Hemiocnus syracusanus ( Grube, 1840 )

Mjobo, Sifiso & Thandar, Ahmed S., 2016, A new genus and a new species in the sea cucumber subfamily Colochirinae (Echinodermata: Holothuroidea: Dendrochirotida: Cucumariidae) in the Mediterranean Sea, Zootaxa 4189 (1), pp. 156-164 : 158-159

Hemiocnus syracusanus ( Grube, 1840)

( Figures 1 & 2 )

Cladodactyla syracusana Grube, 1840:40 .

Cucumaria syracusana Sars, 1857:123 , Pl. 1 fig. 24–29; Théel, 1886:113; Koehler, 1921:155, fig. 106; Cherbonnier, 1956:20. Ocnus syracusanus Panning, 1949:438 , fig. 33, 34.

Pseudocnus syracusanus Panning, 1962:68 , fig. 13, 14 (?).

Pseudocnella syracusana Thandar, 1987:288 , 289.

Diagnosis (from Sars 1857, amended herein). Body sub-cylindrical, colour light-brown in alcohol. Dorsal tube feet in both radii and interradii. Tentacles 10, ventral-most two reduced. Calcareous ring simple, without posterior processes. Body wall thick, rigid. Ossicles of body wall comprise fir-cone-shaped plates, often denticulate at one end, and round, knobbed, often 4-holed buttons. Incomplete baskets may also occur as dichotomously branched rods, usually in association with bases of tube feet. Tube feet with rods; tentacles with rods and rosettes.

Material examined. Zoologisches Museum Hamburg, E2877, Zool. Stat. Europa, Italien, Neapel, 1 spec.; NHMUK, 1982.6.1.6-8, Shigmona, south of Haifa, Dr. Lewinsohn, 4 spec.

Description. This species is well known and hence only a brief description of the Hamburg specimen from Naples follows. Body curved, mouth and anus turned up; colour light brown in alcohol; length 56 mm, width in mid-body 19 mm. Tube feet in two rows ventrally, but scattered dorsally. Anal papillae present. Tentacles 10, ventral-most two reduced. Calcareous ring simple, without posterior prolongations, radials slightly notched posteriorly. Retractor muscles arise from longitudinal muscles at about half body length. Polian vesicle and stone canal not detected. Gonad of numerous, unbranched tubules. Respiratory trees highly branched.

Body wall ossicles comprise large, multi-layered, fir-cone-shaped knobbed plates, denticulate at one end; large knobbed, non-denticulate, round plates; smaller rounded, knobbed buttons/plates; and occasionally incomplete cross-shaped baskets appearing as dichotomously branched rods ( Figure 1 A) also present. Denticulate fir-coneshaped plates 290–340 µm ( Figure 2 A); large knobbed round non-denticulate plates 150–210 µm ( Figure 2 B); small knobbed buttons/plates up to 120 µm, with 4–(8) holes ( Figure 2 C), holes up to 10 µm, knobs up to 30 µm; incomplete baskets typically like those of Pseudocnella sinorbis (Cherbonnier) . Tube feet deposits include perforated rods ( Figure 1 B) and often also incomplete baskets; end-plates present. Tentacle deposits include rods ( Figure 2 D,E) and rosettes ( Figure 1 C), but latter not as numerous as in H. rubrobrunneus n. sp.

Distribution. Mediterranean Sea, Italy, off west coast of Africa.

Remarks. This species was described from the Mediterranean Sea by Grube (1840) as Cladodactyla syracusana but transferred to Cucumaria by Sars (1857). Théel (1886) followed Sars and accepted the species as Cucumaria syracusana , recording its distribution as the Mediterranean Sea and off west coast of Africa. Panning (1949) transferred the species to Ocnus . Grube (1840), Sars (1857) and Théel (1886) did not describe the calcareous ring, but this was done by Panning (1949). Later Panning (1962) transferred the species to Pseudocnus with some reservation. Subsequent to this, Thandar (1987), in his revision of some southern African Cucumariids, erected a new genus Pseudocnella to accommodate three common southern African species and hesitantly also included in it P. syracusanus . The specimen from Hamburg Museum and those in the NHMUK, represent the true syracusanus as their characters match those recorded for this species by various authors. According to Thandar (1987) the genus Pseudocnella is characterized by 10 equal tentacles with only one species ( P. insolens ) having one or more reduced, but not necessarily the ventral-most two, and buttons in the body wall. In addition, all species possess, at least at some stage of their development, an external layer of incomplete baskets. Since syracusanus has an 8+2 arrangement of tentacles, often incomplete baskets in the body wall as well as buttons, it cannot be classified in Pseudocnella . It also not referable to Ocnus because of the presence of large knobbed, multi-layered, often denticulate plates and ‘papulae-like’ extensions dorsally and no complete baskets. The new genus is closer to Pseudocnella than it is to Ocnus .

Panning (1962) reported on 3 specimens from Naples, measuring 29 mm, 45 mm and 58 mm in length. His drawings of the ossicles in Figure 14 (a–i) matches both H. syracusanus and H. rubrobrunneus n. sp. here described, but his Figure 14 (c–e) appears to be of the small specimen since such ossicle types are not found in the body wall of a typical H. syracusanus . It is therefore suspected that Panning (1962) did not clearly distinguish between the two forms he had at hand. Any re-assignation of part of Panning’s (1962) material will require its reexamination, hence until Panning’s material is re-examined this is just a conjecture. Grube’s (1840) description of his Cladodactyla syracusana is rather vague but Sars (1857), as the first reviser, found baskets and multi-layered fir-cone-shaped plates in the body wall. His description of the plates comes very close to the larger specimen here described and so do the descriptions of Koehler (1921) and Cherbonnier (1956). Therefore , there is no doubt that the USNM and that from Hamburg are not conspecieific.

Figures

FIGURE 1. Hemiocnus syracusanus. A. Incomplete baskets from body wall; B. Rod from tube foot; C. Rosettes from tentacles; D. Calcareous ring.

FIGURE 2. Hemiocnus syracusanus. A. Fir-cone-shaped plates from body wall; B. Large round plates from body wall; C. Buttons from body wall; D. Small rods from tentacles; E. Large rods from tentacles; F. Specimen entire.