoic asteroids are also varied, suggesting diversity of habit, see comments on specific taxa (below).

Size is important. Holocene predatory asteriids and astropectinids are large relative to their prey, and certain Paleozoic genera (e.g., Promo- palaeaster, Urasterella) are large relative to most species found around them.

Based on the form and size of channelways and podial and ampullar basins in Paleozoic asteroids, water vascular structures were well differentiated and large, allowing well-developed manipulative abilities. Presence or absence of suckered discs in the Paleozoic is uncertain (the writers are uncon- vinced by the illustration of Gale 1987) but Astro- pecten and Luidia are effective predators today without such structures. Paine (1926) found that suckered discs accounted for only a little over one-half of the adhesion capabilities of the tube feet of Asterias vulgaris; she attributed the remainder to other factors, citing stickiness. Tor- tonese (1947) found that Astropecten can climb and cling to glass walls for long periods. His illustrations suggest that structural differences between suckered (in Marthasterias glacialis) and unsuckered (in Astropecten aranciacus) tube feet are limited. Thus, even if discs were absent from Paleozoic species, no simple behavioral restriction can be inferred.


Ambulacral and adambulacral articular structures, on the whole, are comparatively weakly developed among Paleozoic species. Structures between successive adambulacrals are well developed, however, and cross-furrow structures range from powerful, with a wide range of motion, in Promopalaeaster dyeri, to seemingly rather inflexible, as in Calliasterella. In Calliasterella, the ambulacral adradial surface is broad and flat (Fig. 6D, H), suggesting limited movement across the furrow. Cross-furrow flexure closes and protects this channel; in Calliasterella, protection was provided by the broad adambulacrals (Fig. 5D) and coiling of the arms in the vertical plane (Fig. 6A). In most Paleozoic species, longitudinal ambulacral articular structures seem somewhat limited, although imbricated ossicular shapes demonstrate the potential for significant relative movement. Further, as noted above, articular tissues apparently were developed along the full breadth of the ambulacral, and not restricted to the adradial end, as in Holocene asteroids. Gale (1987:119) rejected Branstrator’s (1975) opinion that muscles linked ambulacral ossicles in the Ordovician Petraster speciosus; the complex articular surfaces and gaps found in this species (Fig. 6F) lead us to agree with Branstrator.

Adambulacral/adambulacral articular structures are least developed, and they abutted over rather small surfaces, but articulation probably was sturdy because ambulacrals and adambulacrals commonly are preserved in or near life positions. These relationships seemingly must reflect strong anchoring tissues; if tissues were strong, then the potential for effective articulation is present.

Certain Paleozoic asteroids (e.g., Devonaster, Hudsonaster) are constructed of hrge block-like ossicles, suggesting inflexibility, yet the amount of displacement necessary between subsequent ossicles in order to achieve significant arm movement is small. One of the smaller and most stout of the Paleozoic genera, Hudsonaster, has large depressions on the abutted side faces of marginals (Fig. 4A, H), implying the presence of significant articular tissues and flexibility. Strong interadambulacral muscle depressions are also found in this genus. Even a relatively small asteroid, such as the Devonaster illustrated here, has about 25 ambulacral/adambulacral pairs along the arm; relative displacement of only a few degrees between subsequent ossicles can provide significant orientation changes along the length of the

arm. Large interadambulacral (Fig. 4E, F) or intermarginal (Fig. 4A, H) tissue depressions suggest flexibility in these genera.

Even if ambulacral column articular structures were relatively weak, compensatory mechanisms seemingly were present. Muscles capable of flexing the arm are present in the inner body wall of Holocene asteroids, and presumably were present in ancient species as well.

Because catch connective tissues (see Moto- kawa 1985; above) are widespread in the phylum, and some locking mechanism occurs in Holocene asteroids, it is probable that Paleozoic species also had this important functional capability. Thus, as Holocene species lock during predation (e.g., Christensen 1957), so ancient species might have locked over prey, then used large tube feet (evi- denced by large basins) for prey manipulation. It is not clear that prominent articulary structures are necessary for effective manipulation of even relatively larger prey.

