A stomach plate to divide them all: a phylogenetic reassessment of the family Tritoniidae (Nudibranchia: Cladobranchia) Author Silva, Felipe De Vasconcelos Departamento de Biología, Facultad de Ciencias del Mar y Ambientales; Universidad de Cádiz; Campus de Excelencia Internacional del Mar (CEI · MAR), Av. República Saharaui, s / n, Ap. 40. 11510 Puerto Real (Cádiz), Spain felipe.devasconcelos@uca.es Author Pola, Marta Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid; Campus de Excelencia Internacional UAM + CSIC, C / Darwin, 2, 28049 Madrid, Spain Author Cervera, Juan Lucas Departamento de Biología, Facultad de Ciencias del Mar y Ambientales; Universidad de Cádiz; Campus de Excelencia Internacional del Mar (CEI · MAR), Av. República Saharaui, s / n, Ap. 40. 11510 Puerto Real (Cádiz), Spain & Instituto Universitario de Investigación Marina (INMAR), Universidad de Cádiz; Campus de Excelencia Internacional del Mar (CEI · MAR), Universidad de Cádiz, Av. República Saharaui, s / n, Ap. 40. 11510 Puerto Real (Cádiz), Spain text Zoological Journal of the Linnean Society 2023 Zool. J. Linn. Soc. 2023-07-11 199 2 445 476 http://dx.doi.org/10.1093/zoolinnean/zlad013 journal article 272041 10.1093/zoolinnean/zlad013 effa6181-8326-4c7d-8c91-809f7fabb862 0024-4082 8432389 C3E2DFF9-A0A6-41EA-A149-0F73A2BEE5E6 Tritonicula Korshunova and Martynov 2020 ( Figs 3I , 4F , 5F , 6F ) Type species: Tritonicula hamnerorum ( Gosliner and Ghiselin 1987 ) , by original designation. Diagnosis: Appendage whitish at the edge of the rhinophore sheath. Series of accessory denticles on the first lateral tooth. Prostatic part of vas deferens conspicuous, located at the proximal end of the penial sheath. Morphology: Body slender, up to 16 mm ( Fig. 3I ). Notum smooth. Oral veil narrow and entire. Four to six simple velar processes, with the outermost ones oħen longer. Seven to 15 pairs of arborescent or poorly arborescent gills. Rhinophore sheath with whitish digitiform appendage on the rim. Ratio jaw/body length: 0.08–0.15. Rachidian tooth tricuspid and smooth ( Fig. 4F ). First lateral tooth bearing five to 12 accessory denticles in the upper region ( Fig. 4F ). Masticatory border of jaws denticulate; with medium-sized (up to 40 µm) denticles with conical bases and sharp cusps. Cuticular folds absent. ODG complex holohepatic ( Fig. 5F ). Gonopore at end of one-third of body length, close to rhinophores. Anus and nephroproct at middle of body length. Conspicuous prostatic portion at the proximal end of penial sheath ( Fig. 6F ). Bursa copulatrix connects to the female opening through the vagina and opens to the exterior together with the female mass gland ( Fig. 6F ). Penis conical or flagelliform. Ampulla oħen fusiform and short ( Fig. 6F ). Species composition: Tritonicula bayeri , Tritonicula hamnerorum , Tritonicula ingolfiana ( Bergh 1899 ) comb. nov. , Tritonicula khaleesi , Tritonicula myrakeenae (Bertsch and Osuna 1986) , Tritonicula pickensi and Tritonicula wellsi . Remarks: The whitish appendage on the rhinophore sheath of Tritoniopsis was first noted in the re-description of Tritonicula wellsi and it is considered an adapted gill (Er. Marcus 1961 , Schmekel and Portmann 1982 ). The number of accessory denticles on the first lateral tooth varies among species, and are also present in the second lateral tooth in Tritonicula bayeri (Ev. Marcus and Er. Marcus 1967 ) . The phylogenetic position of the species Tritonicula wellsi and Tritonicula khaleesi , both originally described as ‘ Tritonia ’ (Er. Marcus 1961 , Silva et al . 2014 ), is molecularly confirmed in Tritonicula by our phylogenetic analyses ( Fig. 2 ). Tritonicula khaleesi was previously transferred to the Pacific genus Marianina on the basis of similar radular and paedomorphic external morphology ( Korshunova and Martynov 2020 ) and subsequently transferred to Tritonicula together with Tritonicula wellsi based on the fleshy extension of the rhinophoral sheath ( Moles et al . 2021 ). Classification of the South Atlantic Tritonicula khaleesi based on morphological characters is particularly challenging because its radular morphology, characterized by rachidian tooth unicuspid, fully denticulate and without accessory denticles on the first lateral tooth, is not found in other tritoniids. We have also extended the reported distribution of Tritonicula khaleesi from Brazil , south-western Atlantic ( Silva et al . 2013 ) to Costa Rica (northwestern Atlantic), based on the specimen (voucher number MZUCR 8300) previously identified as ‘ Tritonia ’ cf. pickensi in Camacho-García et al . (2014) . The deep-sea Atlantic Tritonicula ingolfiana , which has not been studied molecularly, is included based on the poorly arborescent secondary gills, whitish appendage on the rhinophore sheath and accessory denticles on the first lateral tooth ( Bergh 1899 ).