2017 Volume 64 Issue 2 Pages 157-170
Thirty-five museum-held specimens (238.2–940.0 mm total length, TL) of the electric ray Tetronarce formosa (Haas and Ebert, 2006), collected from the Pacific coast of Japan from Ibaraki to Kochi prefectures, and the East China Sea, represent the first records of T. formosa from Japanese waters and include the northernmost record (Ibaraki) for the species (previously recorded only from Taiwan). The specimens are described in detail and the validity of the following characters previously used to separate T. formosa from the closely related species T. tokionis (Tanaka, 1908), confirmed: dorsal surface of body purplish-brown in T. formosa (vs. dark chocolate-brown in T. tokionis), disc oval (vs. essentially circular), disc width 63.6–67.9% of TL (vs. 50.1–52.6 %), posterior margin of caudal fin not emarginated (vs. emarginated), and distance from posterior tip of pelvic fin to origin of lower caudal fin lobe less than three-quarters of caudal fin height and less than half pelvic fin width (vs. more than three-quarters of caudal fin height, and more than half pelvic fin width). Although spiral valve turns were previously regarded as diagnostic, separating T. formosa from T. tokionis, that character is not considered valid, following dissection. Further comparisons of Japanese T. formosa with T. tokionis based on 35 and 5 specimens, respectively, revealed the former to differ from T. tokionis in the following additional characters: cloaca to pectoral fin margin length 27.9–36.5% (mean 32.9%) of TL [vs. 25.1–30.8% (27.5%) in T. tokionis]; caudal fin overall height 19.3–25.6% (22.4%) [vs. 14.2–18.9% (17.0%)]; caudal fin height at dorsal lobe 7.2–11.0% (9.5%) [vs. 5.9–6.7% (6.4%)] in males; snout to maximum disc width 28.1–38.8% (32.0%) [vs. 26.5–27.2% (26.9%)] in females; pelvic fin width 26.1–33.1% (30.0%) [vs. 18.5–18.8% (18.7%)] in females; and caudal fin height at ventral lobe 9.3–12.1% (10.7%) [vs. 5.8–7.6% (6.7%)] in females.
