Living on the edge - first survey of loriciferans along the Atacama Trench Author Sørensen, Martin V. 4143D650-12FC-4914-93F5-2C39339A7156 Natural History Museum of Denmark, University of Copenhagen, 2100 Copenhagen, Denmark. mvsorensen@snm.ku.dk Author Herranz, Maria 6806936F-E381-4098-9D02-620D4847956E Natural History Museum of Denmark, University of Copenhagen, 2100 Copenhagen, Denmark. & Department of Biology, University of Copenhagen, 2100 Copenhagen, Denmark. maria.herranz@bio.ku.dk Author Grzelak, Katarzyna ABFE9734-0BD8-4ED9-A780-469D0058FCED Marine Ecology Department, Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland. kgrzelak@iopan.pl Author Shimabukuro, Mauricio EEE05E1C-C9F5-4FCC-A6C6-5A1D55FF5407 Univ. Brest, CNRS, Ifremer, UMR 6197 Biologie et Écologie des Ecosystèmes marins profonds, 29280 Plouzané, France. & Department of Biology, HADAL & Nordcee, University of Southern Denmark, 5230 Odense, Denmark. & Institute of Oceanography, Federal University of Rio Grande, Rio Grande, RS 96203 - 900, Brazil. shimabukuro@furg.br Author Kristensen, Reinhardt M. 4BA89040-D79E-41C1-A17C-539FBB9B6BA4 Natural History Museum of Denmark, University of Copenhagen, 2100 Copenhagen, Denmark rmkristensen@snm.ku.dk Author Zeppilli, Daniela 6EDD442D-4DB9-46CA-A19D-29C67A055180 Univ. Brest, CNRS, Ifremer, UMR 6197 Biologie et Écologie des Ecosystèmes marins profonds, 29280 Plouzané, France. & Daniela. Daniela.Zeppilli@ifremer.fr text European Journal of Taxonomy 2023 2023-07-14 879 1 162 187 http://dx.doi.org/10.5852/ejt.2023.879.2169 journal article 55108 10.5852/ejt.2023.879.2169 82c79f5d-3a30-4b22-bd1b-2503897d9cef 2118-9773 8155359 BE6ED0BD-4A61-4F50-A8C2-BE84C6F00656 Pliciloricus ukupachaensis sp. nov. urn:lsid:zoobank.org:act: AEF3321F-BCFB-4FF2-A8EC-81BF8E929462 Figs 2–8 Diagnosis Adult Pliciloricus with a mouth cone with narrow basis, but getting conspicuously broader, before gradually narrowing again towards distal end. Introvert Row 1: females with eight regular, club-shaped clavoscalids with 23–25 annulated rings on distal ⅓; Introvert Row 2: three regular spinoscalids alternating with four leg-shaped scalids with three, articulating proximal units and long, spinous end-piece; double organ with fused bases, extending into long, tapering distal tips. Introvert Row 4: fifteen claw-like scalids with serrated shafts, articulating with thinner distal parts, with curved tips. Neck with fifteen single trichoscalids. Trichoscalid plates inconspicuous. Lorica with 22 plicae inclusive broader midventral plica. Anterior lorica margin smooth. Posterior part of lorica forming large anal field with distinct, asymmetrical ornamentation of pentagonal and hexagonal fields, formed by external cuticular ridges. Male morphology unknown. Etymology The species name, ‘ ukupachaensis ’, is derived from ‘Uku Pacha’ – the underworld or ‘inner world’ according to Incan mythology. The name refers to the habitat of this species, in close proximity to the Atacama Trench that reaches into the underworld. Material examined Holotype CHILE • ♀ ; continental slope off Antofagasta, and near the rim of the Atacama Trench ; st. 1; 23°48.72ʹ S , 70°50.04ʹ W ; depth 2560 m ; 6 Mar. 2018 ; R / V Sonne SO261; deep-sea mud; mounted for LM in Fluoromount G on HS slide; NHMD 1177413 . Paratypes CHILE • 1 ♀ ; same collection data as for holotype; mounted for SEM ; NHMD 1177421 • 1 Higgins larva containing a postlarva with an adult inside; same collection data as for holotype; mounted for LM in Fluoromount G on HS slide; see also Table 1 and Fig. 1 ; NHMD 1177414 . Description Adult female Adult females consist of a head with mouth cone and introvert with nine rows of scalids, a neck region with one row of trichoscalids, a plicated lorica and an anal field with asymmetrically arranged fields ( Figs 2A, C , 3–6 , 7A ). The female holotype measures 240 µm in total length and 100 µm in width at its widest point, i.e., near the anterior lorica margin. The mouth cone measures 68 µm in length, has a narrow basis, but broadens out to reach its maximum width of 25 µm about 1/5 from basis, before gradually tapering again towards the distal tip ( Figs 2A , 4A–B , 6A ). It is slightly retracted in both the holotype and adult paratype , which makes it appear broadest basally. The mouth cone is supported by oral ridges, and a narrow buccal tube is visible inside it. The pharynx does not have any distinct internal structures, and no placoids were observed. Fig. 2. Line art illustrations of Pliciloricus ukupachaensis sp. nov. A . Holotype, ♀ (NHMD 1177413), lateral view; for visibility, some Row 6 to 8 scalids have been omitted and their attachment sites are indicated by circles with dashed lines. B . Higgins larva containing a postlarva with an adult (NHMD 1177414), ventral view. C . Detail of anal field in adult (NHMD 1177421); dorsal side is up. The introvert has nine rows of scalids ( Fig. 3 ). The anteriormost Row 1 consists of