Ruff sea scaleworm (Sthenolepis ruffi) and solitary sea scaleworm (Neoleanira solitaria) from 3000 meters sea depth

NEWS - Two marine scaleworms (Sthenolepis, Sigalionidae) from depths of 2350–3221 meters off the coast of Northern California collected as part of a long-term monitoring survey at the San Francisco Deep-Ocean Dredged Material Disposal Site and a baseline study by the US Navy off the coast of Northern California are new species.

Ruff sea scaleworm (Sthenolepis ruffi) has long palps and tentacular cirri, an upper group of neurochaetae with long blades, and a lower group of neurochaetae with non-canaliculate blades. Solitary sea scaleworm (Neoleanira solitaria) stands out among members of the genus by having simple fusiform supracicular neurochaetae in the posterior segments.

S. fimbriarum (Hartman, 1939) and S. spargens (Fauchald, 1972) are found in the Gulf of California, but the two can be easily distinguished by the size of the median antennae and auricles, the type of neurochaetae, and the elytra. S. ruffi is eyeless, has smaller auricles, long median antennae, smooth elytra without fimbriae on the edges and canaliculate blades.

S. ruffin is more closely related to S. spargens, both are eyeless and have small auricles and canaliculate blades. However, S. ruffin has long palps up to 12 segments and short tentacular cirri, five times longer than the tentacular parapodia. S. ruffi and S. spargens have been found at depths of 2350-3400 m, while S. fimbriarum at 18.2 m.

Ruffin is named after the late Robert Eugene Ruff in recognition of his many efforts in deep-sea exploration and collection of marine invertebrates, especially polychaetes. He also performed the first identification of these specimens. The species name is a noun in the genitive case.

In the Eastern Pacific, only two species are N. racemosa (Fauchald, 1972) and N. areolata (McIntosh, 1885). Both are similar to N. solitaria, in having small auricles, long median antennae and rounded boot-shaped ventral ctenidia. However, they differ in the length of the appendages of the first anterior segment, the shape of the branchiae and the type of neurochaetae.

N. solitaria differs from N. areolata in having the dorsal cirri of segment 3 longer, ¼ longer than those in N. areolata. The main feature that distinguishes N. areolata from N. solitaria and from the rest of the Neoleanira is the presence of spur-like processes at the base of the branchiae of the median and posterior regions.

N. solitaria differs from N. racemosa in having longer median and lateral antennae, and longer dorsal cirri of segment 3. N. solitaria has a longer anterior appendage, median and lateral antennae are ¼ longer than those of N. racemosa and regarding the dorsal cirri of segment 3, N. solitaria is twice as long as those of N. racemosa.

Solitaria is a Latin singular feminine adjective meaning 'solitary' or 'alone'. The only specimen of N. solitaria was found after much sampling in an area where other sigalionid species are found. The name also refers to the presence of a solitary fusiform chaeta in the neuropodia of the posterior segment, a characteristic that makes this species unique.

Original research

Christopher Cruz-Gómez & James A. Blake (2024). Description of new species of deep water Sthenolepis Willey, 1905 and NeoleaniraPettibone, 1970 (Annelida, Sigalionidae) from off Northern California, with the redescription of Sthenolepis spargens Fauchald, 1972. Zootaxa 5507 (2): 224–244, DOI:10.11646/zootaxa.5507.2.2

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