Hansenocaris cristalabri 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 : 304-307

publication ID	https://doi.org/ 10.12782/specdiv.27.301
publication LSID	lsid:zoobank.org:pub:DE06A95A-7DC2-41BA-B94B-2E8DDA5FBE86
DOI	https://doi.org/10.5281/zenodo.7544607
persistent identifier	https://treatment.plazi.org/id/03A987D3-FFDF-6909-BA3F-74D67DC1F9C1
treatment provided by	Felipe
scientific name	Hansenocaris cristalabri Olesen and Grygier
status	sp. nov.

Treatment

Hansenocaris cristalabri Olesen and Grygier , sp. nov

[New Japanese name: Tosaka-chou-kou-mushi] ( Figs 1–5 View Fig View Fig View Fig View Fig View Fig )

Diagnosis. In last-stage nauplius, labrum produced ventrally as three-sided pyramidal base topped with elongate, cockscomb-like process bearing row of 9 dagger-like spines along anterior side. Cephalic shield clearly and nearly completely reticulated, divided into discrete facets except for a few continuous submarginal belts in posteriolateral sector, and with pair of rounded, spine-bounded marginal notches far posteriolaterally. Cephalic shield with fewer pores than any other described late-stage facetotectan nauplius: 1 unpaired anterior pore, 6 pairs of simple pores elsewhere, and 3 pairs of pores with emerging setae (2 obvious dorsal pairs, 1 minute anterior pair). Faciotrunk with broad keel along about half of dorsum, bounded by 2 rows of spines. First antenna with 3 apical setae and preaxial spine. Second antenna and mandible devoid of feeding structures (lecithotrophic); setal formulae of their exopods 0: 1: 1: 1: 1: 2 and 0: 1: 1: 1: 2 respectively, their endopods 2 and 2, respectively. First maxillae and dorsocaudal organ (or corresponding pore) absent. Dorsocaudal spine nearly as long as trunk dorsum preceding it, armed along most of length with about 10 irregular rings of large, pointed subsidiary spines.

Type locality. Off pier at the University of the Ryukyus Tropical Biosphere Research Center , Sesoko Station, on Sesoko Island, Okinawa Prefecture, Japan (26°38′09.3″N 127°51′55.2″E) GoogleMaps .

Type material. Holotype, last-stage nauplius mount-ed on SEM stub, Natural History Museum of Demark. NHMD-1174614. Originally collected 10 June 2019, first photographed 12 June 2019, again photographed 14 June 2019 after molt to last-stage nauplius, again photographed 17 June 2019 and fixed same day. Live video of this specimen in these two naupliar instars viewable at https://youtu. be/SCskuhPTCXo, also deposited at https://doi.org/10.6084/ m9.figshare.20430807. Specimen collected and processed by D. Eibye-Jacobsen, M. J. Grygier, and J. Olesen.

Etymology. The Latin name is a genitive compound noun, from Latin “ crista ”, for a comb or plume on an animal’s head, and “ labrum ”, for lip ( Brown 1956), glossed as “crest of the labrum” and referring to the labrum’s extraordinary, cockscomb-like ventral process. The new Japanese name combines the Japanese noun “tosaka”, meaning “cockscomb”, with an existing Japanese name for Facetotecta (“chou-kou-rui”, which refers to the faceted cephalic shield), and “mushi”, meaning “bug” or “worm.”

Description (holotype). A last-stage nauplius larva ( Figs 1C, D View Fig , 2 View Fig , 3 View Fig , 4F View Fig , 5 View Fig ).

Habitus ( Figs 1C, D View Fig , 2A, B View Fig , 3A View Fig ). Cephalic portion of body slightly oblate-oval; trunk portion long and attenuate, resembling champagne glass in outline in dorsal or ventral view. Total length 434–445 µm as measured in different photographs; length, width, and height of domelike cephalic shield 223, 182, and 73 µm, respectively; post-shield length of trunk in dorsal view 240 µm, anterior width and postlabral length of trunk in ventral view 87 µm and 317 µm, respectively; trunk height at posterior end of shield 102 µm. Length (measured from midventral pore) and basal diameter of dorsocaudal spine 123–129 µm and 31–35 µm, respectively, as measured in different photographs. Long axis of trunk, extending from midheight at anterior end of trunk to midheight at base of dorsocaudal spine, downturned 20° with respect to long axis of cephalic shield as defined by its lateral margins ( Fig. 2B View Fig ); dorsocaudal spine then upturned 18° with respect to long axis of trunk.

