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 : 20-21

Y-nauplius Type B

Figs 2 , 7H–M

Type B – Dreyer et al. 2023a: figs 2, 5a, c, tables s1–s2.

Material examined

JAPAN – Okinawa, Sesoko I. , laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 1 LSN; 1991–2005 • 3 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 twice as long as wide; lateral margins tapering gradually towards caudal end with no discontinuity at posterior end of cephalic shield. Dorsum evenly curved in lateral view, with trunk axis downturned 50–55° relative to cephalic axis. Length 250–265 µm (without dorso-caudal spine), 275 µm in lateral view following body curvature; greatest width 160 µm and greatest dorso-ventral thickness 70–75 µm. Labrum weakly elevated, sub-quadrangular, approximately as long as wide; surface not divided into facets by cuticular ridges; pore pattern not examined in detail. Caudal end narrowly truncate, terminating in short (12 µm), triangular dorso-caudal spine positioned unusually far anteriorly on dorsal side and pair of longer (20 µm), narrow, sharply pointed, slightly upcurved and diverging furcal spines.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body practically unpigmented, although naupliar appendages weakly brownish. Gut-like tube packed with orange-brown yolk granules. Telson small, wider than long, significantly shorter than half of thorax length.

Identification and variation

Easily recognizable by its unusually forward-positioned dorso-caudal spine, evenly curved (in lateral view) body and broadly triangular ventral trunk region. No distinct variation was apparent among the few examined specimens.

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. 7. Last-stage nauplii of two different morphospecies of y-larvae (Facetotecta) from Sesoko Island (Okinawa, Japan). A–G. Type D* (“Big brown”). H–M. Type B. Shown either in life (A–B, H–J) or as slide-mounted exuviae (C–G, K–M). Abbreviations: A1 = first antenna; A2 = second antenna; Md = mandible.