Higginsarctus shintai, Hansen & Kristensen, 2021

Hansen, Jesper G. & Kristensen, Reinhardt M., 2021, A new genus and five new species of the subfamily Florarctinae (Tardigrada, Arthrotardigrada), European Journal of Taxonomy 762 (1), pp. 149-184 : 163-166

Higginsarctus shintai gen. et sp. nov.

urn:lsid:zoobank.org:act:599082EE-9564-47C0-9CF9-A1EFD5F71F31

Figs 8–9

Diagnosis (characters uniquely defining the taxon are written in bold)

Characterized by flat, comma-shaped secondary clavae. Unilobed, rectangular antero-lateral alae with weakly undulating distal margins without indentations. Unilobed, rectangular medio-lateral alae with weakly undulating distal margins without indentations. Antero-lateral alae and medio-lateral alae similar in size. Bilobed postero-lateral alae with medial pointed identation. Postero-lateral alae larger than antero-lateral alae and medio-lateral alae. Quadrilobed, rectangular caudal ala with 3 arched indentations, 1 medial and 2 lateral. Medial lobes of caudal ala small and rounded, lateral lobes larger, nearly rectangular. Leg sense organs I–III with similar length.

Etymology

The new species is dedicated to Dr Shinta Fujimoto for his contributions to tardigradology.

Material examined

Holotype FRANCE • ♀; North Atlantic Ocean , English Channel , Bay of Morlaix, Roscoff; 48°43′ N, 03°54′ W; depth 20–30 m; 15 Mar. 1982; R.M. Kristensen leg.; Dentalium sand; NHMD-293904 .

Description

HABITUS. The holotypic female ( Figs 8–9 ) is 173 µm long from the anterior margin of the head to the posterior margin of the body. The body is ovoid, being broadest (106 µm) at the level between the second and third pair of legs. The dorsal cuticle has three transverse inter-segmental folds: one anterior to the first pair of legs, one between the first and second pair of legs and one between the second and third pair of legs.

ALAE. Typical for the genus, eight alae, which are all clearly separated from each other, are present: frontal ala, a pair of antero-lateral alae, a pair of medio-lateral alae, a pair of postero-lateral alae and a single caudal ala ( Fig. 8 ). Both the lateral and caudal alae appear corrugated, having transverse ridges perfectly parallel to each other. The antero-lateral alae and medio-lateral alae are all similar in size and shape being unilobed and rectangular with weakly undulating distal margins without indentations. The postero-lateral alae each have a medial pointed indentation, dividing the ala into two lobes of equal size. The caudal ala has an overall rectangular shape with a deep medial, arched indentation and a pair of lateral, arched indentations dividing the ala into four lobes. The medial lobes are small and rounded whereas the lateral lobes are larger and nearly rectangular. As in all species of the new genus, the proximal halve of the lateral and caudal alae is internally supported by continuous procuticle which sends out branching processes (ramuli) into the distal halve of the alae.

SENSORY ORGANS. The head is not well defined from the body and a complete set of sense organs is present. All the cephalic cirri consist of an hourglass-shaped scapus, a long tubular portion and a protruding flagellum. As in most other species of Florarctinae the scapus of each cirrus appears somewhat outsized, enveloping the internal sensory structures rather than lining them. The internal cirri (51 µm) emerge from the frontal ala at the anterior margin of the head. The external cirri (28 µm) are inserted ventrally and the median cirrus mid-dorsally. Typical for the genus, the primary clava (57 µm) is slightly curved and non-flexible ( Fig. 9A ). A van der Land’s body is visible inside its base. Primary clava and lateral cirrus arise on the same cirrophore, and a common membrane (extended margin of cirrophore) surrounds the base of primary clava and lateral cirrus. A very large and thick cuticular ring supports the cirrophore internally. The secondary clavae are large, comma-shaped flat sacs (19 µm × 8 µm) flanking the mouth cone ( Figs 8 , 9C ). The leg I sense organ (11 µm) is an unsegmented spine with a slightly swollen base and a terminal tube. The sense organs of leg II (9 µm) and III (9 µm) are unsegmented tapering spines. The fourth leg sense organ (8 µm) is an elongate papilla with a basal van der Land’s body and a terminal pore. The cirrus E (46 µm) has a prominent cirrophorus, scapus and a long tapering flagellum.

LEGS, DIGITS AND CLAWS. The legs consist of coxa, femur, tibia and tarsus as found in all species of Florarctinae . A row of numerous cuticular stripes of unknown function marks the transition from femur to tibia ( Fig. 8 ). The external digits are supported by internal hook-shaped peduncles. The external claw is simple and with a calcar. The internal claw has an accessory spine, but no calcar. All the claws are of the same size, however the external claws are thicker basally and the internal claws have an almost straight portion dorsally. An internal partition is evident as a small notch in each claw, dividing the claw in a basal portion and a distal portion.

BUCCO- PHARYNGEAL APPARATUS. The mouth cone is large with a terminal, very refractive cupola, through which the distal part of the stylet sheaths, protrude. The buccal tube ( Fig. 9A–B ) is 48 µm long and thin and has a small refractive bulb anterior to the placoids. The stylets are 50 µm long and very thin, each with a well-developed furca. The placoids are short, thick and slightly curved.

REPRODUCTIVE SYSTEM. Consists of a single ovary bearing several small oocytes. The ovary is 62 µm long and is attached dorsally, at the level of the second pair of legs. The gonopore consists of a rosette with six large cells. The two cuticular seminal receptacles each consist of a spheroid vesicle and an S-shaped genital duct ( Fig. 8 ). The cuticle is slightly elevated at each duct opening but does not form a true papilla. The anus is a trilobed cuticular system consisting of two large lateral lobes and a smaller posterior lobe.

Ecology and distribution

Known only from the type locality.

Figures

Fig. 8. Higginsarctus shintai gen. et sp. nov., holotype, ♀ (NHMD-293904). Ventral overview. Abbreviations: see Material and methods. Drawing by Stine B. Elle.

Fig. 9. DIC-micrographs of Higginsarctus shintai gen. et sp. nov., holotype, ♀ (NHMD-293904). A. Overview. B. Bucco-pharyngeal apparatus. C. Close up on the head, ventral view showing the secondary clava, internal and external cirri. Abbreviations: see Material and methods.