Latrunculia (Latrunculia) tetraverticillata Mothes, Campos, Eckert & Lerner, 2008, sp. nov.

Latrunculia (Latrunculia) tetraverticillata sp. nov.

(Fig. 2 A–E; Tab. I)

Material examined. Holotype: MCNPOR 3695, Brazil, off Santa Catarina State coast (29º11'16"S, 47º54'16"W), 420 m depth, substrate of pebbles, bottom temperature 9°C, salinity 34 ‰, 24.IV.1997, R/V "Antares” coll. Paratype: MCNPOR 3641 (microscope-slide); data similar to that of the holotype.

Comparative material. Latrunculia (Latrunculia) brevis Ridley & Dendy, 1886, collected by HMS “Challenger” Expedition, off Rio de la Plata, Argentina, slide BMNH 1887.5.2.269 (holotype). Latrunculia (Latrunculia) biformis (Kirkpatrick, 1908), collected by Antarctic Terra Nova Expedition, locality unknown, slide BMNH 1910.26.154a. Latrunculia (Latrunculia) bocagei Ridley & Dendy, 1886, collected by HMS “Discovery” Expedition, Falkland Islands, slide BMNH 1887.5.2.237 (holotype).

Description. Small encrusting sponge, 0.7 x 0.6 x 0.1 cm (Fig. 2 A). Surface slightly velvety to the touch, with a single conical, volcano-shaped oscule, 0.1 cm in diameter. Preserved material friable in consistency. External colour in life unknown; in preservative external and internal colour creamy white.

Skeleton. Ectosome with a palisade of anisodiscorhabds perpendicularly arranged (Fig. 2 B). Subectosomal region 90–210 μm thick, with a confused halichondroid arrangement of single strongyloxeas tangentially oriented and common anisodiscorhabds scattered through. The choanosomal skeleton is formed by a very irregular, polygonal reticulation (85–160 μm) formed by tracts of strongyloxeas (30–70 μm) with scarce spongin reinforcement.

Spicules. Magascleres (Fig. 2 C–D): Strongyloxeas smooth, straight, anisodiametric strongyloxeas, slightly fusiform, occasionally may bear a tyle, apical extremity hastate. Microscleres (Fig. 2 E): Anisodiscorhabds consisting of a straight, stout shaft, with a reduced base ornamented with smooth spines, bent downwards. There are only a few isolated spines above the manubrium, and these can vary on abundance and disposition. Two central whorls are of similar diameter (median and subsidiary 2) and bear denticulated edges.

Both are located on half length of the shaft, and oriented perpendicularly to its main axis. The third and fourth whorls (subsidiary 1 and apical) are cup-shaped, placed closer to the apex and also bear denticulated edges. They are generally smaller in diameter than the first ones. The crown is rose-like in its contour. All the whorls are not divided in groups of spines. Immature stages are common. Measurements are given in Table 1.

Distribution. Known only from the type locality.

Etymology. Named after the presence of four whorls along the discorhabd axis.

Diameter 29.9– 40.0– 43.7 39.1– 41.6 –44 Subsidiary 2 Distance 39.1– 43.0– 48.5 32.2– 40.6 –46 In comparison with other Latrunculia species from the Southwestern Atlantic Ocean (e.g., L. biformis, L. brevis and L. bocagei), the new species clearly differs from them in possessing strongyloxeas rather than styles as megascleres, and in the size of these megascleres, which are smaller than those of L. biformis, L. brevis and L. bocagei. Fusiform strongyloxeas (and styles, or styles to strongyloxeas) were recorded in other species within subgenus Latrunculia (e.g., L. basilis, L. palmata and L. novaecaledoniae); however the geographic distribution of these species (Antarctic, Philippines and New Caledonia, respectively ) is remarkably distant from the type locality of the new species. The anisodiscorhab of the new species is morphologically different (see Fig. 3 A–D) from those present in the other three species of Latrunculia found in the Southwestern Atlantic. Moreover, L. brevis has anisodiscorhabds with a short shaft, L. biformis has two distinct types of anisodiscorhabds (additional aciculoanisodiscorhabds), and L. bocagei differs in having the standard three whorls along the anisodiscorhabd axis, but spines of the apical whorl which are slightly curved upwards in a crown-like tuft of blunt, terminally spined projections (Samaai et al., 2006).

Latrunculia multirotalis Topsent, 1905, recorded from the Azores, is morphologically the closest species to the new one, because both species have several whorls of spines along the shaft. However, apart from having disjunctive distributions, the new species differs from L. multirotalis; L. tetraverticillata has strongyloxeas as megascleres, the microscleres are smaller, bear only four whorls not divided in clusters of spines, or denticulated margins, and the shaft thickness is uniform towards the apical whorl.

Hinde and Holmes (1892) recorded Latrunculia sp. (p. 218, Pl. XI, Fig. 37) from fossil material coming from lower Tertiary strata of New Zealand. This fossil species had an anisodiscorhabd that was similar in structure (having four whorls along the shaft) and dimension (length), to that found in L. tetraverticillata sp.nov. However the discorhabds of the new species differ from the fossil microscleres in the absence of secondary spines among the whorls, and also in the structure of the apex, which is formed by a single prominent spine in the fossil material, whereas it is rose-like in the extant species. It is difficult to evaluate the degree of homology between fossil and extant acanthodiscorabds; but the similarity in the acanthodiscorhabd could indicate that similar "latrunculiid" species coexisted in a primary community (Samaai et al., 2006) in the Southern Ocean.