water vascular system of the crinoidea camerata

Water Vascular System of the Crinoidea CamerataAuthor(s): Bruce N. HaughSource: Journal of Paleontology, Vol. 47, No. 1 (Jan., 1973), pp. 77-90Published by: SEPM Society for Sedimentary GeologyStable URL: http://www.jstor.org/stable/1302868 .

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JOURNAL OF PALEONTOLOGY, V. 47, NO. 1, P. 77-90, 3 PLS., 8 TEXT-FIGS., JANUARY 1973

WATER VASCULAR SYSTEM OF THE CRINOIDEA CAMERATA

BRUCE N. HAUGH University of California, Los Angeles

ABSTRACT-Examination of the inner surface of hollow specimens and internal chert molds of Mississippian camerate crinoids has revealed some aspects of their water vascular system. Unlike flexible and inadunate crinoids, an external hydropore has never been reported for any camerate crinoid. Small pores, the so-called respiratory pores, adjacent to the arm bases of some camerate crinoids were previously assigned this function, but this interpretation is rejected with the discovery of a completely internal structure interpreted here as an internal hydropore. The water vascular system of the Camerata consists of a hydropore, stone canal, hydrocoel crescent, and radial water canals leading to the arms as in modern crinoids. However, the plan and symmetry differ from that of modern crinoids and extinct flexible and inadunate crinoids. Four morphologic patterns have been detected; three are characterized by bilateral-trimeral symmetry and one by pentameral symmetry. Based on this information it appears that the ontogenetic development of the Camerata differed from that of the other three classes of crinoids. Respiration was probably aided by a fluid-filled coelomic cavity that may have been an active cloacal pump. The function and morphology of the camerate water vascular system more closely resembles that of living holothurians than any other living group of echinoderms.

INTRODUCTION

NVESTIGATIONS of fossil crinoids have dealt almost exclusively with external morphology

that is useful in taxonomy and classification. There are only occasional brief references in the literature to internal morphology of the theca or to preserved internal parts, although the variety and quality of preservation of these are often remarkable. The great number of classical taxonomic studies of fossil crinoids has resulted in a more detailed morphologic knowledge of fossil, than of extant, crinoids. In view of this, it is surprising that very little is known about the internal morphology of fossil crinoids, and far less has been written about inferred soft-part anatomy, functional morphology, and paleophysiology. Occasional references to respiratory pores (Wachsmuth and Springer, 1879-86, and 1897), nerve tracts as interpreted from external plate ornamentation (Bather, 1900; and Spreng and Parks, 1953), and the convoluted organ as the "stomach" in certain camerate crinoids, represents the present state of our knowledge of soft-part anatomy of fossil crinoids.

A detailed examination of interior surfaces of hollow specimens, internal chert molds of thecae, and preserved silicified organs has resulted in the detection of several organ systems in Mississippian camerate crinoids that cannot be observed or inferred by examination of the exterior. Among these are: the digestive system, nervous systems, coelomic systems, respiratory system, and water vascular system. The

structure, function, and ontogeny of the latter are being treated here and eventually a synthe- sis of the other systems should yield new information that will be useful in studying evo- lutionary trends, paleoecology, and paleophysiology of the camerate crinoids.

MATERIAL

The specimens used in this study are all Mississippian, ranging from Osagian (Burling- ton) through early Meramecian (Salem) in age. A correlation chart showing the occurrence of the crinoids selected for study is given in Text-fig. 1. The specimens studied were obtained from: The Springer Collection (S); United States National Museum (USNM); the Rowley Collection at the University of Illinois (RX); Walker Museum Collection at the Chi- cago Natural History Museum (P); the Mu- seum of Comparative Zoology at Harvard Uni- versity (MCZ); and the Palmer Collection of the United States Geological Survey, Washing- ton, D.C. (USNM).

THE ECHINODERM WATER VASCULAR SYSTEM

In living echinoderms the water vascular system usually has a direct connection to the surrounding sea water through the body wall via one or more small interradial pores. A single pore, the hydropore, may pierce an endoskeletal plate in the CD-interradius, or a sieve plate, the madreporite, may be pierced by holes which unite internally to join the stone canal. The stone canal is a tubular vessel which conducts

77



BRUCE N. HAUGH

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Localities

Salem Spergen Limestone Hill

Upper Harrodsburg Limestone

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Lake Valley (New Mexico)

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Lower

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Muldraugh Formation

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TEXT-FIG. 1-Correlation chart. Collecting localities of camerate crinoid specimens examined for water vascular study.* Burlington Limestone collecting localities are near Burlington, Iowa and Louisiana, Missouri. The Boone Formation locality is near Webb City, Missouri.

fluid from the hydropore or madreporite to the hydrocoel ring, the main distributary vessel which gives rise to radial canals for each of the ambulacral rays of the echinoderm. The termi- nal parts of the water vascular system, the tube feet, may take the form of suction devices or tubular mucus-secreting bodies as in crinoids. The tube feet are used primarily for food gathering, respiration, and locomotion. A different arrangement is present in most holothurians in which there is no external opening for the water vascular system. Fluid for the system is derived from the perivisceral coelom via one to many madreporic bodies that are either attached to the inner surface of the body wall by a dorsal mesentery or hang freely in the coelom from a stone canal (Hyman, 1955). The madreporic body is pierced by numerous random ciliated pores and canals, or it may have a winding, an- nular ciliated groove with pores in the bottom. In modern crinoids the water vascular system opens into the perivisceral coelom via several stone canals from the hydrocoel ring; but the coelom is connected directly with the exterior

by numerous interradial pores, the ciliated fun- nels.

