Cheethamia Shaw, 1967

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 : 1669-1670

Genus Cheethamia Shaw, 1967

( Figure 4 )

Type species

Cheethamia howei, 1967 , by original designation. Cretaceous, Campanian, Saratoga Chalk, Howard County, Arkansas, USA .

Diagnosis

Colony encrusting. Autozooids hexagonal ( Figure 4 (b)); zooidal boundaries grooved or with a raised edge. Cryptocyst convex, extensive, granular. Gymnocyst lacking. Opesia terminal, occupying about one-third of frontal surface, semielliptical, arch-shaped with small opesiular indentations, proximal edge more or less straight, shelf-like occlusor lamina distally; a pair of closely spaced oral spine bases in non-ovicellate zooids ( Figure 4 (c)), four spine bases in zooids budded directly from the ancestrula. Ovicell hyperstomial ( Figure 4 (d)), small, ooecium interior-walled, a convex transverse wall visible within the opesia separating the ovicell from the rest of the zooid. Avicularia vicarious, normally slightly asymmetrical ( Figure 4 (e)), sometimes symmetrical ( Figure 4 (a)), dagger-like, about the same length as an autozooid but half the width; opesia longitudinally elliptical; rostrum long, acutely triangular, straight or slightly curved. Ancestrula similar in size and morphology to budded autozooids ( Figure 4 (f)). Remarks

Unlike Onychocella , the ovicell of Cheethamia is hyperstomial, albeit small in the type species C. howei ( Taylor and McKinney 2006) . The oral spine bases are another feature of C. howei that are lacking in the type species of Onychocella , although oral spines are present in a few Cretaceous species that have been referred to Onychocella (see above). Shaw (1967) transferred Onychocella pinguis Voigt, 1962 from the Maastrichtian of Crimea to Cheethamia , an action supported by Koromyslova (2014) who rediagnosed the genus and added two further Maastrichtian species from eastern Ukraine and Kazakhstan to the genus: Cheethamia subpinguis Koromyslova, 2014 and C. arcuata Koromyslova, 2014 . All of these species share with C. howei one or a pair of oral spine bases but C. pinguis and C. subpinguis differ from the type species in having erect bifoliate colonies.

Range

Cretaceous (Campanian to Maastrichtian).

Figures

Figure 4. Cheethamia howei Shaw. (a) holotype, LSUMG-I 8237; Cretaceous, Campanian, Saratoga Chalk, Howard County, Arkansas, USA. (b–f) NHMUK BZ 4809; Cretaceous, Maastrichtian, Lake Ridge Apartments, Livingston, Alabama, USA; (b) ovicellate and non-ovicellate autozooids and an avicularium; (c) opesia of non-ovicellate autozooid showing occlusor lamina and a pair of closely spaced oral spine bases; (d) ovicellate autozooid with transverse wall visible in opesia; (e) avicularium; (f) ancestrula (lower centre) and first-budded autozooids. Scale bars: a, b, e, f = 500 µm; c = 100 µm; d = 200 µm.