Y-nauplius Type M

Figs 2, 14A–F

Type M – 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 • 3 LSN; 1991–2005 • 6 LSN, 3 of which molted to cyprids; 2018–2019 (Tables 1 and S1).

Description

LAST-STAGE NAUPLIUS (LSN). Lecithotrophic. Body narrowly ovate, almost lanceolate, in dorso-ventral view; about 2.0 times as long as wide; lateral margins without marked discontinuity between cephalic shield and trunk. In lateral view, trunk axis bent ca 30° downwards with respect to cephalic axis. Length 290–310 µm (without dorso-caudal spine), greatest width ca 150 µm, greatest dorso-ventral thickness ca 90 µm. Labrum produced as sub-triangular, nearly semi-circular elevation divided into facets by cuticular ridges; pore pattern not examined in detail but at least 2–3 pores present along posterior half of midline. Caudal end attenuate, terminating in ca 60 µm long, annulate but not obviously spiny dorso-caudal spine, this being turned upwards 30° with respect to trunk axis and accompanied ventrally by pair of triangular furcal spines ca 7–10 µm long.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body overall weakly brownish with distinctly darker-brown telson. Telson portion of gut-like tube containing orange yolk granules. Telson longer than wide and about half as long as thorax.

Identification and variation

Easy recognizable by its general body form, labral outline, long and annulate but not obviously spinose dorso-caudal spine and the distinct brown pigmentation of the cyprid’s telson. Little variation is evident among LSN specimens.

Distribution

Japan (Sesoko Island, Okinawa).