Euritina Canu, 1900

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 : 1676-1677

Genus Euritina Canu, 1900

( Figure 10 )

Type species

Eschara eurita d’ Orbigny, 1851 , by original designation. Cretaceous, Turonian, Sainte- Maure-de-Touraine, Indre-et Loire, France .

Diagnosis

Colony erect, bifoliate ( Figure 10 (a)). Autozooids elongate ( Figure 10 (b)), subhexagonal, rounded distally; zooidal boundaries grooved. Cryptocyst extensive, granular, sloping distally, with proximal and two proximolateral facets ( Figure 10 (c)). Gymnocyst lacking. Opesia terminal, occupying about one-third of frontal surface; inverted pear shaped, longer than wide. Ovicells hyperstomial ( Figure 10 (d)). Avicularia vicarious, symmetrical ( Figure 10 (b,c)), about half the width of an autozooid and somewhat shorter, typically budded at row bifurcations; opesia longitudinally elliptical; rostrum short, rounded, floor smooth.

Remarks

The family-level classification of Euritina has been debated, the genus having been placed in Aspidostomatidae (e.g. Canu and Bassler 1920), Onychocellidae (e.g. Gordon and Taylor 2005, table 2; Taylor and Martha 2017) or Calloporidae (e.g. Taylor and McKinney 2006). Only broken ovicells are known in the type species ( Figure 10 (d)). Although these are clearly hyperstomial, it is unclear whether the ooecium is gymnocystal or cryptocyst-like.

Apart from the type species, Canu (1900) assigned to the genus two other Cretaceous species (Eschara delia d’ Orbigny, 1851 and Euritina welshi Canu, 1900 ) and one Recent species ( Amphiblestrum papillatum Busk, 1884 ). The Recent species, which has tiny adventitious avicularia ( Busk 1884, p. 33, fig. 1), was not listed by Canu and Bassler (1920, p. 257) when they redescribed Euritina and seems not to belong to this genus. Canu and Bassler (1920) listed several additional Paleocene species of Euritina , among which is E. tecta Canu and Bassler, 1920 from the Clayton Formation of Arkansas ( Figure 10 (e,f)). Scanning electron microscope images of the types, kindly supplied by JoAnn Sanner (USNM), show clearly the gymnocystal ooecium ( Figure 10 (f)) of the hyperstomial ovicells in this Danian species. Two new species of multilamellar encrusters were assigned to Euritina by Taylor and McKinney (2006) from the Maastrichtian of the south-eastern USA. Both have facetted cryptocysts but E. metapolymorpha Taylor and McKinney, 2006 is unusual for this genus (and for Onychocellidae ) in that the autozooids and avicularia have a narrow but distinct gymnocyst along their proximal and lateral edges.

Osburn (1950) referred the extant species Reussina arctica ( Osburn, 1950) to Euritina but this species has oral spine bases and the cryptocyst is ringed by large pores (?opesiules) (Gordon 2009, fig. 1A–D), outweighing similarities with the type species of the genus in the facetted structure of the cryptocyst. It is now assigned to Reussinella , a replacement name introduced by Gordon (2009) for Reussina Kluge, 1962 , a junior homonym of Reussina Neviani, 1896 , who placed it provisionally in Microporidae . With the exclusion of this species from Euritina , the upper range of the genus becomes Thanetian, the youngest recorded species being E. torta ( Gabb and Horn, 1862) from the Vincentown Limesand of New Jersey. Provisionally, the oldest known species is the early Cenomanian Euritina denticulata ( Roemer, 1840) (see Taylor and Martha 2017), a species which, however, lacks the facetted cryptocyst typical of Euritina .

Range

Cretaceous (Cenomanian) to Paleocene (Thanetian).

Figures

Figure 10. (a–d) Euritina eurita (d’Orbigny); lectotype, MNHN R61484; Cretaceous, Turonian, Sainte- Maure-de-Touraine, Indre-et Loire, France; (a) bifoliate frond; (b) autozooids and slightly smaller avicularia; (c) autozooids and avicularium (right of centre); (d) broken ovicells. (e,f) Euritina tecta Canu and Bassler; syntypes, USNM 63807; Paleocene, Clayton Formation, Mabelvale, Little Rock, Arkansas; (e) overgrowth; (f) autozooids, some ovicellate (e.g. arrow). Scale bars: a = 1 mm; b, e, f = 500 µm; c, d = 200 µm.