Grantiopsis Dendy, 1892

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 : 242

Genus Grantiopsis Dendy, 1892

TYPE SPECIES. — Grantiopsis cylindrica Dendy, 1892 by monotypy.

DIAGNOSIS. — Lelapiidae with a syconoid or sylleibid organization. The cortex is composed of tangential triactines, and occasionally has an external layer of small diactines perpendicular to the surface. The proximal layer of the choanoskeleton is composed of subatrial triactines and/or tetractines, whose unpaired actines are associated with modified triactines that have very reduced paired actines. These modified triactines are either isolated or form short bundles joined by an organic material, and support the external part of the choanosome.

DESCRIPTION

Grantiopsis has a particular skeleton that is characterized by triactines with reduced paired actines in the wall of the tubes. As is typical for triactines of the tubes, they are associated proximally with the unpaired actines of subatrial triactines. In Grantiopsis species that have a thin wall, such as young G. fruticosa Dendy & Frederick, 1924 , the triactines occasionally occur singly; but in sponges with a thicker wall, such as G. cylindrica , they form distinct bundles ( Fig. 37 ). Their reduced paired actines give them a form similar to diactines. They are parallel and tightly bound by an organic material that is more resistant to dissolution with sodium hypochlorite (which is used usually to dissociate calcareous spicules) than other parts of the skeleton. The nature of this material is unknown. The organization of their choanoskeleton is quite similar to a typical Grantia in which the articulate skeleton of radial tubes is substituted by spicular tracts formed of nail-shaped triactines. These tracts are much more developed and conspicuous in Kebira , clearly pointing to the origin of the Lelapiidae from sponges like the Grantiidae , in which Grantiopsis had previously been classified.

Figures

FIG. 37. — Diagram of a transverse section through the wall of Grantiopsis. Abbreviations: a, atrium; as, atrial skeleton; ss, subatrial spicules;ct, choanosomal spicule tracts composed of nail-like triactines; cx, cortex.