encyclopedia of inland waters || bryozoa

BryozoaT S Wood, Wright State University, Dayton, OH, USA

ã 2009 Elsevier Inc. All rights reserved.

Introduction

General Definition

In the general sense, a freshwater bryozoan is an ani-mal that grows on submerged surfaces as an integratedcluster of multiple units called zooids, each unit capa-ble of feeding and digesting suspended food particlescaptured with ciliated tentacles. These parts are iden-tified with specific terminology: the multiple units arecalled zooids; a cluster of ciliated tentacles is alophophore.Bryozoans form a polyphyletic group with many

issues unresolved. Among freshwater bryozoans thereare at least two phyla and about 100 recognizedspecies. Marine bryozoans are even more taxonomi-cally diverse, with many thousands of known speciesand a rich fossil record.Some clarity is appropriate here regarding the

word bryozoan. This may be used as an adjective(e.g., a bryozoan colony) or as a noun, usually plural(e.g., a population of bryozoans). The word Bryozoa,always capitalized, refers exclusively to one of twobryozoan phyla, also known as Phylum Ectoprocta.The other bryozoan phylum is Phylum Entoprocta.

Major Taxonomic Groups

All freshwater bryozoans are classified in one of threedistinct groups: Phylactolaemata, Ctenostomata, orEntoprocta. These taxa represent a class, an order,and a phylum respectively, as described later in theTaxonomy section. Phylactolaemate and ctenostomebryozoans are structurally similar, but while Phylac-tolaemata is an exclusively freshwater group, Ctenos-tomata is mostly marine, with only a few speciesrepresented in fresh or brackish waters. Entoproctbryozoans, an entirely different group, are almostentirely marine, with only two species known infreshwater.

Ctenostome Bryozoans

Morphology

Colony: Ctenostome bryozoans in fresh water arerelatively small and inconspicuous. In some species,the zooids form a tracery of branching, uniserial linesacross the substratum; in others, the colony is a flat,

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encrusting patch that spreads outward in all direc-tions. Still others appear as a collection of tiny spikesstanding erect on the substratum and joined at thebase by meandering tubules.

Zooid: Regardless of colony form, the zooid isalways composed of two integrated parts: (1) abasal region, usually attached directly to the substra-tum, and (2) a peristome, or tubule, ending in anorifice through which the lophophore is extended(Figure 1).These parts can vary greatly in relativesize, even within the same colony. In Paludicellazooids, the peristome is a short stump, while in Pott-siella and Victorella it often forms the greater part ofan erect zooid.

The zooid is the basic module, or repeating unit ofthe colony, capable of performing all essential lifefunctions. It includes a tentaculate lophophore forcapturing food, a complete gut, various muscles, anervous system, and reproductive organs. The lopho-phore, gut, and associated muscles are bundled ina partially extendable unit called a polypide. Enclos-ing the polypide and the body cavity is a flexiblecuticle, lined on the inside with several sets of parietalmuscles. Contraction of these muscles increasesthe internal hydrostatic pressure and enables thepolypide to extend. Powerful adductor muscles origi-nating at the inner body wall and inserted around theregion of the pharynx serve to rapidly withdrawthe lophophore. When this occurs, the entire gut isbent back upon itself to accommodate the lopho-phore (Figure 1).

The gut begins with a ciliated pharynx where food iscollected, followed by a muscular esophagus whichpasses food to the stomach. The stomach has threeparts, more or less distinct: a receiving cardia, a sac-like cecum, and an ascending limb called the pylorus. Insome species, the stomach is preceded by a thick-walledproventriculus whose function is unclear. Digestedwastes pass through the slender intestine to be com-pacted into a pellet in the rectum and finally releasedthrough the anus at the base of the lophophore.

A small nerve ganglion is located between themouth and the anus, and it sends out tracts of nervesto the lophophore and zooid muscles. There is nonerve communication among the zooids.

Growth of the colony is achieved by asexual bud-ding of new zooids. Most zooids can produce at least

Figure 1 Ctenostome bryozoan, Sineportella forbesi, showing major anatomical structures. Scale bar¼0.2mm. Adapted from

Wood (1996) Sineportella forbesi, a new species of freshwater ctenostome bryozoan from Illinois. Journal of the North AmericanBenthological Society 15(4): 612.

