Gastropoda Cuvier, 1795

Schächinger, Peter M., Schrödl, Michael, Wilson, Nerida G. & Moles, Juan, 2022, Crossing the polar front-Antarctic species discovery in the nudibranch genus Tritoniella (Gastropoda), Organisms Diversity & Evolution (New York, N. Y.) 22 (2), pp. 431-456 : 435-447

publication ID	https://doi.org/ 10.1007/s13127-022-00541-3
publication LSID	lsid:zoobank.org:pub:56BCA5AA-3295-4306-96EE-40673EA79790
persistent identifier	https://treatment.plazi.org/id/0A264109-FFFB-CB0B-FF5B-D1D933C28A27
treatment provided by	Felipe
scientific name	Gastropoda Cuvier, 1795
status

Treatment

Class: Gastropoda Cuvier, 1795 View in CoL

Subclass: Heterobranchia Burmeister, 1837

Order: Nudibranchia Cuvier, 1817

Suborder: Cladobranchia

Family: Tritoniidae Lamarck, 1809

Genus: Tritoniella Eliot, 1907

Type species: Tritoniella belli Eliot, 1907

( Figs. 2–7 View Fig View Fig View Fig View Fig View Fig View Fig )

Tritoniella belli Eliot (1907): 5 View in CoL –29, figs. 1–8 & pl. A&B; Odhner (1934): 287 –292, figs. 54, 56a, 57–60 & pl. III: figs. 30–33; Minichev (1972): 358 –382, fig. 5; Vicente and Arnaud (1974): 537 –539, figs. 3 & 4; Wägele (1989b): 235 –243, figs. 1a, c, d, 4–8, Brueggeman (1998): 28 –36.

Tritoniella sinuata Eliot (1907): 10 View in CoL –29, figs. 9–11 & pl. C; Odhner (1934): 537 –539, figs. 55, 56b & pl. III: figs. 34–37; Vicente and Arnaud (1974): 292 –293, Fig. 4 View Fig .

Type locality Hut Point & McMurdo Bay, McMurdo Sound, Ross Sea; 7–15 m depth.

Diagnosis Colour white. Central ridge broad, without knobs, between rhinophoral sheaths thicker. Notum broad, sparsely covered by knobs. Notal margins smooth. Jaws oval, spike subterminal. Vas deferens short, penial papilla elongated, tip pointed.

Material examined Hut Point , Winter Quarters, 45–55 m depth, 3 spcs., NHMUK 1906.7.5.1 (holotype T. belli ); NHMUK 1919.9.16.3 (holotype T. sinuata ); NHMUK 1906.7.5.2 (paratype T. belli ); 4–18 m, 3 spcs., NHMUK 1906.7.5.4 (paratype T. belli ); NHMUK 1906.7.5.5 (paratype T. belli ); NHMUK 1906.7.5.6 (paratype T. belli ). Kapp Norvegia, Weddell Sea, 71.1916° S 12.2611° W, 309–318 m depth, 1 spc., ZSM 20012172 GoogleMaps , L = 2 3 mm, W = 10 mm, H = 7 mm, COI barcode MW444337 ; 71.1308° S 11.4528° W, 73–137 m depth, 1 spc., 1 dissected, ZSM 20012253 GoogleMaps , COI barcode MW444339 ; 71.1292° S 11.4678° W, 80 m depth, 3 spcs., 1 dissected, ZSM 20012255 GoogleMaps , L = 26 mm, W = 12 mm, H = 11 mm, COI barcode MW444340 , ZSM 20090522 View Materials , L = 27 mm, W = 17 mm, H = 9 mm, COI barcode MW444342 . Austasen Bank , Eastern Weddell Sea, 70.8444° S 10.5889° W, 226–266 m depth, 1 spc., ZSM 20012249 GoogleMaps , COI barcode MW444338 .

