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 : 28-30

Y-nauplius AG*

Figs 2 , 10G–K

Type AG* – 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 • 13 LSN; 1991–2005 • 27 LSN, 21 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 1.7 times as long as wide in ventral view; cephalic shield widely ovate, with sharp discontinuity in body outline leading into trunk. In lateral view, trunk axis bent downwards ca 35° with respect to cephalic axis. Length 270–280 µm (without dorso-caudal spine), greatest width ca 150 µm, greatest dorso-ventral thickness ca 100 µm. Labrum with round-cornered rectangular outline in ventral view; surface divided into facets by cuticular ridges and with midline keel extending posteriorly into 20 µm long median spine; pore pattern not examined in detail, but at least with pair of postero-lateral pores. Caudal end attenuate, terminating in ca 65 µm long, slightly dorsally curved dorso-caudal spine with weak sculpturing of minutely spinose cuticular rings; spine upturned 35° with respect to body axis and accompanied ventrally at base by pair of triangular furcal spines ca 5 µm long.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body unpigmented. Cephalon typically with one or two pairs of distinct yolk granules/vesicles close to anterior margin. Gut-like tube typically with two to four yolk granules in posterior part, one of which most often distinctly orange. Telson longer than wide and about half as long as thorax.

Identification and variation

Recognizable by the combination of its general body shape, the rounded-quadrangular labral outline with a midline keel terminating in a small spine and the cyprid’s relatively slender telson with orange yolk granules in its gut-like tube. Little variation is seen among specimens. The molecular diversity of eight sequenced specimens ( Dreyer et al. 2023a) suggests that this naupliar morphospecies includes two distinct species.

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