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 : 46-48

Y-nauplius Type AJ

Figs 2 , 18G–J

Last-stage lecithotrophic y-nauplius of an undescribed species – Dreyer et al. 2023b: 87–88, 90, 94, fig. 6.

Material examined

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

Description

LAST-STAGE NAUPLIUS (LSN). Lecithotrophic. Body spoon- or ladle-shaped in dorso-ventral view; about 1.6 times as long as wide; cephalic shield widely ovate, with weak but distinct discontinuity in body outline leading into trunk; lateral margins of trunk tapering towards truncate caudal end bearing large dorso-caudal spine with base half as wide as posterior end of trunk. In lateral view, trunk axis downturned ca 50° with respect to cephalic axis. Length ca 350 µm (without dorso-caudal spine), greatest width ca 230 µm, greatest dorso-ventral thickness ca 130 µm. Labrum not examined in detail but apparently produced as trapezoidal elevation; surface structures not examined. Dorso-caudal spine ca 80 µm long, upturned ca 10–15° with respect to trunk axis, flanked ventro-laterally by pair of curved, postero-ventrally directed furcal spines 15–20 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. In earlier phase of LSN, gut-like tube as well as paired lateral diverticula in cephalon packed with brown and clear yolk granules in more or less symmetrical pattern. Telson about as long as wide and less than half as long as thorax.

Identification and variation

Easily recognizable by its general body form and distinctive brown and white coloration. Little variation is seen among specimens except in color pattern, differences possibly being attributable to the degree of development.

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