Axinella alborana, Sitjà & Maldonado, 2014

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 : 152-159

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.

Figures

FIGURE 1. (A) Localization of the Alboran Island in the Mediterranean. (B) Distribution of the 25 studied sampling stations over the bathymetric map of the shelf of the Alboran Island.

FIGURE 6. (A–B) Holotype of Axinella alborana nov. sp. seen from its both sides (MNCN-Sp155-DR44A). (C) Holotype and 3 additional, collected specimens of A. alborana nov. sp. (from left to right, MNCN-Sp3-DR05A, MNCN-Sp146-BV33A, MNCN-Sp155-DR44A, MNCN-Sp146-BV33B). (D) Specimen of Axinella spatula nov. sp., photographed on board immediately after collection. (E) Preserved specimens of A. spatula nov. sp., being the first (from left to right) the holotype (MNCN-Sp145); the remaining specimens are BV33B, MNCN-Sp116-BV15A & B, and MNCN-Sp65-BV21B. (F–G) Blackish specimens (MNCN-Sp57-BV21A and MNCN-Sp57-BV21B, respectively) of A. spatula nov. sp. The former shows an incipient branching, while the latter is clearly branched and with no narrowing at the stalk. (H–J) Syntypes of Tragosia flustra (Topsent, 1892) collected by Topsent in 1888 (Stn. 247. M. O. M. 040272) and in 1886 (Stn. 58. M. O. M. 040044), respectively. The former (H–I) is shown on its both sides, being profusely ramified, while the latter (J) shows only 3 branches.

FIGURE 7. Axinella alborana nov. sp.: (A) Line drawing summarizing the skeletal complement of the Alboranian specimens, consisting of styles (a) and oxeas (b) with acerate, blunt or mucronate ends (c). (B–C) Light microscope view of a style, with examples of the round end. (D–E) Light microscope views of oxeas. Note the varying curving angle, the anisoxea (an) character in some spicules, and the annular swelling (sw) of others. (F) SEM details of oxea ends, being typically either blunt or mucronate. (G) Light microscope view of the skeletal arrangement, showing a style embedded in spongin (s) in the extra-axial skeleton. (H) Light microscope view of oxeas at the extra-axial plumoreticulate skeleton occurring either in paucispicular tracts (pc) or free (sn).