Paraheteropia Borojevic, 1965

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 : 236-238

Genus Paraheteropia Borojevic, 1965

TYPE SPECIES. — Amphiute ijimai Hôzawa, 1916 by monotypy.

DIAGNOSIS. — Heteropiidae with a syconoid organization, an articulate choanoskeleton, and with both cortical and atrial skeletons containing longitudinal diactines.

cx st

ed by the apical actines of giant cortical tetractines. In species of Leucilla that have a leuconoid organization and a thick wall, the choanoskeleton is disorganized, unlike the simpler syconoid genus Amphoriscus ( Fig. 33 ). We understand this to indicate that the simple inarticulate choanoskeleton is a primitive condition. This is an argument against the derivation of the Amphoriscidae from the typical Grantiidae , by reduction of the choanoskeleton and the secondary presence of the apical actines of cortical triactines. The regular presence of subatrial triactines in the Amphoriscidae clearly indicates that they derive from a Sycetta type of organization through the precocious development of a cortical skeleton reinforced by giant tetractines. Since the articulate skeleton of the tubes, typical of adult specimens of Sycon and Grantia , is not found in the Amphoriscidae , the origin of this family lies closer to the Jenkinidae than to Grantiidae . However, it is impossible to decide whether these two families have a common origin or have evolved independently.

In most Leucosoleniida , the thickening of the choanosome is associated with the growth of new spicules in the central part of the choanoskeleton, and with the increasing distance between the cortical skeleton on one side, and the atrial and subatrial skeletons on the other (e.g. Grantessa ramosa , Fig. 32). In the Amphoriscidae , the sponge wall can thicken through the addition of a new layer between the atrial and subatrial skeletons, and the subatrial and cortical skeletons strictly maintain their close primary relationship ( Fig. 33 ). The invasion of the choanoskeleton by spicules derived from the inner atrial skeleton in Paraleucilla is analogous to the invasion of the choanoskeleton from the outer cortical skeleton in the Jenkinidae (e.g. Anamixilla and Uteopsis ). In both families, the primary inarticulate choanoskeleton is preserved, despite the progressive thickening of the sponge wall and the necessity to introduce new skeletal structures to support it.

Figures

FIG. 33. — Diagram of the Amphoriscidae type of inarticulate choanoskeleton (Amphoriscus or Leucilla). Abbreviations: a, atrium; as, atrial spicules; ss, subatrial spicules; st, subcortical tetractines; cx, cortex.