Pseudocnus Panning, 1949

O’Loughlin, P. Mark, Mackenzie, Melanie, Paulay, Gustav & VandenSpiegel, Didier, 2014, Four new species and a new genus of Antarctic sea cucumbers with taxonomic reviews of Cladodactyla, Pseudocnus, Paracucumidae and Parathyonidium (Echinodermata: Holothuroidea: Dendrochirotida), Memoirs of Museum Victoria 72, pp. 31-61 : 42-46

Pseudocnus Panning, 1949

Figure 9 ; table 2

Pseudocnus Panning, 1949: 422–425 .— Panning, 1951: 73– 80.— Panning, 1962: 57–80.— Thandar, 1987: 288–289.— Lambert, 1998: 474–476.— O’Loughlin and Alcock, 2000: 4.

Diagnosis (sensu stricto – see Remarks). Ten equal dendritic tentacles; tube feet in radial series, additional smaller tube feet scattered in inter-radii; ossicles in body wall of two forms, knobbed buttons typically regular in form with four perforations and lacking marginal spines at one end, and single-layered knobbed plates with spines at one tapered end; tentacles with perforated plates, rod-like plates and rosettes.

Type species. Cucumaria koellikeri Semper, 1868 (type locality Mediterranean Sea) (original designation by Panning 1949). Panning (1962) proposed an invalid re-designation of Cucumaria dubiosa Semper, 1868 as type.

Remarks. Panning (1949) designated Cucumaria koellikeri Semper, 1868 (type locality Mediterranean Sea) as type species of his new genus Pseudocnus . Subsequently Panning (1962) came to believe that his re-description ( Panning 1949) of Cucumaria dubiosa Semper, 1868 , as another species of Pseudocnus , was based on a specimen also belonging to C. koellikeri . This was rectified in Panning (1962) when synonymies and full descriptions of both P. dubiosus and P. koellikeri were given and Panning proposed, invalidly, to change the type of Pseudocnus to Cucumaria dubiosa (type locality Peru). The diagnostic description in Panning (1949) of Pseudocnus koellikeri ( Semper, 1868) was accurate. A significant diagnostic difference between these two species is that Pseudocnus dubiosus has eight large and two small tentacles, while Pseudocnus koellikeri has 10 equal tentacles. Our sensu stricto diagnosis of Pseudocnus is based on the descriptions of the type species Cucumaria koellikeri by Koehler (1921, 1927) and Panning (1949, 1962).

Panning (1949) described, then revised (1962), Pseudocnus . In his revision he considered five taxa to be sub-species, all within his “ dubiosus group”: Pseudocnus dubiosus africanus ( Britten, 1910) (junior synonym of Pseudocnella insolens ( Théel, 1886) by Thandar 1987); Pseudocnus dubiosus dubiosus ( Semper, 1868) ; Pseudocnus dubiosus jaegeri ( Lampert, 1885) (junior synonym of Pseudocnella sykion ( Lampert, 1885) by Thandar 1987); Pseudocnus dubiosus koellikeri ( Semper, 1868) ; Pseudocnus dubiosus leoninus (Semper, 1867) . On the basis of significant morphological differences (see Table 2 and new genus below) we raise three of these sub-species to species status: P. koellikeri , P. dubiosus (s.s.), and P. leoninus . As noted above Thandar (1987) transferred the remaining two to Pseudocnella Thandar, 1987 .

Deichmann 1941 stated that Cucumaria salmini Ludwig, 1875 (type locality: Sulawesi, Indonesia) was probably a junior synonym of Cucumaria leonina Semper, 1867 (assumed type locality: “ Singapore ”), because of their similarity and presumed proximity of occurrence, rejecting Ekman’s 1925 conclusion that the type locality for Cucumaria leonina was in error. Panning 1962 however, reaffirmed Ekman’s 1925 conclusion, noting that the type was preserved in “rum from Singapore ”, and considered the type locality for C. leonina to be around the Falkland Islands ( Malvinas). Ludwig (1875) likened the ossicles of his C. salmini to Semper’s 1868 C. dubiosa , and referred to the illustration of a distally spinous plate and knobbed button in Semper’s figures. C. leonina also has this ossicle combination. While we have not restudied the type of C. salmini we consider it unlikely that this tropical Pacific species would be conspecific with a sub-antarctic South American species. We thus raise Pseudocnus salmini out of synonymy (by Deichmann 1941) with Pseudocnus leoninus . We provisionally refer P. leoninus to the new genus (below) on the bases of supportive genetic data and sub-Antarctic occurrence. We do not refer P. salmini to the new genus for three reasons: Ludwig (1875) likened the ossicles to those of C. dubiosa ; tropical occurrence; absence of any indicative genetic data.