External morphology ( Fig. 4 View Fig ) Body 23–27 mm long, 10–17 mm wide, 7–11 mm high; elongated, massive. Colour beige to milky white in preserved specimens ( Fig. 4a–c View Fig ), living specimens completely white ( Fig. 4d View Fig ). Dorsal mantle surface with thick, longitudinal, central ridge, straight or crooked, sometimes with side ridge on right side at 1 2 of length, running close towards end of tail; with knobs and tubercles, interspersed all over notum but the ridges, one knob or small head ridge central on head, not connected to central ridge; central ridge, body margins, and knobs usually with white pigmentation (subepithelial). Notal margin with 5 to 7 extensions per side. Rhinophores with central club, surrounded by many feather-like plumes; rhinophoral sheath large, sometimes extended laterally and connected to the notal margin, margin smooth ( Fig. 4a, c View Fig ). Velum single-lobed or slightly bilobed after preservation; velar margin smooth or with up to 14 extremely short processes; tentacles ear-shaped, small. Lips oval to round, thick ( Fig. 4e View Fig ). Foot 1 2 to 2 3 of notum in width; propodium rounded ( Fig. 4b View Fig ). Genital papilla on right side at 1 3 of body length. Nephroproct and anal opening close together at 1 2 of body length ( Fig. 4c View Fig ).

Jaws and radula ( Fig. 5a–d View Fig ) Jaws oval, light yellow; masticatory border amber; distal ends translucent. Masticatory border long, smooth. Spike subterminal, smooth. Radular formula 41 × 23.1.1.1.23. Rachidian tooth longer than broad; cusp protruding, large. First lateral tooth with extremely short cusp. Lateral teeth progressively hook-shaped, smooth.

Digestive system Oral tube short, muscular. Pharynx muscular, dorsally connected to oesophagus. Salivary glands running ventrolaterally to oesophagus, tilted towards left side. Oesophagus thin, without cuticular lining, internally folded. Stomach connecting oesophagus with intestine; internally folded; three openings to the digestive glands; stomach plates absent. Digestive gland massive, with two types of glandular structures: (1) small, granular, orange in colour, (2) larger, bubble-like, transparent, visibly interconnected through ducts. Intestine, connected dorsally to stomach, making loop to right, below stomach, then loop to left above stomach, ultimately shaping an eight, leading to anal aperture. Anus opens through the epidermis laterally on right side.

Reproductive system ( Figs. 5e, f View Fig , 6a View Fig , 7 View Fig ) Gonad thick, of granular structure, covering digestive gland. Ampulla wide, compactly folded; splitting into vas deferens and vaginal duct. Vas deferens ( Fig. 6a View Fig ) long with 9–13 compact folds. Penial sheath muscular, folded longitudinally inside, embedded in tegument. Penis conical with circular enlargement close to tip. Mucous gland white with plicated folds, capsule gland smaller with reticulated structure. Vaginal opening in a slit ventral to penial opening. Seminal receptacle clubshaped, thick, compactly folded posterior of ampulla; with long duct.

Ecology Occurs at depths from 4 to 318 m ( Eliot, 1907; this study). Scales and spicules of soft corals were present in gut content of dissected specimens ( Wägele, 1989b). Specimens studied from the Ross Sea ingest and store chimyl alcohol as a chemical defence against sea star predators ( Bryan et al., 1998; McClintock & Baker, 1997), although this tactic is proven ineffective against the sympatric anemone Isotealia antarctica Carlgren, 1899 ( McClintock & Baker, 1997). The placement of the egg ribbons is not substrate-specific ( Bryan et al., 1998). Egg mass displayed in bands, spiral in shape, diameter 60 mm, height 8–10 mm, 400 eggs per 5 mm of band length, with a reinforced mucous layer ( Wägele, 1989a). Eggs transparent, oval to round, diameter 600 µm, surrounded by a soft, jelly-like hull. Embryos at veliger state light orange, giving colour to egg mass ( Wägele, 1989a).

Distribution Ross and Weddell Seas ( Eliot, 1907; Wägele, 1989b; this study).

Remarks Two of the specimens depicted by Wägele (1989b; T2 and T11) could not be identified to any of the species described here. While T11 ( Fig. 2a View Fig therein) could be a specimen of T. gnathodentata n.sp. a closer look at the material is needed. Specimen T2 ( Wägele, 1989b, Fig. 1b View Fig ) looks exceedingly different from all the specimens examined especially due to the number of knobs interspersed all over the notum and might be a new species altogether. Tritoniella belli differs from other species by its thick central ridge in combination with its smooth notal margin and, generally, a milky, white colouration. The species is only known from (mb) with a spike (sp). C–D, SEM of radula showing rachidian (rh) teeth, first (fl) and subsequent (cl) lateral teeth. E, SEM of the penial papilla. F, SEM close-up of the penial papilla showing the tip (t)

high-latitude Antarctica. We found some incongruencies while examining specimens from previous studies, that were attributed to T. belli . Most T. belli specimens show more similarities to the T. sinuata holotype than to the T. belli holotype. This could infer that—in case T. belli and T. sinuata are two distinct species—the original T. belli is the rarer of the two. We suspect that the validation of the two species might change with broader sampling in both the Weddell and (most importantly) the type locality, the Ross Sea.

