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Oribatid mites (Acari: Oribatida) ofSouth Georgia, South AtlanticJ. Starý a & W. Block ba Institute of Soil Biology , Academy of Sciences of the CzechRepublic , Na sádkách 7, 37005, České Budějovice, CzechRepublicb British Antarctic Survey , Natural Environment ResearchCouncil , High Cross, Madingley Road, Cambridge, CB3 0ET, UKPublished online: 17 Feb 2007.

To cite this article: J. Starý & W. Block (1995) Oribatid mites (Acari: Oribatida) of South Georgia,South Atlantic, Journal of Natural History, 29:6, 1469-1481, DOI: 10.1080/00222939500770631

To link to this article: http://dx.doi.org/10.1080/00222939500770631

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JOURNAL OF NATURAL HISTORY, 1995, 29, 1 4 6 9 - 1 4 8 1

Oribatid mites (Acari: Oribatida) of South Georgia, South Atlantic

J. STARX2 and W. BLOCK:~*

$Institute of Soil Biology, Academy of Sciences of the Czech Republic, Na stidkdch 7, 37005 ~eskd Bud~jovice, Czech Republic ~British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK

(Accepted 9 September 1994)

Twenty-one species of oribatid mites (Acari: Oribatida), including three new species, are reported from samples collected on the sub-Antarctic island of South Georgia. Fossonothrus wallworki n.sp., Lanceoppia elegantula n.sp. and Ed- wardzetes australis n.sp. are described and figured. Ten additional species, recorded previously, provides a total of 31 species for the island.

KEYWORDS: Mites, Oribatida, sub-Antarctic, South Georgia.

Introduction The oribatid mite fauna of the island of South Georgia is the best known in the

sub-Antarctic and Antarctic region. The first species recorded from this region, Magellozetes antarcticus (Michael, 1895), was described from South Georgia (Dalenius and Wilson, 1958). Later Tfa~ardh (1907) recorded three other species of oribatids in material from this island. The majority of our present knowledge about the oribatid fauna of this sub-Antarctic island has been published in a series of papers by Wallwork (1966, 1970, 1972) and referenced in Block (1992) and Pugh 's synonymic catalogue (1993) of Antarctic Acari.

The present paper describes three new species and records 18 other species from South Georgia and discusses the zoogeographical relationships of the oribatid mite fauna of South Georgia and the sub-Antarctic. The habitat and locality information in the list of identified species refer only to South Georgia.

List of identified species Family BRA CHYCHTHONIIDAE

Eobrachychthonius oudemansi Hammen, 1952

Distribution. Holarctic region, southern Argentina, South Georgia, South Sand- wich Is.

Habitat. Tussock grassland, Festuca erecta with Tortula robusta, Polytrichum sp., Dicranum sp. clumps.

*To whom correspondence should be addressed.

0022-2933/95 $10-00 © t995 Taylor & Francis Ltd.

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1470 J. Star~ and W. Block

Locality. King Edward Cove. Remarks. Semicosmopolitan species.

Liochthonius australis Covarrubias, 1968

Distribution. South Shetland Is., Iles Crozet and Iles Kerguelen. Habitat. Tussock grassland. Locality. King Edward Cove. Remarks. Sub-Antarctic species.

Liochthonius mollis (Hammer, 1958)

Distribution. Antarctic continent (Graham Land), South Shetland Is., South Orkney Is, South Georgia, Iles Crozet and Iles Kerguelen, Chile.

Habitat. Tussock grassland, Rostkovia bog with Tortula robusta and Juncus sp., and moss bank of Polytrichum alpestre, Chorisodontium aciphyllum and Cladonia sp.

Localities. King Edward Cove, Husvik. Remarks. Antarctic and sub-Antarctic species.

Family MALA CONOTHRIDAE Fossonothrus wallworki n.sp.

Distribution. South Georgia. Habitat. Mosses, especially Polytrichum alpestre, and tussock near King Penguin

rookery, Roskovia bog with Tortula robusta and Juncus sp. Localities. King Edward Cove, Maiviken, Husvik, Bay of Isles (Salisbury Plain).

Malaconothrus translamellatus Hammer, 1958

Distribution. Peru, Bolivia, Chile. Habitat. Moss and tussock near King Penguin rookery. Locality. Bay of Isles (Salisbury Plain). Remarks. New record of the genus Malaconothrus for sub-Antarctic; Neotropical

species.

Trimalaconothrusflabelliformis Wallwork, 1970

Distribution. South Georgia. Habitat. Moss bank of Polytrichum alpestre with Chorisodontium aciphyllum and

Cladonia sp. Locality. King Edward Cove. Remarks. Endemic to South Georgia.

Family CAMISIIDAE Platynothrus skottsbergi expansus Wallwork, 1966

Distribution. Southern Chile, South Georgia.

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Oribatid mites of South Georgia 1471

Habitat. Moss ( Polytrichum alpestre) and tussock, Tortula robusta with Roskovia sp., Juncus sp. and Poa annua.

