Polymastiidae Gray 1867

Family Polymastiidae Gray, 1867a

Some peculiar, club-shaped spicules have been found in the studied material that may be assigned to the family Polymastiidae. Some of them have well developed pointed ends and strongly sculptured, club-shaped heads (Figs. 10 K–M). The others have small, weakly defined pointed ends and smooth, slightly club-shaped heads (Figs. 10 N, O). These club-shaped spicules strongly resemble those of Recent polymastiid Sphaerotylus Topsent, 1898. The variability of the studied spicules may be intraspecific, or they may belong to at least two different species. Among seven currently known species of Sphaerotylus, the spicules with sculptured heads (Figs. 10 K–M) occur in Sphaerotylus vanhoeffeni Hentschel, 1914 (described as S. capitatus; compare with Hentschel 1914, fig. 5.5/ Fig. 12 C). This sponge is known from the Antarctic Ocean (Hentschel 1914) and it is also recorded from the Ross Sea, as well as from the coasts of Norway and Canada (as synonym S. capitatus; van Soest et al. 2013). Another species having similar spicules is Sphaerotylus exospinosus Lévi, 1993 which today inhabits New Caledonia, but its spicules possess more strongly sculptured heads (Lévi 1993, fig. 6C). Whereas the spicules with smooth clubshaped heads (Figs. 10 N, O) belong undoubtedly to Sphaerotylus sp., their assignment to a particular Recent species is difficult. Nevertheless, the presence of at least two different species of Sphaerotylus is here postulated.

Spicules that are similar in morphology had been described from the Jurassic of the Alps by Reif (1967; but without a precise attribution), however they have smooth heads and rounded tips (compare with Reif 1967, pl. 12, fig. 1).

There are very few microscleres found in the studied material (except ovoid selenasters and sterrasters which are intermediate in size, between macro- and microscleres). One of them—very characteristic spiraster microsclere (about 50 µm long)—may belong to hadromerid family Spirastrellidae or Clionaidae (Fig. 10 Q). Unfortunately, the more precise assignment of this spicule is not possible due to paucity of the material. Nevertheless, the presence of other clionaid spicules and the absence of spicules belonging to spirastrellids suggest their clionaid affinity.