Tetrastemma freyae, Chernyshev & Polyakova & Vignesh & Jain & Sanjeevi & Norenburg & Rajesh, 2020

Chernyshev, Alexei V., Polyakova, Neonila E., Vignesh, Mohandhas S., Jain, Ruchi P., Sanjeevi, Prakash, Norenburg, Jon L. & Rajesh, Rajaian P., 2020, A histology-free description of a new species of the genus Tetrastemma (Nemertea: Hoplonemertea: Monostilifera) from Hawaii and India, Zootaxa 4808 (2), pp. 379-383 : 380-382

Tetrastemma freyae sp. nov.

( Fig. 1 A–G)

Type material. Holotype No JLN1622.01 ( NMNH), Kaneohe Bay , Oahu, Hawaii, July 2017, depth 3 m, live corals, coll. J.L. Norenburg. Paratype JLN1622.02 ( NMNH), collected with holotype . Paratype No ZSI / MBRC /NE-356 ( ZSI), Covelong (Kovalam) beach (12.7925ºN, 80.2530ºE), Tamil Nadu, India, mussel beds, intertidal, 16 December 2019, coll. M.S. Vignesh.

Other material examined. Three specimens, Covelong (Kovalam), Tamil Nadu, India, mussel beds, intertidal, 21 February 2019 .

GenBank accession numbers. Holotype MT 247877 ( COI), MT 247879 (H3); paratype MT 247878 ( COI), MT 247880 (H3).

Description. External features. Live specimens 2–5 сm long and up to 1 mm wide, with spatulate- to diamondshaped head, bearing four black eyes. Two anterior eyes not distinguishable being masked by patch of cephalic pigment. Oblique cephalic furrows in two pairs: posterior furrows located behind posterior pair of eyes and anterior pair immediately in front of posterior eyes. Body tapering posteriorly, with blunt-rounded tail. General body color pale yellowish, with a patch of black pigment on dorsal surface of head. Patch trapezoid or oval, slightly varying in shape between specimens. Deeply located white pigment (possibly cephalic glands) present near anterior and posterior margins of patch. Some specimens bear small irregularly spaced black spots located dorsally. In holotype, lateral gut pouches visible as two darker lines.

Internal features (on squeezed live specimens). Rhynchocoel as long as body. Basis cylindrical, with truncated and widened posterior part, 105 µm long and 35 µm in maximum width; central stylet 80 µm long. Two accessory stylet pouches each containing two accessory stylets. Gut pouches deeply branched. Ovaries contain 1–2 ovules.

Remarks. A total of 16 described Tetrastemma species have a pale general body color and a dark patch of pigment on the dorsal surface of the head. Four of these, Tetrastemma verinigrum Iwata, 1954 , T. pseudocoronatum Chernyshev, 1998 , T. pimaculatum Chernyshev, 1998 , and T. olgarum Chernyshev, 1998 , have been recorded from Asian waters. Some varieties of Tetrastemma nigrifrons (Coe, 1904) (formerly placed in Quasitetrastemma – see Chernyshev 2004) also have a similar color (see Zaslavskaya et al. 2010). These species possess pear- or ovalshaped basis of the central stylet, whereas the basis in the new species is cylindrical with a flared posterior margin. A similar basis is characteristic for species in the genus Zygonemertes Montgomery, 1897 , as well as Tetrastemma albomaculatum Chernyshev, 2016 . The latter species, unlike T. freyae , has a white spot on the head ( Chernyshev 2016). As the obtained data show, not only the body color, but also the shape of the central stylet basis should be taken into account in ‘histology-free’ descriptions of the new species of Tetrastemma .

DNA barcode analysis. Among the Pacific Tetrastemma species with a dark pigment patch on the head, COI sequences are known for T. pseudocoronatum , T. pimaculatum , T. olgarum , and T. nigrifrons . The p -distances be- tween these species and T. melanocephalum from the European coast are provided in Table 1. The samples of T. freyae from Hawaii and India have p -distances 1.3% for COI and 0.3% for H3, which warrant designating a single species despite the substantial geographical space between these findings.

Etymology. The specific epithet honors Ms Freya Goetz (NMNH) for her invaluable assistance to JLN in support of his field and laboratory work.

Figures

FIGURE 1. Tetrastemma freyae sp. nov. (A, B) holotype: lateral view of the head with everted proboscis (A) and dorsal view of the anterior body (B). (C, F, G) paratype: dorsal view of the anterior body (C); stylet apparatus (F, G). (D, E) two specimens from India, dorsal view (E, squeezed specimen under cover glass). Scale bars: (A-C), 0.5 mm; (D, E), 1 mm; (F), 100 µm; (G), 50 µm.