Trikentrion flabelliforme Hentschel, 1912

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 : 39-41

Trikentrion flabelliforme Hentschel, 1912 Figs 22 A–D, 23 A–E

Trikentrion laeve sensu Carter 1882: 294 (West Australia) (not: Carter 1879)

Trikentrion flabelliforme Hentschel 1912: 373, pl. 13 fig. 9, pl. 20 fig. 32 (Aru Islands, Indonesia); Capon et al. 1986: 6545; Hooper 1991: 1298, Figs 61-62, 109h-I (North and West Australia); Hooper 2002: Figs 18 H–J.

Material examined.

Holotype missing from SMF, but a paralectotype fragment is present in the Natural History Museum, BMNH 1931.8.4.57, which was examined by JH in 2000, type locality: Indonesia, Aru Islands, 4-15 m depth.

ZMA Por. 02426, preserved in alcohol, Siboga Exped. Stat. 273, Aru Islands, Indonesia, pearl banks off Pulau Jedan, 5.4134°S, 134.6677°E, depth 13 m, 23 –12– 1899.

RMNH Por. 978, preserved in alcohol, Siboga Exped. Stat. 273, same data;

ZMA Por. 14022 and 14023, preserved in alcohol, East Point, Darwin, Northern Territories, Australia, 10 m, 29 –11– 1987, coll. J.N.A. Hooper nrs 8 and 9;

ZMA Por. 16049, dry old collection material without data.

Description.

Two distinct shapes, flabelliform (Fig. 22A), 6-26 × 4-19 cm high and wide, 0.2-1.4 cm thick) and digitate (Fig. 22B), up to 15 cm high, with flattened branches of up to 1.5 cm thickness (summary of many specimens described in Hooper, 1991). Flabelliform specimens may have blades at right angles (see Fig 22A). Frequently, the digitate specimens are infested with zoanthids (Fig. 22B). Surface optically smooth, microhispid, with characteristic pattern of fine meandering grooves. Texture firm. Colour orange-red, blood-red (shallow water) to beige (deep water).

Skeleton (Figs 22 C–D): reticulated, square meshed or polyangular (Fig. 22D), with loose extra-axial and spongin-rich axial spicule tracts cored by oxeas, echinated by triactine polyactines; at the surface protruding long thin styles are surrounded by bouquets of short thin styles (Fig. 22C).

Spicules (Figs 23): Long thin styles, short thin styles, oxeas, polyactines, trichodragmas.

Long thin styles (Fig. 23A), curved, slim, 405 –870.3– 1034 × 3 –7.3– 9µm.

Short thin styles (Fig. 23B), thinly fusiform, 182 –334.7– 392 × 0.5 –1.8– 4 µm.

Choanosomal genuine oxeas (Figs 23C, C1), not to be confused with diactinal polyactines, evenly or more angularly curved, apices mucronate and many have minute spines visible under SEM (Fig. 23C1), sizes 135 –287.7– 340 × 5 –16.8– 22 µm.

Polyactines (Figs 23D, D1), rare in some specimens, predominantly three-claded, with prominent spines on the basal ray, and minute apical spines on the lateral rays (Fig. 23D1) visible only under SEM, occasionally strongly curved diactines or - often smaller - tetractines, basal cladi 96 –109.5– 123 × 10 –13.1– 17 µm, lateral cladi 51 –70.0– 84 × 9 –12.6– 17 µm.

Trichodragmas (Figs 23E, E1) with individual raphides showing rugose surface (Fig. 23E1), sizes 35 –59.6– 88 × 6 –8.6– 12 µm.

Distribution.

Arafura Sea, N and W Australia.

Ecology.

Shallow subtidal to offshore deeper water.

Discussion.

The species was erroneously attributed to Carter 1882: 294, allegedly as Trikentrion laeve var. flabelliforme, by Hooper (1991). This is a manuscript name because Carter did not name his Australian flabellate specimen, merely referring it to Trikentrion laeve . That species is West African and described above as a distinct new species.

The two 'growth forms’ are rather distinct, but distribution, skeleton, and spicules are similar and overlapping enitirely, making it impossible to separate the forms further. The digitate form is often overgrown with a zoanthid species, both in Australian (Hooper, 1991) and Indonesian (RMNH Por. 978) specimens. The shape of Trikentrion flabelliforme reminds of Californian Trikentrion catalina and Trikentrion helium , but spiculation in these species differs substantially by their lack of proper choanosomal oxeas. Comparative variation in shape is also recorded for Trikentrion helium (see below).

The apices of the oxeas and the polyactines show minute spines, which is here interpreted as a unique feature. It violates the rule that in Trikentrion only the basal, not the lateral cladi of the polyactines have spines, but there is little correspondence with the lateral cladus spination in Cyamon .

This is the only Trikentrion species that appears to be widespread and common. Chemistry of Trikentrion flabelliforme includes unique indoles ( Capon et al. 1986).

We studied an Indonesian specimen from the ZMA collection labeled Trikentrion elegans Lendenfeld identified by Burton (ZMA Por. 02402, Siboga Exped. Stat. 303, Timor, Samau Island, Haingsisi, 10.2050S, 123.4591E, 23 m), which has the shape and skeletal structure of a small digitate Trikentrion flabelliforme , including ectosomal long thin styles (up to 1350 × 12 µm), short thin styles (300-400 × 1-3 µm), a choanosomal reticulation of robust oxeas (300-400 × 15-20 µm) and large amounts of trichodragmas (60-110 × 5-15 µm), but lacking polyactine spicules entirely. In view of the occasional rarity of these spicules observed in some specimens of Trikentrion flabelliforme , it is likely that it is a ‘deficient’ specimen of this species. Anecdotal records of Trikentrion flabelliforme from northern Australia have also occasionally encountered similarly deficient specimens (B. Alvarez, pers.comm.). The locality of the Siboga specimen is neatly inbetween the type locality and the North and West Australian localities.