Placidoporella, Souto, Javier, Berning, Björn & Ostrovsky, Andrew N., 2016

Souto, Javier, Berning, Björn & Ostrovsky, Andrew N., 2016, Systematics and diversity of deep-water Cheilostomata (Bryozoa) from Galicia Bank (NE Atlantic), Zootaxa 4067 (4), pp. 401-459 : 444-445

Placidoporella n. gen.

Type specie s: Microporella insperata Jullien, 1882 .

Diagnosis. Colony encrusting, uniserial, with c. 40° bifurcations at irregular intervals. Zooids oval, frontal shield lepralioid, bearing numerous pseudopores across entire surface except for sloping part distal to orifice, vertical walls absent, interzooidal communications via 2 small flat distolateral basal pore-chambers; orifice transversely Dshaped, with no oral spines, proximal margin slightly convex, condyles present. Ovicells hyperstomial, terminal; ooecium kenozooidal, resting on frontal shield of maternal zooid distal to orifice and communicating with visceral coelom via 1–2 pores; ectooecium calcified with several pseudopores, laterally covered by imperforate secondary calcification of maternal zooid. Avicularia absent. Ancestrula unknown.

Etymology. Latin placidus, flat, shallow, alluding to the gently convex frontal shield rising from the substratum in the absence of lateral walls, plus - porella , a common suffix for bryozoan taxa with a pseudoporous frontal shield. Gender feminine.

Remarks. Microporella insperata Jullien, 1882 , which is conspecific with the Galicia Bank material and which we select here as the type of the new genus, belongs neither to Microporella Hincks, 1877 nor to the Microporellidae Hincks, 1879 . Owing to the ‘smittinid’ appearance of the ooecium, Placidoporella n. gen. is tentatively placed in the Smittinoidea, although it is difficult to assign it to any of the known families. It is unique in its absence of lateral walls along the proximolateral zooidal margins, having only a pair of extremely reduced, low-arched, distolateral basal pore-chambers, from which one or two zooids are budded. The ooecium is kenozooidal and is positioned on the sloping distal wall of the maternal zooid instead of being produced by the distal zooid as in all other smittinoid taxa. The zooidal orifice is transversely D-shaped and has condyles, whereas other characters in existing Smittinoidea, such as a lyrula (most Smittinidae ) or a sinus ( Bitectiporidae ), are absent. Moreover, oral spines and avicularia are wanting. However, as it is vaguely similar to Galiciapora unica n. gen., n. sp. (see below), we tentatively assign it to the Bitectiporidae .

Placidoporella is morphologically also similar to the new genus and species Cheilonellopsis inflata Gordon, 2014 , which was placed in the Lacernidae mainly owing to its ooecial characters (membranous ectooecium, smooth imperforate endooecium, produced by the distal zooid). The similarities between these two species from distinctly distant regions is remarkable, both sharing the same colony and autozooidal morphology, as well as the budding pattern and the absence of vertical walls with only two distolateral pore chambers remaining (Gordon 2014, figs 8E,F). Differences in ovicell type and formation between C. inflata (ectooecium membranous, ooecial fold formed by the distal zooid) and Placidoporella insperata n. comb. (with calcified ectooecium, kenozooidal origin, positioning on the maternal zooid), however, do not allow placing the two taxa in the same family.

The exact type of ovicell closure in P. insperata is impossible to distinguish in dry material. The proximal ovicell margin parallels that of the primary orifice, indicating that it may be closed by the operculum during embryonic development, i.e. closure is cleithral (subcleithral) sensu Ostrovsky (2008, 2013). Yet the operculum was never seen resting on the ooecial margin, and it is questionable if it can reach the ooecial margin as the ovicell opening is fairly elevated above the primary orifice. It is therefore possible that the closure type is acleithral (pseudocleithral).