Chernyshevia escarpiaphila gen. et sp. nov.

urn:lsid:zoobank.org:act: 11DFF601-BBBA-409F-B072-5A93BA8C349F

Figs 1B–C, 8A–B, 9

Diagnosis

As for the genus; body pale white to pinkish, translucent; up to 10 mm in length.

Etymology

Named after vestimentiferan Escarpia spicata Jones, 1985, on which this species occurs with high abundance.

Material examined

Holotype

COSTA RICA • ♂ (fixed in formaldehyde and prepared as 12 slides with transverse sections, see cybertype); methane seep Mound Jaguar; 9.65556° N, 85.88046° W; depth 1909 m; 25 Jan. 2019; Greg Rouse and Avery Hiley leg.; collected by ROV SuBastian, Dive S0230 S2; found on Escarpia spicata; SIO-BIC N279 (ex SIO-BIC N264).

Paratypes

COSTA RICA • 1 spec. (fixed in formaldehyde and prepared as 7 slides with transverse sections, see cybertype); same collection data as for holotype; MZUCR Nemertea Collection MZUCR-104-01 (ex SIO-BIC N264) • 13 specs (8 fixed in formaldehyde, 5 fixed in ethanol); same collection data as for holotype; GenBank: ON036044, ON021861, ON182039; SIO-BIC N264 • 3 specs (ethanol); methane seep Jaco Scar; 9.119° N, 84.843° W; depth 1604–1854 m; 31 May 2017; Erik Cordes and April Stabbins leg.; collected by HOV Alvin, Dive 4916; GenBank: ON021862, ON182038; SIO-BIC N237 • 2 specs (ethanol); same collection data as for preceding; GenBank: ON036045, ON182037; SIO-BIC N236 • 6 specs (ethanol); same collection data as for preceding; GenBank; ON186253, ON036046, ON021863, ON182036; SIO-BIC N235 • 6 specs (ethanol); methane seep Jaco Scar; 9.118° N, 84.839° W; depth 1752–1802 m; 12 Jan. 2010; Elena Perez and Geoff Cook leg.; collected by HOV Alvin, Dive 4591; SIOBIC N266 • 2 specs (ethanol); methane seep Jaco Scar; 9.117° N, 84.843° W; depth 974–1866 m; 3 Mar. 2009; Elena Perez and Jake Bailey leg.; collected by HOV Alvin, Dive 4509; GenBank: ON186250, ON021859, ON182035; SIO-BIC N112 .

Cybertypes

Images of serial sections of holotype SIO-BIC N279 uploaded as N264a: https://doi.org/10.5281/zenodo.5346245

Images of serial sections of paratype MZUCR Nemertea Collection MZUCR-104-01 uploaded as N264b: https://doi.org/10.5281/zenodo.5346245

Description

Specimens 6–10 mm long and 0.5 mm in diameter (Fig. 8A–B). Body cylindrical. One pair of ventro-lateral cephalic furrows. Head rounded, not demarcated from rest of the body. Body coloration pale whitish to pinkish, body translucent (Fig. 8A). Cerebral ganglia and internal organs visible through body wall (Fig. 8B). Epidermis in foregut region 50 µm thick. Body wall composed of two muscle layers (outer circular, inner longitudinal; Fig. 9C). Combined proboscis and esophagus opening subterminal, ventral (Fig. 9B, D); stomach with pouches, surrounded by thin layer of longitudinal musculature; stomach (Fig. 9D) longer than pylorus; intestinal cecum with unpaired anterior ventral and paired anterior lateral pouches located alongside stomach; intestine with lateral pouches. Precerebral septum closed. Rhynchocoel wall with two very thin muscle layers (outer circular, inner longitudinal), rhynchocoel (Fig. 9G) almost extending to posterior end of body. Proboscis with outer circular, middle longitudinal, and inner circular muscle layers. Number of proboscis nerves indiscernible and proboscis armature not visible. Proboscis pore subterminal, ventral (Fig. 9A–B). Nervous system with outer neurilemma only, without neurochord cells; short dorsal commissure, broad ventral commissure (Fig. 9C). Precerebral nerves forming two dorso-lateral groups. Lateral nerve cords with small accessory nerve, no myofibrillae visible (Fig. 9E). Cerebral ganglia and lateral nerve cords located in longitudinal muscle layer (Fig. 9C–D). Eyes absent. Cerebral organs half the size of brain lobes, close in front of brain, surrounded by cephalic glands (Fig. 9C). Paired cerebral canal simple, unforked, opens ventro-laterally into cephalic furrows (Fig. 9D). Apical organ as depression at anterior tip of head, unpaired, cephalic gland extending to brain, distributed between muscle fibres of head (Fig. 9B, D). Circulatory system consisting of cephalic loop and three postcerebral vessels, mid-dorsal vessel not forming vascular plug (Fig. 9F). Testes sac like, located ventrally, close to lateral nerve cord (Fig. 9G).

Ecology

This species is the most abundant nemertean species collected along the Costa Rica margin. It occurs in close connection to Escarpia spicata with numerous specimens present on the tubes of this vestimentiferan (Fig. 1B–C). The whole epifauna found on the tubes of Escarpia spicata was extracted with a suction sampler.

Remarks

Chernyshevia escarpiaphila sp. nov. is attributed to the new genus Chernyshevia gen. nov. based on the executed phylogenetic analysis. In the phylogenetic analysis, it is sister to Tetrastemma elegans . Both species belong to a well-supported clade containing Vieitezia luzmurubeae, the type species of the genus, and Tetrastemma vittigerum (Fig. 7). A clade containing the five newly described species of the genus Alvinonemertes gen. nov. is sister to this clade. Intraspecific p-distances of the COI gene fragment vary between 2% and 4%.