Pseudostichopus sp.

Pseudostichopus sp.

Material examined. NMV F296875 About NMV * (1) [IN 2021 V 04 046] , NMV F308141 About NMV * (1) [IN 2022 V 08 103] ; NMV F308270 About NMV (2) and NMV F312998 About NMV (1) [IN 2022 V 08 145] .

Diagnosis IOT material. Four specimens with some variation in size and morphology are identified here to genus level Pseudostichopus . One specimen ( NMV F312998) with general morphology and longitudinal muscles of Pseudostichopus but insufficient characters to describe further. Three remaining specimens with some variation in size and morphology: all with round longitudinal muscles indicating Pseudostichopus ; opaque rather than truly transparent skin; ventral mouth with retracted pale yellow to brown peltate tentacles (~14 visible); ventral anus in pygal furrow; ossicles absent from body wall but present in tentacles as irregular rods. Rods mostly smooth and tapering at ends, occasionally spinous, straight to curved, many with a central knob; occasionally slightly thicker and more spinous or serrated on top; rare cross-rods with branched and twisted arms. Some specific morphology and sizes noted below.

NMV F308184: Medium, opaque white, elongate, semicylindrical specimen 10.6 cm long, 3 cm wide, and 2.5 cm high when preserved. Dorsally convex, ventrally flattened, tapering to rounded anterior and posterior ends. Body wall firm, thick, semi-gelatinous. Completely smooth with no wrinkles or obvious papillae or tube feet. Very light evidence of some sand, grit and forams, but looks bare to the naked eye. Up to 14.5 cm before preservation, somewhat curled and shrunken in ethanol. Tentacle ossicle rods (as described above) include irregular tapered rods, many with central swelling, up to 200 μm long; smooth and twisted cross-rods up to 80 μm broken (similar size and shape to fig. 11l in O’Loughlin and Ahearn, 2005); and many broken pieces.

NMV F 296875: Small, soft, brown specimen 2.2 cm long, 0.6 cm wide, and 0.4 cm high when preserved. Strongly raised dorsally and flattened ventrally with smooth opaque skin before preservation, slightly wrinkled and dorsoventrally flattened after. Completely covered in sand, grit and forams. Some radial dorsal papillae, but mostly obscured. Tentacle ossicle rods like those described above, up to 232 μm long, plus some additional thicker broken serrated/spinous examples.

NMV F308270: Small, soft, white specimen 1.8 cm long, 0.6 cm wide, and 0.2 cm high when preserved. Completely covered in sand, grit and forams. Radial ventrolateral margin wrinkled not smooth (when preserved) with a few well-spaced papillae visible, projecting from rounded mounds. Tentacle ossicle rods like those described above but smaller (e.g. 96 μm long) and more broken in this specimen.

Remarks. Variation within species-level characters, along with limitations in our own material, meant further identification based on descriptions or key from O’Loughlin and Ahearn (2005) was not possible. Specimens were possibly closest to Pseudostichopus aemulatus but showed many similarities to P. peripatus , with these species known to be alike. The key uses dense presence or complete absence of an encrusting cover as a major split for Pseudostichopus , including P. aemulatus (bare) compared to P. peripatus (covered), but both species are known to sometimes be encrusted with sand or fauna, as found here. COI is also inconclusive, showing that NMV F296875 (completely covered in sand and forams) has a 4.2% divergence from NMV F308141 (very light sand and forams). Papillae arrangement is also important, but these can be absent in larger specimens (SolÍs-Mar í n et al., 2004) which we observed here for NMV F308141, and unfortunately our other two specimens were also missing most papillae. O’Loughlin and Ahearn (2005) note that P. aemulatus is like P. peripatus but is opaque and off-white (a closer match to our specimens), rather than grey and semitranslucent; smooth, and lacking ridges (which matches at least two of these three specimens); and with dorsal papillae not widely separated and ventrolateral widely separated, which applies to the rare papillae that were seen. Tentacle ossicles fit P. aemulatus but are a closer match in shape to images of P. peripatus ( O’Loughlin and Ahearn, 2005, fig. 11i–l). At 80– 232 μm ossicle sizes are a closer match to P. aemulatus (up to 260 μm) than P. peripatus (up to 360 μm). There is some wrinkling of skin but no obvious serration like that described for Pseudostichopus peripatus and no red-brown tube feet as observed in that species. Without better material for morphological observation, or analysis of additional genes, we identify this IOT material to Pseudostichopus sp.

References. O’Loughlin and Ahearn (2005), SolÍs-MarÍn et al. (2004).

Order Synallactida Miller, Kerr, Paulay, Reich, Wilson, Carvajal and Rouse, 2017 View in CoL

Diagnosis. (see Miller et al, 2017)

Remarks. The order Synallactida was newly erected in 2017 with phylogenetics showing it forms a clear individual clade, and a polytomy with Persiculida and Molpadida ( Miller et al., 2017) . It comprises three families, all with representatives known from Australian waters: Deimatidae Théel, 1882 , Stichopodidae Haeckel, 1896 , and Synallactidae Ludwig, 1894 . As a mostly shallow-water family, Stichopodidae was not seen in the IOT material, but Deimatidae and Synallactidae were both represented.