WATER VASCULAR ENTRANCE

The structure of the water vascular system of all three subclasses of Paleozoic crinoids is poorly known. The presence of an external hydropore or madreporite in the posterior interray of some inadunate and flexible crinoids has been established, and it seems probable that the rather porous, fleshy surface of the tegmen and anal sac provided entrance for water into the interior of the animal. A hydropore has never been reported for any camerate crinoid, and the rigid solid tegmen and anal tube pre- cludes these as areas of water intake. The lack of a hydropore has resulted in the suggestion that small pores, which pierce the theca adjacent to the ambulacral tracts, served as a means of respiration, and as inlets for the water vascular system. These have become known as respiratory pores. Wachsmuth and Springer (1881, p. 52-53) state that the so-called respiratory pores may be the openings for proximal

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CAMERATE WATER VASCULAR SYSTEM

TEXT-FIG. 2-A, Ambulacral area with open respiratory pore: LS, longitudinal septum; HS, hinge socket of pore cover; AMB, main ambulacral opening; OG, open groove of respiratory pore passageway; BG, blind groove of respiratory pore passageway. B, Detail of respiratory pore cover: PCP, pore cover plates formed from modified pinnulars; FrP, first free pinnule of arm. Note: small letters in parentheses indicate corresponding part designations in the plate figures. (Drawings taken from Batocrinus icosidactvlus Casseday, S 589, pl. 3, figs. 7 & 8.)

pinnules that were fixed into the dorsal cup, their function being either genital openings, or water vascular openings, or both. "The proximal pinnules in recent crinoids contain the genital glands, and it is at least not impossible that the pores as rudimentary pinnules, served as genital organs." However, they had not observed pinnules fixed into the theca at that time (although the Springer collection contains specimens with fixed pinnules still attached) for they write: "in all carboniferous crinoids in which the pores are clearly seen, no fixed pinnules can be traced externally in the test, and apparently no free pinnules were attached to the pores, or they should have been found preserved in some of our specimens." Leaving the problem unresolved they conclude that, "those, [pores] we believe, are said to be in part respiratory and so it is possible that the pores of these Crinoids had both functions." (Wachs- muth and Springer, 1881, p. 53).

A typical occurrence of respiratory pores is illustrated in Batocrinus icosidactylus (P1. 1, fig. 18). Arrow A designates an open respiratory pore. This specimen also reveals the presence of small "cover plates" (designated B), which served to close the pore. A close-up view of one of these pores in another specimen of B. icosidactylus is designated A in Plate 3, fig. 8. It should be noted that the lower part of the

passageway is divided into two chambers by a longitudinal septum (Text-fig. 2a). A small slit (B) just below the pore represents the hinge socket of the pore cover plate that articu- lated on the theca. Arrow C indicates the main ambulacral tract. The covering flap that sealed these pores is composed of the two proximal plates (A and A') of a highly modified fixed pinnule (P1. 3, fig. 7; Text-fig. 2b). Adjacent to the pore cover is the first normal, free pinnule of the arm (B). This structure is con- sistent with Wachsmuth and Springer's pro- posal in 1881 but the water inlet function may now be rejected. Based on studies of the internal morphology of these pores and the discovery of a pore, here interpreted as a hydropore, it appears that they are not related to the water vascular system. In addition, because they are present in some, but not all, families of camerate crinoids (Text-fig. 3), it seems unlikely that they would perform such a critical function. Their probable function and morphology will be discussed in a future publica- tion.

If these pores were not associated with water intake, the water vascular system of camerate crinoids must have been completely internal because no other openings pierce the theca (except the ambulacral tracts and the anal opening). Study of the internal thecal surfaces

79



BRUCE N. HAUGH

TEXT-FIG. 3-Phylogenetic relationships of families of camerate crinoids including known ranges marked by horizontal lines. Occurrence of respiratory pores designated by blackened rectangles. (In part after Moore & Laudon, 1943.)

of many specimens of camerate crinoids has shown this to be the case. A vertically sec- tioned specimen of B. icosidactylus (P1. 1, fig. 11; P1. 3, fig. 2) contains structures interpreted as an internal hydropore (P1. 3, fig. 2, A), and a partly eroded sieve area, or madreporite

(B). Both of these structures are situated in the large posterior oral plate in the CD-interray at the base of the anal tube. As will be demon- strated below, this arrangement or special mod- ifications of it occur in all camerate crinoids studied here. Scanning electron microscopy of

80



CAMERATE TWATER VASCULAR SYSTEM

TEXT-FIG. 4-A, Posterior oral plate of Batocrinus icosidactylus Casseday, containing the entrance of the water vascular system: M, madreporite sieve; ScG, stone canal lateral groove; SC, stone canal within the plate; LS, longitudinal septum of stone canal; HP, internal hydropore. (The normal orientation of the plate is inverted so that the dorsal surface faces up). B, Internal tegminal surface near anal vent of Agaricocrinites brevis (Hall), illustrating water vascular entrance: M, open madreporite; HP, internal hydropore; AV, anal vent. C, water vascular entrance of Agaricocrinites splendens Miller & Gurley: MB, specialized madreporic body, similar to living holothurians; SC, trace of stone canal; GG, expanded hind-gut groove.

this pore has revealed that it opens into a short stone canal that is commonly divided by an incomplete, longitudinal septum (P1. 3, fig. 4, A; Text-fig. 4A). Leading away from the hydropore on the internal surface of the posterior oral plate are two lateral channels (B and B') that are judged to record the position of the proximal branches of the stone canal which connected to the hydrocoel crescent. The bilateral symmetry of the water vascular system of camerate crinoids is evident here and this is the case for the system as a whole (Text- fig. 5). The proximal part of the stone canal is completely contained within the posterior oral plate (Text-fig. 4A). It forms a U-shaped passageway leading to a madreporite that opens into the internal cavity of the anal tube. In

some specimens the madreporite seems to have been a sieve structure (PI. 3, fig. 3, A), in others, the end of the stone canal may have been open (P1. 3, fig. 1, A; Text-fig. 4B), and some even possessed a madreporic body (P1. 3, fig. 5, A; Text-fig. 4C) similar to that which is suspended in the coelom of living holothurians (Hyman, 1955, figs. 61, 67). In all cases the entrance to the water vascular system is closely associated with the distal part of the gut, is interradial in position, and is completely internal.

