Massinium granulosum, 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 : 13-17

Massinium granulosum sp. nov.

(figs 8 A,B; 9 A–E, 10A–C, 11 A–F)

Name bearing type: Holotype: AMS: J13578 .

Type locality: Dunwhich (Stradbroke Island, Moreton Bay, Queensland, Australia) Material examined: AMS J 13578 (holotype + paratype, identified as Neothyonidium magnum by F.W.E. Rowe), Dunwhich (Stradbroke Island, Moreton Bay, Queensland, Australia), intertidal, 14.xi.1977, coll. H. Silver.

Diagnosis: Small-sized, U-shaped species, with slightly bloated mid-body with narrow anterior and posterior ends; body wall deposits granuliform, rarely perforated rods.

Etymology: The name granulosum refers to granuliform rods of the body wall.

Holotype description: Specimen well-preserved, calcareous ring and associated structures detached, but still linked to main body by introvert. Body wall firm, but not thick (2–3 mm), slightly rough to the touch. Body form cylindrical, U-shaped, slightly twisted, slightly bloated mid-ventrally with narrower anterior and posterior ends. Length along ventral surface 130 mm; length along dorsal surface 90 mm; height of mid-body about 30 mm; anterior and posterior ends respectively 15 and 10 mm long; introvert approximately 25 mm long. Anterior and posterior body wall with series of slits in interradial areas. Colouration of body yellowish white, slightly paler mid-ventrally; introvert yellowish white. Tube feet of body wall retracted, numerous, small, scattered over entire body, suckers minute, beige. Tube feet of introvert scarce, restricted to the most proximal part, in the radii, in one to two rows. Tentacles 20, in two circles, outer circle of 10 large (only seven intact), inner circle of 10 small alternating in pairs with large ones; outer tentacles 25–40 mm long, shaft yellowish brown without visible annulations, ramifications dark brown; inner tentacles about 5 mm long, colour as in large tentacles. Anus small, surrounded by five minute teeth, quite deciduous, each flanked by several brownish papillae situated in distinct triangular dispositions. Calcareous ring ( Fig. 8 A) 40 mm long, tubular, with radial and interradial plates fused for three quarters of length of calcareous ring, radials posteriorly prolonged, bifurcating, with processes fused to those of neighbouring plates; radial plates with deep anterior notch; interradial plates anteriorly pointed; fragmentation of calcareous ring not obvious due to thick encapsulating membrane.

Polian vesicles four, one sacciform, three tubular, elongated, up to 35 mm long, with tip of one of the latter, deformed and lying in a posterior slit of calacareous ring (fig. 8A & B). Stone canal single, poorly calcified, about 9 mm long, merging inperceptably into ovoid madreporite. Introvert retractor muscles thin and short, originating from anterior end of longitudinal muscles.

Ossicle assemblage. Dorsal and ventral body wall deposits identical, comprising irregular pseudobuttons and granuliform, rarely perforated rods of various shapes, 25–105 Μm long (figs 9A,B; 11 A,B). Introvert with tables only; table disc ovoid, smooth, perforated by four large central holes and smaller holes alternating with these, in 1–2 peripheral circles; spire two-pillared, medium height, 50–75 Μm high and 35–50 Μm wide, with single cross-bar, terminating in 2–4 toothed projections (fig. 9C, 11C). Tube feet of introvert with endplate surrounded by slender and plate-like perforated rods (fig 9D). Peristome with elongated rosette-like rods, 30– 50 Μm long, and other elongated rods, swollen terminally and perforated, 70–110 Μm long (fig. 9E, 11D). Large tentacles devoid of ossicles. Shafts and tips of small tentacles with complex, closed rosettes only (fig. 11E). Longitudinal muscles of body wall with pseudobuttons and elongated granuliform rods, 22–50 Μm long (fig. 10A). Anal papillae with elongated slightly curved rods, terminally expanded and perforated, 45–90 Μm long (fig. 10C, 11F), and few closed rosettes, 15–35 Μm long (fig. 10C). Cloacal retractor muscles with pseudobuttons (fig. 10B).

Remarks. Thandar (1989) described the South African endemic Massinium arthroprocessum ( Thandar, 1989) from False Bay and in 1996 recorded the species also from Durban. In his publication, Thandar (1989: 643) stated that Rowe advised him that ‘an undescribed, similar but not identical form occurs in Queensland ( Australia)”. Upon re-examination of Australian voucher material, identified as Neothyonidium magnum by Rowe, we came across the species Rowe probably implied. It is this species that is here described as new and is clearly sister to the South African form by the presence of characteristic slits in the body wall and simple body wall deposits. However, the South African M. arthroprocessum and the Australian M. granulosum differ clearly from each other in the following four characteristics: (i) body wall colouration in alcohol of M. arthroprocessum is grey speckled with reddish brown, whereas that of M. granulosum is uniform yellowishwhite; (ii) the body wall ossicles are mostly U shaped rods with terminal perforations in M. arthroprocessum , whereas they are more granuliform, seldom perforated and of greater variety in M. granulosum ; (iii) tentacle deposits in M. arthroprocessum comprise slender elongated rods bearing a single perforation at each ending, whereas in M. granulosum only rosettes are present and then only in the small tentacles; (iv) introvert deposits of M. arthroprocessum comprise tables, rods and rosettes, whereas those of M. granulosum tables only.

Figures

FIGURE 8. Massinium granulosum sp. nov., Holotype. A. Calcareous ring; B. Terminal end of the Polian vesicle that is embedded in the calcareous ring. (pv = Polian vesicle; r = radial plate; ir = interradial plate; sc = stone canal; m = madreporite.