A New Species of Limnesia (Acari, Hydrachnellae) from New Zealand

Transactions of the Royal Society of New Zealand : Zoology, Volume 8, Issue 1, 27 January 1966, Page 1

A New Species of Limnesia (Acari, Hydrachnellae) from New Zealand

C. L. Hopkins

By

Marine Department, Fisheries Laboratory, Wellington

Abstract

A new species of Limnesia (s.str.) is described. It is an inhabitant of springs, an unusual environment for this genus.

Introduction

According to Lundblad (1941) the genus Limnesia (s. str.) is of cosmopolitan distribution, though it has not previously been recorded from New Zealand, In the Pacific region species have been described from Australia (Lundblad, 1947) and from other parts of Australasia, from Japan (Uchida and Imamura, 1953) and from South America (Viets, 1954; Lundblad, 1954). The material described in this paper was obtained from a boggy spring seepage (helocrene) in the valley of the Mangakotukutuku River, near Paraparaumu (map reference in sheet N. 156 is 567624). The spring consisted of an area of silt and oozing water largely covered with moss, several metres across. All specimens were preserved in a fluid containing 10 vols. glycerine, 3 vols. acetic acid and 6 vols. distilled water. This preservative causes initial shrinkage of the mites followed by a return to the original size.

Family LIMNESIIDAE Subfamily LIMNESHNAE Genus Limnesia s. str. Koch, 1836

Limnesia reptans n. sp. Material

The description is based on measurements and observations made from adult specimens now lodged in the Dominion Museum, Wellington. Holotype male, dated 9 June 1964. Dominion Museum catalogue number DM 4/341.

Allotype female, dated 9 June 1964. Dominion Museum catalogue number DM 4/342.

Male

Dimensions of the various organs are shown in Table I, and parts are illustrated in figs. 1-8.

Body oval with a somewhat arched dorsum carrying a single median, sclerotised plate on its posterior half. This plate is larger than is usual for the genus. Apart from the dorsal plate and the ventral epimera, the skin is soft and covered with fine ridges.

Colour in life is yellowish brown.

Maxillary organ short and broad, similar to other species of the genus.

Mandible straight with a slightly curved claw which is finely ridged on the ventral surface.

Palp moderately slender. P. I (basal segment) very short, the more massive P. II nearly twice as long. P. 11l slightly more than two-thirds the length of P. II and narrower. P. IV long and slender, longer than P. II and P. 11l together. P. V slim and slightly curved, somewhat longer than P. I, finely clawed at the tip. P. II carries a short, thick, forwardly directed spine slightly distal to the centre of the ventral surface; unlike many other members of the genus, this spine is not seated on a protuberance. P. IV carries a small, ventral papilla about two-thirds of the way towards the distal end, and from this arises a long, forwardly curved hair. A number of short, fine hairs lie at the distal end of P. IV.

Epimera occupying somewhat more than half the ventral surface, the united 3rd and 4th epimera pressed up closely against the united Ist and 2nd median borders of the Ist epimera, forming a bay flanking the maxillary organ and curving inwards behind it, not quite meeting in the mid-line, and extending thence posteriorly for a short distace. A subcutaneous, hookshaped process extends sideways from the posterior end of the Ist epimeron, and ends beneath the 3rd; 2nd epimeron smaller than the Ist. Third epimeron larger with median border bulging towards mid-line immediately anterior to genital area. Fourth epimeron large, of typically Limnesiid triangular shape, its apex directed posterolaterally; 4th epimeron extends a little up the flanks of the body.

External genital area with its anterior end in a slight bay formed by the median borders of the 3rd and 4th epimera on each side. Genital aperture flanked on each side by a lunate genital plate carrying three acetabula. Two acetabula are crowded at the posterior end of the plate, and one lies near the anterior end. A number of small hairs arise along the margin of the plate.

Excretory pore well back from genital area, near hind margin of body.

Legs without swimming hairs though plentifully supplied with short spines. Distal segment of each leg except 4th ending in a pair of sickle-shaped claws. Distal segment of 4th leg without claw, but ending in spine about half the length of the segment (characteristic of the genus).

Female

Similar to the male. Distinguished externally by the bow-shaped sclerite lying at the anterior end of the genital plates.

Discussion

L. reptans can be separated from other members of the subgenus Limnesia by a combination of external characters, viz., the lack of swimming hairs on the legs, the single, large, rectangular plate, on the hind half of the dorsum, and the unusually large 3rd and 4th epimera which lie very close to the genitalia, L. andina Lundblad, from South America, is somewhat similar to the present species, differing mainly in details of the palpi.

The habitat of L. reptans is not typical for the genus, most members of which are associated with vegetation in lakes and slow-moving waters. L. arevaloi Viets, from Southern Europe and North Africa, has been taken from springs (Viets, 1918; Walter, 1935) and a few rheophilous species have been described from South America. Together with many other stream-living Hydrachnellae, and probably all crenophilous species, L. reptans is a crawling form. Here again it differs from most species of Limnesia since the majority are active swimmers.

Lundblad (1947) has decribed three species of Limnesia from Australia. All are typical benthic forms with swimming hairs and appear to be relatively distant in their relationships to L. reptans.

Literature Cited

Lundblad., 0., 1941. Eine Übersicht des Hydrachnellensystems und der bis jetzt bekannten Verbreitung der Gattungen dieser Gruppe. Zoolog. Bidr. Uppsala, 20: 359-379. (2): 1-83. (A.S.): 435-585.

Uchida, T., Imamura, T., 1953. Some water mites from Japan. /. Fac. Sci. Hokkaido Univ. (5.6) Zool. 11 (3): 515-524.

Viets, K., 1918. Eine neue Limnesia-Species. Zool. Anz. 50 (4): 111—112.

Viets, K. H., 1954. Susswassermilben (Hydrachnellae, Acari) aus Sudamerika. Arch, fur. Hydrobiol. 49 (1/2): 1-324.

Walter, C., 1935. Voyage de Ch. Alluaud et P. A. Chappuis en Afrique occidentale francaise (Decembre, 1930 - Mars, 1931): IX Hydracarina. Arch, fiir Hydrobiol. 28: 69-136.

G. L. Hopkins, Fisheries Laboratory, Marine Dept., 327 Willis Street, Wellington.

Male Female Body length 662 677 Body greatest breadth 508 569 Dorsal plate length 169 172 Dorsal plate breadth 91 92 Genital plates length 208 215 Leg length: I 154 129 II 580 637 III 675 712 IV 731 778 Palp segments length: P.I 40 37 P.II 100 123 P.III 78 77 P.IV 152 165 P.V 46 60

Table I.—Dimensions (in μ ).