Zonosagitta nagae ( Alvarino , 1967)

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

Zonosagitta nagae ( Alvarino, 1967)

Figs 6D , 7C , 22A-E

Sagitta nagae : Alvariño, 1967: 55-58 p., fig. 34A-D.

Material examined.

Korea Strait (33°29.662'N, 125°30.881'E), oblique towing with MOCNESS, 32-58 m depth, July 2020, NIBRIV0000895297 (two specimens) ; Korea Strait (33°24.504'N, 127°54.600'E), 0-50 m depth, oblique towing with conical net, May 2019, two specimens ; northern East China Sea (31°30.000'N, 125°17.100'E), 0-50 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895296 (one specimen) .

Description.

Total body length ranged from 11-15 mm. Hooks 6-8. Anterior teeth 11-15 and posterior teeth 15-35, respectively. Rigid and opaque body (Fig. 22A ). Long and dense teeth. Collarette present on neck (Fig. 22B ). Intestinal diverticula absent (Fig. 7C ). Eyes “D” -shaped with “E” -shaped eye pigments (Fig. 22B ). Anterior fins 27.7% of body length and 1.5 times longer than posterior fins. Anterior fins beginning in front of ventral ganglion and partially rayed. Starting points of anterior fins 28.6% and ending points of anterior fins 59.8% of body length, respectively (Fig. 22A, D ). Posterior fins 18.0% of body length. Starting points of posterior fins 67.8% and ending points of posterior fins 91.9% of body length, respectively. Posterior fins connecting with anterior fins partially rayed (Fig. 22A, E ). Seminal vesicles conical-shaped with small indentations and well separated from posterior fins (Fig. 22C ). Eggs reached posterior of anterior fins. Corona ciliata beginning behind eyes and elongated over neck (Fig. 22C ).

Distribution.

This species is found in the epipelagic zone (0-200 m depth) of the Pacific and Indian Oceans ( Pierrot-Bults and Nair 1991). In this study, the species was found in the epipelagic zone (0-120 m depth) of the northern East China Sea, the Korea Strait and the Yellow Sea (Fig. 1 : stations KS03, KS07 and nECS05).

Ecology.

This species appears year-round in most of the seas around Korea, predominantly in the southern and western seas and shows high abundance in areas where warm and cold currents meet ( Park 1970). In summer, the temperature range was 15.49-28.70 °C and the salinity was 30.92-34.01 psu. In winter, the temperature range was 11.47-11.58 °C and the salinity was 32.44-32.49 psu.

Remarks.

The anterior fin of Zonosagitta nagae had a longer rayless zone than the posterior fin, clearly distinguishing it from Z. bedoti . CBE staining showed the following spot pattern on the body surface: an irregular spot pattern continued from the head to the middle of the ventral ganglion; symmetrical dots appeared near the rayless zone of each fin (13 spots on anterior fin, 6 spots on posterior fin).

Figures

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

Figure 6. Shape and position of seminal vesicles A Aidanosagitta regularis (elongated) B Ferosagitta robusta (pear shape) C Pseudosagitta lyra (spherical shape) D Zonosagitta nagae (conical shape) E Flaccisagitta enflata (spherical shape) F Serratosagitta pacifica (seminal shape with chitinous teeth).

Figure 7. Intestinal diverticular (shown by white arrow) A Aidanosagitta regularis (present) B Ferosagitta robusta (present) C Zonosagitta nagae (absent) D Zonosagitta bedoti (absent).

Figure 22. A Zonosagitta nagae (dorsal view) B head C tail D anterior fin E posterior fin. Abbreviations: AF = anterior fin; E = eye; PF = posterior fin; SV = seminal vesicle.