Ventral transverse musculature absent, less glandular structures on body surface. Grasping spines gently or abruptly curved (Tokioka 1965a). Collarette absent, present or small that is almost absent. Intestinal diverticula absent or present. One or two rows of teeth, teeth-rows arranged in comb or fan shape. One paired or two paired lateral fins with or without rayless zone (Alvariño 1967).

Small head. Grasping spines abruptly curved. One row of teeth. Collarette either short or absent. One pair of lateral fins arranged on the posterior trunk and tail.

Slender and transparent body. Lateral fins on the body and tail with rayless zone or partially rayed. Intestinal diverticula absent. Seminal vesicles oval or elongated touching both lateral fins and caudal fins.

Korea Strait (33°30.000'N, 125°54.000'E), 0–90 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895313 (one specimen); northern East China Sea (33°00.000'N, 127°4.098'E), 0–110 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895312 (one specimen).

Total body length ranged between 10.8 and 11.5 mm and tail 27.3–33.7% of body length. Hooks 8–10. Anterior teeth 14. Slender and transparent body (Fig. 11A). Small head. One row of stout teeth arranged in fan shape (Fig. 9B). Collarette and intestinal diverticula absent (Fig. 11B). Grasping spine abruptly curved (Fig. 8A). Round eyes with eye pigments in “E” shape (Fig. 11B). Corona ciliata beginning in front of eyes with round shape (Fig. 11C). Lateral fins 29.4% of body length. Starting points of lateral fins 54.3% and ending points of lateral fins 82.2% of body length, respectively. One pair of lateral fins only rayed on outer edge, with forward ends equidistant from caudal septum (Fig. 11A, E). Caudal fin roughly round in shape (Fig. 11D). Seminal vesicles elongated with anterolateral-edge-opening touching both lateral fins and caudal fin (Fig. 11D).

Figure 11. 

A Krohnitta subtilis (dorsal view) B head C tail D lateral fin. Abbreviations: CC = corona ciliata; CF = caudal fin; COL = collarette; E = eye; GS = grasping spine; IN = intestine; LF = lateral fin; RLZ = Ray less zone; SV = seminal vesicle.

This 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 Indian water (George 1952) and the Tosa Bay in Japan (Ohnishi et al. 2014), while in this study, it was found in the epipelagic zone (0–110 m depth) of the Korea Strait and northern East China Sea (Fig. 1: stations KS05 and nECS04).

This cosmopolitan species can be found in tropical to temperate waters (Alvariño 1967). The temperature ranged between 16.40 and 16.41 °C and salinity was 34.58 psu at the sampling stations of this study.

This species is clearly distinguished from K. pacifica by the presence of a rayless zone in the lateral fin. Furthermore, the presence of a pair of lateral fins with a wide rayless zone and a fan-shaped dentition in K. subtilis collected from Korean waters are consistent with the records of Alvariño (1967) and Bieri (1991). However, the location of the corona ciliata (in front of the eyes, Fig. 11C) of the species found in Korean waters was different from that of the previous records (located behind the eye). No specific pattern was observed through CBE staining on the body surface.

Northern East China Sea (32°29.420'N, 127°29.654' E), 20–100 m depth, oblique towing with MOCNESS, Aug 2020 (one specimen).

Slender and transparent body. Small head. Grasping spines abruptly curved. One row of stout teeth arranged in fan shape. One pair of lateral fins partially rayed, forward and equidistant from caudal septum. Lateral fins positioned at anterior end, at level of caudal septum with rayed lateral fins. Caudal fin damaged. Collarette and intestinal diverticula absent. No seminal vesicle visible.

This species is found in the epipelagic zone (0–200 m depth) of the northern Indian Ocean (Pierrot-Bults and Nair 1991), the Gulf of Mexico (Pierce 1951) and the Japanese coast (Tosa Bay, Sagami and Suruga) (Nagasawa and Marumo 1972; Ohnishi et al. 2014) and, in this study, it was found in the epipelagic zone (20–100 m depth) of the northern East China Sea (Fig. 1: station nECS03).

An inhabitant of the surface layer of the warm oceanic waters (Tokioka 1940). Mature specimen was reported to be 6–8 mm in length (Alvariño 1967). The temperature range in the sampling stations of this study was 18.49–28.84 °C and salinity range was 30.71–34.59 psu.

Only immature individuals could be collected in this study. The specimens of K. pacifica we observed had one pair of fins and the structure of the fin was rayed, except for the base part close to the body. These were distinct characteristics of K. pacifica that differentiated it from K. subtilis. Since seminal vesicles were not observed in all observed Korean specimens, they were classified as immature stage (Alvariño 1967).