eight club-shaped, 134 µm long clavoscalids. The clavoscalids are covered with extremely fine hairs and consist of a narrow base, a smooth, flattened part representing ⅔ of the total scalid length, and a distal end-piece with about 23–25 annulations; they terminate in small, anteriorly bent hooks ( Figs 2A , 3 , 4A–B , 5A–C , 6A–B , 7A ). Row 2 consists of four leg-shaped scalids, three regular spinoscalids, and two scalids fused into a ventral double organ. Each leg-shaped scalid (length: 125 µm) consists of a proximal part with three, fringed, articulating units and a spinous end-piece with two partial constrictions about ⅓ from the distal, anteriorly curved tip. The three regular spinoscalids (length: 91 µm) alternate with the leg-shaped scalids and are located middorsally and midlaterally on the introvert. Each spinoscalid is composed of three units: a short, proximal basis with a distal spike, a short cylindrical mid-piece, and a long, acicular end-piece, covered with minute hairs; the end-piece represents more than 4/5 of the total scalid length, and has a distinct bend ⅓ from the distal bending tip. The double organ consists of two appendages (length: 134 µm) with swollen and fused bases, representing ⅓ of the total length; they narrow abruptly into considerably thinner, distally curved end-pieces; the bases have a line of hair along their inferior margins, whereas the end-pieces have hair along both the inferior and superior margins ( Figs 2A , 3 , 4A–B , 5A–C , 6B, D , 7A ). Fig. 3. Diagram of introvert in Pliciloricus ukupachaensis sp. nov. , showing distribution of scalids and trichoscalid plates. Fig. 4. Light micrographs showing overviews and details of holotype, adult ♀ of Pliciloricus ukupachaensis sp. nov. (NHMD 1177413). A . Lateral overview; dorsal is left and ventral is right. B . Detail of head showing mouth cone, clavoscalids and double organ. C . Detail of introvert showing scalids of Rows 4 to 8, inclusive claw-shaped scalids of Row 4. D . Detail of neck region and anterior part of lorica. E . Posterior part of lorica and lateral half of the anal field. Row 3 consists of fifteen uniform spinoscalids (length: 58 µm), composed of two short, articulating, ovate bases and a long acicular end-piece, densely covered with minute hairs ( Figs 2A , 3 , 5A , 6D ). Row 4 consists of fifteen regular spinoscalids alternating with fifteen claw-like scalids. The spinoscalids (length: 98 µm) are composed of two short, articulating, ovate bases and a long acicular end-piece with a distinct bend ⅓ from its proximal end; end-pieces are covered with minute hairs. Each claw-like scalid (length: 44 µm) is composed of a short basis with hairy, distal margin, a shaft (½ of scalid length) with serration along its inferior margin, and a thinner distal part, with a curved tip; some claw-shaped scalids bend medially, suggesting an articulation between the shaft and the end-piece ( Figs 2A , 3 , 4C , 5A–B , 6C , 7A ). Rows 5 to 8 with spinoscalids that are very uniform. Each row has thirty spinoscalids (lengths: 68 to 73 µm), each consisting of a short basis composed of two ovate units and a long, smooth acicular end-piece with short hairs along their lateral margins ( Figs 2A , 3 , 6D ). Row 9 consists of thirty short, beak-shaped scalids (length: 10 µm) ( Figs 2A–B , 3 , 5B , 6D ). The neck has fifteen uniform, single trichoscalids ( Figs 2A , 3 , 4D , 5A–B , 6D ). The trichoscalids are 79 µm in length, blade-shaped, with a median, longitudinal ridge, and a small, triangular plate covering the proximal attachment point. Trichoscalid plates are extremely weakly defined. There might, however, be a very weak indication of a row with fifteen trichoscalid plates at the base of each trichoscalid. This indication can only be observed with LM though ( Fig. 4D ), and not with SEM, which suggests that the plates are mostly intracuticular thickenings, rather than external structures. Interestingly, however, minute (13 µm long) appendages are attached anterior to seven of the fifteen indistinct trichoscalid plates ( Figs 2A , 3 , 6D inset). These appendages are arranged with one in middorsal position anterior to the corresponding trichoscalid, and are otherwise present radially anterior to every second trichoscalid. This pattern corresponds to the arrangement of Row 2 trichoscalid plates in other species of Pliciloricus (see for instance the description of P. apteryx Sørensen et al. , 2022 ), and we therefore interpret these short appendages ( Fig. 6D inset) as Row 2 trichoscalid plates. Accordingly, the weakly defined trichoscalid plates with attached trichoscalid represent Row 3, whereas there are no trichoscalid plates of Row 1 ( Fig. 3 ). No particular structures were noted in the thorax region. The lorica is composed of 22 plicae, including a broader midventral plica. Numerous, oblique structures, referred to as ‘interplical radii’, radiate from the primary double ridges of the plicae. The