Y-nauplius Type O*

Figs 2, 16F–J

Type O* – Dreyer et al. 2023a: figs 3, 5a, c, tables s1–s2.

Material examined

JAPAN – Okinawa, Sesoko I., laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 5 LSN; 1991–2005 • 66 LSN, 11 of which molted to cyprids; 2018–2019 (Tables 1 and S1).

Description

LAST-STAGE NAUPLIUS (LSN). Lecithotrophic. Body ovate in dorso-ventral view; about 1.6 times as long as wide, with lateral margins showing slight concavity at transition from cephalic shield to trunk. In lateral view, trunk axis downturned ca 40° with respect to cephalic axis. Length 240–280 µm (without dorso-caudal spine), greatest width ca 150 µm, greatest dorso-ventral thickness ca 100 µm. Labrum produced as sub-trapezoidal elevation divided into facets by cuticular ridges; pores not examined in detail, but at least two in posterior half of midline and one pair in postero-lateral corners. Caudal end nearly acute, terminating in smooth, pointed, ca 20 µm long dorso-caudal spine with axis upturned 25° relative to trunk axis, this spine being accompanied ventrally by pair of triangular, ca 5–10 µm long furcal spines.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body overall transparent but with weakly orange- or browncolored yolk granules in central gut-like tube. Typically with pair of transparent vesicles along anterior margin of cephalic shield. Telson approximately as long as wide and about half as long as thorax, with pair of transparent vesicles anteriorly.

Identification and variation

Recognizable by the combination of its ovate/triangular body shape and its small size, general transparency and small caudal spines. Some variation among specimens in body size, length-width ratio and precise size of the caudal spines suggests that this morphospecies may include more than one species.

Distribution

Japan (Sesoko Island, Okinawa).