Ferosagitta robusta (Doncaster, 1902)

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

publication ID	https://dx.doi.org/10.3897/zookeys.1106.80184
publication LSID	lsid:zoobank.org:pub:EFA7EF37-2B83-458D-931D-9A53DB311472
persistent identifier	https://treatment.plazi.org/id/D6DEC187-CB62-5498-9887-280D24B788AC
treatment provided by	ZooKeys by Pensoft
scientific name	Ferosagitta robusta (Doncaster, 1902)
status

Treatment

Figs 3A View Figure 3 , 6B View Figure 6 , 8B View Figure 8 , 9A View Figure 9 , 18A-E View Figure 18

Sagitta robusta : Fowler, 1906: 19-20 p., figs 59-64; Ritter-Záhony 1908: 792 p.; Burfield and Harvey 1926: 100-101 p., figs 33-37; Thomson 1947: 13-15 p.; Alvariño 1962: 187-198 p., figs 1-5; Alvariño 1967: 66-71 p., figs 42A-D; Srinivasan 1979: 32-34 p., fig. 18A-G.

Material examined.

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

Description.

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 View Figure 18 ). Head wide as neck, roughly round or square shaped (Fig. 18A View Figure 18 ). Grasping spines gently curved and not serrated edge of hooks (Figs 8B View Figure 8 , 9A View Figure 9 ). Teeth short and firm (Fig. 9A View Figure 9 ). “B” shaped eyes had “T” shaped eye pigments (Fig. 18B View Figure 18 ). Collarette on neck (Figs 9A View Figure 9 , 18A View Figure 18 ). 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 View Figure 18 ). 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 View Figure 18 ). Seminal vesicles pear-shaped with elongated posterior trunk and anterior roundish knob and touching both posterior and caudal fins. (Fig. 18A, C View Figure 18 ). Conspicuous intestinal diverticula present (Fig. 9A View Figure 9 ). Eggs reached anterior of ventral ganglion. Corona ciliata beginning behind eyes and expanding to anterior of trunk (Fig. 18A View Figure 18 ).

Distribution.

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 View Figure 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.

Remarks.

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.