Tetranemertes kandai ( Kato, 1939 ), 2025

Abato, Jamael C., Hookabe, Natsumi & Kajihara, Hiroshi, 2025, Species Diversity of Tetranemertes (Nemertea: Monostilifera) in Japan, Species Diversity 30 (1), pp. 71-83 : 75-78

Tetranemertes kandai ( Kato, 1939) comb. nov. ( Fig. 5A, B )

Emplectonema kandai Kato, 1939: 251–253 , figs 1, 2, pls 1–6 (type material unknown); Kanda 1939: 166–173, figs 1–4.

Emended diagnosis. A luminescent, reddish-orange Tetranemertes , anterior end almost colorless, posterior end light yellow, ocelli on each side of the head in linear groups, 15–20 in number per group, with hair-like projections on anterior and lower lateral edges of head ( Fig. 5A ), central stylet and accessory stylets slender, acutely pointed, longitudinally fluted, basis rounded, and posteriorly bifurcated ( Fig. 5 ), stylet to basis ratio 1.45.

Remarks. Emplectonema kandai was established based on material associated with the solitary ascidian Chelyosoma siboja Oka, 1906 living on a sandy or muddy bottom, 30–40 m deep in Aomori Bay near the Asamushi Marine Biological Station. This nemertean can emit a pale green luminescence along the entire body length in response to both chemical and mechanical stimuli ( Kanda 1939). In life, E. kandai is filiform in shape, dorso-ventrally flat, 10–15 cm to more than 100 cm in length, 0.1 cm in width, uniformly reddish-orange in body color, with the anterior end being almost colorless, posterior end light yellow; the ocelli are arranged in a linear group, 15–20 in number, each dorsally and ventrally on both sides ( Fig. 5A ); the central stylet is slender, acutely pointed, 0.16 mm in length, glassy, and conspicuously fluted longitudinally; the stylet basis is clubshaped, 0.11 mm in length, with roundly bifurcated terminations; two stylet pouches each has two accessory stylets shorter than the central stylet, fluted as the latter ( Fig. 5B ). The stylet/basis ratio is 1.45.

While members of the two eumonostiliferous hoplonemertean genera Emplectonema and Tetranemertes commonly have an elongated body, they differ in the shape of the head (e.g., rounded in the former; elongated and diamond-shaped in the latter), structure of the cephalic furrows (e.g., two greatly reduced, small arch-like cerebral organ furrows in the former; single V-shaped ventral cerebral organ furrow in the latter), and the arrangement of the ocelli (e.g., four groups or two irregular rows in Emplectonema vs. four longitudinal rows, with two overlapping dorsoventrally on each side in Tetranemertes ). The type species of Emplectonema was recently discovered to be Borlasia camillea Quatrefages, 1846 (now Emplectonema neesii Örsted, 1843 or Neesia neesii ), instead of Emplectonema viride Stimpson, 1857 as had long been accepted among nemertean specialists. In response to this, a case has been submitted to the ICZN for a ruling to set aside the original type fixation and designate E. viride as the type species ( Kajihara et al. 2021); under Article 82.1 of the Code, E. viride is deemed as the type species until a ruling is published. Irrespective of the overlooked type species, the genus concept for Emplectonema has been vague, resulting in almost like a catch-all taxon consisting of any thin-bodied eumonostliferans.

Among 22 species listed as members of Emplectonema ( Norenburg et al. 2024) , the only true congener other than the type species would be E. gracile ( Johnston, 1837) ; E. friederichi Sánchez, 1973 may be a junior synonym of the type species E. viride . Other species currently in Emplectonema will probably be transferred to different genera in future taxonomic studies; E. mitsuii Yamaoka, 1947 (in addition to E. kandai ) is more closely related to other eumonostiliferans than to E. gracile and E. viride ( Kajihara et al. 2011; present study). No matter which of B. camillea or E. viride becomes the type species of Emplectonema upon the ICZN ruling, E. kandai should be transferred to Tetranemertes . Among the 22 Emplectonema species ( Norenburg et al. 2024), E. kandai is the only one where the ocelli are arranged in four rows, as stated and illustrated in its original description ( Kato 1939: fig. 1A, B). We herein propose to transfer the species to Tetranemertes , yielding a new combination, T. kandai comb. nov.

Figures

Fig. 5. Tetranemertes kandai (Kato, 1939) comb. nov. A, Anterior end of body; B, stylet apparatus. Reproduced from Kato (1939: figs 1, 2). © 1938 The Zoological Society of Japan.