STAURORRHAPHIDAE Jenkin, 1908

Borojevic, Radovan, Boury-Esnault, Nicole & Vacelet, Jean, 2000, A revision of the supraspecific classification of the subclass Calcaronea (Porifera, class Calcarea), Zoosystema 22 (2), pp. 203-263 : 240

Family STAURORRHAPHIDAE Jenkin, 1908

TYPE GENUS. — Achramorpha Jenkins, 1908 by original designation.

DIAGNOSIS. — Leucosoleniida with a continuous cortex covering all the choanosome. Cortical tetractines are absent. The organization of the aquiferous system is syconoid, sylleibid or leuconoid. A tangential atrial skeleton is present only in the oscular region. In the atrial cavity, only the paired actines of subatrial chiactines support the atrial surface, while the apical actine is bent and points into the atrial cavity, making its surface hispid.

DESCRIPTION

The Staurorrhaphidae have been proposed by Jenkin (1908a) to include sponges with chiactines (“cruciform” spicules), which are tetractines whose apical actine is bent so that it follows the same line as the unpaired actine, but in the opposite direction ( Fig. 36 ). These spicules are found in the atrial wall: the paired actines are adjacent to the atrial surface, the apical actine is free in the atrial cavity giving the atrial surface a hispid appearance, and the unpaired actine lies in the wall of the radial tubes. Since the same sponges have no tangential spicules in the atrial skeleton, Jenkin (1908a) proposed that chiactines originate from the atrial tetractines. However, as pointed out by Dendy & Row (1913), chiactines have a typical subatrial origin and position. In several other genera of Leucosoleniida , subatrial tetractines are found with the apical actine curved either in the direction of the unpaired actine, thus pointing towards the distal end of the radial tube, or in the opposite direction, pointing into the atrium, such as the case of chiactines. Solely the presence of chiactines would not justify the creation of the family Staurorrhaphidae . However, in sponges included in this family the atrial skeleton is reduced to the region immediately adjacent to the osculum, and in the sponge body there are no atrial tangential tri- or tetractines. As indicated by Dendy & Row (1913), this is an unusual modification of the skeletal organization among the Leucosoleniida and justifies the separation of the two genera, Achramorpha and Megapogon , from other Leucosoleniida . Since in most sponges the atrial cavity is echinated or hispid, probably as a protection from invading organisms, in the Staurorrhaphidae the subatrial tetractines have apparently taken over this function, forming a long apical actine bent towards the atrial cavity. The family Staurorrhaphidae is thus characterized simultaneously by the absence of the atrial tangential skeleton and the presence of subatrial tetractines that are chiactines. All the known species in the Staurorrhaphidae have rather a thin wall with either an inarticulate skeleton, or only a few scattered spicules in the choanoskeleton. Both genera of Staurorrhaphidae are known only from Antarctica.

Figures

FIG. 36. — Diagram of the subatrial skeleton of the Staurorrhaphidae. Note the absence of the atrial skeleton, and the presence of the apical actines of the subatrial tetractines that point inwards into the atrial cavity. Abbreviations: a, atrium; ss, subatrial spicules.