Chalinula tamoiensis, Luna & Bispo & Esteves, 2025

Chalinula tamoiensis sp. nov.

( Tabs. 1, 2; Fig. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Diagnosis. Chalinula encrusting, purple or bright pink coloured in life. Oscula spread and flush with the surface in encrusting specimens and elevated on volcaniform mounds, with a slightly raised oscular rim in thickly encrusting specimens. Surface translucent, showing conspicuously perforated choanosome. Oxeas shorter than 100 µm.

Material examined. Holotype: MNRJ 29853 View Materials —Crena beach (23º08’13.96” S, 44º09’19.84” W), 1 m depth, Ilha Grande, Angra dos Reis, Rio de Janeiro state, Brazil, coll. L. Huguenin and E.L. Esteves, November 29, 2018. A fragment and slides of the holotype were deposited as UERJPOR 422 GoogleMaps . Paratypes: UERJPOR 38— Abraão Island (23º06’52.74” S, 44º09’57.56” W), 2 m depth, Ilha Grande Bay, Angra dos Reis, Rio de Janeiro state, Brazil, coll. E.L. Esteves, May 09, 2013 GoogleMaps ; UERJPOR 505— Jorge Grego Island (23º13’12” S, 44º09’14” W), 12 m depth, Rio de Janeiro state, Brazil, colls. E.L. Esteves and B. Magna, October 18, 2022 GoogleMaps .

Description. Holotype: Thinly encrusting, approximately 2 mm by 5 cm wide, 1 mm thick after fixation in ethanol. Oscula circular to elliptical, 0.9–2.6 mm in diameter, with slightly raised collar rims, 0.3–1.6 mm high, at the top of numerous low volcaniform mounds. Consistency soft, compressible, fragile. Surface translucent, showing conspicuously perforated choanosome. Colour vivid pink in life, beige in ethanol. Paratypes: Thinly to thickly encrusting, 20–50 mm wide, less than 1 mm thick. Surface even, discreetly microhispid, translucent, with subdermal channels. Oscules circular, flush with the surface, 0.6–1.3 mm wide. Consistency soft, fragile. Colour purple (UERJPOR 38) to dark pink in life (UERJPOR 505) and white or brown after fixation in ethanol (UERJPOR 38 and 505, respectively).

Skeleton. Holotype: Ectosomal skeleton absent. Choanosomal skeleton is an irregular reticulation of spongin fibres 27–60 µm in diameter, cored by a spicule in cross section. The inner choanosome is a reticulation of primary ascending fibres 94–120 µm thick, composing meshes 88–288 µm wide. The few discernible secondary fibres are 1–3 spicules long and 18–20 µm thick. Spongin content decreases suddenly in the upper portion of the choanosome, next to the surface, forming a marked zone 1000 µm thick. In this region spongin becomes sparse and nodal, appearing as a denser but still irregular reticulation with a few poorly defined paucispicular primary lines 7–10 µm thick, interconnected irregularly by unispicular secondary lines 2–5 µm thick. Paratypes: Ectosomal skeleton absent. Choanosomal skeleton uniformly anisotropic, formed by ascending parallel paucispicular primary fibres distant 64–105 µm apart, 5–10 µm thick, exceptionally 13 µm thick, interconnected by slightly differentiated secondary lines 2–5 µm thick, with one to three spicules in length, aligned, forming meshes 95–261 µm wide. Spongin scarce, coating spicules.

Spicules. Oxeas fusiform, straight, or slightly curved, with a wide variation in the ends, being mucronate, acerate, hastate or telescopic ( Tab. 1).

Ecology and distribution. Specimens were found in cryptic and exposed areas, encrusting rocky overhangs and slopes at a depth varying from less than one metre to 12 metres. The new species is known only from its type locality, Crena beach ( Ilha Grande ) Jorge Grego and Abraão islands, at the nearby of Ilha Grande, Rio de Janeiro state, Southeast Brazil .

Etymology. The new species was named “tamoiensis ” in recognition of the Area de Proteção Ambiental Tamoios (APA Tamoios) and the Estação Ecológica Tamoios (ESEC Tamoios) for marine biodiversity conservation in Rio de Janeiro state.

Remarks. Chalinula tamoiensis sp. nov. resembles Chalinula nematifera , from the Central Western Pacific and Chalinula molitba from the Tropical Western Atlantic concerning its thinly encrusting growth form and other features. The skeleton is quite variable in Chalinula , so it is impossible or difficult to infer reliable characters for species distinction ( Tab. 2; cf. de Weerdt 2000; de Weerdt 2022). Hence, we rely on the growth form, size and shape of oxeas and other small traits to diagnose the new species. Chalinula nematifera was characterised by Rossi et al. (2015) as a “mauve-coloured coat and white strands covering coral substrate”. De Laubenfels (1954) described it as a “bright purple of a peculiar transparent or translucent nature”. Chalinula nematifera usually covers all over a ramified coral, assuming a thinly encrusting growth habit ( de Laubenfels 1954; Rossi et al., 2015). Chalinula tamoiensis sp. nov. has no obvious white strands on its surface, but it has translucent subdermal channels described by de Laubenfels (1954) which might eventually resemble the characteristic white strands described by Rossi et al. (2015). Even though, it is not the slime described for C. nematifera by de Laubenfels (1954).

The wide variability exhibited by Chalinula molitba approaches this species even more to Chalinula tamoiensis sp. nov., including the purple colour in life, a thinly to thickly encrusting habit, and a skeleton composed of variable amount of spongin and oxeas with similar size range ( de Weerdt 2002). However, Chalinula tamoiensis sp. nov. is never tubular or cushion shaped as commonly observed in the Caribbean populations of the former species. Contrastingly, oscules are positioned on the top of conspicuous volcaniform projections of the holotype of Chalinula tamoiensis sp. nov. or flush with the surface. All other features observed in Chalinula tamoiensis sp. nov. are shared with Chalinula molitba , including the presence of acerate or hastate oxeas with stepped or sharply pointed ends ( de Weerdt 2000, 2002).

The remaining species have more elaborate growth forms, distinct colour patterns or longer oxeas (over 100 µm), then diverging greatly from the new species ( Tab. 2). Chalinula crassiloba (Lamarck, 1814) and Chalinula finitima ( Schmidt, 1870) weren’t discussed, because both species are unrecognizable.