Anatoma richardi (Dautzenberg & H. Fischer, 1896)

Ortega, José Rafael & Gofas, Serge, 2019, The unknown bathyal of the Canaries: new species and new records of deep-sea Mollusca, Zoosystema 41 (26), pp. 513-551 : 518-519

Anatoma richardi (Dautzenberg & H. Fischer, 1896) ( Fig. 3 A-D)

MATERIAL EXAMINED. — 115 sh., DW130.

REMARKS

Geiger (2012: 1108 and distribution map) reported Anatoma tenuis (Jeffreys, 1877) from three localities in the Canaries, ranging from 450 to 900 m, without illustrating these lots. We found in our material three species of Anatoma , viz. Anatoma aspera , A. eximia and the species resembling A. tenuis here illustrated ( Fig. 3 A-D). Whereas for the first two we agree with Geiger’s (2012) identifications, there are issues regarding the last one.

Our specimens have the suture of the last whorl either attached to the abapical keel of the selenizone, or dropping at some distance below this keel (leaving exposed a part of the previous whorl below the keel of the selenizone called “sutsel” by Geiger), with all transitional constructions. This questions the taxonomic value of this character, given by Geiger as a diagnostic of A. tenuis vs A. tenuisculpta (Seguenza, 1880) . The latter species, originally described as a fossil from the Pliocene of southern Italy, is briefly compared to A. tenuis by Geiger (2012: 1106, 1116), and stated to differ, in addition to the sutsel in having a “longer teleoconch I (0.75 vs 0.5 whorl)” and “a wider umbilicus”. Nonetheless in the description provided for A. tenuisculpta , teleoconch I is reported to be 0.5-0.85 whorl so that this difference from A. tenuis is not diagnostic. Our own Canarian specimens have about‰.75 whorl of teleoconch I ( Fig. 3E ). A further feature of the early teleoconch of both A. tenuisculpta as understood by Geiger (2012) and our specimens, is the presence of a single spiral cord on the outer third of teleoconch I, abutting on the beginning of the selenizone ( Fig. 3D ). This feature is found also on other species (e.g. A. aspera ) and is stable on all the specimens we examined, but the lectotype of Scissurella tenuis shows only strong, arched axial ribs fading before reaching the suture, no spiral cord ( Fig. 3E ) and the teleoconch 1 extends hardly more than 0.5 whorl.

Our specimens are most likely conspecific with those reported by Geiger around the Canaries, Azores and Cape Verde Islands in the upper bathyal (310-1340 m), and the same species is also known to us from Galicia Bank off the NW Iberian Peninsula, but these may not be correctly identified as Anatoma tenuis , which has an abyssal type locality south of Greenland and has a discrepant morphology of the early teleoconch.

The fossil neotype of A. tenuisculpta has the last whorl considerably narrower and dropping more distinctly down from the suture, than in any of the Recent specimens here discussed. The specimens from Norway illustrated by Geiger as A. tenuisculpta have a much flatter spire and do not show essential difference with the Canarian specimens, apart from size and a somewhat less expanded last whorl. Conversely, Scissurella richardi Dautzenberg & H. Fischer, 1896 , described from 1300-1396 m off the Azores is certainly the same. For the time being, we find premature to assume the synonymy of Anatoma richardi with either A. tenuis or A. tenuisculpta and propose to use the former name for the Recent Macaronesian species.

Figures

FIG. 3. — Anatoma richardi (Dautzenberg & H. Fischer, 1896): A, B, shell from DW130 (3.7 mm diameter); C, scanning electron micrograph of another shell from the same locality (2.8 mm); D, protoconch and first teleoconch whorl of the same shell; E, protoconch and first teleoconch whorl of the lectotype of Scissurella tenuis Jeffreys, 1877 (USNM 181649,1). Scale bars: 100 µm. Small arrows: protoconch/teleoconch limit; large arrowheads: to the beginning of the selenizone (end of teleoconch I). (E, reproduced with the permission of the National Museum of Natural History, Smithsonian Institution, https://www.nmnh.si.edu/).