Synallactidae 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 : 150

Synallactidae Ludwig, 1894

Table 2, Figure 1

Remarks. Although the Synallactidae (sensu lato) are characterized as deep-water forms that possess peltate tentacles, lack tentacle ampullae, have gonads in one or two tufts, and usually possess body wall ossicles (including tables and rods), this work embraces only those species of Synallactidae that substantially lack body wall ossicles, and have in addition a distinct pygal (posterior) vertical furrow. The pygal-furrowed Synallactidae are characterised by: a generally cylindrical body form; rounded anterior and posterior ends; ventral mouth and anus; presence of a pygal furrow; 18–20 peltate tentacles; absence of tentacle ampullae; a complete cover of small and frequently inconspicuous tube feet; absence of retractor muscles; longitudinal muscles never divided; a solid calcareous ring; radial plates broader than high, anteriorly with a central notch and two central and two lateral low projections, posteriorly with a shallow smooth indentation and two pairs of "teeth" variably evident; interradial plates broad and low, anteriorly with a central spire, posteriorly with a smooth shallow indentation; madreporite sometimes evident externally on the anterior dorsal body surface; single, sac-like, elongate or short, ventral polian vesicle; gonad tubules in two groups, one on each side of the dorsal mesentery; respiratory trees comprising two long unequal branches of alveolar-like clusters along a central strap; ossicles absent from the body wall, but present in the pygal lobes in some species.

Body wall, pygal lobes, tube feet, tentacles, gonads, and respiratory trees were examined for ossicles in all species, and are reported only as found, not as absent. The colour of tentacles and internal anatomical features was noted throughout the study, and found to be not diagnostically reliable. The form of the peltate tentacles, which varies greatly with state of preservation, was found to be not diagnostically reliable. The presence or absence of "teeth" on the posterior indentation of the radial plates of the calcareous ring has been used diagnostically by some authors. This feature was found to be variable and subjective, and depended on the angle from which the plates were viewed. Descriptions of these features have been omitted.

The genera included in this paper have been shifted between the Gephyrothuriidae (now restricted after O’Loughlin, 1998) and Synallactidae (see O’Loughlin, 1998, 2002). In the Zoological Catalogue of Australia Rowe (1995) referred species of pygal-furrowed Synallactidae to the genera Meseres Ludwig, 1894 (incertae sedis below) and Pseudostichopus Théel, 1886 in the Gephyrothuriidae . Following the rediagnosis below of Pseudostichopus Théel , Meseres peripatus Sluiter, 1901 is reassigned to Pseudostichopus . Following examination of the AM collections by one of us (M.O’L), as far as the Australian fauna is concerned, Rowe (1995) correctly identified Pseudostichopus mollis Théel and Pseudostichopus peripatus (Sluiter) material, but wrongly identified some material as Pseudostichopus pustulosus Sluiter, 1901 (= Molpadiodemas pustulosus below). We judge that this material is Pseudostichopus mollis , and that Molpadiodemas pustulosus (Sluiter) is not to date represented in the Australian fauna.

Figures

Figure 1. Characters of pygal-furrowed Synallactidae. a, ventral mouth and anus (M. helios sp. nov., USNM E31104, paratype, 91 mm long); b, ventral peltate tentacles, polian vesicle (P. mollis, TM H2004; anterior end dissected off); c, respiratory tree (P. mollis, TM H2004); d, drawing of dorsal posterior pygal furrow; e, posterioventral view of pygal furrow and anus (M. violaceus, BMNH 86.10.2.150); f, anterior dorsal madreporite (arrow) (P. peripatus, USNM 1008159); g, drawing of calcareous ring (radial plate right, as in P. spiculiferus); h, calcareous ring (M. crinitus sp. nov., USNM E48644, paratype); i, calcareous ring (M. violaceus, BMNH 86.10.2.145).