Steginoporella tiara, Gordon & Voje & Taylor, 2017

Gordon, Dennis P., Voje, Kjetil L. & Taylor, Paul D., 2017, Living and fossil Steginoporellidae (Bryozoa: Cheilostomata) from New Zealand, Zootaxa 4350 (2), pp. 345-362 : 357

Steginoporella tiara sp. nov

( Figs 37–40 )

Etymology. Greco-Latin tiara , turban, alluding to the shape of the arch distal to the opesia.

Material examined. Holotype: IGNS BZ 338 , Lower Pleistocene , Nukumaruan ( Gelasian ), Tewkesbury Formation , Nukumaru Beach, NZMS R22, 637482, Whanganui, New Zealand .

Description. Colony?encrusting (detached from its substratum), unilaminar. Zooids distinct, monomorphic, separated by slightly raised marginal rim with thin shallow suture at zooidal boundary. Zooids very similar in shape and size (small standard deviations of linear measurements), elongate (mean L/W = 1.88), widest in middle third and arranged in regular longitudinal rows, taphonomic separation sometimes occurring between rows. Distal margin convex, sloping, tapering laterally; proximal margin concave. Cryptocystal shelf slightly depressed, flat, occupying about half length of frontal surface, densely and minutely porous. Opesia large, semicircular, occupying distal half of frontal surface, proximal margin bordered by thin raised edge of median process of cryptocyst, which is fused on either side with mandibular pivots. Median process bipartite, having distolateral ‘wings’ that meet mediolateral edges of opesia, the process delineating a small longitudinally elongate, proximomedial pore and a pair of inverted commashaped, opesiule-like lateral openings. B-zooids lacking. Ancestrula and early astogeny not seen.

Measurements. In micrometres: ZL 1013 µm ± 14 (1, 10); ZW 540 µm ± 10 (1, 10); OpL length 291 µm ± 8 (1, 10); OpW 399 µm ± 10 (1, 10).

Remarks. Only a single colony was found in the Tewkesbury Formation (Early Pleistocene, Gelasian), which indicates that it is much less abundant than S. magnifica , which commonly appears in most of the formations in the Whanganui Basin, including the Tewkesbury. Steginoporella tiara n. sp. differs from S. magnifica by having moreelongated zooids and a larger median process that occupies approximately half of the opesia. The distal edge of the median process is continuous with the lateral condyles to form an unbroken straight proximal margin of the opesia, unlike all the other species described herein. Additionally, S. tiara n. sp. has the highest length:width ratio of all known Steginoporella species from New Zealand. Among living taxa, Steginoporella auriculata Harmer, 1900 and Steginoporella connexa Harmer, 1900 share many similarities with Steginoporella tiara n. sp., but the distal cryptocyst is much narrower in both these species.

Distribution. New Zealand endemic, Gelasian only, Whanganui region.

Figures

FIGURES 37 – 40. Steginoporella tiara n. sp., holotype, IGNS BZ 338, Lower Pleistocene, Nukumaruan (Gelasian), Tewkesbury Formation, Nukumaru Beach, Whanganui, New Zealand. 37, rows of elongate zooids with separation at the location of the cuticle between compound walls; 38, row bifurcation; 39, zooid showing the long, narrow cryptocyst; 40, opesia and median process. Scalebars: 37 – 38, 1 mm; 39, 0.5 mm; 40, 0.2 mm.