Bryobrownius willetti (Brown, 1952)

(Fig. 13)

Amphiblestrum willetti Brown, 1952: 89, figs 40, 41. Pyriporoides willetti: Gordon et al. 2009: 295, 297.

Material examined. Holotype: D36574, NHMUK, McDonald’s Quarry, McDonald Limestone, Whaingaroan (Rupelian), Early Oligocene, NZMS 260, Map Sheet J 42, grid reference J42/453578, Kakanui, North Otago, New Zealand.

Redescription. Colony encrusting, unilaminar, multiserial; autozooids more or less suboval or subpyriform, arranged contiguously in quincunx; maximum colony spread c. 3 mm, hence small and spot-like [ZL 274–418 (344); ZW 210–322 (263)]. Gymnocyst quite well developed, continuous around zooid. Cryptocyst and opesia surrounded by a distinct raised rim [CrL 190–203 (198); CrW 152–173 (163)], the cryptocystal shelf fairly extensive, sloping toward opesia, attenuating laterally as far as orificial area. Opesia longer than wide, constricted in middle, imparting a broad dumbbell shape [OpL 83–95 (90)]; distal margin evenly rounded, proximal margin somewhat straighter, sometimes obliquely so. Oral and pericryptocystal spine bases present, up to 10 visible, 11 likely in life; no accessory gymnocystal spine bases on best-preserved zooids. Avicularia interzooidal, more than half autozooid length, cystid with extensive gymnocyst, rostrum elongate, narrow, acute, apparently no pivot bar, opesial foramen wider than rostral palate [AvL 193–263 (236); AvW 188–267 (230)]. Ooecium hyperstomial, smooth with median suture line [OoL 114–152 (140); OoW 135–183 (158)]; ooecial kenozooid visible distally, with circular area indicating presence of foramen and cryptocyst in life. Ancestrula small, circular, with periopesial/pericryptocystal spines [AnL 153; AnW 145].

Remarks. The specimen is considerably recrystallised, which may explain why Brown (1952) failed to note the presence of spine bases and avicularia, and why basal pore-chambers cannot be detected. He described the opesia as trifoliate, but, being longer than wide, it is better described as broadly dumbbell-shaped. He only provisionally included the species in Amphiblestrum, noting that “The affinities of this species are rather indefinite…” (ibid., p. 90). Based on SEM photos of the holotype, Gordon et al. (2009) noted some features in common with Pyriporoides and included it in that genus. Here, we restrict Pyriporoides to species with caudate zooids in uniserial chains.

The ancestrula in the holotype colony is unusually small, being less than half the size of daughter zooids (unless there is a proximal portion missing). There is a hint of periopesial spine bases so it could have been tatiform in life; alternatively, there may have been a cryptocyst, which is likely. Daughter zooids have occluded opesiae, indicating the presence of kenozooidal regeneration within the cystids, but recrystallisation precludes certainty.