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 : 48

Y-nauplius Type AK

Figs 2 , 19A–E

Material examined

JAPAN – Okinawa, Sesoko I. , laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 1 LSN; 1991–2005 • 4 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 1.7 times as long as wide; lateral margins tapering gradually towards caudal end with very slight discontinuity at posterior end of cephalic shield. In lateral view, trunk axis downturned 35–40° with respect to cephalic axis. Length 330–350 µm (without dorso-caudal spine), greatest width ca 200 µm, greatest dorso-ventral thickness ca 100 µm. Labrum weakly produced as bell-shaped elevation; not clearly divided into facets; pores not examined in detail but at least three present, one in posterior midline and one pair in postero-lateral corners. Caudal end rounded, terminating in three almost identical, 20 µm long, narrow-conical, pointed caudal spines; among them, ventro-laterally situated furcal spines narrower at base than dorsalcaudal spine.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body overall weakly brownish, but terminal part of telson with distinct dark-brown pigmentation. Gut-like central tube in telson containing orange yolk granules. Telson about as long as wide, less than half as long as thorax.

Identification and variation

Easily recognizable by its general body form, especially the three equally long, thin caudal spines, and the brown pigmentation of the cyprid’s telson. Variation among specimens was insignificant but few specimens were examined.

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. 19. Last-stage nauplii of four different morphospecies of y-larvae (Facetotecta) from Sesoko Island (Okinawa, Japan). A–E. Y-nauplius Type AK. F–G. Y-nauplius Type AO. H. Y-nauplius Type AM. I–K. Y-nauplius Type AN. Shown either in life (A–B, H) or as slide-mounted exuviae (C–G, I–K). Abbreviations: A1 = first antenna; A2 = second antenna; Md = mandible.