Cornulum johnstoni

Rützler, Klaus, Piantoni, Carla, Van, Rob W. M. & Díaz, Cristina, 2014, Diversity of sponges (Porifera) from cryptic habitats on the Belize barrier reef near Carrie Bow Cay, Zootaxa 3805 (1), pp. 1-129 : 56-57

Cornulum johnstoni (de Laubenfels, 1934)

( Figure 31 )

Synonymy and References. Coelosphaerella johnstoni de Laubenfels, 1934: 21.

Material. USNM 1229001, 1229002 Carrie Bow Cay, South reef, lower surface of Acropora coral plates in exposed zone behind reef crest, 1 m. K. Ruetzler col. 6 Mar 2006. USNM 1229003, Curlew Bank, forereef slope, 21 m; C. Piantoni and M. Parrish col. 21 Aug 2012. USNM 1229004, Curlew Bank, forereef slope, 20 m; C. Piantoni and M. Parrish col. 23 Aug 2012.

Comparative material examined: USNM 22364 Coelosphaerella johnstoni de Laubenfels, 1934 (holotype), Puerto Rico.

External morphology. Minute, whitish fistules protruding from the dead coral substratum. Their dimensions are 1.5–2.5 mm diameter, 3–5 mm height; they are spaced a few millimeters apart from each other, over a surface area of about 10 to 50 cm 2, or more. About half of the fistules are closed at the distal end and seem to serve as incurrent structures, the others (tubules) are open, end in an osculum. The choanosomal parts of the sponge are mostly inside the substratum, penetrating or excavating small cavities that are filled with tissue. The initial impression of this sponge is that of a miniature Siphonodictyon species. Most of the epilithic sponge structures are white, but some from the deeper cave appeared yellowish and purplish gray in life.

Skeleton structure. The megascleres (strongyles/tylotes) occur in netlike criss-cross fashion in the walls of the ectosomal fistules but are not cemented at their ends, as in an isodictyal reticulation. In the choanosome they occur in lesser numbers and without orientation. Microscleres (chelas, toxas) occur in between the strongyles, particularly in the ectosome.

Spicules. Strongyles, with microspined ends that are mostly slightly thickened, approaching the form of tylotes: 202–300 x 5–12 (255 x 7) Μm; palmate isochelas, most with one end twisted 90r in relation to the other: 13–15 (14) Μm; toxas, in large size range: 41–171 x <1–6 (127 x 3) Μm.

Ecology. Very common on shaded substrata and in dark caves, but not easily seen with the unaided eye. Here found to a depth of 21 m, originally described from deep-sea bottoms at 360– 720 m.

Distribution. Caribbean Sea.

Comments. We verified the original description by examining the holotype (USNM 22364). Although the sizes of the strongyles in the type are somewhat larger (345 x 9 Μm, on average), all other morphological characteristic agree fully with our material.

Figures

FIGURE 31. Cornulum johnstoni, spicules (SEM): a, strongyles (tylotes) with microspinded ends (tyles), three ends magnified; b, palmate isochelas; c, toxas.