Higginsarctus Hansen & Kristensen 2021, gen. nov.
Creators: name: Hansen, Jesper G.
name: Kristensen, Reinhardt M.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Tardigrada
Heterotardigrada
Arthrotardigrada
Halechiniscidae
Higginsarctus

description: Genus Higginsarctus gen. nov.
urn:lsid:zoobank.org:act: B191A524-2C5F-4DBD-93BA-7DC1ADB82CC7
Type species
Higginsarctus signeae gen. et sp. nov.
Diagnosis
A genus of Florarctinae characterized by large, rigid and backwards bending primary clavae (shared with Ligiarctus) supported by strong internal cuticular structures at their bases. Secondary clavae occurring as papillae (dome-shaped or spherical) or as flat sacs (round, rectangular or bilobed). Frontal ala, six lateral alae and a single caudal ala present. The proximal part of the alae (except for the frontal) internally supported by procuticle which sends out branching processes (ramuli) into the distal part of the alae. External claws with calcars and with small internal notches; internal claws with accessory spines and small internal notches.
Etymology
The new genus is dedicated to Dr Robert P. Higgins for his contributions to meiofauna research. Higgins +arctus (latinised Greek word), meaning Higgins’s bear.
Remarks
Higginsarctus gen. nov. shares with species of Florarctus, Ligiarctus and Wingstrandarctus the presence of alae, the shape of the cephalic cirri and fourth leg sense organ, the shape of the seminal receptacles, and the presence of internal hook-shaped peduncles. The very characteristic primary clavae, being large, rigid and backward bending, are shared only with Ligiarctus. It is very apparent that this new genus belongs to Florarctinae, perhaps being closest related to Ligiarctus. However, three characters of Higginsarctus gen. nov. set the genus apart from Florarctus, Ligiarctus and Wingstrandarctus, namely the number of lateral alae, the branching processes of procuticle reaching the distal part of the alae, and the presence of a small internal notch both on external and internal claws.
The term ‘caestus’(from Latin = ‘gauntlet’), originally suggested by Renaud-Mornant (1987), has been generally adopted as a term for the supporting procuticle of the alae in species of Florarctus (Fontoura et al. 2017; Hansen & Kristensen 2020). While the procuticle of the alae in species of Florarctus generally forms proximal lobate processes, it is much different in species of Higginsarctus gen. nov. where the entire proximal half of the alae are supported by a procuticle which sends out branching processes into the distal part of the alae. It is therefore suggested to refer to this special configuration of the supporting structure in the alae of Higginsarctus gen. nov. as ‘ramuli’ (plural form of ‘ramulus’ (Latin) meaning ‘a small branch’).
The six species of Higginsarctus gen. nov. described below differ conspicuously in the morphology of the secondary clava. Further distinguishing characters include differences in alae morphology, genital features and ventral cuticular structures (Table 1).
As in Florarctus and Wingstrandarctus, the distal margin of the lateral and caudal alae in species of Higginsarctus gen. nov. are characterised by small or larger indentations. Although being essential to an accurate description of alae morphology of each species, previous studies have not discriminated between types of indentations. Having studied numerous species of Florarctinae we believe that two morphological distinct types of indentations can be recognised, namely the ‘pointed’ type (Fig. 1) and the ‘arched’ type (Fig. 1). Consequently, the two types are discriminated in the species descriptions below. We also suggest considering both types in all future descriptions of species belonging to Florarctinae.
A new genital structure not observed previously in tardigrades is recognised in 4 out of 6 species. It is situated immediately posterior to the gonopore and will be referred to as the ‘genital stoup’ as it resembles the shape of the holy water holder (Figs 2, 4E). Further investigation is needed to determine the exact function of this structure but it likely plays a role in either copulation or oviposition by facilitating the detention of spermatids/spermatozoa. The presence or absence of a genital stoup in Higginsarctus shintai gen. et sp. nov. and H. laurae gen. et sp. nov. cannot be determined with certainty in the present study. Thus, it might be confirmed as an apomorphy of the new genus, pending a closer study of new material.
A special kind of leaf-like structures are present on the ventral cuticle in the two species Higginsarctus signeae gen et sp. nov. (Fig. 2) and H. laurae gen. et sp. nov. (Figs 14, 16C). Such structures have not been discussed or named previously in Florarctinae although they are present in Florarctus heimi Delamare-Deboutteville & Renaud-Mornant, 1965 (see Gąsiorek et al. 2021: fig. 6), and will tentatively be referred to as ‘folia’ (plural form of ‘folium’ (Latin), meaning a thin leaf-like structure or lamella, a leaf, especially a thin leaf or plate (geometry)).
description: Published as part of Hansen, Jesper G. & Kristensen, Reinhardt M., 2021, A new genus and five new species of the subfamily Florarctinae (Tardigrada, Arthrotardigrada), pp. 149-184 in European Journal of Taxonomy 762 (1) on pages 152-154, DOI: 10.5852/ejt.2021.762.1461, http://zenodo.org/record/5211787