Ferosagitta ferox (Doncaster, 1902)

Choo, Seohwi, Jeong, Man-Ki & Soh, Ho Young, 2022, Taxonomic reassessment of chaetognaths (Chaetognatha, Sagittoidea, Aphragmophora) from Korean waters, ZooKeys 1106, pp. 165-211 : 165

Ferosagitta ferox (Doncaster, 1902)

Sagitta ferox : Doncaster, 1902: 212 p.; Fowler 1906: 10-11 p.; Michael 1919: 259-262 p., tables 14-15; Tokioka 1959: 353-358 p., tables 1-4, figs 1-3; Alvariño 1962: 189-190 p., tables 1-5, figs 6-10; Alvariño 1967: 66-67 p., table 11, figs 40-41; Srinivasan 1979: 13-14 p., fig. 6.

Material examined.

Korea Strait (33°24.504'N, 127°54.600'E), 0-50 m depth, oblique towing with MOCNESS, May 2019 (one specimen) .

Description.

Broad head. Rigid and opaque body. Collarette present. Intestinal diverticula present. Grasping spines gently curved. Two rows of stout teeth arranged in comb shape. Two pairs of lateral fins partially rayed, anterior fins beginning at middle of ventral ganglion. Seminal vesicles oval-shaped with an anterior protruding part touching both lateral and caudal fins.

Distribution.

This species is found in the epipelagic zone (0-200 m depth) of the Pacific and Indian Oceans ( Pierrot-Bults and Nair 1991), the coast of Japan (Tosa Bay) ( Ohnishi et al. 2014) and the epipelagic zone (0-100 m depth) of the Korea Strait ( Park 1970). In this study, it was found in the epipelagic zone (0-100 m depth) in Korea Strait (Fig. 1 , station KS07).

Ecology.

This species inhabits the surface layer of the warm water and is mainly dominant in the Kuroshio Current of the Japanese waters ( Chihara and Murano 1997). In this study, the temperature range in the sampling locations was 25.87-28.70 °C and the salinity range was 32.72-33.11 psu.

Remarks.

Only immature individual was collected in this study. We easily distinguished F. ferox amongst the collected specimens by the presence of distinct head as wide as the trunk and the presence of elongated ovoid seminal vesicles on the body. The Korean specimen was classified as immature because the boundary of the seminal vesicles was not obvious and the inside was mostly empty. This characteristic is consistent with Alvariño’s (1967) description regarding the immaturity of this species.

Figures

Figure 1. Sampling stations in Korean waters. Empty circles, sampling stations; filled circles, the stations where the chaetognaths were secured.