Smit, Harry ¹

¹✉ Naturalis Biodiversity Center, P.O. Box 9517, 2300 RA Leiden, the Netherlands.

2026 - Volume: 66 Issue: 3 pages: 800-804

ZooBank LSID: 9F4AA525-8899-4EA1-99BE-BF3B0BA63DC9

Original research

Keywords

Abstract

Introduction

The genus Arrenurus Dugès, 1834 is the most species-rich genus of the water mites with more than 1000 species known (Smit 2020a). The genus has a cosmopolitan distribution, and occurs on every continent except Antarctica. From Australia 63 species are known (Cook 1986; Halík 1940, 1941; Harvey 1998; Lundblad 1941, 1947; Smit 1992, 1997, 1999, 2002, 2003a,b, 2007, 2010, 2021; Smith & Harvey 1989; K. Viets 1955; K.O. Viets 1975, 1981, 1984). Within Australia, Arrenurus species are known from almost all states and territories, only from the Australian Capital Territory no species are known. Most species are known from tropical Australia (in brackets the number of species): Queensland (27), Western Australia (25), Northern Territory (17), New South Wales (14), Tasmania (11), Victoria (9), South Australia (4) and Australian Capital Territory (0).

Currently, 11 subgenera are known within the genus (Smit 2020b). The following subgenera occur in Australia: Arrenurus s.s., Brevicaudaturus Smit, 1997, Dividuracarus Smit, 1997, Megaluracarus K. Viets, 1911, Micruracarus K. Viets, 1991, Rhinophoracarus K. Viets, 1916 and Truncaturus Thor, 1901. The subgenus Dividuracarus is only known from Australia. However, the subgeneric classification is artificial. Cook (1974) stated that ''the subgenera are poorly defined, undoubtedly polyphyletic and are almost meaningless in indicating true relationships for many of the species groups''. Many authors still use the subgeneric subdivision to subdivide this large genus in smaller units.

Most species of the subgenus Truncaturus are small and with a yellowish or brownish idiosoma colour, not only in Australia but also in other bioregions of the world. Here an unusual new species is described, which is not only relatively large, but also dark red, a combination not found in any other Truncaturus species.

Material and methods

The results presented in this paper are based on a collecting trip to New South Wales, Victoria, Tasmania and South Australia in the period November 2025-March 2026. Numbers are given as males/females/deutonymphs. Abbreviations used: asl = above sea level; Cx-I = first coxae; NP = National Park, TMAG = Tasmanian Museum and Art Gallery, Hobart.

Measurements of segments of palp and legs are of dorsal margins. All measurements are in µm. Ventral idiosoma length is measurand from tip of Cx-I to posterior idiosoma margin.

All material is collected by the author. Non-type material is lodged in Naturalis Biodiversity Center, Leiden. The data of common and widespread Arrenurus-species not treated in this paper will be uploaded to Gbif, and can be examined on the website of Atlas of Living Australia (https://www.ala.org.au ) later on.

Results

Genus Arrenurus Dugès, 1834

Arrenurus (Arrenurus) balladoniensis Halík, 1940

Material examined — Victoria. 1 (not sclerotized)/2/0, pond along Tunnel Road, Pomonal, 37°09.103′ S 142°38.117′ E, 214 m asl, 6 Feb. 2026; 2/1/0, Lake Fyans, 37°08.592′ S 142°37.115′ E, 206 m asl, 7 Feb. 2026. South Australia. 4/3/0 (1 male and 2 females not sclerotized), pond Moyhall Road/Brighton Drive, Naracoorte, 36°57.850′ S 140°43.843′ E, 53 m asl, 3 Feb. 2026.

Remarks — Only Halík (1940) mentioned the colour of the idiosoma, being greenish. The colour of the specimens from this study is yellowish.

Distribution — Widespread in Australia, found in Western Australia, Queensland, Northern Territory, New South Wales and Victoria. Reported here for the first time from South Australia.

Arrenurus (Arrenurus) hyalinus Smit, 2010

Material examined — South Australia. 2/3/0, Brownhill Creek, pool at picnic site, Brownhill Creek Recreation Park, 34°59.312′ S 138°38.359′ E, 29 Jan. 2026; 6/4/0, Okaparinga River, waterhole, Okaparinga NP, 35°08.897′ S 138°35.220′ E, 92 m asl, 30 Jan. 2026; 1/2/0, plunge pool The Deep Creek, Deep Creek NP, 35°38.574′ S 138°13.872′ E, 97 m asl, 1 Feb. 2026.

Distribution — A species thus far restricted to South Australia.

Arrenurus (Truncaturus) haswelli Cook, 1986

Material examined — Tasmania. 1/4/0, Big Waterhouse Lake, 40°53.553′ S 147°36.875′ E, 8 m asl, 23 Dec. 2025.

