Trochocyathus (Trochocyathus) patelliformis Cairns, 1999

4. Trochocyathus (Trochocyathus) patelliformis Cairns, 1999 View in CoL

( Figs. 3D–F View FIGURE 3 )

Trochocyathus patelliformis Cairns, 1999: 82–83 View in CoL , figs. 8G and 9A–C.

Material examined: One specimen ( NCPOR/HYD-CIR/0029 ), Central Indian Ridge : R/V MGS Sagar, stn. MGS35A_BD9, 23° 10' 01'' S, 69° 31' 49'' E, 2103 m, 20 th April 2020 GoogleMaps .

Description: Corallum short and patelliform in shape; base attached to a solid substrate ( Fig. 3D View FIGURE 3 ). Examined specimen 15 x 13.2 mm in calicular diameter, 3.3 mm in pedicel diameter, 7.0 mm in height; costae distinct, rounded, and covered with fine, spiny granules ( Fig. 3F View FIGURE 3 ). At lower corallum intercostal grooves as wide as costae but deeper and broader near the calicular edge. Corallum white.

Septa hexamerally arranged in 5 incomplete cycles according to the formula: S1–S2>S3>S4>S5. Septa cycle contains 12 pairs of inserted S5 half-systems with two pairs of S5 and two half-systems having one pair of S5; for a total of 69 septa ( Fig. 3E View FIGURE 3 ). S1–2 relatively large and exsert, and having axial edges straight and granular faces. Septal faces covered with spiny granules. S1 quite large, each having a straight axial edge that meet columella, moderately sinuous peripheral edge; separated from the similar septum by a small notch. S3–S4 less exsert. P2–P4 about 1.8 mm wide. Each cycle becomes increasingly more concave from columella and rises slightly higher in fossa. Fossa shallow. Columella composed of several finely granulated massive papillae fused into an irregular, elongated mass ( Figs. 3D, E View FIGURE 3 ).

Remarks: Trochocyathus (T.) patelliformis is unique within the genus in having a patellate-shaped corallum with P1 being significantly broader than the higher cycle pali, and finely spinose costae. However, the Central Indian Ridge (CIR) specimen differs slightly in that it has a circular shape of the columella, whereas the columella in the specimen described by Cairns (1999) is elongated.

Substrate type: The specimen collected from gabbro, ultramafic rock, and oolitic sand in the ridge system indicates a complex geological environment.

Distribution: Previously recorded in the Hawaiian Islands, the South Pacific, and the Vanuatu region at depths of 1010–1750 m and in Espíritu Santo between 1210–1250 m ( Cairns 1999). The distribution of this species is now extended to include the CIR at a depth of 2103 m.