Deima oloughlini Mackenzie and Davey, 2024

Mackenzie, Melanie, Davey, Niki, Burghardt, Ingo & Haines, Margaret L., 2024, A report of sea cucumbers collected on the first dedicated deep-sea biological survey of Australia’s Indian Ocean Territories around Christmas and Cocos (Keeling) Islands (Echinodermata: Holothuroidea), Memoirs of Museum Victoria (Mem. Mus. Vic.) 83, pp. 207-316 : 264-266

Deima oloughlini Mackenzie and Davey sp. nov.

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sp. MoV. 7322 Material examined. Holotype: NMV F308216 * (1), [IN 2022 V08 117] Indian Ocean , Australia, Cocos (Keeling) Islands Territory, IOT: Rudist Seamount (11° 19' 07" S – 11° 18' 28" S, 99° 07' 58" E – 99° 09' 07" E), 1175–1764 m, Coll: O’Hara et al. Marine Invertebrates Team, RV Investigator , 11 Oct 2022 ; Paratype: NMV F308242 * (1), [IN 2022 V08 131] Indian Ocean , Australia, Cocos (Keeling) Islands Territory, IOT: Cocos (Keeling) (11° 49' 56" S – 11° 50' 37" S, 96° 37' 36" E – 96° 38' 56" E), 1589–1896 m, Coll: O’Hara et al. Marine Invertebrates Team, RV Investigator , 14–15 Oct 2022 .

Diagnosis. Oval-shaped animal, convex dorsally and flattened ventrally, just over twice as long as wide, white to pink. Ventral mouth with circular field around oral opening, circumoral papillae present, clear marginal knobs on tentacles. Ventral anus. Long tapered papillae, some just short of body width in length, in single rows along dorsal (6 pairs) and ventrolateral (4–6 pairs) radii. Ten pairs of ventrolateral tube feet in single rows below papillae, additional post-anal pair of tube feet present behind/above anus, bare midventral apart from present or absent single pair of pre-anal tube feet. Dominant ossicles are irregular perforated plates, typically single layered though occasionally partially imbricating or developing rudimentary secondary layering. Perforations are not uniform, variable in size, shape, number, and position (fig. 37e–g). Smaller irregular branching structures also present (fig. 37g). Full descriptions for each specimen below.

Holotype. NMV F308216 (larger specimen). Body oval-shaped, convex dorsally, flattened ventrally, ~ 110 mm long, 52 mm wide and 30 mm high pre-preservation. Dorsoventrally flattened once preserved. Opaque to white, with a pink to orange tinge around tube feet, oral and anal openings. Anus posterior, ventral. Mouth anterior, ventral, and placed in middle of a circular field fringed by obvious circumoral papillae. Tentacles mostly retracted, but ~12 visible. Eight well-developed marginal knobs on each tentacle, curled inwards to give the appearance of digits on a hand (fig. 37d). Ventrolateral tube feet ten pairs, single-rowed, largest mid-body and smallest at posterior. Cylindrical and slightly tapered to rounded end, each capped with a smaller darker end disc. Additional pair of smaller post-anal tube feet present just above/behind the terminal anus, smaller than all ventrolateral tube feet. Two pre-anal tube feet also present on midventral line but lacking any other midventral tube feet. Papillae cylindrical and rigid at base but bending or breaking to flop over and tapering at tip, variable size but largest ~ 40 mm. Dorsal six pairs, ventrolateral six pairs. Dominant ossicles perforated plates, visible to naked eye, some partially imbricating and giving a crunchy” texture to the dorsal surface. Dorsal ossicle plates are predominantly single layered, variable in size up to 2.1 mm, some with rudimentary branches, knobs, thickening, or anastomosing with a secondary mesh. Thickening and some knobs on plates observed more commonly in perianal samples. Occasionally clustered and imbricating. Perforations are irregular in shape, size, number and placement. Additional ossicles are smaller irregular branching structures up to 0.32 mm that look like individual versions of the initial branches that form multilayers. Ventral with similar single-layered perforated plates to dorsal, but typically smaller (up to 1.5 mm seen here), and often more regular than dorsal plates, with larger perforations clustered towards the centre. Papillae ossicles are elongated and variably curved perforated plates up to 0.8 mm long, some knobbed, thick to thin and branching. Tentacle ossicles thick, straight to curved rods, distally spinous, sometimes centrally bulbous, and up to 0.24 mm long.

