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

Y-nauplius Type E*

Figs 2 , 10A–F

Hansenocaris sp. – Itô 1991: 57, fig. 1 (see the ‘ Itô’s (1991) y-nauplius’ portion of the Discussion below).

Nauplius of undescribed lecithotrophic y-larva – Grygier et al. 2019: 1226–1228, figs 2c–h, 3a–b.

Type E* – 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 • 9 LSN; 1991–2005 • 40 LSN, 29 of which molted to cyprids; 2018–2019 ( Tables 1 and S1 ).

Description

LAST-STAGE NAUPLIUS (LSN) . Lecithotrophic. Body short-handled spoon-shaped in dorso-ventral view; about 1.5 times as long as wide; cephalic shield widely ovate, with sharp discontinuity in body outline leading into trunk. In lateral view, trunk axis bent downwards 50–60° with respect to cephalic axis. Length 210–260 µm (without dorso-caudal spine), greatest width 140–150 µm, greatest dorso-ventral thickness ca 80 µm. Labrum with pentagonal outline in ventral view; free posterior margin extending into 10 µm long median spine; surface divided into facets by cuticular ridges; pores not examined in detail, but at least with pair of postero-lateral pores. Caudal end attenuate, terminating in 40–50 µm long, often slightly curved dorso-caudal spine upturned 50° with respect to trunk axis and armed with spiny ornamentation and accompanied ventrally at base by pair of ca 7 µm long furcal spines.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body weakly brownish-pigmented. Cephalon with one or two pairs of distinct yolk/lipid vesicles close to its anterior margin. Gut-like central tube often with brownish/reddish-colored yolk granules, especially in posterior part. Telson about as long as wide and less than half as long as thorax.

Identification and variation

Recognizable by the combination of its general body shape, pentagonal labral outline, relative slender and often curved dorso-caudal spine, and the pair of distinct yolk granules/vesicles at the anterior margin of the cephalic shield. Little morphological variation is seen between specimens. Molecular diversity revealed by sequencing 15 specimens ( Dreyer et al. 2023a) suggests that this naupliar morphospecies includes two or three distinct species.

Distribution

Japan (Sesoko Island, Okinawa; Tanabe Bay, Wakayama).

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.