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 : 30

Y-nauplius Type W

Figs 2 , 11A–G

Material examined

JAPAN – Okinawa, Sesoko I. , laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 1 LSN; 1991–2005 • 9 LSN, 8 of which molted to cyprids; 2018–2019 ( Tables 1 and S1 ).

Description

LAST-STAGE NAUPLIUS (LSN) . Lecithotrophic. Body spoon-shaped in dorso-ventral view; about 1.8 times as long as wide; cephalic shield circular/ellipsoidal, with discontinuity in body outline leading into trunk. In lateral view, body axis bent downwards 30° with respect to cephalic axis. Length ca 250 µm (without dorso-caudal spine), greatest width ca 130 µm, greatest dorso-ventral thickness ca 80 µm. Labrum balloon-shaped, with surface divided into facets by cuticular ridges, midline produced into keel-like elevation, and free posterior margin bearing small median spine; pores not examined. Caudal end attenuate, terminating in 75–80 µm long, slightly dorsally curved dorso-caudal spine bearing small spines; spine upturned ca 20° to trunk axis and accompanied ventrally at base by pair of ca 10 µm long triangular furcal spines.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body overall weakly brownish-pigmented. Cephalon most often with two to four lipid vesicles along anterior margin and one to three laterally. Telson slightly longer than wide and about half as long as thorax, often with pair of distinct lipid vesicles.

Identification and variation

Recognizable by the combination of its general body shape, the balloon-shaped, keeled labrum with a spine on the posterior margin and the large, rather straight dorso-caudal spine flanked by relatively robust furcal spines. Variation is seen among nauplii in the form of the dorso-caudal spine (either broad-based and more or less straight or more slender and curved); in the morphology of the posterior margin of the labrum (spine sometimes absent/diminutive, margin sometimes weakly serrate); and among unmolted cyprids in the number of lipid vesicles.

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