Microporella rusti, Martino & Taylor & Gordon & Liow, 2017

Martino, Emanuela Di, Taylor, Paul D., Gordon, Dennis P. & Liow, Lee Hsiang, 2017, New bryozoan species from the Pleistocene of the Wanganui Basin, North Island, New Zealand, European Journal of Taxonomy 345, pp. 1-15 : 9-12

Microporella rusti sp. nov.

urn:lsid:zoobank.org:act:95F31C54-CEAA-41A4-964B-9848063DE6D6

Fig. 4 , Table 4

Diagnosis

Colony large, encrusting. Autozooids hexagonal, with coarsely granular and perforated frontal shield. Marginal areolar pores conspicuous. Orifice semielliptical. Oral spines absent. Ascopore crescentic and finely toothed, with a proximal saucer-shaped rim. Avicularia rare, usually single, directed distally or distolaterally, proximal edge level with or proximal to the ascopore. Ovicell unknown.

Etymology

Named after Dr Seabourne Rust for his important contributions to the knowledge of fossil bryozoans from the Wanganui Basin.

Material examined

Holotype

NEW ZEALAND: Nukumaru Limestone , Waiinu Beach , Nukumaruan, Pleistocene ( GNS BZ 336 ).

Paratypes

NEW ZEALAND: same collection data as for holotype ( NHMUK PI BZ 7834, NHMUK PI BZ 7835).

Description

Colony encrusting, large, unilaminar ( Fig. 4A ). Ancestrula similar to later autozooids but smaller, about 230 μm long by 180 μm wide, budding one distal and two distolateral autozooids, surrounded by six autozooids ( Fig. 4D ). Later autozooids arranged quincuncially, hexagonal, longer than broad (mean L/W = 1.22), with shallow interzooidal furrows, varying in size, some very narrow (ZW = 250–300 μm), others broad, almost as wide as long (ZW = 550–570 μm), usually located at colony bifurcations, their width equivalent to the two or three distal zooids succeeding them ( Fig. 4E ). Frontal shield convex, coarsely granular, with small (about 5–10 μm), sparse, circular pseudopores varying in number, numerous in some zooids (approximately 50–60) but fewer seen in others, perhaps because of concealment by diagenetic cement or sediment particles. Marginal areolar pores conspicuous, about 40–55 μm long, slit-like, at least six per zooid, located at each corner, sometimes with an additional one along distal and lateral zooidal margins. Orifice distally placed, semielliptical or transversely D-shaped, surrounded by a slightly raised and thick margin, wider than long ( Fig. 4B ). Oral spines absent. Ascopore located in distal part of an ascopore field below orifice, small, crescentic, finely toothed ( Fig. 4B ). Ascopore field surrounded by a smooth rim, higher and wider proximally, forming a saucer-shaped structure often levelled off ( Fig. 4 E–F). Avicularia rare, usually single, only once observed paired ( Fig. 4F ), small, located on distolateral zooidal margin, roughly at same level as ascopore or slightly distal or proximal, triangular, with pointed rostrum directed distally or distolaterally and complete crossbar. Ovicells not observed in any of more than one hundred colonies studied, presumed absent at least in the fossil populations studied.

Remarks

Microporella is one of the most species-rich cheilostome genera, with an increasing number of new species having been recognized since the availability of SEM, which has allowed subtle differences in skeletal morphology to be observed ( Taylor & Mawatari 2005). Six species, Recent and fossil, have their type occurrence in New Zealand (based on http://www.bryozoa.net, accessed 16 May 2016) and many others have a wider distribution that includes New Zealand. Among Cenozoic species reported previously from the area, M. ordo Brown, 1952 and nominal M. hyadesi (Jullien, 1888) lack oral spines. Microporella ordo ( Fig. 5 ) was described from the Wanganui Basin at Castlecliff (about 0.55 Ma, Castlecliffian, Late Pleistocene) and differs from the new species in having more numerous marginal areolar pores, a frontal shield with a coarser granulation and more-numerous and larger pseudopores, larger and constant avicularia, the proximal orificial margin with a coarse denticulation, a reticulate ascopore, and zooids arranged in well defined longitudinal rows. Microporella hyadesi ( Fig. 6 ), first described from Recent material from Cape Horn and the Falkland Islands, was reported by Brown (1952: 257) from several New Zealand localities of Middle Oligocene to Pliocene age. It is likely that M. hyadesi sensu Brown (1952) is a closely related species but distinct from the nominal species ( Rust 2009). It differs from M. rusti in having ovicells, often paired smaller avicularia, a smaller orifice, a reticulate ascopore and no obvious marginal pores at the zooidal corners.

Distribution

Common in the Nukumaru Limestone (2.29–2.08 Ma, Nukumaruan, Pleistocene) and the Nukumaru Brown Sand (2.03–1.97 Ma, Nukumaruan, Pleistocene) encrusting bivalve shells, often associated with Anomia trignopsis Hutton, 1877 ( Rust 2009) . Rare in Castlecliffian (0.58–0.52 Ma, Pleistocene) strata.

Figures

Fig. 4. Microporella rusti sp. nov. A–C. Holotype (GNS BZ 336), Nukumaruan, Pleistocene, Nukumaru Limestone, Waiinu Beach, New Zealand. A. View of two colonies growing side by side. B. Close-up of two autozooids lacking avicularia, showing the orifice and ascopore. C. Close-up of zooids at the growing edge. D. Paratype (NHMUK PI BZ 7834), same provenance as holotype, showing ancestrula (a) and early astogeny. E–F. Paratype (NHMUK PI BZ 7835), same provenance as holotype. E. Group of zooids. Note the large zooid at the centre preceding row division. F. Group of zooids. Note the zooid at the centre bearing two avicularia. Scale bars: A = 500 µm; B = 50 µm; C–F = 200 µm.

Fig. 5. Microporella ordo Brown, 1952. A–C. Holotype (NHMUK D36809), Wanganui, Castlecliffian Horizon CU3, Pleistocene, NZGS Loc. 4013 Castlecliff, New Zealand. A. Frontal view of the linear colony fragment. B. Close-up of an autozooid. C. Close-up of the orifice and ascopore. D. Paratype (NHMUK D36806), same provenance as holotype, view of the linear colony fragment. Scale bars: A, D = 200 µm; B = 100 µm; C = 20 µm.

Fig. 6. Microporella hyadesi (Jullien, 1888) sensu Brown 1952 (NHMUK D36796 and D36797), Southland, Waianan, Middle Miocene, base of the uppermost Mt. Brown “E” Limestone, Junction of Weka Creek, Weka Pass Stream, Waipara, Canterbury, New Zealand. Two colony fragments including autozooids and ovicellate zooids. Scale bars = 200 µm.