Invertebrates _ Bryozoa 251

three buds: one distal (i.e., opposite from the paren-tal zooid) and two or more lateral buds. The proximalend of a zooid (i.e., extending from the parentalzooid) is often greatly elongated and uniformly nar-row, functioning much like a stolon. A single septumseparating adjoining zooids is perforated to alloworganic continuity.Hibernaculae: It is axiomatic that invertebrates liv-

ing in freshwater habitats include in their life cycles astage resistant to unfavorable conditions. In ctenos-tome bryozoans, such stages are thick-walled packagesof germinal tissue and yolk reserves known as hiberna-culae. In Victorella pavida, the hibernaculum is a flat,external bud cemented to the substratum. In severalHislopia species, the hibernaculum is formed whenthe entire zooid fills with yolky material and deve-lops thickened walls. Paludicella produces two typesof hibernaculae: one is an irregularly shaped bodyattached to the substratum, and the other is a fusiformbody occupying the internal space of a normal zooid.There are so far no experimental data concerning theresistance of these structures to environmental stresses,nor is it known how long they can remain viable.

Feeding and Digestion

Digestion in ctenostome bryozoans is believed to beextracellular, although little is actually known aboutthe digestive physiology. From observations of lopho-phore and gut activity, it is apparent that much energyis spent in the capture, manipulation, and digestion offood. Raw food particles are generally small, unicel-lular, and compact, including diatoms, green algae,cyanobacteria, and protists. Most digestion occurs inthe stomach, where combined effects of internal cilia-tion, muscular mixing, and chemical action graduallyreduce the size and volume of food particles. No fur-ther change is seen in gut contents as they are passedthrough the intestine to the rectum.

Reproduction

Colonies are generally hermaphroditic. In Pottsiella,both eggs and sperm usually mature simultaneouslyin the same zooid, while in Hislopia, a zooid may pro-duce either eggs or sperm, but not simultaneously. Thereappears to be great opportunity for self-fertilization,

252 Invertebrates _ Bryozoa

although outcrossing has also been demonstrated.Developing eggs may be brooded internally (Victor-ella) or externally (Paludicella, Pottsiella), developinginto nonfeeding, motile gastrulae. In Hislopia spp.,eggs are released freely into the water where theybecome planktotrophic larvae.

Figure 2 Tubular colony of a phylactolaemate bryozoan,Plumatella javanica. Scale bar¼ 1 cm. Photo by Nattawut Intorn.

Life History

Species in temperate regions generally overwinter asdormant hibernaculae and emerge in the late spring.Seasonal variation in sexual activity is unknown.New hibernaculae are formed apparently in responseto deteriorating environmental conditions. In tropicalclimates, all species are active throughout the yearwith continuous sexual and asexual reproduction.Hibernaculae are formed continuously through thenormal process of colony or zooid senescence.

Ecology

Freshwater ctenostomes in temperate regions mostoften occur in flowing waters. In tropical waters,however, such species as Hislopia and Victorellaalso thrive in quiet ponds. Little else is known oftheir ecology. Basic aspects of predation, interspecificcompetion, dispersal, and environmental toleranceshave yet to be explored.

Figure 3 Compound, globular colonies of a phylactolaemate

bryozoan, Pectinatella magnifica, removed from the water where

they were growing on twigs. Photo by Charlene Luoma.

Phylactolaemate Bryozoans

Morphology

Colonies: In phylactolaemate bryozoans, the coloniesare either tubular or globular, according to the spe-cies. Tubular colonies are branched at varyingdegrees, and the branches usually remain attachedto the substratum throughout most of their length(Figure 2). Free branches also occur, and undercrowded conditions may grow erect, even adheringto adjacent zooids to form a low mound or a contin-uous blanket across the substratum. These forms varywith species and are also strongly influenced by envi-ronmental factors.In globular colonies, zooids are clustered in a com-

mon sac, which is capable of slow, creeping motility.Upon reaching a certain size, a sac can pinch offdaughter colonies which either move apart or remainin place to produce a large compound colony. InPectinatella and Asajirella, such compound coloniessecrete a gelatinous material which increases theirvolume and provides substratum for an increasingnumber of zooid sacs on the outer surface (Figure 3).In both tubular and globular colonies, the zooids

are integrated seamlessly in a single colony unit.

What appears as occasional septa in tubular coloniesare actually ring-like structural elements which sel-dom impede the free flow of coelomic fluid circulatedby peritoneal cilia.

