Parasagitta elegans (Verrill, 1873)

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

Parasagitta elegans (Verrill, 1873)

Fig. 17A-E

Sagitta elegans : Verrill, 1873: 332-333 p.; Conant 1896: 211-212 p.; Fowler 1906: 31-32 p.; Lea 1955: 22-28 p., plate 3.

Material examined.

East Sea (37°33.198'N, 131°14.598'E), 0-100 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895306 (five specimens) .

Description.

Total body length ranged between 32.5 and 37.0 mm. Tail 14.7-20.6% of body. Hooks 11-12. Anterior teeth 9-10 and posterior teeth 22-29, respectively. Rigid and opaque body (Fig. 17 ). Collarette absent (Fig. 17A ). Intestinal diverticula present, but not obvious. Anterior fins 18.8% of body length. Anterior fins beginning at middle of ventral ganglion and partially rayed. Starting points of anterior fins 38.5% and ending points of anterior fins 57.5% of body length, respectively (Fig. 17D ). Posterior fins 22.3% of body length and 1.2 times longer than anterior fins. Starting points of posterior fins 67.7% and ending points of posterior fins 88.7% of body length, respectively. Posterior fins well-separated from anterior fins (Fig. 17E ). Seminal vesicles elongated (Fig. 17C ). Caudal fin roundish triangular-shaped (Fig. 17C ). Square eyes “+” shaped eye pigments (Fig. 17B ). Corona ciliata beginning in front of eyes and expanding to anterior trunk (Fig. 17B ).

Distribution.

This species is found in the Epipelagic (0-200 m depth), mesopelagic (200-500 m depth) and bathypelagic zones (1000-2000 m depth) of the Pacific, Indian and Atlantic Oceans ( Terazaki 1998; Choe and Deibel 2000) and the epipelagic and mesopelagic zones of the East Sea ( Park 1970). In this study, it was found in the epipelagic zone (0-100 m depth) of the East Sea.

Ecology.

A cold-water species, P. elegans is mainly found in the northern part of the Pacific Ocean ( Bieri 1959). The spawning season is winter and fully mature individuals are ≥ 30 mm in length ( Park 1970). The temperature range in the sampling stations of this study was 8.20-11.97 °C and the salinity range was 34.11-34.20 psu.

Remarks.

The absence of a rayless zone in the anterior and posterior fins and a collarette in anterior body and the presence of small seminal vesicles extending along the body in the Korean specimens of Parasagitta elegans were consistent with previous records ( Chihara and Murano 1997). Adult specimens (> 40 mm) collected in this study had small intestinal diverticula. CBE staining showed a spot pattern dividing the centre from the head to the tail septum. We observed one specimen for CBE staining pattern: dorsomedian line small, 60 dots; dorsolateral line not observed due to damage; lateral line, 42 dots; receptors on the lateral fin not found; anterolateral receptors on the caudal fin, 2 dots; posterior receptors on the caudal fin not found.

Figures

Figure 17. A Parasagitta elegans (dorsal view) B head C tail D anterior fin E posterior fin. Abbreviations: AF = anterior fin; E = eye; PF = posterior fin; SV = seminal vesicle.