Placospongiidae Gray, 1867b

Łukowiak, Magdalena, 2015, Late Eocene siliceous sponge fauna of southern Australia: reconstruction based on loose spicules record, Zootaxa 3917 (1), pp. 1-65 : 26-27

Family Placospongiidae Gray, 1867b

In the studied material, I have found abundant spherical, ellipsoidal, and kidney-shaped spicules with numerous, short rays and/or rounded-polygonal plates between the grooves ( Figs. 13 A–D) called selenasters. In spite, their relatively big sizes (60–90 µm of length) they are interpreted as microscleres. These verrucose or pitted spicules are characteristic for hadromerid family Placospongiidae . The family includes three genera: Onotoa de Laubenfels, 1955a, Placospherastra van Soest, 2009, and Placospongia Gray, 1867b (van Soest et al. 2013) and the selenasters occur only in Placospongia . According to Atlas of Living Australia (accessed on 23rd of August 2013), there are currently two species of this genus that occur in Australian waters: P. melobesioides Gray, 1867b and P. carinata ( Bowerbank, 1858) . Considering the morphology and the size of selenasters, the studied spicules may belong to each of these species and their assignment to a particular species is not possible.

The selenasters are usually accompanied in placospongiids by tylostyles. Some tylostyles had been found in the studied sample (see Figs. 10 D–F) but their attribution is not sure because these types of spicules may also appear in some other hadromerid families (e.g., Clionaidae , Polymastiidae ). Also, the pycnaster microscleres that are characteristic for Placospongia , have been found (see Figs. 24 M, O) but they are bigger than those of presentday placospongiids and, as in the case above, the assignment is unsure because they may also occur in a wide range of sponge taxa. However, the co-occurrence of these two morphotypes with typical placospongiid selenasters makes their attribution to placospongiid very probable.

The selenasters are abundant in the fossil record. These microscleres were already described e.g., form the Jurassic of Europe (Hartman et al. 1980; Hinde 1883 as Rhaxella ), Cretaceous ( Carter 1871, pl. 9; Zittel 1876, pls. 4.52–55; Gruber & Reitner 1991, pl. 1, fig. 1; described as sterrasters), and Miocene of the Central Atlantic ( Bukry 1978, pl. 12, fig. 6), as well as the Upper Jurassic of Poland by Trammer 1982 (fig. 8Y; described as rhax).

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.

FIGURE 13. Spicules of sponges of the order Hadromerida; A – D—Different types of selenasters of Placospongia sp., family Placospongiidae; E—Micraster of the Tethya cf. omanensis, family Tethyidae; F – H—Oxyasters of the Tethyastra oxyaster, family Tethyidae.

FIGURE 24. Spicules of sponges of the order Chondrosida and unassigned spherical / astrose micorscleres; A— Chondrilla nucula, family Chondrillidae; B – L— Chondrilla secunda, family Chondrillidae; M – Q—Different types of other spherical microscleres; R – U—Different types of oxyspherasters.