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 : 27

Y-nauplius Type AH*

Figs 2 , 9I–N

Type AH* – 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 • 11 LSN; 1991–2005 • 31 LSN, 28 of which molted to cyprids; 2018–2019 ( Tables 1 and S1 ).

Description

LAST-STAGE NAUPLIUS (LSN) . Lecithotrophic. Body spoon-shaped in dorso-ventral view; about twice as long as wide; cephalic shield widely ovate, with sharp discontinuity in body outline leading into trunk. In lateral view, trunk axis bent downwards 30–35° with respect to cephalic axis. Length 240–270 µm (ventral view in life, without dorso-caudal spine), greatest width 175 µm, greatest dorso-ventral thickness ca 110 µm. Labrum with goblet-shaped outline in ventral view, its free, rounded posterior margin being extended into medium-sized (15 µm long) medial spine (‘stem’ of ‘goblet’); labral surface divided into facets by cuticular ridges; pore pattern not examined. Caudal end attenuate, terminating in robust, 90 µm long dorso-caudal spine armed with smaller spines and accompanied ventrally at base by pair of triangular furcal spines ca 10 µm long; axis of dorso-caudal spine bent upwards at 30° with respect to trunk axis.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Body weakly brownish with many yolk granules/lipid vesicles concentrated dorsally, one typically being situated in midline anterior to nauplius eye, and with clusters of small vesicles posterior to compound eyes. Telson about as long as wide, about half as long as thorax.

Identification and variation

Recognizable by the combination of its general shape, the large, spinose dorso-caudal spine and the large, goblet-shaped labrum with a free posterior extension continuing into a median spine overhanging the mouth region. Little morphological variation is seen between specimens, most or all of which have internal lipid vesicles/yolk granules distributed as described above. Molecular diversity revealed by sequencing 13 specimens ( Dreyer et al. 2023a) suggests that this naupliar morphospecies comprises three cryptic species.

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. 9. Last-stage nauplii of four different morphospecies of y-larvae (Facetotecta) from Sesoko Island (Okinawa, Japan). A–C. Hansenocaris cristalabri Olesen & Grygier, 2022. D–E. Hansenocaris aquila Olesen & Grygier, 2022. F–H. Y-nauplius Type AC. I–N. Y-nauplius Type AH*. Shown either in life (A–B, F–H, I–J), as slide-mounted exuviae (D–E, K–N) or in SEM (C). Abbreviations: A1 = first antenna; A2 = second antenna; Md = mandible. A–E from Olesen & Grygier (2022).