Hemimycale smaragdina sp. nov.

(Table 2; Figures 2–3)

Diagnosis. Hemimycale occurring in the Pacific with a combination of emerald-green color (in life) and subtylotes to strongyles reaching less than 210 µm in length and up to ca. 3 µm in thickness.

Type locality. San Ambrosio Island, Desventuradas Islands Archipelago, SE Pacific.

Material examined. MNHNCL POR 15018 (holotype), San Ambrosio Island (-26.33634; -79.88571), Desventuradas Islands Archipelago, SE Pacific, 20 m depth, coll. C. F. Gaymer, 21 February 2013 (Station M18; see Friedlander et al. 2016); fragment of the holotype deposited under MNRJ 18626 .

Description. Habit, thinly encrusting, up to 2 mm thick, covering 10 cm × 4 cm in life (Fig. 2A–B); preserved specimen fragmented (Fig. 2C–D). Porefields, roundish to irregular, larger (ca. 1 cm wide) and with low borders (Fig. 2B). Oscules, like small short tubes (1–3 mm in diameter) and scattered on the surface (Fig. 2B). Subectosomal canals, absent. Consistency, delicate. Texture, soft. Color in life, emerald-green (externally and internally), and in ethanol, dark-green. In preserved state, narrow and shallow circular depressions visible on the surface due to the contraction of the porefields and oscules (Fig. 2D).

Skeleton. Plumose, with sinuous bundles of subtylotes (Fig. 3A–B). Subtylotes in bouquets or obliquely arranged beneath the surface. Among the bouquets, embryos up to 75 µm in diameter with smaller spicules than the ones in the sponge body (Fig. 3C). Presence of volcanic dark debris in the ectosomal and choanosomal regions.

Spicules. Megascleres (Table 2): subtylotes to strongyles (Fig. 3D–E), straight and smooth, 114–176.5 (±32.5)– 205/1.8–2.4 (±0.4)–3 µm.

Substrate, depth range and ecology. Volcanic rocks, 20 m depth. The holotype was in the north face of San Ambrosio Island (Desventuradas Islands Archipelago) and carries algae and hydrozoans. Following Friedlander et al. (2016), the north face of San Ambrosio Island is exposed to sunlight and sheltered from the direct impact of waves as well as marked by a barren zone of sea urchins ( Centrostephanus rodgersii A. Agassiz).

Distribution. Southeast Pacific: Desventuradas Islands Archipelago (type locality).

Etymology. The specific epithet smaragdina, used as a noun in apposition, is derived from the Latin word smaragdus (in greek, “smaragdos”) for ‘emerald’, which is the color/hue (emerald-green) of the new species when alive.

Remarks. Only 13 species of Hemimycale are currently known worldwide according to the WPD (de Voogd et al. 2024). Hemimycale smaragdina sp. nov. is distinguished from its congeners by the emerald-green color in combination with smaller subtylotes to strongyles, that reach only up to 205 µm in length and 3 µm in thickness (Table 2). Furthermore, the new species can be easily identified in the field by its characteristic emerald-green color in combination with visible porefields on the surface, differentiating it from other encrusting species occurring in the SE Pacific.

Hemimycale smaragdina sp. nov. represents the fourth record of Hemimycale for the entire Pacific Ocean (Table 2), until very recently devoid of any record at all for this genus. The previously known species came from Galápagos Islands (viz., H. harlequinus Sim-Smith, Hickman & Kelly, 2021 and H. nathani Sim-Smith, Hickman & Kelly, 2021) and California (viz., H. polyboletus Turner & Lonhart, 2023). Of those, only H. nathani has spicules with dimensions that can be comparable to the ones in the new species. However, H. nathani has an orange to yellow color in life and trumpet-shaped porefields. These characters are not present in H. smaragdina sp. nov.

Hemimycale funchalensis Santín & Ribeiro, 2024 (in Santín et al. 2024) and H. viridis (Keller, 1891) also have spicules with dimensions comparable to the ones in H. smaragdina sp. nov. (Table 2). Both species exhibit a dark-green hue and turn to gray when preserved. The new species is emerald-green, turning to dark-green upon preservation. Conspecificity of these three species is rather unlikely biogeographically, as each occurs in a different ocean, viz. H. funchalensis in the eastern Atlantic (Madera Island), H. viridis in the western Indian Ocean (Red Sea and Madagascar) and the new species in the southeast Pacific (Desventuradas Islands). Therefore, we consider H. smaragdina sp. nov. and its emerald-green color to belong to a different species, other than H. funchalensis or H. viridis . It will be interesting to compare the genetics of all three species in the future.