Scolanthus triangulus sp. nov.

Figs. 1, 11; Table 3

Diagnosis. With small, scattered nemathybomes containing nematocysts longer than 60 μm. Length of whole animal in contraction to 11 mm, diameter to 4 mm.

Material examined. Holotype: CAS 175210, San Diego, California, Bight 0 3, Sta. 4633, 34.047°N 119.655°W, 23­Aug­2003, 85 m. Paratypes: CAS 175207, collected with holotype (2 specimens); CAS 175209, San Diego, California, Bight 0 3 Sta. 4419, 34.12233°N 119.331°W, 19­Aug­ 2003, 132 m (2 specimens); CAS 175204, San Diego, California, Bight 0 3 Sta. 4035, 34.28417°N 119.507°W, 18­Aug­ 2003, 271 m(3 specimens); CAS 175208, San Diego, California, Bight 0 3 Sta. 4086, 33.83531°N 118.47°W, 21­Jul­ 2003, 85 m (3 specimens).

External anatomy. Tentacles filiform, 16. Column elongate to blunt cone in contraction (Fig. 11 A). Scapus with small, sparsely scattered nemathybomes; in some specimens, nemathybomes of scapus sparser and less prominent distally than proximally. Periderm thin, tightly adherent, fine grained.

Internal anatomy and histology. Parietal and retractor muscles relatively weak (Figs. 11 B, C). Retractor muscle small, with relatively few, widely spaced, unramified branches (Fig. 11 C). Parietal muscle trianguloid; central lamella and lateral branches of approximately equal thickness (Fig. 11 B). Branches of parietal muscle closer to body wall grouped, attached to the mesentery by single, slightly longer lamella. All examined specimens either infertile or male.

Nemathybomes large, single, sunken into mesoglea, protruding into epidermis (Figs. 11 D, F.). Epidermis and mesoglea relatively uniform in thickness throughout body; mesoglea thicker than epidermis or gastrodermis. Aboral end slightly drawn in at center, with slightly smaller nemathybomes than column (Fig. 11 D).

Cnidom. Spirocysts, basitrichs (Figs. 11 E, G–M; see Table 3 for size and distribution).

Etymology. The species epithet is a masculine adjective based on the Latin root “triangul­” referring to the triangular cross­sectional shape of many preserved specimens, and should be translated as “the triangular Scolanthus .”

Distribution and habitat. Occurs most commonly on steep outer shelf; most specimens collected between 71 and 132 m. As this is the deeper end of the sampling range for various Sanitation Districts’ sampling programs, its bathymetric range may extend deeper.

Similar species. Scolanthus triangulus superficially resembles E. olguini, although it has smaller and less prominent nemathybomes. The two differ in the details of internal anatomy and in the size of the cnidae. In general aspect, it resembles S. callimorphus, having a similar number of tentacles and arrangement of nemathybomes, and nemathybome nematocysts of similar size. However, S. triangulus has much smaller retractor muscles than S. callimorphus, and S. callimorphus has much larger basitrichs in the tentacles (13–69 μm: Schmidt 1979).

Remarks. This species is hard to differentiate from E. olguini without examination of the nematocysts of the nemathybomes.