Localities. King Edward Cove, Maiviken, Hestesletten, Husvik, Bay of Isles (Salisbury Plain).

Family OPPIIDAE Austroppia crozetensis (Richters, 1908)

Distribution. South Orkney Is., South Sandwich Is., South Georgia, Marion Is., Iles Crozet, lies Kerguelen and Macquarie Is.

Habitat. Mosses (Polytrichum alpestre), Poa flabellata tussock with Festuca erecta, Deschampsia sp., Acaena decumbens with Tortula robusta, Roskovia bog and lichens.

Localities. King Edward Cove, Maiviken, Hestesletten, Husvik, Bay of Isles (Salisbury Plain, Rosita Harbour).

Remarks. Sub-Antarctic species.

Globoppia intermedia Hammer, 1962

Distribution. Chile, South Orkney Is., South Sandwich Is., South Georgia, Iles Crozet, Iles Kerguelen.

Habitat. Tussock grass turves. Locality. Husvik.

Globoppia intermedia iongiseta Wallwork, 1970

Distribution. South Sandwich Is., South Georgia, Iles Crozet, Iles Kerguelen, Heard Is., southern Chile.

Habitat. Tussock grass, Acaena decumbens, Festuca erecta, Poa flabellata, Deschampsia sp., Tortula robusta, Rostkovia bog, mosses Polytrichum alpestre and Dicranum sp.

Localities. King Edward Cove, Maiviken, Husvik, Bay of Isles (Salisbury Plain).

Globoppia scotiae (Wallwork, 1970)

Distribution. South Georgia (Wallwork, 1970). Habitat. Mosses above beach. Locality. Royal Bay (Moltke Harbour). Remarks. Endemic to South Georgia.

Lanceoppia elegantula n.sp.

Distribution. South Georgia. Habitat. Tussock grass, Festuca erecta and mosses. Localities. King Edward Cove, Royal Bay (Moltke Harbour).

Family AMERONOTHRIDAE Alaskozetes antarcticus (Michael, 1903)

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1472 J. Star) and W. Block

Distribution. Antarctic continent (Wilkes and Scott Sectors, Graham and Palmer Lands), South Shetland Is., South Orkney Is., South Georgia, Marion Is., Iles Kerguelen, Macquarie Is.

Habitat. Tussock influenced and damaged by King Penguin guano. Locali~. Bay of Isles (Salisbury Plain). Remarks. Antarctic and sub-Antarctic species.

Alaskozetes antarcticus intermedius Wallwork, 1967

Distribution. Continental Antarctic (Palmer and Graham Lands), South Orkney Is., South Sandwich Is., South Georgia, Iles Kerguelen.

Habitat. Poa flabellata. Localities. King Edward Cove, Maiviken, Hestesletten, Bay of Isles (Salisbury

Plain). Remarks. Antarctic and sub-Antarctic species. The validity of this subspecies and

the systematics of the polymorphic genus Alaskozetes are not clear and require critical study.

Antarcticola georgiae WaUwork, 1970

Distribution. South Georgia, Iles Kerguelen. Habitat. Tussock, Deschampsia sp. and lichens on peat. Localities. Maiviken, Bay of Isles (Rosita Harbour). Remarks. Rare sub-Antarctic species.

Family CERA TOZETIDAE Edwardzetes elongatus Wallwork, 1966

Distribution. Southern Chile, South Georgia, South Sandwich Is. Habitat. Tussock, Acaena decumbens, Deschampsia sp., Tortula robusta, Poa

annua, Rostkovia bog, moss banks of Polytrichum alpestre with Chorisodontium aciphyllum.

Localities. King Edward Cove, Maiviken, Hestesletten, Husvik, Bay of Isles (Salisbury Plain, Rosita Harbour).

Edwardzetes australis n.sp

Distribution. South Georgia. Habitat. Lichens on peat, Festuca erecta grassland, tussock. Localities. King Edward Cove, Maiviken.

Magellozetes antarcticus (Michael, 1895)

Distribution. Antarctic continent (Graham Land), South Shetland Is., South Georgia, Iles Kerguelen, southern Argentina and southern Chile.

Habitat. Tussock, Acaena decumbens, Tortula robusta, Poa flabellata and Festuca erecta.

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Oribatid mites of South Georgia 1473

Localities. King Edward Cove, Husvik, Bay of Isles (Salisbury Plain).

Magellozetes processus Hammer, 1962

Distribution. Southern Chile, Iles Kerguelen. Habitat. Tussock turves, Festuca erecta. Locality. Husvik. Remarks. New record for South Georgia.

Porozetes polygonalis quadrilobatus Wallwork, 1966

Distribution. Southern Chile, South Georgia. Habitat. Tussock, Acaena decumbens, Tortula robusta, Poa flabellata, Festuca

erecta and Rostkovia bog. Localities. King Edward Cove, Maiviken, Husvik.