Fluid for the water vascular system was, therefore, not directly derived from an external source through the respiratory pores but rather came from an internal coelomic space. It also seems unlikely that the so-called respiratory

TEXT-FIG. 5-Schematic plan diagrams of the morphologic variation of the camerate water vascular system. Roman numerals indicate juncture points of radial canals to the hydrocoel; other abbreviations as in previous text-figures.

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EXPLANATION OF PLATE 1

All specimens except Figures 3, 11, 12, 13, 18, and 19 are internal chert molds.

FIG. 1 -Physetocrinus ventricosus (Hall). Probably Burlington Limestone. Dorsal view of tegminal surface showing Type 2 water vascular plan; X 1.0. (R. R. Rowley Coll.) RX 360.

2-Megistocrinus evansii (Owen & Shumard). Burlington Limestone near Louisiana, Mo. Dorsal view of tegminal surface; note filling of stone canal and anal vent but no evidence of radial canals or hydrocoel, Type 4 plan; X 1.0. (R. R. Rowley Coll.) RX 359.

3-Physetocrinus ventricosus (Hall). Probably Burlington Limestone. Inner surface of tegmen with radial canal grooves (arrow); compare with mold of Fig. 4; X 1.0. (Edwin Kirk Coll.) USNM 170559.

4-Physetocrinus ventricosus (Hall). Burlington Limestone near Louisiana, Mo. Dorsal view of tegminal surface showing radial canal ridges for comparison with grooves on an original specimen of Fig. 3; X 0.66. (R. R. Rowley Coll.) RX 350.

5-Cribanocrinus whitei (Hall). Lower Burlington Limestone, Burlington, Iowa. Dorsal view showing ambulacral areas but no trace of water vascular system, Type 4 plan; X 1.0. MCZ 2272.

6-Strotocrilins glyptus (Hall). Burlington Limestone, Louisiana, Mo. Dorsal view showing multiple radial canals and complex central region, Type 2 plan; X 1.0. (R. R. Rowley Coll.) RX 362.

7-Agaricocrinites "convexus" (Hall). Burlington Limestone, Louisiana, Mo. Dorsal view showing Type 3 plan where radial canals disappear centrally; note filling of stone canal on posterior oral plate in center of specimen; X 1.0. (R. R. Rowley Coll.) RX 353.

8--Dorycrinus roemneri (Meek & Worthen). Burlington Limestone, Louisiana, Mo. Dorsal view with deep slots representing former location of subtegminal radial canals of Type 4 plan; Roman numerals indicate juncture of radial canals with hydrocoel; X 1.0. (R. R. Rowley Coll.) RX 358.

9-Actinocrinites "lowei" (Hall). Boone Chert, Webb City, Mo. Dorsal view of a well-preserved specimen with Type 2 plan; Roman numerals indicate junction of radial canals and hydrocoel; X 1.0. (Ernest J. Palmer Coll.) USNM 177130.

10--Etrochocrinus sp. Boone Chert, Webb City, Mo. Dorsal view of specimen with broad, flat radial canal ridges; Type 3 plan; X 1.0. (Ernest J. Palmer Coll.) USNM 177132.

11-Batocrinus icosidactylus Casseday. Salem Limestone, Spergen Hill, Ind. Side view of vertically cut hollow specimen showing internal hydropore (A) and sieve area (B); X 1.3. S 589.

12-Gilbertsocrinus tuberosus (Lyon & Casseday). Muldraugh Formation, Crawfordsville, Ind. Dor- sal view of hollow specimen with no evidence of water vascular system; Type 4 plan; X 1.0. UCLA 48288.

13-Dorycrinus unicornis (Owen & Shumard). Burlington Limestone, Burlington, Iowa. Area around anal vent with madreporic body (A) embedded in posterior oral spine plate, and stone canal grooves (B and B'); X 3.3. MCZ 207.

14-Strotocrinus glyptus (Hall). Burlington Limestone, Louisiana, Mo. Dorsal view of large specimen with well-preserved anastomosing radial canals and complex central area; Type 3 plan; X 0.73. (R. R. Rowley Coll.) RX 356.

15-Strotocrinus regalis (Hall). Burlington Limestone, Louisiana, Mo. Dorsal view with well-preserved single radial canals and Type 1 plan; canals convergent to one point (Roman nu- meral); X 1.0. (R. R. Rowley Coll.) RX 363.

16-Uperocrinus longirostris (Hall). Burlington Limestone, Louisiana, Mo. Dorsal view of specimen with Type 3 plan; X 1.0. (R. R. Rowley Coll.) RX 354.

17-Dorycrinus missouriensis (Shumard). Burlington Limestone, Louisiana, Mo. Dorsal view with faint impressions of radial canals; Type 4 plan; note stone canal joining hydrocoel on posterior side of hydrocoel between IV and V; X 1.0. (R. R. Rowley Coll.) RX 357.

18-Batocrinus icosidactylus Casseday. Salem Limestone, Spergen Hill, Ind. Exterior side view of specimen with cover plates formed from preserved fixed pinnules (B) and respiratory pores (A); X 1.2. S 589.

