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 : 15-16

Y-nauplius Type A*

Figs 1C , 2C , 4

Pacific Type I – Itô 1986a (partim): 86, fig. 1h–i. — Watanabe et al. 2000: 6, 10–11, fig. 21, corrected fig. 6. — Olesen et al. 2022: 556, 578–579, 585, 587–588, figs 2, 14d, 15, table 6. — Dreyer et al. 2023b: 85, 99, 112–113, figs 2, 5.

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

Material examined

JAPAN – Okinawa, Sesoko I ., laboratory pier; 26°38ʹ09.4ʺ N, 127°51ʹ55.2ʺ E • 1 spec.; 20 Sep. 1991 • 1 spec.; 18 Oct. 2018; JA-2018-055 , voucher unavailable. Sixty or more specimens belonging to this type were photographed during fieldwork in 2018/19, 12 of which were sequenced for molecular work in Dreyer et al. (2023a).

Description

NAUPLIUS OF UNKNOWN STAGE.Planktotrophic. Body approximately droplet-shaped in ventral view, about 1.4 times as long as wide; lateral margins tapering gradually towards caudal end with no discontinuity at posterior end of cephalic shield. Body nearly straight in lateral view, with trunk axis downturned ca 15° relative to cephalic axis. Length 190 µm (based on SEM), greatest width 135 µm, greatest dorso-ventral thickness 60 µm. Labrum sub-quadrangular, not divided into facets by cuticular ridges, bearing (at least) one pore in midline and two more pores in postero-lateral corners (both covered with dirt or secretions in illustrated specimen); posterior margin with median cluster of setae. First antenna divided into two distinct segments, distal of which carries two postaxial and three apical setae. Second antenna and mandible both with median feeding apparatus, including one spine on coxa and basis of each. Second antennal endopod two-segmented with setal formula 1:2, 2:2; exopod six-segmented with setal formula 1:0, 2:1, 3:1, 4:1, 5:1, 6:2. Mandibular endopod two-segmented with setal formula 1:2, 2:2; exopod five-segmented with setal formula 1:0, 2:1, 3:1, 4:1, 5:2. Transverse fold ventrally behind labrum carrying pair of putative paragnaths. Ventral side of trunk with about five transverse rows of cuticular ridges. Postero-lateral margins lined with complicated arrangement (basically two rows) of laterally projecting spines; these forming scale-like structures, with three of these being particularly prominent (numbered 1–3 in Fig. 4A, D ): #2 projecting farthest; scales #1 and #2 each with embedded pore. Trunk terminating in pair of slender furcal spines, with robust dorso-caudal spine projecting dorsally, preceded by semi-globular dorso-caudal organ. Cephalic shield incompletely divided into facets and bearing setae and pores, but these details not shown or described here.

Identification and variation

Recognizable among other planktotrophic nauplii by the combination of its small size, the projecting postero-lateral scale #2, the dorso-caudal organ on the trunk’s dorsal side, the dorsally projecting dorso-caudal spine and (in live specimens) the red-orange-colored gut-like central tube.

Distribution

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

Remarks

Twelve specimens, sorted as Type A*, were sequenced by Dreyer et al. (2023a). They grouped together in the resulting phylogenetic tree, but with a large molecular variation among them, suggesting that Type A* is composed of multiple species. Those of our specimens that have been examined with SEM ( Fig. 4 ; Dreyer et al. 2023b: fig. 2) resemble one of Itô’s Pacific Type I specimens ( Itô 1986a: fig. 1h, j) but differ from Itô’s other specimen ( Itô 1986a: fig. 1a–g), supporting Grygier’s conclusion ( Grygier 1991) that the specimens treated by Itô (1986a) as ‘Pacific Type I’ did not merely represent different instars but were not conspecific.

Figures

Fig. 1. Field work to collect y-larvae (Facetotecta) at Sesoko Island (Okinawa, Japan) in 2018 and 2019. A. Example of newly collected y-nauplii (19 specimens) and y-cyprids (1 specimen). B. Seven lecithotrophic y-nauplii showing internal yolk and pigment, too early in development to be identified except for a specimen of Type AM and possible specimens of Types K and AG. C. Two common morphospecies of planktotrophic nauplii, Types A* and I*. D. Tray with code-labelled petri dishes used for rearing. E. Sesoko Island. F. Pier of Sesoko Station. G. Sorting and photography of y-larvae in the lab. A–C from Olesen et al. (2002).

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. 4. Planktotrophic (feeding) y-nauplius of morphospecies Type A*. A. Ventral view. B. Lateral view. C. Naupliar feeding apparatus of right side. D. Postero-lateral spines of left side, dorso-caudal organ, dorso-caudal spine and furcal spines. The naupliar feeding apparatus, postero-lateral spines, dorsocaudal organ and dorso-ventrally flattened body (especially the first of these) are the key characters for separating planktotrophic y-nauplii from lecithotrophic y-nauplii. Abbreviations: Bas = basis; Cox = coxa; En = endopod; 1–3 = postero-lateral spine rows on trunk.