Higginsarctus lassei, 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 : 166-170

Higginsarctus lassei gen. et sp. nov.

urn:lsid:zoobank.org:act:5086AB3C-F4CD-48ED-AE57-6D35C2EB14D7

Figs 10–11

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

Characterized by flat, oval secondary clavae. Unilobed antero-lateral alae with weakly undulating distal margins without indentations. Bilobed medio-lateral alae with medial pointed indentations.

Medio-lateral alae smaller than antero-lateral alae. Bilobed postero-lateral alae with a medial arched identation. Postero-lateral alae larger than antero-lateral alae. Quadrilobed, rectangular caudal ala with 3 arched indentations, 1 medial and 2 lateral. Medial lobes of caudal ala smaller than lateral lobes. Leg sense organs I–III with similar length. Genital stoup present.

Etymology

The new species is dedicated to Lasse G. Hansen, the son of the first author.

Material examined

Holotype CHILE • ♀; South Pacific Ocean ; 33°53′ S, 87°51′ W; depth 2475 m; 17 Jul. 1966; R.P. Higgins leg.; (RH 1270), R/V Anton Bruun, cruise 17; NHMD-293913 .

Description

HABITUS. The holotypic female ( Figs 10–11 ) is 143 µm long from the anterior margin of the head to the posterior margin of the body. The body is ovoid, being broadest (89 µm) at the level between the second and third pair of legs. The dorsal cuticle has four transverse inter-segmental folds: one anterior to the first pair of legs, two 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 ( Figs 10 , 11A ). The antero-lateral alae are unilobed with weakly undulating distal margins without indentations. The medio-lateral alae which are smaller than the antero-lateral alae, each have a medial pointed indentation dividing each ala into two lobes of equal size. The postero-lateral alae which are larger than both the antero-lateral and medio-lateral alae, each have a medial arched indentation in the distal margin, dividing the ala into two lobes of equal size. The caudal ala has a deep medial, arched indentation and a pair of lateral, arched indentations dividing the ala into four lobes. The medial lobes are smaller than the lateral lobes. 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 well defined from the body by a constriction 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 (41 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 (33 µm) mid-dorsally. Typical for the genus, the primary clava (58 µm) is slightly curved and non-flexible ( Fig. 11C ). 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 oval flat sacs (11 µm × 7 µm) flanking the mouth cone. The leg I sense organ (12 µm) is an unsegmented spine with a slightly swollen base and a terminal tube. The sense organs of leg II (12 µm) and III (11 µm) are unsegmented tapering spines. The fourth leg sense organ (13 µm) is an elongate papilla with a basal van der Land’s body and a terminal pore. The cirrus E (48 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 . 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 ( Fig. 10 ) is large with a terminal, very refractive cupola. Only traces of the buccal tube (44 µm), stylets (47 µm), placoids and pharyngeal bulb are visible.

REPRODUCTIVE SYSTEM. Consists of a single ovary bearing numerous small oocytes and a single larger ovum. The ovary is 72 µm long and is attached dorsally, at the level of the first pair of legs. The gonopore consists of a rosette with six large cells. Posterior to the rosette, the cuticle forms what appears in LM to be a broad fold which we interpret as the genital stoup. The two cuticular seminal receptacles each consist of a spheroid vesicle and an S-shaped genital duct. 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. 10. Higginsarctus lassei gen. et sp. nov., holotype, ♀ (NHMD-293913). Ventral overview. Abbreviations: see Material and methods. Drawing by Stine B. Elle.

Fig. 11. PhC-micrographs of Higginsarctus lassei gen. et sp. nov., holotype, ♀ (NHMD-293913). A. Ventral overview. B. Dorsal overview showing the metameric folds of the dorsal cuticle. C. Close up on the head, ventral view showing the weak indication of secondary clava (white solid arrow), internal cirri and primary clavae with van der Land’s body. Abbreviations: see Material and methods.