19-Dorycrinus unicornis (Owen & Shumard) Burlington Limestone, Burlington, Iowa. Interior area near anal vent with madreporic body (A) in the spine plate over the anal vent; X 3.3. MCZ 207.

20-Eretmocrinus sp. Burlington Limestone, Louisiana, Mo. Dorsal view with well-exposed peripheral radial canals (A) and stone canal filling (B); X 1.0. (R. R. Rowley Coll.) RX 30.

21-Physetocrinus asper (Meek & Worthen). Burlington Limestone, Louisiana, Mo. Dorsal view with well-preserved radial canals extending to free arms; Type 1 plan with convergence to one point (I); interradial grooves (N) are former location of hyponeural nerves; X 1.0. (R. R. Rowley Coll.) RX 351.

22-Platycrinites "discoideus" (Owen & Shumard). Burlington Limestone, Louisiana, Mo. Dorsal view with faint impressions of subtegminal ambulacral tracts; filling of stone canal in posterior oral plate is prominent; note growth lines on plate impressions; X 1.0. (R. R. Rowley Coll.) RX 361.

82



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pores provided a significant source of sea water to be used as a respiratory medium.

MORPHOLOGY OF THE WATER VASCULAR SYSTEM

The morphologic plan of the water vascular system in camerate crinoids may be detected in well preserved hollow specimens and on chert molds of thecal interiors. Impressions of other visceral systems are also present. The location of the water vascular system may be detected along the inner surface of the tegminal plates. The trace of the water vascular system commonly forms a single-stranded radial network that is convergent at the internal hydropore or

madreporite (P1. 1, fig. 3; P1. 2, fig. 1). In

living echinoderms the diameter of the hydrocoel ring and radial water vessels is very small, much less than the width of the grooves here interpreted as evidence for their presence in fossil specimens. The grooves on the inner surface of the tegmen of camerate specimens, therefore, indicate only the plan of the water vascular system, not the size of the vessels. The

former water vessels may have been suspended in the grooves by mesenteries attached to the sides of these grooves. In the free arms the radial water vessels of the Camerata probably resided beneath the open food grooves of the ambulacral system as in modern crinoids. Once inside the tegmen, the radial vessels turned up- ward toward the inner surface of the tegmen, becoming dissociated from the ambulacral system. Within the tegmen the food grooves become tubular tracts that attach to the fore-gut at a lower level. The coelomic canals of the arms also diverge from the "food tubes" and connect to the perivisceral coelom below the fore-gut. Thus, these three systems do not re- main intimately associated with one another inside the tegmen. The former location of the hyponeural nervous system is represented by tracts, in the form of raised ridges, that lie interradially alongside the ambulacral areas. The arm ossicles have a corresponding raised nerve ridge along each side of the ambulacral groove. Double hyponeural nerves also characterize the arms of modern crinoids.


All figures 3.75 magnification; figures 1 and 7 are originals, all others internal chert molds.

FIG. 1-Physetocrinus ventricosus (Hall). Probably Burlington Limestone. Inner tegminal surface around anal vent showing radial canal grooves and hydrocoel groove with three points of attachment (Roman numerals); Type 2 plan. (Edwin Kirk Coll.) USNM 170559.

2--Actinocrinites "lowei" (Hall). Boone Chert, Webb City, Mo. Well-preserved chert mold showing three-fold convergence of radial canals (Roman numerals) and bifurcate anterior radial canal near arrow I; Type 2 plan. (Ernest J. Palmer Coll.) USNM 177130.

3-Platycrinites "discoideus" (Owen & Shumard). Burlington Limestone, Louisiana, Mo. Prominent filling of stone canal (A) in posterior oral plate with ambulacral traces (B) leading toward it; slot below (A) indicates former position of the remainder of the stone canal leading to the anal vent, extreme bottom of photo; Type 4 plan. (R. R. Rowley Coll.) RX 361.

4-Megistocrinus evansii (Owen & Shumard). Burlington Limestone, Louisiana, Mo. Prominent filling of stone canal (A) with radiating ambulacral impressions (B) but no trace of radial canals or hydrocoel; anal vent filling, extreme lower part of photo; Type 4 plan. (R. R. Rowley Coll.) RX 359.

5-Eretmocrinus sp. Burlington Limestone, Louisiana, Mo. Radial water canal (A) exposed at pe- riphery, becoming subtegminal centrally; stone canal filling (B) on posterior oral plate (C); remaining oral plates (D) surround the larger posterior oral plate; Type 3 plan. (R. R. Row- ley Coll.) RX 30.

6-Physetocrinus asper (Meek & Worthen). Burlington Limestone, Louisiana, Mo. Chert mold with well-preserved bifurcate anterior radial canal (A and A') and convergence of all canals to one point (I) over the stone canal; lower smooth area is anal vent; Type 1 plan. (R. R. Rowley Coll.) RX 351.

7-Gilbertsocrinus tuberculosus (Hall). Burlington Limestone, Burlington, Iowa. Unusual preservation of madreporite (A) and internal hydropore (B) for this genus; most specimens show no trace of the water vascular system; Type 4 plan. S 15.

8-Strotocrinus glyptus (Hall). Burlington Limestone, Louisiana, Mo. Anastomosing radial canals with convergence to three centers (Roman numerals) on the hydrocoel; the end of the anterior canal is bifurcate; note the round nature of the radial canal fillings indicating that the original canals were intrategminal in some places and deeply aftegminal in others; Type 2 plan. (R. R. Rowley Coll.) RX 356.

