Axinella alborana Sitjà & Maldonado 2014, nov. sp.
Creators: name: Sitjà, Cèlia
name: Maldonado, Manuel
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Porifera
Demospongiae
Halichondrida
Axinellidae
Axinella
Axinella alborana

description: Axinella alborana nov. sp.
(Figs. 6A–C, 7; Tables 2, 3, 4)
Etymology. This species is named after the Alboran Island, where it occurs abundantly.
Material examined. Holotype MNCN-Sp155-DR44A from type locality Stn. 44 (Table 1, Fig. 1), a rocky bottom at depths of 135 to 152 m on the Alboran Island shelf. Thirty-three paratypes designated: MNCN- Sp03DR05A to C from Stn. 5; MNCN-Sp13-DR07A & B from Stn. 7; MNCN-Sp14-BV13A & B from Stn. 13; MNCN-Sp34-BV14A to F from Stn. 14; MNCN-Sp19-DR29A to D from Stn. 29 m; MNCN-Sp146-BV33 A to N from Stn. 33; MNCN-Sp191-BV41 from Stn. 41; and MNCN-Sp155-DR44B from Stn. 44 (Table 1, Fig. 1).
Comparative material: Syntype material of Axinella flustra (Topsent, 1892) = Tragosia flustra Topsent, 1892, since no holotype was designated by Topsent (1892) for this species (Table 3). Syntypes were two specimens (MOM-040044) from Bay of Biscay (Stn. 58; 43º40’N 8º55’W, 134 m deep, 7 August 1886) and two specimens (MOM-040272) from Azores (Stn. 247; 38º23.500’N 30º20.333’W, 318 m deep, 30 August 1888).
Macroscopic description. Erect, stalked, flattened sponge, typically attached to small fragments of rocks or shell fragments (Fig. 6A–C; Table 4). The stalk is either cylindrical or compressed, no longer than one quarter of the total sponge length, and hardly recognizable in some specimens. The flattened part of the body is flexible and relatively rectangular, except for the apical margin of the lamina that may be irregularly lobate. Some specimens show an incipient, terminal ramification; none is markedly divided nor further branched. The sponges measure 10– 28 mm in height, with a lamina up to 19 mm in wideness and 1–2 mm in thickness. The surface is irregularly hispid, with no aquiferous opening discernible. The color ranges from creamy to reddish orange in life, clearing after preservation in ethanol.
Skeleton. Megascleres are styles and oxeas (Table 4). Styles are slightly curved at a third of their length (Fig. 7A–B), with a regular round end that occasionally forms one or two slight subtyles and/or annular swellings (Fig. 7C). The pointed end is usually sharp, but rarely blunt ends occur. Styles measure 630– 2375 x 5–20 µm, although two specimens showed a low proportion (<1%) of abnormally shorter or longer styles, measuring respectively down to 580 µm and up to 3000 µm in length (Table 1). Oxeas are slightly or markedly fusiform, curved once or twice, either symmetrically or asymmetrically (Fig. 7A, D). Points are usually acerate; anisoxeas are fairly common and variations like mucronate and blunt ends are frequent, depending on the specimen (Fig. 7D). Occasionally they are centrotylote, with annular or subspherical swellings (Fig. 7D) being smooth or rarely rugose. They measure 260–650 x 5–20 µm, but shorter oxeas, down to 180 and 125 µm in length, occur respectively in 2 of the studied specimens. As a rule of thumb, oxeas are more abundant than styles.
An axial skeleton is discernible in the stalk, made of ascending compact tracts of oxeas embedded by spongin and crossed by isolated (i.e., not packed) oxeas arranged confusedly. From the axial skeleton, an extra-axial plumoreticulate skeleton emerges, consisting of ascending loose pauci—and multispicular tracts of oxeas reinforced with some spongin (Fig. 7G). In the extra-axial region, there are isolated inter-crossed oxeas forming a confusing reticule-like arrangement (Fig. 7H). Long styles, either isolated or in small groups (2–4), project outward from the spongin cover of the extra-axial tracts, piercing the sponge surface to make it hispid.
Distribution and ecology notes. The individuals were collected at the deep shelf (87 to 173 m) of the Alboran Island, from rocky, detritic-organogenic gravel, and rhodolith bottoms.
Taxonomic remarks. No previously known Axinella spp. in the Atlantic-Mediterranean area have characteristics similar to those of the new species (Table 3). The external morphology of A. alborana nov. sp. bears some external resemblance to A. flustra (Fig. 6H–J), especially to Topsent's (1904) syntypes from Stn. 247 (Fig. 6H–I). Nevertheless, both species strongly differ skeletally, having A. flustra trichodragmata and shorter oxeas (Table 3). Axinella vaceleti Pansini, 1984 is also a flabellate species, but with a marked fan-shaped, undulating lamina, which is also larger (50–60 mm high) and thicker (4–5 mm) than that of the A. alborana nov. sp. specimens. Additionally, A. vaceleti has smaller spicules, specially the styles, ranging from 270 to 1450 µm (Pansini 1984).
Specimens of Axinella alborana nov. sp. were investigated for the first time about twenty years ago, as part of a study on the deep-shelf Alboranian sponges carried out by Maldonado (1993). Nevertheless, no description of material was published at that time because of the risk that the small individuals now described as A. alborana nov. sp. might correspond to juvenile stages of some poorly known, large Axinella spp. growing at the ill-known deep shelf. However, our recent exploration of those deep-shelf habitats using an ROV has revealed that there is no dense population of any other large Axinella spp. in the areas where A. alborana nov. sp. occurs. In the light of these findings, the idea that the dense undergrowth of small individuals might correspond to juvenile sponges makes no sense and these small sponges can indeed be identified as adults of A. alborana nov. sp.
description: Published as part of Sitjà, Cèlia & Maldonado, Manuel, 2014, New and rare sponges from the deep shelf of the Alboran Island (Alboran Sea, Western Mediterranean), pp. 141-179 in Zootaxa 3760 (2) on pages 152-159, DOI: 10.11646/zootaxa.3760.2.2, http://zenodo.org/record/4908941