SYCANTHIDAE Lendenfeld, 1891

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 : 228

Family SYCANTHIDAE Lendenfeld, 1891

TYPE GENUS. — Sycantha Lendenfeld, 1891 by original designation.

D IAGNOSIS. — Leucosoleniida with an irregular syconoid organization, and the skeleton primarily supported by triactine spicules, with occasionally diactines in the distal cones.The large central atrium bears numerous short radial tubes lined by choanoderm. Radial tubes are grouped and fused proximally, each group communicating through a wide opening with the atrial cavity. The distal free or coalescent cones are intercalated by large inhalant spaces, which often reach the external surface of the atrial skeleton.When coalescent, distal cones can have tangential triactines, but there is no continuous cortex covering the choanosome and delimiting the inhalant cavities externally.

DESCRIPTION

We propose to include a small group of Leucosoleniida , which are derived from sponges with a sycettid type of organization and have a particular type of growth, in the family Sycanthidae , in a similar scope to the subfamily Sycanthinae proposed by Lendenfeld (1891). In these sponges, a thin wall surrounds a large atrial cavity that has numerous short radial tubes, which are not regularly distributed on the central atrium but form groups which communicate with the central atrialcavity by a large opening. Distally, the grouped radial tubes bear individual cones (e.g. Sycantha ), which may become coalescent and protected by tangential spicules similar to those present in the radial tubes (e.g. Dermatreton ). Despite the presence of these spicules, a continuous cortex is not formed, but rather a loose cortical network perforated by large openings of the inhalant cavities covers the distal regions of the radial tubes. The inhalant spaces left between the groups of radial tubes are quite large, and can reach the external face of the atrial wall, giving the external side of the sponge a honeycombed appearance. Lendenfeld (1891) observed that the radial tubes communicate among them- selves in the proximal region, and that the water flow passes from one tube to another through pores, before reaching the atrial cavity. Dendy (1892b), and subsequently Jenkin (1908a) who had the opportunity to examine the type specimen described by Lendenfeld (1891), refuted this interpretation.Both Jenkin (1908a) and Dendy & Row (1913) considered Sycantha tenella Lendenfeld, 1891 as an aberrant species of Sycon . However, having observed sponges with a similar type of growth in the National Antarctic Expedition collections, Jenkin (1908a) proposed the genera Tenthrenodes , Hypodictyon and Dermatreton for sponges with chambers that are fused in the proximal region, in an almost identical manner to that in the genus Sycantha (Dendy & Row, 1913) . We thus consider that Tenthrenodes and Hypodictyon are synonyms of Sycantha , while we retain the genus Dermatreton for sponges with linked choanocyte chambers that have developed an external tangential meshwork that is supported by tangential spicules, corresponding topologically to a cortex, but differing from it by the fact that it does not delimit an inhalant aquiferous system externally.