Wide head. Two rows of teeth. Collarette wide and extending through full body. One pair of rayed lateral fins located on the tail. Intestinal diverticula absent. Only one genus has been described within this family: Pterosagitta (Costa, 1869).

A previous phylogenetic study reported that Pterosagittidae is genetically quite close to Sagittdae (Gasmi et al. 2014; Nair et al. 2015; Peter et al. 2020; Müller et al. 2019). In this study, a recent research paper was reviewed and Pterosagittidae was marked as invalid (Table 1).

Northern East China Sea (32°30.000'N, 127°5.100'E), 0–120 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895299 (one specimen).

Total body length ranged between 6.5 and 9.1 mm and tail 38.4–40.1% of body length. Hooks 8. Anterior teeth 10 and posterior teeth 12. Rigid and translucent body (Fig. 12). Wide and angular head (Fig. 12). Wide collarette extending over entire body and reaching anterior of seminal vesicles (Fig. 12A. C). Rectangular eyes with “T” shaped eye pigments (Fig. 12B). Intestinal diverticula absent (Fig. 3B). Lateral fins 20.7% of body length. Starting point of lateral fins 65.2% and ending points of lateral fins 86.3% of body length, respectively. One pair of lateral fins triangular-shaped and completely rayed, with forward ends at level of caudal septum (Fig. 12A, D). Seminal vesicles posteriorly elongated with anterior knob touching lateral fins (Fig. 12C–D). Eggs reaching middle of body. Corona ciliata anteriorly opened with horseshoe shape beginning in neck region and ending just behind eyes (Figs 10B, 12A).

Figure 12. 

A Pterosagitta draco (dorsal view) B head C tail D lateral fin. Abbreviations: CC = corona ciliata; COL = collarette; E = eye; LF = lateral fin; PT = posterior teeth; SV = seminal vesicle.

This species is located 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 epipelagic zone (0–200 m depth) of the Caribbean Sea (Michel,1984), the coastal waters surrounding India (George 1952) and the Tosa Bay in Japan (Ohnishi et al. 2014). In this study, it was found in the epipelagic zone (0–120 m depth) of the northern East China Sea (Fig. 1: station nECS02).

This species is widely distributed in warm water masses and appears all year round in Korean waters, except in the Yellow Sea (Kim 1987). The temperature range of the Caribbean Sea was reported as 22–29 °C, and salinity range was 33–38 psu (Michel 1984). At the sampling stations of this study, the temperature ranged between 15.83–28.80 °C and salinity ranged between 31.38–34.60 psu.

The largest specimen collected in this study was 9.1 mm in length, which was at stage 4 maturity. It was smaller than the specimen from New Zealand (16 mm) reported by Lutschinger (1993). It had characteristics consistent with the Pterosagitta draco reported from the Pacific (Alvariño 1967; Michel 1984), such as the presence of two rows of teeth, one pair of lateral fins, a corona ciliata located between the back of the eye and the neck and a broad collarette extending from the head to seminal vesicles. We observed one specimen for CBE staining pattern: dorsomedian line, 8 dots; dorsolateral line, 25 dots; lateral line, 10 dots; receptors on the lateral fin, 2 dots; anterolateral receptors on the caudal fin, 3 dots; posterior receptors on the caudal fin, 6 dots.

Two rows of stout teeth arranged in comb shape. Two pairs of lateral fins on the trunk and tail.

Intestinal diverticula either absent or present. Grasping spines serrated. Two rows of teeth. Two pairs of lateral fins either with rayless zone or completely rayed.

Korea Strait (33°24.504'N, 127°54.600'E), 0–50 m depth, oblique towing with MOCNESS, May 2019, NIBRIV0000895311 (two specimens); Korea Strait (33°33.600'N, 127°34.002'E), 0–96 m depth, oblique towing with conical net, Feb 2020 (one specimen); northern East China Sea (32°33.000'N, 126°30.000 E), 0–100 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895310 (three specimens); northern East China Sea (32°00.000'N, 127°4.098'E), 0–120 m depth, oblique towing with conical net, Feb 2020, two specimens.