interplical radii are easily observed in LM as well as SEM ( Figs 4D , 5D , 6C ). The anterior lorica margin is straight, and there is no indication of marginal spikes ( Figs 2A , 4D ). In both adult specimens, the holotype and the paratype mounted for SEM, the lorica has a highly characteristic, nearly 90° bend on the ventral side ( Figs 4A , 5 , 7A ). Posteriorly, the lorica forms a large anal field ( Figs 2A, C , 4A, E , 5A, D , 6E–F ). The anal field is ovoid and limited by a strong ridge, which also marks the posterior limit of the lorical plicae. Numerous cuticular ridges present within the anal field form different pentagonal and hexagonal fields. Whereas the fields closest to the ventral side show a certain level of bilateral symmetry, the shape and arrangement of the remaining fields are more irregular, and overall the anal field ornamentation must be considered as asymmetrical. A single pair of P-flosculi are present in the dorsalmost portion of the anal field; a crescentic anal opening, flanked by a pair of oval thickenings, is present close to the ventral margin of the area. Internal anatomy was difficult to observe, but two groups of circular muscles are present in the trunk, arranged as an anterior and a posterior group. Last instar Higgins larva and postlarva Last instar Higgins larva with head and trunk, the latter divided into a thorax region and a loricated abdomen ( Figs 2B , 7B–E , 8 ). It measures 267 µm in length and 158 µm in width at its broadest point, medially on the abdomen. Fig. 5. Scanning electron micrographs showing overviews of adult paratypic ♀ of Pliciloricus ukupachaensis sp. nov. (NHMD 1177421). A . Ventral overview. B . Right side lateral overview. C . Frontal overview. D . Lorica, dorsocaudal view. Fig. 6. Scanning electron micrographs showing details of adult paratypic ♀ of Pliciloricus ukupachaensis sp. nov. (NHMD 1177421). A . Mouth cone and basal parts of double organ. B . Double organ with clavoscalids in the background. C . Detail showing the interplical radii on the dorsal side of the lorica. D . Scalids and trichoscalids on the ventral side of the introvert and neck; inset shows close-up of area marked with dashed frame. E . Anal field; dorsal side is up. F . Detail showing flosculus on the anal field. The head of the single, paratypic larva was retracted and detailed information on the introvert morphology could not be obtained. Pharyngeal armature consists of oral teeth with tripartite anterior tips and inner armature ( Figs 2B , 7D , 8A, C–D ). The thorax has four transverse folds and numerous (> 22) longitudinal folds. The abdomen has numerous (> 90) indistinct longitudinal lines, which are so weakly developed that they can hardly be referred to as plicae. Two pairs of anterior, simple, unbranched setae are located on the abdomen about ¼ from its anterior margin: anterolateral setae measure 25 µm in length, whereas anteroventral setae are slightly shorter, measuring 22 µm in length. Posterior setae include thin and simple posterodorsal setae (length: 36 µm), swollen and stiff posterolateral setae (length: 18 µm), and the acicular and rigid terminal setae (length: 25 µm) attaching between the toes ( Figs 2B , 7B–E , 8A–B, E–H ). Fig. 7. Confocal laser scanning micrographs of Pliciloricus ukupachaensis sp. nov. showing 3D reconstruction of (A) adult ♀ holotype (NHMD 1177413) and Z-stack projections (B–E) of paratypic Higgins larva containing a postlarva with an adult (NHMD 1177414). A . Lateral overview; dorsal is left and ventral is right. B . Caudal view; ventral side is up. C . Dorsal overview. D . Overview focused medially in specimen. E . Ventral overview. Fig. 8. Light micrographs showing overviews and details of paratypic Higgins larva of Pliciloricus ukupachaensis sp. nov. , containing a postlarva with an adult (NHMD 1177414). A . Overview, focused medially in specimen. B . Ventral overview. C . Prepharyngeal armature, focused on oral teeth. D . Prepharyngeal armature, focused on internal armature. E . Anterior part of lorica, ventral view. F . Posterior part of lorica, dorsal view. G . Posterior part of lorica, focused medially in specimen. H . Posterior part of lorica, ventral view. The toes are long and slender (total toe length: 91 µm) and divided into three portions: relatively broad bases (62 µm), slender mid-pieces each with a central, internal canal (length: 24 µm), and short, abruptly narrowing tips (length: 5 µm) ( Figs 2B , 7B, E , 8B, E, H ). The Higgins larva contains a postlarva, which is nothing but a cuticle without any further, observable structures. The postlarva is nearly globular and about 152–155 µm in diameter. A developing adult stage of unknown sex is present inside the postlarva, filled with refringent vesicles. The adult scalids of the introvert appear to be well-developed, but internal organs are still not developed, and the lorica is so thin that it appears undifferentiated ( Figs 2B , 7B–E , 8A–B ).