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 : 41

Y-nauplius Type Y

Figs 2 , 16A–E

Type Y – Dreyer et al. 2023a: figs 4, 5a, c, tables s1–s2.

Material examined

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

Description

LAST-STAGE NAUPLIUS (LSN). Lecithotrophic. Body ovate in dorso-ventral view; about 1.6 times as long as wide; lateral margins without discontinuity in body outline between cephalic shield and trunk. In lateral view, longitudinal axes of cephalon, trunk and dorso-caudal spine nearly in same plane. Length 360–400 µm (without dorso-caudal spine), greatest width ca 240 µm, greatest dorso-ventral thickness ca 150 µm. Labrum produced as wide, nearly square, trapezoidal elevation divided into facets by cuticular ridges; with four pores, two in posterior midline and pair along postero-lateral margins. Caudal end attenuate, terminating in 80–90 µm long, spinulose dorso-caudal spine accompanied ventrally by pair of tiny furcal spines situated slightly forward of its base.

CYPRID VIEWED THROUGH CUTICLE OF LSN. In early-phase LSN, developing cyprid filling entire nauplius, but distinct ‘empty’ area present later on between cyprid and LSN’s lateral margins. Telson with dark-brown tip. Gut-like central tube with row of yolk granules, some colored orange: yolk granules/lipid vesicles clustered in central part of cephalon; lipid vesicles present anteriorly in cephalon. Telson about as long as wide and about half as long as thorax.

Identification and variation

Easily recognizable by its large size and racket-shaped body (in dorso-ventral view), with a clearer distinction between the trunk and the dorso-caudal spine than in Type X. Size variation among specimens is probably attributable, at least in part, to squeezing and distortion of exuviae during mounting on slides.

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