Trikentrion helium Dickinson, 1945

Soest, Rob van, Carballo, Jose Luis & Hooper, John, 2012, Polyaxone monaxonids: revision of raspailiid sponges with polyactine megascleres (Cyamon and Trikentrion), ZooKeys 239, pp. 1-70 : 42-44

Trikentrion helium Dickinson, 1945 Figs 24 A–E

Trikentrion helium Dickinson 1945: 15, pl. 20 figs 39-40 (Mexican Pacific); Luke 1998: 10 (La Jolla, Southern California).

? Trikentrion catalina ; Gómez et al. 2002: 230, fig. 5 (Mexican Pacific).

Material examined.

Holotype AHF-NMHLA L-35535 (D33), preserved in alcohol, Hancock Pacific Expeditions, Mexican Pacific, Cedros island, South Bay, approximately 28.07°N, 115.3°W, 18-27 m depth, Velero Station 287-34, 10 March 1934.

Description. Undulating thin-bladed sheets together forming a bushy mass (Fig. 24A) of 7 × 5 × 5 cm. The surface bears a thick spicule brush of 3 mm thickness. Conistency firm, brittle. Colour reddish brown (alcohol).

Skeleton: built chiefly by polyactines (no oxeas), supporting the bases of long styles, which are surrounded by dense brushes of short thin styles.

Spicules: long thin styles, short thin styles, polyactines among which numerous diactinal forms, trichodragmas.

Long thin styles (Figs 24B, B1), variably thinner and thicker, but not divisible in two thickness categories, 952 –1808.1– 3393 × 18 –25.8– 42 µm.

Short thin styles (Fig. 24C), usually curved, and often with a subterminal tyle, 372 –438.0– 510 × 2.5 –3.1– 3.5 µm.

Polyactines (Fig. 24D), predominantly wide-angled triactines (Fig. 24D), with basal cladi provided with course conical spines (Fig. 24D2), lateral cladi usually much longer than basal cladi, with smooth, rounded endings (Fig. 24D3); basal cladi 66 –105.4– 144 × 8 –22.1– 30 µm, lateral cladi 96 –146.5– 192 × 7 –23.6– 36 µm; few, mostly smaller, tetractinal polyactines occur, with cladi 27-63 × 9 µm; more frequently diactinal reduced polyactines (Fig. 24D1) occur, asymmetrical, sometimes style-like, smooth, recognizable by an excentric swollen tyle, 192 –235.2– 306 × 13 –19.8– 27 µm.

Trichodragmas (Fig. 24E) abundant, occurring throughout the choanosomal and ectosomal regions, 84 –100.7– 123 × 10 –12.1– 15 µm. Individual raphides less than 0.5 µm in thickness.

Distribution.

The holotype was collected in the Southern Californian Bight (Mexican Pacific). Luke (1998) records several specimens from La Jolla, California (USA). If specimens of Gómez et al. (2002) belong to this species, it occurs in the Sea of Cortez and further south along the Mexican Pacific coast.

Ecology.

Rocks and reefs at depths of 15-28 m.

Discussion.

The trichodragmas were not cited in the original description. Trikentrion helium shares the dominance of three-claded polyactines with relatively long lateral cladi with Trikentrion catalina (see below), to which it seems closely related. This species differs quite strongly from the other Trikentrion species by its possession of numerous diactinal or style-like reduced polyactines, which resemble, but clearly are not proper, oxeas like those of Trikentrion muricatum and Trikentrion flabelliforme . The spicules are recognizable as polyactines by the substantial difference between the smoothly rounded end, resembling the ends of the lateral cladi of the three-claded polyactines, and the dissimilar pointed end which shows an irregular surface and is connected to the other end by a swollen, often irregular middle part. Their lengths coincide with the added lengths of a lateral and a basal clade of the three-claded forms. Such reduced diactinal polyactines are also common in Cyamon neon .

The specimens described by Gómez et al. (2002) under the name Trikentrion catalina were branching erect rather than bladed, but branches were typically flattened, 2-4 mm in thickness. We reassign these specimens to Trikentrion helium , because they apparently possess oxea-like polyactines [described as oxeas but confirmed as reduced polyactines by one of us (JLC)], whereas in Trikentrion catalina there are neither oxeas forming the main skeleton as in Trikentrion flabelliforme nor diactinal polyactines as in Trikentrion helium . The difference in shape between the type of Trikentrion helium and Gómez et al.'s specimens is here considered to be mere variation (comparable to variation in Trikentrion flabelliforme , see above) but further studies might reveal there is more specific diversity along the Pacific coast of Mexico.