Marianina Pruvot-Fol, 1931

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 : 465

Marianina Pruvot-Fol, 1931

( Fig. 3F )

Mariana Pruvot-Fol 1930 , Bull. Mus. Natl. Hist. Nat., 2: 229. Aranucus Odhner 1936 , Mém. Mus. Roy. Hist. Nat. Belg, 2(3): 1090.

Type species: Marianina rosea ( Pruvot-Fol 1930) , by original designation. To date, this is a monotypic genus.

Diagnosis: Secondary gill bifid. Rhinophore sheaths with outwardly projecting triangular lobe. Rachidian tooth unicuspid and fully denticulate, first lateral tooth fully denticulate, few lateral teeth per row.

Morphology: Body slender, up to 20 mm ( Fig. 3F ). Notum smooth. Oral veil reduced, entire. Four simple velar processes. Whitish rhinophore sheath bears triangular lobe projecting outwards. Three to seven pairs of bifid white gills. Rachidian tooth unicuspid and denticulate (with several accessory denticles). First lateral differentiated denticulate with blunt cusp. Masticatory border of jaws denticulate with small granuleshaped denticles. ODG complex cladohepatic. Cuticular folds present. Gonopore at one-third of body length, before first pair of gills. Anus and nephroproct before middle of body length. Bursa copulatrix connects to the female opening through the vagina and opens to the exterior together with the female mass gland. Penis elongated. Ampulla oval.

Remarks: A thorough survey of the literature revealed that the available information on the Indo-West Pacific Marianina rosea is scarce. Most of the available anatomical data comes from the original descriptions by Pruvot-Fol (1930) and Odhner (1936), and some characters were reported only once, e.g. the presence of cuticular folds in the stomach ( Odhner 1936). Marianina was recovered as a sister-group to Tritoniopsis in our phylogenetic analyses, which is consistent with recent studies ( Valdés et al. 2018, Korshunova and Martynov 2020). This monotypic genus is one of the most aberrant genera of Tritoniidae : the small body size, reduced oral veil, low number of bifid ‘cerata-like’ gills, unique radular morphology and cladohepatic ODG complex have led researchers in the past to consider Marianina as a monotypic family, Marianinidae (= Aranucidae ). These numerous unique adaptations and the confirmed molecular placement within Tritoniidae are considered solid evidence for the paedomorphosis of this genus ( Korshunova and Martynov 2020).

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.