Hymedesmia (Hymedesmia) santarositae sp. nov.

(Figure 2; Table 1)

Material examined. Holotype ― MNRJ 12843 (Vouchers: RBINS-IG 32240 -POR12843, MHNG 85676), Isla Santa Rosa 2, Reserva Nacional de Paracas, Ica Region (14.31950S, 76.16456W), depth 8 m, coll. F. Azevedo, Y. Hooker & Ph. Willenz (10/XII/2008).

Diagnosis. Hymedesmia (H.) with arcuate chelae, microstrongyles and sigmas.

Description (Figs 2A–B). Thinly encrusting sponge (≈ 15.2 cm 2), less than 1 mm thick (0.2 to 0.8 mm, Fig. 2A). Consistency very soft and fragile. Surface smooth, with visible oval to circular areolated porefields (3.4 x 1.3 cm largest and smallest diameters) and subectosomal canals, oscula visible in situ (≈ 0.2–0.4 cm). (Fig. 2B). Color brownish beige in life (in situ) and beige transparent when preserved in ethanol.

Skeleton (Figs 2C–D). Ectosomal skeleton with ectosomal strongyles to subtylotes forming longitudinal bundles from surface to substrate (Fig. 2C). Subectosomal and choanosomal skeletons overlapping, composed of typical hymedesmioid structure, consisting of a basal layer of spongin, with acanthostyles I and II erect on the substrate (Fig. 2C). Isochelae, sigmas and microstrongyles (Fig. 2D) appear scattered in the sponge, and some acanthostyles I lay parallel to, or flat on the substrate.

Spicules (Figs 2E–N; Table 1). Ectosomal diactines: strongyles to subtylotes, smooth, straight (Fig. 2G) with rounded ends (Fig. 2 H –I), 129– 153.1 –187 (± 16.3) × 3.6– 4.5 –5.2 (± 0.4) × 3.8–5.0 µm (tyle, N = 3) (Figs 2G–I). Choanosomal acanthostyles I (Fig. 2E): larger, apex tapering gradually, acerate tip, base occasionally with a more or less distinct swelling; shaft straight to slightly curved, spines slightly curved or conical and spread from base to mid shaft, 158– 206.2 –270 (± 31.9) × 5.4– 8.3 –11.1 (± 1.9) µm. Choanosomal acanthostyles II (Fig. 2F).: straight, tapering gradually, acerate tip and round base, spines spread all along the spicule, curved, those at the base bent as hooks, 76– 83.8 –96 (± 5.0) × 4.9– 6.1 –7.9 (± 0.7) µm. Arcuate isochelae (Figs 2M–N): one free spatulate ala and two lateral alae semi-fused with the shaft; shaft characteristically curved, bow-shaped, 17– 19.1 –21 (± 1.1) × 2.4– 3.7 –4.8 µm. Sigmas (Fig. 2J): C shape, tips straight and acerate, 27– 29.4 –33 (± 2.2) × 2.9– 3.2 –3.9 (± 0.3) µm. Microstrongyles (Figs 2K–L): smooth, curved and robust, rounded ends, 24– 28.6 –34 (± 2.7) × 2.3– 3.4 –4.6 (± 0.5) µm.

Ecology. Specimen collected from a nearly vertical rocky substratum, at 8m depth. Growing over tubes of polychaetes.

Distribution. Known only from its type locality, Isla Santa Rosa.

Etymology. The species name, “ santarositae ” refers to its type locality also called Isla Santa Rosa.

Remarks. Hymedesmia (H.) santarositae sp. nov. differs from all other Hymedesmia species (table 2) by the presence of microstrongyles as microscleres, in addition to arcuate chelae and sigmas.