Flaccisagitta enflata (Grassi, 1881)

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

Flaccisagitta enflata (Grassi, 1881)

Figs 3A , 6E , 10D and 14A-E

Spadella enflata : Grassi, 1883: 13 p., fig. 7.

Sagitta inflata : Ritter-Záhony, 1908: 13-15 p., fig. 4A-D; Srinivasan 1979: 18-19 p., fig. 9.

Sagitta enflata : Aida, 1897: 15-16 p., fig. 6; Fowler 1906: 69 p., figs 9-17; Ritter-Záhony 1909: 791-792 p.; Michael 1919: 242-244 p., fig. 28, table 1; Burfield and Harvey 1926: 95-96 p., fig. 5; Pierce 1951: 221-222 p., fig. 4, table 12; Alvariño 1967: 29-34 p., fig. 17A-G; Michel 1984: 18-19 p., figs 2, 20.

Sagitta enflata f. gardineri : Tokioka, 1959: 91-92 p., table 19

Flaccisagitta enflata : McLelland, 1989: 159 p., figs 7A and 12B

Material examined.

Korea Strait (32°59.175'N, 124°29.595'E), 20-25 m depth, oblique towing with MOCNESS, Nov 2019, NIBRIV0000895309 (three specimens) ; northern East China Sea (32°0.000'N, 127°4.098'E), 0-110 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895308 (four specimens) ; northern East China Sea (32°30.000'N, 126°30.000'E), 0-100 m depth, oblique towing with conical net, Feb 2020 (one specimen) .

Description.

Total body length ranged between 12.7 and 15.4 mm. Tail 14.1-17.6% of body length. Hooks 8-10. Anterior teeth 6-10 and posterior teeth 10-17, respectively. Transparent body, inflated towards middle (Fig. 14 ). Triangular-shaped head (Fig. 14A ). Collarette absent (Figs 3A , 10D ). Blunt teeth (Fig. 14B ). Round eyes with star-shaped eye pigments (Fig. 14B ). Intestinal diverticula absent (Fig. 10D ). Anterior fins 17.0% of body length. Anterior fins began at middle of body at far distance back of ventral ganglion and partially rayed. Starting points of anterior fins 43.7% and ending points of anterior fins 64.4% of body length, respectively (Fig. 14A, D ). Posterior fins 20.5% of body length and 1.2 times longer than anterior fins. Starting points of posterior fins 71.9% and end points of posterior fins 92.5% of body length, respectively. Posterior fins well-separated from anterior fins (Fig. 14A, E ). Caudal fin roundish, fan-shaped and fully rayed (Fig. 14C ). Seminal vesicles touching caudal fin, but separated from posterior fins, spherical in shape with rupture in middle in mature specimen (Fig. 14C ). Corona ciliata beginning in front of eyes and reaching neck (Figs 10D , 14A , 14B ).

Distribution.

This cosmopolitan species is found in the epipelagic (0-200 m depth) and mesopelagic zones (200-500 m depth) of the Pacific, Indian and Atlantic Oceans ( Pierrot-Bults and Nair 1991), the coastal area of Japan (Tosa Bay; Ohnishi et al. 2014) and the epipelagic zone (0-150 m depth) of the Korea Strait ( Park 1970). In this study, it was found in the epipelagic zone (0-110 m depth) of the northern East China Sea (Fig. 1 : stations KS08, nECS01 and nECS04).

Ecology.

This is used as an indicator species of warm currents in water surrounding Korea ( Park 1970). The temperature range in the sampling stations was 16.52-28.80 °C and the salinity range was 28.96-33.22 psu.

Remarks.

The transparent and flaccid body, star-shaped eye pigments and seminal vesicle morphology were consistent with those recorded in previous studies by Alvariño (1967) and Nagasawa (1976). Two types of Korean Flaccisagitta enflata have been reported, a small type: 10-20 mm long and a large type: 20-28 mm long ( Park 1970). In this study, only the small type (<20 mm) of F. enflata was collected. We observed seven specimens for CBE staining pattern: dorsomedian line, 12 dots; dorsolateral line,> 150 dots; ambiguous lateral line, receptors on the lateral fin, 2 dots (easily damaged); anterolateral receptors on the caudal fin, 4 dots; posterior receptors on the caudal fin, 7 dots. The pattern of dorsomedian dots lined up behind the ventral ganglion and the pattern of dorsolateral dots intensively scattered ahead of ventral ganglion.

Figures

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

Figure 3. Appearance of body A transparent and flaccid body (Flaccisagitta enflata) B translucent body (Pterosagitta draco) C opaque and rigid body (Aidanosagitta crassa).

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 10. Position and shape of corona ciliata A Aidanosagitta regularis B Pterosagitta draco C Serratosagitta pacifica D Flaccisagitta enflata.

Figure 14. A Flaccisagitta enflata (dorsal view) B head C tail D anterior fin E posterior fin. Abbreviations: AF = anterior fin; AT = anterior teeth; CC = corona ciliata; E = eye; IN = intestine; PF = posterior fin; SV = seminal vesicle.