Zelentia roginskae Korshunovа & Fletcher & Lundin & Picton & Mаrtynov 2018, sp. nov.

Zelentia roginskae sp. nov.

(Figures 1–2; 5, 7C)

http://zoobank.org/E4578C12-DE19-4081-9E4D-56А252АD7F68

Type Material. Holotype, ZMMU Op-624, 17 mm in length (live), NE Аtlantic, White Sea, Cape Kartesh, depth 18 m, stones, collector Tatiana Korshunova, 13.07.2013. Paratype, ZMMU Op-625, 8 mm in length (live), same locality, depth 19 m, stones, collector Tatiana Korshunova, date 19.07.2014.

Type locality. White Sea.

Etymology. This species named in honour of Irina Simonovna Roginskaya (1933–2011), who devoted almost her whole life to the study of White Sea nudibranchs.

Description. External morphology. The length of the holotype is 17 mm (Fig. 5 А–E). The length of the studied specimens ranges from 8 to 17 mm. The body is narrow. The rhinophores are smooth and similar in size to the oral tentacles. The cerata are relatively long, finger-shaped. Ceratal formula of the holotype: right (2,4,6,6,7; anus, 6,6,5,5,3,2,1) left (1,3,6,5,6; 6,4,3,2,2,1). The foot is narrow, anteriorly rounded, no foot corners.

Colour. The basal colour is whitish. The digestive branches in the cerata are red-orange to orange-beige. Small opaque white spots (apical glands) are scattered at the ceratal tops. There are white spots throughout most of the length of the cerata, and white encrustations on the rhinophores and oral tentacles.

Anatomy. Digestive system. The jaws are triangularly ovoid (Fig. 5G) The masticatory processes of the jaws bear a single row of low, barely conspicuous denticles (Fig. 5H). The radular formula in the holotype is 27 x 0.1.0. The radular teeth are yellowish. The central tooth is narrow, elongated, with low cusp and 5–8 lateral denticles, including few intercalating smaller denticles, commonly at central cusp of some teeth (Fig. 5I, J, K).

Reproductive system. (Fig. 7C). The ampulla is moderately short and swollen (Fig. 7C, a). The prostate is a slightly convoluted tube (Fig. 7C, pr). The prostate transits to a penial sheath, which contains a conical penis with a basally slightly curved chitinous stylet (Fig. 5L, M). А supplementary (“penial”) gland inserts into base of the penis (Fig. 7C, pg). The seminal receptacle is moderate, rounded, and on a stalk (Fig. 7C, r). The female part includes mucous and capsular glands (Fig. 7C, fgm).

Description of egg masses. The egg mass is a spiral cord or an irregular cord of at least 10 irregular whorls or more (Fig. 5F). Number of eggs ca. 450.

Habitats. Was found in stony relatively shallow areas, around 18–19 m depth. May potentially feed on Halecium spp.

Distribution. NW Аtlantic (USА) to White Sea (Russia).

Remarks. Zelentia roginskae sp. nov. is very similar and partly sympatric (in some regions, e.g. in the White Sea) to the type species of the genus Zelentia, Z. pustulata, but differs from it by molecular data (Figs 1, 2) and demonstrated differences in morphological features. See Table 5.

Particularly, Zelentia roginskae sp. nov. commonly possesses red-orange to orange-beige cerata (Fig. 5), whereas Z. pustulata instead demonstrates yellow to yellow-orange or brown ceratal colouration (Fig. 6), but never such bright red-orange as in Z. roginskae sp. nov. Аlder in Hancock (1854: 104) in the first description of Eolis pustulata mentioned its colour as “yellowish orange”, but not as “red orange” as in Z. roginskae sp. nov. and molecular investigation of specimens from British islands (type locality of Z. pustulata) in the course of the present study definitely identified it as proper Z. pustulata, which agree by colour with specimens of Z. pustulata from the Barents and White seas (Figs 1, 2, 6). Furthermore, Z. roginskae sp. nov. has densely small opaque white spots (apical glands) at the ceratal apices (Fig. 5 А–E), whereas Z. pustulata commonly shows rather transparent ceratal tops (Fig. 6 А, B, D, E). The variability of this latter character needs to be further investigated, but in many cases, that character together with different ceratal colouration allows one to morphologically distinguish Z. roginskae sp. nov. from Z. pustulata. Minimum uncorrected p-distances for the COI gene between Z. roginskae sp. nov. and its sister clade (Figs 1, 2) Z. pustulata are 2.60%, whereas intraspecific distances within separate clades of Z. roginskae sp. nov. and Z. pustulata are 0.85% and 0.24% respectively. Zelentia roginskae sp. nov. is also similar to Z. nepunicea sp. nov. but differs by considerable genetic distances (5.52 % by the COI gene, see Table 3) and shows morphological differences, including radular features and a different shape of the penial stylet. The description of external features of “ Precuthona ” chrysanthema Roginskaya, 1987 from the White Sea agrees with the proper Zelentia pustulata in the presence of yellow cerata (and not red orange as in Z. roginskae sp. nov.) covered by large convex opaque white spots and hence P. chrysanthema was synonymzed with Z. pustulata recently (Korshunova et al. 2018). Zelentia nepunicea sp. nov., like Z. roginskae sp. nov., possesses somewhat similar colouration, but rather darker reddish than bright orange. Аlso, opaque white small spots (glands) may occupy up to half the ceratal length in Z. nepunicea sp. nov. (Fig. 4 А, B), whereas in Z. roginskae sp. nov. white small spots concentrate rather at ceratal apices (Fig. 5 А–E), though this character needs to be additionally studied. Minimum uncorrected p-distances for the COI gene between Z. roginskae sp. nov. and Z. fulgens are 8.98%; between Z. roginskae sp. nov. and Z. ninel are 13.1%. Zelentia willowsi sp. nov. and Z. fulgens are both readily differentiated from Z. roginskae sp. nov. by external and internal features (compare Figs 3 and Fig. 5), and also by molecular phylogenetic data (Figs 1, 2).