Massinium albicans, Samyn, Yves & Thandar, Ahmed S., 2010

Samyn, Yves & Thandar, Ahmed S., 2010, Two new species in the phyllophorid genus Massinium (Echinodermata: Holothuroidea) with redescription of Massinium magnum, Zootaxa 2399, pp. 1-19 : 8-12

Massinium albicans sp. nov.

(figs 5A–M, 6A–F, 7)

Neothyonidium magnum ; Cherbonnier 1980: 656, fig 20A–Q; Féral & Cherbonnier 1986: 102, fig. 40T (non N. magnum )

Name bearing type: Holotype: MNHN EcHh 3096; 2 paratypes MNHN EcHh 3087. Type locality: Chenal Devarenne, New Caledonia.

Material examined: MNHN EcHh 3096 (holotype), Chenal Devarenne ( New Caledonia), 15–20 m depth, 1979, coll. Menou; MNHN, EcHh 3087 (2 paratypes), Baie de Canala ( New Caledonia), 15–20 m depth, 1979, coll Menou.

Diagnosis: Medium-sized, U-shaped species with bloated mid-body with short anterior and long posterior ends. Tables of introvert of two types: those with small ovoid to octagonal disc, perforated by four large and 1–2 small holes alternating with the large ones, and those with more (15–20), small peripheral holes. Introvert tube feet with tables with reduced spire and perforated plates of various shapes and sizes.

Etymology: The name albicans refers to the yellow-whitish colouration of the body wall and the introvert.

Holotype description: Specimen entire, well-preserved, but calcareous ring detached from introvert due to previous dissection. Body wall firm, rather thick (1–4 mm), slightly rough to the touch. Body form cylindrical, U-shaped, slightly contracted, bloated, with narrow anterior and posterior ends. Introvert well extended, attached to main body. Length of specimen along ventral surface 150 mm; along dorsal surface 75 mm; height of mid-body 50 mm; anterior and posterior ends approximately 35 and 60 mm long; introvert 50 mm long. Colouration of body and introvert yellowish white. Tube feet of body wall yellowish, numerous, small, mostly retracted except on bloated ventral portion, uniformly scattered over entire body, very small suckers. Tube feet of introvert brownish, darker proximally, aligned in radial areas in two well-defined rows, absent in distal 10 mm. Tentacles 20, according to original description, 10 large, 10 small, arranged in two circles; outer tentacles 35–40 mm long, shaft whitish with brownish annulations at base, ramifications blackish; inner tentacles arranged in pairs in the radii, uniform white, 5–8 mm long. Anus small, perhaps surrounded by five (only three counted) small, slender, well calcified teeth, each flanked by a group of terminal podia. Calcareous ring (fig. 7) 70 mm long, tubular with radial and interradial plates fused for five sevenths of the length of calcareous ring, radials prolonged and their processes fused posteriorly, fragmentation of calcareous ring not obvious due to encapsulating thick membrane. Polian vesicles four, three long ones, up to 105 mm (one terminally bifid), and one short, white. Stone canals two, one small, 3.5 mm long, poorly calcified, the other considerably elongated, 15 mm long, and well calcified, both arising together, each inperceptably merging into the madreporite. Introvert retractor muscles thick and short, originating at anterior third of the body.

Ossicle assemblage. Body wall deposits, 15–50 Μm long, site dependent: anterior deposits comprise predominantly pseudobuttons and some rosettes (fig. 5A), mid-body wall deposits additionally comprise elongated pseudobuttons with few holes (fig. 5B, 6A&B), posterior deposits comprise mostly rosettes (fig. 5C). Ventral tube feet with irregular perforated plates (fig. 5D) and small, 15–20 Μm long, pseudobuttons (fig 5E). Introvert with tables (figs 5F, 6C) and very scarce rosettes of only 20–25 Μm long. Tables with round to oval smooth discs, 70–90 Μm long, perforated by four central holes of which two are larger than the alternating two, and numerous smaller holes in 2–3 peripheral circles; spire two-pillared, medium to high, with 1–2 cross-bars, terminating in two or more, often diverging, toothed projections. Tube feet of introvert with rosettes, tables and multilocular plates (figs 5G–J, 6D–E). Rosettes simple to complex, 20–40 Μm long, open type, with distal endings mostly swollen (fig. 5G, 6D). Multilocular plates of various shapes, 50–150 Μm long, with mostly larger central perforations and no branched ends (fig. 5J, 6E). Tables scarce, if present, of introvert type with discs complete, but spire mostly reduced to knobs (fig. 5H, 6E). Peristome with complex, elongated rosettes, 30–60 Μm long, with swollen distal endings, often anastamosing (figs 5K, 6E). Shaft and tips of large and small tentacles with deposits similar to those of peristome (fig. 5L). Longitudinal muscles of body wall with rods, rosette-like plates and pseudobuttons. Longitudinal muscles of introvert and of cloacal retractor muscles (fig. 5N) with rosettes only. Gonoduct with rosettes and lattice-like plates (fig. 5M).

Paratypes description (2 complete specimens). Morphology as in holotype. The ossicle assemblage could not be assessed due to preservation in acidic Bouin’s fluid which dissolved all the calcareous structures.

Ecology: According to Féral and Cherbonnier (1986), this species lives buried in sand or mud on the outer slope of the reef. They further report that in high current environments population density is low, whereas in calmer conditions population density is high and that the species is still visible during the day, but more active during the night. Although listed as rare, the authors report its presence around the whole of New Caledonia, at depths of 3– 30 m.

Remarks: Cherbonnier (1980) noted that the ossicle assemblage of the introvert of his New Caledonian specimen differs from that described by Sluiter (1901). Cherbonnier (1980) therefore examined the slides prepared by Sluiter and discovered that, in addition to the tables with a small ovoid to octagonal disc, perforated by four large holes and 1–2 small perforations alternating with the large holes, numerous other tables with more (15–20), small peripheral holes were also present in the introvert of his New Caledonian specimen (cf. Cherbonnier 1980: fig. 20 F). Cherbonnier (1980) further noted that the spire of these tables is rather low, ending in four short smooth to spiny points (Cf Cherbonnier 1988: fig. 20K). However, in Sluiter’s preparations he failed to locate tables that have their disc and spire similar to those he illustrates (cf. Cherbonnier 1980: figs 20 F,J,L,N). He correctly questioned if his, Sluiter’s or Domantay’s (1933) records are the true N. magnum . After examination of the holotype, he concluded that the tables in the introvert of his material correspond best with the holotype.

We disagree with Cherbonnier’s (1980) decision because the tables in the New Caledonia material, here described as a new species, have their discs perforated with more holes and show the spires terminating in pronounced tooth-like projections. Moreover, we note there is a marked difference in the plate-like deposits of the introvert tube feet of the of the two species. While those of M. magnum are highly irregular with their terminal ends branched (figs 1C, 2C), those of M. albicans are more regular, never with branched terminal ends, and with much more smaller perforations (figs 5J, 6F). Moreover, the peristomial deposits in both species vary considerably (cf. figs 1D, 2D with figs 5K, 6F). Lastly, the colouration of the introvert of M. albicans and M. magnum is markedly different (cf. Massin 1999, fig 113a with Cherbonnier & Féral 1986: 103).

M. albicans is perhaps endemic to New Caledonia.