Paratype. NMV F308242 (Smaller specimen): Body oval-shaped, convex dorsally, flattened ventrally, ~ 52 mm long and 25 mm wide pre-preservation. Semitransparent, grey to off-white dorsally and pink to orange ventrally. Anus posterior, ventral, almost terminal. Mouth anterior, ventral, and placed in middle of a slightly raised circular field fringed by retracted circumoral papillae. Tentacles retracted other than single exposed disc ~ 4 mm wide with six well-developed marginal knobs (4 larger and 2 smaller tapering digits) visible. Ventrolateral tube feet ten pairs, single-rowed. Cylindrical with dark tips, largest mid-body and smallest at posterior. Additional pair of separate smaller post-anal tube feet present just behind/ above the anus, smaller than all ventrolateral tube feet. Midventral tube feet completely absent. Papillae in single rows, rigid, conical, often broken, cylindrical at base and tapering at tip, variable size but largest ~ 22 mm (i.e., nearly full width of body). Dorsal six pairs, ventrolateral approximately four pairs. Dominant ossicles are perforated plates. Dorsal plates predominantly single layered, with some starting to develop additional rudimentary branches or mesh for multilayers. Plates often quite large (e.g. 2.1 mm measured for broken plates – fig. 37f). Perforations are irregular in shape and size (e.g. 56–125 μm for central perforations, with some larger again towards the plate edge) and number. Additional ossicles are rare smaller irregular branching structures. Ventral ossicles are perforated plates like dorsal, but typically smaller (e.g. up to 857 μm, fig. 37e).

Remarks. Deima oloughlini Mackenzie and Davey sp. nov. is morphologically very similar to D. validum validum Théel, 1879 as redescribed by Hansen (1975), only distinguished by reduced typical number of dorsal papillae, a body ratio of just over 2:1 compared with 5:3, and most noticeably by a smaller ossicle size range and reduced layering of ossicles, with mostly single-layered rather than multilayered plates with less-uniform perforations. IOT specimens of D. validum validum also appear more domed dorsally than Deima oloughlini Mackenzie and Davey sp. nov. and with thicker, crunchier scales. Deima oloughlini Mackenzie and Davey sp. nov. is distinguished morphologically from D. validum pacificum Ludwig, 1894 chiefly by the reduced number of dorsal papillae, and the inclusion of rudimentary secondary mesh/branching on plates. D. validum pacificum is only known from the eastern Pacific at 1618–2487 m, which also makes it unlikely. Hansen (1975) noted that D. validum subspecies have both geographic and bathymetric differences. In Table S2 we also note distinguishing features between Deima oloughlini Mackenzie and Davey sp. nov., and the species previously synonymised (synonymy retained here) into D. validum validum by Hansen: D. atlanticum Hérouard, 1898 , D. blakei Théel, 1886 , D. fastosum Théel, 1879 , and D. mosaicum Ohshima, 1915 . Of these, D. oloughlini Mackenzie and Davey sp. nov. is closest to the West Indian D. blakei , which was noted for typically single-layered perforated plates. The type specimens of D. blakei were collected from a similar depth (1048–1115 m) from St Vincent in the Caribbean. The type description is somewhat confused by discussing seven specimens split into two lots of characteristics. Our specimens are both clearly distinguished from four of the type series specimens based on uniform rather than asymmetrical placement of appendages. The remaining three specimens from the type series (which Théel noted as looking more like D. validum ) are a closer match to our larger specimen for tube feet and papillae, though Hansen noted an additional pair of papillae for some D. validum (as D. blakei ) specimens re-examined from the type location ( Hansen, 1975). There is little ossicle detail in the type description for D. blakei , just noting they were perforated plates like Oneirophanta mutabilis , with minimal secondary layering, but Deima oloughlini Mackenzie and Davey sp. nov. differs from the type location material re-examined by Hansen (1975), by typical ossicle size, and perforation shape and placement. Deima oloughlini Mackenzie and Davey sp. nov. ossicle plates are up to 2.1 mm dorsally and 1.5 mm ventrally, compared to 1.5 mm and 1.2 mm for D. validum (as D. blakei ), and are also lacking the “remarkably large” central perforations of D. blakei , with large and small perforations varying across the plate, particularly in dorsal ossicles. Deima oloughlini Mackenzie and Davey sp. nov. also differs from those D. blakei specimens subsequently reported from other locations as described in the synonymy by Hansen (1975). The high genetic differentiation between Deima oloughlini Mackenzie and Davey sp. nov. and its sister species D. validum (COI: 12.7%) is in line with accepted genetic differentiation between other sea cucumber species (e.g. Arndt et al., 1996; O’Loughlin et al., 2011; Gubili et al., 2017). While differences in external morphological features are more cryptic with such variability in the genus, the phylogenetic evidence combined with a clear difference in ossicles gives us the confidence to erect Deima oloughlini Mackenzie and Davey sp. nov. here.

Etymology. Named in honour of our late mentor and friend, P. Mark O’Loughlin, for his substantial contribution to holothuroid taxonomy, and his willingness to encourage and mentor so many in the field.

Distribution. These two specimens only: Indian Ocean, Australian IOT, Cocos (Keeling) Islands Territory, Cocos (Keeling) Stn. and Rudist Seamount Stn.

Full bathymetric range. 1175–1896 m.

References. Arndt et al. (1996), Gubili (2017), Hansen (1975), Hérouard, (1898), O’Loughlin (1998), O’Loughlin et al. (2011), Ohshima (1915), Sluiter (1901a), Théel (1879 and 1886).