Calyssopora volcano Grischenko & Gordon & Melnik 2018, n. sp.

Calyssopora volcano n. sp.

(Figs 2M, 28–30)

Material examined. Holotype: ZIRAS 1/50714, colony attached to nodule particle, YMG R.V. Yuzhmorgeologiya cruise YMG4–14, Stn 357, 18 January 2016, 14.03237° N, 131.74563° W, 5073 m. Paratype 1: ZIRAS 2/50715, colony attached to nodule particle, YMG R.V. Gelendzhik cruise GLD4–12, Stn 251, 6 April 2013, 12.80823° N, 132.69682° W, 4837 m. Paratype 2: ZIRAS 3/50716, colony attached to nodule particle, YMG R.V. Yuzhmorgeologiya cruise YMG4–14, Stn 325, 20 December 2015, 13.58832° N, 131.68838° W, 5031 m. Additional material: YMG18–01, Stns 7, 15, 24, 33; YMG4–04, Stn 57; YMG4–06, Stns 70, 92, 99, 101, 103; YMG4–07, Stn 139; GLD4–09, Stns 173, 178, 185, 198; GLD4–11, Stn 216; GLD4–12, Stn 271; YMG4–13, Stns 274, 283, 291, 300; YMG4–14, Stns 348, 358. Total specimens examined 27.

Etymology. Anglicized spelling of the Italian vulcano, alluding to the volcano-like gonozooid with its craterlike ooeciopore; used as a noun in apposition.

Description. Colony erect, thickly pedunculate, with autozooidal peristomes radiating outwards around periphery of capitulum (Fig. 28), up to maximum of 22 peristomes in single irregular whorl. Skeletal surface of column with weakly defined ridges and furrows, granular-tubercular (Fig. 29A–C), with sparse pores; surface ultrastructure with irregularly arranged crystallites lacking obvious preferred growth direction (Fig. 29H). Capitulum of submature colony infundibuliform (Fig. 30L), bottom of funnel comprising deep alveolar chambers delimited by trabeculae (Fig. 30O). Additional thin walls cross gaps between adjacent peristomes at colony periphery where additional autozooidal chambers develop to fill vacancies in whorl as colony expands (Figs 29J, 30A, I, O); some of these openings seem to represent adjacent extrazooidal spaces, their openings narrowed in mature colony (Fig. 29B). Increasing calcification reduces openings in calyx center to expanding porous platform that serves as irregular open ‘floor’ to gonozooid(s) (Fig. 30O).

Autozooidal peristomes in single subregular series, skeletal surface like that of column, with sparse, simple pores (Fig. 29G) having irregular outline, tending to be in single longitudinal series on lower side (Fig. 29L). Developing apertures slightly irregular, subrounded (Fig. 29A, K) or having bilateral symmetry, opening obliquely outwards and downwards (Fig. 29L). No spinules or prickles on inner surface of peristome tubes (Fig. 29K, L).

Gonozooid large and capacious (Fig. 28A, B), 1–2 per mature colony (Fig. 28C, D). Floor of gonozooid not discrete and continuous. If solo, gonozooid in center of calyx or to one side, chamber roof sloping upwards to ooeciostome (Fig. 29A–D), resembling volcanic cone in profile, with lateral ridges and furrows and porous cancelli that are mostly on periphery of gonozooid (Fig. 29D); ooeciopore variably elevated, subcircular to suboval (Fig. 28A, C, E). Surface microstructure of gonozooid like that of column and zooidal peristomes, with weak imbrication of irregular crystallites (Fig. 29H).

Ancestrula not seen in isolation, but evidently erect judging from smallest (four-zooid) colony stages seen (Fig. 30A, B). Trabeculae form in center of developing colony to support colony elevation and expansion, with extrazooidal alveolar spaces between trabeculae (Fig. 30A, C, I, K, M, O).

Measurements (mm). Holotype, ZIRAS 1/50714 (Fig. 28A, B): Colony height 1.78; capitulum 2.07 × 1.98; base at substratum 0.85 × 0.93 with narrowest cross-section 0.60 × 0.64; ZL 0.591–0.980 (0.809 ± 0.122); PeL 0.372–0.597 (0.492 ± 0.069); PeD 0.137–0.177 (0.155 ± 0.013); ApL 0.152–0.185 (0.172 ± 0.011); ApW 0.128–0.153 (0.138 ± 0.009). Gonozooid (n = 1): GZL 0.644; GZW 0.817; OsL 0.155; OsW 0.127; OsH 0.138; OpL 0.133; OpW 0.119.

Remarks. Calyssopora volcano n. sp. differs from Calyssopora vasiformis n. sp. (below) in overall form and the number of peristomes, and from Calyssopora clarionensis n. sp., in having volcaniform gonozooids in which the frontal surface rises to a frontally facing ooeciostome with a crater-like ooeciopore. The gonozooid in A. clarionensis is rather more bulging than volcaniform, and the ooeciostome is strongly curved and hood-like.

Dartevellopora granulosa Gordon & Taylor, 2010 was only doubtfully included in Dartevellopora when described. In some respects, it resembles the species of Calyssopora, but differs in that there is a clear differentiation between a smoothly spreading skirt-like base and pustulose erect part of the column. The center of its capitulum is less calyciform than in Calyssopora, comprising a subhorizontal platform with evenly distributed circular pores, unlike the open alveolate and trabecular mesh of Calyssopora. Until fertile colonies of D. granulosa are found, its generic attribution must remain problematic.

Distribution. Recorded from 26 stations within coordinates 12.51953– 14.16490° N, 129.04471– 134.60008° W, at depth range 4672–5149 m.