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BRUCE N. HAUGH

Where radial water canals rested against the tegmen the water vascular system will be referred to here as aftegminal [af=toward, in contact]. The grooves that contained radial canals and the hydrocoel are especially well preserved in the actinocrinitids where they seem to have been deeply impressed into the plates. In specimens of Strotocrinus the radial canals even penetrate into the internal surface of tegminal plates in some places and rest in deep grooves in others. Where the radial canals and hydrocoel crescent were completely within the plates they will be referred to as intrategminal [intra=inside]. Chert molds with a deep aftegminal or intrategminal water vascular system possess radial canal molds with a nearly circu- lar cross-section (P1. 2, fig. 8). On the chert molds, the position of radial canals is recorded by raised ridges wherever the former radial canals rested against the tegmen. A comparison of figures 3 and 4 of Plate 1, which represents the original interior surface and internal chert mold of two specimens of Physetocrinus ventricosus, will reveal the equivalence of these two different modes of preservation.

The radial canals of some camerate crinoids were aftegminal peripherally, and became subtegminal [sub=below] centrally near where they connected to the hydrocoel crescent and stone canal. This is especially well shown in a specimen of Eretmocrinus (P1. 1, fig. 20; PI. 2, fig. 5) where the canals are evident peripherally (A) and disappear subtegminally where they connect with the stone canal (B) near the anal tube. The anterior radial canal seems to have been farther below the inner surface of the tegmen than the others. The water vascular grooves commonly extend to the four oral plates (P1. 2, fig. 5, D) that surround the posterior oral plate (C). The deep grooves situated interradially represent the former location of hyponeural nerves.

The internal chert molds and interiors of many specimens reveal no evidence for radial canals or the hydrocoel crescent. The only evidence of water vascular elements is the filling of the stone canal associated with the posterior oral plate (P1. 1, figs. 2 and 22; P1. 2, figs. 3 and 4, A). In these specimens it is apparent that the water vascular system was largely subtegminal, the only contact with the tegmen

plates being at the posterior oral plate where the filling of the stone canal is represented by a short stub. The location of the ambulacra (B) is represented by slightly raised ridges.

Four basic morphological patterns of the arrangement of radial canals and hydrocoel crescent have been observed in camerate crinoids. Simplified plan diagrams of these are given in Text-fig. 5; in addition, plan drawings of ac- tual specimens are provided in Text-fig. 6. The four patterns are here referred to as Types 1, 2, 3, and 4.

The radial canal tracts of Type 1 all converge to a point over the stone canal so that no well-defined hydrocoel crescent is present (P1. 1, figs. 15 and 21; PI. 2, fig. 6; Text-fig. 6a, b). The radial canal tracts of Type 1 are aftegminal for their entire extent. This pattern has been detected only in actinocrinitids and seems to be the least common of the four types. The bilateral symmetry of the overall pattern is evident (Text-fig. 6), and this symmetry also affects the proximal end of the anterior radial canal (P1. 2, fig. 6, A and A') as well as the stone canal. The bilateral symmetry plane is anterior to posterior (A-ray to CD-interray).

Type 2 is characterized by radial canal tracts that are completely aftegminal and converge to three centers (Roman numerals) on the hydrocoel crescent (PI. 1, fig. 9; P1. 2, fig. 2). The proximal end of the anterior radial canal is again divided as in Type 1, and the symmetry plane has the same orientation. Type 2 also appears to be typical of the actinocrinitids (Text-fig. 6c-i).

In Type 3, the radial canal tracts are aftegminal peripherally and become subtegminal centrally at or before they reach the oral plates (P1. 1, figs. 10 and 20; P1. 2, fig. 5; Text-fig. 6j-m). From study of specimens of Agarico- crinites convexus and Uperocrinus longirostris (P1. 1, figs. 7 and 16) it appears that the radial canal tracts converge to three points on the hydrocoel crescent as in Type 2. The symmetry plane is again anterior to posterior. This is further supported by scanning electron micrographs of the divided stone canal of Batocrinus icosidactylus, which has a Type 3 pattern. Type 3 appears to characterize batocrinids and desmidocrinids, the latter being transitional to Type 4.

TEXT-FIG. 6-Water vascular network of typical camerate crinoids: figures a-b, Type 1; figures c-i, Type 2; figures j-m, Type 3; figures n-o, Type 4. Stippled area is the location of the anal vent. (a) Stroto- crinus regalis, (b) Physetocrinus asper, (c) Physetocrinus ventricosus, (d) Actinocrinites sp., (e) Actinocrinites lowei, (f) Actinocrinites sp., (g) Physetocrinus ventricosis, (h-i) Strotocrinus glyptus, (j) Eretmocrinus sp., (k) Eutrochocrinus sp., (1) Uperocrinus longirostris, (m) Agaricocrinites con- vexrus, (n) Dorycrinus missouriensis (o) Dorycrinus roemeri.

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Completely subtegminal radial canal tracts characterize the Type 4 pattern (P1. 1, figs. 2 and 22; P1. 2, figs. 3 and 4). Fortunately, several chert mold specimens of Dorycrinus roemeri and D. missouriensis (P1. 1, figs. 8 and 17) reveal the plan of the water vascular canals. In D. missouriensis shallow grooves on the chert mold, indicating ridges on the original, mark the position of the radial canals. The pattern indicated differs from that of Types 2 and 3. Here, the canals converge to five places (Roman numerals) on the hydrocoel. It is also apparent that the stone canal connects to the hydrocoel on the posterior end (C and D-rays) rather than the anterior end (A-ray). The hydrocoel in these types is a complete ring, as in modern crinoids (Text-fig. 6n-o). The bilateral symmetry plane remains in an A-CD alignment. Unfortunately, the dorycrinids are the only ones studied with radial canals supported on raised ridges in the tegmen. All the other specimens with a Type 4 plan show no signs of the radial canal plan. Gilbertsocrinus tuberculosus (P1. 2, fig. 7) has a madreporite (A) and stone canal (B) preserved in the tegmen, but G. tuberosus (P1. 1, fig. 12) does not. Apparently, the stone canal was completely free of the posterior oral plate. Chert molds of Cri- banocrinus whitei, likewise, show no sign of a stone canal incorporated in the posterior oral plate (P1. 1, fig. 5).