Total body length ranged within 11.8 and 13.7 mm. Tail 23.4–24.9% of body length. Hooks 6–7. Anterior 10–13 and posterior teeth 16–25. Rigid and opaque body (Fig. 13A). Small head (Fig. 13A, B). Grasping spines serrated on edge (Fig. 8C). Collarette absent (Fig. 10C, 13A). Rectangular eyes with “T” shaped eye pigments (Fig. 13B). Intestinal diverticula absent (Fig. 10C). Anterior fins spanned 21.9% of body length. Anterior fins completely rayed beginning between ventral ganglion and caudal septum. Starting point of anterior fins 34.6% and ending points of anterior fins 55.1% of body length, respectively (Fig. 13A, D). Posterior fins 26.2% of body length and 1.2 times longer than anterior fins. Starting points of posterior fins 63.7% and ending points of posterior fins 89.7% of body length, respectively. Posterior fins well-separated from anterior fins (Fig. 13A, E). Caudal fin triangular shaped (Fig. 13A, C). Seminal vesicles touched or closed to lateral fins and well-separated from tail fin (Fig. 13C) with elongated knob facing obliquely forward and teeth-like appendages forming 5–10 distal protrusions. Eggs reached anterior of anterior fins. Collarette beginning in front of eyes and extended over neck (Fig. 10C, 13A).

Figure 13. 

A Serratosagitta pacifica (dorsal view) B head C tail D anterior fin E posterior fin. Abbreviations: AF = anterior fin; AT = anterior teeth; CC = corona ciliata; COL = collarette; E = eye; PF = posterior fin; PT = posterior teeth; SV = seminal vesicle.

This species is found in the epipelagic (0–200 m depth) and mesopelagic zones (200–500 m depth) of the Pacific and Indian Oceans (Alvariño 1967; Pierrot-Bults and Nair 1991), the epipelagic zone of Red Sea, Californian waters (Pierrot-Bults 1976) and the Tosa Bay in Japan (Ohnishi et al. 2014). In this study, it was distributed in the epipelagic zone (0–50 m depth) of the Korea Strait and northern East China Sea (Fig. 1: stations KS06, KS07, nECS01 and nECS04).

This species mainly inhabits Indo-pacific warm-water masses (Bieri 1959). In the Pacific Ocean, it is a known indicator species of the Kuroshio Water Mass (Kim 1987). In this study, the temperature range of sampling locations was 16.37–20.57 °C and salinity ranged between 34.48–34.61 psu.

The seminal vesicles are used as an important morphological feature to identify the genus Serratosagitta. S. serratodentata has thick collarette tissue in front of the seminal vesicles and two projections at the anterior-lateral corner. The seminal vesicles touch the end of posterior fins (Alvariño 1961). The seminal vesicles of S. pseudoserratodentata have one projection at the front corner, with small teeth at the anterior end. The seminal vesicles are well-separated from the posterior fins and caudal fin (Alvariño 1961). In the S. pacifica (nine specimens), the number of protrusions vary between 5 and 10. The inner serrated row of the grasping spine and the “teeth cells” forming protrusions at the anterior margin of the seminal vesicles were consistent with previous records (Alvariño 1967; Pierrot-Bults 1976). We observed three specimens for CBE staining pattern: dorsomedian line 43 dots; dorsolateral line, 54–69 dots; lateral line, 24 dots; receptors on the lateral fin, 10 dots; anterolateral receptors on the caudal fin, 2 dots; posterior receptors on the caudal fin, 3–4 dots. The dorsomedian dots are patterned as small spots that cross the centre of the body and larger symmetrical spots on dorsolateral line dots.

Flaccid and opaque body. Collarette absent. Intestinal diverticula present. Grasping spine gently curved and not serrated. Intestinal diverticula present. The anterior fins begin between ventral ganglion and caudal fin and are shorter than posterior fins.

Northern East China Sea (32°29.420'N, 127°29.654'E), 20–100 m depth, oblique towing with MOCNESS, Aug 2020 (one specimen).

Small head. Two pairs of lateral fins with rayless zone. Intestinal diverticula small. Seminal vesicles divided into a small anterior knob and elongated posterior part and well-separated from posterior fins, but touching caudal fin. Corona ciliata elongated oval-shaped beginning in neck.

This cosmopolitan species is found in the epipelagic zone (0–200 m depth) of the Pacific, Indian and Atlantic Oceans (Pierrot-Bults and Nair 1991) and the epipelagic zone (0–200 m depth) of the Japan coast (Sagami Bay and Suruga Bay) (Nagasawa and Marumo 1972). In this study, it was found in the epipelagic zone (20–100 m depth) of the northern East China Sea (Fig. 1, station nECS03).

Mesosagitta minima is abundant in mixed waters of the western North Atlantic Ocean (Pierce 1951). Mature specimens ranged within the size of 7–8 mm (Park 1970). The temperature range measured in the sampling stations was 18.49–28.84 °C and salinity range was 30.71–34.59 psu.

