Family CELLARIIDAE Fleming, 1828

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Family CELLARIIDAE Fleming, 1828

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

This large family was established by Lamouroux, 1821. It comprises about ten genera worldwide and perhaps more than 100 species, principally within the type genus Cellaria Ellis & Solander (1786). Busk (1884) gave the first detailed account of the family, based upon ten species of Salicornia (=Cellaria) and two species of Melicerita. He divided Cellaria into three groups on the basis of the branching mode of each species, but did not give them formal taxonomic ranking; Hastings (1947) noted that the morphologies defining each group intergraded. Subsequent attempts to recognize independent generic groups within Cellaria have proved unsuccessful; Cellariaeforma Rogick (1956) and Neocellariaeforma d'Hondt (1984) were each characterized by features seen within the type species of Cellaria, and in most other species of the genus, and were not considered separable from Cellaria by Hayward (1995). The family is abundantly represented in the southern hemisphere (see Gordon 1984, 1986); nine species of Cellaria and a single species of Melicerita are known from Australia. Rogick (1956) first reviewed the Antarctic fauna, which now totals 20 species in the genera Cellaria, Paracellaria Moyano (1969), Swanomia Hayward & Thorpe (1989) (formerly Mawsonia), Stomhypselosaria Canu & Bassler (1927), and Melicerita Milne-Edwards (1836).

Bock (1982) listed several species of Cellaria occurring from southern Australia, and described C. pilosa, which differs from most forms in possessing long, uncalcified spines, which originate from the proximal end of each zooid. Wass & Yoo (1983) listed numerous specimens of C. rigida from a wide range of localities, and a species of Melicerita was part of a rooted 'sand fauna' described from fairly deep water (366 m) off the Victorian coast by Cook (1979). The alleged identity of fossil Cellaria dennanti from the Australian Tertiary with Antarctic specimens has been shown to be incorrect (Hayward & Ryland 1993).

The Pacific genus Mesostomaria Canu & Bassler (1927) has been discussed by Gordon (1984). M. hastingsae d'Hondt & Redier (1977) from Kerguelen has been referred to Cellaria clavata by Hayward & Thorpe (1989).

All cellariids develop slender, erect colonies, branched or rod-like. In Cellaria branches consist of rigid, cylindrical nodes linked by chitinous joints. In other genera branches may be flat-sectioned, and dichotomies may be rigidly calcified. The frontal shield of the zooid consists of a concave cryptocyst, and there is a reduced, semicircular or semielliptical opesia, almost exactly coincident with the operculum.

Colonies of Cellaria consist of cylindrical, jointed branches which divide dichotomously, or through the development of lateral, adventitious branches. The joints (nodes) consist of one to several short, cuticular tubes, continuous with the zooids constituting the base of the new internode, or of bundles of twisted and knotted cuticular rhizoids budded from the frontal surfaces of zooids on either side of the jointing plane. Colonies are anchored to the substratum by similar rhizoids originating from the proximal internodes of the colony. Internodes consist of whorls of two to many zooids; number of zooids in a whorl and internode length vary little within each species. In Paracellaria the node is a simple fracture plane, secured by knotted rhizoids; Paracellaria and Swanomia develop dichotomously branching cylindrical colonies but are unjointed. In Melicerita Milne-Edwards (1836) the colony is typically flat-sectioned, with acute edges, and may be narrowly sabre-like or lobate, with infrequent and irregular branching.

Zooids tend to be rectilinear, hexagonal and in alternating rows in Melicerita, but either rhomboidal or hexagonal in cylindrical branched genera. The cryptocyst is concave between the raised ridges of the lateral walls, but often convex medially, and in many species of Cellaria with paired longitudinal ridges, of unknown significance, bounding the median half of the frontal shield. The D-shaped opesia rarely constitutes more than one quarter total zooid length, and is exactly coincidental with the operculum. In almost all cellariids paired condylar processes (denticles) are present within the proximo-lateral corners of the opesia, massively developed in Swanomia, and there may be opposing distal denticles as well. Avicularia occur in most species and may be interzooidal, as in most species of Cellaria, or obviously vicarious, as in the massive avicularia of Swanomia. In Stomhypselosaria a single vicarious avicularium is present at the proximal end of each branch, immediately distal to the dichotomy.

Ovicells of Cellaria and Melicerita are immersed within the colony, with an independent aperture immediately distal to the maternal opesia. This type of ovicell has been termed endotoichal. Ovicells of Paracellaria, Stomhypselosaria and Swanomia are fundamentally the same as those of Cellaria but the larger aperture is provided with a bulging distal hood which projects markedly from the colony surface. Kenozooids are characteristic of Melicerita; they occur at the termination of zooid rows, contributing the smooth, acute edges to the colony.

Cellariids are frequently abundant on coarse grounds, their flexible, jointed colonies appearing adapted to withstand considerable current movement. They attach to a wide variety of substrata and many species of Cellaria seem to select organic substrata, including shell, large hydroids and other bryozoans. Biology and ecology are poorly known. The Antarctic Swanomia membranacea (Thornely 1924) develops stout, thickly calcified colonies to 50 mm or more high, and is perhaps perennial. Conversely, Melicerita obliqua (Thornely 1924), another endemic Antarctic species, invests heavily in sexual reproduction and has poor regenerative ability, and is perhaps relatively short-lived as a consequence (Winston 1983).

The fossil record of the family extends from the Late Cretaceous (Taylor 1993); Cellaria and Melicerita have a Tertiary distribution in Europe and Australia.

Diagnosis

Colonies erect, jointed or unjointed, attached by rhizoids. Branches cylindrical or flattened bilaminar. Zooids subhexagonal or rhomboidal, with extensive imperforate cryptocyst; opesia restricted to a semicircular area with a covering operculum. Avicularia interzooidal or vicarious. Ovicells endotoichal, often with opening separated from opesia.