Pyriporoides circularis Gordon 1989

Pyriporoides circularis (Gordon, 1989)

(Figs 3–5)

Daisyella circularis Gordon, 1989: 1327, figs 3C, D. Pyriporoides circularis: Gordon et al. 2009: 289.

Material examined. Holotype: NIWA 724 (H-537), NIC Wellington, Stn F 127, 49°22.0’ S, 176°16.0’ E, 1280 m, NE Campbell Plateau, 28 January 1965. Other material: NIWA 23442, 95604, Stn TAN 0306 /5, 51.035° S, 164.6072° E, 973–990 m, Christable Seamount, 14 April 2003; NIWA 95680, Stn T 39, 49.5033° S, 178.7433° E, 995 m, N of Antipodes Island, 14 March 1981; NIWA 98144, Stn S 45, 54.025° S, 171.075° E, 1262 m, SE margin of Campbell Plateau, 21 September 1978.

Redescription. Colony comprising encrusting uniserial runners. Autozooids mostly with circular, sometimes oval, dilatation, with abruptly produced long filiform cauda that is mostly longer than the dilatation, often several times so [DL 443–589 (506); CL 521–1067 (741); DW 322–500 (415); CW 39]. Each zooid with two pairs of lateral pore-chambers and one mid-distally; mid-distal pore-chamber opening variable, ranging from an obvious transverse slit to a tiny hole in the same colony. Daughter zooids produced from two, three, or all four (or none) of the lateral pore-chambers, total colony spread c. 20 mm. Gymnocyst encircling entire autozooid, proximally and laterally extensive, narrowest distally, sloping to substratum. Opesia and cryptocystal shelf surrounded by a raised broadly oval cryptocystal rim, mostly of equal height throughout but sometimes a little higher proximally, which has minute parallel ridges on its edge, these merging into the granulations on its inner face and on the broad flat cryptocystal shelf; this shelf continuing around entire opesia, narrowing distad, steeper and smooth at distal end [CrL 232–367 (316); CrW 233–289 (258)]. Opesia a little broader distally, otherwise more or less dumbbellshaped, constricted just distal of midlength by smooth rounded projections; lower edge of distal opesial rim more or less straight, its middle part typically produced shortly downwards; proximal opesial rim gently rounded or semi-straight, typically obliquely so [OpL 132–178 (160)]. Operculum flap-like, occupying area of opesia distal to constriction. Articulated pericryptocystal spines 8–14 in number, all more or less erect, the spine bases in the proximal half tending to indent the cryptocystal rim. Additional gymnocystal spines common or absent, ranging from 0–15 in number. No avicularia. Ooecium about as long as wide, smooth-surfaced, with a small triangular exposure of granular endooecium proximofrontally, sometimes on a short carina, with a tiny central foramen; ooecial opening not closed by zooidal operculum [OoL 183–233 (213); OoW 188–228 (199)]. Ooecial kenozooid either wholly concealed from frontal view or, in the same colony, projecting a short distance around the base, smooth-surfaced or with a short articulated spine. Occasional kenozooids forming within the linear chains of zooids. Ancestrula not seen.

Remarks. Additional material discovered since the first description of the species has shed light on the ooecium, previously unknown, and has highlighted unexpected variation in spine number, especially on the laterally sloping gymnocyst. Gordon (1989) reported a total of 28 spines, based on his figure 3D. Re-examination of the holotype has shown that two circular impressions on the cryptocystal rim of the illustrated zooid were not actually spine bases, reducing the total number to 26, comprising 11 pericryptocystal spines and 15 additional spines on the sloping gymnocyst. Other zooids in the holotype colony (which comprised just five zooids) have variations of 12 + 8, 9 + 12, and 8 + 8 spines.

The new material was initially identified as P. circularis by light microscopy but subsequently thought to represent a new species when examined by SEM—whereas there are 9–14 pericryptocystal spines, the same zooids have either no additional gymnocystal spines or just 1–2. The dilatation is often less circular than in the holotype. Given that almost all other characters partly accord with the metrics for the holotype, this additional material is presently equated with P. circularis. One exception is the areal width of the cryptocystal rim, which is smaller than in the holotype and non-overlapping. The measurements in the redescription are based on both the holotype and the new material.

Distribution. Endemic to the New Zealand EEZ, where it is known only from the extensive subantarctic Campbell Plateau from Christable Seamount (actually isolated just to the west of the plateau), northeastwards to the area north of Antipodes Island, including the saddle between Pukaki Rise and Bounty Plateau, and southeastwards to the edge of the Campbell Plateau, at depths of 887–1280 m on metamorphosed limestone.