Nudonychocella Voigt and Ernst, 1985

Taylor, Paul D., Martha, Silviu O. & Gordon, Dennis P., 2018, Synopsis of ‘ onychocellid’ cheilostome bryozoan genera, Journal of Natural History (J. Nat. Hist.) 52 (25 - 26), pp. 1657-1721 : 1689-1690

Genus Nudonychocella Voigt and Ernst, 1985

( Figure 19 )

Type species

Nudonychocella nuda Voigt and Ernst, 1985 , by original designation. Cretaceous, late Maastrichtian ( Tuffeau de Maastricht ), Maastricht, Netherlands .

Diagnosis

Colony encrusting ( Figure 19 (a)). Autozooids subhexagonal, rounded distally. Opesia occupying entire frontal surface in post-ancestrular zooids with no preserved cryptocyst or gymnocyst ( Figure 19 (a,d); in ancestrula, proximal cryptocyst occupying more than half of frontal area ( Figure 19 (b,c)), opesia terminal, semi-elliptical, proximal edge concave, lacking opesiular indentations and constrictions. Ovicells?immersed, preserved only as small caplike structures ( Figure 19 (e)). Avicularia vicarious, symmetrical ( Figure 19 (f)), pointed, without preserved cryptocyst, about half or more of the width of an autozooid.

Remarks

The ancestrula is critical to the placement of this genus in Onychocellidae as it preserves the typically onychocellid, shelf-like cryptocyst ( Figure 19 (b,c)) that is missing in zooids from later astogeny. A bioimmured example of N. nuda shown by Voigt and Ernst (1985, fig. 2.1) was interpreted by these authors as moulding the unmineralised frontal membrane but is equally likely to have moulded a cryptocystal frontal wall that was lost through leaching, probably because it had a more soluble mineralogy of aragonite or high-Mg calcite ( Taylor and McKinney 2006, p. 104).

Two additional Cretaceous species are suggested as belonging to Nudonychocella . Membranipora subsimplex d’ Orbigny, 1852a , which can be found in the Campanian of SW France ( Figure 19 (c–f)), resembles the type species in lacking preserved frontal calcification in zooids from late astogeny but retains a cryptocyst in the first budded autozooid ( Figure 19 (c)) as well as the ancestrula. Aplousina incompta Taylor and McKinney, 2006 , from the Maastrichtian of the south-eastern USA, may perhaps be better placed in Nudonychocella even though avicularia have not been observed and occasional autozooids from the zone of astogenetic repetition preserve remnants of a cryptocyst.

Range

Cretaceous (Campanian to Maastrichtian).

Figures

Figure 19. (a,b) Nudonychocella nuda Voigt and Ernst; holotype, SMF 25383; Curfs Quarry, near Berg, Limburg, Netherlands; (a) encrusting colony, growing from top right to lower left, showing autozooids and avicularia; (b) early astogeny with the ancestrula (lower left), two budded autozooids and an avicularium (upper right). (c–f) Nudonychocella subsimplex (d’Orbigny). (c,d) NHMUK BZ 8218; Campanian,Aubeterre Formation,Plage des Nonnes,Meschers,Charente Maritime,France;(c) ancestrula and three budded autozooids, the distal autozooid with a completely preserved cryptocyst; (d) autozooids and avicularia (arrowed); (e,f) NHMUK BZ 8219; Campanian, Biron Formation, Aubeterre-sur- Dronne, Charente, France; (e) ovicellate autozooid with cap-like ovicell arrowed; (f) avicularium surrounded by autozooids. Scale bars: a = 1 mm; b, c, f = 200 µm; d = 500 µm; e = 100 µm.