The radial water canals of most camerates appear to have been single tracts, however, some Type 1 and 2 actinocrinitid specimens had multiple, anastomosing radial canals. Stroto- crinus glyptus (PI. 1, figs. 6 and 14; P1. 2, fig. 8) is a good example of this, yet S. regalis (P1. 1, fig. 15) usually has single canals. The central area of S. glyptus is quite complex and variable but three points of convergence are in- variably present (P1. 2, fig. 8). The very ir- regular pattern of the radial canals in S. glyptus and Teleiocrinus rudis were interpreted as nerve tracts by Wachsmuth and Springer (1885, p. 62) and they concluded that camerate crinoids possessed an adoral motor nervous system rather than an aboral motor nervous system as in modern crinoids. Adoral nerve tracts were present in camerates, but were interradial in position (P1. 1, fig. 21, N) and probably represent hyponeural nerve tracts homologous to those of living crinoids.

FUNCTIONAL PHYSIOLOGY OF THE WATER

VASCULAR SYSTEM

The primary function of the water vascular system of living crinoids, and presumably of ancient ones, is two-fold; to serve as an hy-

draulic pressure system for movement of podia in food-gathering operations, and to aid in respiration by absorbing oxygen and voiding meta- bolic waste. Although the entrance and im- mediate source of fluid varies in different echinoderms, there is an interradial external opening to the sea water at some embryonic stage in all living echinoderms, and this seems to have been a common adult condition in many primitive groups of Paleozoic echinoderms. An external opening is neither necessary nor most efficient for proper functioning of the water vascular system. Flow of water through the system is negligible. In experiments with echinoids, Fechter (1965) detected no movement of water through the madreporite in a 24 hour period of normal tube foot operation. Under strong contraction of all of the tube feet, only 5 milliliters of fluid (total ambulacral volume, 3500 milliliters) were displaced from the madreporite. It appears that one important function of an external hydropore or madreporite, therefore, is to maintain a pressure balance between the surrounding sea water and the interior of the animal for most efficient operation of the tube feet, or podia. The madreporite or hydropore may also be important for elimination of certain kinds of waste products from the axial organ through the axial sinus, with which it connects. This is thought to be a defense mechanism against foreign organisms and par- ticles (Millott, 1967). An internal hydropore or madreporite such as is found in holothurians and camerate crinoids can perform efficiently all these functions and has several advantages over external types. It is less prone to fouling by debris on the tegmen. This is believed to be a problem because cilia in the pore canals of external madreporites beat outward, whereas those of internal madreporic bodies beat inward (Nichols, 1966). When tube feet are protracted and in operation, the system, or parts of it, must be closed to increase pressure slightly above that of the water column. An internal system might be more efficient in this regard, and still be able to compensate for external pressure variation by changes in the volume of a coelomic cavity.

In the Camerata where the internal hydropore or madreporite is situated in the proximal part of the anal tube or adjacent to a simple anal vent, it appears likely that fluid was derived from the posterior part of the gut or from coelomic spaces surrounding the gut. The

hind-gut probably functioned not only to void undigested food, but also in respiration and as a source of water vascular fluid. An expanded, passive, fluid-filled sac or an active cloacal

86




pump may have been connected with the hind- gut in the anal tube or CD-interray area of the tegmen (Text-fig. 7). Several lines of evidence support this contention. Studies of the preserved silicified gut associated with the convoluted organ indicate that the proximal part of the gut from the mouth to a point near the base of the anal tube or vent was calcified and fairly rigid. This segment is preserved as a silicified round tube in many specimens. From a point where the gut leaves the convoluted organ and extends distally into the anal tube or vent it is rarely preserved. Instead, a small pile of silicified "spicular mush" is commonly present, indicating that the hind-gut may have been flexible but contained embedded spicules. The ponderous anal tube possessed by some camerates has been presumed to function as a "chimney" to discharge waste well above the arms to prevent recycling. However, many camerates have a simple anal vent through the tegmen inside the circle of arms, indicating this was not a great problem. This is also true of many flexible and inadunate crinoids which do not have a long anal sac or tube. The opening at the end of long anal tubes is small indicating that waste may have been in a nearly fluid state, and simply dissolved in the sea water. A more likely function for the anal tube was for support of a modified hind-gut or coelom, which acted either as a passive water-filled sac or as a cloacal pump. A cross section at the base of the anal tube of a specimen of Actino- crinites verrucosus reveals a small hind-gut (PI. 3, fig. 6, A) with a large space (B) surrounding it that could have housed either of these structures. Water could have been brought in through the anal opening by a cloaca, or if a passive sac were present water may have entered with food through the ambulacral openings. The pattern of nerve innervation (Text-fig. 7) by the aboral nerve system in the CD-interray suggests the former interpretation, but is not proof of it. In those forms that do not possess an anal tube (e.g. desmidocrinids and platycrinitids) the hind-gut and associated mechanisms must have been housed inside the theca in the CD-interray. The anal vent is commonly a rather large hole in these forms that lack a long anal tube, and the theca is slightly inflated in that interray compared with those that have such a tube. These agarico- crinids and dorycrinids possess a special madreporic body (PI. 1, figs. 13, A, and 19, A; Text- fig. 4C), which perhaps served as an efficient absorptive body from a smaller reservoir which was contained in the tegmen proper. The posterior oral plate is especially large and inflated

