HETEROPIIDAE 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 : 233-236

Family HETEROPIIDAE Dendy, 1892

TYPE GENUS. — Heteropia Carter, 1886 by original designation.

DIAGNOSIS. — Leucosoleniida with a syconoid or leuconoid organization. The choanoskeleton is composed of a proximal layer of subatrial triactines and a distinct distal layer of pseudosagittal triactines and/or pseudosagittal tetractines, often separated by an intermediate layer that is supported by several rows of triactines and/or tetractines. The atrial skeleton is well-developed.

DESCRIPTION

The family Heteropiidae is characterized by the presence of a layer of subcortical pseudosagittal spicules. At a first glance, these spicules may seem to be sagittal triactines with the paired actines adjacent to the cortex, and the unpaired actine turned inwards in a position symmetrical to that of the subatrial spicules. However, as indicated by Poléjaeff (1883) and Dendy & Row (1913), both the length and the form of the paired actines in these spicules are unequal. The longer paired actine is perpendicular to the cortex, while the shorter one as well as the unpaired actine are adjacent to the cortex ( Fig. 29 ). This position is clearly observed for the distal triactines of the radial tubes in sycon-like sponges that we now place in the genus Syconessa . This indicates that the formation of pseudosagittal spicules precedes the formation of a cortex and appears early in the evolution of the Heteropiidae , immediately after

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the acquisition of the sycettid type of organization. The evolutionary pathway of the Heteropiidae , well-represented by the genus Syconessa , diverges from sponges that are very similar to Sycon . In the type species Syconessa syconiformis (Borojevic, 1967a) , the choanoskeleton is inarticulate, or has only a few spicules in the proximal part of the choanoskeleton. The corticalization of such a sponge can lead both to the genus Sycettusa , which is characterized by a thin body wall with the choanosome devoid of its own skeleton, and to Grantessa , in which the choanoskeleton is articulate. It should be noted that several species of Grantessa have a very thin and/or poorly defined cortex, and the distal cones of the radial tubes are still decorated by tufts of diactines (e.g. Grantessa ramosa Haeckel, 1872 ), clearly showing their relationships to sponges with a sycon-like organization.

Corticalization has apparently arisen several times in the Leucosoleniida . In the family Heteropiidae , corticalization associated with the maintenance of the choanoskeleton of the tubes that is reduced to subatrial and subcortical spicules has given rise to the genus Sycettusa , whilst the corticalization associated with the thickening of the choanosome has produced Grantessa . The subsequent transition to the leuconoid type of organization is seen in the genus Vosmaeropsis . Similar progression is observed among the Leucosoleniida that lack pseudosagittal spicules, in which the first route has given rise to the Jenkinidae and the Amphoriscidae , and the second the Grantiidae .

The family Heteropiidae contains a series of genera that are analogous to those of the family Grantiidae , the sole difference being the presence of subcortical pseudosagittal spicules. In any calcaronean sponge with a strong cortex, some subcortical spicules may be in the position and have the shape of pseudosagittal spicules, due to the restriction of their growth by the rigidity of the cortical skeleton. They should not be interpreted as an indication that the sponge belongs to the family Heteropiidae (see discussion on Amphiute paulini Hanitsch, 1894 in Borojevic 1965: 665- 670). Consequently, the regular presence of a dis- DESCRIPTION

We propose to divide the genus Grantessa (as defined by Dendy & Row 1913) into two groups: one with an inarticulate choanoskeleton, to be called Sycettusa , and the other with an articulate choanoskeleton, to be called Grantessa . As stated earlier, we consider that the former genus evolved by the corticalization of sponges with an inarticulate skeleton similar to Syconessa syconiformis (Borojevic, 1967) , thereby maintaining this characteristic of the choanoskeleton (Fig. 31). The sponges assembled in the genus Sycettusa can be divided into two groups, one common in the Arctic region and the other in the Indo-Pacific. The relationship between these two groups remains to be established. The Arctic group includes Sycettusa (Sycaltis) glacialis (Haeckel, 1872) , S. (Ebnerella) kuekenthali (Breitfuss, 1896) , S. (Ebnerella) lanceolata (Breitfuss, 1898) , S. (Amphoriscus) murmanensis (Breitfuss, 1898) , S.(Amphoriscus) thompsoni (Lambe, 1900) and S. (Ebnerella) nitida (Arnesen, 1901) . The Indo-Pacific group includes S. stauridia Haeckel, 1872 , S. (Sycortis) sycilloides (Schuffner, 1877) , S. (Amphoriscus) poculum (Poléjaeff, 1883) , S. (Grantessa) simplex (Jenkin, 1908b) , S.(Grantessa) glabra (Row, 1909) and S.(Grantessa) hastifera (Row, 1909) .

Haeckel (1872) proposed the subgenus Sycettusa for the single species S. stauridia from the Red Sea, which is a typical syconoid Heteropiidae with an inarticulate choanoskeleton, and we retain this genus and species name in the same combination.

Figures

FIG. 29. — Diagram of one parasagittal (p) and two sagittal (s) spicules in Heteropiidae. The arrow indicates the unpaired angle, and u indicates the unpaired actine. The double line represents the cortex (cx). Note that the two paired actines of the parasagittal spicules are of quite different sizes, and they are always in a subcortical position with the longer paired actine directed inwards.