Zooids: In contrast to ctenostome bryozoans, thephylactolaemate zooids are relatively large androbust (Figure 4). The lophophore bears from 20 toover 100 ciliated tentacles, the globular speciesalways having more than 50 and the tubular speciesfewer than this. In Fredericellidae, the 20–25 tenta-cles are all arranged in a circle around the mouth.However, a larger number of tentacles requires thatthe lophophore be inflected on one side to becomeslightly U shaped.

The zooid body wall is more highly structured thanthat of ctenostome bryozoans. In tubular colonies,the nonliving ectocyst is a chitinous layer that variesin thickness and opacity. The ectocyst of globularcolonies is soft, thick, transparent, and surprisingly


strong. Below the ectocyst is a well-organized layer ofcircular muscles that maintains a constant hydrostaticpressure. This is underlain by a layer of longitudinalmuscles, followed by basement membrane and cili-ated peritoneum.The gut begins with the mouth, lying adjacent to a

stubby, ciliated lobe (epistome) that may function infood selection. Captured food particles are collectedin a ciliated pharynx and then swallowed through the

Figure 4 Stylized view of three zooids in a tubular

phylactolaemate bryozoan, with a swimming ‘larval’ colony.

Scale bar¼0.2mm.

Figure 5 Scanning electron micrographs of two statoblasts of a ph

(a) floatoblast and (b) sessoblasts. Scale bar¼50 mm.

esophagus into a spacious stomach. Here they aresubjected to vigorous mixing by regular waves ofperistaltic contraction. Stomach contents are fedslowly through a small valve to the intestine andrectum, where they are packed together, infusedwith a mucus, and ejected as a pellet through the anus.

A single nerve ganglion lies in an area between thepharynx and the anus, sending paired nerve tracts tothe lophophore, gut, and orificial musculature. Inaddition to gut musculature, there is a pair of strongmuscles to withdraw the polypide, a ring of musclesto open and close the orifice, as well as muscles tomanipulate the lophophore and the individualtentacles.

Extending from the exterior tip of the stomachcecum is a single cord of tissue (funiculus) thatattaches to the inner body wall. The funiculus is thesite of statoblast formation and spermatogenesisdescribed below.

Statoblasts: These are the specific dormant struc-tures produced asexually by phylactolaemate bryozo-ans. They are essentially capsules of chitin containingyolk and germinal material, capable of survivingexposures to harsh chemicals, temperature extremes,and desiccation. Upon the return of suitable condi-tions, a suture around the statoblast weakens and thecapsule splits roughly in half as a new zooidgerminates.

In Fredericellidae, the statoblast is a simple bean-like structure, normally anchored to the substratumby a thin, form-fitting circle of chitin. In all otherfamilies, the statoblast is released freely into thewater, where it floats with the benefit of special gas-filled chambers around the periphery. This type ofstatoblast is known as a floatoblast (Figure 5(a)). InLophopodidae, buoyancy is achieved only upon des-iccation when the chambers fill with air.

Among species of Plumatellidae and Stephanellidae,a sessile statoblast also may be formed (Figure 5(b)).

ylactolaemate bryozoan (Plumatella geimermassardi ).


This so-called sessoblast is cemented directly to thesubstratum, essentially securing the favorable locationfor the next generation. The plumatellid sessoblastsdiffer from the sessile statoblasts of Fredericellidae bytheir more complex outer structure and by themeans ofattachment.Statoblast morphology is species specific and

highly detailed, with some features detectable onlyby scanning electron microscopy. Many species, espe-cially plumatellids, can be positively identified onlyby their statoblasts.


Phylactolaemate bryozoans ingest a wide variety ofparticles, including both unicellular and filamentouscyanobacteria, diatoms, chlorophytes, protists, roti-fers, nematodes, and detritus. However, examinationof the pellet reveals that most of these particlesremain intact, and indeed many emerge from thegut alive and apparently unharmed. Radioactivelylabeled bacteria fed to one plumatellid species werelater detected in the bryozoan tissues, suggesting thatbacteria may provide much of the nutrition. If this istrue, then the particulate material ingested by thesebryozoans may simply be carriers of bacteria, pre-sumably dislodged by the mechanical action of thestomach.

