Molpadiodemas atlanticus ( Perrier, 1898 ) O'Loughlin & Ahearn, 2005

O'Loughlin, P. Mark & Ahearn, Cynthia, 2005, A review of pygal-furrowed Synallactidae (Echinodermata: Holothuroidea), with new species from the Antarctic, Atlantic and Pacific oceans, Memoirs of Museum Victoria 62 (2), pp. 147-179 : 153

Molpadiodemas atlanticus ( Perrier, 1898) comb. nov.

Figures 3a, b , 4a–d , 6a, b

Pseudostichopus atlanticus Perrier, 1898: 1665 .— Perrier, 1902: 333–338, pl. 17 figs 15–20.— Mortensen, 1927: 386–387.— Deichmann, 1930: 87–88.— Deichmann, 1940: 209, 211.— Heding, 1942: 5.— O’Loughlin, 2002: 315.

Molpadiodemas acaudum Heding, 1935: 78–80 , pl. 6 figs 1–2.— Heding, 1940: 354–357.— Deichmann, 1940: 209, 211.— Heding, 1942: 4–5.

Molpadiodemas atlanticus .— Heding, 1940: 353–359.

Meseres atlanticus .— O’Loughlin, 1998: 497.— Thandar, 1999: 376–379, fig. 4.

Meseres acaudum .— O’Loughlin, 1998: 497, fig. 1g –h.

Material examined. Pseudostichopus atlanticus Perrier, 1898 . Holotype. North Atlantic , off the Azores, 42°19'N, 23°31'W, 4060 m, Talisman stn 134, 1883, MNHN EcHh 2772. Paratype. 42°19'N, 23°36'W, 4060– 4010 m, MNHN EcHh 658.

Molpadiodemas acaudum Heding, 1935 . Paratype. North Atlantic , 60°17'N, 54°5'W, 3230 m, Ingolf stn 37, 1885, ZMUC.

Other material. Pacific Ocean , New Zealand, Chatham Is, 2610–2668 m, USNM E49319 (1) ; Chile, 34°07’S (incorrectly recorded as N in Théel, 1886), 73°56'W (incorrectly as E), 4069 m, Challenger stn 298, BMNH 1886.10 . 2.149 (1); 33°31'S, 74°43'W, 3950 m, Challenger stn 299, BMNH 1886.10 . 2.185 (1); Peru, 3500 m, USNM 1020067 (1) ; California , off Point Conception, 4100 m, 1073654 (1); Oregon, 3021 m, USNM E16475 (1) ; 3700 m, E16488 (3); Clipperton Fracture Zone , 13°08'– 13°53'N, 129°51'– 129°55'W, 4801–4923M, E31100–E31102 (3); E31107, E31108 (2); E31121– E31123 (3); E31125 (1); E53278 (1); NMV F101845 (1).

Atlantic Ocean , Bahamas, 4828–4873 m, USNM 1021592 (10) ; NE of Bahamas, 4930–4940 m, E49466 (9); West European Basin , 4780–4795 m, E38320 (1); Caribbean Sea, Venezuelan Basin, 13°30'– 14°50'N, 64°45'– 67°30'W, 3411–5062 m, E38789– E38791 (20); E38798 (1); E39266 (20); 1023352 (1); NMV F101846 (2).

Description. Large, up to 210 mm long; body rounded in section, sometimes sac-like, sometimes with slight brim, usually no detrital attachments; body wall moderately thick, soft leathery or firm gelatinous, frequently smooth surface, frequently wrinkled ventrally; uniform cover of very small tube feet, frequently not evident or in pits, most evident ventrally and pygally, from 0.1 mm long, 0.2 mm diameter up to 1.0 mm long, 0.3 mm diameter, cylindrical and firm if extended; ossicles frequently abundant in tentacles and gonads, sometimes rare or absent; tentacle ossicles frequently irregular thin rods slightly to strongly curved with ends intertwined to create small perforations, less frequently irregular straight to curved, narrow to wide, smooth to laterally spinous, variably perforated rods, ossicles variable in length, up to 500 µm long; gonad ossicles irregular rods, frequently with thin lateral branches joined to create extensive irregular lace-like mesh, non-spinous, up to 420 Μm long.

