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 : 18-19

Y-nauplius Type C

Figs 2 , 6G–L

“Bumblebee” – Olesen et al. 2022: 578, 585, 587, figs 14b, 15, table 6. — Dreyer et al. 2023b: 99, figs 3a–e, 7.

Type C – Dreyer et al. 2023a: figs 1c, 2, 5a, c, s1–s2, tables s1–s2; 2024: 8, fig. 1.

Undescribed species of “y-larvae” – Olesen 2024: fig. on p. 15.

Material examined JAPAN – Okinawa, Sesoko I., laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 8 LSN; 1991–2005 • 40 LSN, 27 of which molted to cyprids; 2018–2019 ( Tables 1 and S1 ).

Description

LAST-STAGE NAUPLIUS (LSN) . Lecithotrophic. Body narrowly ovate in dorso-ventral view; about twice as long as wide; lateral margins tapering gradually towards caudal end with no discontinuity at posterior end of cephalic shield. In lateral view, trunk axis downturned 30–45° relative to cephalic axis. Length 250–275 µm (without dorso-caudal spine), greatest width 150 µm, greatest dorso-ventral thickness 70 µm. Labrum weakly elevated, broadly trapezoidal with rounded posterior corners and approximately as long as wide; not divided into facets by cuticular ridges; bearing five pores: row of three posteriorly in midline and pair in left and right postero-lateral corners. Caudal end rounded, terminating in short (ca 7–10 µm), conical dorso-caudal spine and pair of short (10 µm), broad, upwardly curved furcal spines.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Thorax brown, telson brown/black. Orange yolk granules concentrated centrally in cephalon posterior to nauplius eye and in posterior part of gut-like central tube. Telson approximately as long as wide and less than half as long as thorax, with notably bulging anterior half.

Identification and variation

Easily recognizable by the combination of its obtuse-ovate shape, distinctive black-brown-orange coloration (on which the nickname is based) and the three short, broad caudal spines. There is very little variation among specimens except for changes in pigment distribution as cyprid development progresses within the LSN cuticle, and only insignificant molecular variation was found among seven sequenced specimens (Olesen et al. 2022; Dreyer et al. 2023a, 2024).

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. 6. Last-stage nauplii of two different (morpho)species of y-larvae (Facetotecta) from Sesoko Island (Okinawa, Japan). A–F. Hansenocaris demodex Olesen et al., 2022 (all paratypes). G–L. Type C (‘Bumblebee’). Shown either in life (A–B, G–H) or as slide-mounted exuviae (C–F, I –L).Abbreviations: A1 = first antenna; A2 = second antenna; Md = mandible.