Mesosagitta minima (Grassi, 1881)

Mesosagitta minima (Grassi, 1881)

Spadella minima : Grassi, 1883: 15 p.

Sagitta minima : Aida, 1897: 15 p., fig. 5; Michael 1908: 74 p.; Michael 1919: 248-249 p.; Tokioka 1940: 5 p.; Thomson 1947: 19 p.; Prado 1961: 39-41 p.; Alvariño 1967: 59-61 p., figs 36, 37; Ducret 1974: 166 p., table.1; Srinivasan 1979: 24-26 p., fig. 13; Michel 1984: 25-26 p., fig. 34; McLelland 1989: 163 p., table.1, figs 8D, 12D.

Material examined.

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

Description.

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.

Distribution.

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 View Figure 1 , station nECS03).

Ecology.

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.

Remarks.

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.