Reproduction

In addition to asexual reproduction by statoblasts orcolony fission, phylactolaemate bryozoans alsoinclude a sexual process in their life cycle. Coloniesare hermaphroditic, with spermatogenesis occurringon the funiculus and ova appearing in a single grape-like cluster on the inner body wall (Figure 4). Despitegenetic evidence of outcrossing, it is not known howsperm exit one colony and enter another. Most ferti-lized ova disintegrate, while a few develop in specialpouches formed in the body wall, eventually openingto the outside. The end product is an unusual larva-like mobile colony released to the surrounding water(Figure 4). This rounded, oblong structure is entirelyciliated on the outer surface and encloses a bodycavity with two complete polypides. Equipped withsensory tissue at one end, the mobile colony can swimfor several hours and has been shown to discriminateamong various types of possible substrata. Settling isachieved when the nonsensory end adheres to aselected substratum, the ciliated mantle peels back,and the two zooids emerge to feed. The entire settlingprocess normally takes about 15–30min.

Life History

For most species in temperate climates, the life cyclebegins with the germination of overwintered stato-blasts. Late spring is a time of rapid colony growthand statoblast production. Gametogenesis also occursat this time over a period of 1–2weeks. Many popu-lations decline during midsummer, but return in thefall when the earlier statoblasts germinate.

In warmer climates, nearly all species are activethroughout the year. Sexual activity plays a signifi-cant role in establishing new colonies. The obligatorydormant period of statoblasts is highly variable, withmany floatoblasts germinating within days of theirrelease. However, there are always exceptions tothese general trends. Asajirella has an annual growthcycle, and several other species are attuned to theprogression of rainy and dry seasons.

Ecology

Substrata: Phylactolaemate bryozoans grow on awide variety of submerged substrata, especiallythose that are chemically inert, such as rocks, musselshells, plastic, glass, and rubber. Old submergedwood is often colonized, but new wood usually isnot. Macrophytes often support vigorous growths ofcertain species. In quiet waters, nearly all bryozoancolonies occur on the underside of the substratumwhere they are protected from settling particles.

Predation: Knowledge of phylactolaemate preda-tors is based almost entirely on indirect evidence. Forexample, statoblasts found in the fish gut suggestpredatory activity. Plumatellid colonies that arecaged to exclude fish are shown to grow more luxuri-antly than those exposed to possible fish predators.The coelomic fluid of certain lophopodid bryozoansis toxic to fish, but whether this has any usefulprotective role against fish predation has not yetbeen demonstrated.

When bryozoans are scarce in a lake, they can usu-ally be found on boat hulls, floating buoys, danglingrope, and other substrata that are inaccessible to snails,flatworms, caddisfly larvae, and other potential creep-ing predators. In Southeast Asia, heavy predation bythe invasive golden apple snail (Pomacea canaliculata)has been observed and measured. This is the mostserious known predator of phylactolaemate bryozoansand may be responsible for the decline of many popu-lations in that region.

Dispersal: Patterns of distribution for many phy-lactolaemate species suggest dispersal by migratingwaterfowl. This is particularly evident along theEast Asian/Australasian Flyway as well as the greatcoastal north–south flyways of North and South


America. Further evidence comes from the recoveryof viable statoblasts from the feet, feathers, and gutsof ducks and geese.

Entoproct Bryozoans

Morphology

The following description is based largely on Urna-tella gracilis Leidy, 1851, which until 2005 was theonly known entoproct species represented in freshwaters. The basic zooid is composed of a segmentedmuscular stalk arising from a flat basal plate andbearing a bulbous calyx (Figure 6). The calyx holdsmost of the major organs, including the gonads, gut,and 6–16 short, ciliated tentacles. Lateral compres-sion makes the calyx nearly twice as long as it is wide.The entire structure of stalk and calyx may measureup to 5mm in height. A second and third zooid maybud from the same basal plate, and additional budsmay arise from segments of the stalk.The area of the calyx encircled by tentacles is called

the atrium. This accommodates openings for themouth and anus. Food capture and handling involvesconsiderable ciliary activity. Ciliated tentacles bring

Figure 6 Stylized view of three zooids of an entoproct bryozoan, U

internal structures. Ovum, testes, and protonephridia are embedded

water laterally between them and toward the centerof the atrium, then upward and away from the zooid.Food particles captured by the tentacles move into themouth and from there through a ciliated esophagus toa spacious stomach also lined with cilia. Here theentire collection of ingested particles is rotated rap-idly by ciliary action. Waste particles travel to a cili-ated intestine and collect briefly in the rectum beforebeing ejected into the stream of water propelled out-ward from the atrium.

