Pseudosagitta lyra (Krohn, 1853)

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

Pseudosagitta lyra (Krohn, 1853)

Figs 6C , 16A-E

Sagitta lyra : Aida, 1897: 15 p., fig. 4; Fowler 1906: 33 p.; Ritter-Záhony 1908: 10-13 p., fig. 1A-E; Burfield and Harvey 1926: 98 p., figs 18-24; Thomson 1947: 10-11 p.; Alvariño 1967: 23-26 p., fig. 14A-O; Lea 1955: 28-30 p., plate 3; Srinivasan 1979: 20-21 p., fig. 10A-F; Michel 1984: 22-23 p., fig. 27.

Flaccisagitta lyra : McLelland, 1989: 162 p., figs 7D, 7E and 12C.

Material examined.

Korea Strait (33°48.924'N, 126°48.666'E), 40-70 m depth, oblique towing with MOCNESS, May 2019, NIBRIV0000895307 (one specimen) .

Description.

Total body length ranged between 16.0 and 60.0 mm. Tail 14-20% of body length. Hooks 8-9. Anterior teeth 4-9 and posterior 8-10, respectively. Large, flaccid and opaque body (Fig. 16 ). Intestinal diverticula absent (Fig. 16B ). Collarette absent (Fig. 16A and B ). Eyes square shaped with “H” shaped eye pigments (Fig. 16B ). Anterior fins beginning at ventral ganglion, anterior of anterior fins with ray less zone and angular shape, conspicuously longer than posterior fins (Fig. 16A, D ). Posterior fins with rayless zone connected with anterior fins by tegumentary bridge (Fig. 16A, E ). Caudal fin roundish and completely rayed (Fig. 16C ). Eggs reaching middle of posterior fins (Fig. 16A ). Corona ciliata not clear (Fig. 16B ). Seminal vesicles spherical and opening in middle of edge (Fig. 16C ). Seminal vesicles touching neither of posterior or caudal fins, located closer to posterior fins (Fig. 16C ).

Distribution.

This species is found in the mesopelagic (500-1,000 m depth) and bathypelagic zones (1,000-2,000 m depth) of the Pacific, Indian and Atlantic Oceans ( Pierrot-Bults and Nair 1991) and the Tosa Bay in Japan ( Ohnishi et al. 2014). In this study, it was distributed in the epipelagic zone (40-70 m depth) of the Korea Strait (Fig. 1 , station KS06).

Ecology.

This species has a high prevalence in warm waters ( Park 1970). In this study, specimens collected around Jeju Island were mainly distributed at water depths> 50 m. The temperature range in the sampling stations was 16.47-21.34 °C and the salinity range was 34.17-34.52 psu.

Remarks.

In Korean specimens, the position and length of the fins, distance between the anterior and posterior fins and shape of the seminal vesicles were morphologically consistent with the previous records of Pseudosagitta lyra ( Alvariño 1967; Michel 1984; Lutschinger 1993). As one of the larger species of arrow worm, P. lyra reaches a maximum size of 42 mm ( Michel 1984; Lutschinger 1993). However, the largest of the Korean specimens collected in this study was 60 mm in length. Pseudosagitta scrippsae can be easily confused with P. lyra , with similar size and position and shape of the fins and seminal vesicles. However, P. scrippsae can be differentiated by the presence of a distinct collarette around the neck ( Chihara and Murano 1997). No specific pattern was observed through CBE staining on the body surface.

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 16. A Pseudosagitta lyra (dorsal view) B head C tail D anterior fin E posterior fin. Abbreviations: AF = anterior fin; E = eye; PF = posterior fin; SV = seminal vesicle.