Colour. Body and tube feet brown to grey-brown to off-white; frequently some residual mauve markings.

Distribution. North Atlantic, 3230–4060 m ( Perrier, 1902, as P. atlanticus ; Heding, 1935, as M. acaudum ); south-east Atlantic, 3155–3255 m ( Thandar, 1999); West European Basin, 4780–4795 m (this paper); Venezuelan Basin, 3411–5062 m (this paper); Pacific Ocean, off Chile, 3950–4069 m ( Théel,1886; see below); Pacific Ocean, 2610–4923 m (this paper).

Remarks. In agreement with the opinions of Deichmann (1940) and Heding (1942), M. acaudum was made a junior synonym of P. atlanticus by O’Loughlin (2002). That decision is confirmed here.

Théel (1886) noted that two Challenger specimens, taken in the Pacific Ocean off Chile at stations 298 and 299, closely resembled Pseudostichopus villosus but lacked tube feet. Both specimens were examined in this study, and determined as P. atlanticus . Théel (1886) reported sizes up to 280 mm long. The larger specimen is now only 150 mm long.

The very small dark brown attachments on the body which were noted by O’Loughlin (2002) and Théel (1886) are judged to be epibiotes. O’Loughlin (2002) judged the “mulberry” bodies in the body wall of P. atlanticus , illustrated by Perrier (1902) and Thandar (1999), and referred to by Théel (1886) as present in some specimens of P. villosus , to be detrital accretions and not holothurian ossicles. That opinion is maintained here.

The presence of P. atlanticus in the Pacific Ocean is confirmed by the numerous USNM specimens determined in this study. O’Loughlin (2002) summarised P. atlanticus distribution records as Atlantic Ocean only. This work extends the distribution to the Pacific Ocean, and to greater depths (at least 5062 m).

Amongst Molpadiodemas species the distinguishing characters of M. atlanticus are: large, sac-like form; even cover of small tube feet, frequently inconspicuous; frequent presence of large, irregular, open mesh-like gonad ossicles.

Figures

Figure 3. a–b, M. atlanticus (NMV F101845, 210 mm long); a, ventral view; b, small epibiotes on body wall. c–e, M. constrictus sp. nov. (USNM 1022815, paratypes); c, dorsal view (51 mm long); d, ventral view (51 mm long); e, tube feet. f–g, M. crinitus sp. nov. (USNM 1023615, holotype, 96 mm long); f, ventral view; g, ventrolateral tube feet. h, M. depressus, pygal furrow, gelatinous body, lateral brim (NMV F101849). i–k, M. epibiotus sp. nov. (USNM 1008183, holotype, 110 mm long); i, ventral view, posterior taper; j, ventral mouth, epibiote concavities (arrows); k, ventral view, epibiote concavity (left arrow), few tube feet (central arrow). l, M. helios sp. nov., tentacle digits, tube feet (lower right) (USNM E31104, paratype). m–o, M. involutus (NMV F101850, 40 mm long); m, ventral view, serrated margin; n, dorsal anterior view, globigerines attached; o, posterior ventrolateral tube feet.

Figure 4. Tentacle ossicles (SEM). a–d, Meseres atlanticus, a–c (USNM E49466), d (USNM 1020067). e–h, M. crinitus sp. nov. (USNM E48662). i–l, M. depressus (USNM E53279). m–p, M. epibiotus sp. nov. (USNM 1008310, paratype). q–t, M. helios sp. nov., q–r (USNM E31104, paratype), s–t (USNM E31117, paratype). u–x, M. involutus (USNM E49256).

Figure 6. Gonad ossicles (SEM). a–b, Meseres atlanticus (USNM E53278). c–d, M. helios sp. nov. (USNM E31106, holotype). e–h, M. neovillosus sp. nov. (USNM 1008458, paratype). i–l, M. porphyrus sp. nov. (USNM E38795, holotype). m–p, M. ustulatus sp. nov. (USNM 1022493, holotype).