Mycale (Aegogropila) crassissima (Dendy, 1905)

(Fig. 22A–H)

Examined material. Sample HL 168: Vietnam, Hang Trai Island, Hang Du II Lake, intertidal, 26 April 2004.

Comparative material: holotype of Mycale (Aegogropila) crassissima Dendy, 1905 BMNH 1907.2.1.56 (Fig. 22 J-O); holotype of Mycale (Aegogropila) pectinicola Hentschel, 1911 ZMB Por 4404 (Fig. 31 A-I).

Description. The sponge is rounded, irregularly cushion-shaped, about 20 cm 2 and covers three branches of a colony of Carijoa riisei as a thick mass (Fig. 22A). Numerous parts of the branches of the octocoral are free from the sponge, but where the sponge is present it completely covers the octocoral and also the polyp openings. The surface is reticulated and the consistency is firm. The sponge is yellow in situ (Fig. 22A) and beige when preserved in ethanol.

Skeleton. The ectosomal skeleton consists of an irregular reticulum of single mycalostyles and tracts of spicules with limited spongin (Fig. 22B) and scattered microscleres. In the choanosome ascending tracts of mycalostyles open into fans (Fig. 22C). Numerous chelae in rosettes are in the upper part of the tracts.

Spicules. Mycalostyles: slightly curved, with a slightly swollen head and a constricted neck; the axis of the mycalostyles increases in thickness in the middle part of the spicule, which ends with a hastate tip (Fig. 22D), 428 – (464.1 ± 23.8) – 495 x 10 – (15 ± 1.3) – 20.5 μm. Anisochelae in two size classes: anisochelae I of usual shape, with upper alae well developed (Fig. 22E), 50 – (67.7 ± 6.2) – 75 μm; anisochelae II with reduced alae at one end and a small frontal ala, hook-like, with a small tooth (Fig. 22F), 15 – (18 ± 1.1) – 35 μm. This character is clearly visible with SEM. Sigmas “C” shaped (Fig. 22G) very thin, 20 – (41.2 ± 8.6) – 52.5 μm. Raphides very abundant, often in trichodragmas (Fig. 22H), 22.5 – (24.7 ± 1.8) – 27.5 μm long. Microxeas, smooth, very small (visible only with SEM), up to 2.5 μm long (Fig. 22I).

Distribution and remarks. Ceylon ( Dendy 1905), Aru Island (Hentschel 1912), Nicobar and Andaman Archipelagos and Indonesia (Hooper et al. 2000); this species was previously recorded in Vietnam by Dawydoff (1952) and Azzini et al. (2007). Samples were recorded at the intertidal level in a dark tunnel connecting a marine lake in Ha Long Bay to the open sea.

Only three species belonging to the subgenus Aegogropila with raphides are present in the Indo-Pacific area (van Soest et al. 2011): Mycale (A.) pectinicola Hentschel, 1911, M. (A.) pellucida (Ridley, 1884) and M. (A.) crassissima (Dendy, 1905) . The re-examination of the holotype of M. (A.) pectinicola confirmed the presence of isochelae, so that this species has to be moved to the subgenus Zygomycale (see M. (Z.) parishi). Mycale (A.) pellucida is characterised by very large chelae (about 100 µm) and raphides (60 µm). The spicule complement of our specimen is consistent with Dendy’s (1905) description of M. (A.) crassissima both in shape and size: Dendy (1905) described and illustrated the mycalostyles (490 x 16 µm) with “developed oval heads narrower than the middle of the shaft, from which they are separated by a well marked constriction”. The size of the sigmas and raphides is also similar (36 and 20 x 3.6 µm respectively). The main difference compared to our specimen is in the anisochelae that Dendy (1905) described as belonging to a single category of about 60 x 2.4 µm. The reexamination of its holotype revealed the presence of a second category of anisochelae (Fig. 22 J) and also of very small microxeas (Fig. 22 K), both overlooked by Dendy (1905) . These anisochelae II (about 14 µm long) are clearly characterized by reduced alae and by a small frontal ala, with a small tooth; the microxeas are smooth and very small (up to 2 µm long). Additional spicules are mycalostyles (470–520 µm) (Fig. 22 L), anisochelae I (50–95 µm) (Fig. 22 M), sigmas (20–45 µm) (Fig. 22 N) and raphides in trichodragmas (25 µm) (Fig. 22 O) as reported and illustrated by Dendy (1905) .