Doridunculus punkus, Moles & Wägele & Uhl & Avila, 2016

Moles, Juan, Wägele, Heike, Uhl, Gabriele & Avila, Conxita, 2016, Bipolarity in sea slugs: a new species of Doridunculus (Mollusca: Nudibranchia: Onchidoridoidea) from Antarctica, Organisms Diversity & Evolution 17 (1), pp. 101-109 : 103-105

D. punkus n. sp.

( Figs. 1 , 2 , 3 , 4 , and 5 ) (See 3D PDF of the reconstructed anatomy of the whole specimen and a more detailed anterior part in Supplementary Material 1 and 2, respectively) http://zoobank.org/NomenclaturalActs/ 69A41 F49-FAEC-4A6F-ADD6-0657084A5745.

Holotype Adult specimen, 16 mm. Austasen, eastern Weddell Sea (71° 7.15 ′ S, 11° 26.23 ′ W) collected by Agassiz trawl on 29 December 2003, at 228-m depth ( PS65/280 – 1 ). Deposited in SNSB Zoologische Staatssammlung München (catalog number ZSM Moll 2016113 ).

Type locality Austasen, eastern Weddell Sea ( Antarctica).

External morphology ( Figs. 1 and 2a, b ) Live animal measured 16 mm ( Fig. 1a ), when preserved 15 × 6 × 6 mm (length:width:height). Color translucent white, brownish digestive gland seen postero-laterally by transparency. Body high, elongated, pentagonal in transverse section ( Fig. 1b ); mantle rim protruding; oral veil rounded, slightly folded laterally; oral tentacles grooved; notum rounded posteriorly ( Fig. 1c ); foot narrow, notched anteriorly, tapering posteriorly, mid-dorsal ridge present in tail ( Fig. 1d ). Posterior part not covered by notum. Rhinophores bearing seven diagonal lamellae, retractile within smooth cavities. Notum dorsally keeled, starting right in front of rhinophores, extending posteriorly to gills, forming a protuberance tilted toward left side of gills ( Fig. 1e ); average height of keel about 2 mm. Dorsal notum heterogeneously covered by pointed, conical, spiculated papillae; smaller in notal periphery and at sides of dorsal keel ( Fig. 1c ). Gills five, shortly pinnate, arranged in semicircle ( Fig. 1a, c, f ); anal papilla small, placed just behind gills. Genital pore small, situated antero-laterally beneath notum rim. Spicules conspicuous, fusiform, irregularly multiknobbed, sometimes with median crown of knobs ( Fig. 2a ); densely lying within notum, imparting rough texture, forming dense network toward epidermis ( Fig. 2b ).

Digestive system ( Figs. 2c, d , 3 , and 4c) Mouth lying ventrally, opening at base of oral veil, right in front of foot edge, in vertical furrow. Oral tube pyriform, surrounded by follicular oral glands. Oral disk thin, smooth, cuticular; demarcating transition into pharynx. Pharynx bulbous ventrally; two thick longitudinal muscles arise from postero-lateral part reaching gonad laterally ( Fig. 4c ). Jaws ear-shaped, without distinct ornamentation. Odontophore placed at rear part of pharynx. Radular formula 41 × 10.1.0.1.10 ( Fig. 2c, d ). Innermost lateral hook-shaped, with one longitudinal denticle at middle part (see white arrows in Fig. 2d ), flatened at base. Marginal teeth romboid in shape, presenting outer pointed cusp; decreasing in size toward lateral rim. Rachidian not observed. Salivary glands paired, saccular, small; lying behind pharynx, connected to it through small, thin, tubular ducts. Oesophagus thin, originating from posterior part of pharynx; passing through nerve ring, widening toward ventral side, reaching stomach far posteriorly; partly covered by gonad. Stomach completely surrounded by holohepatic digestive gland, situated in posterior third of viscera ( Fig. 3a, b ). Digestive gland presenting reticulated pattern, more pronounced toward periphery. Intestine thin, originating mid-dorsally from stomach, widening, becoming compressed, forming pronounced loop to right side, returning toward left side, ending in anal papilla.

Reproductive system ( Figs. 4a – c and 5 ) Triaulic. Gonad placed in middle region of body in front of digestive gland; globular in appearance, presenting up to 60 follicles. Gonoducts large connecting in front of gonad, converging into thin, tubular ampulla. Ampulla lying on gonad, extending ventrally ( Fig. 4a ). Vas deferens originating from distal gonoduct close to ampulla, leading into big, folded prostate; prostate making counterclockwise loop alongside body wall, connecting dorsally to thick distal vas deferens, proximally making short loop ( Fig. 4b ). Penis small, short, apparently unarmed; placed inside large, globe-shaped, muscular, penial sheath, lying close to genital atrium in right antero-lateral side of body ( Fig. 4a, b ).

Vaginal duct originating from proximal oviduct, close to ampulla forming a very short uterine duct, entering saccular receptaculum seminis. Bursa copulatrix saccular, roundish, originating from thin duct distally from vagina, placed in central transverse position. Vagina relatively short, opening into genital atrium. Oviduct short, placed at distal gonoduct leading to capsule gland. Capsule gland extending far posteriorly into gonad. Membrane and mucus glands not clearly distinct from each other, embracing capsule gland, extending lateroventrally close to body wall ( Fig. 4c ). See overall schematic outline of reproductive system in Fig. 5 .

