Tritoniopsis Eliot 1905

Silva, Felipe De Vasconcelos, Pola, Marta & Cervera, Juan Lucas, 2023, A stomach plate to divide them all: a phylogenetic reassessment of the family Tritoniidae (Nudibranchia: Cladobranchia), Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 199 (2), pp. 445-476 : 464

Tritoniopsis Eliot 1905

( Figs 3C , 4C , 5C , 6C )

Tritoniopsilla Pruvot-Fol 1933 , Mem. L’ Inst. D’ Egypte, 21: 90.

Type species: Tritoniopsis brucei Eliot 1905 , by original designation.

Diagnosis: Alternate oral processes. Numerous, fully arborescent gills. Rachidian tooth unicuspid and denticulate, first lateral tooth undifferentiated, few lateral teeth per row.

Morphology: Body slightly broad, length up to 100 mm ( Fig. 3C ). Oral veil broad, bilobed or entire. Nine to 13 velar processes alternating in size. Fourteen to 20 pairs of arborescent gills, mostly uniform. Ratio jaw/body length: 0.11–0.15. Rachidian tooth unicuspid ( Fig. 4C ). Central cusp strong, sharp and long; small denticles present in the lower region of the base. Laterals slender, hooked and sometimes denticulate. Small number of lateral teeth (up to ten per half row). Masticatory borders of jaws differentiated or smooth. Cuticular folds absent. ODG complex large (more than two-thirds of total animal length) ( Fig. 5C ). Gonopore at one-third of body length, furthest from rhinophores. Anus and nephroproct at midbody length or beyond. Female gland mass large ( Fig. 6C ). Bursa copulatrix pyriform or oval. Penis flagelliform or conical.

Species composition: Tritoniopsis brucei , Tritoniopsis elegans and Tritoniopsis flydis .

Remarks: Apartfromthediagnosticsynapomorphies, Tritoniopsis is characterized by medium-sized species (up to 100 mm) with an elongated ODG complex, and a large female gland mass ( Odhner 1936, Er. Marcus and Ev. Marcus 1970). The masticatory border of the jaw is smooth in Tritoniopsis brucei and Tritoniopsis elegans ( Eliot 1905, Yonow 2017), and differentiated as comprised of irregular cell-like structures in Tritoniopsis flydis (Er. Marcus and Ev. Marcus 1970) . Tritoniopsis was recovered as a sister group to Marianina in our phylogenetic analyses ( Table 2 ). Both genera have unicuspid and denticulate rachidian teeth which are easily distinguished: the unicuspid rachidian of Tritoniopsis is stronger with a few small denticles in the lower region of the base ( Fig. 4C ), while the unicuspid rachidian of Marianina is narrower and fully denticulate with larger cusps ( Odhner 1936).

Figures

Figure 3. Representative species of genera of Tritoniidae (with exception of Paratritonia). A, Tritonia hombergii (MNCN15.05/93379) (Portaferry, Ireland); B, Candiella plebeia (MNCN15.05/93393) (Portaferry, Ireland); C, Tritoniopsis elegans (MB28-0045061) (Zavora, Mozambique); D, Tritonidoxa capensis (MNCN15.05/93399) (Scoưburg, South Africa); E, Tritoniella belli (Antarctica); F, Marianina rosea (French Polynesia); G, Myrella challengeriana comb.nov.(Bahía Camarones, Argentina); H, Tochuina gigantea (Agnew Pass, USA); I, Tritonicula khaleesi (MZUSP113165) (Fortaleza, Brazil); J, Marionia cucullata (Golfo Nuevo, Argentina); (K) Marioniopsis levis ‘1’ (MNHNC/ MB28-004895) (Nacala, Mozambique). Photo A and B, courtesy of B. Picton; photo C and K courtesy of Y.Tibiriça; photo D courtesy of V. Fraser; photo E courtesy of M. Caballer; photo F courtesy of G. Rouse; photo G and J, courtesy of N. Baưini; photo H courtesy of S. Thiebaud; photo I by F. Silva.

Figure 4. Scanning electron micrographs of radulae of analysed key species of Tritoniinae and Marioniinae subfam. nov.: A, tricuspid rachidian teeth and differentiated first lateral of Tritonia hombergii (ZMBN 83471); B, tricuspid rachidian teeth and differentiated first lateral with single accessory denticle (circled) of Candiella plebeia (MNCN15.05/93393); C, unicuspid rachidian teeth and undifferentiated first lateral of Tritoniopsis elegans (MNHNC/MB28-004506); D, tricuspid rachidian teeth and differentiated first lateral of Tritonidoxa capensis (MNCN15.05/93399); E, unicuspid rachidian teeth and undifferentiated first lateral of Tochuina gigantea (NHMD-115967); F, tricuspid rachidian teeth and differentiated first lateral with several accessory denticles (circled) of Tritonicula hamnerorum (MNCN15.05/93378); G, tricuspid rachidian teeth and differentiated first lateral of Marionia blainvillea (NHMD115968); Scale bars: A, D, E = 60 μm; B, C = 22 μm; F = 20 μm; G = 110 μm.

Figure 5. Digestive system arrangements of analysed key species of Tritoniinae and Marioniinae subfam. nov., dorsal view: A, Tritonia hombergii (ZMBN 83471); B, Candiella plebeia (MNCN15.05/93393); C, Tritoniopsis flydis (GR7-DMC00040); D, Tritonidoxa capensis(MNCN15.05/93399); E, Tochuina gigantea (NHMD-115967); F, Tritonicula hamnerorum (MNCN15.05/93378); G, Marionia blainvillea (NHMD115968). Abbreviations:a, anus; aodg, anterior ODG complex; e, esophagus; i, intestine; odg, ovotestis-digestive gland complex; s, stomach; podg, posterior ODG complex.

Figure 6. Reproductive system arrangements of analysed key species of Tritoniinae and Marioniinae subfam. nov., dorsal view:A, Tritonia hombergii (ZMBN 83471); B, Candiella plebeia (ZMBN 83471); C, Tritoniopsis flydis (GR7-DMC00040); D, Tritonidoxa capensis (MNCN15.05/93399); E, Tochuina gigantea (NHMD-115967); F, Tritonicula hamnerorum (MNCN15.05/93378); G, Marionia blainvillea (NHMD115968). Abbreviations: ag, albumen gland; am, ampulla; bc, bursa copulatrix; fo, female opening; fgm, female gland mass; hd, hermaphrodite duct; o, oviduct; p, penis; pp, prostatic portion; ps, penial sheath; v, vagina; vd, vas deferens.