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 : 32-33

Y-nauplius Type U*

Figs 2 , 12A–D

Type U* – Dreyer et al. 2023a: figs 4, 5a, c, tables s1–s2. — Olesen et al. 2024 : fig. 2f–g.

Material examined

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

Description

LAST-STAGE NAUPLIUS (LSN). Lecithotrophic. Body widely ovate in dorso-ventral view; about 1.4 times as long as wide; cephalic shield nearly circular, with minor discontinuity in body outline leading into trunk. In lateral view, longitudinal axes of cephalon, trunk and dorso-caudal spine all in approximately same plane. Length 460 µm (ventral view in life, without dorso-caudal spine), greatest width ca 330 µm, greatest dorso-ventral thickness ca 30 µm. Labrum shorter than wide, a nearly rectangular low elevation weakly divided into facets by cuticular ridges; bearing four pores, two in midline posteriorly and pair situated outside of left and right ridge-defined labral margins. Lateral margins of trunk bearing spine rows. Caudal end obtuse, terminating in 75 µm long dorso-caudal spine with at least three annular ridges bearing several subsidiary spines, accompanied ventrally and slightly forward of its base by pair of tiny, vestigial furcal spines.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Occupying only central part of LSN near midline, leaving large fraction of outer portions of disc ‘empty’. Lacking distinct pigmentation, except for some small dark pigment spots in telson. Yolk granules of gut-like central tube mostly concentrated in telson. Lipid vesicles present anteriorly and laterally in cephalon. Telson about as long as wide and about half as long as thorax.

Identification and variation

Easily recognizable by its flat ‘disc-shaped’ form (the broadest of the lecithotrophic y-nauplii encountered at Sesoko Island) and the central position of the developing cyprid within.

Distribution

Japan (Sesoko Island, Okinawa); Taiwan (Keelung).

Remarks

Itô (1987b: figs 1–3) described three forms of wide, flat y-nauplii (Types VIIIa-c) from Tanabe Bay ( Japan: Wakayama Prefecture) that are the closest described forms in the literature to Type U* from Okinawa. Although they differ from Type U* in having antero-lateral indentations in the body margin, they might be earlier instars of either Type U* or something closely related to it. Because detailed morphological and molecular comparison with Itô’s material has not been done, we do not treat any of these forms as synonymous here.

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