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 : 37-39

Y-nauplius Type AI

Figs 2 , 14G–L

Material examined

JAPAN – Okinawa, Sesoko I. , laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 2 LSN; 1991–2005 • 8 LSN, 6 of which molted to cyprids; 2018–2019 ( Tables 1 and S1 ).

Description

LAST-STAGE NAUPLIUS (LSN). Lecithotrophic. Body narrowly ovate in dorso-ventral view; about 1.6 times as long as wide; lateral margins with only modest discontinuity in body outline between cephalic shield and trunk. In lateral view, trunk axis bent downwards ca 10–20° with respect to cephalic axis. Length 210–240 µm (without dorso-caudal spine), greatest width ca 120 µm, greatest dorso-ventral thickness ca 80 µm. Labrum weakly elevated, hoe-shaped in ventral view, approximately 1.2 times as long as wide; surface divided into plates by cuticular ridges; pore pattern not examined in detail but at least three pores present in midline: one anteriorly, two posteriorly. Caudal end acuminate, terminating in ca 30 µm long dorso-caudal spine usually with two or three annuli, this being upturned ca 10–20° with respect to trunk axis and accompanied ventrally by pair of furcal double-spines ca 5 µm long (i.e., each furcal spine bifid from base).

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body overall weakly brownish, but telson and anterior part of cephalon distinctly darker brown. Gut-like central tube and central part of cephalon packed with yolk granules/lipid vesicles and often with orange-colored vesicle in telson. Telson sub-triangular, about as long as wide, about half as long as thorax.

Identification and variation

Easily recognizable by its overall shape and size, furcal double-spines, relatively small dorso-caudal spine and the developing cyprid’s brown telson. Variation is evident in the size of the dorso-caudal spine.

Distribution

Japan (Sesoko Island, Okinawa).

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. 14. Last-stage nauplii of two different morphospecies of y-larvae (Facetotecta) from Sesoko Island (Okinawa, Japan). A–F. Y-nauplius Type M. G–L. Y-nauplius Type AI. Shown either in life (A–B, G–I) or as slide-mounted exuviae (C–F, J–L). Abbreviations: A1 = first antenna; A2 = second antenna; Md = mandible.