Nervous system ( Fig. 4d ) Cerebral ganglia large, interconnected by short commissure; laterally oral nerve (N1) reaching mouth; labial nerve (N2) reaching anterior part of oral tube; rhinophoral nerve (N3) connected through small rhinophoral ganglia to cerebral ganglia, innervating rhinophores. Neither optical nerve, optic ganglion, nor eyes detected. Pleural ganglia attached to cerebral ganglia, without visible connectives. Statocysts present on ventral side of pleural ganglia, close to pharynx. Pedal ganglia large, interconnected by long commissure; with two lateral nerves running to ventral side. Two buccal ganglia, small, neighboring, lying at base of salivary glands, partly surrounded by them.

Circulatory and excretory systems ( Fig. 3 ) Pericardium flattened, placed at posterior part of body, above kidney, intestine, and digestive gland. Heart placed in longitudinal axis, no obvious distinction between auricle and ventricle. Aorta and blood gland not observed. Kidney lying below pericardium, extending back behind digestive gland; no nephroduct observed.

Ecology The single specimen of D. punkus n. sp. was found in a detritus-rich benthic bottom at 228-m depth. The community was dominated by sessile phyla, such as sponges ( Cinachyra , Clathria , Isodyctia , Iophon , Tedania ), bryozoans ( Alcyonidium , Carbasea , Isoschizoporella , Notoplites , Reteporella ), gorgonians ( Thouarella , Primnoisis ), ascidians ( Aplidium , Cnemidocarpa ), and pterobranchs ( Cephalodiscus ). Vagile fauna such as nudibranchs ( Doris , Doto , Tritonia , Tritoniella ), sea cucumbers, and polychaetes were also collected at the same station.

Etymology D. punkus n. sp. is named after the Mohican hairstyle of the punks, referring to the presence of one keel in the dorsum.

Remarks

D. punkus n. sp. differs from its congeners by the small folded oral tentacles, rounded (instead of bilobed) posterior notum, and by having a notal rim not covering the foot. The new species presents a single dorsal keel, while D. echinulatus presents two keels, more or less separated ( Sars 1878; Odhner 1907), and D. unicus lacks them ( Martynov and Roginskaya 2005). Both D. punkus n. sp. and D. echinulatus lack a rachidian tooth. In D. unicus , the rachidian is present and it is similar to that of Akiodoris and Armodoris ( Millen and Martynov 2005) . A hook-shaped inner lateral tooth is an autapomorphy of the herein described species, not found in any of the described species of Akiodorididae . The stomach of D. punkus n. sp. is completely enveloped by the digestive gland, while it is fully free in D. unicus ( Martynov and Roginskaya 2005) . Cerebral and pleural ganglia are separated in D. punkus n. sp., similarly to Armodoris ( Millen and Martynov 2005) . In D. punkus n. sp., eyes were not observed; this character was not specified in D. echinulatus ( Sars 1878; Odhner 1907), while D. unicus possesses eyes ( Millen and Martynov 2005).

Figures

Fig. 1 Live photograph (a) of Doridunculus punkus n. sp. and volume rendering (b–f) of the preserved animal. a Dorsal view. b Frontal view. c Dorsal view. d Ventral view. e Left-lateral view. f Right-lateral view. fo foot, gi gills, ke keel, m mouth, mr mantle rim, ot oral tentacles, rh rhinophores

Fig. 2 Micro-CT photographs of sclerotized structures of Doridunculus punkus n. sp. a Transverse section of the cephalic region showing spicules’ arrangement in the body wall. b Detail of the notal spicules. c Lateral view of the buccal mass. d Distal part of the radula (approximate scale); close-up showing inner lateral teeth, note longitudinal denticles (white arrows). fo foot, ja jaw, ke keel, mr mantle rim, od oral disk, rad radula, tu tubercles

Fig. 3 Macro-scan (0.4×) reconstruction of Doridunculus punkus n. sp. a Right-lateral, general view of all reconstructed organs. b Left-lateral view of the digestive system.a anus, cg cerebral ganglia, dgl digestive gland, gi gills, ht heart, int intestine, ja jaws, gon gonad, kid kidney, m mouth, mmgl membrane + mucus glands, od oral disk, oes oesophagus, ot oral tube, pen penis, peg pedal ganglia, per pericardium, pha pharynx, plg pleural ganglia, pro prostate, rad radula, rh rhinophore, sto stomach, vag vagina, vd vas deferens

Fig. 4 Micro-CT reconstruction of the anterior body region of Doridunculus punkus n. sp. (4×). a Antero-lateral view of the reproductive system; membrane + mucus glands and vagina not depicted; asterisk showing connection between distal ampulla and prostate. b Frontal view of the reproductive system. c Ventral view of digestive, nervous, and reproductive systems. d Frontal view of the nervous system; missing nerves are depicted with white-dashed lines. am ampulla, bc bursa copulatrix, bg buccal ganglia, cg cerebral ganglia, cgl capsule gland, ga genital atrium, gon gonad, ln lateral nerves, mmgl membrane + mucus glands, N1 oral nerve, N2 labial nerve, N3 rhinophoral nerve, od odontophore, oes oesophagus, pen penis, peg pedal ganglia, pha pharynx, plg pleural ganglia, pro prostate, rad radula, rhg rhinophoral ganglia, rm retractor muscles, rs receptaculum seminis, st statocyst, vag vagina, vd vas deferens

Fig. 5 Schematic outline of the reproductive system of Doridunculus punkus n. sp. am ampulla, bc bursa copulatrix, ga genital atrium, gon gonad, nigl nidamental glands (capsule, membrane, and mucus glands), pen penis, pro prostate, rs receptaculum seminis, vag vagina, vd vas deferens