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 : 23

Y-nauplius Type G

Figs 2 , 8E–G

Type G – Dreyer et al. 2023a: figs 3, 5a, c, tables s1–s2.

Material examined

JAPAN – Okinawa, Sesoko I. , laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 3 LSN; 1991–2005 • 21 LSN, 6 of which molted to cyprids; 2018–2019 ( Tables 1 and S1 ).

Description

LAST-STAGE NAUPLIUS (LSN). Lecithotrophic. Body widely ovate in dorso-ventral view; about 1.2 times as long as wide; lateral margins tapering gradually towards caudal end with no marked discontinuity at posterior end of cephalic shield. In lateral view trunk axis downturned a full 90° relative to cephalic axis, with furcal spines directed anteriorly from end of trunk (i.e., anatomically ventrally but parallel to cephalic axis). Body length ca 300–320 µm (following body curvature in lateral view) (without dorso-caudal spine), greatest width 220 µm, greatest dorso-ventral thickness ca 100 µm. Labrum elevated, trapezoidal, about as long as wide with distinct posterior margin and with surface divided into facets by cuticular ridges; pore pattern not examined. Caudal end rounded, terminating in very short (8 µm), conical dorso-caudal spine and pair of long (40 µm), distally curved, talon-like furcal spines with pair of double-spines at (anatomically) dorsal base of each.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body weakly brown-pigmented. Many lipid vesicles present in dorsal part of cephalon, and, in some specimens, a dense concentration of yolk granules in central gut-like tube. Lateral margins of cephalic region with clusters of crystalline-like particles.

Identification and variation

Easily recognizable by the combination of its right-angle bend of the body, the large, talon-like furcal spines (‘medium talon’ in comparison to the most similar morphospecies, Types F and H), accompanied by small, basal double-spines, and the lateral clumps of crystalline particles within the margins of the cephalic shield (possibly remnant from the LSN).

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