Tritoniella gnocchi n. sp.

( Figs. 6b View Fig , 8 View Fig –9)

Tritoniella sp. 1 Moles, Berning et al. (2021).

ZooBank registration urn:lsid:zoobank.org:act:0A027FAA-5B9A-4A0E-AEDB-660A65489119

where parallel lines are depicted. D, T. gnathodentata n. sp., ring surrounding pp depicting connective tissue. E, T. schoriesi n. sp. F, T. heideae n. sp.

Type locality Burdwood Bank East , South Falkland Islands, 54.4666° S 55.6808° W GoogleMaps ; 561–572 m depth.

Diagnosis Colour white. Notum bloated, central ridge only anterior, faint. Notal margin with serrated extensions. Jaws subquadrangular, spike terminal. Rachidian with linear, lateral grooves. First lateral pointing upwards. Subsequent laterals with sharp tips, curved inwards. Vas deferens short, penial papilla stout, tip flattened.

Material examined Burdwood Bank East , South Falkland Islands, 54.4666° S 55.6808° W. 561–572 m depth: 1 spc., sequenced and dissected, SIO-BIC M13502 (holotype), L = 21 mm, W = 10 mm, H = 11 mm, COI barcode MW444343 GoogleMaps .

Etymology The name stems from the fact that this species externally reminds of the Italian gnocchi, especially after preservation.

External morphology ( Fig. 8 View Fig ) Body 21 mm long, 10 mm wide, 11 mm high; bloated. Colour beige in preserved specimen ( Fig. 8a View Fig ), living specimen translucent white ( Fig. 8d View Fig ). Mantle surface smooth, bloated; lacking knobs and tubercles; ridge faint, only seen on anterior part of mantle, connecting rhinophores. Notal margin with up to 15 extremely short, serrated extensions per side. Rhinophoral sheath extended, laterally connected to notal margin, margin smooth ( Fig. 8a View Fig ). Velum single-lobed; velar margin with 4 extremely short processes; tentacles conical, small, pointing outwards. Lips round ( Fig. 8e View Fig ). Foot 1 3 of notum in width ( Fig. 8b View Fig ).

Jaws and radula (Fig. 9a–d) Jaws subquadrangular, amber in colour, darker at masticatory border. Masticatory border long, coarse. Spike terminal (reaching farther than rest of jaws), coarse. Radular formula 71 × 62.2.1.2.62. Rachidian tooth as long as broad; cusp pointing upwards; with linear grooves laterally. First two lateral teeth with blunt cusp, curved upwards. Subsequent outer lateral teeth progressively hook-shaped, smooth, pointing downwards; inner lateral teeth with sharp tip curved inward.

Male reproductive system ( Figs. 6b View Fig , 9e, f) Specimen probably early adult. Vas deferens short, 4 folds. Penial papilla flat, cone-shaped, densely ciliated.

Ecology Occurs at depths from 561–572 m (this study). Plates, spindle sclerites, and inner axis of gorgonian present in gut content of the dissected specimen, belonging to the gorgonian family Primnoidae (Fig. 9g –h). Plate shape elongated-squarish, oval or arrow-like, with tubercles on inner side and a longitudinal central crest (Fig. 9g). Spindles spherical, rod-like—straight or curved—or irregular; tuberculated (Fig. 9h).

Distribution The singleton was found at Burdwood Bank east, south of the Falkland Islands (this study).

Remarks Tritoniella gnocchi n. sp. differs from its congeners by a faint, anterior central ridge and a short and bloated body. Internally, this is the only species with a terminal spike in the jaws.

Tritoniella prinzess n. sp.

( Figs. 6c View Fig , 10–11 View Fig View Fig )

Tritoniella sp. 2 Moles, Berning et al. (2021).