Cephalic shield ( Figs 3A–C View Fig , 4F View Fig ). Ornamented with dense, nearly symmetrical pattern of reticulate ridges outlining many so-called plates, or facets, as well as 4 pairs of submarginal elongate belts in posteriolateral sectors. Limited numbers of setae (2 obvious dorsal pairs and 1 minute anteriolateral pair) and simple pores (6 pairs, 1 unpaired, plus posteriolateral pair of pits) situated within these plates or along ridges delimiting them ( Figs 2B, I View Fig , 3A, C–M View Fig ; Table 1 View Table 1 ). Ridges obvious but not especially prominent in SEM photos, some fainter ones perhaps representing new plate divisions compared to preceding instar (cf. Itô 1990). Faint and extremely fine vermiculation evident within plates, but plate surfaces essentially smooth. Pair of shallow, triangular indentations present in anterolateral margins (probably artifact associated with adjacent crosswise fold in ventral cuticle). Pair of shallow, rounded notches present in far posterolateral margins, each flanked anteriorly and posteriorly by a spine, and with posteriorly-facing pit on shield margin immediately behind posterior spine ( Figs 2E, N View Fig , 3N View Fig ).

Cephalic shield’s plates or facets centered on roundedquadrangular ‘window’ (W) at about one-third length along midline. Remainder of plate description based on homology assumptions indicated by color-coding in Fig. 4 View Fig . Among ‘frontal’ plates (labelled in Figs 3C View Fig , 4F View Fig ; see also Fig. 3A View Fig ), primordial plate F-1 represented by pair of small pentagonal plates flanking W and by transverse row of 4 small plates preceding these and W. Primordial plate F-2 possibly represented by array of 6 small plates preceding F-1 region, including transverse central pair and 2 longitudinally oriented lateral pairs. Primordial plate F-3 possibly represented by next more anterior 2×2 array of plates, and F-4 by next more anterior 2 or 3 transverse plates (site of boundary between original F-4 and original ‘Brim’ unknown). Unpaired, ridge-encircled pore 1 * present on midline anteriorly.

Among ‘occipital’ plates (labeled in Fig. 3C View Fig , 4F View Fig ; see also Fig. 3A, B View Fig ), large O-1 and O-2 pairs present successively behind W. Set of 20 small plates with clear lateral boundaries but somewhat asymmetrical internal arrangement (presumably derived from primordial plates O-3, O-4, and O-5) present behind O-2 pair, with pair of small, ridge-bounded pores (9r and 9l) externally near anterior ends of lateral bounding ridges ( Fig. 3H View Fig ). These plates succeeded by welldefined rectangular array of small quadrilateral or pentagonal plates in 4 longitudinal rows of 6 plates each (presumably derived from axial parts of primordial plates O-6 and O-7), with third pair of outer plates distinctly smaller than rest. These followed by middle 4 of 6 plates in transverse row along shield’s posterior margin, an area not included in Itô’s (1990) nomenclature.

Among identifiable ‘intermediate,’ ‘polygonal,’ and ‘marginal’ plates (labeled in Figs 3C View Fig , 4F View Fig ; see also Fig. 3A View Fig ), plate pair I-1 heptagonal, maintaining its primordial identity and not subdivided, each member of pair with large, ridgebounded pore (4r and 4l) posteriorly. Each I-1 plate preced-ed by 2 rows of sometimes bisected plates, evidently derived from primordial P-1 and, more anteriorly, from primordial M-1 plates (most anterior plates possibly derived from Brim, not M-1), with large, ridge-bounded pore (2r and 2l) at anteriolateral corner of each array ( Fig. 3L View Fig ). Small anteriolateral pair of pores each containing minute seta (3r and 3l; Fig. 3J View Fig ) present along ridges extending posteriorly from middle of lateral sides of putative P-1 regions, these ridges evidently dividing regions corresponding to plates P-2(a) and M-2(a) of H. furcifera (cf. Fig. 4B View Fig ). Large, ridge-bound-ed submarginal pore (7r and 7l) present near outer posterior corner of putative M-2(p) area (if not in Brim-derived area; see Fig. 3L View Fig ). Putative derivatives of primordial ‘intercalary,’ ‘elongate,’ and ‘crescentic’ (I-, E-, and C-) plates all quite narrow and long; anterior ends of primordial C-1 and (laterally adjacent) I-3 plates marked by 2 obvious pairs of setae (5r and 5l, 6r and 6l) flanking primordial F-1 region ( Fig. 3E View Fig ). Two other pairs of large, ridge-encircled pores present on shield, including 1 pair (8r and 8l) situated posteriolaterally within primordial plates E-2 ( Fig. 3F View Fig ) and another more posterior and slightly more lateral pair (10r and 10l) of uncertain positional homology (P-5 or P-6 area) ( Fig. 3G View Fig ).