Last is the nature of food available in the Paleozoic. Among Holocene asteroids, apparently asteriids alone can cope with the large, well-protected bivalves organisms such as bivalve molluscs (Jangoux 1982: 143), but bivalves of this heavily protected type were not present in Paleo- zoic seas, whose faunas were largely dominated by relatively small brachiopods, bryozoans, pel- matozoans, and generally smaller molluscs. Ordo- vician and later Paleozoic asteroids could have had significant ecological roles as predators in their communities by collecting and ingesting the relatively small and passive organisms that dominated their sea floors.

Comments on life modes of spec$c taxa. - Ossicles of both Salteraster and Promopalaeaster wilsoni were relatively small and more or less imbricated, suggesting flexible bodies. Interadambulacral musculature was strong, the water vascular system well developed, and both species were large relative to species around them. These taxa seemingly could have fed on either large or small prey. They are commonly preserved in orientations that suggest considerable flexibility in life (Fig. 4C). Promopaleaster wilsoni, UI X-4935, was preserved on calcarenite megaripples; overburden was stripped away and therefore no information is available on the burial event. Although ossicles are relatively small, suggesting a flexible body, the specimen is upright, undistorted, and resting directly on the calcarenite; it seemingly was


buried in its life habitat and orientation, and not introduced by current action.

Promopalaeaster dyeri and P. magnif cus share a number of important features with Holocene members of the Asteriidae; the latter are effective predators on large, solitary invertebrates, and the fossils probably were as Well. Both asteriids and the fossils are of similar overall form, large relative to many associated species, and flexible (because ossicles are small but imbricate). Arms are long and sturdy, with fairly small discs allowing a broad range of arm movements. In both, proximal ambulacrals are foreshortened, and tube feet are quadriserial (biserial distally in Promopalaeaster). In both, proximal adambulacrals from adjacent arms abut across the inter- brachium (Fig. 3K), apparently providing an effective structure for moving materials into the mouth (Blake 1987). Cross furrow ambulacral, and interadambulacral articular structures are strong in both, although Promopalaeaster might lack the strong interambulacral musculature and ambulacral-adambulacral musculature present in the asteriids. A depressed oral frame allows asteriids to envelope their prey; Promopalaeaster seems similarly constructed (Fig. 3E, K).

In Petraster, marginals are small enough not to significantly inhibit flexure (Fig. 6G). Transverse channels separate marginals aborally; these are superficially similar to the fascioles found today in many paxillosidans (e.g., Astropecten) and some other genera (e.g., Pseudarchaster, Valvatida). The channels in modem species convey and pro- tect water currents over the surface. In Petraster, abactinals are small but stout, paxilliform ossicles that contacted one another by means of prominent articular flanges, the ossicles are largely separated by papular openings (Fig. 6G, I). In Holocene asteroids, such surfaces are highly flexible.

The three or four proximal-most ambulacrals are progressively graded in sue (Fig. 6G), providing space in the interior for a large gut. In Holocene sediment-feeding (Sloan 1980; Jangoux 1982) porcellanasterids and ctenodiscids, a similar shape (produced by deflection of the first ambulacrals) is present; by analogy, Petraster probably also was a sediment feeder. Holocene genera spend much of their time nestled in shallow depressions, covered by sediment, but no evi- dence is available as to the life position of Petraster.

Deuonaster eucharis, with its stout, closely fit-

ted ossicles is a constructional form lacking an obvious Holocene parallel; certain rather stout ophidiasterids (e.g., Neoferdina) perhaps are closest. Deuonaster fossils typically are undistorted, suggesting either a relatively inflexible body, or at least one that contracted with death. Well-defined interadambulacral gaps for muscles, truncated adradial adambulacral margins, and spaces for ambulacral cross furrow muscles all demonstrate capacity for a wide range of arm movement. Clarke (1912), noting an Occurrence of Deuonaster and larger bivalves, suggested Deuonaster was a predator. Blake (1981) argued that morphology and sue make it an unlikely predator but, like ophidiasterids, it was probably a small particle feeder.

Conclusions (1) Important changes in ambulacral and water vascular structure evolved in asteroids during the latter part of the Paleozoic. Ambulacral structure will be important in further developing a tax- onomy for Paleozoic asteroids, but major taxonomic revision is premature.

(2) Ampullae may or may not have been present in Ordovician asteroids, but commodius podia1 basins suggest presence of ampullae or an ampullar precursor.

