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 : 21-23

Y-nauplius Type F

Figs 2 , 8A–D

Type F – 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 • 2 LSN; 1991–2005 • 5 LSN, 1 of which molted to cyprid; 2018–2019 ( Tables 1 and S1 ).

Description

LAST-STAGE NAUPLIUS (LSN) . Lecithotrophic. Body ovate in dorso-ventral view; about 1.4 times as long as wide; lateral margins tapering gradually towards caudal end with no discontinuity at posterior end of cephalic shield. Dorsum evenly but strongly curved in lateral view, with trunk axis downturned 65° relative to cephalic axis. Length ca 300 µm (anteroventral view, without dorso-caudal spine), 310 µm in lateral view following curvature of body, greatest width 220 µm, greatest dorso-ventral thickness ca 70 µm. Labrum elevated, pentagonal, about as long as wide, with distinct and free posterior margin; other details unknown. Body narrowly rounded, terminating in short, conical dorso-caudal spine and pair of longer (25 µm), curved, robust furcal spines situated ventrally slightly forward from caudal end.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body overall weakly brownish, but pigment most heavily concentrated in telson and in naupliar appendages. Central-dorsal gut-like tube devoid of distinct yolk granules except for some orange granules in trunk. Telson much shorter than wide, distinctly less than half as long as thorax. About six lipid vesicles present along anterior margin of cephalon and four along posterior margin of labrum.

Identification and variation

Easily recognizable by the combination of its distinctly downturned trunk region, short, conical dorso-caudal spine and robust but still unremarkably long, curved furcal spines positioned forward from the caudal end. The last feature makes this a ‘short-talon’ morphospecies in comparison to the next two described below.

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