Cephalic part of faciotrunk ( Figs 2A, B View Fig , 5A, B View Fig ). Three pairs of limbs (uniramous first antennae, biramous second antennae and mandibles; Fig. 5 View Fig ) all arising from single large pair of rounded-crescentic or reniform areas of arthrodial membrane ( Figs 2A, B View Fig , 5A, B View Fig ). These limbs flanking labrum and surrounded externally by flat faciomarginal area with 3 or 4 concentric cuticular ridges joined by sparse connecting ridges ( Figs 2A View Fig , 5A View Fig ); ridge pattern most regular anteriorly (2 rows of lozenges) and posterolaterally (similar to but faint-er than that of adjacent dorsal surface). No obvious pair of pores between first antennae and anterior cephalic margin, but pair of ventral pores (11r and 11l) immediately adjacent to faciomarginal area’s posteriolateral margins ( Fig. 2A View Fig ).

Labrum ( Figs 1D View Fig , 2A–D View Fig , 5A, B View Fig ). Proximal part expressed as narrow, triangular pyramid, posterior width 27 µm, lateral diagonal length 44 µm, height 35 µm, with large unpaired pore 16* situated proximally on midline of posterior face slightly distal to transverse slit-like depression ( Fig. 2F, G View Fig ). Pyramid encircled with cuticular ridge near base, leading to possibly paired slit-like depression across front ( Fig. 5B View Fig ), also with cuticular ridge defining its entire anterior midline. Pyramid topped with 79 µm long, ventrally directed, tapered, and somewhat rounded in cross-section cockscomblike process ( Figs 2C View Fig , 5A View Fig ); inclined circular ridge delimiting it from pyramidal base leading to weak, slit-like furrow posteriorly ( Fig. 5A View Fig ). This process armed with single row of 9 distally directed dagger-like spines arising from within shallow longitudinal groove along anterior face. Proximal 2 spines ≤7 µm long, others considerably longer, up to about 19 µm as measured along distal side, and apical 2 spines sharing common base. Pyramidal base flanked by faint ridges on facial cuticle, forming 2 elongate lozenges on each side, these being connected to several wedge-shaped ridge arrays present farther anteriorly out to innermost of abovementioned concentric ridges ( Figs 2A View Fig , 5B View Fig ).

First antenna ( Figs 2A, B View Fig , 5A–C View Fig ). Two-segmented, excluding narrow, arcuate sclerite at base upon which proximal end of first segment articulates and very thin, hemiannular sclerite with tapered ends present within postaxial half of articulation between two main segments (best visible in Fig. 5C View Fig ). Unarmed first segment short and cylindrical (11 µm long, 15 µm in diameter) with rounded slight protrusion of distal half of preaxial side. Distal segment 42 µm long, digitiform with proximal 60% of preaxial side moderately swollen, showing faint indications of subdivision at 20% and 70% length, and bearing arrays of minute spinules mostly on distal half. This segment thickest (19 µm) at one third length, half as thick distally, with 3 apical setae: 1 extremely short seta and 1 simple seta of medium length (32 µm) arising adjacent to each other on postaxial rim (shorter one outer), and 1 long seta (60–70 µm) with single(?) row of very short setules arising mid-apically. Additional spine present on preaxial face at distal end of swollen region, associated with distal subdivision trace.

Second antenna ( Fig. 2A, B View Fig , 5A, B, D View Fig ). With unarmed, ring-like sclerite at base (precoxa?), unarmed cylindrical coxa slightly thicker than long (16×12 µm), shorter unarmed basis 8 µm long, and 2 rami. Six-segmented exopod 31–32 µm long, bearing 6 setae. All segments fully annular: first segment short and unarmed; second a little longer with 1 minuscule seta; next 3 segments again longer and equal in size among themselves, bearing 1 long seta each; apical segment minute and bearing 1 long inner and 1 short (28 µm) outer seta. Endopod 1-segmented, cylindrical, 6 µm long and 3 µm thick, thus slightly longer than first 2 exopodal segments combined, bearing 2 long and nearly equal apical setae. At least some setae of antenna 2 setulate, but precise distribution of setules unclear.

