Pachastrellidae Carter, 1875

Łukowiak, Magdalena, 2015, Late Eocene siliceous sponge fauna of southern Australia: reconstruction based on loose spicules record, Zootaxa 3917 (1), pp. 1-65 : 18-19

Family Pachastrellidae Carter, 1875

Sponges belonging to the family Pachastrellidae are defined as having various tetraxons, i.e. calthrops, shortshafted triaenes, mesotriaenes, mesotriaene-derived desmas, or long-shafted triaenes in combination with streptasters and monaxonic microscleres ( Maldonado 2002). Some spicules in the investigated material clearly correspond to this description. These are, for example, short-shafted mesodicho- ( Fig. 5 A), dicho- ( Fig. 5 B), and mesotriaenes ( Figs. 5 D, F, G), and other similar spicules (e.g., Figs. 5 C, E, H–K) that, in most cases, may be assigned to the family Pachastrellidae . However, only some of these spicules are characteristic enough to assign them to the genus/species level. On the other hand, some of them (e.g., spicules with branched clads; Figs. 5 E, H) also resemble those occurring in other taxa, i.e. geodiid genus Penares Gray, 1867a , discussed earlier.

Very characteristic triaenes with strongly branched clads that clearly resemble those of Recent pachastrellid Brachiaster Wilson, 1925 have been found in my material ( Fig. 5 L). Today, there is only one species of Brachiaster known from the Philippines— B. simplex Wilson, 1925 (van Soest et al. 2013). On the other hand, the only fossil representative of this family— Brachiaster claudlevii Pisera & Bitner 2007 , was recorded from the same Late Eocene deposits of southwestern Australia ( Pisera & Bitner 2007). Unfortunately, neither the spicules of Recent B. simplex , nor those of B. claudlevii are identical with those described here (compare with Pisera & Bitner 2007, figs. 3, 4, 7; Wilson 1925, figs. 51.8, 9). Only the spicule described as B. simplex shown by Maldonado (2002 and Fig. 6 A) resembles closely the described here spicules. It is impossible to decide whether the studied spicules belong to a new species, or if they fall within the variability range of known Brachiasters.

Other, quite similar morphologically spicules are characteristic triaenes that bifurcate in many different planes and parts of the clads. Such spicules characterize present-day astrophorid Triptolemma de Laubenfels, 1955b ( Fig. 5 M). There are two Recent species of Triptolemma recorded from this part of the world: T. strongylata Bertolino, Pica, Bavestrello, Iwasaki & Calcinai, 2011 noted from Japan, and T. cladosum ( Sollas, 1888) known from Indonesia (van Soest & Hooper 2002b; van Soest et al. 2013). The sponges belonging to this genus penetrate the tissue of other sponges ( Maldonado 2002). The studied triaenes resemble closely the spicules of Triptolemma cladosum (for example, compare with Fig. 6 B) and considering the fact that today T. cladosum inhabits adjacent areas (Hooper & van Soest 2002), it is possible that the spicules discussed here belong to the ancestor of this species. On the other hand, some of the spicules described above as pachastrellid may also be assigned to Triptolemma (e.g., Figs. 5 A, E, H) but they also may belong to other pachastrellid genera, e.g., Brachiaster bearing very similar spicules.

Megascleres of Triptolemma were already described from the Eocene of New Zealand by Hinde & Holmes (1892).

Figures

FIGURE 5. Spicules of sponges of the order Astrophorida; A—Mesodichotriaene, family Pachastrellidae; B—Dichotriaene, family Pachastrellidae; C – G—Mesotriaenes of Pachastrella - like sponge, family Pachastrellidae; H – J—Calthrops of Calthropella sp., family Calthropellidae; K—Spicule of the order Astrophorida; L—Triaene of Brachiaster cf. claudlevii, family Pachastrellidae; M—Triaene of Triptolemma cladosum, family Pachastrellidae; N – O—Calthrop and dichotriaene of Dercitus (Stoeba) - like sponge, family Ancorinidae.

FIGURE 6. Short-shafted mesodichotriaenes of recent pachastreallids (order Astrophorida); A— Brachiaster simplex (from Maldonado 2002); B— Triptolemma cladosum (from Maldonado 2002, redrawn from Sollas 1888).