Trochosodon Canu and Bassler, 1927

Bock, Philip E. & Cook, Patricia L., 2004, A review of Australian Conescharellinidae (Bryozoa: Cheilostomata), Memoirs of Museum Victoria 61 (2), pp. 135-182 : 163-164

Trochosodon Canu and Bassler, 1927

Trochosodon Canu and Bassler, 1927: 11 .— Canu and Bassler, 1929:

493.— Harmer, 1957: 744.

Type species. Trochosodon linearis Canu and Bassler, 1927 (original designation).

Description. Colonies forming a low cone, orifices both radially and quincuncially arranged, antapical marginal series of zooids tubular, projecting, often prominent; frequently without avicularia. Adapical pores and kenozooids present, among large rounded root pores; lunate pores also reported to be present. Avicularia and ovicells present. Antapical cancelli usually rare or absent.

Remarks. Canu and Bassler (1927, 1929) considered that Trochosodon was characterised by the absence of avicularia. The type species, T. linearis ( Canu and Bassler, 1927: 11, 42, pl. 1 fig. 12; 1929: 493, pl. 1 figs 11–13), was from Sibuko Bay, Borneo (Albatross stn 5586), from a depth of 247 fathoms (625 m). The unique figured colony was 2.5 mm in diameter, with approximately 6–8 zooids per whorl and a strong tendency for the orifices to be arranged radially. The marginal peristomes were prominent and the antapical surface was convex, with little structure except some scattered pores, that may have been minute avicularia. No avicularia appear to have occurred on the adapical surface near the peristomes. Canu and Bassler (1929: 494, pl. 70 figs 7–10) also described T. quincuncialis from the same station. It was distinguished by its quincuncially arranged orifices but pl. 70, fig. 10 clearly shows some series to be radially arranged; it is probable that the two species are synonymous. Canu and Bassler (1927, 1929) gave no details of the primary orifices except that they were sinuate. Their figures were all retouched but pl. 70 fig. 12 perhaps shows a few adapical pores. Harmer (1957: 744) noted difficulties in defining Trochosodon , remarking “it is not easy to establish a clear distinction between this genus and Conescharellina ”, maintaining that all the abyssal species, including T. linearis that he assigned to the genus, possessed avicularia. However, he could not have examined the unique type specimen of T. linearis sensu stricto and it seems possible that his Siboga specimens belonged to a distinct species (see below). Generally, the distinguishing features of Trochosodon include prominent, tubular marginal peristomes and virtual or complete absence of antapical cancelli. Gordon (1989) introduced several abyssal species from the New Zealand region but the only authentic past records from Australia appear to be those of T. ampulla (Maplestone) , described below and three hitherto unnamed species from Cape York, Queensland, figured by Cook and Lagaaij (1976) and Cook (1981), from Challenger stn 185, from 279 m, a locality that was not mentioned by Busk (1884). These colonies are here referred to T. aster sp. nov., T. anomalus sp. nov. and T. praecox sp. nov., bringing the total of species described from Australia to seven. Ovicells were described by Harmer (1957) in T. optatus (see below). These appear to be asymmetrical and have ridged frontals, resembling those of specimens of T. fecundus sp. nov. from north-western Australia, that are, however, symmetrically developed. Similarly ridged ovicells were reported in C. striata by Silén (1947) but these were also asymmetrically developed, like those of C. catella , as described by Harmer (1957), and almost certainly of T. asymmetricus sp. nov. A suite of independent character states distinguishing “ Trochosodon ” from “ Conescharellina ” is thus far from complete or consistent. However, the wide diversity of species assigned to Conescharellina itself, suggests that this genus will certainly require eventual revision, including a definition of its type species and a review of all other taxa referred to it (see Silén, 1947: 34). Until this is accomplished, it is probably wisest to maintain Trochosodon for a group of species that are fairly consistent and differ slightly from most other forms assigned to Conescharellina . Australian species are introduced here from New South Wales, Victoria, north-west Australia and Queensland. Although they exhibit a mosaic of characteristics some of which can be regarded as “typical” of Conescharellina , they are considered here to be distinct enough to be assigned provisionally to a generic group and referred to Trochosodon . Harmer (1957) considered this to be mainly an abyssal genus but material included here also derives from shallow depth.