Mandible ( Fig. 2A, B View Fig , 5A, B, E, F View Fig ). Similar to second antenna but smaller, with no clear pre-coxa; coxa longer (13 µm) than basis (8 µm) and of slightly greater diameter (14 µm); articular facet of basis with exopod beveled. Exopod 31–33 µm long, 5-segmented, bearing 5 setae: 1 each (all long) on second to fourth segments and 2 unequal setae on tiny apical segment, shorter one (21µm) outer. Endopod 1-segmented, 6 µm long and 4 µm thick, reaching to midlength of second exopodal segment, bearing 2 long apical setae. At least some mandibular setae setulate, but precise distribution of setules unclear.

Hind part of faciotrunk. Trunk divisible into long, sparsely ornamented anterior part, heavily and concentrically ornamented posterior part, and heavily armed dorsocaudal spine. Anterior two thirds of venter with short and sparse transverse ridges, 3 of them at front end being more obvious and longer; in posterior third, ridges well expressed and bearing small spinules; in between, somewhat swollen and rounded area largely unornamented, but with several paired clusters of spinules possibly representing thoracopodal setae of next-instar cypris y ( Fig. 2A View Fig ). Anterior-most ridges flanked by pair of narrow but thick-lipped, slightly arcuate, transverse invaginations ( Figs 2A View Fig , 5A View Fig ), these at least 12 µm long but partly obscured in all photographs and presumably related to anterior struts of internally developing cypris y’s “ghost” (presence of which not confirmed, requiring examination of shed last naupliar exuviae; see Grygier et al. 2019). Anterolateral part of trunk below distinct longitudinal ridge ornamented with weak, parallel, dorsoventrally oriented ridges ( Fig. 2B View Fig ). Area dorsal to posterior part of same longitudinal ridge together with remainder of dorsal side of trunk with about 15 slightly produced, obviously but irregularly and sparsely denticulate transverse ridges ( Figs 2B View Fig , 5A View Fig ), posterior 10 or so of which encircling whole body although to some degree discontinuous ventrally. Most of posterior half of trunk dorsum slightly compressed to form low dorsal “keel” bounded by 2 rows of spines ( Fig. 3A, B, O View Fig ). Longest ridge spines on trunk about half as long as distance between successive ridges. Two presumably paired (right side not visible), ridge-encircled pores (12l and 13l) present laterally below “keel”, associated with fifth and seventh ridges anterior to furcal spines ( Fig. 2B, K, L View Fig ); additional tiny pore (14l) present between and below them. Dorsocaudal organ (or positionally equivalent mid-dorsal trunk pore) absent.

Pair of somewhat upcurved, sharply pointed, and proximally spinose furcal spines arising anterioventrally to midventral (anal?) pore below base of dorsocaudal spine, each furcal spine 15 µm long along its central axis ( Figs 1C, D View Fig , 2A, B, O, P View Fig , 3B View Fig ). Midventral (anal?) pore 15* itself situated on slightly raised transverse oval, with weak, arcuate transverse ridge behind it ( Fig. 2P View Fig ). Dorsocaudal spine ( Figs 1C, D View Fig , 2A, B, L, M View Fig , 3A View Fig ) armed along entire length, except for its sharply pointed tip, with about 10 irregular rings of large, pointed spines up to about 11 µm long, proximal ones slightly curved, distal ones straight. Pair of faint ridges extending out from base of each spine, all such ridges together imparting embossed scale-like appearance to surface of spine ( Fig. 2O, P View Fig ).

Earlier and later developmental stages. General appearance of holotype specimen as photographed alive 5 days prior to fixation ( Fig. 1A View Fig ), and again before molt to laststage naupliar instar ( Fig. 1B View Fig ), much like that of last-stage nauplius (e.g., labrum with large, cockscomb-like process), but lacking pigmented pair of developing compound eyes or any other internally developing cyprid structures such as thoracopods, and having significantly more internal yolklike material than last-stage nauplius. Within last-stage nauplius ( Fig. 1C, D View Fig ), compound eyes of internally developing cyprid about 8.8 µm long, 6–6.5 µm wide in ventral view ( Fig. 1C View Fig ), presumptive labrum of cyprid with small distal knob but no evidence of any unusual structure ( Fig. 1D View Fig ).