Only immature individuals could be collected in this study. We easily distinguished M. minima amongst the collected specimens by the relatively small head and unique body shape that thickens towards the tail. These Korean specimens were classified as immature because seminal vesicles and ovaries were absent and undeveloped short eggs (mentioned in description of Alvariño (1967) as a feature of the second stage of development) were observed in the body.

Transparent or translucent body. Collarette absent. Intestinal diverticula absent. The anterior fins begin at a far distance behind the end of the ventral ganglion. Seminal vesicles spherical shaped.

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).

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).

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.

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).

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.

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.

Korea Strait (33°24.504'N, 127°54.600'E), 0–50 m depth, oblique towing with MOCNESS, Nov 2019, NIBRIV0000895298 (one specimen).

Total body length ranged between 15 and 49 mm. Tail 19–24% of body length. Hooks 4–11. Anterior teeth 2–4 and posterior teeth 2–9, respectively. Large and translucent body (Fig. 15). Intestinal diverticula absent (Fig. 15B). Collarette absent (Fig. 15A). Eyes “D” shaped with “T” shaped eye pigments (Fig. 15B). Anterior fins short, beginning at middle of body between ventral ganglion and caudal septum, round-shaped and partially rayed (Fig. 15A, D). Posterior fins well-separated from anterior fins and partially rayed (Fig. 15A, E). Caudal fin roundish triangular-shaped and completely rayed (Fig. 15A, C). Seminal vesicles spherical with anterolateral edge opening (Fig. 15C). Seminal vesicle touching or close to tail fin and well-separated from lateral fins (Fig. 15C). Eggs reaching forward end of anterior fins. Corona ciliata beginning in front of eyes and reaching neck (Fig. 15B).

Figure 15. 

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

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), in the Indian coast (George 1952), the Tosa Bay in Japan (Ohnishi et al. 2014), the Korea Strait and south of East Sea (Park 1970). In this study, it was found in the epipelagic zone (0–50 m depth) of the Korea Strait (Fig. 1: station KS07).

This species is considered as an indicator species of the Kuroshio warm current and fully-grown adults inhabit depths of < 200 m (Park 1970). In this study, individuals under Stage 3 were mainly found between the Jeju Straits (0–100 m depth). The temperature range in the sampling stations was 16.52–20.57 °C and salinity range was 34.48–34.61 psu.

Though mainly immature individuals were reported in previous studies from Korea, in this study, adults longer than 40 mm were collected for the first time. The Korean species was consistent with those found in previous studies by Alvariño (1967) and Michel (1984) in terms of body size, length and shape of the egg, presence of small and round anterior fins in the middle of the body and the absence of bridge connecting the anterior and posterior fins. As the adult Flaccisagitta hexaptera is large (> 20 mm), it can be difficult to distinguish the adult Flaccisagitta enflata from the immature F. hexaptera. However, it is possible when noting that the eggs of F. hexaptera are long and thin, whereas those of F. enflata are large and short. Another feature relevant for the diagnosis of F. hexaptera is the number of conspicuous anterior teeth which never exceed four, while it is eight in F. enflata. No specific pattern was observed through CBE staining on the body surface.

Flaccid and transparent body (but more opaque than Flaccisagitta). Collarette absent. Intestinal diverticula absent. Two pairs of lateral fins partially rayed and connected with a tegumentary bridge. Anterior fins beginning at the rear end of ventral ganglion and longer than posterior fins.

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

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).

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.

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).

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.

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.

Slender and either opaque or translucent body. Collarette absent or small (almost absent). Intestinal diverticula present or absent. Grasping spines not serrated. Two rows of teeth. Two pairs of lateral fins completely rayed.

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

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).

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.

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.

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.

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.

Rigid and opaque body. Collarette present. Intestinal diverticula present. Grasping spines not serrated. Two pairs of lateral fins completely or partially rayed.

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

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.

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).

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.

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.

Yellow Sea (34°5.502'N, 124°36.000'E), 0–75 m depth, oblique towing with conical net, Aug 2019, NIBRIV0000895305, (one specimen).

