(Figs 2A–E, 3–5)
‘? Incertae sedis no. 4’ Harmelin & d’Hondt 1982: 13, pl. 4, figs 1–2; d’Hondt & Schopf 1985: 950, pl. 8, fig. 5.
‘Cyclostome indéterminé’ d’Hondt & Schopf 1985: 949, pl. 8, fig. 3.
Material examined. Holotype: ZIRAS 1/50667, colony detached from nodule, YMG R.V. Gelendzhik cruise GLD4–12, Stn 238, 11 March 2013, 13.44587° N, 132.91008° W, 4772 m. Paratype 1: ZIRAS 2/50668, colony detached from nodule, YMG R.V. Yuzhmorgeologiya cruise YMG4–04, Stn 61, 5 September 2005, 13.59717° N, 130.65212° W, 5008 m. Paratype 2: ZIRAS 3/50669, colony detached from nodule, YMG R.V. Gelendzhik cruise GLD4–08, Stn 153, 26 July 2009, 13.15205° N, 133.89166° W, 5014 m. Paratype 3: ZIRAS 4/50670, colony detached from nodule, YMG R.V. Gelendzhik cruise GLD4–12, Stn 259, 10 April 2013, 12.86148° N, 132.82182° W, 4910 m. Paratype 4: ZIRAS 5/50671, colony detached from nodule, YMG R.V. Gelendzhik cruise GLD4–09, Stn 176, 24 December 2010, 12.93062° N, 133.56097° W, 4865 m. Paratype 5: ZIRAS 6/50672, colony attached to nodule particle, YMG R.V. Gelendzhik cruise GLD4–09, Stn 190, 3 January 2011, 13.38432° N, 133.51833° W, 4838 m. Additional material: YMG18–01, Stns 17, 23, 27, 32; YMG4–04, Stns 52, 53, 54, 55; YMG4–06, Stns 65, 68, 73, 85, 94, 96, 105, 106, 110, 114; YMG4–07, Stns 116, 117, 120, 125, 134, 136, 141, 143; GLD4–08, Stns 144, 145, 146, 150, 154, 155, 157, 160, 161, 164; GLD4–09, Stns 165, 166, 169, 170, 173, 174, 181, 185, 193, 194, 197, 199; GLD4–11, Stns 212, 214, 215, 217, 218, 219, 224, 225, 226, 227, 231, 233; GLD4–12, Stns 235, 236, 245, 246, 253, 255, 258, 260, 262, 263, 264, 265, 272; YMG4–13, Stns 275, 276, 282, 285, 289, 292, 293, 295, 305, 308, 310, 319, 321; YMG4–14, Stns 324, 326, 328, 329, 330, 331, 332, 334, 335, 336, 338, 340, 342, 343, 346, 349, 350, 352, 354, 356, 358, 359, 361, 363, 364, 365. Total specimens examined 203.
Etymology. Latin and Greek, helix, a coil or spiral, alluding to the common form of the colony; used as a noun in apposition.
Description. Colony uniserial, semi-erect, white, comprising chain of zooids borne above solid substratum by elongated prop-like supports (Figs 2A–E, 3A–G), typically one (very rarely two) per zooid, body cavity of zooid continuous with that of prop (Fig. 5E). Zooidal chain varied in disposition, either straight and more or less parallel to substratum or often ascending as open helicospiral, with up to 2.5 turns (Fig. 3C) depending on age; many colonies have form somewhat intermediate between these extremes. Branching of uniserial stem uncommon, typically near colony origin, rarely further along stem (Fig. 3E). Maximum colony length or diameter 12.60 mm; maximum colony height 3.74 mm. Most zooids seen in colonies ~24 (holotype; Fig. 3A, C) and 26 (Fig. 2E).
Autozooids comprising proximal and distal components; axial proximal component forms part of continuous uniserial stem of colony, while distal component forms erect peristome of varying length. Frontal peristomial surface typically curving obliquely frontalwards from axial frontal surface; distal peristomial surface forming much sharper angle (up to 90°) with frontal wall of daughter zooid. Autozooidal surface wholly gymnocystal (i.e. exterior-walled), with weak longitudinal and transverse striae or wrinkles (Figs 4B, C, J, K), latter more apparent in zooidal peristomes; at higher magnification exterior surface made up of wall-perpendicular needle-like crystallites (Fig. 4P, Q). Very tiny simple pseudopores occurring sparsely in zooidal walls (Fig. 4O–Q). Peristomial opening circular, very thin-walled (Figs 4J–M), becoming thicker through accretion of additional layers of crystallites. Interior surface of peristomes lined by distally imbricated foliated fabric of wedge-shaped crystallites (Fig. 4N) that tend to be shorter and chunkier in proximal axial walls of zooids, especially around interior openings of pseudopores (Fig. 4D). Zooidal axial and peristomial lengths generally similar, but can be independently variable, with peristomes slightly shorter than, or up to more than twice length of proximal axial portion of zooid (Fig. 3G).
Budding of daughter zooids achieved by development of partition from floor of parent zooid (Fig. 4B, C) that slopes frontalwards under elevating peristomial portion, with completed parent zooids overlapping proximal portion of daughter zooids; thus parts of 2–3 zooidal chambers seen in transverse section of stem (Fig. 4A). In lessattenuated colonies with tight helicospiral form, axis becomes thicker (Fig. 3A, B) and budding sites are condensed.
