Sphaerasclera, McFadden, Catherine S. & Ofwegen, Leen P. van, 2013

McFadden, Catherine S. & Ofwegen, Leen P. van, 2013, Molecular phylogenetic evidence supports a new family of octocorals and a new genus of Alcyoniidae (Octocorallia, Alcyonacea), ZooKeys 346, pp. 59-83 : 64-65

Sphaerasclera gen. n. Figs 2-3

Type species.

Eleutherobia flammicerebra Williams, 2003, by original designation.

Diagnosis.

Soft corals with a capitate growth form, with a distinct, spherical polyparium raised on a sterile stalk. Polyps monomorphic. Anthocodial sclerites absent. Sclerites of colony surface and interior are large, tuberculate spheroids and smaller radiates. Sclerites permanently colored. Azooxanthellate.

Etymology.

From the Latin/Greek sphaera- meaning a sphere or ball and Greek sclero-, hard, denoting the large, spheroidal sclerites that characterize this genus. Gender: fem.

Remarks.

Williams’s (2003) assignment of Eleutherobia flammicerebra to Eleutherobia necessitated emending the diagnosis of that genus to include capitate growth forms. Eleutherobia flammicerebra does share other character states-such as monomorphic polyps that lack sclerites and tuberculate spheroids and radiates in the surface of the polyparium and stalk (Figs 2-3)-with some species of Eleutherobia . Molecular phylogenetic analyses suggest that Eleutherobia flammicerebra is, however, not closely related to morphologically similar members of Eleutherobia such as Eleutherobia rotifera (Thomson, 1910) but instead falls into the Anthomastus - Corallium clade of octocorals (Fig. 1). Based on its distinctive colony growth form and unique phylogenetic position, we hereby designate a new genus, Sphaerasclera , and new combination, Sphaerasclera flammicerebra (Williams, 2003) for this species.

Unlike all other members of the Anthomastus - Corallium clade, Sphaerasclera gen. n. appears to have monomorphic rather than dimorphic polyps. As discussed by Williams (2000b), however, siphonozooids may be difficult to detect in contracted, preserved material. The large, densely packed, spherical sclerites in the coenenchyme of Sphaerasclera flammicerebra comb. n. obscure the finer details of the colony surface, and also make this species very difficult to section for histological study of the polyps. For now we concur with Williams (2003) that the species is monomorphic, but entertain the possibility that future observation of living specimens might reveal the presence of siphonozooids.

Although Sphaerasclera gen. n. differs by having monomorphic polyps, it does share other morphological characters with Paraminabea and Anthomastus , the two genera with which it is most closely allied phylogenetically (Fig. 1). Anthomastus likewise includes species with capitate growth forms, but in that genus the autozooids have sclerites, and the sclerites in the surface and interior of the colony include rods and needles in addition to radiates ( Bayer 1993). Like Sphaerasclera gen. n., Paraminabea lacks sclerites in the polyps and its coenenchymal sclerites are predominantly radiates and spheroids ( Williams and Alderslade 1999). The colony growth form of Paraminabea , however, is digitiform, hemispherical or lobate rather than capitate. Moreover, Paraminabea has a unique molecular synapomorphy, a mitochondrial gene rearrangement that distinguishes it from all other genera of octocorals ( Brockman and McFadden 2012). Screening of mitochondrial gene junctions suggests that Sphaerasclera flammicerebra comb. n. and Anthomastus both retain the ancestral octocoral mt gene order, and do not share the derived state found in Paraminabea ( Brockman and McFadden 2012).

Paraminabea and Anthomastus are both classified in family Alcyoniidae , and for convenience we have also assigned Sphaerasclera gen. n. to that family. All other genera of Alcyoniidae , however, belong to the Holaxonia - Alcyoniina clade of Octocorallia , far removed phylogenetically from the Anthomastus - Corallium clade (Fig. 1). In addition to Paraminabea , Anthomastus and Sphaerasclera gen. n., the Anthomastus - Corallium clade also includes all members of Coralliidae Lamouroux, 1812 and Paragorgiidae Kükenthal, 1916, two families of gorgonians that have historically been assigned to the sub-ordinal group Scleraxonia . Although it is clear from the phylogenetic evidence that the soft coral taxa that fall within this clade should be removed from Alcyoniidae , we defer their reassignment to another family pending an in-depth analysis of the morphological character states shared among the seemingly heterogeneous genera and families that are united within Anthomastus - Corallium .

Our records extend the known geographic distribution of Sphaerasclera flammicerebra comb. n. from Palau ( Williams 2003) to New Caledonia and Mauritius. The colony growth forms and sclerites of specimens from these widespread localities closely match that of the type material from Palau (Figs 2-3).