ZooBank registration urn:lsid:zoobank.org:act:9B67C543-4B1D-4201-AF6B-F9EF47DCC39E

Type locality Ardley Island, King George Island, South Shetland Islands, 62.2103° S 58.9139° W GoogleMaps ; 20–40 m depth.

Diagnosis Colour translucent white with white knobs, central ridge comprised of single knobs, mantle margin with continuous large knobs. Jaws subquadrangular, spike subterminal. Vas deferens short (juvenile), penial papilla elongated.

Material examined Ardley Island, King George Island, South Shetland Islands, 62.2103° S 58.9139° W, 20–40 m depth: 1 spc., sequenced and dissected, ZSM 2041002 View Materials (holotype), L = 17 mm, W = 10 mm, H = 6 mm, COI barcode MW444344 GoogleMaps .

Etymology This species is named after the oldest German confectionary Café Prinzess (1686, Regensburg, Germany) that sells chocolates in the form of molluscs. The species name is to be considered as a noun in apposition for nomenclature.

External morphology ( Fig. 10 View Fig ) Body 17 mm long, 10 mm wide, 6 mm high. Colour milky white in live and preserved specimens, with distinct white pigmentation in apex of dorsal knobs and mantle margin. Central ridge straight, mainly composed of knobs. Head ridge and ridge between rhinophoral sheaths absent. Notal margin lined with knobs, with 4 extensions per side. Rhinophoral sheath laterally connected to notal margin, margin with tubercles ( Fig. 10a View Fig ). Velum bilobed, velar margin with 10 extremely short processes. Lips oval ( Fig. 10d View Fig ). Foot ¼ of notum in width ( Fig. 10e View Fig ).

Jaws and radula ( Fig. 11a–d View Fig ) Jaws subquadrangular; light brown; yellow to amber at masticatory border. Masticatory border short, coarse. Spike subterminal, coarse. Radular formula 49 × 60.1.1.1.60. Rachidian tooth as long as broad; cusp extremely short, with fine ridge in the middle. First lateral tooth not visible on the SEM images. Outer lateral teeth progressively hook-shaped, thick, smooth.

Male reproductive system ( Fig. 6c View Fig ) The specimen is a juvenile. Vas deferens ( Fig. 6c View Fig ) very short, 2 folds. Penial papilla short, conical, without any characteristic features yet developed.

Ecology Occurs at depths from 20–40 m (this study). Spindle sclerites of gorgonians were present in gut content of dissected specimen, belonging to Primnoidae ( Fig. 11e–f View Fig ). Spindle rod-like, straight, curved, or irregular; usually densely tuberculated ( Fig. 11f View Fig ).

Distribution This singleton was found only off King George Island (this study).

Remarks Tritoniella prinzess n. sp. differs from its congeners by thick and white-sparkled knobs constructing the central ridge, also lining the notal margin.

Tritoniella gnathodentata n. sp.

( Figs. 6d View Fig , 12 View Fig –13, S2)

Tritoniella sp. 3 Moles, Berning et al. (2021).

ZooBank registration urn:lsid:zoobank.org:act:E238FCB4-8036-414D-8B10-F51776F66C1E

Type locality South Georgia, 53.8069° S 37.2170° W GoogleMaps ; 140–144 m depth.

Diagnosis Colour white, body conical, anteriorly broad. Central ridge slim, notum with few knobs. Notal margin with many extensions. Jaws quadrangular, spike subterminal, masticatory border with rows of denticles. Consecutive laterals very thin. Vas deferens long, penial papilla stout, flattened.

