Y-nauplius Type AF

Figs 2, 17A–E

Undescribed form-taxa of lecithotrophic y-larvae – Grygier et al. 2019 pars: 1228, fig. 3f.

Type AF – Dreyer et al. 2023a: figs 4, 5a, c, tables s1–s2. — Olesen et al. 2024: fig. 2c.

Material examined

JAPAN – Okinawa, Sesoko I., laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 2 LSN; 1991–2005 • 12 LSN, 8 of which molted to cyprids; 2018–2019 (Tables 1 and S1).

Description

LAST-STAGE NAUPLIUS (LSN). Lecithotrophic. Body short, with unusually bloated trunk region; widely ovate in dorso-ventral view; about 1.35 times as long as wide; cephalic shield very widely ovate, with sharp discontinuity in body outline leading into trunk. In lateral view, trunk axis downturned ca 60° with respect to cephalic axis. Length 210–240 µm (ventral view in life, without dorso-caudal spine), greatest width ca 170 µm, greatest dorso-ventral thickness ca 130 µm. Labrum conical in lateral view and drawn into hypodermic-needle like distal extension; other features of labrum not examined. Caudal end truncate, terminating in broad, conical, ca 40 µm long dorso-caudal spine directed postero-dorsally, with its axis upturned ca 50° from trunk axis, and ventral pair of triangular furcal spines ca 5 µm long, these being widely separated both from each other and from dorso-caudal spine, sitting on distinct, conical bases.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Overall weakly brownish, but more distinctly brown in telson region. Gut-like tube filled with yolk granules; some of these partly brown or black but those in telson often colored orange; some specimens with additional lipid vesicles spread out within cephalon and smaller vesicles behind compound eyes. Telson small.

Identification and variation

Easily recognizable by its bloated or blimp-like form, conical labrum with hypodermic-needle-like extension and extremely robust, conical dorso-caudal spine. Some variation exists in the size of the dorso-caudal spine and its angle of orientation with respect to the trunk axis.

Distribution

Japan (Sesoko Island, Okinawa).