Taxonomic diversity of marine planktonic ‘ y-larvae’ (Crustacea: Facetotecta) from a coral reef hotspot locality (Japan, Okinawa), with a key to y-nauplii Author Olesen, Jørgen 6B569425-6BE7-4A73-B165-87E0C097715A Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK- 2100 Copenhagen Ø, Denmark. jolesen@snm.ku.dk&jolesen@snm.ku.dk&thecostracans@gmail.com Author Grygier, Mark J. 0A2FB16C-56B0-45E5-BB7B-61C3F0F7D46D National Museum of Marine Biology & Aquarium, 2, Houwan Rd., Checheng, Pingtung 944401, Taiwan. thecostracans@gmail.com&jolesen@snm.ku.dk&thecostracans@gmail.com text European Journal of Taxonomy 2024 2024-03-25 929 1 1 90 https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2479/11077 journal article 293299 10.5852/ejt.2024.929.2479 f7dd08c6-e206-4d97-8c9d-7432c5df72b2 2118-9773 10876286 832192E7-A85A-4971-BA2F-D7420D299E8D Hansenocaris aquila Olesen & Grygier, 2022 Figs 2 , 9D–E Hansenocaris aquila Grygier &Olesen, 2022: 307 , fig. 6. Hansenocaris aquila Olesen et al. 2024 : fig. 2. Material examined JAPAN Okinawa , Sesoko I. , laboratory pier, 26°38ʹ09.4ʺ N , 127°51ʹ55.2ʺ E 2 LSN ; 1991–2005 ( Tables 1 and S1 ). Description LAST-STAGE NAUPLIUS (LSN) . Lecithotrophic. Body spoon-shaped in dorso-ventral view; about twice as long as wide; cephalic shield broadly rounded, with sharp discontinuity in body outline leading into trunk. In lateral view, trunk axis bent downwards ca 40° with respect to cephalic axis. Length 400 µm (ventral view of mounted exuvia, without dorso-caudal spine), greatest width ca 210 µm, dorso-ventral thickness ca 120 µm. Labrum with goblet-shaped outline in ventral view, its free posterior margin extending into large medial spine (‘stem’ of ‘goblet’), preceded by four small spines on labral midline; labral surface divided into facets by cuticular ridges. Trunk dorsum with four longitudinal rows of spines. Caudal end attenuate, terminating in 100 µm long, robust dorso-caudal spine armed with many smaller spines and accompanied ventrally at base by pair of small, ca 5 µm long furcal spines; long axis of dorso-caudal spine upturned 15° with respect to trunk axis. CYPRID VIEWED THROUGH CUTICLE OF LSN. No live specimens examined. Identification and variation Easily recognizable by its labrum with the posterior margin extended into a large, eagle-beak-like median spine preceded by ca four small spines on the midline; also distinguished by the four dorsal rows of longitudinal spines on the trunk and the very long, robust and distinctly spinose dorso-caudal spine. Distribution Japan (Sesoko Island, Okinawa ).