Remarks — Smit (1999) pointed on the variation in shape of the female genital plates. The females of Smit had much narrower genital plates compared to the females illustrated by Cook (1986). The females of this study show the same variation in shape of the genital plates. Moreover, there is a considerable variation in size of the females. The females of this study are 1015-1668 long and 804-1055 wide, the females of Smit (1999) were 960-1140 long and 757-883 wide. The paratype females of Cook (1986) were 1125-1155 long and 881-897 wide

Distribution — Only known from Tasmania.

Arrenurus (Truncaturus) insolitus n. sp

ZOOBANK: 77C47C5C-D337-4911-AD22-9EF03DFD03BF

(Figure 1)

Material examined

Holotype male, Little Pine Lagoon, Little Pine Lagoon Conservation Area, Tasmania, Australia, 41°59.883′ S 146°36.685′ E, 1009 m asl, 12 Jan. 2026 (TMAG). Paratype: one female, same data as holotype (TMAG).

Diagnosis

Male: Male and female relatively large, colour of the idiosoma dark red; dorsal shield of male incomplete, dorsal shield of female complete; male idiosoma with a straight posterior margin.

Description

Male holotype — Idiosoma colour dark red, 778 long and 672 wide, ventrally 794 long. Idiosoma posteriorly straight, anteriorly convex (fig. 1a). Dorsal shield incomplete. All glandularia striated; associated setae of Dgl-4 distanced from glandularia. Cx-I extending slightly beyond anterior idiosoma margin. Medial margin of Cx-IV longer than medial margin of Cx-III. Genital plates longer than wide, straight (fig. 1b), genital field 405 long; gonopore70 long. Excretory pore near posterior idiosoma margin. Length of P1-5: 32, 80, 48, 78, 64. P2 medially with four stout setae (fig. 1c), dorsally with two stout setae; P1 dorsally with one stout seta, P3 dorsally with one seta, P4 dorsally with two fine setae. Length of I-leg-4-6: 154, 164, 150. Length of IV-leg-4-6: 186, 162, 178; IV-leg-4 without spur. Legs with many swimming setae.

Female paratype — Idiosoma colour dark red, dorsally 1077 long and 859 wide, ventrally 1021 long. Due to its very dark colour it's not visible if the glandularia are striated as in the male. Dorsal shield complete, 883 long and 705 wide. Cx-I not extending beyond anterior idiosoma margin. Medial margin of Cx-IV longer than idiosoma margin of Cx-III. Gonopore 138 long, with small sclerotized areas anteriorly and posteriorly. Genital field 462 long, genital plates straight, directed obliquely towards lateral idiosoma margin, longer than broad (fig. 1d). Length of P1-5: 34, 80, 68, 84, 44; palp as in male but P2 medially with five setae. Length of I-leg-4-6: 166, 178, 170. Length of IV-leg-4-6: 235, 211, 203. Legs with many swimming setae.

Etymology

Named for its unusual shape and colour for a Truncaturus species (Latin: insolitus = unusual, strange, uncommon, odd).

Remarks

The new species is the sixth Truncaturus species from Australia. Species of the subgenus Truncaturus are usually small and coloured yellowish or brownish. The new species is an exception, it is relatively large and the colour is dark red. Three other Australian Truncaturus are also large, i.e. A. haswelli Cook, 1986, A. indentatus Smit, 2010 and A. novaecambricus Smit, 2010. Arrenurus haswelli and A. indentatus differ from the new species in having the posterior idiosoma margin with a median cleft. The male of Arrenurus novaecambricus is larger (850-907), the posterior idiosoma margin is concave, the genital plates are shorter and slightly bowed and the idiosoma colour is yellowish brown.

Arrenurus (Megaluracarus) maria Smit, 1999

Material examined — Tasmania. 0/17/0 (palp of one female mounted), Big Waterhouse Lake, 40°53.553′ S 147°36.875′ E, 8 m asl, 23 Dec. 2025; 1/1/0, roadside pond Argonaut Road, St Helens, 41°19.191′ S 148°12.748′ E, 11 m asl, 30 Dec. 2025. Victoria. 5/0/0, small lake in Caledonian Creek, Ross Creek State Forest, 37°40.368′ S 143°42.269′ E, 401 m asl, 9 Feb. 2026.

Distribution — Previously known from Tasmania only, and reported here for the first time from Victoria.

Acknowledgements

I am indebted to the Department of Natural Resources and Environment Tasmania and the Department of Environment and Water for their permission to collect in national parks and nature reserves of Tasmania and South Australia, respectively. The area managers of Southeast Forests National Park and Deua National Park (both in New South Wales) gave permission to collect in these national parks.

References

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