Axinella Schmidt, 1862

Sitjà, Cèlia & Maldonado, Manuel, 2014, New and rare sponges from the deep shelf of the Alboran Island (Alboran Sea, Western Mediterranean), Zootaxa 3760 (2), pp. 141-179 : 152

Genus Axinella Schmidt, 1862

Diagnosis. Ramose, bushy or lamellate habit. Surface generally smooth, with choanosomal spicules projecting slightly. Oscules, when visible, with stellate morphology (i.e., superficial canals leading to opening ‘imprinted’ in superficial skeleton). Ectosome without specialized skeleton. Choanosomal skeleton differentiated in axial and extra-axial regions; axial skeleton compressed or vaguely reticulated. Extra-axial skeleton plumose or plumoreticulate. Megascleres styles, or styles and oxeas, or oxeas; when both present, one type may be rare; modifications of megascleres common in several species. Microscleres, if present, microraphides and raphides, mostly in tightly packed trichodragmata (sensu Alvarez & Hooper 2002).

Remarks. Recent molecular work based on 18S rRNA, 28S rRNA, and CO1 has suggested that the genus Axinella is polyphyletic, containing at least two major clades ( Gazave et al. 2010; Morrow et al. 2012). One of the clades? the proper " Axinella clade"? revolves around the type species, Axinella polypoides Schmidt, 1862 , while the other, which includes species such as Axinella damicornis (Esper, 1794) , Axinella verrucosa (Esper, 1794) , and Axinella corrugata (George & Wilson, 1919) , shows greater affinities to agelasid sponges than to the A. polypoides clade. The name "Cymbaxinella clade" has been proposed to allude these latter molecular-based group, following the phylocode ( Gazave et al. 2010). As no morphological synapomorphies can be found to decide when an " Axinella -like" species should be allocated to the "Cymbaxinella" clade or the " Axinella " clade ( Gazave et al. 2010), whenever the molecular information is not available for a species, a serious practical gap rises between the phylocode proposal and the traditional Linnean classification. Subsequent work based on 28S rRNA and CO1 molecular markers has revealed that the " Axinella -like" members of the "Cymbaxinella" clade are closer to encrusting species, such as Hymerhabdia typica Topsent, 1892 (formerly in Bubaridae ) and Prosuberites spp. (formerly in Suberitidae ), than to Agelas spp. On those arguments, a new family Hymerhabdiidae was erected in the Order Agelasida to assemble together Prosuberites spp. , Hymerhabdia spp. , those " Axinella " species in the "Cymbaxinella" clade, and some species formerly in the genus Stylissa ( Morrow et al. 2012) . But again, no morphological clues have been provided to decide in the absence of molecular information when either a newly described or an old, revisited "Axinella-like" species could belong to this new family. Tentatively, Morrow and coworkers (2012) have suggested that "true Axinella " species, such as A. polypoides , have raphides in trichodragmata, while those in the "Cymbaxinella" clade of Agelasida "apparently lack this spicule type ". Following this tentative argument, we cannot rule out the possibility that at least one of new species herein described as Axinella but lacking raphides (i.e., Axinella alborana nov. sp.) could be reallocated into another genus in the future if newly collected specimens can ever be analyzed by molecular methods and the emerging molecular clades are finally given taxonomic status. Likewise, this could also be the case of the rare Axinella vellerea Topsent, 1904 , which is herein morphologically revisited in detail.