Meseres Ludwig, 1894

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 : 177

Meseres Ludwig, 1894

Meseres Ludwig, 1894: 34 , 36, 38.— Perrier, 1902: 359.— Rowe,1995: 284–285.— O’Loughlin, 1998: 497.— O’Loughlin, 2002: 303–305.

Type species. Meseres macdonaldi Ludwig, 1894 (monotypy).

Diagnosis (emended from O'Loughlin, 2002). Up to 30 mm long; completely lacking ossicles; thin translucent body wall; body rounded anteriorly, posteriorly; mouth, anus ventral; lacking pygal furrow; ventrolateral margin with series of pyramidal protuberances surmounted by typically 3 digitate projections / (? tube feet); close body cover of small papillae / (? tube feet) and thin tubular appendages (probably epibiotic); 15 small shield-shaped tentacles; lacking tentacle ampullae; five small radial and five interradial plates in ring; longitudinal muscles undivided; unbranched gonad tubules on each side of dorsal mesentery; respiratory tree comprising two thin-walled tubes with sacs.

Material examined. Meseres macdonaldi Ludwig, 1894 . Lectotype (designated here). Pacific Ocean , off Costa Rica, Cocos I., 5º56'N, 85º10'W, 2149 m, RV Albatross stn 3362, 26 Feb 1891, USNM 30501 (1). Paralectotypes. Pacific Ocean, off Colombia, Malpelo I., 4º3'N, 81º31'W, 1644 m, RV Albatross stn 3380, 5 Mar 1891, USNM 18190 (5 now unrecognisable specimens).

Remarks. The diagnosis of Meseres by O'Loughlin (2002) was based on the species assigned at that time to Meseres , and not exclusively on the type species M. macdonaldi . The emended diagnosis is based solely on the description of the type material by Ludwig (1894), and some observations on the remaining type material. The syntypes of M. macdonaldi were taken off Costa Rica at 2149 m ( USNM 30501 (1)), and off Colombia at 1644 m ( USNM 18190 (5)). All are in very poor condition, but a single syntype ( USNM 30501) retains some recognisable tissue and body parts. For the purpose of having a precise type locality for this type species of Meseres , and some specific tissue for possible molecular analysis, the syntype registered alone is designated here as lectotype.

The characters of M. macdonaldi were not illustrated by Ludwig (1894), and all of the type material is in an advanced state of decomposition. Whether the body was covered with tube feet or papillae remains subjective. The upper limit of 15 tentacles (in this study Synallactidae species 30 mm long have more than 15 tentacles), and complete absence of ossicles, indicate that Meseres does not belong in the Synallactidae . Meseres has most of the characters of the Gephyrothuriidae as re-diagnosed by O'Loughlin (1998), with the exception of digitate tentacles. Ludwig (1894) described small shield-shaped tentacles, but there is no evidence as to what precise form they took. It is relevant to note that one of the two species of the Gephyrothuriidae reviewed by O'Loughlin (1998), Hadalothuria wolfii Hansen , had ventrolateral protuberances surmounted by rudimentary (?) tube feet. This feature appears to be shared with M. macdonaldi . The description of shield-shaped tentacles is an obstacle to referring the genus to the Gephyrothuriidae and Meseres , as exemplified by its type species, is treated here as incertae sedis.

Sluiter (1901) and O'Loughlin (1998, 2002) referred species to Meseres principally on the basis of a distinctive ventrolateral margin, and Rowe (1995) on the basis of “gonads in two discrete bunches of divided or undivided tubules, one on each side of the dorsal mesentery”. All of these species referred to Meseres had 18–20 tentacles, a distinct pygal furrow, and tentacle ossicles, and are hence not congeneric with M. macdonaldi . Except for the type species M. macdonaldi , and Meseres (?) torvus ( Théel, 1886), all species previously referred to Meseres are reassigned above to Molpadiodemas Heding or Pseudostichopus Théel. O’Loughlin (2002) listed Molpadiodemas Heding, 1935 , Trachostichopus Heding, 1940 and Plicastichopus Heding 1940 as junior synonyms of Meseres Ludwig, 1894 . These three genera are removed from the synonymy, and are discussed under Molpadiodemas and Pseudostichopus above.

O’Loughlin (2002) referred Stichopus (?) torvus Théel, 1886 to Meseres , based on the original description and the comparison with Meseres macdonaldi by Ludwig (1894). The single type specimen was collected in the South Pacific Ocean off Chile at 2516 m. A subsequent examination (Apr 2002) of the type revealed the following: strongly contracted, 160 mm long (210 mm in Théel 1886); cylindrical; irregular double rows of large tube feet on paired radii; dorsal and lateral surfaces covered with long conical papillae of varying sizes, largest ventrolaterally, rare branching; small pygal furrow present as a split above anus (possible artefact); longitudinal muscles round, deeply split (probable artefact); gonad tubules short, sac-like, branched; ossicles not detected in body wall, tentacles, papillae, tube feet, gonad, or respiratory trees. The calcareous ring was not Pseudostichopus -like. These characters have little affinity with Molpadiodemas Heding or Pseudostichopus Théel , and torvus is referred back to the original combination Stichopus (?) torvus.