Total body length ranged between 10.0 and 11.5 mm. Tail 27.8–35.0% of body length. Hooks 6–8. Anterior teeth 9–10 and posterior teeth 12–20, respectively. Rigid and opaque body (Fig. 18). Head wide as neck, roughly round or square shaped (Fig. 18A). Grasping spines gently curved and not serrated edge of hooks (Figs 8B, 9A). Teeth short and firm (Fig. 9A). “B” shaped eyes had “T” shaped eye pigments (Fig. 18B). Collarette on neck (Figs 9A, 18A). Anterior fins 22.4% of body length. Anterior fins beginning just at posterior of ventral ganglion. Starting points of anterior fins 33.1% and ending points of anterior fins 56.5% of body length, respectively (Fig. 18A, D). Posterior fins 25.8% of body length and 1.2 times longer than anterior fins. Starting points of posterior fins 62.6% and ending points of posterior fins 88.4% of body length, respectively. Posterior fins separated from anterior fins and partially rayed. Caudal fin roughly round-triangle shaped, completely rayed (Fig. 18C). Seminal vesicles pear-shaped with elongated posterior trunk and anterior roundish knob and touching both posterior and caudal fins. (Fig. 18A, C). Conspicuous intestinal diverticula present (Fig. 9A). Eggs reached anterior of ventral ganglion. Corona ciliata beginning behind eyes and expanding to anterior of trunk (Fig. 18A).

Figure 18. 

A Ferosagitta robusta (dorsal view) B head C tail D anterior fin E posterior fin. Abbreviations: AF = anterior fin; AT = anterior teeth; CC = corona ciliata; E = eye; PF = posterior fin; PT = posterior teeth; SV = seminal vesicle.

This species is found in the epipelagic zone (0–200 m depth) of Pacific and Indian Oceans (Pierrot-Bults and Nair 1991), the west coast of Florida (Pierce 1951), Indian coast (George 1952) and the Tosa Bay in Japan (Ohnishi et al. 2014). In this study, specimens were found in the epipelagic zone (0–75 m depth) of the Yellow Sea (Fig. 1: station YS03). Ferosagitta robusta is a typical Indo-pacific warm-water species (George 1952). The horizontal distribution range is wider than the vertical range and many individuals are mainly found in the surface layer (Park 1970). In this study, this species rarely appeared under low temperature conditions and their presence was predominant in the sea area affected by warm currents. The temperature range in the sampling stations was within 25.87–28.70 °C and salinity range was 32.72–33.11 psu.

Characteristics of the species in Korean waters, such as the conspicuous intestinal diverticula, head and body width and the seminal vesicles shape, are consistent with previous records (Alvariño 1967; Chihara and Murano 1997). The main difference between this species and another congeneric species of Korea, F. ferox, is the shape of the seminal vesicles. Seminal vesicles of F. robusta are very conspicuous, touching both posterior end of posterior fins, while that in F. ferox are not so conspicuous and are close to both posterior fins and caudal fin (Alvariño 1962). We observed one specimen for CBE staining pattern: dorsomedian line, 49 dots; dorsolateral line, 38 dots; lateral line, 30 dots; receptors on the lateral fin, 6 dots; anterolateral receptors on the caudal fin, 4 dots; posterior receptors on the caudal fin not observed due to damage.

Rigid and opaque body. Intestinal diverticula present. Collarette present or absent. Grasping spine gently curved and not serrated. Two rows of stout teeth arranged in a comb shape. Two pairs of lateral fins completely rayed.

Korea Strait (34°41.577'N, 127°50.460'E), 0–20 m depth, oblique towing with conical net, Feb 2021 (one specimen).

Rigid and opaque body. Narrow collarette and extending to half distance from neck to ventral ganglion. Intestinal diverticula present. Grasping spine gently curved. Two rows of stout teeth arranged in comb shape. Two pairs of lateral fins completely rayed, anterior fins beginning at end of ventral ganglion. Seminal vesicles oval-shaped with opening at anterolateral edge, position of seminal vesicles well separated from caudal fin, but touching posterior fins.

This species is found in the epipelagic zone (0–200 m depth) of the Pacific and Indian Oceans (Pierrot-Bults and Nair 1991) and the coastal waters of the Philippines, India and Hong Kong (George 1952; Tse et al. 2007; Noblezada and Campos 2008; Lie et al. 2012).

A mature specimen has been reported to be 8 mm is size (Alvariño 1967). This species shows a diurnal vertical migration in the summer off the Hong Kong coast (Lie et al. 2012). The temperature range in the sampling stations of this study was 16.40–16.41 °C and the salinity was 34.58 psu.

Only one immature individual was collected in this study. Aidanosagitta neglecta is similar to A. regularis in morphological characteristics including collarette. However, the former had much larger seminal vesicles, thus they can be easily distinguished from each other. Aidanosagitta neglecta collected from Korean waters was smaller than the previously reported adult specimens, but seminal vesicles were obviously swollen in an oval shape. Despite the presence of swollen seminal vesicles, the Korean specimen was considered as immature because its size was smaller than the known record of the adult (Alvariño 1967).

