Cyamon amphipolyactinum, Soest, Rob van, Carballo, Jose Luis & Hooper, John, 2012

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 : 12-14

Cyamon amphipolyactinum sp. n. Figs 4 A–E, 5

Material examined.

Type specimen: HolotypeZMA Por. 22412, encrusting a stone, preserved in alcohol.

Type locality: Mauritania, off Banc d’Arguin, 19.0833°N, 16.4167°W, on sandstone ridge, dredged, 12-18 m. coll. R.W.M. van Soest & J.J. Vermeulen, Mauritania II Exped. Stat. 49, 11 –06– 1988.

Description.

Encrusting a sandstone flake accompanied by several other encrustations (position of holotype indicated by arrow in Fig. 4A). Lateral size of holotype approximately 4x3 cm, thickness up to 3 mm. Color red in life, light orange brown in alcohol. Surface irregularly grooved and venous. Consistency soft, easily damaged.

Skeletal structure: A basal mass of polyactine spicules pierced by erect single or bundled thick styles, alternated by long thin styles protruding beyond the surface. At the periphery, the long styles are surrounded by bouquets of thin (tylo-)styles.

Spicules: of five types, long thin styles, short thin styles, short thick styles, large polyactines and small double polyactines.

Long thin styles (Figs 4B, B1), flexuous or curved snake-like, most were broken in the slides, size (based on 7 complete spicules): 1058 –1294.0– 1643 × 6 –9.3– 12 µm.

Short thin styles (Figs 4C, C1), curved, faintly tylote at the base, 288 –374.9– 456 × 2 –3.2– 4 µm.

Short thick styles (Figs 4D, D1), characteristically curved in the upper half, heads relatively thick with lower half narrowing strongly towards a sharp point, size varying strongly, 204 –352.1– 558 × 9 –17.4– 33 µm.

Large polyactines (Figs 4E, E1), in full-grown condition with all cladi ending in prominent, heavily spined knobs (Fig. 4E1) except one, the basal cladus, which is bluntly pointed. Cladi are less heavily spined towards the centre and at low magnification appear smooth. Growth stages may be partly or entirely without spines, but they are recognizable as unfinished by their irregularly undulating surface. The number of cladi varies between three and seven. In the largest spicules the cladi may be occasionally bifid. Basal cladi usually slightly shorter than the remaining cladi. Overall length of cladi regardless of condition is 18-51 × 3-10 µm.

Three-claded forms (rare), basal cladus 36-39 × 8-9 µm, lateral cladi 39-51 × 7-10 µm.

Four-claded forms (most common), basal cladus 18-51 × 3-9 µm, lateral cladi 22-51 × 3-9 µm.

Five-claded forms (also common), basal cladus 21-36 × 6-10 µm, lateral cladi 30-48 × 7-10 µm.

Six-claded forms (rare), basal cladus 21-36 × 4-5 µm, lateral cladi 24-38 × 4-6 µm.

Small double polyactines (Figs 4E and F), here termed amphipolyactines as they are obviously proliferated at both ends of the basal cladus. At first glance they resemble amphiasters or metasters (family Pachastrellidae Carter, 1875), but when studied with SEM they are similar in structure and ornamentation to the larger polyactines, but lack the swollen apices of the cladi of the larger ones. Cladi number from 5 to 10 (average 6.4) and they are spined in full-grown condition, smooth when still unfinished. Longest axis, presumably homologous to the basal cladus, is 18-30 × 1-4 µm, cladi 9-24 × 1-3 µm.

Etymology.

The name is an adjective that reflects the possession of unique small double polyactines, unprecedented in Cyamon and sponges in general.

Distribution

(Fig. 5). So far known only from the sandstone ridges of coastal flats of the Banc d’Arguin, Mauritania, West Africa.

Ecology.

In shallow-water (12-18 m), highly sedimented environments, in the company of many other sand dwelling sponges such as Ciocalypta Bowerbank, 1862 and Polymastia Bowerbank, 1864 (cf. Van Soest 1993: Pl. I fig. a).

Discussion.

The new species stands out among all described Cyamon and Trikentrion species by having unique double micro-polyactines. Further striking characters of the new species are the prominent heavily spined bulbous knobs of the large po lyactines, which are only similarly developed in Californian Cyamon koltuni Sim & Bakus, 1986, and the high frequency of five-claded polyactines, which has been to that extent reported only for Cyamon quinqueradiatum (Carter, 1880) and Cyamon koltuni . The structure of the skeleton and the overall spiculation is shared with the type species of the genus, Cyamon vickersii and its close relative Cyamon agnani . Differences are the sizes of the spicules and the less prominent bulbous knobs on the cladi of the polyactines in the latter two species.

The remaining species appear more distinct with differences in the megascleres (apparent lack of thin styles in Cyamon spinispinosum and Cyamon koltuni ), or the polyactine spicules (predominantly three cladi in Cyamon neon and Cyamon argon , smooth cladi except basal cladus in C. quinqueradiatum and Cyamon arguinense sp. n., irregular polyactines in Cyamon spinispinosum , lack of bulbous endings of the cladi and more densely overall spined in Cyamon quadriradiatum (Carter, 1880), and Cyamon aruense Hentschel, 1912).