Anyuta anastema Grischenko & Gordon & Melnik 2018, n. sp.

Anyuta anastema n. sp.

(Figs 2N, O, 39–41, 53)

Material examined. Holotype: ZIRAS 1/50718, colony detached from nodule, YMG R.V. Gelendzhik cruise GLD4–09, Stn 180, 26 December 2010, 13.03863° N, 133.39428° W, 4919 m. Paratype: NIWA 127725, colony detached from nodule, YMG R.V. Yuzhmorgeologiya cruise YMG4–14, Stn 359, 19 January 2016, 14.08687° N, 131.78558° W, 5122 m. Additional material: YMG18–01, Stn 29; YMG4–06, Stn 71; YMG4–07, Stns 119, 133; GLD4–08, Stn 144; GLD4–11, Stn 227; YMG4–13, Stns 281, 283; YMG4–14, Stns 338, 360. Total specimens examined 12, two (the largest) with dimorphic zooids.

Etymology. Greek, anastema, height, tallness, alluding to the elevated form of the colony with the branches lifted up, used as a noun in apposition.

Description. Colony erect, pedunculate and subcalyciform, with outwardly flaring capitulum of short branches (Fig. 39A, B). Stalk (column) cylindrical, tapering proximally before expanding to form circular disk (Fig. 39C, D). Branches of type colony disposed more or less in two clusters, each comprising two fascicles of zooids with associated structures. Length of outwardly inclined branches shorter than stalk. All surfaces interior-walled, with variably imbricating platy microstructure or the plate-like crystalline ‘tablets’ commonly irregular and less angular (Fig. 40C).

Autozooidal tubes numbering 4–5 in each of the fascicles, the tubes indicated by their entire, round peristomial rims (Figs 39C, D, 40D–G, I, 41A, E, I). Exterior skeletal surface of peristomial walls minutely irregular and uneven (Fig. 40B, G), lightly textured, with variable expression of partial longitudinal and/or transverse ridges, striae and convexities. Pores simple, open, of variable shape, sparse. Peristomial rim even or slightly uneven, smooth or minutely granular. Skeletal ultrastructure of interior surface of peristomes similar to that of exterior but smoother and crystallites less discrete; no spinules or pustules. CT scans reveal that interzooidal communication pores are very sparse (Fig. 53A, B).

Center of sides of capitulum with alveolar/kenozooidal chambers (Figs 39A, 40A, 41I, M, 53A). Alveoli forming as low walls, typically arcuate, on upper surfaces. As these walls grow, the extrazooidal cavities they enclose become deeper, cupuliform, and kenozooid-like, filling in spaces between autozooidal peristomes, sometimes in stepwise series. Some alveoli very elongate, extending up frontal longitudinal faces of autozooidal peristomes (Figs 39A, 40A) and abfrontally as flattened alveoli/kenozooids (Fig. 53A).

Stalk with subparallel longitudinal ridges separating furrows in which are simple communication pores in generally linear series; ridges flare outward to circular base, giving appearance of pleated skirt (Fig. 40J). CT scans reveal c. 18 highly elongate-triangular kenozooidal chambers in basal part of stalk; these wider basally, acicular distally, surrounding ancestrular protoecium in palisade arrangement (Fig. 53D, E); these lacking porous communications with neighbors or exterior colony surface.

In autozooidal clusters of mature colonies are smaller-diameter tubes with their openings encircled by subhorizontal subcircular flanges (Figs 39A, B, D, 40A, B, D–I), interpreted as gonozooids. Peristomial rim of smaller tubes somewhat inclined over opening (inferred ooeciopore), slightly reducing its diameter (Fig. 40K). Encircling flange white, suggestive of different type of carbonate from rest of colony; a ring of tiny perforations around inner edge of flange against side of inferred ooeciostome (Fig. 40K, L).

Ancestrular zooid not seen in isolation; earliest growth stage encountered comprising three zooids (Fig. 41A–D)—erect ancestrular peristome flanked laterofrontally by pair of daughter zooids budded from its base and concealing it frontally, its abfrontal surface coarsely ridged, with sparse pores. Peristomial tubes of ancestrular zooid and two daughters elongating and increasing in height and wall thickness. Developing colony becoming vasiform (Fig. 41J–L, N–P); budding of additional zooids from distal abfrontal parts of autozooids, with ~3 walls forming sides of each bud (Fig. 41I, M). Developing colony stem typically with longitudinal ridges and alveolar furrows, these less obvious with secondary calcification.

Measurements (mm). Holotype, ZIRAS 1/50718 (Figs 39–40): Colony height 4.41; capitulum 3.28 × 2.80; base 1.03 × 0.95; stalk height 2.78; narrowest diameter 0.40 × 0.34; ZL 0.873–1.460 (1.147 ± 0.204); PeL 0.330–0.565 (0.448 ± 0.076); PeD 0.231–0.248 (0.241 ± 0.006); ApL 0.210–0.243 (0.228 ± 0.009); ApW 0.193–0.218 (0.202 ± 0.008). Dimorphic zooids (n = 4): GZH 0.152–0.211 (0.181 ± 0.024); GZD 0.251–0.325 (0.271 ± 0.036); GZFD 0.181–0.199 (0.188 ± 0.007); OpD 0.091–0.101 (0.094 ± 0.007).

Remarks. Anyuta anastema n. gen., n. sp. is represented in the Russian-sector collection by twelve specimens. The capitulum of the smaller of the two largest colonies is skewed and less symmetrical than in the holotype colony and the alveoli are more open and elongate.

Distribution. Recorded from 12 stations within coordinates 12.55602– 14.32132° N, 129.11345– 134.51190° W, at depth range 4690–5213 m.