(3) Ampullae were external in known Ordovician asteroids, internal and above the ambulacrals in Deuonaster (Devonian), and internal and above the ambulacrals in Calliasterella (Carboniferous). In Calliasterella, ambulacrals and adambulacrals are offset, as they are in all Holocene asteroids; in all other described Paleozoic asteroids, the ossicles of the two types are paired, although currently undescribed specimens suggest the offset pattern was becoming widespread during the late Paleozoic.

(4) Transformation of the earlier growth pattern to the later, demands no obviously unlikely or non-functional evolutionary event.

(5) The closely articulated ossicular arrangements of many Paleozoic species probably reflect firm anchoring of water vascular tissues rather than serious limitations in potential for movement. Displacement of ampullae above the ambulacrals, however, allowed offset of ambulacrals on adjacent adambulacrals and evolution of more complex articular structures.


(6) Ordovician asteroids are morphologically varied, with many features implying occupancy of a broad range of ecological niches. First, (a) a single structural plan is found in asteroids of all ages. In addition, among Ordovician asteroids, there is the presence; (b) of a diversity of morphologies; (c) of individuals of large size; (d) of large and complex water vascular structures (indicated by tissue scars on ossicles); (e) of well- developed ambulacral articular structures in at least many species; ( f ) probably of musculature in the body wall, and catch connective tissues to aid movement; (g) of many smaller, rather passive species to serve as potential prey.

(7) Promopalaeaster dyeri and P. magn$cus are considered to have been active predators, Petraster a sediment feeder, and Devonaster a small particle feeder. Feeding habits of Salteraster sp. cf. S. grandis and Promopalaeaster wilsoni are unclear, but both were flexible and capable of complex movement.

Acknowledgemen,%. - We are indebted to A. B. Smith [B. M. (N.H.)] for review, and to the following individuals for per- mission to study materials in their care, and for loan of specimens: Frederick J. Collier, National Museum of Natural History (USNM); Matthew H. Nitecki, Field Museum of Natural His- tory (FMNH); Ronald Eng, Museum of Comparative Zoology (MCZ); and Christina Strimple, for the specimen of Cal- liasterella [reposited with the Illinois State Geological Survey with the remainder of the materials of Kesling & Strimple (1966), ISGS]. University of Illinois specimens are designated UIX-6461. Joan Apperson and Jessie Knox helped with illustrations. DBB's research was supported in part by a grant from the National Science Foundation.

References Agassiz, A. 1869: On the habits of a few echinoderms. Pro-

ceedings of the Boston Society of Natural History 13,104-107. Blake, D. B. 1981: The new Jurassic sea star genus Eokainnster

and comments on life habits and the origins of the modern Asteroidea. Journal of Paleontology 55, 33-46.

Blake, D. B. 1982: Somasteroidea, Asteroidea, and the affinities of Luidia (Platasterias) latiradiata. Palaeontology 25, 167- 191.

Blake, D. B. 1983: Some biological controls on the distribution of shallow water sea stars. Bulletin of Marine Science33,703- 712.

Blake, D. B. 1987: A classification and phylogeny of post- Paleozoic sea stars (Asteroidea: Echinodermata). Journal of Natural History 21, 481-528.

Blake, D. B. & Guensburg, T. E. 1986: Functional and phylogenetic implications of some well preserved Paleozoic sea stars. Geological Society of America, Abstracts with Programs 1986, San Antonio, 542-543.

Branstrator, J. W. 1975: Podial efficacy of some Ordovician asteroids IEchinodermata) from North America. Bulletins of Atnerican.Paleonto1ogy 67, 57-69. < . ". .

Branstrator, J. W. 1979: Asteroidea (Echinodermata). In Pojeta, J., Jr. (ed.): Contributions to. the Ordovician Paleontology of Kentucky and Nearby States. U.S. Geological Suruey Professional Paper 1066. F1-F7.

Christensen, A. M. 1957: The feeding behavior of the sea star Euasterias troschelli Stimpson. Limnology and Oceanography 2 , 180-197.

Christensen, A. M. 1970: Feeding biology of the sea-star Astro- pecten irregularis Pennant. Ophelia 8, 1-134.

