Aplysina minima Hentschel 1914

Aplysina minima Hentschel, 1914

(Fig. 25, Tab. 21)

Aplysina minima Hentschel, 1914: 137, pl. 4, fig. 18. Burton 1929: 447. Koltun 1964: 111, 1976:197.

Material. 1 specimen from station 048-1 (SMF 11774), 602.1 m, 70° 23.94' S, 8° 19.14' W, 12.01.2008.

Description. Observed specimen (Fig. 25 A) oval-rounded, about 1.5 cm high, overgrowing bryozoan colonies. Surface irregular, bristled by thin conules formed of protruding spongin fibres. In some parts, surface bearing regularly arranged pores. Color in ethanol lightly brown-beige.

Skeleton (Fig. 25 B–D) made up of primary fibres running mostly parallel to each other towards surface, there forming thin, vague surface conules. Primary fibres interconnected by secondary fibres. These additionally forming a kind of slimmed reticulation, where replacing primary fibres. In some cases, primary fibres developing into thinner secondary fibres, a distinct differentiation often hard to recognize. Reticulum of secondary fibres alone less organized than that of primary and secondary fibres. Skeleton altogether rather poorly organized, only partially clearly structured, mainly in outer parts of the body. Primary fibres usually about 40 µm thick. Fibre length between knots highly variable, ranging between 70 and 330 µm, with a mean of 185 µm. Secondary fibres much thinner, about 14 µm wide. Length between knots very variable in secondary fibres, with additional occurrences of much wider lengths, especially where primary fibres are interconnected. Length 150–770 µm, mean 174 µm. See Tab. 21 for detailed information on fibre sizes. Sand grains or other foreign material not found incorporated in spongin fibres, although overgrown bryozoans generally integrated into tissue.

Remarks. Burton (1929) described a very awkward specimen of this species, which has a huge amount of foreign spicules incorporated within the tissue, even forming a dense layer within the ectosome, thus pointing toward a possible specialization implied by this spicule incorporation. However, no other specimens recorded showed this special feature. Still, Koltun (1964) reported a certain amount of foreign material incorporated within the sponge tissue, also Hentschel (1914) recorded a distinct amount of foreign material within the holotype. Our specimen has also incorporated some foreign material, mainly bryozoans, which served as substrate for the sponge. The high concentration of foreign material reported by Burton (1929), remains uncommon for the species. The question occurs, whether his material represents a different species.

Even the assignment of the species to the genus Aplysina seems questionable. According to the currently valid definition of the genus as given by Bergquist and Cook (2002) it is characterized by having only one kind of fibres. Also, the family Aplysinidae is characterized by being organized in a three-dimensional mode, not in a twodimensional plane. The actual species A. minima possesses primary and secondary fibres, as shown above and also by Hentschel (1914) and Koltun (1964). Also a tendency to form two-dimensional reticula seems present, although some parts of the skeleton are organized three-dimensionally. Therefore a necessary revision of the species including its holotype might prove that it does not belong to the genus Aplysina, maybe not even to the order Verongida.