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 : 19

Y-nauplius Type D*

Figs 2 , 7A–G

“Big brown” – Grygier et al. 2019: fig. 4. — Olesen et al. 2022: 578, 585, 587– 88, figs 2, 14c, 15, table 6.

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

Material examined

JAPAN – Okinawa, Sesoko I. , laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 4 LSN; 1991–2005 • 35 LSN, 23 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 ca 30–45° relative to cephalic axis. Length 310–360 µm (without dorso-caudal spine), greatest width 170 µm, greatest dorso-ventral thickness 60–70 µm. Labrum weakly elevated, approximately as long as wide and sub-pentagonal in outline; surface not obviously divided into facets by cuticular ridges; bearing five pores: row of three in midline posteriorly and pair situated at lateral margins on right and left sides. Body terminating in long (ca 50 µm, width at base ca 12 µm), straight, smooth or weakly terraced dorso-caudal spine with long axis either in same plane as trunk axis or upturned ca 20° relative to latter and pair of shorter but still prominent (15–20 µm), fairly sharp, dorsally or dorso-medially curved furcal spines.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body overall markedly brownish-pigmented. Orange yolk granules seen most clearly in cephalon and telson, sometimes also concentrated centrally in body but often more widely distributed. Telson of variable outline in ventral view, as long as wide or longer, approximately half as long as thorax.

Identification and variation

Easily recognizable by the combination of its brown coloration and somewhat extended overall body shape, the lengths of the three caudal spines and (at least in some) the obvious medial component of the furcal spines’ curvature. Morphological variation among specimens in body size, the angle between the dorso-caudal spine and the hind-body, and the size and degree of curvature of the furcal spines suggests that more than one species may be involved. The molecular diversity of 13 specimens sequenced by Dreyer et al. (2023a) also suggests that this morphospecies consists of two or three separate species.

Distribution

Japan (Sesoko Island, Okinawa), Taiwan (Wanghaixiang Fishing Harbour, Keelung).

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. 7. Last-stage nauplii of two different morphospecies of y-larvae (Facetotecta) from Sesoko Island (Okinawa, Japan). A–G. Type D* (“Big brown”). H–M. Type B. Shown either in life (A–B, H–J) or as slide-mounted exuviae (C–G, K–M). Abbreviations: A1 = first antenna; A2 = second antenna; Md = mandible.