Spirastrellidae Ridley & Dendy, 1886

Łukowiak, Magdalena, 2015, Late Eocene siliceous sponge fauna of southern Australia: reconstruction based on loose spicules record, Zootaxa 3917 (1), pp. 1-65 : 26

Family Spirastrellidae Ridley & Dendy, 1886

Astrose microscleres called anthasters with bifurcate expansions of the ray tips ( Figs. 10 I, J, P, R) occur in the studied sediments. There is some variability of these spicules in the studied material—they vary from the ones with short, thick, moderately bifurcate tips ( Fig. 10 J), to ones with well developed, long and slender rays with strongly bifurcating ray-tips ( Fig. 10 P). Spicules of similar morphology occur in various taxa, e.g., in the astrophorid family Ancorinidae ( Rhabdastrella Thiele, 1903 ) and the chondrosid family Chondrillidae ( Chondrilla grandistellata Thiele, 1900 ), but the studied spicules are most similar in morphology to those of spirastrellid Diplastrella megastellata Hechtel, 1965 (compare Hechtel 1965, pl. 58, fig. 12B with Figs. 10 I, P, R), being, however bigger than those in this modern species. Even though the spicules described by Hechtel are smaller, the expansions of their ray-tips closely resemble those of the studied spicules.

Today, Diplastrella megastellata is described only from the Caribbean and has never been recorded from the Australia so far, but there is Diplastrella sp. found in southern part of Australia (for more details see McEnnulty et al. 2011). Because strong resemblance of the spicules described here to those of Recent Diplastrella megastellata , they may belong to this species, or to other extinct (or unknown) species. The rest of anthasters found in the studied assemblage (see Fig. 10 J), despite displaying features that may also suggest Chondrilla or Stelletta affinity (see Hinde & Holmes 1892) may, in my opinion, be variants of Diplastrella anthasters.

The rest of the spicule morphological types (tylostyles and oxyasters) that are similar to those which appear in Recent D. megastellata are also found in the studied material ( Figs. 10 D, E compare with Hechtel 1965, fig. 12A). It supports earlier conclusion based on anthasters.

Similar, but not identical spicules have already been described by Hinde (1910, pl. 2, fig. 16) from the Eocene deposits in the same area (Norseman, W Australia).

Figures

FIGURE 10. Spicules of sponges of the order Hadromerida; A – C—Mucronate tylostyles of Cliona cf. mucronata, family Clionaidae; D – F—Tylostyles of the order Hadromerida; G, H—Tylostyles of Terpios sp., family Suberitidae; I, J, P, R—Anthasters of Diplastrella cf. megastellata, family Spirastrellidae; K – M—Spherostyles of Sphaerotylus sp. 1, family Polymastiidae; L – O—Spherostyles of Sphaerotylus sp. 2, family Polymastiidae; Q—Microsclere spiraster of family Spirastrellidae or Clionaidae; S – Y—Verticillate strongyles of Dotona pulchella Carter, 1880, family Clionaidae.