Calyptotheca triquetra Harmer 1957

Calyptotheca triquetra (Harmer, 1957)

(Figure 6, Table 6)

Schizomavella triquetra Harmer, 1957: 1027, pl. 66, figs 1–3; Ristedt & Hillmer 1985: 137, pl. 3, fig. 12. Metroperiella triquetra: Liu et al. 2001: 582, pl. 46, figs 1, 2.

Calyptotheca triquetra: Tilbrook 2006: 227, pl. 49E, F.

Material examined. Bryomol Reef: MTQ G26473, 16°27.343' S, 139°52.712' E, 41 m.

GBR: MTQ G25470, G25418, north Heron Island, Tenements 1, 23°25'59.124" S, 151°55'37.38" E, 20 November 2010, coll. K. Tilbrook.

Description. Colony encrusting. Autozooids irregularly hexagonal (c. 0.4 × 0.3 mm; Table 6). Frontal shield convex, pseudopores elongate-oval to slit-like (average 27 per zooid), appearing to radiate from centre of zooid, with long axis directed toward medial avicularium, small and widely spaced, not extending to zooid borders. Zooid borders marked by distinct, raised rims and irregularly spaced, elongate areolar-septular pores. Lateral walls between zooids with uniporous septula.

Primary orifice pyriform, as wide as long (c. 0.08 × 0.08 mm), broadest distally, anter rounded, lunula extending along lateral margins, appearing continuous with condyles, poster with semicircular sinus, condyles rounded, serrate.

Each zooid with a single, oval, suboral, medial avicularium on an inflated cystid, directed proximolaterally, mandible triangular, curved basally. Ovicells not present.

Mean Standard Range N Deviation

Zooid length 0.363 0.049 0.32–0.43 5 Zooid width 0.271 0.050 0.21–0.32 5 Orifice length 0.085 0.008 0.08–0.10 5 Orifice width 0.085 0.009 0.07–0.09 5 Adventitious avicularium length 0.049 0.003 0.046–0.053 4 Adventitious avicularium width 0.032 0.003 0.028–0.035 4 Diameter of perforations in frontal shield 0.006 0.001 0.004–0.009 10 Number of perforations in frontal shield 27.3 5.271 19–38 10 Remarks. Calyptotheca triquetra is distinguished by its suboral avicularium with triangular, basally curved mandible and pyriform orifice with serrate condyles. It resembles C. lardil n. sp. at low magnification as both have suboral, medial avicularia on a swollen cystid, but the avicularium of C. lardil n. sp. is subrounded (approximately round), with a protuberance on the proximal side of the cystid.

Harmer (1957) described the ovicells of Calyptotheca triquetra as large and globose, and Tilbrook (2006, p. 227, pl. 49F) described them as partially immersed, with radiating pores like those of the frontal shield, sometimes with a central umbo. Both Harmer (1957) and Tilbrook (2006) noted that the distinctive pattern of radiating pseudopores in Calyptotheca triquetra becomes partially obscured with secondary calcification and increased thickening of the frontal shield, which may account for the Solomon Islands specimens of Tilbrook (2006) appearing to have lessinflated cystids, but it was noted that some were more inflated and basally curved than others.

Distribution. Calyptotheca triquetra occurs from Southeast Asia to Melanesia, with records from East Timor and Flores, Indonesia (Harmer 1957), the Philippines (Ristedt & Hillmer 1985), China (Liu et al. 2001), Heron Island, GBR, the Solomon Islands (Tilbrook 2006) and the GoC. The single, small (c. 2 mm diameter), infertile colony from the GoC, was encrusting the underside of Steginoporella sp. at 41 m depth.