Hemimycale harlequinus Sim-Smith & Hickman & Kelly 2021, sp. nov.

(Fig. 21, Table 6)

Material examined. Holotype — MCCDRS9462, Guy Fawkes Island, 0.515° S, 90.527° W, 15 m, 10 Sep 2003. Paratypes — MCCDRS9461, Guy Fawkes Island, 0.515° S, 90.527° W, 26 m, 26 Jul 2003; MCCDRS9463, Guy Fawkes Island, 0.515° S, 90.527° W, 18 m, 5 Feb 2003. Other material— MCCDRS9465, Rabida Island, 0.406° S, 90.713° W, 14 m, 18 Nov 2003; MCCDRS9458, Cousins Rock, Santiago Island, 0.235° S, 90.574° W, 11 Nov 2003; MCCDRS9459, Daphne Minor Island, 0.394° S, 90.351° W, 17 m, 30 Jan 2004; MCCDRS9460, Gordon Rocks, Santa Cruz Island, 0.567° S, 90.142° W, 24 m, 20 Jul 2003; MCCDRS9457, Cape Marshall, Isabela Island, 0.018° S, 91.205° W, 30 m, 17 Nov 2003; MCCDRS9464, Los Hermanos Islands, 0.867° S, 90.782° W, 9 m, 18 Jan 2003.

Type locality. Guy Fawkes Island.

Habitat and distribution. Collected from Guy Fawkes Island, Gordon Rocks, Daphne Minor Island, Rabida Island; Isabela Island, Santiago Island, Los Hermanos Islands; 9–30 m. Commonly observed from the central archipelago, typically found growing on rock or black coral (Antipathes galapagensis Deichmann, 1941).

Description. Thinly encrusting sponge, base ≤ 15 mm thick, densely covered in trumpet-shaped papillae topped with circular to irregular, areolate porefields. Conspicuous single or septate cylindrical or volcano-shaped oscules, are frequently interspersed between the papillae. Papillae and oscules are delicate and membranous and collapse when preserved. Colour in life variable from cream to pink to orange, colour in ethanol tan (Fig. 21A–D). A pink and cream form occurs where the encrusting base is pink and the areolate porefields are cream (Fig. 21B). Texture of the main body is soft; papillae are brittle when preserved.

Skeleton. No defined ectosomal skeleton. The choanosome contains wispy, plumose tracts of megascleres that fan out into brushes at the surface (Fig. 21E). The choanosome is filled with large cavities and scattered debris, spicule density is low (Fig. 21F). Megascleres are primarily strongyles. Sharply curved sub/tylostyles are present at a much lower abundance. There is no differentiation between the location of the two types of megascleres.

Spicules. Megascleres— Strongyles, slender, occasionally faintly polytylote, with faint, subtylote tips that are often slightly inequiended; 275 (184–332) × 5 (2–8) µm (n = 120) (Fig. 21G & I). Sub/tylostyles, curved with a rounded head and a sharply pointed tip; 286 (181–376) × 6 (4–11) µm (n = 120) (Fig. 21H & J).

Etymology. Named for the variable colouration of the species (Latin nominative singular in apposition).

Remarks. Only seven species of Hemimycale have been described, none of which are from the eastern Pacific. Initially, it was thought that the different coloured specimens might comprise several species, but the spicule complement and skeletal architecture are consistent between specimens. Colour variation is not unprecedented in the genus; the type species, H. columella (Bowerbank, 1874), occurs in a similar colour range of pink, pale orange and bright red.