....C\ ? ~J.-C t mray

^H?^o

AN ANR to Cnvoluted

/ / Organ

TEXT-FIG. 7-Reconstruction of the proximal water vascular system and cloacal reservoir of a generalized camerate crinoid: A, anus; AAN, aboral anal nerves; ANR, aboral nerve ring (posterior part only); AMN, aboral motor nerves; AT, anal tube; C-R, cloacal reservoir; G, gut; POP, posterior oral plate; other abbreviations as in previous text-figures. (Nerve pattern depicted in the lower part of the diagram is located in the CD-interray of the dorsal cup.)

in torms such as Agaricocrinites, and is commonly spinose, as in Dorycrinus unicornis, where the madreporic body projects into the base of the spine (P1. 1, figs. 13 and 19). These specimens also have a tegminal mesh-work below the anal vent that may have been an attachment site for muscles and mesenteries of the hind-gut coelomic sac or cloaca. The smooth areas to either side of the vent (B and B') were probably occupied by the stone canals. The madreporic bodies in some species of Agaricocrinites were fixed to the inner surface of the tegmen adjacent to the hind-gut (P1. 3, fig. 5). Here, the madreporic body (A) is adjacent to an expanded part of the hind-gut (B) and a constricted distal part (C).

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BRUCE N. HAUGH

Diaqrammatic Ontogeny of Generalized Camerate Crinoid

TEXT-FIG. 8-Proposed ontogeny of a generalized camerate crinoid compared to a modern crinoid (main body coeloms not included): Axl and Axr, axocoel left and right; Hci and Hcr, hydrocoel left and right; M, mouth; PhC, perihaemal coelom; PL, pleural lobe; V, vestibule; other abbreviations as in previous text-figures. (In part, after Dawydoff, 1948.)

In general, it appears that the function and morphology of the camerate water vascular system more closely resembles that of living holothurians than that of living crinoids. It derived fluid from an internal source that also served a respiratory function in the absence of special interradial water pores through the endoskel- eton.

SYMMETRY, ONTOGENY, AND PHYLOGENY

The symmetry of the camerate water vascular system is primarily bilateral-trimeral, modified to a secondary pentamerism by branching of radial canals in the B and E-rays (Text-fig. 5) to form the canals of the C and D-rays. The pattern is reminiscent of cystoids such as Cary- ocrinites, and the presence of primary trimer- ism of the radial elements seems to indicate re- tention of a primitive echinoderm symmetry.

Bather (1900, p. 11) and others have maintained that the earliest brachiate echinoderms had only three arms (e.g. Echinosphaerites aurantium (Gyllenhahl), consisting of anterior (A), right (B), and left (E) rays because the hydropore, gonopore, and anal opening occupy the posterior side preventing extension of the hydrocoel into this area. The five rays were produced by secondary branching to increase food gathering efficiency, while still avoiding the CD-interray. This is exactly the condition maintained in the Camerata. Some of the desmidocrinids and probably the platycrinitids attained a nearly pentameral symmetry with five primary radial extensions from the hydrocoel (Text-fig. 6n-o).

The ontogenetic sequence that produced the typical camerate symmetry was probably some- what different from that of modern crinoids

88




and other living echinoderms. All echinoderms pass through bilateral larval stages before they undergo torsion and lose certain parts of their bilateral coeloms. An early larval stage in all living echinoderms, except crinoids, is the dipleurula, a bilateral ciliate form with an elon- gate anterior-posterior axis and straight gut (Text-fig. 8). A tripartite bilateral coelomic arrangement consisting of axocoel, hydrocoel, and somatocoel from anterior to posterior is present. During development the larva becomes fixed by its pre-oral (anterior) lobe and under- goes a remarkable metamorphosis wherein the right axocoel and hydrocoel are lost (Text-fig. 8). The hydrocoel ring and radial canals in modern adult echinoderms arise from the larval left hydrocoel, which curves around to assume a crescent shape. This hydrocoel crescent per- sists very late in the ontogeny and finally becomes a complete ring. The hydropore and stone canal arise from the left axocoel at an early stage and are in communication with sea water in all echinoderm larvae.

The striking bilateral symmetry of the water vascular system of the Camerata, especially of the stone canal and anterior ray, suggests a different ontogenetic derivation. Beginning with the dipleurula (not found in living crinoids) three bilateral coeloms were probably present. The right and left axocoel each gave rise to a separate stone canal and these later fused into one distally and connected with the exterior by a medial pore (Text-fig. 8). This condition has been suggested by Bather (1900, p. 4) as the adult condition for his "dipleurula ancestor." In fact, it is present in some ab- normal asteroid auricularia larvae (Dawydoff, 1948). From this stage the larva probably underwent torsion, as indicated by the curved gut and convoluted organ (peri-gastric coelom) in adult camerates. However, the right and left axocoels and hydrocoels were retained, each forming half of the water vascular system (Text-fig. 8). Each hydrocoel curved poste- riorly giving off one primary radial water canal, the B and E canals, but did not join in the CD-interray. The C and D radial water canals were formed by secondary branching. Anteriorly, each hydrocoel sent out one primary radial water canal which merged with each other, producing the primary, bifurcate anterior canal. A short bridge finally joined the two hydrocoels anteriorly between the bifurcate stone canals, completing the adult hydrocoel crescent. In those forms with an internal madreporic body and five radial canals on the hydrocoel, the stone canals connected to the posterior end of each larval hydrocoel. Deriva-

tion of the adult water vascular system from both larval hydrocoels is presumably a primitive echinoderm trait. In this regard, the ontogeny of camerate crinoids appears to be different from that of flexible and inadunate crinoids (Lane and Webster, 1967), which were probably more like modern crinoids. If this is so, it is probable that the camerate and inadunate lines separated and rapidly diverged very early in the Paleozoic, or perhaps even the Late Precambrian, long before flexible crinoids evolved from the inadunates. Considering all three extinct subclasses, the inadunate and flexible crinoids are more closely related and more like living types ontogenetically, while the camerate crinoids retained a more primitive ontogenetic development.

