Aglaona, Chaban & Ekimova & Schepetov & Chernyshev, 2022

Chaban, Elena M., Ekimova, Irina A., Schepetov, Dimitry M. & Chernyshev, Alexei V., 2022, The new genus Aglaona: the first abyssal aglajid (Heterobranchia: Cephalaspidea: Aglajidae) with a description of two new species from the north-western Pacific Ocean, Zoological Journal of the Linnean Society 196, pp. 198-214 : 204

GENUS AGLAONA GEN. NOV.

Z o o b a n k r e g i s t r a t i o n: u r n: l s i d: z o o b a n k. org:act: 05553D3C-3DCF-4F61-B91B-952A8E62F268

Type species: Aglaona rudmani sp. nov.

Diagnosis: Headshield and posterior shield without posterior lobes. Parapodia small. Foot short, extending to half of shell length. Posterior end of posterior shield angulated or truncated. Shell internal, bulloid, oval, up to 4.0 mm in length, apex obtuse, spire partly visible; spiral sculpture with chains of narrow pits; parietal callus wing-like. Gizzard plates absent; radula 2:1:0:1:2; laterals bearing numerous small denticles on internal border. Copulatory system with short prostate; large, conical, penial papilla armed with a small, triangular chitinous plate or a large, chitinous multicusped stylet. Yellow gland and sensory bristles not detected.

The new genus includes two new species: Aglaona rudmani sp. nov. and A. valdesi sp. nov..

Comparison: The new genus differs from all described genera of the family Aglajidae by the presence of an internal and well-developed bulloid shell.

Etymology: The genus name is a contraction of the family name Aglajidae , in which it is placed, and the philinoid genus Laona A.Adams, 1865 , to which it resembles in external and internal morphology.

Remark: The callus of cephalaspidean shells is often thin and looks like a narrow band along the inner lip of the aperture tapering to its anterior part (see Philine guineensis Ev.Marcus & Er.Marcus, 1966 or Ph. schrammi Malaquias, Ohnheiser, Oskars & Willassen, 2016 in Malaquias et al., 2016: figs 4D, 9E). Sometimes in taxonomical descriptions the callus morphology is not mentioned at all or noted only as ‘parietal callus present’. The simple narrow callus mentioned above was described as ‘ribbon-like’ for the philinids Spiraphiline hadalis Chaban et al., 2019 and Spiraphiline kurilokamchatica Chaban et al., 2019 ( Chaban et al., 2019a). However, shells of Aglaona have a different morphology of the callus: it is narrow in the apical part of the shell, steadily widening to the middle of the body whorl, it then narrows rapidly to the columellar part of the aperture ( Fig. 4C ). We name this callus form as ‘wing-like’ and consider it an important character of the new genus.

Figures

Figure 4. Aglaona rudmani gen. & sp. nov. dorsal view of the holotype (A); ventral view of a paratype (B); paratype shell, ventral view, SEM the ‘wing-like’ callus is marked with an arrow (C); shell apex, SEM (E); shell spiral sculpture, SEM (D); radula, SEM (F); lateral teeth (G); copulatory system (SEM) (H); sketch, dissected penial sheath (I); chitinous stylet of penis SEM (J). Abbreviations: ej, ejaculatory duct opening; f, foot; pr, penial prostate; sh, headshield; psh, penial sheath; st, penial stylet. Scale bars: 2 mm (C), 1 mm (A, B), 500 µm (H), 400 µm (E), 200 µm (D), 100 µm (F, J), 50 µm (G).