Plicatellopsis expansa (Thiele, 1905)

(Figure 7, Table 7)

Synonyms. Plicatella expansa Thiele, 1905: 427–428 . Fig. 21, 48a–c. Plicatellopsis expansa (Thiele, 1905): Burton, 1932: 332, Fig. 36.

Type locality. Iquique, Chile (20°12′0″S 70°10′0″W) .

Material examined. Fourteen specimens. MNRJ 11247 and MNRJ 11248, Grano de Oro, Pucusana, Lima (12°29′29.10′′S 76°47′58.10′′W), 10 m depth, coll. Y. Hooker, E. Hajdu & Ph. Willenz, 20.IX.2007 . MNRJ 12151 and MNRJ 12152, Blanca Island, Matarani, Arequipa (17°00′31.50″S 72°07′19.90″W), 20–45 m depth, coll. Y. Hooker, U. Zanabria & Ph. Willenz, 28.XI.2008 . MNRJ 12868 and MNRJ 12873, San Gallán Island, Paracas, Ica (13°50′19.20″S 76°28′19.20″W), 14.9 m and 21.3 m depth, respectively, coll. Y. Hooker & F. Azevedo, 14.XII.2008 . UCSUR 07-000001, Bajada Huamán, Pucusana, Lima (12°28′13.40″S 76°47′28.24″W), 14–16 m depth, coll. A. Indacochea & B. Cóndor-Luján, 05.II.2010 . UCSUR 07-000036, Station P 05, Pachacamac Islands, Lima (12°17′31.45″S 76°54′17.78″W), 15 m depth, coll. B. Cóndor-Luján, 27. V.2018. UCSUR 07-000037 and UCSUR 07-000056, Station P 03, Pachacamac Islands, Lima (12°18′15.05″S 76°53″47.98″W), 15 m depth, coll. B. Moreno, 26.V.2018 and 03.III.2019 , respectively. UCSUR 07-000042, Station A 03, Asia Island, Cañete, Lima (12°46′58.51″S 76°37′18.40″W), 10 m depth, coll. B. Moreno, 17.VIII.2018 . UCSUR 07-000055 and UCSUR 07-000060, Station P 04, Pachacamac Islands, Lima (12°17′46.46″S 76°54′20.04″W), 15 m depth, coll. B. Moreno, 04.III.2019 . UCSUR 07-000066, La Vuelta, Pucusana, Lima (12°28′01.89″S 76°47′55.36″W), 30 m depth, coll. D. Cuba, 29. V.2019.

Description. Massive with rounded to elongated lobes that can form branches (resembling hand gloves). The largest specimen collected (UCSUR 07-000060) is 8.8 x 6.1 x 4.8 cm (length x width x height). Small oscula (diam. ≤ 2 mm) scattered or arranged in rows on the surface, some on the top or sides of the branches. Smooth surface that may or may not be velvety. Soft texture and consistency compressible.

Colour. Bright to dark yellow alive (Fig. 7A, B) and dirty white or light beige to beige in ethanol. Specimens from Blanca Island (MNRJ 12151 and 12152) were partially covered by a thin film of red macroalgae which gave them an orange appearance (Fig. 7C).

Skeleton. Ectosomal skeleton, a palisade of small subtylostyles, which can give the surface a velvety appearance or not, depending on the density of spicules. Extra-axial skeleton, bundles of larger subtylostyles. Axial skeleton, composed of tracts of large subtylostyles loosely arranged (Fig. 7D). Abundant spongin.

Spicules. Megascleres. Subtylostyles I, large, choanosomal, slender, almost straight and few slightly curved, and with sharp apex (350–870 x 5–20 μm, Fig. 7E, Table 7). Subtylostyles II, small, ectosomal, slender, straight or slightly bent and with sharp apex (130–452 x 2–9 μm, Fig. 7F, Table 7). Tyles are weakly pronounced (I: 5–15, II: 2.5–8.8 μm; Fig. 7G, H).

Ecology. This species occurs on rocky substrates, mostly found in light protected habitats such as crevices or roofs or growing on vertical walls (MNRJ 12873). It was found associated with red macroalgae, bryozoans, cnidarian polyps, sea anemones (Anthotoe chilensis), echinoids ( Arbacia spatuligera), brachiopods ( Discinisca lamellosa), hermit crabs and nudibranchs (eggs and adults of Okenia lunia, Phidiana lottini, Flabellina cf. cerverai). Some small crustaceans were observed near or inside the oscula of MNRJ 12873.

Geographical and bathymetrical distributions. SE Pacific: North Chile (Iquique, Thiele 1905), central (Pucusana, Pachacamac and Asia Islands, 12° S) and southern Peru (San Gallán and Blanca Islands, 13 and 17° S, respectively, this study). MEOW in Peru: Humboldtian ecoregion (Spalding et al. 2007). Subtidal: from 10 to 45 m depth (Thiele 1905, this study).

Remarks. The analysed specimens from Peru mostly match the original description of P. expansa from Iquique (Chile, 30 m depth, Thiele 1905) in skeleton organisation and composition, and spicule sizes (Table 7). No detailed information of the external morphology was provided in the original description; thus, herein, we describe the colour alive (yellow) and habitus (branched with rounded lobes) of this species. It is important to mention that no other record of P. expansa was found in the literature but that of Gerasimova et al. (2008) who highlighted the presence of styles in the skeleton of the holotype material.