Material examined South Georgia, 53.8069° S 37.2170° W, 140–144 m, 2 spcs., 1 dissected, SIO-BIC M12606 (holotype), L = 24 mm, W = 10 mm, H = 8 mm, COI barcode MW444345 GoogleMaps , SIO-BIC M12648 (para - type), L = 42 mm, W = 22 mm, H = 15 mm, COI barcode MW444348 ; 55.0515° S 35.3955° W, 119 m depth, 2 spcs., 1 dissected and sequenced, SIO-BIC M12939 (paratype), L = 33–35 mm, W = 13–14 mm, H = 9–11 mm, COI barcode MW444349 GoogleMaps . Shag Rocks, 53.4240° S 42.0177° W 149–160 m depth: 1 spc., SIO-BIC M12618B, L = 3 2 mm, W = 10 mm, H = 9 mm, COI barcode MW444347 GoogleMaps ; 53.4532° S 42.0579° W, 169–186 m depth: 9 spcs., SIO-BIC M12609, L = 12–26 mm, W = 5–12 mm, H = 3–8 mm, COI barcode MW444346 GoogleMaps ; 53.7211° S 41.4627° W, 180 m depth: 2 spcs., SIO-BIC M13488, L = 22–26 mm, W = 9 mm, H = 7–8 mm, COI barcode MW444350 GoogleMaps ; 53.5343° S 41.6339° W, 132–133 m depth: 2 spcs., 1 dissected and sequenced, SIO-BIC M13489, L = 20–21 mm, W = 8 mm, H = 6–8 mm, COI barcode MW444351 GoogleMaps . Discovery Bank, 60.1457° S 34.9199° W, 427–751 m depth, 1 spc., SIO-BIC M13492, L = 38 mm, W = 10 mm, H = 9 mm, COI barcode MW444352 GoogleMaps .

Etymology The name indicates the diagnostic presence of dentition on the masticatory border of the jaws.

External morphology ( Fig. 12 View Fig ) Body 12–42 mm long, 5–22 mm wide, 3–15 mm high; elongated, often conical with a broad head. Living specimens milky white to translucent pink. Dorsal mantle surface with central ridge, straight or wavy, often broken, sometimes with side ridge on right side at 1 2 of length, running to 3 4 of the total length; with few knobs. One knob or small head ridge central on head, not connected to central ridge; body margins, and knobs with white pigmentation (subepithelial). Notal margin with 5 to 7 extensions per side. Rhinophoral sheath large, sometimes extended laterally and connected to notal margin, margin smooth ( Fig. 12a, c View Fig ). Foot 1 2 of notum in width ( Fig. 12b View Fig ).

Jaws and radula (Figs. 13a–d, S2a–d) Jaws subquadrangular to quadrangular; amber in colour; masticatory border darker. Masticatory border long; with several rows of conspicuous denticles. Spike internal, with denticles. Radular formula 47–53× 54–63.1.1.1.54–63. Rachidian tooth as long as broad; cusp very distinct, acute; with a lateral small cusp per side. First lateral tooth with thick, short cusp. Outer lateral teeth very thin, progressively hook-shaped, smooth.

Male reproductive system ( Figs. 6d View Fig , 13e, f, S2e, f) Vas deferens long, 15 folds. Penial papilla short; with broad, flat tip.

Ecology Occurs at depths from 119–751 m (this study). Plates and spindle sclerites of gorgonians present in the gut content of dissected specimens, belonging to Primnoidae (Fig. 13g –h). Plates elongated squarish, oval, or irregular; thick or thin; dorsally with tubercles on inner side, sometimes with longitudinal central crest; ventrally smooth (Fig. 13g –h). Spindles spherical, rod-like, or irregular; generally tuberculated (Fig. 13g).

Distribution Shag Rocks and South Georgia (this study); 119–751 m depth.

Remarks Tritoniella gnathodentata n. sp. externally differs from its congeners by a conical body shape, faint central ridge, and prominent margin knobs. Internally, this is the only species with denticles on the masticatory border (found in all three specimens dissected from South Georgia and Shag Rocks).

Tritoniella schoriesi n. sp.

( Figs. 6e View Fig , 14 View Fig –15)

Tritoniella sp. 4 Moles, Berning et al. (2021).

ZooBank registration urn:lsid:zoobank.org:act:11869CAF-3AA3-4541–8219-408B66CE49D6

Type locality Coronation Island , South Orkney Islands, 60.5509° S 45.1761° W GoogleMaps ; 222–278 m depth.

Diagnosis Colour white to bright orange. Central ridge slim, elevated, notum broad with many knobs. Notal margin with many extensions, strongly serrated. Jaws subquadrangular, spike subterminal. Vas deferens long, penial papilla elongated, tip pointed.

