Zoosyst. Evol. 96 (1) 2020, 115–122 | DOI 10.3897/zse.96.49676 A new marine tardigrade genus and species (Arthrotardigrada, Styraconyxidae) with unique pockets on the legs Shinta Fujimoto1, Naoto Jimi2 1 Research Center for Marine Biology, Graduate School of Life Sciences, Tohoku University, 9 Sakamoto, Aomori, Aomori 039-3501, Japan 2 National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan http://zoobank.org/44F42F00-8B76-4C95-961D-4FC588C50BF0 Corresponding author: Shinta Fujimoto ([email protected]) Academic editor: Pavel Stoev ♦ Received 26 December 2019 ♦ Accepted 25 February 2020 ♦ Published 23 March 2020 Abstract A marine heterotardigrade Cyaegharctus kitamurai gen. et sp. nov. (Arthrotardigrada, Styraconyxidae) is described from Daidokut- su, a submarine cave off Iejima island, Okinawa Islands, Ryukyu Archipelago, Japan. It is easily distinguished from all other styr- aconyxids by its pocket organs (putative sensory structures) on all legs in addition to the usual leg sensory organs. Its combination of other character states, such as the dorso-ventrally flattened body, ovoid primary clavae, conical secondary clavae, large terminal anus, internal digits with proximal pads and peduncles, external digits with developed peduncles and all digits with three-pointed claws in adult female, supports the erection of a new genus and species. Key Words meiofauna, Pacific Ocean, sensory organs, submarine cave, Tardigrada Introduction et al. 2020). In addition to these ten genera, Fujimoto et al. (2017) reported an undescribed genus related to Styr- Marine tardigrades, specifically arthrotardigrades, exhib- aconyx and Tetrakentron from a submarine cave in Japan it remarkable morphological diversity (see comprehen- (for detail of this cave see Yamamoto et al. 2009). How- sive drawings of arthrotardigrade genera in Fontoura et ever, Fujimoto et al. (2017) did not make any remarks al. (2017) and drawings of additional genera in Fujimoto on the undescribed genus’ morphology and only provid- and Yamasaki (2017) and Fujimoto and Ohtsuka (2019)). ed two voucher micrographs of a specimen used for their Styraconyxidae Kristensen and Renaud-Mornant, 1983 is molecular phylogenetic study (provided by MorphoBank one of the arthrotardigrade families and it is comprised (O’Leary and Kaufman 2012) at http://doi.org/10.7934/ of 38 species and subspecies of ten genera: Angursa Pol- P2234). Herein, we describe this taxon as a new genus lock, 1979 (eight species), Bathyechiniscus Steiner, 1926 and species, based on detailed morphological observation (monotypic), Lepoarctus Kristensen and Renaud-Mor- of additional material collected from the same cave. nant, 1983 (monotypic), Paratanarctus D’Addabbo Gal- lo et al., 1992 (monotypic), Pleocola Cantacuzène, 1951 (monotypic), Raiarctus Renaud-Mornant, 1981a (five Material and methods species), Rhomboarctus Renaud-Mornant, 1984 (three species), Styraconyx Thulin, 1942 (15 species and sub- The type material was collected from Daidokutsu, a sub- species), Tetrakentron Cuénot, 1892 (monotypic) and marine cave off Iejima island, Okinawa Islands, Ryukyu Tholoarctus Kristensen and Renaud-Mornant, 1983 (three Archipelago, Japan (26°43'N, 127°50'E) (Yamamoto et al. species and subspecies) (Guidetti and Bertolani 2005; De- 2009) in 2013 and 2019 by Koshin Yasumura (KY) and gma and Guidetti 2007; Degma et al. 2019; Pérez-Pech the first author (SF). For extraction of meiofauna, the cave Copyright Shinta Fujimoto, Naoto Jimi. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 116 Fujimoto, S. & Jimi, N.: A new marine tardigrade with unique leg pockets sediment samples were stirred with tap water and the su- in the Cthulhu Mythos from Eddy C. Bertin’s short sto- pernatants were concentrated using a 30 μm opening mesh ry Darkness, My Name Is and arctus, a Latinised Greek net to separate coarse sediment and to wash away seawater. word meaning bear. Subsequently, the meiofauna and fine sediment were sepa- rated using LUDOX HS-40 colloidal silica (Sigma-Aldrich Remarks. The presence of pocket organs distinguishes Co., St. Louis) and a 32 μm opening mesh net (e.g. Giere the new genus and species from all other members of the 2009). The type material was sorted under a stereomicro- phylum (see Description of holotype and Discussion scope and fixed in 2–4% buffered formaldehyde. Speci- for further information on the new structure). For this mens for light microscopy were mounted in distilled water uniqueness, it is difficult to infer the new taxon’s taxo- for brief observation (only for the holotype) and mounted nomic position, based solely on this morphology. Here in glycerol. Differential