Type C (collarette type): East Sea (37°33.198'N, 131°14.598'E), 0–100 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895304 (one specimen); Yellow Sea (35°22.550'N, 126°5.366'E), 0–16.5 m depth, oblique towing with conical net, Jul 2020, five specimens; Korea Strait (34°13.698'N, 127°35.400'E), 0–28 m depth, oblique towing with conical net, Feb 2020 (one specimen). Type N (naked type): Yellow Sea (35°17.316'N, 126°10.483'E), 0–6.4 m depth, oblique towing with conical net, Jul 2020, NIBRIV0000895303 (three specimens).

Type C: total body length ranged within 9.9 and 11.2 mm. Tail 26.6–29.8% of body length. Rigid and opaque body (Fig. 19). Head small. Collarette beginning at neck and reaching middle of body (Fig. 19A). Round eyes star-shaped eye pigments. Corona ciliata beginning from neck, elongated to anterior of ventral ganglion (Fig. 19A, B). Intestinal diverticula present (Fig. 19C). Two pairs of lateral fins completely rayed (Fig. 19E, F). Anterior fins 18.1% of body length. Anterior fins beginning at posterior of ventral ganglion. Starting points of anterior fins 29.6% and ending points of anterior fins 46.6% of body length, respectively (Fig. 19D). Posterior fins 23.0% of body length and 1.3 times longer than anterior fins. Starting of posterior fins 62.0% and ending points of posterior fins 86.9% of body length, respectively. Posterior fins well separated from anterior fins beginning at middle of body (Fig. 19A, D). Seminal vesicles longitudinally elongated (Fig. 19D). Eggs reaching posterior of ventral ganglion.

Figure 19. 

A Aidanosagitta crassa Type C (dorsal view) B Aidanosagitta crassa Type N (dorsal view) C head and neck D tail E anterior fin F posterior fin. Abbreviations: AF = anterior fin; CC = corona ciliata; COL = collarette; E = eye; IN = intestine; ID = intestine diverticula; PF = posterior fin; SV = seminal vesicle.

Type N: total body length ranged between 8.1 and8.2 mm. Tail 27.0–30.0% of body length (Fig. 19B). Collarette beginning at anterior of ventral ganglion and reaching posterior of ventral ganglion (Fig. 19B). Anterior fins 19.1% of body length. Anterior fins beginning at posterior of ventral ganglion. Starting points of anterior fins 34.0% and end points of anterior fins 54.6% of body length, respectively (Fig. 19B). Posterior fins 24.6% of body length and 1.3 times longer than anterior fins. Starting points of posterior head 60.9% and ending points of posterior fins 88.2% of body length, respectively. Posterior fins well-separated from anterior fins beginning at middle of body (Fig. 19A, B).

This species is found in the neritic water of the Pacific Ocean (Pierrot-Bults and Nair 1991), the neritic coastal water of Hong Kong (Tse et al. 2007) and the Tosa Bay of Japan (Ohnishi et al. 2014). In this study, it was found in the epipelagic zone (0–100 m depth) of the East Sea, Korea Strait and Yellow Sea (Fig. 1, stations ES01, YS01, YS02 and KS01).

Aidanosagitta crassa appears in high abundance throughout the year in the relatively low saline waters of the Yellow Sea and coast of Jeju (Park 1970). This species rarely appears in the summer warm waters of southern Korea. The body length varies according to the season and it has been reported that they are large (type C) in winter and small in summer (type N) (Park 1970). Specimens of type C die after spawning and those of type N dominate the new generation (Park 1970). We obtained specimens from the East Sea in winter and the Yellow Sea in summer.

Previous researchers classified Aidanosagitta crassa into three types according to the distribution of the collarette: C type, covers from the neck to the body; N type, covers only the ventral ganglion; and I type, covers the ventral ganglion and partially covers the body (Park 1970). In this study, specimens of types C and N were collected and the Korean type C from the Yellow Sea had the same morphological characteristics of the collarette as the original description of this species reported by Tokioka (1939). Similarly, type N, which appeared together with type C at other stations of the Yellow Sea, was consistent with the morphological characteristics of the collarette of A. crassa and Aidanosagitta crassa f. naikaiensis (Tokioka 1939). It has been reported that the three types of A. crassa appear at different periods depending on environmental factors (water temperature and salinity) of the specific sea area; however, in this study, both types appeared simultaneously in the Yellow Sea. A more detailed ecological investigation of the impact of environment factors on the succession of the three types of A. crassa is necessary. We observed four specimens for type C of A. crassa CBE staining pattern: dorsomedian line, 14 dots; dorsolateral line, > 100 dots; lateral line, 8 dots; receptors on the lateral fin, 8 dots; anterolateral receptors on the caudal fin, 4 dots; posterior receptors on the caudal fin, 6 dots. The pattern of dorsomedian dots was small spots that crossed the centre of the body and larger symmetrical spots on dorsolateral line dots. In addition, we observed three specimens for type N of A. crassa CBE staining pattern: dorsomedian line, 35 dots; dorsolateral line, 34 dots; lateral line, 12 dots; receptors on the lateral fin, not observed; anterolateral receptors on the caudal fin, 2 dots; posterior receptors on the caudal fin, 4 dots.

