Calyptotheca churro n. sp.

(Fig. 5, Table 3)

Material examined. Holotype: MTQ G26521, washed up on Shark Beach, Heron Island, GBR, 23°26.6039' S, 151°55.1293’ E, 12 November 2010, attached to brown seaweed, coll. P. Bock.

Paratype: MTQ G26525, same data as for holotype.

Etymology. The epithet is taken from the Spanish churro, meaning fritter, specifically a fried dough pastry of Spanish-Portuguese origin, for the appearance of the suboral umbo.

Description. Colony encrusting, unilaminar; autozooids rectangular to irregularly polygonal (c. 0.4 x 0.3 mm; Table 3); frontal shield flattened, pseudopores rounded, sparsely distributed, (average 15 per zooid), often absent proximally; nodular thickening forming thick ridges across frontal shield, most pronounced proximal to orifice; younger zooids flatter with less developed nodules; interzooidal boundaries marked by thin raised lines of calcification. Kenozooids occasionally replacing autozooids, lacking orifice, with or without pseudopores, adventitious avicularia and nodular thickening.

Primary orifice wider than long (c. 0.11 x 0.14 mm); lunula extending laterally, continuous with condyles; sinus a wide shallow arc; condyles small, rounded, not serrate; suboral umbo continuous with nodular ridges across frontal shield, less developed in younger zooids.

Adventitious avicularia small, oval to rounded-subtriangular (c. 0.06 x 0.05 mm), marginal, in one or both distal angles and sometimes in proximal angles or absent; directed mediofrontally; proximal opesia semi-elliptical, rostral foramen semicircular, crossbar complete. Vicarious avicularia absent.

Ooecium prominent, with distinct nodular thickening, wider than long (c. 0.3 x 0.35 mm); pseudopores of similar size but in greater density than those of frontal shield, with cormidial secondary calcification; orifice dimorphism present, ovicellate orifice wider than autozooid orifice (c. 0.16 vs 0.13 mm); suboral umbo prominent, with multiple ridges and blunt apex, extending as high or higher than ovicell.

Remarks. Calyptotheca churro n. sp. is distinguished by pronounced nodular thickening on the frontal shields and ooecia and prominent umbones, especially on ovicellate zooids. The species belongs to the C. wasinensis subgroup with which it shares numerous oval, marginal adventitious avicularia and suboral ridges or umbones. But no members of the group share the pronounced nodular thickening and suboral umbo of C. churro n. sp.

Calyptotheca churro n. sp. most resembles C. wasinensis in having similar dimensions of the primary orifice (though C. churro n. sp. is more oval, c. 0.11 x 0.14 vs 0.11 x 0.12 mm), smooth condyles and a distinct suboral umbo that is more pronounced on ovicellate zooids, and a lack of vicarious avicularia (see Cumming & Tilbrook 2014). Calyptotheca wasinensis does not have the pronounced nodular thickening on frontal shields and ooecia, has less-prominent umbones, and a distinct growth form of foliaceous, anastomosing bilaminar sheets.

Apart from lacking the pronounced nodular thickening and suboral umbones of C. churro n. sp., C. conica and C. wulguru n. sp. differ in growth form and in having vicarious avicularia. Calyptotheca nivea and C. porelliformis have foliaceous growth forms and larger autozooids (Hayward & Cook 1983, p. 72–73) and C. fossulata has zooids that are twice as large [(NHMUK 2014a,b; c. 0.42 x 0.26 vs 0.80 x 0.53 mm], no suboral umbo and no cormidial secondary calcification (Harmer 1957, p. 1020).

Distribution. Calyptotheca churro n. sp. is known only from specimens washed up on Shark Beach, on the eastern side of Heron Island, attached to brown seaweed, and the precise locality of origin is therefore uncertain.