Mycale (Carmia) tenuichela sp.nov.

Figs 48 a–h

Material examined. Holotype ZMA Por. 11435, Seychelles, Mahé, Praslin Island, NW coast, Chevalier Bay, 4.2833°S 55.7°E, depth 2–10 m, SCUBA, coll. R. W.M. van Soest, Netherlands Indian Ocean Expedition stat. 703, field nr. IOP-E 703/04, 17 December 1992 (live color red).

Paratype ZMA Por. 11643, Seychelles, Mahé, La Digue Island, SE coast, 4.3833°S 55.8333°E, depth 7 m, SCUBA, coll . R. W.M. van Soest, Netherlands Indian Ocean Expedition stat. 735, field nr. IOP-E 735/02, 23 December 1992 (orange) .

Descriptio n (Fig. 48a). Thin crust on dead coral rubble, orange-red in life, beige in alcohol. Size 2 x 2 cm lateral expansion, only a few mm in thickness. Surface smooth, no obvious openings (preserved). Consistency soft, easily damaged.

Skeleton (Fig. 48b). Tight spicule tracts traverse through the sponge from the substratum to the surface, more or less parallel, ending in spicule brushes. Thickness of tracts 30–60 µm. Separate loose bundles of raphidotoxas/ raphides are scattered between the skeletal tracts, random, not clearly localized. Individual mycalostyles and raphides/raphidotoxas are similar in length and and only slightly different in thickness, thus may be easily confused. Rosettes of anisochelae I are likewise scattered among the tracts, not very common. Overall presence of microscleres is low. The sections contained also much debris, sand grains, but these were not organized as part of the skeleton. Choanosomal tissue is grainy.

Spicules (Figs 48 c–h). Mycalostyles, anisochelae in three size categories, sigmas not certainly present, raphides/raphidotoxas, trichodragmas.

Mycalostyles (Figs 48c,c 1), thin, almost vestigial, with wide axial canals, straight, with elongate heads and blunt opposite ends, 201– 251.8 –289 x 2– 2.7 – 3.5 µm.

Anisochelae I (Fig. 48d), narrow-shaped, but lower part of upper median alae verging slightly outwards, free part of the shaft 35% of spicule length, 25– 32.8 – 40 µm.

Anisochelae II (Fig. 48e), overall similar to anisochelae in shape, but narrower-shaped, without outward verging upper median alae, lower median alae with conical upward protrusion, 20– 22.4 – 25 µm.

Anisochelae III (Fig. 48f), narrow, reduced with feebly developed lateral alae, 9– 13.4 – 16 µm.

Sigmas (Fig. 48g), rare, not certainly proper (only a few were observed in spicule slides and sections), not clearly separated in categories, all thin (1–2 µm in thickness), 21–52 µm.

Raphides/raphidotoxas (Figs 48h,h 1), thin, curved, but not symmetrical (so technically not toxas or raphidotoxas, but presumed to be homologous to raphidotoxas), in loose bundles, 1 µm or less in thickness, length 50– 279 – 350 µm.

Trichodragmas (Fig. 48i), 6–11 x 3–4 µm, individual raphides/microxeas 5–8 x 0.5 µm.

Distribution and ecology. Seychelles, Mahé area, on shallow reefs, 2– 10 m.

Etymology. The name is a compound noun, composed of tenuis (L.) = thin, slender, and chela, referring to the unusual slim anisochelae I and II.

Remarks. It proved rather difficult to pinpoint the exact properties of this species, because the specimens were very thin and small patches on coral rubble, which also harbored other such thin veneers, including other sponges of haplosclerid and microcionid affinity. These neighbors and also the debris and other inclusions caused contamination of the slides with a variety of spicules. Because two specimens were obtained, we were able to recognize the morphological characters, guided by the similar shapes of the characteristically thin and narrow anisochelae. There are similarities with above described Mycale (Carmia) rhaphidotoxa in habitus, skeletal structure and size and shape of most spicule types. Especially the narrow anisochelae I and II are similar to those of M. (C.) rhaphidotoxa, but are even more slimly built than in that species. However, the large robust sigmas described in M. (C.) rhaphidotoxa were definitely absent in the Seychelles specimen, and it is possible that the few thin sigmas reported here are contamination from neighbouring sponges and not proper. Since both specimens have them, we assume here that they are proper despite their rarity. An additional difference is the presence of tiny trichodragmas. These were not common and at first only detected under SEM, but subsequently recognized also in sections and spicule slides.

Below we describe a species new to science from Lombok, Indonesia, named after the commander of H.M.S Siboga, G.F.Tydeman, which is also rather similar in overall microsclere complement to the present species, including having short trichodragmas. Differences are the possession of robust sigma I and proper toxas, both lacking in the present species. Anisochela I of the present species is much slimmer and different in overall shape

Vacelet & Vasseur (1971) described a Mycale sp. 2 from Madagascar, which showed some similarities with the present species. They reported no sigmas (apart from two serrated sigmas, which were obviously foreign), similar mycalostyles, several categories of anisochelae and raphides. The difference with the above described specimen (and also with M. (C.) rhaphidotoxa) was the presence of small toxiform microscleres, not found in our specimens. No trichodragmas were mentioned by Vacelet & Vasseur, but these could have been easily overlooked.