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 : 34

Y-nauplius Type V

Figs 2 , 12E–G

Type V – Dreyer et al. 2023a: figs 4, 5a, c, tables s1–s2.

Not Nauplius V – Hansen 1899: 47–49, table 3, fig. 6. — Schram 1970: 53, 64.

Material examined

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

Description

LAST-STAGE NAUPLIUS (LSN). Lecithotrophic. Body narrowly ovate in dorso-ventral view; about 1.6 times as long as wide; lateral margins tapering gradually towards caudal end with indistinct concave transition between cephalic shield and trunk. In lateral view, body almost straight, with trunk axis downturned ca 10–15° with respect to cephalic axis. Length 340–370 µm (without dorso-caudal spine), greatest width ca 230 µm, greatest dorso-ventral thickness ca 100 µm. Labrum not examined in detail. Lateral margins of trunk with rows of 5–10 µm long spines. Caudal end rounded and terminating in fairly sharply pointed, 10–15 µm long dorso-caudal spine accompanied ventrally by similarly sharp pair of ca 10 µm long, triangular furcal spines.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body overall transparent, but rows of brown pigment spots present along lateral margins of cephalon early in cyprid development, with more extensive brownish coloration developing later on. Gut-like tube packed with yolk granules along most of its length. Lipid vesicles clustered in mouth/labrum region of cephalon, with a few more present anterior to nauplius eye. In early LSN, telson wider than long and about half as long as thorax, but more elongate in later-phase LSN.

Identification and variation

Easy recognizable by its overall disc-shaped body, spine-lined trunk margins and broadly rounded caudal end with a relatively small dorso-caudal spine. The two examined specimens differ somewhat in size ( Table S1 ), and only the larger one has rows of pigment spots along the margins of the developing cyprid’s cephalon.

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. 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.