Stygarctus keralensis Vishnudattan, Bijoy Nandan, Hansen & Jayachandran 2021, sp. nov.
Creators: name: Vishnudattan, N. K.
name: Nandan, S. Bijoy
name: Hansen, J. G.
name: Jayachandran, P. R.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Tardigrada
Heterotardigrada
Arthrotardigrada
Stygarctidae
Stygarctus
Stygarctus keralensis

description: Stygarctus keralensis Vishnudattan, Bijoy Nandan, Hansen & Jayachandran sp. nov.
(Figs. 2–7, Table 1)
Diagnosis. Cephalic region is marked by the presence of a set of cephalic cirri, a pair of club shaped primary clavae and bent sausage shaped secondary clavae; five micro-spines on first and four on the second funnel shaped lateral processes; presence of minute spikes on the third lateral processes; moderately sculptured cephalic and caudal plate with unsculptured body plates I-III; caudal plate with pair of dorsal antero-lateral lobes, pair of ventro-lateral lobes, pair of round lateral processes and pair of caudal spikes; ventral plates present on body segment I-III; pair of terminal bifurcated dorsal spines fringed with thin cuticle; ventral pores/muscle attachments present on all the body segments; female genital structure with double looped seminal receptacle duct along with a bow shaped internal thickening present in between female gonopore and anus.
Materials examined. Holotype: MB /SBN/VD1: adult female mounted in glycerol.
Paratypes: MB /SBN/VD2, VD3, VD4 and VD5: four adult female mounted in glycerol; MB /SBN/VD6, VD7: two adult male mounted in glycerol.
Stygarctus gourbaultae paratype (USNM 62017) from Smithsonian; Stygarctus gourbaultae holotype (MNHN AT50) from Museum National d’Histoire Naturelle, Paris.
Type locality: Vadakara beach, in front of old sea bridge, Calicut, Kerala, Southwest coast of India (11°60.077’N, 75°57.702’E) on February 2020.
Type depositories: Seven specimens were submitted in the Marine Biology museum (voucher no: MB /SBN/ VD1- 7), of the Department of Marine Biology, Microbiology and Biochemistry, Cochin University of Science and Technology (CUSAT).
Description of holotype. The body length (from anterior rim of cephalic plate to the base of caudal spikes) of adult female specimen is 129.6 μm with 45.2 μm width. Body is slightly curved ventrally. Moderately sculptured dorsal cephalic plate with horizontal markings on medio-lateral lobes and vertical markings between lateral lobes. Dorsal body plates I-III are rigid, translucent and unsculptured without any markings (Figs. 2, 7A); ventral region is composed of three ventral plates (Fig. 3). Cephalic plate is composed of medial lobe, a pair of medio-lateral and lateral lobes. A conical shaped anteriorly protruded mouth cone on ventral side in between ventral lobes. A pair of bend sausage-shaped secondary clavae (12.5 μm) arise from the anterior portion of ventral lobes. Lateral cirrus (16.2 μm) with short scapus (3.4 μm) and flagellum (12.8 μm) attached to each lateral lobe just anterior to the bulbshaped, paired primary clava (5.1 μm).
A pair of internal cirri (13.5 μm) each with short scapus (2 μm) and flagellum (11.5 μm) attached to medial lobe emerging from the cirrophore. A pair of external cirri (12 μm) each with short scapus (2 μm) and flagellum (10 μm) arise from the mid portion of ventral lobe. An unpaired median cirrus (12.9 μm) with short scapus (2.5 μm) and flagellum (10.4 μm) inserted mid-dorsally, posterior to medial lobe, at level of incision between medio-lateral and lateral lobes. Thin sheets are present on the margin of lateral lobes (Fig. 2). A pair of horizontally arranged subcephalic muscle attachments/pores is present just posterior to the mouth cone (Figs. 3, 5A).
Three rigid dorsal body plates with funnel shaped lateral processes ends up in thin sheets at lateral margins. Five micro-spines on the first and four micro-spines on the second lateral processes (Fig. 7D). Three-five minute spikes on the third lateral processes (Fig. 5B). A pair of dorsal spines (29.29 μm) with strong terminal bifurcation fringed with thin cuticle arising from the caudal rim of the second dorsal body plate. A ventral pore/muscle attachment in posterior mid region of the first segment (5.91 μm posterior to lower portion of pharyngeal bulb); a second ventral pore, 12.67 μm posterior to the first ventral pore present at the middle of the second segment; a third ventral pore is also present at the posterior mid region of the third segment (Fig. 3).
The posterior region is characterised by moderately sculptured dorsal caudal plate with irregular markings. Caudal segment is constituted by a pair of dorsal antero-lateral lobes, pair of ventro-lateral lobes, pair of round lateral processes and a pair of caudal spike with a pointed end (29.36 μm). Dorsal antero-lateral lobe is comparatively smaller than the lateral lobe with slightly thinner margins with a pointed end (Fig. 5C). Ventro-lateral lobe is square shaped with a bend towards posterior side. Lateral process is thinner at its lateral margin. Minute spikes are absent on the round lateral processes (Fig. 5C). An unpaired ventral pore/muscle attachment is present just anterior to female gonopore. A pair of Cirri E (26.9 μm) each with proximal portion (9.6 μm) and flagellum (17.3 μm) arise from the portion between antero-lateral lobe and round lateral process. Caudal spikes are bordered by thin sheets at its lateral margins starting from its base and weakens at the mid length of caudal spike. A pair of papilla-like leg IV sense organ (2 μm) is found attached at the base of each fourth leg. Four pairs of legs with four claws attached directly on each leg with two thin filaments on median claws. Fourth pair of legs (av. 23.9 μm, n =7) are longer than all other legs (av. 15.3 μm, n = 7). Claw lengths of fourth pair of legs (av. 9.7 μm, n =7) are also longer than the claw length of other leg pairs (av. 5.3 μm, n =7).
Rosette-like female gonopore consisting of six minor plates opens ventrally is sighted 5.54 μm anterior to the anus (Fig. 7C). A bow shaped internal thickening is found in between the seminal receptacles (Fig. 4C). A pair of seminal receptacles with sinuous ducts forming a larger and a smaller loop. The sinus duct starts from the lateral plane below the level of gonopore and forms a larger swirl around the opening and forms another smaller loop towards the internal thickening and run back to the opening. (Figs. 4 C, 5 D-F). Terminal anus composed of two cuticular lobes is present in between the base of caudal spikes.
description: Published as part of Vishnudattan, N. K., Nandan, S. Bijoy, Hansen, J. G. & Jayachandran, P. R., 2021, A new Tardigrade species, Stygarctus keralensis sp. nov. (Arthrotardigrada Stygarctidae) from the intertidal zone of Southwest coast of India, pp. 381-391 in Zootaxa 4985 (3) on pages 383-388, DOI: 10.11646/zootaxa.4985.3.5, http://zenodo.org/record/4956227