Plesiocleidochasma Soule, Soule & Chaney, 1991

Berning, Björn, 2012, Taxonomic notes on some Cheilostomata (Bryozoa) from Madeira, Zootaxa 3236, pp. 36-54 : 47-48

Genus Plesiocleidochasma Soule, Soule & Chaney, 1991

Plesiocleidochasma Soule et al., 1991: 474 ; Tilbrook 2006: 290.

Schedocleidochasma Soule et al., 1991: 480 ; Tilbrook 2006: 293; Zágoršek 2010: 166. Type species: Lepralia porcellana var. normani Livingstone, 1926 .

Diagnosis (amended). Colony encrusting uni- to multilaminar, multiserial. Zooecia ovoid, hexagonal or polygonal, few distal pore-chambers present; frontal shield imperforate except for a few marginal areolar pores; secondary calcification during ontogeny may be extensive, obscuring surficial primary features. Primary orifice cleithridiate, poster with smooth inner rim (not beaded) forming strong proximally directed condyles, anter rounded or bluntly arrow-shaped; oral spines usually present in young zooids only. Ovicell globose, hyperstomial, ooecium imperforate with calcified ectooecium quickly covered and disguised by hypercalcification of distal zooid(s); proximal ooecial margin variably shaped, often with lateral incisions and a central ectooecial fenestra of different shape and size, occasionally with horizontal bars merging medially to form a labellum; not closed by operculum. Avicularia adventitious, single or paired, mono- or dimorphic, generally situated close to orifice, rostrum usually acute, seldom wide and/or rounded distally, with a variably developed internal shelf that may form a triangular or trifoliate distal opesia; crossbar usually complete and with ligula. Ancestrula tatiform with well-developed proximal gymnocyst.

Remarks. Schedocleidochasma Soule, Soule & Chaney, 1991 (type species Schedocleidochasma porcellaniforme Soule, Soule & Chaney, 1991 ) is here synonymised with Plesiocleidochasma Soule, Soule & Chaney, 1991 , which was introduced earlier in the same publication. Soule et al. (1991) distinguished these genera mainly based on presumed differences in formation of the proximal ooecial margin. Whereas Plesiocleidochasma has a simple median labellum framed by lateral incisions, the labellum in Schedocleidochasma is produced by lateral horizontal bars merging in the centre, leaving a transverse, slit-like fenestra. However, in several species there are intermediate stages between these morphological ‘end-members’. For instance, in Plesiocleidochasma mediterraneum Chimenz, Gusso & Soule, 2003 there is a small median fenestra in the labellum, which would rather place it in Schedocleidochasma , but which is covered during ontogeny, and only then resembles the characteristic imperforate labellum of Plesiocleidochasma . In contrast, Lepralia porcellana Busk, 1860 (see below), originally placed in Schedocleidochasma by Soule et al. (1991), does have a central fenestra, which is, however, small and rounded rather than slit-like, while lateral bars were not observed to contribute to the formation of the fenestra. Moreover, the lateral incisions are absent or only very faintly developed in this species. It thus appears that a range of different morphologies of the proximal ooecial margin exist in this species group and that a clear dividing line between taxa cannot be drawn. As all other characters are identical or interchangeable, the separation of these genera is, in my opinion, unjustified.

The generic diagnosis is therefore amended to include characters hitherto reserved for Schedocleidochasma . Information on the ancestrula, which has been figured by Pizzaferri & Berning (2007: fig. 4A) for the first time, is also incorporated.

Recent species included in the genus Plesiocleidochasma are: P. normani ( Livingstone, 1926) , P. cleidostomum ( Smitt, 1873) n. comb., P. fallax ( Canu & Bassler, 1929) , P. immersum ( Soule, Soule & Chaney, 1991) n. comb., P. laterale ( Harmer, 1957) , P. mediterraneum Chimenz Gusso & Soule, 2003 , P. perspicuum ( Hayward & Cook, 1983) n. comb., P. porcellaniforme Soule, Soule & Chaney, 1991 n . comb., P. porcellanum ( Busk, 1860) n. comb., and P. septemspinosa Tilbrook, 2006 .