Family LABIOPORELLIDAE Harmer, 1926

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Family LABIOPORELLIDAE Harmer, 1926

Compiler and date details

July 2001 - Dr Philip Bock

Labioporellidae Harmer, S.F. 1926. The Polyzoa of the Siboga Expedition. Part 2. Cheilostomata Anasca. Siboga-Expéditie Report 28B: 183-501 [280].

Introduction

The family Labioporellidae was introduced by Harmer (1926) for the genus Labioporella, but this genus has since been included in the Steginoporellidae (for example Cook 1964). Originally, Labioporella was distinguished by the absence of avicularian or B-zooids with tentacles, but these occur in the avicularia of Labioporella dipla Marcus (Cook 1964). In addition, one species of Steginoporella, S. mandibulata Harmer (1926) has avicularia with no tentacles or viscera, further reducing the difference between the two families . However, the genus Siphonoporella, which has no avicularia or B-zooids, also shares several characteristics with Labioporella. Harmer (1926) was not certain whether or not Siphonoporella required a distinct family of its own. It appears that Labioporella and Siphonoporella share sufficient features to allow their inclusion together in the family Labioporellidae, and Labioporella would seem to be more naturally placed here, than in the Thalamoporellidae (Ryland & Hayward 1992).

The characters of the Labioporellidae are principally those of the cryptocyst and polypide tube, and secondarily of the avicularia where present. The cryptocyst is well developed proximally, descending eccentrically to the basal wall. The polypide tube is only slightly developed, and is placed on one or other side of the mid-line; there are no lateral expansions.

The name Labioporella was introduced by Harmer (1926) as a replacement name for Labiopora Levinsen (1909) with the type species L. crenulata. Species of Labioporella have smaller colonies and zooids than those of Steginoporella, and the zooids have fewer tentacles, ranging from 12-14 in number. Avicularia are often rare, and usually have a proximal cryptocyst and a subspatulate mandible. Four species are known from Australia, but no detailed comparative analysis has been made to confirm whether these species are really distinct, or if additional species are present. The common species from southern Australia is usually identified as L. bursaria, first described and assigned to Amphiblestrum by MacGillivray (1887) who reported it from Victoria. Membranipora bimamillata MacGillivray (1885) appears to be a senior synonym of L. bursaria. MacGillivray's additional records of this species are as Biflustra jugalis (1890) from South Australia, and as Membranipora rossellii (1879). It has also been recorded from the Great Barrier Reef by Ryland & Hayward (1992 ), from N. Cottesloe, W.A, by Silén (1954) and from Adelaide, S.A. by Harmer (1926). A species of Labioporella was figured by Maplestone (1905) from Lord Howe Island, as Thalamoporella howensis, which may have been of L. bimamillata. Another record was by Wass & Yoo (1983) who figured an unnamed species from Bass Strait. The reason for the difficulty of identification of this species appears to be the thick cuticle, which largely obscures the details of the cryptocyst. The only record of L. crenulata (Levinsen) from Australia is that given by Harmer (1926) from Torres Strait. L. crenulata has a more expanded avicularian mandible. In the absence of avicularia, it is very difficult to distinguish between one species and another.

The genus Siphonoporella was introduced by Hincks (1880) for the Australian species, S. nodosa (Hincks 1880). Levinsen (1909) included Membranipora delicatissima (Busk 1861) in the genus. Both have small gymnocysts, thinly calcified, but distinct, sometimes nodular cryptocysts, and long eccentrically placed polypide tubes; avicularia are absent. However, a bryozoan collected from southwestern Australia, which appears to be close to Siphonoporella nodosa, has at least one avicularium. Colonies encrust algae from Western Australia (Hastings 1966).

Labioporella has a long fossil record, extending from the Eocene of southern England (Cheetham 1966): at least one species is recorded from the Miocene of southern Australia (Canu & Bassler 1935). Colonies of Siphonoporella are too delicate to have been preserved as fossils.

Diagnosis

Colonies erect or encrusting. Zooids subrectangular, with proximal perforate cryptocyst descending at the sides, rarely forming opesiules or opesiular indentations. Cryptocyst forming a central or lateral polypide tube. Interzooecial avicularia with spatulate mandible. Larval brooding presumed to be internal; brooding zooids not differentiated.