Nacellida Lindberg, 1998

Sharina, Svetlana N. & Chernyshev, Alexei V., 2022, The taxonomic position of brooding limpets of the genera Erginus and Rhodopetala (Patellogastropoda), Zoologischer Anzeiger 299, pp. 200-206 : 205

Order Nacellida Lindberg, 1998 .

Suborder Lottiina W. Ponder, Lindberg & J. Ponder et al., 2020 .

Family Rhodopetalidae Lindberg, 1981 stat. nov.

( = Erginidae Chernyshev 2018 syn. nov.)

Type genus: Rhodopetala Dall, 1921 .

Diagnosis. Shell conical or helcioniform, without radial ribs or with very fine riblets, consists of four (crossed-lamellar, myostracum, crossed-lamellar, and complex prismatic) or five (crossed-lamellar, myostracum, crossed-lamellar, foliated, and complex prismatic) layers. Radula 0.3.0.3.0, with lateral teeth approximately equal in size and shape. Ctenidium absent or rudimentary. Pallial tentacles absent. Pallial cavity enlarges into brooding pouch to accommodate embryos and juveniles.

Composition. The genera Rhodopetala and Erginus .

Comparison. The family Rhodopetalidae differs from the other four families of Lottiina ( Lottiidae , Acmaeidae , Eoacmaeidae , and Neolepetopsidae ) by the presence of special brooding pouch for accommodation embryos and juveniles. In the radula structure, Rhodopetala and Erginus strongly resemble members of the family Acmaeidae , but differ from them in the shell structure.

Genus Rhodopetala Dall, 1921 .

Type species: Nacella rosea Dall, 1872 .

Diagnosis. Shell helcioniformes, submarginal apex positioned at anterior quarter of shell. Ctenidium rudimentary, situated medially at back of nuchal cavity. Shell consists of five (crossed-lamellar,

myostracum, crossed-lamellar, foliated, and complex prismatic) layers; interior central area with a silvery metallic luster.

Composition. Only type species, Rhodopetala rosea ( Dall 1872) . For description of the species, see Lindberg 1981.

Genus Erginus Jeffreys, 1877 .

Type species: Patella rubella Fabricius, 1780 .

Diagnosis. Shell conical, apex subcentral. Ctenidium absent. Shell consists of four (crossed-lamellar, myostracum, crossed-lamellar, and complex prismatic) layers; interior central area porcelaneous, without a silvery metallic luster.

Composition. Two subgenera with six Recent and two fossil species.

Subgenus Erginus Jeffreys, 1877 .

Diagnosis. Subcephalic tentacle (‘penis’) absent. Anal papilla small and simple. Pericardium elongated posteriorly. Protoconch relatively small, teleoconch with wide and flat radial ribs, not lost in adult shell.

Composition. Two species, Erginus rubellus (O. Fabricius, 1780) и E. galkini Chernyshev & Chernova, 2002 . For descriptions of the species, see Lindberg 1983 and Chernyshev & Chernova 2002.

Subgenus Problacmaea Golikov & Kussakin, 1972 .

Type species: Problacmaea moskalevi Golikov et Kussakin, 1972 .

Diagnosis. Subcephalic tentacle (‘penis’) present (except Erginus apicinus ). Anal papilla large, with folds. Pericardium elongated laterally. Protoconch relatively large, teleoconch without radial ribs, lost in adult shell.

Composition. Four Recent species: Erginus moskalevi ( Golikov & Kussakin 1972) , E. sybariticus ( Dall 1871) , E. apicinus ( Dall 1879) , and E. puniceus Lindberg, 1998 . For descriptions of the species, see Golikov & Kussakin 1972; Lindberg 1983, 1988a.

Remarks. The genus Problacmaea was erected by Golikov & Kussakin (1972). Lindberg (1988a) and then Chernyshev & Chernova (2005) considered Problacmaea as a subgenus of Erginus . Chernyshev (2018) has suggested reassigning the genus rank to Problacmaea . Unfortunately, only two COI sequences are known for Erginus rubellus , which makes it impossible to conclude whether Erginus and Problacmaea are genera or subgenera. For this reason, we consider Problacmaea as a subgenus of Erginus .