About 25 protonephridia make up a complex osmo-regulatory/excretory system in the calyx. Embedded inmesenchyme, these structures communicate with theexterior through a single canal which opens as a porebeside the anus. Additional protonephridia are foundin the stalk.


Feeding by entoproct zooids never involves large oractive particles. The material ingested by Urnatella isprimarily detritus along with small diatoms and uni-cellular green algae. Particles do not go directly to themouth, but instead impinge on the outer side of thetentacles. Impinging on special ciliary organelles, they

rnatella gracilis, with parts of the calyx cut away to show

in mesenchyme tissue. Scale bar¼ 0.5mm.


are carried by cilia down to the mouth opening. Themechanics and physiology of digestion in this groupare entirely unknown.

Figure 7 A handful of plumatelid bryozoans from the cooling

water intake structure of power generating facility. Divers

recovering this material reported a bed of bryozoans more than0.5m thick.

Life History

The dormant structure in the life cycle of Urnatellaresides in the stalk. Abrupt changes in temperature,pH, or other conditions cause the calyx to drop off,leaving only the stalk. The zooid may remain in thiscondition for weeks or months, even overwinteringin temperate regions. The return of suitable condi-tions brings out one or more new calyses. During theactive growing season, new buds replace old ones ata regular rate. There are reports of young zooidsdropping off the parental stalk and somersaultingor creeping slowly across the substratum to becomeestablished nearby.Zooids are hermaphroditic, and sexual activity is

believed to be seasonal even in tropical waters. Eggsare fertilized and brooded internally. There is evi-dence of swimming larvae, and while these havenever been described, they probably resemble thenonfeeding larvae of marine Pedicellinidae.

Ecology

Urnatella occurs on a wide variety of firm substrata inflowing or turbulent water. It tolerates a broad rangeof physical and chemical conditions. Described initi-ally from North America, its range appears to haveexpanded to nearly every continent.

Biological Fouling

Bryozoans with tubular, branching colonies becomean expensive nuisance when they clog pipelines, fil-ters, submerged pumps, and other structures handlingwater from lakes and rivers (Figure 7). This is espe-cially problematic for irrigation lines, water andwastewater treatment plants, and industrial coolingsystems. Sessile statoblasts and hibernaculae limit thetreatment options by resisting harsh chemical andphysical conditions. The choice of effective treatmentdepends on the species involved, access to the fouledsurfaces, careful timing, and the final use of the water.

Study Methods

Collecting

Bryozoans are common and easily found, especiallyin moderately eutrophic waters with abundant rockor wood substrata. Most species can be found in

water less than 1m deep. Bryozoans normally growon the underside of the substratum, especially in stillwater. Good places to search include quiet bays,inlets, or ponds, areas immediately downstream of asmall dam or spillway, and almost any freshwatermarina (dangling tires, ropes, and boat fenders).Experienced bryozoologists often look first for buoy-ant statoblasts at the waterline of floating objects oron any piece of plastic foam. A small hand lens(10–14�) is useful for this purpose. If living coloniesare desired, they should be collected along with thesubstratum on which they are growing.

Laboratory Culture

Maintaining living bryozoans in the laboratoryrequires proper orientation and suitable water. Mostcolonies grow best when they are upside down andsheltered from settling particles by their own substra-tum.Water should be slightly alkaline, gently aerated,and should contain sufficient particulate food. Excel-lent conditions usually exist in well-established,unfiltered aquaria containing large goldfish, but thebryozoans must be protected from browsing bythe fish.

Taxonomy

Phylum Entoprocta (synonymous with Kamptozoa).Zooids composed of a flexible, muscular stalk cappedby an expanded calyx which bears major organ sys-tems and a marginal ring of short, ciliated tentacles.