Panning (1962) created two groups of species assigned to Pseudocnus Panning, 1949 : those with both distally spinous pine-cone-shaped knobbed plates and knobbed buttons in the body wall were assigned to the “ dubiosus group”; those that lacked knobbed buttons were assigned to the “ laevigatus group”. We agree with this distinction between two morphologically distinct groups. Our limited genetic data support a “ laevigatus group” clade ( Fig. 9 ), and this clade shows geographic cohesion; all species live in the sub-antarctic – Antarctic region. Pseudocnus leoninus , the only sub-antarctic member of Panning’s “ dubiosus group” (with a complete cover of tube feet and numerous knobbed buttons in the body wall), genetically groups with Panning’s “ laevigatus group” ( Fig. 9 ). We describe a new genus below, Laevocnus O’Loughlin gen. nov., that includes most species of Panning’s “ laevigatus group”, and provisionally includes P. leoninus .

In contrast, North Pacific species assigned to Pseudocnus (including P. curatus , P. lubricus , P. californicus ) are closely related to North Pacific species of Cucumaria (Arndt et al. 1996, Michonneau et al. in prep.), and do not cluster near the Laevocnus clade. Lambert (1998) judged that sub-species Cucumaria fisheri astigmata Wells, 1924 is conspecific with Pseudocnus lubricus (H. L. Clark, 1901) . Lambert (1998) further judged that Cucumaria curata Cowles, 1907 should be retained in Pseudocnus and proposed a third “ curatus group” for Pseudocnus species. Pseudocnus curatus (Cowles) has smooth buttons, with a few perforations only, in the body wall.

Thandar (1987) transferred four species from Pseudocnus to his new genus Pseudocnella Thandar, 1987 : Cucumaria sinorbis Cherbonnier, 1952 (type species), Cucumaria insolens Théel, 1886 (junior synonym Cucumaria leonina var. africana Britten, 1910 ), Semperia sykion Lampert, 1885 (junior synonym Cucumaria jaegeri Lampert, 1885 ), and Cucumaria syracusana Grube, 1840 .

P. cornutus ( Cherbonnier, 1941) (Patagonia) was included in the “ laevigatus group” by Panning and fits geographically there also. It differs from Pseudocnus species sensu stricto by having two smaller ventral tentacles, having tube feet radial only, and lacking buttons. It groups with species of the new genus (below) by having tube feet confined to the radii and lacking buttons, but differs by having two smaller tentacles and having rod-plate ossicles and not plates in the tentacles. We provisionally refer P. cornutus to Laevocnus (below).

The species that remain assigned to Pseudocnus exhibit a range of contrasting morphological characters: 10 dendritic tentacles that may be equal or eight large and two small ventral; tube feet completely restricted to radii, largely restricted to radii, or uniformly distributed around body; macroscopic external anal scales present or absent; ‘calcareous’ ring calcified or not; body wall ossicles in different combinations with single-layered perforated knobbed plates with one end tapered and distally spinous (pine cone shape, pear shape) present or absent, knobbed buttons present or absent, multi-layered perforated knobbed plates present or absent, incomplete baskets present or absent, thick smooth buttons with few perforations only present or absent. We judge that species with such different combinations of morphological characters are not congeneric (see Table 2). None occurs in southern cold temperate to Antarctic waters. A further review of the species that remain assigned to Pseudocnus is needed.

Figures

Figure 9. Maximum likelihood tree for Laevocnus clade, based on COI sequences, GTR+I model, 100 bootstrap replicates, Cladodactyla sicinski as outgroup. Filled circles>0.95 bootstrap support.