Hansenocaris demodex Olesen, Dreyer, Palero & Grygier, 2022

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 : 16-18

Hansenocaris demodex Olesen, Dreyer, Palero & Grygier in Olesen et al., 2022

Figs 2 , 5A–B , 6A–F

Hansenocaris demodex Olesen, Dreyer, Palero & Grygier in Olesen et al., 2022: 570 , figs 3–15, table 6.

Hansenocaris demodex – Dreyer et al. 2023a: figs. 2, 5a, c, tables 3–6, s1–s2; 2023b: 85, 90, 94, 95, 97–100, 115, 118; 2024: 8, fig. 1. — Olesen et al. 2024 : fig. 1.

Material examined

JAPAN – Okinawa, Sesoko I. , laboratory pier, 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 1 LSN; 1991–2005 • 9 LSN, 4 of which molted to cyprids; 2018–2019 ( Tables 1 and S1 ).

Description

LAST-STAGE NAUPLIUS (LSN) . Lecithotrophic. Body narrowly ovate, almost lanceolate in dorso-ventral view; subcylindrical and semi-vermiform; about 2.6 times 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 30° relative to cephalic axis. Length 352–390 µm (without dorso-caudal spine), greatest width 140 µm, greatest dorso-ventral thickness 100 µm. Labrum a triangular elevation twice as long as wide, not divided into facets by cuticular ridges, bearing five pores: two in mid-line centrally, one in mid-line at posterior margin and pair at left and right lateral margins. Caudal end rounded, terminating in short, blunt, mucronate dorso-caudal spine preceded at some distance on ventral surface by pair of tiny furcal spines.

CYPRID VIEWED THROUGH CUTICLE OF LSN. Cyprid body overall brownish-pigmented, most notably in anterior part of cephalic shield, anterior thoracic segments and posterior tip of telson. Orange and brownish yolk granules concentrated in longitudinally-oriented central gut-like tube, this being broadened somewhat in telson, much more so in anterior part of thorax. Pair of lipid vesicles present laterally in cephalic shield. Telson large, about as long as thorax, narrowly cordate in dorso-ventral view with anterior end wider than thorax and with rounded posterior margin.

Identification and variation

Easily recognizable based on the combination of its elongate, semi-vermiform shape, brown or yellow color, elongate labral region, short, blunt dorso-caudal spine, small furcal spines and (within the LSN) the cyprid’s very long, posteriorly rounded telson. Olesen et al. (2022) described morphological variation among LSN specimens in the size and bluntness of the dorso-caudal spine, the symmetry of the cephalic shield’s facet array and the pigmentation of the cyprid developing within the LSN (Sesoko Island: brownish; Green Island: yellowish; such also being the coloration of earlier naupliar stages). The minor molecular variation between all sequenced specimens tends to confirm their conspecificity (Olesen et al. 2022; Dreyer et al. 2023a).

Distribution

Japan (Sesoko Island, Okinawa), Taiwan (Green Island and Xiaoliuqiu Island).

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. 5. Scanning electron micrographs of three significantly different kinds of last-stage lecithotrophic (non-feeding) y-nauplii (Facetotecta) illustrating key characters (general body size and shape, and morphology of labrum and caudal spines) used herein to separate and describe 34 y-naupliar morphospecies, with various measurements explained directly on the figure. A–B. Hansenocaris demodex Olesenet al., 2022, ventral view with detail of labral area.C. Hansenocaris cristalabri Olesen & Grygier, 2022 (holotype, NHMD), lateral view. D–F. Type K, lateral view with details of labrum and caudal spines. A–B from Olesen et al. (2022); C from Olesen & Grygier (2022).

Fig. 6. Last-stage nauplii of two different (morpho)species of y-larvae (Facetotecta) from Sesoko Island (Okinawa, Japan). A–F. Hansenocaris demodex Olesen et al., 2022 (all paratypes). G–L. Type C (‘Bumblebee’). Shown either in life (A–B, G–H) or as slide-mounted exuviae (C–F, I –L).Abbreviations: A1 = first antenna; A2 = second antenna; Md = mandible.