Korea Strait (33°33.600'N, 127°34.002'E), 0–96 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895302 (one specimen); northern East China Sea (32°33.000'N, 126°30.000'E), 0–100 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895301 (one specimen); northern East China Sea (32°30.000'N, 127°5.100'E), 0–120 m depth, oblique towing with conical net, Feb 2020 (one specimen).

Total body length ranged within 6.1 and 6.7 mm. Tail 30.5–31.7% of body length. Hooks 6. Anterior teeth 3–4 and posterior teeth 5–6, respectively. Rigid and opaque body (Fig. 20). Head small, triangular shaped (Fig. 20B). Round eyes with “B”-shaped eye pigments (Fig. 20B). Collarette expanding to seminal vesicles (Fig. 20A). Corona ciliata beginning from neck to anterior of ventral ganglion (Fig. 10A). Anterior fins 12.3% of body length. Anterior fins beginning at posterior of ventral ganglion. Starting points of anterior fins 37.3% and ending points of anterior fins 50.9% of body length, respectively (Fig. 20D). Posterior fins 22.0% of body length and 1.8 times longer than anterior fins. Starting points of posterior fins 62.9% and ending points of posterior fins 84.7% of body length, respectively. Posterior fins not connected to anterior fins, beginning in front of caudal septum and both anterior fins and posterior fins completely rayed (Fig. 20D, E). Caudal fin fully rayed and roughly round or triangle-shaped (Fig. 20C). Intestinal diverticula present (Figs 7A, 20B). Seminal vesicles longitudinally elongated along body (Fig. 20C). Eggs reaching posterior of ventral ganglion.

Figure 20. 

A Aidanosagitta regularis (dorsal view) B head C tail D anterior fin E posterior fin. Abbreviations: CC = corona ciliata; COL = collarette; E = eye; SV = seminal vesicle.

This species is found in the epipelagic (0–200 m depth) and mesopelagic zones (200–500 m depth) of Pacific and Indian Oceans (Pierrot-Bults and Nair 1991) and the epipelagic zone (0–100 m depth) of the Tosa Bay in Japan (Ohnishi et al. 2014). In this study, it was found in the epipelagic zone (0–120 m depth) of the Korea Strait and northern East China Sea (Fig. 1, stations KS06, nECS01 and nECS02).

This species is considered a warm-water Indo-Pacific indicator species because many individuals appear in high-temperature and high-salinity water and the distribution range is limited to the areas affected by warm currents (Park 1970).

Amongst the Korean specimens, the collarette was differently inflated, thick and covered the body surface. However, the position and shape of the corona ciliata and fins were consistent with the original description (Aida 1897). Aidanosagitta regularis is similar to A. bedfordii; however, these two species can be distinguished by the morphological difference in the eye pigments (elongated vs. roundish). We observed two specimens for CBE staining pattern: dorsomedian line, 28 dots; dorsolateral line, 34 dots; lateral line, 44 dots; receptors on the lateral fin, 3 dots; anterolateral receptors on the caudal fin, 2 dots; posterior receptors on the caudal fin, not observed due to damage.

Rigid and opaque body. Collarette almost absent. Intestinal diverticula absent or present. Grasping spines not serrated. Two pairs of lateral fins completely rayed.

Yellow sea (33°0.111'N, 125°29.581'E), 0 – 86 m depth, oblique towing, July 2020.

Small, rigid and opaque body. Small head. Collarette almost absent (thin on neck). Eyes square-shaped with no eye pigments observed in this study. Intestinal diverticula absent. Forward end of anterior fins not visible. Posterior fins beginning in front of caudal septum and closing to seminal vesicles, completely rayed. Seminal vesicles elongated with small indentations and touching both lateral and caudal fins.

This species is found in the epipelagic (0–200 m depth) and mesopelagic zones (200–500 m depth) of Pacific, Indian and Atlantic Oceans (Pierrot-Bults and Nair 1991). This species appears in most of the seas across Korean waters.

Sagitta bipunctata is known as a cosmopolitan species, appearing in temperate and tropical seas; it is an indicator species of high salinity and the presence of oceanic water (Pierce 1953). The temperature range in sampling stations of this study was 15.08–22.17 °C and the salinity range was 31.77–34.01 psu.

