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 : 34-35

Y-nauplius Type X

Figs 2 , 13A–E

Type X – Dreyer et al. 2023a: figs 4, 5a, c, tables s1–s2. — Olesen et al. 2024: fig. 3d–e.

En levende nauplius-y – Høeg 2005: 18, unnumbered LM photograph.

Not Type X – Itô 1987a: 913, 916–917, fig. 2a. — Kikuchi et al. 1991: 69, 72–73, tables 1, 3, fig. 2b. — Watanabe et al. 2000: 7, 9, fig. 5. — Kolbasov & Høeg 2003: 3, 13.

Material examined

JAPAN – Okinawa, Sesoko I. , laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 1 LSN; 1991–2005 • 9 LSN, 3 of which molted to cyprids; 2018–2019 ( Tables 1 and S1 ).

Description

LAST-STAGE NAUPLIUS (LSN). Lecithotrophic. Body elongate-ovate in dorso-vental view, i.e., racket- or snowshoe-shaped, about 1.7 times as long as wide (excluding dorso-caudal spine); cephalic shield ovate/ellipsoidal, with no discontinuity in lateral body outline between shield and trunk. In lateral view, longitudinal axes of cephalon, trunk and dorso-caudal spine all approximately in same plane. Length 330–360 µm (ventral view in life, without dorso-caudal spine), greatest width ca 220 µm, dorso-ventral thickness not measured. Labrum produced as low, nearly square elevation, posterior two-thirds of which trapezoidal owing to lateral insertions of first and second antennae; surface weakly divided into facets by cuticular ridges; pore pattern not studied in detail. Caudal end attenuate/acuminate, terminating without marked discontinuity in broad-based ca 100 µm long, multi-annulate and heavily spinose dorso-caudal spine accompanied ventrally by pair of triangular furcal spines ca 10 µm long.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body overall transparent but with brownish pigmentation appearing later in LSN phase. In early-phase LSN, lateral margins of cyprid’s cephalon with clusters of crystal-like particles and gut-like tube packed with brown/white yolk granules, those in telson being orange in some specimens. Telson about as wide as long and half as long as thorax during early phase of LSN, becoming more elongate later.

Identification and variation

Easily recognizable by its large size and snowshoe- or racket-shaped body. Little variation is apparent among LSN 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. 13. Last-stage nauplii of two different morphospecies of y-larvae (Facetotecta) from Sesoko Island (Okinawa, Japan). A–E. Y-nauplius Type X. F–J. Y-nauplius Type K. Shown either in life (A–B, F–H) or as slide-mounted exuviae (C–E, I–J). Abbreviations: A1 = first antenna; A2 = second antenna; Md = mandible.