Poecillastra tavianii, 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 : 409-412

Poecillastra tavianii n. sp.

( Figs 2 A–D; Figs 3 A–J)

Materials examined. Type material. Holotype: SARD10 b (12) [ MSNG 57361 ], 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: MUZAC 6314 — Nora Canyon (38°42.49’N– 8°54.55’E), south Sardinian continental margin, southern Tyrrhenian Sea, 440 m depth, Leg. Simonepietro Canese, 16.11.2013 .

Other examined material. SARD 10b (9b, 13, 25, 26); MUZAC 6315; MUZAC 6316.

Type locality: Sardinian continental margin

Diagnosis. Encrusting or cushion shaped Poecillastra , characterized by two categories of oxeas, short-shafted triaenes in form of dichotriaenes, mesodichotriaenes and plagiotriaenes, three categories of spirasters and one of plesiasters. Spiny microxeas very rare.

Description. Holotype SARD10b (12) [MSNG 57361]: the studied specimens are very small and fill the corallite cavities of Madrepora oculata colonies or encrust their branches ( Figs 2A, B, D ). Diameter of 4 x 3 mm and a thickness of about 2 mm, however it could depend on the cavity in which it is housed. The surface is villose, due to the presence of bundles of long thin oxeas protruding outside the sponge body. Oscules are flush, roundish, irregularly distributed. Consistency is hard but compressible. The colour in life shows tinges of azure and becomes white after alcohol preservation.

Skeleton ( Fig. 2C ). There is not clear distinction between the ectosome and the choanosome. Dichotriaenes with cladome tangential to the surface are detectable in the ectosome which is cut across by bundles of oxeas ( Fig. 2C ). Oxeas and triaenes are rather disorderly arranged in the choanosome. Microscleres are scattered through the whole sponge body without a superficial concentration.

Spicules ( Fig. 3 A–J). Megascleres are oxeas in two size categories and short shafted dicho- and plagiotriaenes. Dichotriaenes ( Fig. 3A ), with one or more clads missing, frequently malformed and often showing rounded extremities. The cladome of the symmetrical spicules measures 225 (319.4) 390 µm: protoclads 50 (114) 160 x 15 (20) 22.5 µm, deuteroclads 50 (88.2) 145 x 10 (13) 20 µm. Rhabdome straight or slightly curved with hastate or blunt end, measuring 210 (304.2) 400 x 20 (23.7) 30 µm. Plagiotriaenes, sometimes malformed, with cladome 135 (206) 290 µm in diameter; clads measure 95 (145.7) 220 x 10 µm. Short rhabdome with hastate or blunt end, measuring 150 (235.8) 350 x 10 µm. Some plagiotriaenes having clads and rhabdome almost of the same length may be regarded as pseudocalthrops ( Fig. 3B ). Only in the paratypes collected in the Nora Canyon mesodichotriaenes were observed ( Fig. 3C ). They are not abundant but frequent, with epirhabdome measuring 235 (241) 248 x 29 (29) 30 µm and rhabdome sensu strictu measuring 303 (309) 383 x 28 (25) 30 µm (for the definitions of epirhabdome and rhabdome sensu strictu see Maldonado 1993). The protoclades of the bifurcate clades measures 85 (116) 174 x 28 (29) 30 µm. The deuteroclades measure 37 (61) 86 x 11 (17) 23 µm.

Oxeas in two size-categories. The larger ones are curved or sinuous, sometimes centrotylote ( Fig. 3D ). Their extremities are hastate, stepped, blunt or rounded, assuming so the shape of styles. They measure 630 (1048) 1449 x 7.5 (13.4) 22.5 µm. The second category ( Fig. 3E ) differs from the first for the spicule thinness. They are slightly curved or sinuous, sometimes centrotylote, with rounded extremities and measure 570 (1237) 1311 x 2.5 (3.4) 5 µm.

Microscleres are acanthomicroxeas, spirasters and plesiasters. Microxeas are not abundant, straight or slightly curved, uniformely microspined and sometimes centrotylote ( Fig. 3F ). They measure 105 (141.4) 172 x 2.5 µm.