About 150 marine species and two species knownexclusively from freshwater.Family Urnatellidae. Segmented, branching stalk

arising from an irregular basal plate, muscles extend-ing through each segment, stolons absent. One spe-cies, Urnatella gracilis Leidy, 1851, reported fromevery continent except Africa and Australia.Family Pedicellinidae. Unsegmented stalk with

muscles extending through its entire length, individ-ual zooids joined by narrow stolons. One species,Loxomatoides sirindhornae Wood, 2005, currentlyknown only from Thailand.Phylum Bryozoa or Phylum Ectoprocta, these

names are used interchangeably (synonymous withPolyzoa). Zooid composed of an outer sheath (zooe-cium) and an inner bundle of organs (polypide),including major organ systems and ciliated tentacles,which may be partially extended for feeding.Class Gymnolaemata Allman, 1856. Tentacles gen-

erally numbering fewer than 20 and arranged in acircle around the mouth, zooid lacking epistome andstatoblasts. Exclusively marine except for Order

Table 1 Summary of features among freshwater bryozoans in the C

Family Distinguishing features

Arachniidae Zooids flat, proximal tubules anastomosing

Hislopidae Zooids flat, proximal tubules short or absent

Paludicellidae Spindle-shaped zooids in linear series, lophophor

Pottsiellidae Variable zooid morphology, 18–22 tentacles

Victorellidae Variable zooid morphology, 8 tentacles

Table 2 Summary of features among freshwater bryozoans in the C

Family Distinguishing features Reprspec

Cristatellidae Colony globular, statoblast buoyant withwiry spines radiating from the fenestra

Crist

Fredericellidae Colony tubular, zooids widely spaced;

statoblast sessile and bean-like

Fred

Hyalinellidae Colony tubular, free statoblasts large andwithout spines

Hyal

Lophopodellidae Colony globular, free statoblasts initially

nonbuoyant

Loph

Pectinatellidae Colony globular, free statoblastsbuoyant with spines radiating from

periphery

Pect

Plumatellidae Colony tubular, forming both free andsessile statoblasts

Plum

Stephanellidae Same as plumatellidae, but sessoblasts

attached on opposite side

Step

Ctenostomata, which includes a few freshwater spe-cies. Ctenostome bryozoans are characterized by anuncalcified zooecium in which the parietal muscles ofzooids are attached to flexible frontal walls; the orificehas a squarish appearance when the polypide is with-drawn. The few freshwater species are distributedamong five families (Table 1).

Class Phylactolaemata Allman, 1856. Tentaclesgenerally numbering more than 20, the lophophoreinflected dorsally to form a double U or V (except inFredericellidae). Exclusively freshwater or slightlybrackish habitats. An epistome is present, andzooids are capable of forming statoblasts. About 90species in seven families occurring exclusively infreshwater (Table 2).

Systematics

Because of their many morphological similarities,phylactolaemate and gymnolaemate bryozoans areclassified in the same Phylum Ectoprocta (Bryozoa).

lass Gymnolaemata

Representativespecies

Distribution

Arachnidiumray-lankesteri

Lake Tanganyika

Hislopia lacustris Tropical Asia,

Central and

South Americae projects obliquely Paludicella

articulata

Worldwide

Pottsiella erecta North and Central

AmericaVictorella pavida Worldwide

lass Phylactolaemata

esentativeies

Distribution

atella mucedo Holarctic

ericella sultana Worldwide

inella punctata Holarctic, Australia and tropical Asia

opodella carteri Worldwide

inatella magnifica North America, expanding into Europe andwestern Asia

atella repens Worldwide

hanella hina North America, western Asia


However, the tools of molecular genetics do not con-firm a close relationship. Fundamental differences indevelopment and morphology further suggest consid-erable distance between these groups. Phylactolaematebryozoans may, in fact, be no closer to gymnolaematesthan they are to brachiopods or phoronids. As forentoproct bryozoans, the absence of a true lopho-phore, enigmatic origins of the body cavity and proto-stomian elements of its embryology would appear toplace this group in an entirely different realm.

Glossary

Bryozoan – An animal of the Phylum Ectoprocta(Bryozoa) or Entoprocta, having modular growthform and capturing suspended food particles withciliated tentacles.

Cecum – The central part of a bryozoan stomachfeaturing a blind pouch.

Cardia – The region of a bryozoan stomach receivingfood from the esophagus.

Ctenostome – A bryozoan classified in the PhylumEctoprocta, Class Gymnolaemata, Order Ctenosto-mata.

Cyphonautes – A roughly triangular, laterally com-pressed, planktotrophic larvae produced by certainnonbrooding gymnolaemate bryozoans in marineand freshwater habitats.

Distal – Referring to the region of a bryozoan zooidfurthest from the parental zooid.

Ectocyst – The nonliving outer layer of a bryozoanzooid.

