Gnathia trimaculata Coetzee, Smit, Grutter & Davis 2009

Gnathia trimaculata Coetzee, Smit, Grutter & Davis, 2009

(Figs. 4, 5 B, C)

Material examined. 5 males, 3 females, and 2 praniza larvae, from gill chambers of a blotched fantail ray Taeniura meyeni Müller & Henle, 1841, caught in gill net, Nakagusuku Bay (26º N, 127º E), Okinawa Island, Ryukyu Archipelago, Japan, 25 May 2007, coll. Y. Ota (NSMT-Cr 20427). 1 praniza larva from gills of the silky shark Carcharhinus falciformis (Bibron, 1839) caught in gill net, Nakagusuku Bay, 22 June 2006, coll. Y. Ota (NSMT-Cr 20428). 4 males, 2 females, and 1 unfed larva from the same locality and host as the above specimens, coll. Y. Ota (KMNH IvR 500, 415). 1 praniza larva from gill chamber of the whipray Himantura sp., caught in gill net, Nakagusuku Bay, 14 May 2007, coll. Y. Ota (KMNH IvR 500, 416). 1 male and 1 female, from gills of the Javanese cownose ray Rhinoptera javanica Müller & Henle, 1841, caught in gill net, Nakagusuku Bay, 16 May 2007, coll. Y. Ota (NMV J46719). 2 praniza larvae from gill chambers of the whipray Himantura sp., caught in gill net, Nakagusuku Bay, 14 May 2007, coll. Y. Ota (NMV J46720).

Remarks. The size range of the males was 5.2–7.6 mm (mean ± SD; 6.17 ± 0.68 mm, n = 11), the size range of the females was 5.1–5.6 mm (5.41 ± 0.20 mm, n = 6) and the size range of the praniza larvae was 6.2–7.8 mm (7.03 ± 0.67 mm, n = 5).

The male, female, and the larva of Gnathia trimaculata were described from the Great Barrier Reef, Australia (Coetzee et al., 2009).The specimens of G. trimaculata from Ryukyus were larger than the ones from the GBR, the males (Fig. 4 A, B) from the Japanese fishes had higher number of setae (n = 21) on the external margin of peduncle 4 of antenna 2 than the GBR specimens. Female (Fig. 4 C–E): Article 3 of pylopod is more distinct then that of GBR specimens. Palp article 4 of maxilliped is not narrow. Praniza larva (Fig. 4 F): Some live specimens have no black spots. Brown lines present on lateral margins in alcohol.

Discussion. The distribution range of G. trimaculata is fairly wide. Gnathiid larvae actively swim to attach the host fishes (Monod, 1926; Wägele, 1988) and host fishes’ movement or migration is thought to increase the distribution range of the gnathiids (Tanaka, 2007). Therefore, some larval gnathiids potentially disperse widely. In particular, some large host fishes have high mobility. A tiger shark Galeocerdo cuvier can move over 100 km per day (see Fig. 3 in Heithaus et al., 2007) and migrated over 8000 km in 99 days (Heithaus et al., 2007). Actually, twenty larvae of G. trimaculata attached gills of a tiger shark (total length; 160 cm) (Ota, unpublished data). Thus, G. trimaculata may extend their distributions by their host’s movement.