Family MICROPORELLIDAE Hincks, 1879

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Family MICROPORELLIDAE Hincks, 1879

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

The family Microporellidae Hincks (1879), is characterised by zooids with a semicircular orifice, generally without condyles, and a suboral ascopore. Apart from these distinctive features, and the common presence of basal pore-chambers, the family appears somewhat heterogeneous, although the range of morphological expression is such that intermediates between the component genera can be found. Thus a decision on whether these genera can be retained in the one family, or spread between three families, cannot be made until detailed work is carried out on the stratigraphic distribution and palaeogeography of the genera, as well as the ontogeny of zooids and ovicells in living representatives of key taxa.

The frontal shield ranges from being entirely cryptocystidean, with evenly distributed pseudopores and granulations (e.g. Microporella Hincks 1877) to having a smooth peripheral gymnocyst surrounding a cryptocystidean area that has sparse, complex pseudopores (e.g. some species of Fenestrulina Jullien 1888). In Calloporina Neviani (1895), pseudopores tend to be very sparse or entirely lacking (C. lunata (MacGillivray 1860) is a notable exception). Instead, conspicuous septular pores, somewhat areolate, occur along the margins. In Microporella and Fenestrulina, there is no outward distinction between septular pores and pseudopores. Ovicells differ too. In Microporella the ovicellular surface resembles that of the frontal shield. The same generally obtains for species of Fenestrulina; i.e., if the frontal shield is smooth with marginal pores, so is the ovicell. If it is evenly perforated with complex pseudopores, so is the ovicell, though there are some exceptions. In Calloporina, on the other hand, the ovicell has a smooth frontal area bordered by a distinctive porous crescent. Oral spines can occur in all three genera. Avicularia are paired or single in Microporella and Calloporina but entirely lacking from Fenestrulina. The crossbar is complete and the mandibles range from shortly triangular to nearly setiform. The ascopore is crescentic and toothed in both Microporella and Fenestrulina (sometimes grating-like in the former), but a smooth slit or circular hole in Calloporina. The ancestrula tends to be tatiform in all three genera but can resemble 'adult' zooids in Fenestrulina. In some species of Microporella and at least one of Fenestrulina (which may represent a new genus) the proximal corners of the ovicells are extended proximally (lappets) to flank or even embrace the orifice and/or ascopore. Colonies of Microporella and Fenestrulina tend to be mostly white or even hyaline and semitransparent, whereas those of Calloporina tend to be coloured pink or red (though there are exceptions in the latter two genera). Thus overall, there seem to be no collective characters that consistently separate the genera.

Members of the family have representatives in all seas. As presently conceived, the family includes eight genera of which at least three occur commonly in Australian waters. These are reasonably speciose for Bryozoa (Microporella 5, Fenestrulina 10, Calloporina 4); these figures including known undescribed species. These species are all encrusting, occurring on algae, coral, the undersides of boulders, or on rock faces, depending on the species.

Ryland & Hayward (1992) revised some records of the widely distributed Microporella orientalis from the Great Barrier Reef, and noted the occurrence there of the rarely reported M. lunifera (Hayward & Ryland 1995). They introduced two new species of Fenestrulina in these papers, but the largest number of species of this genus occurs from Antarctic and subantarctic waters. Hayward (1995) described nine species from these regions, as well as two species of the erect, bilaminar genus Adelascopora. Bock (1982) and Wass & Yoo (1983) figured several species of Calloporina from southern Australia. Ryland & Hayward (1992) described and redefined M. orientalis from the Great Barrier Reef, together with one new form of Microporella. They also recorded a large colony of Fenestrulina caseola Hayward (1988), previously known only from the Mascarene Islands in the Indian Ocean.

Bock (1982) recorded Calloporina from southern Australia, C. canaliculata (MacGillivray 1860) being found encrusting Sargassum, whereas C. lunata (MacGillivray 1860) encrusted shells or rock. Bock also included records of Microporella and Fenestrulina, but the identifications need revision. There are several undescribed species of all three genera in Bass Strait.

The numbers of Antarctic and subantarctic species has been greatly increased by the investigations of Hayward & Thorpe (1988) and Hayward & Ryland (1990). The exclusively southern genus Adelascopora Hayward & Thorpe is represented by two species, A. divaricata (Canu 1904), first described from the Tertiary of Patagonia, and A. secunda. Both have erect, bilaminar branched colonies and the zooids have no avicularia. The ovicells are markedly different from other Microporellidae, having only a thinly calcified entooecium and a wholly membranous ectooecium. Hayward & Ryland (1990) recorded no fewer than 18 species of Microporellidae from the Antarctic and subantarctic. One new species of Calloporina, and 13 species of Fenestrulina, 9 of them new, were included.

The family dates from at least the Early Miocene (Taylor 1993). Adelascopora was first described from the Tertiary of Patagonia, and Calloporina has Australian and European Tertiary members. MacGillivray (1895) described several species assignable to Microporella and Fenestrulina from the Tertiary of Victoria, and Hayward & Taylor (1984) introduced a new species, M. stenoporta, from the Quaternary and Recent of Antarctica.

The affinities of the family and constituent genera are uncertain, but it is agreed that an ascopore is a derived feature and any ancestor would have had a sinusoid ('schizoporellid') orifice. Some species currently attributed to Escharina sensu lato closely resemble Microporella in having a similar frontal shield and ovicell and paired lateral-oral avicularia. On the other hand, the ovicell of Calloporina greatly resembles that of Chiastosella Canu & Bassler (in Bassler 1934), which is almost certainly ancestral. On the basis of the frontal shield it seems possible that Fenestrulina may be derivable from Calloporina; on the other hand, some species of Fenestrulina have a typical lacernid ovicell, i.e., globular with a smooth imperforate endooecium and membranous ectooecium. These difficulties explain why the superfamily Schizoporelloidea has for so long defied splitting into constituent family groupings with any degree of certainty.

Diagnosis

Colony well calcified, encrusting, sometimes multilaminar, occasionally erect. Zooids with a lepralioid frontal shield, with prominent marginal pores, and often with pseudopores. Orifice semi-circular, straight proximally, with a median, suboral ascopore. Avicularia, if present, adventitious and oral. Ovicells hyperstomial; with marginal pores and often with pseudopores frontally, sometimes combining with a raised peristome to form a spiramen.