(Figures 4 c, 37)
Material. Holotype: USNM 1229076, Carrie Bow Cay forereef, inner reef slope (near sand rough), between sheets of coralline algae under coral overhang, 20 m; K. Ruetzler col. 14 May 1975.
Paratype: USNM 1229077, Same location as holotype.
Diagnosis. Myrmekioderma with smooth, even or slightly bumpy surface, with long, smooth oxeas and styles, short, microspined oxeas, and one size class of raphids.
External morphology. Crusts on dead coral and coralline algae, penetrating crevices and forming multiple layers. Size, as sampled, up to 8 x 6 cm, 3–9 mm thick, depending on spaces between substratum pieces. Firm consistency, difficult to compress. Surface smooth or slightly bumpy, rough to the touch, with a few dispersed oscula (1–2 mm diameter). Color is orange at the surface, yellowish orange to ochre in the interior.
Skeleton structure. The ectosome shows a layer of embedded sediment and phalanx of perpendicular small acanthoxeas. The choanosome contains large oxeas and styles, acanthoxeas, and raphids in criss-cross fashion, without orientation except for a few short tracts.
Spicules. Long, thin, smooth oxeas and styles, with frequent modifications to strongyloxeas of large size range: 304– 1050 x 5–16 (897 x 13) Μm; microspined oxeas, with common styloid, strongylote, or (rare) tylostyloid modifications: 289–440 x 7–16 (365 x 12) Μm; very thin (0.1–0.5 µm), smooth raphids, about 7–130 µm long, in preparations often wrapped around megascleres making length determinations difficult.
Ecology. In the shade of a forereef coral overhang, encrusting and invading crevices of rubble, 20 m.
Distribution. Belize.
Etymology. The species name reflects the growth pattern in sheets, sandwiched between layers of coralline algae and coral rubble: lamina (Latin) = plate, sheet.
Comments. Two other species of Myrmekioderma occur in similar reef habitats, M. gyroderma (Alcolado) (Diaz et al., 1993: 303, figs. 39, 45; as M. rea) and M. rea (de Laubenfels) (see below). Our new species differs from both by lacking meandering surface grooves and thick, robust oxeas as megascleres. The microspined acanthoxeas are similar to those of M. rea (see below), whereas in M. gyroderma they are replaced by smooth, short and stout oxeas.