Psolidium helenae Ong & O’Loughlin, 2019

Ong, Joo Yong, Wong, Helen P. - S., O, P. Mark & Loughlin, 2019, Two new tropical psolid sea cucumbers from the Strait of Johor, Singapore (Echinodermata: Holothuroidea) with a key to Psolidium species from the tropical East Indian-West Pacific region, Raffles Bulletin of Zoology 67, pp. 206-216 : 208-210

Psolidium helenae Ong & O’Loughlin , new species

( Figs. 1–5 )

Psolidium species b.— Ong & Wong, 2015: 275, Table 1.

Material examined. Holotype: ZRC.ECH.0300, Singapore, CMBS spec. no. JS-1196, stn. SW23, East Johor Strait , Pulau Ubin, Chek Jawa, seagrass bed, collected by hand, 1°24.748′N 103°59.711′E, 0.3–0.4 m, seagrass and green algae, coll. Helen Wong et al., 17 October 2012.

Description. Preserved body 18 mm long (including posteriorly projecting anal cone 1.5 mm long), 10.5 mm wide mid-body, 8 mm high anteriorly, 6 mm high posteriorly; thick imbricating rugose scales dorsally and laterally, scales up to about 2.5 mm wide, ventral sole lacking scales; sub-rectangular form ventrally with rounded anterior and posterior ends, mouth dorso-anterior, lacking oral valves, short anal cone directed posteriorly, lacking anal valves. Cucumariid-type calcareous ring; radial plates with anterior notch for longitudinal muscle attachment, notch posteriorly, lacking posterior prolongations; inter-radial plates tapered to an anterior point, posterior indentation. Ten dendritic tentacles, eight large, two ventral smaller. Gonad tubules not branched. Up to three tube feet penetrate each scale dorsally and laterally, tube foot discs about 0.15 mm diameter; margin of the ventral sole with wide band of close-set tube feet extending to the edge of the sole, band about 6 tube feet wide, not in transverse rows, lacking discrete outer series of smaller marginal tube feet; close-set band of tube feet along mid-ventral radius, about five tube feet wide, ventral tube feet disc diameters about 0.25 mm.

Dorsal and lateral multi-layered ossicles (scales), plates and distally spinous cupped crosses; small plates irregularly oval in form and size, smooth, lobed marginally, not knobbed, typically 2–6 perforations, 66–133 µm long; cupped crosses variable in form, 56–109 µm long, typically with four bifid arms that are distally finely spinous, arms joining distally on a few crosses to form cups. Dorsal tube feet with endplates and elongate perforated support plates; endplates up to 104 µm diameter; short, wide, curved, perforate, marginally spinous endplate support ossicles, up to about 114 µm long. Sole with knobbed plates only, irregularly oval, typically 4–5 perforations, large knobs around margin, some surface knobs, plates up to 157 µm long by 96 µm wide. Ventral tube feet with tube foot support plates, elongate, perforated, variably marginally knobbed, up to about 240 µm long. Tentacles with rod plates, rods and rosettes; plates usually wide mid-rod, multi-perforate over plate, variable form, up to 450µm long, 134 µm wide mid-rod; rod-plates inter-grade with curved rods, largest perforate mid-rod and distally; rods inter-grade with fine non-perforate rods about 40 µm long; rosettes irregularly oval, about 20–45 µm long.

Live dorsal colour orange over the lateral scales becoming yellow along the upper dorsal surface; small pale yellow spots (tube feet ends) scattered over the dorsal and lateral sides; introvert and tentacles pale yellow-brown with black markings; mouth red. Preserved dorsal and lateral colour grey to pale brown with black flecking. Preserved ventral sole white, tentacles white with black markings, introvert white.

Distribution. Singapore: East Johor Strait, Chek Jawa, seagrass bed, 0.3–0.4 m.

Etymology. Named helenae in appreciation of the generous, gracious, considerable and much appreciated supportive contribution of Helen Pei-San Wong (of the Tropical Marine Science Institute of the National University of Singapore).

Remarks. Psolidium helenae Ong & O’Loughlin , new species, is distinguished from all other tropical East Indian– West Pacific region Psolidium species in the key above and by the following combination of characters: a low profile; a band of tube feet around the periphery of the sole up to six-wide; an absence of smaller outer marginal tube feet on the sole; a band of mid-ventral tube feet on the sole about five-wide; distally spinous cupped cross ossicles present dorsally.

Figures

Fig. 1. Dorsal view of live holotype of Psolidium helenae Ong & O’Loughlin, new species (ZRC.ECH.0300; 18 mm long preserved).

Fig. 2. Ventral view of live holotype of Psolidium helenae Ong & O’Loughlin, new species (ZRC.ECH.0300; 18 mm long preserved).

Fig. 3. Lateral view of preserved holotype of Psolidium helenae Ong & O’Loughlin, new species (ZRC.ECH.0300; 18 mm long preserved).

Fig. 4. SEM holotype ossicle views for Psolidium helenae Ong & O’Loughlin, new species (ZRC.ECH.0300). A, scale from dorsal body wall, showing canals for tube feet; B, endplate from sole tube foot; C, supporting rod from sole tube foot; D, supporting knobbed plates from sole; E, rod plates from tentacles; F, plates from dorsal body wall; G, endplate from dorsal body wall; H, cupped cross from dorsal body wall; I, rosette from tentacle.

Fig. 5. Ossicles of holotype Psolidium helenae Ong & O’Loughlin, new species (ZRC.ECH.0300), taken by light microscope. A, plates from dorsal body wall; B, endplates from dorsal tube feet; C, cupped crosses from dorsal body wall; D, cupped plates from dorsal body wall; E, knobbed plates from sole; F, rods from tentacles; G, supporting rods from tube feet; H, rod plates from tentacles; I, supporting plates from tube feet; J, rosettes from tentacles.