Hansenocarididae Olesen and Grygier, 2022

Olesen, JØrgen & Grygier, Mark J., 2022, Two New Species of Lecithotrophic Nauplius y with Remarkable Labra from Okinawa, Japan, and a Family-Group Name for y-Larvae (Crustacea: Thecostraca: Facetotecta: Hansenocarididae fam. nov.), Species Diversity 27 (2), pp. 301-317 : 303-304

Family Hansenocarididae Olesen and Grygier , fam. nov

[New Japanese name: Chou-kou-mushi-ka]

Diagnosis. Mostly agreeing with the diagnosis proposed for Subclass Facetotecta by Chan et al. (2021: 34), but with additional detail that is subject to change as more taxa are described. Known only from ortho- and metanauplii, cyprid larvae, and ypsigons; adults unknown or unrecognized.

Nauplii [based in part on Grygier (1991, 1996), thus also on M. J. Grygier’s unpublished data]: cephalic shield posteriorly abutting on free, exposed trunk dorsum; frontolateral horns and frontal filaments absent. Common plan of cephalic shield ridges fully or partially outlining moreor-less stereotypical turtle-shell-like pattern of plates (facets) in early instars, plates commonly becoming complexly subdivided and/or re-fused in later instars. Common posi-tions of ‘window’ plate and dorsal setae (of which no more than 4 pairs present) and certain pores on cephalic shield. Ventral side of cephalic region flat, round, with wide rim (‘faciomarginal cuticle’). First antenna with up to 8 setae on distal segment only. Maximal second antennal armature of 1 coxal spine, 1 basal spine, 2-segmented endopod with spine and seta on proximal segment and 2 apical setae on distal, and 6-segmented exopod with short seta on second segment, 1 long seta each on next 3 segments, and long and short seta on distal segment. Maximal mandibular armature similar except basis maximally with 1 spine and 1 seta, and exopod 5-segmented with 1 seta each on first 4 segments, 2 setae on apical segment. Second antenna and mandible essentially unchanged in segmentation and armature from second through final instar except for rare loss of 1 protopodal spine. Paragnaths either absent or rudimentary and unarmed. No ventral setation except for rare occurrence of pair of setae representing first maxillae. Trunk region often complexly subdivided by ridges. Caudal end asetose, but usually with pair of furcal spines and terminal dorsocaudal spine, these being of various sizes and possessing various subsidiary spination depending on taxon. Round, knob-like ‘dorsocaudal organ’ of unknown function present posteriorly on dorsum of trunk region mainly in planktotrophic forms, possibly represented by similarly positioned pore in some lecithotrophic forms. Exuvium of last nauplius of lecithotrophic forms often containing fine, membranous trace (“ghost”) of ventral thoracic parts of cyprid formerly held within, this being connected by internal struts to pair of anterioventral invaginations of trunk wall.

Cyprids [based in part on Itô (1985), Kolbasov et al. (2007), HØeg et al. (2014); also on J. Olesen’s unpublished SEM data]: non-feeding, with boat-like, univalved head shield or carapace not covering whole body and free from thorax. Carapace with lattice organs and often with complex pattern of surface sculpturing featuring anterior meshwork and longitudinal ridges. Head with pair of prehensile first antennae bearing hook (occasionally absent) and uni-or usually bi-articulate palp on presumed third segment (proximal segmentation often obscure); knob-like vestiges of naupliar second antennae and mandibles sometimes present. Pair of sessile compound eyes, each composed of about 9 ommatidia with tripartite crystalline cones. Eyes often (not confirmed in some) flanked by 2 pairs of sensory organs (‘bifurcate paraocular processes,’ ‘postocular filamentary tufts’). Large, ventrally produced labrum bearing apical and posterior hooks usually present, its form and armament taxon-specific to some degree. Thorax 6-segmented and bearing 6 pairs of biramous limbs, with first 2 tergites fused to each other dorsally (in at least some taxa), last 2 segments with pleural extensions. Coxa and basis of thoracopods separate or (in sixth pair) fused, exopods 2-segmented (rarely 1-segmented) with 3 apical natatory setae (2 setae in first pair), endopods 2- or 3-segmented with 2 apical and 1 subapical natatory setae (subapical seta absent in first pair). Abdomen consisting of 1 or, much more usually, 3 short somites with or without sharp ventrolateral extensions, and large, oblong telson, latter heavily ornamented with cuticular ridges defining 6 rows of dorsal and lateral plates, thus appearing pseudo-segmented. Telson similarly ornamented ventrally and bearing 0–6 serrate spines along posterioventral margin and pair of small, setose, unsegmented or (perhaps superficially) 2-segmented furcal rami on posterior face.

Ypsigon stage [based on Glenner et al. (2008), Chan et al. (2021), Dreyer et al. (in press)]: unsegmented, slug-like, slightly motile despite lacking appendages. Lined externally by extremely thin (epi)cuticle. Internal cellular contents comprising epithelium beneath cuticle, derivatives of former cyprid nervous system (including large anterior neuropile and degenerating compound eyes), muscle bands, and elongate mass of cells filled with lipid vesicles. No ovarial or testicular tissue present.

Type genus. Hansenocaris Itô, 1985 .

Remarks. As reviewed by Dreyer et al. (in press), a putative family-group name “ Hansenocarididae ”, with or without attribution to Itô (1985), has been cited in a few print and internet sources, but Itô never proposed such a name in any of his works. Our action herein is the first to make this family-group name available for y-larvae in accordance with the relevant provisions of Chapter 4 of the International Code of Zoological Nomenclature ( International Commission on Zoological Nomenclature 1999). The new Japanese name combines the existing Japanese name for Facetotecta (“chou-kou-rui”, which refers to the faceted cephalic shield; Ohtsuka 2000), and “mushi”, meaning “bug” or “worm.”