Tritonia nigritigris, Valdés & Lundsten & Wilson, 2018

Valdés, Ángel, Lundsten, Lonny & Wilson, Nerida G., 2018, Five new deep-sea species of nudibranchs (Gastropoda: Heterobranchia: Cladobranchia) from the Northeast Pacific, Zootaxa 4526 (4), pp. 401-433 : 404-408

publication ID	https://doi.org/ 10.11646/zootaxa.4526.4.1
publication LSID	lsid:zoobank.org:pub:3CFFF3AC-C447-4FCE-B6F8-D2B7BAE8B678
DOI	https://doi.org/10.5281/zenodo.5971394
persistent identifier	https://treatment.plazi.org/id/F357AF10-798E-4339-BD7A-D473BDD9BA83
taxon LSID	lsid:zoobank.org:act:F357AF10-798E-4339-BD7A-D473BDD9BA83
treatment provided by	Plazi
scientific name	Tritonia nigritigris
status	sp. nov.

Treatment

Tritonia nigritigris View in CoL sp. nov.

( Figs. 2A View FIGURE 2 , 3A View FIGURE 3 , 4–5 View FIGURE 4 View FIGURE 5 )

Type material. Holotype: Guide Seamount, Pacific Ocean (37.036532, -123.330875), 1733.4 m depth, ROV Doc Ricketts (dive 882), 15 Aug 2016, 82 mm preserved length, dissected ( LACM 3553 View Materials ), GenBank accession numbers: MH 756138 View Materials ( COI), MH 756133 View Materials (16S).

Description. Body elongate, narrow ( Fig. 2A View FIGURE 2 ). Notum outline with four invaginations, completely surrounded by numerous, densely packed glandular projections ( Fig. 2A View FIGURE 2 ), giving the animal a ruffled appearance. Dorsum covered with numerous, densely packed elongate tubercles or projections, oriented in different directions, forming a zigzagging pattern in some areas. Velum wide, forming two triangular lateral projections, with several frontal irregular indentations. Rhinophores short and wide, with 9 simple lamellae, located on anterior end of notum. Rhinophoral sheaths elongate, with 12 branched papillae around distal edges. Foot smooth, rounded posteriorly, visible dorsally at posterior end and in notum invaginations. Genital and anal openings on right side of body. Background color of notum black. Dorsal tubercles primarily white to greyish-brown near posterior notum, giving the body a light appearance, becoming darker towards head, turning completely black on anterior notum; this gives a black and white appearance with a greyish transitional area mid-length, forming a wedge of black pigment. Notum edge primarily white, except for anterior-most end that becomes dark grey. Velum completely black. Rhinophoral sheaths black with grey edges. Rhinophores with black stalks and beige sheath papillae and clubs. Foot dark grey, surrounded by a thin white line.

Digestive system with large, muscular buccal bulb ( Fig. 4A View FIGURE 4 ). Esophagus wide, connecting anteriorly into buccal bulb, where two large, flat salivary glands connect. Intestine emerging dorsally from left side of digestive gland, forming a loop towards the right side of body where it opens into the anus ( Fig. 3A View FIGURE 3 ). Radular formula 44 × 50.1. 50 in holotype. Rachidian teeth narrow, with a large, sharp central cusp about twice as large as tooth bases and 3 irregular denticles on each side of central cusp ( Fig. 5A View FIGURE 5 ). Lateral teeth hook-shaped, with sharp, elongate cusps lacking denticles ( Fig. 5B View FIGURE 5 ). Outer lateral teeth very elongate with reduced bases ( Fig. 5C View FIGURE 5 ). Jaws elongate, with no differentiate masticatory border ( Fig. 5D View FIGURE 5 ).

Reproductive system with large, highly convoluted ampulla forming several loops ( Fig. 4B View FIGURE 4 ), opening on female gland complex where the prostate connects. Prostate narrow, elongate, forming a single loop and expanding into a wide and muscular deferent duct, which connects with a simple, conical penis. Vagina elongate, narrow, expanding abruptly in its distal 1/4 th and opening into the spherical bursa copulatrix. The seminal receptacle is a small spherical evagination located close to mid-length in the vagina.

