Spirastrella mollis Verrill 1907

Spirastrella aff. mollis Verrill, 1907

(Fig. 7 A‒F)

Selected synonymy: Spirastrella aff. mollis Verrill, 1907:344.

Material examined. CNPGG –584 Sisal Banks reefs (21°26'28.2”N, 90°17'34”W), depth 15 m, 02/XII/2001.

Description. Thinly encrusting sponge 0.5–2 mm thickness, adhered to bryozoan and pieces of coral (Fig. 7 A) making a cavernous whole mass 4.3 cm long and 2.6 cm in width. The surface is smooth as well as microhispid on mounds in all around the mass, velvety in appearance but harsh when touched, becoming strongly hispid underneath the coral rubble or in hidden fissures or holes, no oscules nor pores visible to the naked eye in preserved specimens. The consistency is difficult to know owing to the thinness of the sponge, but the sponge is not easily compressible due to the many small conch fragments within the flesh. Color alive not recorded, unfortunately, no photograph in situ was taken, and color in alcohol is beige.

Skeleton. The ectosome has a thin cortex 200 µm thick that consists mainly of spirasters and tips of tylostyles protruding up to 140 µm beyond the surface. The narrow area of the choanosome is formed by a palisade of tylostyles tufts with the tips directed upwards, below which, spirasters are abundant everywhere (Fig. 7 B). Small and round channels were seen below the cortex.

Spicules. Macroscleres are straight and slightly curved tylostyles with fusiform tips 260–624 × 7.8–14 µm, mainly with a round head but oval-shaped are also present 12–15 µm in diameter (Fig. 7 C), few ones with annular swelling bellow the neck. Microscleres are spirasters approaching amphiasters in two size categories (Fig.7 D): size I is 20.8–57 µm long (Fig 7 F), it bends once to twice but it is difficult to discern, its rays are conical up to 20 µm long with broad bases from about 5.2 µm; size II is 5.4–26 µm long (Fig. 7 E), it shows a slender shaft in one to three bends sometimes straight, with smaller conical rays (sizes including spines).

Distribution and ecology. Bermuda Island, intertidal to 0.5 m (Verrill 1907), Carrie Bow Cay, Belize (Rützler et al. 2014), now in Yucatan, México coral reefs from the present work. Hence, first record of the species for the Gulf of Mexico.

Remarks. There is some controversy around Spirastrella mollis due to a brief original description, lack of spicular measurements and loss of the type-specimen (Boury-Esnault et al. 1999). The spirasters of S. mollis, and also in S. coccinea in the plates of Rützler et al. (2014), are quite different from the present specimen, suggesting existence of three different species, S. coccinea, S. mollis, and S. hartmani. The latter, corresponds to the furcate and plurifid spirasters (Boury-Esnault et al. 1999), not in synonymy with S. mollis.

Four species of Spirastrella have been recorded in the Gulf of Mexico and adjacent waters, so far. These are Spirastrella coccinea (Duchassaing & Michelotti 1864), S. coccinopsis de Laubenfels, 1953, S. hartmani Boury- Esnault et al. 1999, and S. mollis. The task to tell them apart to correctly identify the species is intricate due to the shared and overlapping traits. For example, the spicule geometry and skeletal arrangement are very similar among all four species. They all have similar sizes, and very little data available other than the original descriptions. In an attempt to delimit differences within some Spirastrella species, a comparison was made from the present material and three spirastrellas sheltered in the CNPGG, which are different indeed (see Table 1).

Catalog Color Surface type Consistency Growth shape Tylostyle Spirasters number