Family SCHIZOPORELLIDAE Jullien, 1883

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Family SCHIZOPORELLIDAE Jullien, 1883

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The family Schizoporellidae Jullien (1883) and the genus Schizoporella Hincks are among the more familiar of bryozoan taxa, partly because some species of Schizoporella are marine foulers and also because the family, in the broad sense, is a large one, characterised by species with the distinctive 'schizoporellid' orifice, i.e., with a median U- or V-shaped sinus in the proximal rim, and pseudopores at least somewhere in the frontal shield. In recent years, however, it has come to be appreciated that the range of character states in the family is too large for it to be regarded as a single taxonomic entity, and attempts have been made to split it.

In the strict sense, the Schizoporellidae are characterised not only by the sinusoid orifice but a zooidal frontal shield that is evenly distributed with pseudopores. Adventitious avicularia usually occur, often in proximity to the orifice, and the ovicell has an outer skeletal surface in some ways resembling that of the frontal shield. It is this last feature that is of particular help in deciding which genera may be included in the family, because it does appear that some genera with relatively few pseudopores may nevertheless be schizoporellid. The ontogeny of the ovicell of Schizoporella has not been fully studied, but it appears that the two layers that normally make up the ovicell structure (internal entooecium and external ectooecium) are calcified and fused together in Schizoporella, with the intervening space obliterated. This arrangement, plus the resemblance of the ovicellular calcification to that of the frontal shield, differs significantly from that in several suites of genera previously attributed to the Schizoporellidae.

Schizomavella is here assigned to the Bitectiporidae, Buffonellodes to the Buffonellodidae , Lacerna to the Lacernidae, and Schizobrachiella to the Stomachetosellidae.

At present, only the genera Schizoporella and Stylopoma remain strictly referable to the Schizoporellidae here. The genera Chiastosella, Escharina, Hippomenella, Nimba, and Robertsonidra all require revision and assignment to one or more new families. In addition, a new genus is required for Schizoporella acuminata Hincks (1881), a widespread species from South Australia figured by Wass & Yoo (1983).

In the first category, that of Schizoporellidae in the strict sense, the immigrant, fouling species Schizoporella errata, was recorded from Port Adelaide by Brock (1985) and figured by Gordon & Mawatari (1992), whereas S. unicornis was recorded from north Queensland by Hall (1984). Eleven species of Stylopoma have been described from Australian waters (Tilbrook 2001). Most are coral-associated, and the pink colonies of S. velatum were the second most common species on this substratum in the samples from the Great Barrier Reef described by Ryland & Hayward (1992) and Hayward & Ryland (1995). The massive colonies of S. viride are green (Colin & Arneson 1995), and the large ovicells are visible to the naked eye. Even larger ovicells occur in S. magniovicellata Silén (1954) from Western Australia. This species has erect, bilaminar colonies. S. schizostoma is the most southerly species, and is described from Victoria, where locally it can be very common on jetty pilings and shells; a specimen was figured by Bock (1982), but with the misidentified name Arthropoma cecilii.

The genus Robertsonidra has been discussed by Ryland & Hayward (1992) and Hayward & Ryland (1995); several species occur from the Great Barrier Reef, as does Nimba saxatilis, which has uniserial chains of encrusting zooids. Hippomenella is a genus which may require revision. Two species have been recorded from Australia: H. bituberosa Brown, figured by Wass & Yoo (1983) from southern Australia, and H. avicularis (Livingstone), which was described as H. spatulata by Harmer (1957) from Queensland. Escharina pesanseris is a circumtropical to subtropical form which has paired avicularia beside the orifice, each with a distinctive mandible shaped like the webbed foot of a bird (hence the species name). It has been figured from the Kermadec Ridge by Gordon (1984) and from the Great Barrier Reef by Ryland & Hayward (1992), and is a common reef-associated species.

The genus Chiastosella is so similar in character to Calloporina (Microporellidae), that both groups of species probably require a family of their own. Brown (1954) first noted parallel groups of species in these genera, Calloporina with an ascopore, and Chiastosella with a median orifice sinus. Both have large, hyperstomial ovicells, with a crescent of distal septular pores. Chiastosella daedala was figured from South Australia by Wass & Yoo (1983).

Most of the schizoporellids mentioned above are strictly encrusting, occurring on rock faces, rocks, and shell gravel, and less commonly on algal holdfasts. Given the taxonomic uncertainties surrounding the family, little can be said about the age and affinities of the Australian fauna. Certainly Chiastosella, 'Hippomenella', and some of the unnamed genera occur in the Victorian Miocene (MacGillivray 1895; Brown 1958).

Diagnosis

Colony well calcified, encrusting with unilaminar or frontally budded expansions, occasionally bilaminar. Zooids with lepralioid frontal shield, often with pseudopores. Orifice with a proximal sinus. Avicularia adventitious, occasionally interzooidal and very large. Ovicell hyperstomial, sometimes very large, with similar structure to the zooid frontal, entooecium and ectooecium fused.