Biology. This species was collected at 1733.4 m depth on the Guide Seamount, about 55 nautical miles off Davenport, California ( Fig. 1 View FIGURE 1 ). The specimen was collected on a steep section of volcanoclastic rock. Dense populations of Keratoisis sp. (isidid octocoral) were observed in close proximity. Other organisms included comatulid and hyocrinid crinoids, primnoid octocorals, Evoloplosoma cf. claguei (sea star), additional unidentified sea stars, Acesta sp. (bivalve), Farrea sp. (hexactinellid sponge), and large and abundant Macrouridae (rattail fishes).

Phylogenetic position. Based on available sequence data and the phylogenetic analyses conducted, Tritonia nigritigris sp. nov. is sister to the Antarctic species Tritoniella belli Eliot, 1907 ( Fig. 6 View FIGURE 6 ).

Etymology. The species name is derived from the unique coloration of the holotype, in particular the broken, black stripes, which are reminiscent of those of a tiger.

Remarks. The most common species in relatively deep-waters of the eastern Pacific is Tritonia tetraquetra ( Pallas, 1788) , previously recognized as T. diomedea Bergh, 1894 . Martynov (2006) considered that Pallas (1788) original description of Limax tetraquetra from the Kuril Islands corresponded to a specimen of the species commonly identified as T. diomedea (see Behrens & Hermosillo 2005) and therefore proposed to use the name T. tetraquetra for this species. Here we cautiously follow Martynov’s (2006) opinion, but clarification of the taxonomic status of this species requires comprehensive examination of specimens across its broad range (from the Kuril Islands to Panama), because as in other nominal species with similar ranges, multiple cryptic species may be involved.

Tritonia nigritigris View in CoL sp. nov. is externally different from other species of Tritonia View in CoL described to date. The most similar species morphologically is the deep-water species T. newfoundlandica Valdés et al., 2016 View in CoL , described from the North Atlantic ( Valdés et al. 2016). Both T. nigritigris View in CoL sp. nov. and T. newfoundlandica View in CoL have narrow, elongate bodies with the anterior end wider, tapering posteriorly into a pointy, triangular end. However, whereas T. newfoundlandica View in CoL is uniformly black, with the rhinophores, rhinophoral sheaths, velar appendages, and secondary gills brownish-red and the dorsum is smooth, lacking tubercles. On the contrary T. nigritigris View in CoL sp. nov. has a more complex coloration of black, white and grey, and the dorsum is tuberculate.

The only two other deep-water species of Tritonia View in CoL (found below 500 m depth) known to date are T. ingolfiana Bergh, 1899 View in CoL described by Bergh (1899) from the mid-Atlantic ridge based on a single specimen collected at 887 m depth, and T. episcopalis Bouchet, 1977 View in CoL described from 1035–2170 m depth also in the Atlantic. Bergh (1899) described his preserved specimen T. ingolfiana View in CoL as grayish blue with yellow rhinophores. This is different from T. nigritigris View in CoL sp. nov., which has a black to white body and the rhinophores, gills and velum are much lighter even in the preserved specimens. Other differences include the shape of the penis, which is very elongate and tightly packed in the penial sheath of T. ingolfiana View in CoL ( Bergh 1899: pl. 3 fig. 9), whereas the penis of T. nigritigris View in CoL n. sp. is much shorter and straight. Tritonia episcopalis View in CoL as well as T. newfoundlandica View in CoL have a characteristic scoop in the penis, which is absent in T. nigritigris View in CoL n. sp. The external coloration of T. episcopalis View in CoL is bright violet with the gills of the same color and the rhinophores red, whereas in T. nigritigris View in CoL n. sp. the body is black to white.

The sister species of Tritonia nigritigris n. sp., Tritoniella belli , is very distinct externally. Tritoniella belli ranges in color from uniform milky-white or translucent to yellow or orange in specimens ( Wägele 1989b). As in T. nigritigris n. sp. the mantle edge is wavy and can be smooth or have finger-like processes. However, specimens of T. belli have a smooth dorsum typically with a longitudinal median ridge, whereas T. nigritigris n. sp. has a tuberculate dorsum and no ridge. In the phylogenetic analyses presented here, both T. nigritigris n. sp. and T. belli form a monophyletic group sister to Tritonia , supporting the separation of Tritoniella from Tritonia . Under this scenario, T. nigritigris n. sp. should be considered a member of Tritoniella . However, the phylogeny of Tritonia is poorly understood and several critical species have not yet been sequenced. Also, morphologically, T. nigritigris n. sp. appears more similar to some species of Tritonia than to T. belli making difficult to find morphological synapomorphies for Tritoniella . Until all these issues are resolved, we prefer to maintain T. nigritigris n. sp. in Tritonia .