Antarctotetilla leptoderma

Antarctotetilla leptoderma (Sollas, 1886)

Synonymy: Tetilla leptoderma Sollas, 1886; Tethya stylifera Lendenfeld, 1907; Tetilla grandis Sollas, 1886; Tetilla grandis var. alba Sollas, 1886.

Material examined: holotype of Tetilla leptoderma NHM 89.1.1.3 Sollas, 1886, Rio de la Plata, Argentine; Antarctotetilla leptoderma, CEAB.POR.BIO.500a ANT 27112, Newmayer, Antarctic coasts, -70° 51.52‘S, 10° 36.72‘W, 236–285 m depth, 0 1 April 2011; CEAB.POR.BIO.500e ANT 27107,Newmayer, Antarctic coasts, -70° 56.05‘S, 10° 30.05‘W, 211–243 m depth, 25 March 2011 and CEAB.POR.BIO.500c ANT 27109, Newmayer, Antarctic coasts, - 70° 47.54‘S, 10° 29.56‘W, 272–288 m depth, 28 March 2011; Antarctotetilla leptoderma, CEAB. POR. BIO.500d ANT 27108, South Orkneys, Subantarctic region, - 61° 8.59‘S, 43° 58.37‘W, 346–397 m depth, 19 February 2011; Antarctotetilla leptoderma, CEAB. POR. BIO.500b ANT 27111, South Georgia, Subantarctic region, -54° 26.12‘S, -35° 41.54‘W, 265–266 m depth, 16 February 2011.

GenBank accession numbers (Carella et al. 2016): CEAB.POR.BIO.500a ANT 27112 (KT124319, KT124343, KT124329 and KT124365), CEAB.POR.BIO.500e ANT 27107 (KT124351 and KT124358), CEAB.POR.BIO.500c ANT 27109 (KT124354), CEAB.POR.BIO.500d ANT 27108 (KT124323 and KT124347) andCEAB.POR.BIO.500b ANT 27111 (KT124318, KT124341, KT124328 and KT124362).

Description (Fig. 4). Sub-spherical or ovoid sponges with a variable size between 4 and 8 cm in diameter (Fig. 4a). Large individuals compact; young individuals softer and more compressible. Surface conulose and corrugate, smooth to touch. Only one large oscule placed on top. Pores grouped in small depressions scattered over the entire surface (Fig. 4c), but mostly concentrated at the equatorial zone and between the grooves formed by the conical elevations. Color dirty white or brown in living specimens, greenish in alcohol. Not a real cortex but a pseudocortex (Fig. 4d–e), which consists of a loosely arranged auxiliary oxeas perpendicular to the surface. Root tufts composed of anatriaenes are used as anchors to fix the sponge to the substrate.

Spicules (Fig 5; Table1). Megascleres: oxeas I (Fig. 5a) large and fusiform: 5800–7045–8400 µm x 60 –71–85 µm. Auxiliary small oxeas II (Fig. 5b): 510– 1075–1600 µm x 7.5–17.6–35 µm. Anatriaenes I (Fig. 5f): 2800– 6995.8–11380 µm x 15–22 –27.5 µm in size (rhabdomes thickness measured at the base of clades) with long and thin clades: 120–186.2–280 µm; rhabdomes fusiform, thicker at the middle and filiform at the terminal part. Anatriaenes II: 2000–3510–7450 µm x 8.7–14.8–20 µm in size (Fig. 5e) with short clades: 35–57.9–90 µm and fusiform rhabdomes. Protriaenes I (Fig. 5d): 2580–6301.4–11800 µm x 12.5–21.5–37.5 µm, with clades of 60– 158–270 µm long, usually one clade longer than the other two; rhabdomes tapering from the base of the clades to end in a filamentous termination. Protriaenes II (Fig. 5c): 1600–2752.5–5780 µm x 5–10 –12.5 µm, with clades: 25–106.2–190 µm in length, usually one clade longer than the other two; rhabdomes tapering to a filiform end. Trichodal protriaenes (Fig. 5g –h) very small with filamentous rhabdomes: 420–750.6–1235 µm x 2.5–4.3–5 µm long and thin, 10–34.2–105 µm long clades. Microscleres: sigmaspires (Fig. 5i): 10–14.7–22.5 µm in length.

Skeletal arrangement. Choanosomal skeleton made of bundles of oxeas with protriaenes and anatriaenes spirally arranged from the central part to the sponge periphery. Only oxeas and protriaenes protrude three mm the surface forming the spicular tufts of the conical elevations (Fig. 4b). Auxiliary oxeas arranged in palisade at the sponge periphery and scattered in the choanosomal zone. Trichodal protriaenes scattered at the peripheral zone, mostly concentrated around pore and oscule areas. Sigmaspires present throughout the sponge.

Distribution and habitat. Antarctic coasts (Newmayer), Subantarctic (South Georgia and South Orkneys), Argentina (off Rio de la Plata—Sollas 1886—Malvinas—Sarà et al. 1992), Kerguelen (Lendenfeld 1907), Chile (Desqueyroux-Faúndez 1989), South Shetland Islands (Ríos et al. 2004), New Zealand (Szitenberg et al. 2013). The specimens live in sediment and rocky substrates from 45 meters to more than 600 meters of depth.

Remarks. Antarctotetilla leptoderma has been repeatedly put in synonymy with A. grandis (Burton 1929; Boury-Esnault & Van Beveren 1982). However both species clearly differ in several morphological characters. The main morphological differences between both species are the globular body shape, the smooth surface, and the numerous small oscules situated on short conical elevations in A. grandis versus an elongate ovoid shape, the surface small protrusions, and a single large oscule in A. leptoderma.