Axinella vellerea Topsent, 1904

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 : 162-163

Axinella vellerea Topsent, 1904

( Figs. 2B , 9 , 10 ; Tables 2, 3)

Material examined. Thirteen specimens collected from the deep shelf of Alboran Island: MNCN-Sp51-DR05A & B from Stn. 5; MNCN-Sp148-BV33 from Stn. 33; MNCN-Sp196-BV41 from Stn. 41; MNCN-Sp142-DR44 A to I from Stn. 44 ( Table 1 , Fig. 1 )

Comparative material: Syntype material of Axinella vellerea Topsent, 1904 (since no holotype was originally designated by Topsent), consisting of two specimens from Stn. 866 at Azores Islands (38º52.833’N 27º23.083’W; water depth: 599 m; 2 August 1897), and currently stored at the Monaco Museum (MOM-040631) .

Macroscopic description. Specimens are erect, columnar, undivided or with two-tree incipient, lobule-like ramifications ( Fig. 9A–H ). The sponges measure 10–30 x 5–8 mm. The consistency is fleshy but hardly flexible. The surface is irregular, grooved, and porous. In some specimens, the oscules can be observed in the translucent epithelium folding the grooves, which run usually vertically, parallel to the longest axis of the body. The hispidation of the ectosome is short and not very dense, mostly verifiable under the dissecting microscope. The animal color in ethanol is ochre or pale brown.

Skeleton. Megascleres are only styles and, in some individuals, a very low number of oxeas. Styles occur in a wide range of shapes and sizes, but without making discernible categories. They are slightly curved to somewhat angulate, some curved nearly the round end, similarly to rhabdostyles ( Fig. 10A–B ). The round end may be regular, but subtyles and annular swellings are also common, either in terminal or subterminal position ( Fig. 10A–C ). The point is usually acerate, but sometimes stepped or even blunt ( Fig. 10A ). Spicule malformations occasionally occur as well. Styles measure 470– 1725 x 11–30 µm, but diameters smaller than 15 µm are uncommon. Some scattered oxeas have been observed in some specimens, in which case they are angulated or have a two-point curvature ( Fig. 10D ), sometimes asymmetrical; they may also be centrotylote. When present, they measure 700– 1120 x 5–20 µm.

The skeletal arrangement consists of a somewhat central, compressed, plumoreticulate axis from which a plumoreticulate extra-axial skeleton spreads ( Fig. 10E ). The ascending extra-axial tracts become thinner as they reach the surface, and their terminal styles pierce the ectosome causing hispidation. Moderate spongin embeds the spicules but without forming fibres ( Fig. 10F ); spongin becomes less abundant in the extra-axial region.

Distribution and ecology notes. The individuals were collected from depths ranging from 102 to 173 m, on rock, gravel or dead rhodolith pieces. The collected material makes the first Mediterranean record of this rare species. To date only four specimens had previously been reported: three of them collected from a 599 m deep, gravel bottom at Azores ( Topsent 1904), and one from 200–290 m depths at the Folden fiord of the Norwegian Sea ( Burton 1931).

Taxonomic remarks. The size of the examined syntypes of A. vellerea (97 x 40 mm and 45 x 18 mm) is slightly larger than that of any of the Alboranian individuals, being the remaining aspects of the external morphology notably similar between both specimen groups ( Fig. 9A–H ). The largest syntype also shows two branches better developed ( Fig. 9F–G ) than the incipient branches often characterizing the Alboranian individuals ( Fig. 9A–E ). Regarding the spicules, the Alboranian specimens and the syntypes of A. vellerea show styles in nearly identical size and shape ranges (Table 3). A small skeletal difference is that oxeas are not found in neither the original description by Topsent (1904) nor in our re-examination of the syntypes. Burton (1931) did report occasional "oxeote styles" in his Norwegian specimen. In the Alboranian, specimens, we found oxeas in only a minority of individuals and always in low abundance. Therefore, the oxeas appear to be a variable element in the spicule complement of A. vellerea , as it is also the case of other Axinella spp.

As previously noticed by Topsent (1904), A. vellerea and Axinella vasonuda Topsent, 1904 bear similarity in both their external morphology and the skeletal organization. Nevertheless, A. vasonuda is characterized by having oxeas as main spicule type, showing only scarce styles, the occurrence of which is limited to the peripheral zones of the skeleton.

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 2. Benthic communities on the deep shelf of the Alboran Island in which sponges are important members. (A) View of a rhodolith bottom dominated by cnidarians and sponges. The most abundant sponges were Phakellia ventilabrum (Pv), Phakellia robusta (Pr), and Bubaris vermiculata (Bv). (B) Detail of a rhodolith, largely encrusted by Bubaris vermiculata (Bv). (C) View of a gently sloping rocky bottom, showing large specimens of Phakellia robusta (Pr) and Poecillastra compressa (Pc) together with a dense "canopy" of small digitiform, claviform and globiform sponges, such as Axinella vellerea (Av) and Crella pyrula (Cp). (D) Individual of Vulcanella aberrans (Va) surrounded by small globiform and digitiform sponges. (E) Benthic community on the outcrops dominated by cnidarians, including the octocoral Corallium rubrum. Abundant massive, submassive and encrusting sponges are common under the gorgonian forest. (F) Large astrophorid (Geodia spp.) sighted from the ROV on the top of an outcrop. (G) Collected specimen of Crella (Yvesia) pyrula (MNHN-Sp136-DR44). (H) Collected specimen of Rhizaxinella gracilis (MNHN-Sp22-BV14). (I) A solitary specimen of Axinella salicina located by the ROV on a coarse-sand and gravel bottom, a substrate type that generally shows low abundance of sponges.

FIGURE 9. Axinella vellerea Topsent, 1904. (A–B) One of the collected Alboranian specimens (MNCN-Sp51-DR05A) shown on its both sides and bearing an incipient branching. (C) A branchless Alboranian specimen (MNCN-SP51-DR05B) of A. vellerea photographed on graphic paper. (D-E) Another unbranched Alboranian specimen (MNCN-Sp142-DR44A) attached to a piece of gravel, shown on its both sides. (F) Photograph of the holotype (the large sponge to the right) and the syntype (to the left) of A. vellerea, collected by Topsent in 1897 (Stn. 866. M. O. M. 040631). (G) Close up of the holotype of A. vellerea, being clearly ramified and larger than most specimens collected from the Alboran Island. (H) Close up of the syntype of A. vellerea, showing an incipient branch.

FIGURE 10. Axinella vellerea Topsent, 1904: (A) Line drawing summarizing the skeletal complement of the Alboranian specimens. Styles (a) are in a wide variety of shapes, with a round end that can be regular or showing one or more swellings (b) and a distal end (c) that can be regular to blunt, sometimes with mucronate variations. Oxeas (d) occur in varying size and shapes, with ends ranging from acerate to mucronate (e). (B) Light microscope view of a style with a subtylote end. (C) SEM detail of three typical morphologies (i.e., subterminal ring, subtylote, and regular) of the round end of styles. (D) Light microscope view of a double-bent oxea. (E) Light microscope view of plumose arrangement in the extra-axial skeleton. (F) Detail of styles embedded by spongin (s).