Micropora mikesmithi, Taylor & Villier, 2022

Taylor, Paul D. & Villier, Loïc, 2022, Cretaceous microporid cheilostome bryozoans from the Campanian historical stratotype of southwest France, Geodiversitas 44 (18), pp. 515-525 : 517-519

Micropora mikesmithi n. sp.

( Fig. 1 )

urn:lsid:zoobank.org:act:4A53195C-D71D-42E2-838B-8FA0C06D4EB4

TYPE MATERIAL. — Holotype. NHMUK PI BZ 8809 , Aubeterre Fm , Archiac, Charente-Maritime ( France). — Paratypes. NHMUK PI BZ 8363, Aubeterre Fm , rock face behind car-park, Aubeterre-sur-Dronne, Charente ( France) ; NHMUK PI BZ 8655, Aubeterre Fm , roadcutting at junction of D5 and C18, east of Saint-Privat-des-Prés, Dordogne ( France) ; SU.2021.1.1.0, Aubeterre Fm , roadcutting along the freeway RN10, Pont-du-Noble , Reignac, Charente ( France) .

TYPE LOCALITY. — Aubeterre Fm, Archiac, Charente-Maritime ( France).

ETYMOLOGY. — Named for Mike Smith, enthusiastic volunteer at the NHMUK, who helped during fieldwork in the Campanian of SW France.

OCCURRENCE. — Upper Campanian, Barbezieux and Aubeterre formations.

DESCRIPTION

Colony encrusting, multiserial, sheet-like, unilamellar. Autozooids longer than wide, ZL 354-597 μm (N colonies 4; N zooids 26; mean 446; SD 58 μm), ZW 231-355 μm (N colonies 4; N zooids 26; mean 288; SD 30 μm), the proximolateral margins typically concave and the distolateral margins convex with well-rounded distal ends. Frontal wall entirely lacking gymnocyst; cryptocyst forming most of the frontal surface, gently convex, depressed beneath the raised rims outlining the zooids, lacking paired tubercles at the distolateral corners, texture granular; cryptocystal pores not evident (quite possibly obscured by diagenetic neomorphism of the skeleton); opesiules located adjacent to the raised zooidal rim in the distal half of the zooid, long and narrow, curved, either a single pair or two pairs in which case the more proximal opesiules are shorter in length. Orifice semielliptical, wider than long, OL 44-52 μm (N colonies 2; N zooids 10; mean 47 μm; SD 3 μm), OW 89-109 μm (N colonies 2; N zooids 10; mean 97 μm; SD 7 μm), the proximal edge straight or slightly concave. Ovicells small, moderately raised, the ooecium rounded rectangular, wider than long, 84-97 µm long by 168-181 µm wide, calcification continuous with the cryptocyst of the distal zooid; orifices of ovicellate zooids significantly wider than those of non-ovicellate zooids, about 90 µm long by 175 µm wide. Avicularia absent in ovicellate zooids but present in all non-ovicellate zooids, located immediately distal of the orifice, oriented transversely, small, about 100-104 µm long by 64-89 µm wide, the opesia round and the rostrum rounded triangular in shape; presence of condyles or a pivotal bar uncertain. Ancestrula and early astogenetic stages not observed.

REMARKS

As mentioned above, the lack of modern descriptions of species of putative Micropora from the Late Cretaceous makes comparisons with the new species difficult. However, the Maastrichtian species Micropora biforis ( Marsson, 1887) from Germany and the Netherlands has a pair of rounded opesiules close to mid-length, whereas the opesiules of M. mikesmithi are more slit-shaped, located further distally and consist of two pairs. In both Marsson’s species and Micropora multicrescens Brydone, 1936 , there is no indication of the presence of avicularia distal to the autozooids. Micropora mohli ( Hagenow, 1851) resembles the new species but the avicularia are directed almost distally in contrast to the transverse orientation seen in M. mikesmithi .

Colonies of M. mikesmithi encrust shells of the bivalve Pycnodonte vesiculare ( Lamarck, 1806) .

Figures

FIG. 1. — Micropora mikesmithi n. sp.: A-C, paratype, NHMUK PI BZ 8363, Aubeterre Fm, rock face behind car-park, Aubeterre-sur-Dronne, Charente: A, part of the colony; B, group of autozooids with avicularia distal of the orifices; C, autozooid at the growing edge; D-E, holotype, NHMUK PI BZ 8809, Aubeterre Fm, Archiac,Charente-Maritime:D, part of the colony;E, three ovicellate autozooids lacking an associated avicularium,and one infertile autozooid (left) with an avicularium; F, paratype, NHMUK PI BZ 8655, Aubeterre Fm, roadcutting at junction of D5 and C18, east of Saint-Privat-des-Prés, Dordogne, orifice and avicularium. Scale bars: A, D, 500 μm; B, E, 200 μm; C, F, 100 μm.