Rectonychocella Canu and Bassler, 1917

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 : 1695-1696

Genus Rectonychocella Canu and Bassler, 1917

( Figure 24 )

Type species

Onychocella solida Nordgård, 1908 , by original designation. Recent, Norwegian Sea, Atlantic Ocean, c. 75 km off the eastern coast of Iceland.

Diagnosis

Colony encrusting, occasionally growing free of substrate ( Figure 24 (a)). Autozooids subhexagonal, rounded; zooidal boundaries grooved. Cryptocyst extensive, granular. Gymnocyst lacking. Opesia terminal, occupying variable proportion of frontal surface from more than half to less than one-third, variable in shape from oval to pear shaped or inverted pear shaped, lacking opesiular indentations and lateral constrictions. Ovicells immersed ( Figure 24 (c)); opesia in ovicellate autozooids enlarged, cormidial. Avicularia vicarious, symmetrical ( Figure 24 (b,c)), slightly longer and narrower than an autozooid; opesia longitudinally elliptical to elongate inverted pear shaped; condyles present on opposite sides of the avicularian opesia; rostrum rounded arch shaped, floor pustulose.

Remarks

Founded on a Recent type species, Onychocella solida Nordgård, 1908 , the symmetrical avicularia were the main character used by Canu and Bassler (1917) to distinguish Rectonychocella from Onychocella . Canu and Bassler (1920) later added four new species of Late Eocene bryozoans to Rectonychocella .

Rectonychocella was regarded as a junior synonym of Smittipora Jullien, 1882 by Bassler (1953), presumably because the two genera shared symmetrical avicularia. This view has been supported by others (e.g. Gordon and Taylor 1999; Gerovasileiou and Rosso 2016). On the other hand, the large, ovoidal opesiae of the autozooids in Rectonychocella contrast with the smaller, semielliptical opesiae with opesiular indentations found in Smittipora , which favours keeping the two genera separate.

As noted by Hayward (1974), the oft-cited Mediterranean species Rectonychocella disjuncta Canu and Bassler, 1930 belongs neither to this genus nor to Smittipora as it has hyperstomial ovicells.

Range

?Eocene (Priabonian) to Recent.

Figures

Figure 24. Rectonychocella solida Nordgård; Recent, Labrador Sea off SW Greenland (63°30’S, 54°25ʹW), 582 fathoms; NHMUK 11.10.1.641; (a) part of a colony; (b) avicularium flanked by two non-ovicellate autozooids; (c) ovicellate autozooid (left) and avicularium (right). Scale bars: a = 1 mm; b, c = 500 µm.