Synallactidae Ludwig, 1894

Family Synallactidae Ludwig, 1894 View in CoL

Diagnosis. (adapted from SolÍs-MarÍn, 2003 and Smirnov, 2012 for Miller et al., 2017 erection of Synallactida ). Body usually flattened, with a ventral sole with ambulacral feet, dorsal surface with papillae. Head of the stone canal usually in connection with the body wall, sometimes opening outwards through it. Respiratory trees well developed. Tentacular ampullae absent. No Cuvierian organs. Gonad in two tufts, lying to either side of mediodorsal mesentery. Radial muscle bands typically undivided. Stone canal attached to the body wall and sometimes open externally. Calcareous ring can be well-developed, reduced, or altogether absent. Ossicles: tables, rods, sometimes C-shaped bodies, very rarely buttons.

Remarks. Cosmopolitan, often seen as an important epibenthic group in abyssal footage, but one of the least-studied deep-sea sea cucumbers ( SolÍs-MarÍn, 2005). At the species level, the differences in morphological characters can be quite subtle, obscuring taxonomic distinctions ( SolÍs-MarÍn, 2003), and many genera including “pygal-furrowed” groups were removed from this family when they were found to be polyphyletic ( Miller et al., 2017). Synallactidae is widespread in Australian waters. Of the ten genera now currently accepted worldwide, three have been previously recorded for Australia: Bathyplotes , Paelopatides , and Synallactes . All three are reported here for the IOT material, along with the first record for Scotothuria . Family diagnosis (above) chiefly follows SolÍs-MarÍn (2003) but has been amended to include Smirnov’s (2012) summary of ossicle types, and gonad in two tufts only, following the removal of Mesothuria (one tuft) during the revision by Miller et al. (2017). Future revision may still be required.