Tetrastemma polyakovae Sagorny & Döhren & Rouse & Tilic 2022, sp. nov

Tetrastemma polyakovae sp. nov. urn:lsid:zoobank.org:act: 0A69EED8-5057-4882-A12C-AB4FC69B7B63 Fig. 8M–N Diagnosis Tetrastemma polyakovae sp. nov. can be attributed to the genus Tetrastemma based on the strong support for a sister group relationship between the three species of this genus included in the analysis. Etymology For Dr Neonila E. Polyakova, in recognition of her contributions to the study of deep-sea nemerteans. Material examined Holotype COSTA RICA • spec. (ethanol); methane seep Mound 12; 8.93030° N, 84.31260° W; depth 997 m; 24 Oct. 2018; Jorge Cortés and Oliver Ashford leg.; collected by HOV Alvin, Dive 4978; GenBank: ON186259, ON036056, ON021857, ON182051; SIO-BIC N258. Paratype COSTA RICA • 1 spec. (ethanol; entirely used up in DNA extraction; only image and DNA available); same collection data as for holotype; 8.93° N, 84.31° W; depth 996–999 m; GenBank: ON036057, ON021858, ON182050; MZUCR Nemertea Collection MZUCR-101-01 (ex SIO-BIC N 255). Description Specimens 15 mm long and 1 mm in diameter. Body rounded. Two pairs of cephalic furrows. Head not demarcated from rest of body, rounded. Body coloration pale orange to brownish. Internal organs well visible through body wall (Fig. 8M–N). Remarks The new species is attributed to the genus Tetrastemma based on the executed phylogenetic analyses. This species is sister to Tetrastemma strandae sp. nov. (Fig. 7). Intraspecific pairwise p-distances are 2%, whereas interspecific distances between T. polyakovae sp. nov. and the two newly described species vary between 7% and 8%. Distance between this species and Tetrastemma stimpsoni is 12.5%.
Published as part of Sagorny, Christina, Döhren, Jörn von, Rouse, Greg W. & Tilic, Ekin, 2022, Cutting the ribbon: bathyal Nemertea from seeps along the Costa Rica margin, with descriptions of 2 new genera and 9 new species, pp. 132-174 in European Journal of Taxonomy 845 (1) on pages 161-162, DOI: 10.5852/ejt.2022.845.1959, http://zenodo.org/record/7258852