Dimorphomicropora crestulata ( Ducasse, 1958 )

Taylor, Paul D. & Villier, Loïc, 2022, Cretaceous microporid cheilostome bryozoans from the Campanian historical stratotype of southwest France, Geodiversitas 44 (18), pp. 515-525 : 522-523

Dimorphomicropora crestulata ( Ducasse, 1958)

( Fig. 4 )

MATERIAL. — Holotype: UB C.B.917 , Ducasse Collection ( Ducasse 1958: pl. 7, fig. 3), probably Barbezieux Fm (foram biozone CVI), RN 730, close to police station, Mirambeau, Charente-Maritime . Other material: NHMUK PI BZ 8271, 8272, Aubeterre Fm, cliff north of town, Meschers, Charente-Maritime .

OCCURRENCE. — Upper Campanian, Barbezieux and Aubeterre formations.

DESCRIPTION

Colony erect, consisting of cylindrical branches, complete bifurcations not observed, probably articulated during life. Branches 8- to 10-serial, longest observed branch 2.4 mm, branch width 0.42-0.61 mm wide increasing to about 1 mm when fertile zooids are present. Colony base unknown. Autozooids longer than wide, ZL 395-526 µm (N colonies 2; N zooids 8; mean 439 µm; SD 43 µm), ZW 184-211 µm (N colonies 2; N zooids 8; mean 194 µm; SD 14 µm), elongate hexagonal. Frontal wall cryptocystal, margins raised, centre depressed, smooth textured; cryptocystal pores lacking; single pair of opesiules located proximolaterally of orifice within depressed central part of cryptocyst, longitudinally elliptical, some with a transverse bar subdividing the opening internally. Orifice subcircular, 94-118 µm in diameter, sometimes with a slight proximal embayment, rim salient. Fertile autozooids clustered, ooecia helmet shaped, about 220 µm long by 200-240 µm wide, calcification smooth, continuous with the cryptocyst of the distal zooid, orifice of ovicellate zooids round, slightly larger than those of non-ovicellate zooids, about 120-150 µm long by 140-160 µm wide. Mandibulate polymorphs unknown.

REMARKS

This species was introduced by Ducasse (1958) in her thesis as Micropora crestulata . Although it is clearly congeneric with Dimorphomicropora , it was not mentioned in the publication of Ducasse & Vigneaux (1960) when introducing this genus. Most specimens of D. crestulata come from the Aubeterre Formation in coastal localities south of Royan where D. voigti also occurs. However, the type specimen is slightly older having been collected by Ducasse (1958) from an inland site at Mirambeau which exposes the Barbezieux Formation.

The subcircular orifice of D. crestulata allows this species to be distinguished from D. voigti . Scanning electron micrographs of D. rugica kindly provided by Oliver Kesselhut (Aachen) show similarities with D. crestulata ; however, this Maastrichtian species sometimes has a lip extending over the proximal edge of the orifice, a feature not seen in D. crustulenta . The poorly preserved lectotype of Micropora transversa (d’Orbigny, 1851) from the Upper Maastrichtian of Contentin is possibly a senior synonym of either D. crestulata or D. rugica , but better material of M. transversa is needed before either of these synonymies can be accepted.

Figures

FIG. 4. — Dimorphomicropora crestulata (Ducasse, 1958): A, holotype (Ducasse 1958: pl. 7, fig. 3), UB C.B.917 Ducasse Collection, probably Barbezieux Fm (foram biozone CVI), RN 730, close to police station, Mirambeau, Charente-Maritime, dilated branch with ovicellate zooids; B, C, NHMUK PI BZ 8271, Aubeterre Fm,cliff north of town,Meschers,Charente-Maritime;B, well-preserved branch;C, detail of autozooids;D, NHMUK PI BZ 8272, Aubeterre Fm,cliff north of town, Meschers, branch. Scale bars: A, 500 μm; B, C, D, 200 μm.