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An Illustrated Glossary of Terms used in Bryozoan Taxonomy and Ecology

Compared to many invertebrate groups bryozoan species are quite easy to distinguish from one another (although putting a name on a species from a poorly known area may be another story!).  The skeletal characters used in traditional taxonomy are species specific and differences in them have been linked to directly linked to genetic differences.  Not only that, but most of the important characters needed for an identification can be seen in living or preserved colonies at magnifications of 50-100X under a good dissecting microscope.  However, the proliferation of terms used to describe these animals, whose basic structures and colonial nature are so different from our own, can easily discourage a student or non-specialist from making the attempt.  The following is an alphabetical guide to terms used in bryozoan taxonomy.  When possible they are illustrated with drawings or SEM pictures.




Ancestrula = first zooid of a colony, formed from the settled and metamorphosed larva.  Often smaller and morphologically distinct from the zooids that bud from it, it is sometimes useful taxonomically.  In some species it is still visible in mature colonies, in other species it is overgrown or decays as the colony grows.
Areolae = marginal pores in the frontal walls of zooids.
Ascus =flexible sac beneath the frontal wall of ascophoran zooids. 
Autozooid = normal feeding individual of a bryozoan colony.
Avicularium = a modified cheilostome zooid with an operculum bigger than that of a regular zooid and/or transformed into a spoon-, beak- or blade-like mandible.  The mandible is opened and closed by enlarged muscles; other internal organs are missing or rudimentary.  Adventitious avicularia are located on the lateral,  frontal, or basal wall of an autozooid and are usually smaller than the supporting autozooid.  Vicarious avicularia replace an autozooid in the budding series, and are usually in the same size range as the autozooids of the colony.  Interzooecial avicularia are placed in the budding series and communicate with at least two zooids, but are smaller than autozooids in size. Pedunculate "bird's head" avicularia are found in some groups.
Clonal = resulting from asexual reproduction or budding.

Colony = group of genetically identical, asexually produced, and physically and physiologically linked individuals.  The ecology of colonial animals is very different in some ways than that of solitary animals and resembles that of clonal plants.

Condyles = small, paired skeletal projections on which the operculum of autoozoids or the mandible of an avicularium hinges.
Costae = the modified spines which form a frontal shield over the frontal membrane of cribrimorph cheilostome zooids.
Cross-bar = a bar of calcified skeletal material on which the mandible of an avicularium is hinged.
Cryptocyst = frontal wall skeletal structure formed by calcification of an interior wall which grows out parallel to, but beneath, the frontal membrane.  In a living zooid there is coelomic fluid filled space between the cryptocyst and the frontal membrane, as well as uncalcified spots for the passage of muscles and connections to the main body cavity of the zooid.

Decumbent = flat-lying, used in reference to the position of zooids as the growing edge of the colony.

Distal = the direction toward the growing edge of the colony and away from the ancestrula, the origin of colony growth.
Erect = used in two senses:  (1) colonies with bushy or tree-like growth forms;
(2) zooids with deep body cavities and short frontal walls, often with the orifice displaced medially.
Frontal = in the direction of the orifice bearing surface of the zooid or colony.
Frontal budding = secondary budding of zooids from the frontal membrane of the initial or previous zooid layer.
Frontal membrane =  uncalcified frontal body wall, consisting of an outer cuticle produced by an underlying epidermis.
Frontal wall = calcareous frontal skeletal covering of zooid.  May be formed in several ways, and may also be modified by secondary calcification over the life of the zooid.  Structure and texture of the frontal wall is an important taxonomic character in cheilostome bryozoans.
Gymnocyst = frontal wall formed by deposition of calcification between the outer cuticle and the epidermis of the frontal membrane.  It may have "pores", uncalcified areas in the cuticle.
Heterozooid = non-feeding cheilostome polymorph, with different musculature and function.
Introvert = portion of polypide that extends from the zooid and bears the lophophore to feed.   
Kenozooid = polymorph lacking polypide and most or all internal structures, muscles, etc.
Lappets = lateral extensions of the calcification of the peristome.
Lophophore = feeding organ composed of a circle (or horseshoe in most phylactolaemates) of ciliated tentacles.
Lyrula = A tooth-like projection of calcification located in the center of the proximal edge of the orifice.
Mandible = the enlarged and thickened operculum of an avicularium, modified for defense or cleaning.
Mural rim = raised inner edge of the gymnocyst.
Operculum = flap-like fold of body wall, reinforced by cuticle (and/or calcification, that closes the orifice in cheilostomes.
Opesia = non-calcified area under the frontal membrane, bordered by cryptoyst, allows for operation of zooid hydrostatic system.
Opesiule = groove or hole in cryptocyst for passage of parietal muscles.

Oral =adjacent to the orifice.

Orifice = opening through which lophophore and introvert are protruded.
Ovicell = brood chamber, usually mostly calcified and located at the distal end of the maternal zooid.  Embryos are brooded until they develop into non-feeding larvae, which swim briefly, then settle and metamorphose to found a new colony.  
Palate = the space beneath the mandible of an avicularium (homologous to the orifice or opesia of an autozooid).
Peduncle = proximal portion of a bird's head avicularium, modified into a stalk.
Peristome = a raised collar or rim of calcification surrounding the primary orifice.  Its opening, called the secondary orifice is often different in shape from the primary orifice.
Polypide tube = an extension of cryptocyst covering the retracted tentacle sheath in some families of anascans, e.g., Steginoporellidae.

Polymorph = a zooid differing in morphology and function from ordinary feeding zooids (autozooids).  May have a reproductive, defensive, connective or supporting function.

Pores = gaps in calcification of zooid walls.  In dead, cleaned skeletal zooids (used in taxonomy), these are open holes, but in live zooids, they are covered by cuticle and may be plugged by tissue as well.
Primary orifice = the opening in the body wall through which the lophophore is protruded, located directly under the operculum in cheilostomes, or the zooid closure in ctenostomes and cyclostomes.
Proximal = in the direction of the origin of colony growth, the ancestrula.
Rostrum = a suboral spike of calcification, usually bearing an avicularium or the beaklike distal end of an aviciularium on which the closed mandible rests.
Scutum = a modified marginal spine (forked, enlarged, or flattened) which overarches the frontal membrane in the family Scrupocellariidae.

Secondary calcification = additional deposition of calcification  occurring as a zooid ages (and/or) is grazed or injured.  Since this can greatly change the appearance of zooids, for taxonomic purposes it is important to look at recently budded zooids near the growing edge of the colony, as well as those in the older regions.

Setae = elongate bristle-like mandible of a vibraculum.
Sinus =  an indentation or slit in the proximal end of a zooid peristome or the U or V-shaped indentation in the proximal margin of the orifice in ascophoran cheilostomes that allows water to enter the ascus.
Spatulate = spoon or broadly blade-shaped (avicularian mandibles).
Spine = a tubular or flattened projection of calcified body wall and coelomic cavity, sometimes jointed.
Stolon =  tubular kenozooids or extensions of autozooids.
Umbo = a mound-shaped sub-orifical projection of frontal wall calcification.
Vibraculum = an avicularium with an long bristle-like mandible.  In living colonies motion of vibracula may show coordinated sweeping movements.

Zoarium = bryozoan colony.

Zooecium = skeleton of a zooid.
Zooid = individual of a bryozoan colony.