Hansenocaris undetermined

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, European Journal of Taxonomy 929 (1), pp. 1-90 : 50-51

Y-nauplius Type AM

Figs 2 , 19H

Material examined

JAPAN – Okinawa, Sesoko I. , laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 1 LSN; 2018–2019 ( Tables 1 and S1 ).

Description

LAST-STAGE NAUPLIUS (LSN) . Lecithotrophic. Body lollipop-shaped in dorso-ventral view; about 1.6 times as long as wide; cephalic shield large and circular, with sharp discontinuity in body outline leading into trunk. In lateral view, longitudinal axes of cephalon, trunk and dorso-caudal spine in approximately same plane. Length 420 µm (without dorso-caudal spine), greatest width ca 260 µm, dorso-ventral thickness not measured but body apparently quite flattened. Labrum not examined in detail. Caudal end attenuate, terminating in ca 160 µm long, smooth dorso-caudal spine flanked ventrally at base by pair of small, thorn-like furcal spines ca 20 µm long.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body overall weakly brownish but with lateral margins of cephalon and terminal part of telson distinctly darker brown. Gut-like tube packed with yellow yolk granules, these being markedly concentrated in central part of cephalon. Telson about as long as wide and less than half as long as thorax.

Identification and variation

Easily recognizable by its general form, especially the large rounded cephalic shield and very long, smooth dorso-caudal spine, and by the cyprid’s distinct pattern of brown pigmentation. Only one specimen was available, so variation could not be checked.

Distribution

Japan (Sesoko Island, Okinawa); Taiwan (Green Island) (unpublished).

Figures

Fig. 2. Y-naupliar (Facetotecta) diversity at Sesoko Island (Okinawa, Japan). A. Schematic life cycle of y-larvae (modified from Itô 1991; Glenner et al. 2008). B. Overview of 34 morphospecies of lecithotrophic last-stage y-nauplii obtained by laboratory rearing of earlier-stage nauplii collected in the plankton; three of them represent formally described species while 31 remain undescribed. C. Nine types of planktotrophic y-larvae, of which only Type A* is treated in detail in this paper. All photos in B and C are to the same scale. Figure also used in Olesen (2004). Examples of live video of most of the y-naupliar morphospecies can be seen at https://youtu.be/er0mYLswV-c and are also deposited at Figshare.com: https://doi.org/10.6084/m9.figshare.24953568.v1.

Fig. 19. Last-stage nauplii of four different morphospecies of y-larvae (Facetotecta) from Sesoko Island (Okinawa, Japan). A–E. Y-nauplius Type AK. F–G. Y-nauplius Type AO. H. Y-nauplius Type AM. I–K. Y-nauplius Type AN. Shown either in life (A–B, H) or as slide-mounted exuviae (C–G, I–K). Abbreviations: A1 = first antenna; A2 = second antenna; Md = mandible.