Psychropotes longicauda Théel, 1882

Psychropotes longicauda Théel, 1882 View in CoL

Psychropotes longicauda Théel, 1882: 96–98 View in CoL , pls. 27: 1, 28, 35: 13–17, 37: 10. — Hansen, 1975 (in part): 115–126, fig. 49: 1–5. — Rogacheva et al., 2009: 473–474, fig. 7.— Gebruk et al., 2014: 161. — Gubili et al., 2017: 288–296. — Gebruk et al., 2020: 1–5, fig. 1.

Non: Psychropotes longicauda View in CoL var. fusco-purpurea Théel, 1882: 99, pls. 29: 1, 35: 11.

Non: Psychropotes longicauda var. monstrosa Théel, 1882: 98– 99 , pls. 29: 2, 30, 39: 1.

Non: Psychropotes longicauda var. antarctica Vaney, 1908: 419– 420 .

Material examined. NMV F308333 About NMV * (1) [IN 2022 V 08 196] .

Diagnosis of IOT material. Single specimen, elongate and semicylindrical, with a rounded dorsal surface, slightly constricted before additional dorsoanterior bulging, flattened ventrally, and flattened at each end once preserved, ~ 125 mm long, 37 mm wide and 20 mm high (preserved).Soft but unusually firm for this typically gelatinous species and almost black shipboard (see Remarks). Dark purple to violet/red preserved. Unpaired dorsal appendage of same colour as body, fin-like in appearance, and very close to posterior end; firm rather than flaccid and gelatinous, almost the width of body but shorter than expected (approximately one fifth the size of specimen). Anus ventral. Mouth ventral. Eighteen tentacles with very round firm discs and knobbed margins. Anterior brim of more than ten tube feet, variable in size, fused for most of their length but free and round at ends. Similar for a much smaller posterior brim, with approximately ten tube feet, more regular in length. Ventrolateral tube feet large and free, approximately seven each side. Paired to zigzag series of large to small midventral tube feet. No dorsal papillae observed in this specimen, usually minute. Ossicles irregular spinous crosses and rods. Dorsal body wall ossicles (fig. 21e, f) slender and spinous to thick and serrated crosses, with and without central apophyses, most broken here. Ventral body wall ossicles (fig. 21 g –k) typically stout, slightly curved crosses, with or without broken central apophyses, arms up to ~91 μm long with scattered spines mostly distal (fig. 21g –i). Also, slender crosses with longer arms up to 350 μm with or without central apophysis (fig. 20j, k), and rare rods. Tentacles with curved to straight, smooth to spinous or branched rods up to 640 μm long.

Remarks. We have placed our specimen in P. longicauda for now with the usual reservations, and in particular noting that Gubili et al. (2017) assessed P. longicauda as a cryptic species complex and Gebruk et al. (2020) redescribed and split the species. The 16S sequence groups with that of P. longicauda from California, USA (fig. S1). Our specimen was collected from a station with manganese nodules, so the black colour and firmer texture here may be artifacts rather than typical. Ossicles and external morphology key closest to P. longicauda in the Galathea Report ( Hansen, 1975) , with ossicles and features a good match other than the IOT specimen having a slightly reduced dorsal appendage. Ossicles and preserved whole-body dimensions from the original description in the Challenger Reports ( Théel, 1882) agree with the IOT specimen, but again the dorsal appendage for our specimen is much shorter and more tapered than the “very large” 120 mm one noted in the original description, and those illustrated by Gebruk et al. (2020) or photographed by Ross (2012). The IOT specimen also shows some similarities to the variety now accepted as P. fuscopurpurea Théel, 1882 known only from the type locality in the Southern Indian Ocean south of Australia at ~ 3560 m. The differences between these species were covered well in the redescriptions by Gebruk et al. (2020), with our specimen judged a closer match to the ossicles from P. longicauda .

Distribution. Australian IOT (this work), Indian Ocean sector of the Antarctic, Pacific Ocean: Kermadec Trench area. *

Full bathymetric range. 3431–5414 m * (IOT 3431–5414 m).

Type locality (for specimen noted as “best” for species). Southern Indian Ocean , Southern Ocean (northwest of Casey Station Antarctica), ~ 3614 m .

*Prior to Gebruk et al. (2020), which restricted geographic distribution to the Indian Ocean sector of the Antarctic and the Kermadec Trench area (depth 3560–5414 m), distribution was considered cosmopolitan at 2210–5173 m.

This species was previously recorded in AFD and from western, eastern and southern Australia at depths of 815–4890 m in ALA (January 2024). Note that the NMV Catalogue records one of these specimens (from the Great Australian Bight) at a depth of 4890–5032 m. This IOT material represents a geographic and small bathymetric range extension for the species .

References. AFD (2024), ALA (2024), Gebruk et al. (2014), Gebruk et al. (2020), Gubili et al. (2017), Ross (2012), Théel (1882).