Clarke, J. M. 1912: Early adaptation in the feeding habits of star-fishes. Journal of the Academy of Natural Sciences of Philadelphia. 2nd series 15, 114-118.

Downey, M. E. 1970 Zorocallida, new order, and Doraster constellatus, new genus and species, with notes on the Zoroas- teridae (Echinodermata: Asteroidea). Smithsonian Con- tributions to Zoology 64. 18 pp.

Eylers, J. P. 1976: Aspects of skeletal mechanin of the starfish Asterias forbesii. Journal of Morphology 149, 353-368.

Fell, H. B. 1963: The phylogeny of sea-stars. Philosophical Transactions of the Royal Society of London B 246,381-435.

Gale, A. S. 1987: Phylogeny and classification of the Asteroidea (Echinodermata). Zoological Journal of the Linnean Society 89, 107-132.

Guensburg, T. E. 1984: Echinodermata of the Middle Ordo- vician Lebanon Limestone, Central Tennessee. Bulletins of American Paleontology 86, no. 319. 100 pp.

Heddle, D. 1967: Versatility of movement and the origin of asteroids. In Millott, N. (ed.): Echinoderm Biology, 125-141. Academic Press, New York.

Hyman, L. H. 1955: The lnuertebrates N Echinodermata. 764 pp McGraw-Hill Book Co. Inc., New York.

Jangoux, M. 1982: Food and feeding mechanisms: Asteroidea. In Jangoux, M. & Lawrence, 3. M. (eds.): Echinoderm Nutrition, 117-159. A. A. Balkema, Rotterdam.

Kesling, R. V. 1%9a: Silicaster, a new genus of Devonian starfish. Contributions from the Museum of Paleontology, The Uniuersity of Michigan 22, 249-261.

Kesling, R. V. 1969b: Three Permian starfish from Western Australia and their bearing on revision of the Asteroidea. Contributions from the Museum of Paleontology. The Llni- uersity of Michigan 22, 361-376.

Kesling, R. V. & Strimple, H. L. 1966: Calliasterella americana, a new starfish from the Pennsylvanian of Illinois. Journal of Paleontology 40, 1157-1166.

Kolata, D. R. 1975: Middle Ordovician echinoderms from northern Illinois and southern Wisconsin. The Paleontological Society Memoir 7 . 74 pp.

McKnight, D. G. 1977: A note on the order Zorocallida (Asteroidea: Echinodermata). New Zealand Oceanographic Institute Recordr 3, 159-161.

Menge, B. A. 1982: Effects of feeding on the environment: Asteroidea. In Jangoux, M. & Lawrence, J. M. (eds.): Echinoderm Nuhition, 521-552. A. A. Balkema, Rotterdam.

Motokawa, T. 1985: Catch connective tissue: The connective tissue with adjustable mechanical properties. In Keegan, B. F. & O'Conner, B. D. S. (eds.): Echinodermata, -74. A. A. Balkema, Rotterdam.

Motokawa, T. 1986: Morphology of spines and spine joint in the crown-of-thorns starfish Acanthter planci (Echinodermata, Asteroida). Zoomorphology 106, 247-253.

Nichols, D. 1972 The water-vascular system in living and fossil echinoderms. Palaeontology IS, 51%538.

Paine, V. L. 1926: Adhesion of the tube. feet in starfishes. The Journal of Exoerimentai Zoolopv 45. 361-366.


Raymond, P. E. 1912: On two new Paleozoic starfish (one of these found near Ottawa), and a new crinoid. Ottawa Natu- ralist 26, 77-81.

Rottger, R., Astheimer, H., Spindler, M. & Steinborn, J. 1972: Okologie von Asrerocheres lilljeborgi, eines auf Henricia san- guinolenta parasitisch lebenden Copepoden. Marine Biology 13, 259-266.

Schmid, P. H. & Schaerer, R. 1981: Predator-prey interaction between two competing sea star species of the genus Astropecten. Marine Ecology 2 , 207-214.

Schondorf, F. 1909a: Palaozoische Seesterne Deutschlands. I. Die echten Asteriden der Rheinischen Grauwacke. Palae- ontographica 65, 37-112.

Schondorf, F. 1909b: Die Asteriden des Russischen Karbon. Palaeontographica 65, 323-338.

