Microchlamylla gracilis zfi, Korshunova, Tatiana, Martynov, Alexander, Bakken, Torkild, Evertsen, Jussi, Fletcher, Karin, Mudianta, I Wayan, Saito, Hiroshi, Lundin, Kennet, Michael Schroedl, & Picton, Bernard, 2017

Korshunova, Tatiana, Martynov, Alexander, Bakken, Torkild, Evertsen, Jussi, Fletcher, Karin, Mudianta, I Wayan, Saito, Hiroshi, Lundin, Kennet, Michael Schroedl, & Picton, Bernard, 2017, Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda), ZooKeys 717, pp. 1-139 : 37

Microchlamylla gracilis zfi subsp. n. Fig. 31

Type material.

Holotype. ZMMU Op-501, 11 mm long (fixed), Franz Josef Land, Northbrook Island, 26.08.2013, depth 20 m, coll. O.V. Savinkin.

Etymology.

After common acronym in Russian “ZFI” (Zemlya Franza Iosifa) for Franz Josef Land.

Type locality.

Franz Josef Land.

Diagnosis.

Discontinuous notal edge, background colour translucent white, digestive gland in cerata dark red, apical parts of cerata with white pigment, rachidian tooth with up to ten distinct denticles, delineated from central cusp, lateral teeth with up to eleven denticles on teeth edge, penis conical.

Description.

External morphology (Fig. 31 A–D). Body relatively narrow. Foot and tail moderate, anterior foot corners long. Oral tentacles long. Rhinophores ca. 1.5 times longer than oral tentacles, slightly wrinkled. Dorsal cerata finger-shaped to fusiform, forming several clusters along dorsal edges. Apices of cerata gradually pointed, with elongate cnidosac. Distinct notal edge remains mostly below cerata clusters. Digestive gland diverticulum fills significant volume of the cerata. Anal opening on right side below second large cluster cerata. Reproductive openings lateral, below first anterior cluster of cerata.

Colour (Fig. 31A, B, D). Background colour translucent white. Digestive gland diverticula dark red. Rhinophores background colour similar to body; along dorsal side of rhinophores runs thin white line. Dorsal sides of oral tentacles covered with thin opaque white line. Apical parts of cerata with opaque cap of white pigment.

Jaws (Fig. 31F). Masticatory process more than one-third as long as jaw body. Edge of masticatory processes bears several denticles that continue to form several reduced rows of denticles on the body of the masticatory processes.

Radula (Fig. 31G). Radula formula: 21 × 1.1.1. Rachidian tooth elongate-triangular with very broad cusp up to 1/2 of the tooth length, with a peculiar notch at the base. Rachidian tooth bears between seven and ten well-defined lateral denticles not adpressed towards the cusp. Some denticles form clusters, outermost denticles are considerably enlarged. Cusp is delineated from the adjacent first lateral denticles. Lateral teeth (Fig. 31G) broadly triangular with obtuse and attenuated posteriorly outer process and between five and eleven sharp denticles of various lengths on the internal edge.

Reproductive system (Fig. 31H). Diaulic. Hermaphroditic duct leads to swollen short ampulla. Vas deferens is long, broad, comprising at least three whorls, no distinct prostate. Penial sheath is narrow. Oviduct connects through insemination duct into female gland complex. Vagina short and indistinct. Receptaculum seminis oval, swollen. Distal receptaculum seminis present.

Ecology.

Associates with hydroid colonies usually at depths around 20 m. Apart from the holotype, several more specimens of this new subspecies can be traced from the original in situ photographs, but they were not collected. The egg mass is narrow cord that forms irregular, compressed pink or off-white spirals (Fig. 31E). Reproduction recorded in August.

Distribution.

So far known only from the northernmost locality, Franz Joseph Land Archipelago.

Remarks.

Microchlamylla gracilis zfi subsp. n. differs considerably from Microchlamylla gracilis gracilis by a peculiarly enlarged base with a prominent notch of the cusp of the rachidian radular teeth (compare Fig. 30H and Fig. 31G). In M. gracilis gracilis such a character was never reported before, either in literature (e.g., Odhner 1939; Thompson and Brown 1984) or according to our study of the specimens from geographically very distant regions, including the White Sea and southwest Norway. The lateral denticles of the rachidian teeth of M. gracilis zfi subsp. n. demonstrate considerable differences from M. gracilis gracilis in the presence of clustered denticles and very enlarged outermost lateral denticles (compare Fig. 30H and Fig. 31G). In addition, the vas deferens is much broader in M. gracilis zfi subsp. n. and differs considerably from M. gracilis gracilis (compare Fig. 30I and Fig. 31H). Thus, morphologically M. gracilis zfi subsp. n. is well-distinguished from the nominative subspecies; however, according to the molecular data, these two taxa are similar (maximal COI p-distance is 0.62% whereas mean COI p-distance value within the M. gracilis clade is 0.56%) and therefore we here consider their status to be at the subspecies level. More study is clearly necessary in this case. Microchlamylla gracilis s. l. was never reported prior to this study from Franz Josef Land and the presence of a separate taxon in this region can be explained also by isolation of this Archipelago from the main North Atlantic streams. This agrees with other our findings; namely, the presence of a new species of paracoryphellid Ziminella circapolaris sp. n. at Franz Josef Land (this study) and a new species of the onchidoridid genus Adalaria ( Martynov and Korshunova 2017).