Smenospongia cf. echina (de Laubenfels, 1934)

(Figures 2 b, 42)

Synonymy and references. Polyfibrospongia echina de Laubenfels, 1934: 25; van Soest (1978): 70, fig. 23.

Material. USNM 1229146, Curlew Bank forereef cave, 20 m. C. Piantoni col. 2 Jul 2007.

Comparative material examined: USNM 22315 Polyfibrospongia echina (holotype) from Puerto Rico, 59– 72 m.

External morphology. An elongate cushion of 50 x 30 mm, 15 mm thick, with two oscula with elevated rims on top, 4 and 6mm in diameter. Surface covered with rounded conules, 1–1.5 mm tall, 2–3 mm apart. Pore (ostial) fields appear in the depressions between the conules. The consistency is spongy, elastic compressible, even in preservation alcohol. Color was brownish yellow in life and changed to a medium gray in alcohol, which became stained light purple during fixation.

Skeleton. Primary fibers are fasciculated, three or more ending inside or near each conule. They measure 40–60 (49) µm in diameter and are cored by few sediment particles, mainly sponge spicules. A fine striation is barely visible under transmitted light. Stretches of pith show only in a preparation in epoxy resin, not in regular mounting medium (Permount, Fisher Scientific, USA). Secondary fibers are richly branched, resembling those of a bath sponge (Spongia spp.) but have a more golden color. They measure 8–35 (23) µm, are clear except for a faint striation and free of sediment particles; meshes are about 70 x 70 µm to 300 x 550 µm in diameter. As in the primaries, stretches of pith become visible in epoxy-resin-embedded material only. These stretches can be just 50 µm or up to 600 µm long and occupy 13–33% of the fiber diameter (up to 40 % at some nodes).

Ecology. Inside a forereef cave, 20 m.

Distribution. Belize.

Comments. In his original description, de Laubenfels (1934) pointed out skeletal similarities of his Polyfibrospongia echina with spongiid commercial sponges, particularly the elaborate meshwork of the secondary fibers and sediment-cored primaries (like in Spongia spp., except that they were fasciculated, not evenly distributed). He described detritus particles coring the primary fibers but did not mention occurrence of pith. Van Soest (1978), however, restudied the holotype and illustrated (fig. 23) pithed primary fibers. We reexamined the holotype as well and confirmed the skeleton structure, including cored primaries, and presence of pith. The main difference between the specimens is that the type shows conical processes whereas our material is cushion-shaped. Because the type specimen is badly macerated we cannot evaluate the significance of these differences. De Laubenfels’ (1936:15) description of a specimen of S. echina from the Dry Tortugas is problematic because the specimen he deposited (USNM 22482) turns out to be Hyrtios violaceus (Duchassaing & Michelotti, 1864), a very different sponge and obviously a mistake.

On the generic level, our material agrees with the definition of Smenospongia (Wiedenmayer, 1977; Cook & Bergquist, 2002) by having aerophobic properties (turning from yellow to purplish gray or black upon exposure to air), fasciculated primary fibers cored by small sediment particles, and a well-developed secondary fiber reticulum. Conflicting with the diagnosis is presence of some pith in parts of both fiber types. Since appearance of pith seems to be connected to processing techniques (epoxy resin versus synthetic histological mounting media) we maintain placement in Smenospongia until further investigations may suggest otherwise.