ACKNOWLEDGMENTS

The author thanks Dr. N. Gary Lane for aid in preparation and reading of the manuscript, and for his help in obtaining specimens. This research could not have been accomplished without the aid and cooperation of: Dr. Porter M. Kier and Mr. Thomas Phelan, U. S. Na- tional Museum; Dr. John L. Carter, University of Illinois; Dr. Eugene S. Richardson, Jr., Chi- cago Natural History Museum; Dr. Bernhard Kummel, Museum of Comparative Zoology at Harvard University; and Dr. Mackenzie Gor- don, Jr., U. S. Geological Survey. I would also like to thank Dr. Porter M. Kier and Dr. David L. Meyer for reading the manuscript and of- fering suggestions for its improvement. The scanning electron micrographs were made through the cooperation of Dr. J. William Schopf and Mrs. Carol Lewis of the U.C.L.A. Paleobiology Laboratory with the aid of N.S.F. Grant GA 23741. Other research funds have been provided by the Society of the Sigma XI Grants-in-Aid of Research Committee, and The Geological Society of America, grant number 1482-71.

Technical illustrations and drafting were done by Mrs. Jeanie Martinez.

REFERENCES

Bather, F. A. 1900. In E. R. Lankester (ed.), A Treatise on Zoology. Adam and Charles Black, London. 344 p.

Dawydoff, C. 1948. Embryologie des Echino- dermes: 277-362. In P. P. Grasse (ed.), Traite de Zoologie. 11. Masson et Cie, Paris.

Fechter, H. 1965. Uber die Funktion der Madre- porenplatte der Echinoidea. Z. Vergl. Physiol. 51: 227-257.

Hyman, L. 1955. The Invertebrates: Echinoder- mata, The Coelomate Bilateria. 4. McGraw-Hill, New York. 763 p.

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BRUCE N. HAUGIH

Lane, N. G. and G. Webster. 1967. Symmetry Planes of Paleozoic Crinoids. Univ. of Kansas Paleont. Contrib., Paper 25: 14-16.

Millott, N. 1967. The Axial Organ of Echinoids, Re-interpretation of its Structure and Function. In N. Millott (ed.), Echinoderm Biology. Zool. Soc. London, Symposia 20:53-63.

Nichols, D. 1962. Echinoderms. Hutchinson Univ. Library. London. 200 p.

Spreng, W., and J. Parks, Jr. 1953. Evolution in

the Basal Plates of Monocyclic Camerate Cri- noids. Jour. Paleontology 27 (4) :585-595.

Wachsmuth, C., and F. Springer. 1879 [1880]-86. Revision of the Palaeocrinoidea. Acad. Nat. Sci. Philadelphia, Proc. 862 p.

1897. The North American Crinoidea Cam- erata. Harvard Coll., Mus. Comp. Zoology, Mem. 20. 20-21 :837.

MANUSCRIPT RECEIVED MARCH 14, 1972


Figures 1, 3, and 4 are scanning electron micrographs; all others are photomicrographs.

FIG. 1-Agaricocrinites brevis (Hall). Burlington Limestone, Burlington, Iowa. Edge of posterior oral plate bordering the anal vent; (A) indicates an open madreporite; the stone canal transects the edge of the plate and emerges on the interior of the theca, internal hydropore, near number 1. UCLA 35218.

2-Batocrinus icosidactylus Casseday. Salem Limestone, Spergen Hill, Ind. Vertically cut hollow specimen with the internal hydropore (A) and madreporite (B) at the base of the anal tube. S 589.

3-Steganocrinus pentagonus (Hall). Lake Valley Limestone, near Lake Valley, N. M. Porous area (A) of madreporite and internal hydropore with longitudinal septum. UCLA 48286.

4-Batocrinus icosidactylus Casseday. Salem limestone, Spergen Hill, Ind. Internal hydropore with longitudinal septum (A) and tracts of bifurcate stone canal (B and B') demonstrating bilateral symmetry of the water vascular system. S 589.

5-Agaricocrinites splendens Miller & Gurley. Muldraugh Formation, Crawfordsville, Ind. Internal madreporic body (A) bordering expanded portion of hind-gut groove (B) and constricted part (C). UCLA 48287.

6-Actinocrinites verrucosus (Hall).. Lower Harrodsburg Limestone, Canton, Ind. Cross section of anal tube with small hind-gut (A) lying within the large anal tube cavity (B). Walker Mu- seum Coll. P 19286.

7, 8-Batocrints Icosidactylus Casseday. Salem Limestone, Spergen Hill, Ind. 7, The two expanded proximal pinnulars (A and A') of the fixed pinnule, forming a movable pore cover for the respiratory pore; first free pinnule (B). S 589. 8, Area around ambulacral opening (C) showing an open respiratory pore (A) with longitudinal septum and hinge socket (B) for ar- ticulation of the pore cover. S 589.

90



JOURNAL OF PALEONTOLOGY, V. 47, PLATE 3 Haugh

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