Spirasters are the most abundant microscleres and may be tentatively separated into three different types. Type I ( Fig. 3G ): long and rather straight axis (22.5 (28.7) 42.5 µm long) with short, conical, spiny rays 2.5 µm long. Type II ( Fig. 3H ): rather short, twisted axis (17.5 (24) 30 µm long) with conical spiny rays longer (5 (6.3) 7.5 µm) than in type I. Type III ( Fig. 3I ): intermediate between metaster and spiraster, with rather short twisted axis (15 (17.7) 25 µm long) and cylindrical spiny rays about 5 µm long. Plesiasters ( Fig. 3J ) 37.5 (51.7) 80 µm long with entirely spiny rays 15 (20.5) 25 µm long.

Etymology. The specific name “tavianii” is in honour of the senior researcher Marco Taviani to recognize his contribution in the investigation of deep-sea benthic communities of the Mediterranean Sea.

Distribution. Currently known only for the Sardinian continental margin.

Remarks. The new species has been ascribed to the genus Poecillastra Sollas, 1888 having as microscleres several types of asterose microscleres and a single category of microxeas ( Maldonado 2002; Cardenas et al. 2011; 2012). No other Poecillastra species has the combination of characters described above. The possession of shortshafted mesodichotriaenes is unique for this genus.

According to the literature ( Maldonado 1993), short-shafted mesotriaenes (mesocalthrops or mesodichotriaenes) are extremely rare spicules recorded only in a few species belonging to Calthropellidae ( Calthropella (Calthropella) pathologica ( Schmidt, 1868) (sensu Von Lendenfeld 1903; Lévi 1973) and C. (Pachataxa) enigmatica Lévi & Lévi, 1983 ) and some Pachastrellidae ( Characella Sollas, 1886 , Triptolemma Sollas, 1888 , Brachiaster Wilson, 1925 genera and Pachastrella ovisternata Lendenfeld, 1894 ). No species with this spicular category has ever been described before in the family Vulcanellidae .

Only 5, out of the 25 species of Poecillastra considered valid, have dichotrianes among the megascleres: P. ciliata Wilson, 1925 , P. rudiastra Pulitzer-Finali, 1983 , P. symbiotica Topsent, 1902 , P. tenuirhabda Lendenfeld, 1907 and P. tuberosa ( Lévi, 1964) . P. ciliata , P. tenuirhabda and P. tuberosa clearly differ from the new species in the size of megascleres (both oxeas and triaenes) and in the type and size of asterose microscleres. In addition they were recorded from significantly distant areas such as Philippine Islands, South Indian Ocean and South Africa, respectively. P. rudiastra , is known from a single specimen collected off Calvi ( Corse) that Pulitzer-Finali (1983, p. 472) entirely used for a spicule slide. It differs from the new species in the presence of anatriaenes and in the shape of microscleres. Since Pulitzer-Finali found just a single dichotriaene in his preparation, he regarded as uncertain the presence of them in the spiculation of P. rudiastra . P. symbiotica differs from P. tavianii n. sp. in the larger size of oxeas and dichotriaenes (cladome up to 1800 µm versus 400 µm), in the shape and size of spirasters and microxeas. In addition, P. symbiotica has a peculiar ecology as emphasized by the specific name ( Topsent 1902; 1904a) and is known only from the Azore Islands. P. tavianii n. sp. is characterized by two types of oxeas, the presence of plagio-, dicho- and mesodichotriaenes and the abundance and variety of spirasters.

Figures

FIGURE 2. Poecillastra tavianii n. sp., (A) Holotype SARD10b (12) [MSNG 57361], (B) Paratype MUZAC 6314 (rectangle) (arrows indicate paratypes MUZAC 6315 (named 1) and MUZAC 6316 (named 2) inside the corallites of M. oculata); (D) detail of Paratype [MUZAC 6314] in the M. oculata corallite; (C), skeletal architecture of the holotype (transverse section). Scale bars: A = 1 mm; B = 1 cm; C = 500 µm, D = 1.5 mm.

FIGURE 3. Poecillastra tavianii n. sp., SEM images of spicules: (A) Dichotriaenes; (B) Pseudocalthrop; (C) Mesodichotriaenes (paratype MUZAC 6314); (D) Oxeas I; (E) Oxeas II; (F) Acanthomicroxea; Spirasters (G) type I; (H) type II; (I) type III; (J) Plesiasters. Scale bars: A, B, C, D, E = 100 µm; F = 20 µm; G, H, I, J = 5 µm.