Molpadiodemas atlanticus R. Perrier 1898
Creators: name: Bohn, Jens Michael
Publisher: name: Zenodo
Year: 2006
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Holothuroidea
Aspidochirotida
Synallactidae
Molpadiodemas
Molpadiodemas atlanticus

description: Molpadiodemas atlanticus (R. Perrier, 1898)
(Figs 9 A, 10)
Pseudostichopus atlanticus R. Perrier, 1898: 1665
Molpadiodemas acaudum Heding, 1935: 78 –80, pl. 6 (figs 1–2) Molpadiodemas atlanticus. O'Loughlin & Ahearn, 2005: 153, figs 3(a–b), 4(a–d), 6(a–b) [synonymy]
Material. M 48/1­343: 1 Ψ (ZSM 20020019). M 48/1­347: 1 ɗ (ZSM 20043076).
Additional Material. 1 Ψ (ZSM 20043140), FS "Meteor", station M 3/24, Agassiz trawl 2, 42°26.8' N, 14°49.0' W to 42°40.9' N, 14°49.2' W, 5270 m, Agassiz trawl, 11 Mar, 1966, det. C.G. Ahearn (USNM), 2004.
Description. The specimens range from 76 to 100 mm in length and 24 to 54 mm in width. The body is more or less cylindrical with rounded anterior and posterior ends, of a dirty­white colour (preserved) and without encrusting foreign bodies. Mouth ventral, encompassed by 20 prominent brown tentacles, which often are retracted and thus difficult to make out. The anus is ventral in position, enclosed in an inconspicuous pygal furrow. Filiform tube feet, lacking a sucking disc, are found sparsely scattered on the ventral side (often visible as small brown spots) but could not be detected dorsally. The body wall is thick and rugose.
The calcareous ring is prominent. Longitudinal muscles are flat and wide. There is a single ventral polian vesicle. The gonad consists of a tuft of branching tubules on both sides of the dorsal mesentery. The intestine forms a large loop, and the respiratory trees originate with a common trunk from the right side of the cloaca.
Calcareous deposits are scarce. Isolated deposits are present in the tentacles, which are irregularly rod­like, sometimes bent, often branching and with a tendency to form an irregular network, resulting in few to several perforations (Fig. 9 A). No deposits could be detected in the body wall, in the tube feet, in the gonads nor in the respiratory trees.
Remarks. In an long­needed and extensive review of the pygal­furrowed Synallactidae (O'Loughlin & Ahearn 2005) all hitherto known species as well as several new species are described, and detailed information is presented, including their synonymy and distribution.
Molpadiodemas atlanticus differs from its congeners by a combination of the following characters (O'Loughlin & Ahearn 2005): body large and sac­like; even cover of tube feet, frequently inconspicuous; frequent presence of large, irregular, open mesh­like gonad ossicles. The two Angola Basin specimens are assigned to M. atlanticus, although they lack the characteristic calcareous deposits in the gonad. Also the third specimen investigated (see additional material), which was determined by C.G. Ahearn in 2004 as belonging to this species, lacks calcareous deposits in the gonad. According to O'Loughlin and Ahearn (2005: p. 153) the lack of calcareous deposits in tentacles or gonads is not uncommon: "…ossicles frequently abundant in tentacles and gonads, sometimes rare or absent;…". But based on the body form (large and sac­like), the inconspicuous tube feet and the overall resemblance of the Angola Basin specimens with the specimen determined by C.G. Ahearn, the author is convinced, that the specimens are conspecific.
Distribution. (Fig. 10) Northern and south­eastern Atlantic Ocean, northern and southern Pacific Ocean, 2610–5415 m (Heding 1935; IFREMER BIOCEAN; O'Loughlin & Ahearn 2005; Perrier 1902; Thandar 1999; herein).
description: Published as part of Bohn, Jens Michael, 2006, Crinoidea and Holothuroidea (Echinodermata) of the abyssal Angola Basin — Results of the DIVA­ 1 expedition of FS " Meteor " (Cruise M 48 / 1), pp. 1-31 in Zootaxa 1276 on pages 16-19, DOI: 10.5281/zenodo.173337