Fatkullinidae, Grischenko, Gordon & Morozov, 2018

Grischenko, Andrei V., Gordon, Dennis P. & Morozov, Taras B., 2018, Fatkullina imitata n. sp., second species of a unique cheilostome bryozoan genus with reversed-polarity zooidal budding, and new family Fatkullinidae, Zootaxa 4508 (1) : -

Family Fatkullinidae n. fam.

Type genus: Fatkullina Grischenko, Gordon & Taylor, 1998 .

Diagnosis. Colony encrusting, unilaminar, darkly pigmented. Zooids with or without reversed-polarity budding. Frontal shield lepralioid, evenly pseudoporous. Primary orifice with median sinus and weakly developed condylar ridges. Oral spines and avicularia absent. Ooecia, if present, imperforate or with only a single pseudopore. Mural septula uniporous, set in buttressed recesses. Ancestrula externally resembling post-ancestrular zooids, but internally with reduced umbonuloid area suborally that also includes possible vestigial costal elements. Immediate periancestrular zooids part of an ancestrular complex.

Remarks. As noted by Zágoršek & Gordon (2013), the family Stomachetosellidae is very heterogeneous. It is based on the type genus and species Stomachetosella crassicollis Canu & Bassler, 1917 , early Oligocene, Mississippi, USA, which has erect stems that range from subvincularian to bilamellar/flabellate fronds in which the zooids, opening on all sides, have a regularly perforated pseudoporous lepralioid frontal shield. The orifice has a tapering rounded poster and condyles appear to be lacking. Ooecia are evenly pseudoporous, somewhat like the frontal shield. According to Canu & Bassler (1920) there is an inconspicuous avicularium near the orifice in some zooids.

Winston & Hayward (2012) compared the characters of S. crassicollis to those of living species attributed to Stomachetosella , concluding that the latter are unrelated to the former. They established a new genus, Stomacrustula , for all "the Recent species formerly attributed to Stomachetosella ", making new combinations for three of them— Stomacrustula cruenta ( Busk, 1854) (the designated type species), S. sinuosa ( Busk, 1860) and S. hincksi ( Powell, 1968) . Without explaining why, they did not make new combinations for the ten other Recent species. Stomacrustula was not attributed to a family but left incertae sedis. Stomacrustula species differ particularly from S. crassicollis in that the ooecium, if present, is imperforate or has only a central pore, and there are no avicularia. Note, however, that S. cruenta lacks ooecia ( Dick & Ross 1988).

Because Stomacrustula has much in common with Fatkullina , we provisionally include it in Fatkullinidae n. fam. pending confirmatory gene-sequence data. Inter alia, species in both genera have a very similar darkpigmented, unilaminar encrusting colony form and zooidal frontal shield and they mutually lack oral spines and avicularia. Additionally, both have deeply recessed septular pores. Grischenko et al. (1998) previously hypothesized that an ooecium-lacking form like S. cruenta may have been ancestral to Fatkullina . Fatkullina differs from Stomacrustula most obviously in having reversed-polarity zooidal budding, but there are also no ooecia in Fatkullina whereas they are well-developed in Stomacrustula (except, as noted, in the type species).

Some other living taxa attributed to the Stomachetosellidae can also be provisionally included in the Fatkullinidae . For example, the monotypic Arctic genus Lepralioides Kluge, 1962 is very similar to Stomacrustula , differing only in having a very broad, shallow orificial poster instead of a discrete sinus, and the single-pored ooecium is covered by secondary calcification (with sutures) formed by 2–3 neighboring zooids, which is not the case in Stomacrustula . The Boreal-Arctic, North Pacific genus Pachyegis Osburn, 1952 also shares several of the characters of Fatkullina —the type species, P. princeps Norman, 1903 , has reddish-brown to black pigmentation, a thickly calcified pseudoporous frontal shield, communication pores located in buttressed recesses and no oral spines. It is unclear if a suboral structure in some zooids is an avicularium or an opening pertaining to a gland. The ooecium resembles that in Lepralioides (http://www.iopan.gda.pl/ekologia/Atlas_of_Arctic_ Bryozoa /robaki/ Porella_princeps/ Type /index.html). Further work needs to be carried out to determine what other putative stomachetosellids, if any, may be transferred to Fatkullinidae .