Hymedesmia (Hymedesmia) quadridentata, Cardone & Pansini & Corriero & Bertolino, 2019

Cardone, Frine, Pansini, Maurizio, Corriero, Giuseppe & Bertolino, Marco, 2019, Two new species of deep-sea sponges (Porifera, Demospongiae) from submarine canyons of the Sardinian continental margin (western Mediterranean Sea), Zootaxa 4688 (3), pp. 407-419 : 412-415

Hymedesmia (Hymedesmia) quadridentata n. sp.

( Figs 4 A–B; Figs 5 A–G)

Materials examined. Type material. Holotype: SARD10 b (9) [ MSNG 57362 ], Coda Cavallo Canyon (40°54.75’N– 9°54.9’E), north-est Sardinia, Tyrrhenian Sea , 256–264 m, Leg. Simonepietro Canese, 29.08.2013.

Paratype: SARD10 b (9a, 13) (only slide), Coda Cavallo Canyon (40°54.75’N– 9°54. 9’E), north-est Sardinia, Tyrrhenian Sea , 256–264 m, Leg. Simonepietro Canese, 29.08.2013 .

Type locality: Sardinian continental margin

Diagnosis. Thinly encrusting Hymedesmia characterized by two categories of acanthostyles, anisotylotornotes, two categories of chelae in form of unguiferate chelae and arcuate isochelae, two categories of sigma.

Description. Holotype SARD10b (9) [MSNG 57362]: the sponge is thinly encrusting, less than 1 mm thick, on dead colonies of Madrepora oculata . The surface is hispid due to the acanthostyles, erect on the substrate, that protrude through the thin dermal membrane. Consistency is soft. The alcohol preserved sponge looks transparent, without a defined colour ( Fig. 4A ).

Skeleton ( Fig. 4B ). The ectosomal skeleton consists in a tangential layer of anisotylotornotes and scattered microscleres, both chelae and sigmas. The choanosomal skeleton is hymedesmioid, with acanthostyles in two size categories, echinating the substratum, with their heads embedded in a thin layer of spongin. Microscleres are dispersed also in the choanosome.

Spicules ( Figs 5 A–G). Acanthostyles straight or slightly curved in two size categories. They have roundish heads and spines uniformly distributed in the proximal part of the shaft. The distal part is less spiny, especially in the larger spicules. The spines are generally blunt on the spicule heads. The larger acanthostyles measure 265 (390) 550 x 10 (15.3) 20 µm ( Fig. 5A ). The smaller acanthostyles measure 55 (124.2) 215 x 7.5 (9.2) 12.5 µm ( Fig. 5B ).

Anisotylotornotes ( Fig. 5C ) straight or slightly curved with mucronate and more or less oval extremities. They measure 170 (194) 235 x 2.5 µm. Unguiferate chelae ( Fig. 5D ), with regularly round shaft and constantly four teeth at each extremity, measuring 17.5 (22.3) 25 x 2.5 µm. Arcuate isochelae ( Fig. 5E ) with a slightly curved shaft are 20 (22) 25 µm long. Sigmas, “C” and rarely “S” shaped, in two size-categories. The larger sigmas are 35 (55.5) 82.5 µm long ( Fig. 5F ); the smaller ones 12.5 (14.8) 17.5 µm ( Fig. 5G ).

Etymology. The name refers to the number of teeth of the unguiferate chelae.

Distribution. The species has been observed only on the M. oculata reef in the Coda Cavallo Canyon (Sardinia, Italy).

Remarks. For the choanosomal basal hymedesmioid skeleton, composed of two sizes of acanthostyles standing singly erect on the substrate, we attributed the new species to the genus Hymedesmia (Hymedesmia) .

This new species of Hymedesmia (Hymedesmia) is characterized by the presence of two types of chelae. Twenty-two species of the genus were reported from the Mediterranean Sea ( Pansini and Longo 2003; van Soest et al. 2019), but none of them has unguiferate chelae. Only H. (H.) mutabilis Topsent, 1904b that was recorded in the same area ( Taviani et al. 2017; Bertolino et al. in press), shows two size-categories of arcuate isochelae. A geographically close species, H. (H.) mucronata ( Topsent, 1904b, Plate XIV, Figure 4 ) from the North Atlantic, has two different types of chelae: arcuate isochelae (26 µm long) and a sort of unguiferate chelae of the same length, with two or three widely spaced teeth at each extremity. Furthermore, the comparison between Hymedesmia (H.) quadridentata n. sp. and the North Atlantic Hymedesmia (Hymedesmia) species with sigmas did not show overlapping spicular patterns (see Tab. x Cárdenas and Thollesson 2016). H. (H.) mucronata is close to our Hymedesmia but differs from it in having just one size category of sigmas (25–35 µm long) much smaller than ours and in the shape of unguiferate chelae.

H. (H.) unguifera Burton, 1929 from the Antarctic presents unguiferate chelae of small size (12 µm long) with three teeth, but is devoid of sigmas.

According to the microsclere size differences and to the peculiar shape of unguiferate chelae (round shaft and four teeth at both extremities) we erect a new species for Hymedesmia (H.) quadridentata n. sp.

Figures

FIGURE 4. Hymedesmia (Hymedesmia) quadridentata n. sp., (A) Holotype SARD10b (9) [MSNG 57362]; (B) Skeletal architecture (transverse section). Scale bars: A = 1.5 cm; B = 50 µm

FIGURE 5. Hymedesmia (Hymedesmia) quadridentata n. sp., SEM images of spicules made from the SARD10b (9) [MSNG 57362]: (A) Acanthostyles I and detail of heads; (B) Acanthostyles II; (C) Ectosomal tylotes; (D) Unguiferate chelae; (E) Isochelae; (F) Sigmas I; (G) Sigmas II. Scale bars: A = 50 µm; B = 20 µm; C = 30 µm; D, E, G = 10 µm; F = 20 µm.