Mycale (Kerasemna) tenuityla

Mycale (Kerasemna) tenuityla (Pulitzer-Finali, 1982)

Figs 65 a–c, 66a–e

Kerasemna tenuityla Pulitzer-Finali, 1982a: 106, figs 16–17.

? Desmacella humilis; Pulitzer-Finali 1993: 293.

Mycale (Arenochalina) tenuityla; Van Soest & Hajdu 2002: 678, figs 5H–I; Calcinai et al. 2006: 201.

Material examined. MSNG 46937, holotype, fragment and slide, Australia, Heron Island, NW end of northern shore, depth 11 m, SCUBA, coll. G. Pulitzer-Finali, field nr. HER.23, 26 April 1979.

RMNH Por. 8328, France, Mayotte, Ranikiki reef, 12.9412°S 45.0718°E, SCUBA, coll. N.J. de Voogd, field nr. MAY02–028, 4 May 2013; RMNH Por. 8866, Taiwan, Penghu Islands, SiYuPing, SCUBA, coll. N.J. de Voogd, 23.2733°N 119.5051°E, field nr. PES166, 29 July 2014.

Description (Fig. 65a,a 1, 66a,b). Massive-lobate with hollow interior. Walls strengthened by algal thallus. Overall similar to M. (K.) humilis, but no clearly tubular habit has been collected so far. Size up to 9 cm in height, 4.5 cm in lateral expansion. Color in life white or shades of red, algal thallus purple. Preserved, color changes to beige (Fig. 66b).

Skeleton (Figs 65 b–c). A reticulation of algal strands and thick spongin encased spicule tracts, up to 750 µm in diameter and connected by thinner tracts of about 60 µm in diameter (Fig. 65b), together enclosing a hollow interior. Between the tracts and strands there is a web-like tissue membrane containing a dense mass of toxodragmas and scattered sigmas (Fig. 65c). No chelae were detected.

Spicules (Figs 66 b–e). Mycalostyles, sigmas, toxodragmas.

Mycalostyles (Fig. 66c,c 1), straight, stocky, head faintly developed, 183– 221.9 –252 x 3– 4.7 – 7.5 µm; type specimen: 183– 204.7 –212 x 3– 4.1 – 5 µm.

Sigmas (Figs 66d,d 1), thin, symmetrical, with ends often faintly spined, 20– 25.8 – 31 µm; type specimen: 22– 25.9 – 31 µm.

Toxodragmas (Figs 66e,e 1), similar in shape and size to M. (K.) humilis, 39– 44.4 –51 x 4– 6.3 – 9 µm; 39– 44.9 – 51 x 5– 6.1 – 9 µm.

Distribution and ecology. Northeast Australia, Mayotte, Taiwan, in shallow-water reefs.

Remarks. The species is delimited against M. (K.) humilis by the more restricted habitus (not tubular), the absence of anisochelae and trichodragmas, and perhaps also the thinner megascleres. Specimens of the present species consistently have the sigma endings faintly spined, visible only under SEM. The spines were not observed in M. (K.) humilis, although roughened endings did occur in its sigmas. The similarity in size and shape of the shared spicules and the apparent wide sympatry (both occur over eastern and western parts of the region) rather strongly suggests the possibility that these differences could fall within the variation of a more variable M. (K.) humilis. For the time being we emphasize the spicular differences.

It is also urgent to re-examine Desmacella arenifibrosa Hentschel, 1911: 314 and Biemna microxa Hentschel, 1911: 316, which do not seem to be Desmacella and Biemna, but may prove to be reduced members of subgenus Mycale (Kerasemna). We refrain from formally reassigning these species, but merely point out that they might belong here.

Key to the Mycale (Kerasemna) species of the region

1 Anisochelae present........................................................................ M. (K.) humilis

- Anisochelae absent........................................................................ M. (K.) tenuityla

Global diversity and distribution of the subgenus Mycale (Kerasemna)

The above results from our Indo-West Pacific Mycale (Kerasemna) are presented in the map of Fig. 67 of the distribution over the world oceans summarized as the numbers of species found in Marine Ecoregions of the World (cf. Spalding et al. 2007. The subgenus is with certainty only known by two species from the tropical Indo-West Pacific waters, but may be also present in the tropical Atlantic (cf. Burton 1932).