interference contrast microscopy we use other comparable morphological characters to in- (DIC) was conducted using an Olympus BX53 and phase fer its taxonomic position. The new taxon’s three-pointed contrast microscopy (PhC) was conducted using an Olym- claws and peduncles indicate its affinity to the following pus BX41. One specimen for scanning electron microsco- four genera of Styraconyxidae: Raiarctus, Styraconyx, py (SEM) was post-fixed in 2% OsO4 for 2 h, dehydrated Tetrakentron and Tholoarctus (van der Land 1975; Kris- through a series of ethanol and acetone, critical point dried tensen and Higgins 1984; Jørgensen et al. 2014). (BAL-TEC CPD-030), osmium coated (Filgen OPC40) The new taxon’s epicuticular pillars are not developed and observed using JEOL JSM-7001F. Type material was to the degree of Raiarctus’s characteristic pillars (Jør- deposited in the Zoological Collection of Kyoto Universi- gensen et al. 2014). In addition, the new taxon has its ty (KUZ). Adobe Illustrator CS6 and Photoshop CS6 were seminal receptacles opening near the gonopore, in con- used to prepare figures and to obtain morphometric data. trast to those of the latter genus opening laterally apart from the gonopore (Jørgensen et al. 2014). Styraconyx harbours species covering a wide range of Systematics character states and has been regarded as a non-mono- phyletic group (Kristensen and Renaud-Mornant 1983; Family Styraconyxidae Kristensen & Renaud- Kristensen and Higgins 1984). Due to this problematic Mornant, 1983 state, many of the new taxon’s character states fall with- in the range of Styraconyx, i.e. morphology of cephal- Cyaegharctus gen. nov. ic cirri, primary clavae, usual leg sensory organs, claws http://zoobank.org/5F0BA732-F1A4-4BBE-B1E0-691BFB410C2A and digits (including peduncles) and seminal receptacles (Kristensen and Higgins 1984). However, the new tax- Type species. Cyaegharctus kitamurai gen. et sp. nov. on’s compact conical secondary clavae differ from Sty- raconyx’s flat sac to dome-shaped ones (Kristensen and Diagnosis. Styraconyxidae with dorso-ventrally flat- Higgins 1984). Further, although it is not included in the tened body; cuticle smooth; epicuticular pillars present; generic diagnosis (Kristensen and Higgins 1984), it is cephalic region with complete set of cephalic cirri, ovoid apparent from all the original descriptions of Styraconyx primary clavae and compact conical secondary clavae; species that they have a cylindrical body shape differing median cirrus and internal cirri at anterior margin of ce- from the new taxon’s dorso-ventrally flattened body and phalic region; external cirri latero-ventral to internal cir- also the anus is not known to be developed as the large ri; lateral cirri and primary clavae sharing common base bi-lobed anus of the new taxon (Thulin 1942; Robotti at antero-lateral position of cephalic region; secondary 1971; Kristensen 1977; Renaud-Mornant 1981b; Pollock clavae between internal and external cirri; buccal appara- 1983; Kristensen and Higgins 1984; D’Addabbo Gallo et tus with stylet supports; cirri E spine-like; seminal recep- al. 1984, 1989; Chang and Rho 1998; Bartels et al. 2015; tacle ducts opening anterior to gonopore; terminal anus Pérez-Pech et al. 2020). with pair of large longitudinally elongate lobes; dorsal The new taxon and Tetrakentron both have a dor- side of each leg with usual sensory organ on proximal so-ventrally flattened body, but the latter genus has short part of femur and pocket organs at distal margin of femur; legs with strongly developed claws (van der Land 1975). internal digits each with proximal pad and thin peduncle; The latest diagnosis of Tetrakentron by van der Land external digits with proximal developed peduncles; claw (1975) is brief and we here present some other differenc- sheaths present; adult female with three-pointed claws es, based on information that van der Land (1975) did on all digits; four-claw juvenile with three-pointed claws not implement in the diagnosis and additional informa- on internal digits and single-pointed claws on external tion provided by subsequent literature (Kristensen 1980; digits; three-pointed claws each with accessory and sec- Kristensen and Hansen 2005). One difference is that, in ondary hooks less developed compared to primary hook. contrast to the new taxon, Tetrakentron has unique pe- duncles, which van der Land (1975) called ‘drop-shaped’ Etymology. The genus name is masculine and derives (already illustrated in its original description (Cuénot from two words, Cyäegha, a deity of darkness and caves 1892); for detailed drawing see van der Land (1975)). zse.pensoft.net Zoosyst. Evol. 96