Olisthella alma Gordon & Taylor, 2017, n. sp.

Olisthella alma n. sp.

(Fig. 11)

Material examined. Holotype: NIWA 98231, Alma, Otago, New Zealand Fossil Record Number for outcrop J41/ f0088, Waiareka Volcanic Formation, Runangan (Priabonian), Late Eocene, 45.1154° S, 170.9074° E, from a tuff in a low road-cutting, 50 m south of Alma Motel on east side of main south road (SH1). Paratype: NIWA 98232, same locality as holotype.

Etymology. Alluding to the type locality, the name used as a noun in apposition.

Description. Colonies spot-like, comprising up to 17 non-caudate contiguous autozooids; maximum spread of fertile colonies c. 1.7 mm, hence small and spot-like. Individual zooids oval [ZL 332–456 (384); ZW 266–367 (318)], arranged in quincunx with at least two pairs of lateral septula as well as one distal and one proximal. Gymnocyst encircling entire autozooid at colony margin, narrow from frontal view, especially laterally and distally, but zooid relatively high, steeply sloping to substratum. Cryptocyst comprising a very broad, flat shelf surrounded by a raised rim that is circular to oval; radial length of shelf midproximally 99–152 (116) µm (i.e. same length as opesia), surface even, with indications of lineations trending more or less radially from rim towards opesia; texture in life uncertain owing to diagenesis. Opesia longer than wide, typically slightly wider in distal third than proximal third, with slight narrowing of middle third [OpL 99–157 (116); OpW 76–111 (90)]; distal margin evenly rounded, proximal margin weakly rounded to not quite straight. Eight articulated spines, extending around the distal half of the opesial margin only, the bases slightly broader proximad; only one additional spine on the gymnocyst laterally. No avicularia. Ooecium subglobular, more or less as wide as long or slightly wider, texture in life uncertain owing to irregularities in preserved surface, the inferred ooecial heterozooid completely concealed beneath it [OoL 178–200 (191); OoW 176–211 (196)]. Ancestrula not identified.

Remarks. This species is represented by three colonies, one with a complete ooecium, a second with to frontal broken ooecia, and a third non-ovicellate. Olisthella alma n. sp. most resembles O. contigua n. sp. —the cryptocyst is broad and extensive and opesial shape is not very dissimilar, but zooids of O. alma n. sp. are far smaller, the spine bases are not completely pericryptocystal and there is only one accessory spine.

Lee et al. (1997) described the paleoecological setting as a warm-water (subtropical), mobile volcaniclastic (basaltic) pebble and cobble rockground in a current-swept channel about 25–50 m depth several kilometres from the Late Eocene shoreline.

Distribution. Known only from the Runangan (Priabonian) stage at the type locality in north Otago, South Island, New Zealand.