Prop-like supports elevate colony after its founding. These greatly variable in size and form. Some props have widened (up to three times wider than their mean diameter) bases at their points of contact with substratum. Typically, one prop per autozooid, originating near point where internal partitioning of daughter autozooid takes place (Figs 4A, 5E); sometimes additional prop interpolated in series (e.g. Fig. 3G). Props can be length of peristome or very much longer and almost filiform (Fig. 3B). Short, stumpy props that do not reach substratum appear to represent repaired broken props. Where they encounter substratum, proximal ends of props have short branches that splay out over irregularities (Fig. 5A–C). Tiny sparse pseudopores occur in prop walls (Fig. 5F).
Gonozooid not seen.
Ancestrula erect (Fig. 5G–L). Protoecium short, rounded, squat, imperforate, broader than peristome that emerges from its dome, with scarcely any differentiation in calcification. Peristome typically bent in direction of initial colony growth.
Measurements (mm). Holotype, ZIRAS 1/50667 (Fig. 3A, C): Colony height 3.74, length 2.91, width 2.58 (L × W = helix in frontal view); ZL 1.373–1.918 (1.628 ± 0.181) (n = 8); PrL 0.458–2.443 (1.518 ± 0.999) (n = 3); PrD 0.120–0.186 (0.145 ± 0.035) (n = 3); PeL 0.243–0.442 (0.318 ± 0.067) (n = 8); PeD 0.177–0.186 (0.181 ± 0.003) (n = 4); ApL 0.170–0.178 (0.173 ± 0.003) (n = 4); ApW 0.162–0.170 (0.165 ± 0.004) (n = 4).
Paratype 1, ZIRAS 2/50668 (Fig. 3B): Colony height 3.39, length 6.41, width 4.88 (L × W = size of coil in frontal view); ZL 1.443–2.288 (1.989 ± 0.287) (n = 6); PrL 1.211–3.165 (2.373 ± 0.672) (n = 6); PrD 0.073–0.104 (0.082 ± 0.012) (n = 6); PeL 0.516–0.893 (0.776 ± 0.137) (n = 6); PeD 0.174–0.185 (0.180 ± 0.004) (n = 6); ApL 0.165–0.173 (0.168 ± 0.003) (n = 6); ApW 0.155–0.164 (0.160 ± 0.004) (n = 6).
Paratype 5, ZIRAS 6/50672 (Fig. 3G): Colony height 2.52, length 6.92; ZL 1.823–2.838 (2.261 ± 0.338) (n = 6); PrL 0.628–0.993 (0.834 ± 0.149) (n = 6); PrD 0.083–0.138 (0.108 ± 0.019) (n = 6); PeL 0.924–1.581 (1.214 ± 0.244) (n = 6); PeD 0.178–0.198 (0.190 ± 0.007) (n = 6); ApL 0.173–0.185 (0.180 ± 0.004) (n = 6); ApW 0.161–0.187 (0.174 ± 0.009) (n = 6).
Non-type specimen YMG4–14, Stn 326 (Fig. 5G–I): AnPeD 0.156 (n = 1).
Remarks. In the collections examined for this study, Pandanipora helix n. sp. is represented by 203 colonies, which makes it all the more remarkable that not one bears a gonozooid. One possibility is that it never has gonozooids, but, among living cyclostomes, only species of Cinctiporidae unequivocally lack such structures (Boardman et al. 1992). Insofar as cinctiporids have exceptionally large autozooids, it appears likely that oogenesis and embryo formation takes place within them (see Schwaha et al. 2018). Zooidal size in Pandanipora helix n. sp. is not exceptional and there seems no reason that a peristomial gonozooid like that in Peristomatopora should not be present. Gonozooids were also notably absent from most colonies in the large collection of Antarctic cyclostomes studied by Ostrovsky & Taylor (1996) and Ostrovsky (1998a). What is striking is that non-fertile colonies otherwise were of the same size as those bearing gonozooids, thus supporting the idea that incubation chambers will develop only if a colony is fertilized by alien sperm (Ryland 1996). In other words, sperm limitation may be a reason for the lack of gonozooids in many colonies. Experiments conducted on two cyclostome species by Jenkins et al. (2015) showed restrained female investment in the absence of mating opportunity; either the production of female zooids and progeny is much reduced in reproductive isolation, or development of gonozooids begins, but ceases further development in the absence of mating opportunity. Another possibility in Pandanipora helix is that incubation chambers are produced but are shed after release of embryos. Alternatively, gonozooids may be very fragile, and lost during the process of collection from the seafloor and subsequent processing of the polymetallic nodules.
Harmelin & d’Hondt (1982) illustrated an unnamed species from 3392–3429 m depth off the coast of Surinam that conforms to the characters of the genus. D’Hondt & Schopf (1985) reported this same species again from 943 m off Recife and 3459–3783 m on the equatorial mid-Atlantic Ridge. What they interpreted as ‘épines autozoéciales’ appear in their illustrations to be broken prop-like supports, of proportionately smaller diameter than in P. helix n. sp. Even closer to P. helix in appearance, and almost certainly conspecific, was a colony from 6065–6079 m in the central North Pacific north of the Hawaiian seamount chain. Based on this evidence, it appears likely that P. helix n. sp. may be fairly widespread in the abyssal north Central Pacific, with an undescribed sibling species in the abyssal tropical Atlantic.
Our material shows up to five brown bodies retained in zooidal chambers (Fig. 5E), indicating multiple regression and regeneration of polypides.
Distribution. Recorded from 118 stations within coordinates 12.26676– 14.64985° N, 129.08802– 134.67060° W, at depth range 4677–5280 m.