Only one immature individual was collected in this study. Sagitta bipunctata can be distinguished from other Korean species by the following characteristics: absence of intestinal diverticular, presence of completely rayed lateral fins and the restricted position of collarette on the posterior part of the body. The seminal vesicles of Korean specimen were not sufficiently mature compared to the description of Alvariño (1967).

Rigid or flaccid and transparent or opaque body. Collarette small (almost absent). Intestinal diverticula absent. Grasping spines not serrated. Two pairs of lateral fins partially rayed. Anterior part of anterior fins elongated and rayless. Anterior fins longer than posterior fins.

Korea Strait (33°0.000'N, 125°18.000'E), 0–75 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895300 (one specimen); northern East China Sea (31°30.000'N, 126°28.998'E), 0–82 m depth, oblique towing with conical net, Feb 2020 (one specimen).

Total body length ranged from 16–17 mm. Tail 3.71% of body length. Hooks 7. Anterior teeth 27–28 and posterior teeth 30–35, respectively. Opaque and rigid body (Fig. 21). Head wider than body (Figs 7D, 21A). Short and dense teeth. Intestinal diverticula absent (Figs 7D, 21B). “D”-shaped eyes with star-shaped eye pigments (Fig. 21B). Corona ciliata beginning behind eyes and elongated over neck (Fig. 21B). Anterior fins 26.5% of body length. Anterior fins beginning at middle of ventral ganglion, anterior of anterior fins narrow with rayless zone and posterior of anterior fins partially rayed. Anterior fins 1.3 times longer than posterior fins. Starting points of anterior fins 34.3% and ending points of anterior fins 60.0% of body length, respectively (Fig. 21A, D). Posterior fins 19.8% of body length. Starting points of posterior fins 63.7% and ending points of posterior fins 89.7% of body length, respectively. Posterior fins connected with anterior fins (Fig. 21A). Caudal fin triangular-shaped and completely rayed (Fig. 21C). Seminal vesicles spherical in shape with lateral rupture in mature specimen (Fig. 21C).

Figure 21. 

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

This species is found in the epipelagic zone (0–200 m depth) of the Pacific and Indian Oceans (Pierrot-Bults and Nair 1991) and the Tosa Bay in Japan (Ohnishi et al. 2014). In this study, it was found in the epipelagic zone (0–100 m depth) of the Korea Strait and northern East China Sea (Fig. 1: stations KS09 and nECS06).

Zonosagitta bedoti is used as an indicator species in the front area where warm and cold water meet (Park 1970). The temperature range in the sampling location in this study was between 14.62 and 15.01 °C and the salinity range was 33.67–33.81 psu.

Zonosagitta bedoti and Z. nagae are similar in morphology at the immature stage. However, because adult Z. nagae are relatively larger, immature Z. nagae may be misidentified as Z. bedoti. Adults of both species can be distinguished from each other by the shape of seminal vesicles and eye pigments. Zonosagitta nagae has an “E”-shaped eye pigment, while Z. bedoti has a star-shaped eye pigment. The spot pattern on the body surface found through CBE staining is as follows: irregular spot pattern which continued from the head to the ventral ganglion and six spots along the outside of the body were symmetrical around the tail.

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).

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).

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.

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).

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.

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).

Korea Strait (34°17.868'N, 128°15.854'E), 0–60 m depth, oblique towing with MOCNESS, Feb 2020 (one specimen).

Rigid and transparent body. Collarette present. Intestinal diverticula absent. Grasping spine gently curved. Two rows of stout teeth arranged in comb shape. Two pairs of lateral fins partially rayed, anterior fins begin at the end of ventral ganglion. Seminal vesicles elongated with an anterior protruding part usually roughly round and touching both lateral fins and caudal fin.

The species is found in the epipelagic zone (0–200 m depth) of the Pacific and Indian Oceans (Pierrot-Bults and Nair 1991) and off the coast of Philippines (Noblezada and Campos 2008). In this study, it 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: station KS02).

Z. pulchra is considered to be a neritic species (Bieri 1959; Pierrot-Bults and van der Spoel 2003). The temperature range in the sampling stations of this study was 11.95–14.79 °C and the salinity range was 33.59–34.00 psu.

Only one immature individual was collected in this study. The examined Korean specimen belongs to the genus Zonosagitta by the absence of intestinal diverticular and the presence of rayless zone in the anterior part of anterior fins. This Korean specimen was identified as Z. pulchra because its anterior fins were more angled than those of Z. bedoti or Z. nagae. The seminal vesicles of Korean specimen were not sufficiently mature compared to description of Alvariño (1967).