Isodictya toxophila Burton 1932

Isodictya toxophila Burton, 1932

(Fig. 16, Tab. 12)

Isodictya toxophila Burton, 1932: 286, pl. 52, figs. 2, 3, text-fig. 18. Koltun 1964: 43, pl. 8, figs. 19–22. Barthel et al. 1990: 122, 1997: 48. Gutt & Koltun 1995: 231. Campos et al. 2002b: 761–764, figs. 99–104, tab. 13.

Material. 1 large fragmentary specimen from station 048-1 (SMF 11816), 602.1 m, 70° 23.94' S, 8° 19.14' W, 12.01.2008. Material examined for comparison: BMNH 1928.2.15.158, Discovery expedition, Stn. 39 R.N.CLI.ii, wet specimen.

Description. Specimen of station 048-1 (Fig. 16 A–C) fragmentary, consisting of a thin, blade-like structure, probably growing like a relatively round plate on or above the ground. Thickness about 1 cm, with ends bluntly rounded, never sharp, no distinct tapering apparent. Surface on both sides of plate (Fig. 16 B–C) bearing rows of pores in quite regular arrangement. Consistency firm, only slightly brittle, not flexible. Color in ethanol light beige.

Skeleton: Skeleton formed of primary plumose tracts of oxeas (Fig. 16 D), running parallel to sponge surface towards rounded, distal parts of body. Rectangular to these are interconnecting, much less-organized secondary tracts of oxeas. Toxas free in choanosome. Chelae mainly arranged in lines at surfaces of epidermis and of pores, with alae oriented outwards (Fig. 16 E).

Spiculation (Tab. 12): Main spicules almost straight oxeas (Fig. 16 F–G) with sharp pointed ends, 640 µm long and 33 µm wide. Microscleres toxas and palmate isochelae. Toxas (Fig. 16 H–I) with relatively vague kink in the middle, 240 µm long and 4 µm wide. Palmate isochelae (Fig. 16 J–L) very slender; with strongly reduced outer alae, middle alae distinctly formed without extensions of inner falxes. Chelae 75 µm long.

Remarks. Isodictya toxophila shows a wide variability in outer shape. This is best shown in the study by Burton (1932) who illustrated one fragmentary specimen of blade-shape, which has a surface with numerous small oscules/pores and an underside of a quite irregular structure, thus somewhat resembling our new specimen. He also described specimens of irregular massive growth with some large oscules at the top. Koltun (1964) also reported specimens with “Body globular (with large oscules)”. Several (fragmentary) specimens are figured in Ríos (2006). These show intermediate growth, but with a tendency to form flattened structures without distinct oscules. Within the genus Isodictya, there seem to exist two distinct morphotypes with regard to the outer morphology: one of a fluffy, fibrous growth like that characteristic of I. doryphora, and another one of a massive, often flattened growth and firm consistency as that of I. toxophila. On the basis of this observation, it might be possible to subdivide Isodictya into two subgenera. The occurrence of chelae in the surface tissue of epidermis and pores might be considered an indication of a putative carnivory in this sponge, analogous to the epidermal chelae in cladorhizids.