Acanthascinae Schulze

Reiswig, Henry M. & Stone, Robert P., 2013, <strong> New glass sponges (Porifera: Hexactinellida) from deep waters of the central Aleutian Islands, Alaska </ strong>, Zootaxa 3628 (1), pp. 1-64 : 43-44

Subfamily Acanthascinae Schulze

Synonymy. Acanthascinae Schulze, 1897: 550, 1904: 177 ; Ijima 1898: 52, 1904: 127, 1927: 355; Tabachnick 2002: 1442.

Subfamily diagnosis. Saccular Rossellinae with discoctasters. (modified from Tabachnick, 2002: 1448 for the genus Acanthascus ).

Remarks. Here we formally reject Tabachnick's (2002: 1442) abolition of the subfamily Acanthascinae and propose its reinstatement. We consider the presence of discoctasters as a unique defining feature, at least as important and distinct as the presence of strobiloplumicomes as a defining feature of Lanuginellinae . Schulze's (1893) description of discoctaster structure made it clear that these microscleres have branching of primary rays and fusion of three adjacent components all within the cubic spicule centrum; the bundles of fused primary rays, emanating from the eight apices of the cubic centrum, undergo secondary branching to produce bundles of nearly parallel secondary rays tipped with small discs. We interpret the origin of this special spicule organization as an important innovation that sets the group of descendents apart from other Rossellidae . Tabachnick's (2002: 2992) argument that "discomultiasters" of some caulophacids are superficially similar to discoctasters is considered insignificant to the argument that discoctasters are a unique spicule type. The large externally visible primary rays of those spicules are not formed by regular branching and fusion of internal primary rays to form a basic cubic symmetry and have no relevance to the uniqueness of proper discoctasters.

Tabachnick's (2002) primary argument for grouping the three classically recognized genera, Acanthascus , Rhabdocalyptus and Staurocalyptus as subgenera under the single genus Acanthascus rests upon his contention that presence and absence of hypodermal pentactins cannot be considered an important character within Rossellidae . This he supports with the fact that hypodermal pentactins may be absent in some species of Hyalascus and Aulosaccus , and uses that argument to join Aulochone and Crateromorpha within a single genus group, and extends that to join the three Acanthascinae genera within a single genus, Acanthascus . We concur that expression of hypodermal pentactins is variable within the Rossellidae , but we contend that use of selected characters to define subtaxa in different phyletic groups is not inherently defensible. It may be practical to make assumption that a given character, e.g., presence/absence of a spicule type, be used to define genera within a family, but this must be recognized as a subjective presumption that should not be employed carte blanche. On this basis, we do not support grouping the three classical genera within a single genus. However, review of this issue and the group as a whole has led us to conclude that the original diagnoses of the genus-level groups are likely flawed. Their distinction should be first based not upon presence and absence of hypodermal pentactins per se, but upon the presence/absence of a lattice of hypodermal pentactins supporting dermalia, which is absent in Acanthascus and present in Rhabdocalyptus and Staurocalyptus . We reinstate the three genera and provide a new diagnosis for each of them.

Genus Acanthascus Schulze

Synonymy. Acanthascus Schulze, 1886: 49 ; part (subgenus Acanthascus ) of Tabachnick 2002: 1447. Acanthosaccus Schulze, 1899: 65 ; Mehl 1992: 92. Part of Bathydorus - B. dawsoni Lambe, 1892: 73 .

not Rhabdocalyptus Schulze, 1886: 5 . Not subgenus Rhabdocalyptus Tabachnick 2002: 1449 . not Staurocalyptus Ijima, 1897: 53 . Not subgenus Staurocalyptus Tabachnick 2002: 1451 .

Type species: Acanthascus cactus Schulze, 1886

Genus diagnosis. Acanthascinae without a continuous hypodermal lattice of large pentactins supporting dermal spicules; occasional individual hypodermal pentactins may occur but they do not form a continuous support for dermalia (new).

Remarks. The group, Acanthascus , is restored to genus status as proposed above under Acanthascinae . Original description of the type species, A. cactus , was based upon one specimen obtained by Doederlein in or around Sagami Bay, Japan in the early 1880s. Specimens from the West Coast of North America with similar spiculation have often been assigned to A. cactus , but, because they lack conspicuous conulation of the body surface, doubt remains that the two populations from coastal NE Pacific and Japan, are genetically linked. A new diagnosis is formed here to accommodate specimens of Acanthascinae that have a few hypodermal pentactins but which do not form a continuous support for dermalia.