Plocamione matarani Recinos & Pinheiro & Willenz & Hajdu 2020, sp. nov.

Plocamione matarani sp. nov. (Figure 4, Table 3)

Type locality: Peru, Matarani, Isla Blanca, Arequipa Region.

Holotype. MNRJ 12131, Isla Blanca (17.0088° S– 72.1222° W), Matarani, Peru, 33 m depth, coll. Y. Hooker & U. Zanabria (26/XI/2008).

Diagnosis. Only Plocamione with two categories of subectosomal styles, ectosomal megascleres (styles) always larger than 200 µm, but never as large as 500 µm, echinating acanthostyles in a single category which can be as small as 100 µm, and choanosomal acanthostrongyles, also in a single category, which can reach over 300 µm in length.

Description (Fig. 4A). Thinly encrusting sponge (ca. 1 mm thick), reaching over 15 cm in its largest diameter. Surface uneven, bumpy, with trapped sediment. Oscula not seen. Colour orange in life, beige in preservation.

Skeleton (Fig. 4B). Ectosomal skeleton with large piercing subectosomal styles surrounded by a loose bouquet of smaller ectosomal styles (and possibly toxiform oxeas). Choanosomal skeleton microcionid with architecture constructed over a dense, criss-cross layer of acanthostrongyles; as fibre nodes cored by large, stout styles, and echinated by acanthostyles; on top of which, although seemingly not always, sit the ectosomal bouquets.

Spicules (Figs 4C–P). Ectosomal styles (229–350.3–405 / 2–4– 6 µm): slender, smooth, slightly or markedly curved, tapering gradually, rounded heads and hastate tips (Fig. 4G). Subectosomal styles I (1068–1295.6–1551 / 12– 19.7– 25 µm): large, slender, smooth, slightly curved, tapering gradually, rounded heads and hastate tips (Figs 4 C–D). Subectosomal styles II (263–452.5–689 / 11–19.6– 26 µm): coring fibre nodes, stout, smooth, straight or slightly curved, tapering gradually to sharp apices, rounded heads and hastate tips (Figs 4 E–F, 4H). Choanosomal acanthostrongyles (126–159.8–363 / 5–8.9–11/ 5–7.1– 10 µm, length/ width thicker/ thinner ends): aniso-, curved and slightly sinuous, spined at both ends only, spines conical and rounded heads, the heads vary in width (Figs 4 I–K). Echinating acanthostyles (93–156.7–231 / 8–10.8– 14 µm): echinating fibre nodes, short, straight or slightly curved, spines generally concentrated on their apical half, a few at the base, spines conical or bent as hooks, verrucose at tyle heads, acerate tips (Figs 4 L–P). One toxiform oxea was seen, possibly homologous to the styles of the bouquets.

Bathymetric distribution and ecology. The sponge was sprawling over vertical rocky substrate at 33 m depth, associated to many brachiopods, anthozoans, sea urchin, and another encrusting sponge (yellow coloured).

Distribution. Known only from Isla Blanca, Matarani, in Peru.

Etymology. The species name, matarani, refers to the type locality of the species, Isla Blanca, off Matarani

Remarks. The new species is by far the shallowest ever found in Plocamione, whose previously known shallowest depth was 182 m, off New Zealand (P. ornata). The latter is one of only two species in the genus known from the Pacific, the other being P. pachysclera (from 400 m deep waters off New Caledonia). Plocamione matarani sp. nov. is quite distinct from every other known Plocamione by a series of spicule characteristics highlighted below in a one by one comparison with other congeners (Table 3, including taxonomic authorities). Considerably larger subectosomal spicules set P. dirrhopalina Topsent, 1927 apart from the new species, while considerably smaller set P. hystrix (Ridley & Duncan, 1881; ca. 2000 m depth) and P. ornata apart. Plocamione dirropalina further differs by its much larger ectosomal megascleres, and much smaller acanthostrongyles, aside its deeper than 1200 m Mediterranean habitat. Much smaller acanthostrongyles strengthen P. ornata ’s distinction from the new species, as they do for P. carteri (Ridley & Duncan, 1881) and P. clopetaria (Schmidt, 1870; ca. 490 m depth). Lastly, P. pachysclera, whose originally reported acanthostyles, given their abundance and stoutness, are to be equated with the acanthostrongyles of additional Plocamione spp., can be easily set apart from the new species by this referred stoutness (albeit its shorter ‘plocamiid’ megasclere), as well as the seemingly unique occurrence of two categories of ectosomal megascleres. However, the likelihood that P. pachysclera indeed belongs in Plocamione appears weak to us, starting from its unique bushy-ramose habit, when every other Plocamione has been reported to be encrusting. Lévi & Lévi (1983) chose Raspailia as their preferred assignment for the species, recognizing though that the ectosomal acanthostyles in their species appeared quite distinct from the usual slender styles and oxeas in other Raspailia spp., while mentioning that the stout acanthostyles in the New Caledonian sponge, concentrated at the base, albeit morphologically distinct, suggested affinity with Plocamione. It is possible that this sponge actually belongs in a new genus.