Aechmellina, Taylor & Martha & Gordon, 2018

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 : 1667-1668

Genus Aechmellina gen. nov.

( Figure 3 )

Type species

Aechmella falcifera Voigt, 1949 . Cretaceous, early Campanian, Gonioteuthis quadrata belemnite Zone, White Chalk, Lägerdorf, Schleswig-Holstein, Germany .

Diagnosis

Colony encrusting. Autozooids subhexagonal, rounded distally ( Figure 3 (b)); zooidal boundaries raised with a medial groove. Cryptocyst extensive, granular. Gymnocyst lacking. Opesia terminal, occupying about one-third of frontal surface; hemi-elliptical with opesiular indentations, proximal edge concave ( Figure 3 (c)); operculum semicircular. Ovicell immersed, visible as a slight convexity in the proximal cryptocyst of the distal zooid ( Figure 3 (c)). Avicularia interzooidal, symmetrical, small, numerous, scattered between the autozooids; opesia longitudinally elliptical; rostrum short, pointed ( Figure 3 (d)).

Etymology

From Aechmella , with the commonly used suffix ‘- ina ’.

Remarks

A large number of Late Cretaceous and Danian onychocellid species have been assigned to Aechmella . Systematists describing these species have wrongly interpreted Aechmella as a genus characterised by opesiular indentations and numerous small avicularia, neither of which occurs in the Eocene type species (see above). We therefore introduce the new genus Aechmellina for their reception. There are some similarities between this genus and Smittipora but the latter does not have multiple small avicularia and the ovicellate zooids have considerably larger opesiae than non-ovicellate zooids.

Aside from the type species, the following species (listed alphabetically) are referred to Aechmellina: Homalostega anglica Brydone, 1909 ; (see Voigt 1959); Aechmella bassleri Voigt, 1924a ; Homalostega biconvexa Brydone, 1909 (see Voigt 1959); Cellepora hippocrepis Goldfuss, 1826 (see Voigt 1924b); Aechmella indefessa Taylor & McKinney, 2006 ; Aechmella latistoma Berthelsen, 1962 , Aechmella linearis Voigt, 1924a ; Aechmella parvilabris Voigt, 1924a ; Aechmella pindborgi Berthelsen, 1962 ; Semieschara proteus Brydone, 1912 (see Voigt 1985); Monoporella seriata Levinsen, 1925 (see Voigt 1959); Aechmella stenostoma Voigt, 1930 ; Reptescharinella transversa d’ Orbigny, 1852 (see Voigt 1957); Aechmella ventricosa Voigt, 1924a . Several additional unnamed Late Cretaceous ‘ Aechmella ’ species can also be transferred to Aechmellina , including those cited as Aechmella sp. from the Maastrichtian of California ( Taylor 2008), late Campanian to Maastrichtian of Arabia ( Di Martino and Taylor 2013), and Cenomanian of Devon, United Kingdom ( Taylor and Martha 2017).

Congeneric species of Aechmellina show minor differences from the type species, notably: in the cryptocyst, which in some species (e.g. A. seriata ) is convex; in the proximal edge of the opesia, which may be raised slightly to form a rim continuous with the arched distolateral edge (e.g. A. anglica ); and in the form of the avicularia which vary from short and rounded (e.g. A. stenostoma ) to long and pointed (e.g. A. indefessa ).

Range

Cretaceous (Cenomanian) to Paleocene (Danian).

Figures

Figure 3. Aechmellina falcifera. (a) holotype, SMF 26280, early astogeny; Cretaceous, early Campanian, Goniotheutis quadrata Zone, White Chalk, Lägerdorf, Schleswig-Holstein, Germany. (b–d) NHMUK BZ 757; early Campanian, Sehnde-Höver, Lower Saxony, Germany; (b) autozooids and avicularia; (c) opesiae of two autozooids, that on the upper left fertile; (d) avicularium. Scale bars: a = 1 mm; b = 500 µm; c = 200 µm; d = 100 µm.