Schondorf, F. 1910: Uber einige 'Ophiuriden und Asteriden' des englischen Silur und ihre Bedeatung fur die Systematik palaozoischer Seesterne. lahrbuchern des Nassauischen Ver- eim fur Naturkunde in Wiesbaden 63, 2W256.

Schuchcrt. C. 1915: Revision of Paleozoic Stelleroidea with special reference to North American Asteroidea. Bulletin United States National Museum 88, 1-312.

Sloan, N. A. 1980: Aspects of the feeding biology of asteroids. In Barnes, M. (ed.): Oceanography and Marine Biology Annual Reoiew 18. 57-124.

Spencer, W. K. 1914: British Palaeozoic Asterozoa. Palae- ontographical Society of London Memoir, 1-56.

Spencer, W. K. & Wright, C. W. 1966: Asterozoans. I n Moore, R. C. (ed.): Treatise on Invertebrate Paleontology, Pan U, Echinodermata 3,4107. Geological Society of America and University of Kansas Press, Lawrence.

Tortonese, E. 1947: Struttura istologica dei pedicelli e par- ticolarita locomotrice de alcuni asteroidi. Monitore Zoologico Italian0 56. 7f81 .

Wainwright, S. A. 1982: Structural systems: hydrostats and frameworks. In Taylor, C. R., Johansen, K. & Bolis, L. (eds.): A Companion to Animal Physiology, 325-338. Cam- bridge University Press, Cambridge.

Appendix: Material studied Salteraster grandis (Meek), holotype FMNH 10836, primary radius 65 mm. disc radius 8 mm. specimen quite complete but details not well preserved; Upper Ordovician (Richmondian), Indiana.

Salteraster sp. cf. S. grandis (Meek), UI X-5775, see Guensburg (1984). primary radius about 65 mm, disc radius about 7 mm, disc details largely lost but many arm details well preserved forming basis of discussion here; Middle Ordovician (Black Riveran), Tennessee.

Promopalaeaster wihoni (Raymond), UI X-4935, see Kolata (1975), primary radius about 55 mm, disc radius about 9 mm, aboral surface exposed; Middle Ordovician (Trentonian), Illinois.

Promopalaeaster dueri (Meek), FMNH 10989, longest arm interval about 37 mm but much longer in life, both surfaces of disc exposed; Upper Ordovician (Maysville), Cincinnati, Ohio.

Promopalaeaster magnificus (Miller), FMNH 10981, longest arm interval about 35mm with a few ossicles extending to about 60 mm, oral surface exposed; Upper Ordovician (Rich- mondian), Jefferson Co., Indiana. Syntype USNM 40883-A, fragment of disc, parts of two ambulacral; Upper Ordovician (Maysville), Cincinnati, Ohio area.

Promopalaeaster sp., UI X-6461, six small fragments, all apparently from a single specimen, mostly of ambulacral column ossicles; Upper Ordovician (Richmondian), Kentucky.

Petraster speciosus (Miller and Dyer), holotype MCZ 554, primary radius about 32mm. disc radius about 17mm. aboral surface exposed, specimen is relatively complete but many surface details are leached; Upper Ordovician (Richmwdian), Ohio. USNM 418218, 418219, small fragments, Ulrich collec- tion, Upper Ordovician (Maysville), Covington, Kentucky and Cincinnati, Ohio.

Deoonaster eucharis (Hall) USNM 385017, 385018, both with primary radius about 20 mm, disc radius 7 mm, part of disc and several arms; Middle Devonian (Hamiltonian), New York.

Calliasterella americana (Kesling and Strimple), ISGS 42P1-4. specimens of Kesling and Strimple, and 42P180, new fragments showing ambulacral details, made available by Christina Strimple; Pennsylvanian (Missourian) Illinois.

Calliasterella was based on a single Pennsylvanian species (C. mira) from the Soviet Union. Schondorf (1909b) recognized similarities between Calliasterella and modern forcipulates, and he compared Calliasterella with the extant asteriid Marthasterias glacialis. Downey (1970) assigned the Cdiasteridae and Zoroasteridae to her new order Zorocallida, but McKnight (1977) restricted zorocallidans to modern taxa. Pennsylvanian (Missourian), Illinois.

the water vascular system and functional morphology of paleozoic asteroids

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