Ectoproct – A bryozoan classified in the Phylum Ecto-procta (Bryozoa).

Endocyst – The living tissues of the inner body wall ofa bryozoan zooid, including muscles, glands, andperitoneum.

Entoproct – A bryozoan classified in the PhylumEntoprocta.

Epistome – A small, ciliated lobe projecting obliquelyover the mouth of a phylactolaemate bryozoan.

Floatoblast – A type of free statoblast capable ofbuoyancy.

Funiculus – A cord of tissue extending from the stom-ach caecum to the inner body wall in ectoproctbryozoans, site of spermatogenesis and statoblastformation.

Hibernaculum – An asexually produced dormantstructure in the life cycle of all freshwater andsome marine bryozoans.

Lophophore – The feeding organ of ectoproct bryozo-ans composed of ciliated tentacles.

Orifice – The opening in an ectoproct bryozoanthrough which the lophophore is extended.

Phylactolaemate – A bryozoan classified in the Phy-lum Ectoprocta (Bryozoa), Class Phylactolaemata.

Polypide – A slightly extendable bundle of organs inectoproct bryozoans, including the complete gut,lophophore, and nerve ganglion.

Proximal – Referring to the region of a bryozoanzooid closest to the parental zooid.

Pylorus – The region of the bryozoan stomach passingdigested food to the intestine.

Sessoblast – A type of statoblast cemented directly tothe substratum.

Statoblast – A specialized hibernaculum in phylacto-laemate bryozoans.

Zooecium – The body wall of an ectoproct bryozoan,including both ectocyst and endocyst.

Zooid – The basic repeating module of a bryozoancolony, including all structures necessary for sus-tained life.

Further Reading

Allman GJ (1856) A Monograph of the Fresh-Water Polyzoa,Including all the Known Species, Both British and Foreign.London: Ray Society.

Hayward PJ (1985) Ctenostome Bryozoans. London: Linnaean

Society of London and Estuarine and Brackish-Water Sciences

Association.Hondt J-Ld’ (1983) Tabular keys for identification of the recent

ctenostomatous Bryozoa. Memoires de l’Institut Oceanographi-que 14: 1–134.

Lacourt AW (1968) A monograph of the freshwater Bryozoa –Phylactolaemata. Zoologische Verhandelingen. No. 93. Leiden:

E.J. Brill.

Nielsen C (1989) Entoprocts: Keys and notes for the identificationof the species. Synopses of the British Fauna (New Series), vol.41. The Linnean Society of London and The Estuarine and

Brackish-water Sciences Association. Leiden: E.J. Brill.

Nielsen C (2002) The phylogenetic position of Entoprocta, Ecto-procta, Phoronida, and Brachiopoda. Integrative and Compara-tive Biology 42: 685–691.

Smith DG (2001) Pennak’s Freshwater Invertebrates of theUnited States: Porifera to Crustacea. New York, NY: JohnWiley and Sons.


Wood TS (2001) Bryozoans. In: Thorp J and Covich A (eds.)

Ecology and Classification of North American Freshwater Inver-tebrates, pp. 505–525. San Diego, CA: Academic Press.

Wood TS and Okamura B (2005) A New Key to the FreshwaterBryozoans of Britain, Ireland and Continental Europe, withNotes on their Ecology. Ambleside, UK: Freshwater BiologicalAssociation Publication.

Wood TS (2005) Study methods for freshwater bryozoans.Denisia16: 103–110.

Wood T and Lore M (2005) The higher phylogeny of phylactolae-mate bryozoans inferred from 18S ribosomal DNA sequences. In:

MoyanoHI, Cancino JM, andWyse-Jackson PN (eds.) Bryozoan

Studies 2004: Proceedings of the 13th International BryozoologyAssociation, pp. 361–367. London: Taylor and Francis.

Wood TS, Anurakpongsatorn P, and Mahujchariyawong J (2007)

Introduction to the Freshwater Bryozoans of Thailand.Bangkok: Biodiversity Research and Training Program.

Relevant Website

www.nhm.ac.uk/hosted_sites/iba. www.civgeo.rmit.edu.au/bryozoa/

iba.html – International Bryozoology Association.

http://www.nhm.ac.uk/hosted_sites/iba

http://www.civgeo.rmit.edu.au/bryozoa/iba.html

http://www.civgeo.rmit.edu.au/bryozoa/iba.html

encyclopedia of inland waters || bryozoa

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