Y-nauplius Type K Figs 2, 5D–F, 13F–J Type K – 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 • 27 LSN, 6 of which molted to cyprids; 2018–2019 (Tables 1 and S1). Description LAST-STAGE NAUPLIUS (LSN). Lecithotrophic. Body widely ovate in dorso-ventral view; about 1.3 times as long as wide; cephalic shield very wide-ovate, with some discontinuity in body outline leading into trunk. In lateral view, trunk axis downturned ca 55° with respect to cephalic axis. Length 190–220 µm (ventral view in life, without dorso-caudal spine), greatest width ca 140 µm, greatest dorso-ventral thickness ca 65 µm. Labrum produced as sub-trapezoidal elevation with surface divided into facets by cuticular ridges; bearing total of five pores: three near midline posteriorly and one postero-lateral pair along left and right labral margins. Caudal end truncate, terminating in simple, ca 5 µm long dorso-caudal spine, this upturned ca 10° relative to trunk axis and flanked ventrally by pair of triangular furcal spines ca 10 µm long. CYPRID VIEWED THROUGH CUTICLE OF LSN. Body generally transparent or weakly brownish. Cephalic shield often with a few small, transparent lipid vesicles along anterior margin. Posterior part of gut-like tube containing small, orange yolk granules. Telson twice as long as wide and significantly shorter than thorax, often not clearly demarcated from latter. Identification and variation Recognizable by the combination of its short, compact body, truncate caudal end and very small dorso-caudal spine. No significant variation recognized among specimens. Type K is the smallest lecithotrophic morphospecies treated in this work. Distribution Japan (Sesoko Island, Okinawa).

Published as part of Olesen, Jørgen & Grygier, Mark J., 2024, Taxonomic diversity of marine planktonic ' y-larvae' (Crustacea: Facetotecta) from a coral reef hotspot locality (Japan, Okinawa), with a key to y-nauplii, pp. 1-90 in European Journal of Taxonomy 929 (1) on pages 35-37, DOI: 10.5852/ejt.2024.929.2479, http://zenodo.org/record/10876286