◂ Fig. 9 Characteristic body parts of Tritoniella gnocchi n. sp. specimen SIO-BIC M13502 (holotype). A, jaws. B, scanning electron micrograph ( SEM) of jaws showing masticatory border (mb) with a spike (sp). C, SEM of the radula showing rachidian (rh) teeth, first (fl) and subsequent (cl) lateral teeth. D, SEM of the radula showing a lateral tooth. E, SEM of the penial papilla. F, SEM of the tip (t) of the penial papilla. G, SEM of the gut content, showing plates and capstan sclerites. H, SEM of the gut content showing a gorgonian tuberculated spindle

Material examined Coronation Island , South Orkney Islands, 60.5509° S 45.1761° W, 222–278 m depth: 1 spc., SIO-BIC M12599 (holotype), L = 36 mm, W = 10 mm, H = 8 mm, COI barcode MW444353 GoogleMaps . Ardley Island , King George Island, Bransfield Strait, 62.2103° S 58.9139° W, 20–40 m depth: 1 spc., dissected and sequenced, ZSM 20110202–02 View Materials (paratype) GoogleMaps , L = 54 mm, W = 26 mm, H = 27 mm, COI barcode MW444354 .

Etymology This species is named after Dirk Schories who collected and documented the analysed specimens while SCUBA diving at King George Island.

External morphology ( Fig. 14 View Fig ) Body 36–56 mm long, 10–26 mm wide, 8–27 mm high. Colour beige in preserved specimens ( Fig. 14a–c View Fig ), living specimens translucent white to bright orange ( Fig. 14d View Fig ). Dorsal mantle surface with faint longitudinal central ridge, straight, with a side ridge on the right side, at 1 2 of body length; short head ridge central on the head, not connected to central ridge; with subepithelial white pigmentation below knobs and tubercles, interspersed all over notum. Notal margin with up to 11, strongly serrated extensions per side. Rhinophoral (fl) and subsequent (cl) lateral teeth. D, SEM of the radula showing lateral teeth. E, SEM of the gut content, showing rod-like and spindle sclerites. F, detail of the gut content showing a spindle sclerite sheath large, extended laterally and connected to notal margin; ridge between sheaths extremely elevated, more than central ridge ( Fig. 14a View Fig ). Velum bilobed; velar margin with up to 12 extremely short processes; oral tentacles large, ear-shaped, elongated laterally. Lips oval ( Fig. 14e View Fig ). Foot 1 2 of notum in width ( Fig. 14b View Fig ).

Crossing the polar front—Antarctic species discovery in the nudibranch genus Tritoniella … 445

Jaws and radula (Fig. 15a–d) Jaws subquadrangular; lower part pointed; amber in colour; masticatory border darker. Masticatory border very long, coarse. Spike coarse. Radular formula 68 × 109.1.1.1.109. Rachidian tooth as long as broad; with small lateral cusps on both sides of median cusp. First lateral tooth with blunt cusp. Outer lateral teeth hook-shaped, smooth; inner lateral teeth with sharp tip curved inward.

Male reproductive system ( Figs. 6e View Fig , 15e, f) Vas deferens very long, 25 folds. Penial papilla long, bud-shaped; with circular enlargement close to the tip; tip cone-shaped.

Ecology Occurs at depths from 20–278 m (this study). Plates, spindle sclerites and inner axis of gorgonians were present in the gut content of the dissected specimens, belonging to Primnoidae (Fig. 13g –h). Plates elongated squarish or oval, with dense, coarse tubercles on inner side (Fig. 13g). Spindles rod-like, straight or bifurcated, tuberculated (Fig. 13h).

Distribution Known from Ardley, King George, Coronation, and South Orkney Islands (this study); 20–278 m depth.

◂ Fig. 13 Characteristic body parts of Tritoniella gnathodentata n. sp. specimen SIO-BIC M12648 (paratype). A, jaws. B, scanning electron micrograph ( SEM) of the jaws showing masticatory border (mb) with a spike (sp) with indentation. C, SEM of the radula showing rachidian (rh) teeth, first (fl) and subsequent (cl) lateral teeth. D, SEM of the radula showing lateral teeth. E, SEM of the penial papilla. F, SEM of the penial papilla showing tip (t). G–H, SEM of the gut content, showing sclerites

Remarks Tritoniella schoriesi n. sp. differs from its congeners by a thin, elevated central ridge, a strongly serrated and wavy notal margin, and a bright orange colouration (even though this might be dietary dependent; Rossi et al., 2021).