Deltocyathus cameratus Cairns, 1999

5. Deltocyathus cameratus Cairns, 1999 View in CoL

( Figs. 4A–C View FIGURE 4 )

Deltocyathus cameratus Cairns, 1999: 95 View in CoL , figs. 12G–I, 13A; 2004: 280.— Kitahara & Cairns 2009: 244–245 View Cited Treatment , fig. 1I.—Kitahara et al. 2013: 206, fig. 2.— Kitahara & Cairns 2021.

Material examined: One specimen ( NCPOR/HYD-CIR/0027 ), Central Indian Ridge : R/V MGS Sagar, stn. MGS35A_D11, 23° 11' 25'' S; 69° 32' 51''E, 2007 m, 15 th April 2020 GoogleMaps .

Description: Corallum shaped as a shallow bowl, with a slightly convex base, 10.8 mm in calicular diameter and 4.2 mm in height. Calice circular with a jagged margin. C3 and adjacent pair of C4 project outward as small triangular to rectangular lancets. Intercostal grooves prominent at calicular edge and coarsely pointed spines; intercostals grooves between C3 and C4 shallower than others; C1 and C2 start at centre of the base; C4 smaller compared with C3. Conical shape base. Corallum white.

Septa hexamerally arranged in four complete cycles (S1>S2>S4>S3). S1 only independent septa, 1.5 mm exsert, and reach 1/2 distance to columella. Each S1 possesses a lamellar paliform lobe that encircles the columella, creating the first palar crown. S2 less wide and exsert than S1. S3 smallest septa but have the tallest pali. Each S3 fuses to flanking S 2 in acute lamellar structure ( Fig. 4A View FIGURE 4 ). S4 less exsert but slightly wider than S3. Each pair of S4 fuses flanked S3 with a porous lamella that extend lower in theca almost to columella. All septa uniformly thin and have straight axial margins. Every septa and palar face roughly granulated. P1-3 uniform in width, and separated from their corresponding septa by wide notches. Axial edges of P1 and P2 merge to columella, even though P2 rise slightly higher in fossa. Axial edges of every pair of P3 strongly fused to their adjacent P2; this fusion being imperforate and reaching as high as S3–P3 notch. Fossa shallow to nonextant with a well-developed papillose columella formed by 10–15 robust and granular rods ( Figs. 4A–C View FIGURE 4 ).

Remarks: In comparison to the other four non-spined Deltocyathus species as described by Kitahara & Cairns (2009), the CIR specimen has well-developed lamellar fusions of the S4 to P3 and P3 to P2, a lancetted calicular margin, and the corallum is divided into 24 elliptical chambers.

Substrate type: The specimen collected from the medium-grained basalt covered by a thick Fe-Mn crust in the ridge system indicates a geological environment typical of mid-ocean ridges.

Distribution: Previously documented in the Pacific Ocean, this species has been reported from the Wallis and Futuna region at depths ranging from 707 to 777 m ( Kitahara & Cairns 2009), in the Vanuatu region at depths of 305 to 1010 m ( Cairns 1999), and other various locations, including the Lord Howe Rise, Elizabeth Reef, and Britannia at depths of 512 to 1175 m ( Cairns 2004). It has also been recorded in Erromango and Malakula at depths ranging from 419 to 1078 m ( Cairns 2004). The new record reported herein extends its distribution to the CIR at a depth of 2007 m.