Pseudocnus marionensis Theel 1886

Pseudocnus marionensis (Théel, 1886)

Cucumaria serrata var. marionensis Théel, 1886: 74 –75, pl. 4 fig. 3.

Cucumaria laevigata (Verrill, 1876).— Ekman, 1927: 396 –403, fig. 15 (part non Pseudocnus laevigatus (Verrill, 1876)). Pseudocnus laevigatus.— Pawson, 1971: 288 –289.— Rowe & Clark, 1975: 187 –188 (non P. laevigatus).

Distribution. Marion Is, 92–1007 m (Théel 1886).

Remarks. Ekman (1927) judged that Cucumaria serrata Théel, 1886 (and Théel’s varieties intermedia and marionensis) were junior synonyms of Cucumaria laevigata (Verrill, 1876). Cucumaria serrata var. intermedia Théel, 1886 (Heard and Kerguelen Islands) is raised out of synonymy above. Cucumaria serrata var. marionensis Théel, 1886 (Marion Is) is raised out of synonymy here. The maximum lengths of the specimens (60 mm) and ossicles (150 µ m) (from Théel 1886, Pawson, 1971, Rowe & Clark 1975) support the recognition by Théel (1886) of this variety.

Pawson (1971) examined littoral specimens from Marion I. that he judged to be Pseudocnus laevigatus. He reported a maximum length of 38 mm, and average ossicle length of 133 µ m. In discussing the holothuroids of Marion I., Rowe (in Rowe & Clark 1975) affirmed the Ekman (1927) synonymy of Cucumaria serrata var. marionensis with Pseudocnus laevigatus. Rowe reported the largest specimen as 60 mm long (55 mm in Théel 1886), and largest pear shaped ossicles as 150 µ m long (same as Théel 1886). The material examined by Pawson and Rowe appears to be conspecific with Theel’s variety. These sizes are significantly smaller than for the Kerguelen specimens of P. laevigatus (130 mm, 200 µ m) and P. intermedia (80 mm, 176 µ m) discussed above. While recognizing the Théel variety I do not reject the possibility that Pseudocnus laevigatus also occurs on the Marion Is, as both P. laevigatus and P. intermedia both occur on the Kerguelen Is. Pawson (1971) reported two distinct colour forms (white and orange) for his Pseudocnus laevigatus on Marion I, possibly indicating two species.

Pawson (1971) observed ventral brood-pouches on one Marion specimen, and Rowe (in Rowe & Clark 1975) observed them on only the largest syntype of the Théel variety.

The variety Cucumaria serrata var. marionensis Théel, 1886 is raised here to species status, and assigned to Pseudocnus Panning, 1949 for the reasons given above for Pseudocnus intermedia. This species (type locality Marion Is) is distinguished diagnostically from Pseudocnus intermedia (Théel, 1886) (type locality Heard and Kerguelen Is) by the size parameters referred to above. It is distinguished amongst Pseudocnus species by radial series only of tube feet, and presence of both knobbed spinous pear-shaped ossicles and knobbed oval buttons, both shorter than 150 µ m long. The two ossicle forms are similar to the Magellanic species Pseudocnus dubiosus leoninus (Semper, 1868), but that species has a complete cover of tube feet.