Cuthona methana Valdés & Lundsten & Wilson 2018, sp. nov.
Creators: name: Valdés, Ángel
name: Lundsten, Lonny
name: Wilson, Nerida G.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Nudibranchia
Fionidae
Cuthona
Cuthona methana

description: Cuthona methana sp. nov.
(Figs. 2 F–G, 15A–D, 16–17)
Type material. Holotype: Hydrate Ridge, off Oregon (44.67012, -125.0987), 587–610 m depth, ROV Jason II (dive 593), 4 Sep 2011, 4 mm preserved length (SIO-BIC M12413).
Paratype: Hydrate Ridge, off Oregon (44.67012, -125.0987), 587–610 m depth, ROV Jason II (dive 593), 4 Sep 2011, 6 mm preserved length, dissected (SIO-BIC M12412).
Description. Body elongate, wide (Figs. 2E), with several elongate, dorso-lateral cerata. Cerata arranged in densely packed rows, running from behind oral tentacles to posterior end of body (Figs. 2E, 15B, 15D). Cerata increase in size in each row, lateral cerata typically shorter, dorsal cerata longer. Oral tentacles elongate and wide (Figs. 15A, 15C). Foot corners tentacular, very small (Figs. 15A, 15C). Rhinophores elongate, smooth (15B, 15D). Reproductive opening on right anterior portion of body (Fig. 15B, 15D). Anal opening lateral, posterior to pericardium (Fig. 15B, 15D). Body color cream-white, semi translucent, with viscera visible through skin as a palepinkish mass (Fig. 2 F–G). Oral tentacles same color as body, with pink-orange bases, rhinophores pink-orange. Cerata translucent white, with cream digestive branches and opaque white cnidosacs.
Digestive system with large, muscular buccal bulb (Fig. 16A). Esophagus narrow, short, connecting anteriorly into buccal bulb. Digestive gland with lateral branches entering cerata. Intestine emerging dorsally from left side of digestive gland, forming a loop towards right ventral side of body and running posteriorly to open into anus.
Radular formula 25 × 0.1.0 in paratype (SIO-BIC M12412). Radular teeth narrow (Fig. 17A), with arch-shaped base and single central, elongate, sharp cusp. Each tooth with 3 elongate denticles on each side of cusp (Fig. 17B). Jaws elongate (Fig. 17C), masticatory border with a row of denticles bearing a series of tubercles (Fig. 17D).
Reproductive system with very short, oval ampulla (Fig. 16B), opening into female gland complex next to prostate opening. Prostate tubular, short, forming two loops, expanding into oval, muscular deferent duct. Penis simple, elongate. No vagina nor bursa copulatrix were observed, probably due to the small size of the specimen dissected.
Biology. This species was collected at 587 m depth on Hydrate Ridge, an area of methane seeps about 44 nautical miles off Newport, Oregon (Fig. 1). Both animals were collected off inactive rocks around seep areas. The holotype was collected from E7 sterile rock 8 and the paratype from E7 large rock 20a (Levin lab experiments).
Etymology. This species is named for the methane seep environment where it was found.
Remarks. Molecular data could not be generated for Cuthona methana, but this species is morphologically different from all other species of Cuthona described from the Eastern Pacific.
Cella et al. (2016) proposed a new taxonomy for species previously assigned to Cuthona including the resurrection of Tenellia A. Costa, 1866 and the introduction of several new genera. Although this classification scheme is not as complex as that by Korshunova et al. (2017), it also based on poorly resolved trees and makes the placement of species not studied genetically, such as Cuthona methana sp. nov., more difficult. The phylogenetic relationships of aeolids are in a state of flux due to lack of resolution for lower branches, and only next generation sequencing techniques appear to provide resolution for critical nodes (Goodheart et al. 2017). Because it is virtually impossible for us to determine the phylogenetic position of Cuthona methana sp. nov. in Cuthona, Tenellia, or any of the new genera described by Cella et al. (2016), it is here conservatively regarded as a member of Cuthona.
Among the known Eastern Pacific species, Cuthona methana sp. nov. is only externally similar to C. divae (Ev. Marcus, 1961), but lacks the brown to pink pigment digestive branches in the cerata and the rhinophores are pinkish, instead of translucent white (Behrens & Hermosillo 2005). Internally, the radula of C. divae (described by MacFarland, 1966 —under the name Cuthona rosea MacFarland, 1966) has a triangular rachidian tooth with numerous lateral denticles, very different from that of C. methana, which has a much narrower rachidian tooth with only 3 denticles on each side of the cusp.
description: Published as part of Valdés, Ángel, Lundsten, Lonny & Wilson, Nerida G., 2018, Five new deep-sea species of nudibranchs (Gastropoda: Heterobranchia: Cladobranchia) from the Northeast Pacific, pp. 401-433 in Zootaxa 4526 (4) on pages 420-424, DOI: 10.11646/zootaxa.4526.4.1, http://zenodo.org/record/2611755