Holothuria (Metriatyla) alex Samyn

Samyn, Yves & Vandenspiegel, Didier, 2016, Sublittoral and bathyal sea cucumbers (Echinodermata: Holothuroidea) from the Northern Mozambique Channel with description of six new species, Zootaxa 4196 (4), pp. 451-497 : 460-462

Holothuria (Metriatyla) alex Samyn sp.nov.

( Fig. 4 A – F)

Material examined. Type material: IE-2007-779 (holotype, sampled in front Mahajamba Bay)

Comparative material examined. ZMB Ech 1681 (holotype of Holothuria (Metriatyla) martensii ; Semper, 1868 ( Fig. 5 ); Ambon, Indonesia, leg. V. Martens, unknown depth) ; MNHN EchHh 3894 ( Holothuria (Metriatyla) horrida Massin, 1987 , erroneously identified as H. martensii Semper, 1868 , Tuléar, Mahavatsy, Madagascar, coll. Thomassin, 15.IX.1962, unknown depth) ; MNHN EchHh 3906 ( Holothuria (Metriatyla) horrida Massin, 1997 , erroneously identified as H. martensii Semper, 1868 , Tuléar, devant labo, st. 450, Madagascar, coll. Thomassin, 23.IX.1962, unknown depth) ; MNHN EchHh 7030 ( Bohadschia vitiensis (Semper, 1868) , erroneously identified as H. martensii Semper, 1868 , Antsirane, Madagascar, coll. Decary, 1919, unknown depth).

Type locality. Madagascar, Mahajamba Bay , Station CP 3218 (Decimal coordinates: -14.97; 46.94)

Etymology. This very handsome species is named after Alex Samyn , first daughter of Reen Tallon and Yves Samyn, in recognition of her support, when her dad is writing up his taxonomic work at home. The species epithet has been put in apposition.

Known geographical distribution. For now only known from the type locality.

Taxonomic description (holotype). External anatomy — 55 mm long and 24 mm wide at mid body, tapering acutely posteriorly. Trivium flat, separated from more convex bivium by fringe of well-developed lateral papillae (fig. 4A,B). Mouth ventral, surrounded by collar of reduced papillae, especially ventrally. Number of tentacles could not be determined due to contraction. Anus terminal, unguarded by papillae. Color in alcohol: bivium dark beige with some darker spots forming more or less two transversal lines with beige, evenly spread, papillae; trivium brown, with evenly scattered beige tube feet.

Internal anatomy: specimen partly eviscerated, leaving only part of the gut, the right respiratory tree and the oral structures. Calcareous ring narrow. Single short stone canal, 4 mm long, ending in spherical madreporite. Polian vesicles not observed. Gonad not observed. Gut filled with very fine mud. Longitudinal muscles very flat, bifid, only 3 mm wide. Cuvierian tubules not observed.

Ossicles: Tentacles with spiny rods, occasionally with some perforations, 110 – 480 µm long (fig. 4C). Ventral and dorsal body wall with tables, buttons and few fenestrated ellipsoids. Tables with disc on average 60 µm across, perforated by irregularly distributed central holes and 14 to 16 peripheral holes, rim of the disc undulating, edge smooth to spiny, spire low (1 – 2 cross beams) with four pillars (30 – 38µm high) ending in simple spiny crown (fig. 4D). Buttons very wide (31 – 48 µm wide and µm 50 – 68 long), smooth to knobbed with a central bridge (fig. 4D). Dorsal papillae with tables, plates and numerous ellipsoids (36 – 50µm wide, 45 – 53µm long); plates flat or tridimensional (123 – 185µm long,), tables similar to those of the body wall with a few tables with a higher spire (43 – 72µm, up to five cross beams, fig. 4F). Lateral papillae with numerous fenestrated ellipsoids in addition to plates and tables similar to those of the dorsal papillae (fig. 4E). Longitudinal muscles and cloaca devoid of ossicles.

Remarks. It is with some doubt that we assigned this species to the subgenus Metriatyla as its ossicle assemblage does not completely fit with the diagnosis of the subgenus. H. alex sp. nov. differs from the other species in Metriatyla in having tables with discs that, when the spire is low, are turned upwards and are nodulous. H. alex also presents fenestrated ellipsoids, whereas no other species in Metriatyla does so.

In terms of external morphology H. (M.) alex sp. nov. is close to H. (M.) kurti Ludwig, 1891 (see below for description). H. alex can however easily be separated from that species because it lacks the ‘spatulate’ tables that characterize H. kurti (cf fig. 7C) and because of its very characteristic ellipsoids (fig. 4 E,F) and wide buttons (fig. 4D) which are absent in H. kurti ..

At a first glance one could also think that H. alex sp. nov. is just a juvenile form of the species described as H. ocellata ( Jaeger, 1833) by Teo & Ng (2009). However, the coloration pattern (papillae surrounded by a dark ring in H. ocellata (sensu Teo & Ng 2009) which is not the case in H. alex ), the form of the lateral rim of papillae (fused papillae in H. ocellata (sensu Teo & Ng 2009), not so in H. alex ), and especially the ossicle assemblage (tack-like tables present in H. ocellata (sensu Teo & Ng, 2009), absent in H. alex ) is significantly different.

H. alex sp. nov. also resembles H. martensii Semper, 1868 in presenting tables with reduced disc and with tall, smooth spires. We studied the ossicle assemblage of the holotype of H. martensii (fig.5) and of three specimens from Madagascar which Cherbonnier (1988) identified as H. martensii . We came to the conclusion that H. alex is markedly different because it presents fenestrated spheres, tables with an upward turned disc and wide buttons. Of the three specimens Cherbonnier (1988) identified as H. martensii , one turned out to be Bohadschia vitiensis (Semper, 1868) and two Holothuria (Metriatyla) horrida Massin, 1987 .

Figures

FIGURE 4. Holothuria (Metriatyla) alex sp. nov. A – B: Dorsal (A) and ventral (B) views of holotype; C – F: SEM photos of ossicles from tentacles (C), dorsal body wall (D), lateral papillae (E) and dorsal papillae (F). Scale bars: A, B = 1 cm; C, E, F = 20 µm; D = 10 µm.

FIGURE 5. Holothuria (Metriatyla) martensii Semper, 1868. Label and dorsal view of the holotype.