Family PARAKALUMNIDAE Sandenia georgiae (Oudemans, 1914)

Distribution. South Georgia. Habitat. Moss above beach. Locality. Royal Bay (Moltke Harbour). Remarks. Endemic to South Georgia.

Fossonothrus wallworki n.sp. (Figs 1A-B, 2A-D)

Diagnosis Epimeral setae formula 2-1-3-3, exobothridial setae as long as rostral ones,

notogaster without transverse ridges.

Description Measurements. Length 586.3-645-8 #m, width 318.4-365.2/~m, mean length 615-2 /~m, mean width 345.2 ffm, holotype (female) length 604-0/zm and width 340-3 #m. Colour light ochre yellow, surface of body with minute granular microsculpture (not easily seen), thin layer of cerotegument.

Prodorsum (Fig. 1 A) with two conspicuous sclerotized lamellar ridges, all prodorsal setae smooth and fine, rostral setae, shorter than distance between their insertions. Fine lamellar setae twice as long as rostral setae and equal to distance between their insertion points. Interlamellar setae shorter than length of prodorsum and the distance between their insertion points. Exobothridial setae equal in length to rostral setae. Posterior part of prodorsum without sclerotised ridge.

Notogaster (Fig. 1A) oval with 15 pairs of smooth notogastral setae, setae e2 2 × and h2 4 × as long as other notogastral setae. Setae ps2 and ps3 inserted on ventral

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1474 J. Star~ and W. Block

', [ ' /

I l',\ / ,t

l, i ]

" 1 J

A

A ,200 l~m B FIG. 1. Fossonothrus wallworki n.sp., (A) dorsal view of body without legs; (B) ventral view

of body without legs.

part of body. Two pairs of sclerotized ridges present, inner pair longer and stronger, anterior part between insertions of setae el and d 1 bent. Outer pair of ridges less distinct and shorter than inner pair.

B

D , lOO l~m C

FIG. 2. Fossonothrus wallworki n.sp., (A) left leg I in antiaxial view; (B) left leg II in antiaxial view; (C) left leg III in antiaxial view; (D) left leg IV in antiaxial view.

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Oribatid mites of South Georgia 1475

Epimeral region (Fig. 1B), surface of epimerae smooth, without distinct sculpturing. Epimeral setae short, fine and smooth, formula 2-1-3-3.

Ventral plates (Fig. IB), genital plate approximately as large as anal, surface of genital and anal plates smooth. Eight pairs of genital setae, fine and smooth, 2-3 × as long as epimeral setae. Three pairs of adanal aetae, one pair of anal setae, all smooth, fine and longer than genital setae. Setae ps2 2 × as long as ps3, inserted on sclerotised ridges.

Legs (Figs 2A-D), all tridactylous, with lateral claws longer but thinner than median one. Chaetotactic formulae I 1-5-2(1)-4(1)-10(3)-3, II 1-5-2(1)-3(i)-10(1)-3, III 2-3-1-2(1)-10-3, IV 0-3-1-2-10-3.

E~mology The new species is named in honour of Professor John A. Wallwork, renowned

acarologist, ecologist and authority on the taxonomy of oribatid mites of the Antarctic and sub-Antarctic,

Types Holotype and 15 paratypes in ethanol are deposited in the collections of The Natural

History Museum, London, 10 paratypes in ethanol are deposited in the British Antarctic Survey, Cambridge, UK.

Material examined South Georgia, King Edward Cove, Roskovia bog near freshwater pool, 15

September 1971, leg. W. Block. Other localities: South Georgia, King Edward Cove, south side of small valley behind Gun Hut, Tortula robusta with Rostkovia sp. and Juncus sp., 14 November 1971, leg. W. Block; South Georgia, Salisbury Plain, Bay of Isles, moss and tussock on slope near King Penguin rookery, 19 November 1971, leg. W. Block; South Georgia, King Edward Cove, moss Polytrichum alpestre, March- April 1981, leg. M. B. Usher and R. G. Booth; South Georgia, Maiviken, moss Polytrichum sp., March 1981, leg. M. B. Usher and R. G. Booth; South Georgia, reindeer exclosure, tussock turves extract, 17 February 1980. leg. T. D. Heilbronn and R. K. Headland.

Remarks The genus Fossonothrus Hammer, 1962 has comprised two species up to the

present: the type species Fossonothrus latus Hammer, 1962 described from South America and Fossonothrus novaezealandicus Hammer, 1966 from New Zealand. Fossonothrus watlworki n.sp. has characters intermediate between these two species. Fossonothrus novaezealandicus Hammer, 1966 differs from the new species by the presence of three pairs of setae on epimere I, distinctly shorter notogastral setae e2, and h2 and longer lamellar setae (Hammer, 1966). Fossonothrus latus Hammer, 1962 is different from the new species in having transverse ridges connecting median longitudinal ridges, the presence of three pairs of~setae on epimere I and four pairs on epimere IV (Hammer, 1962a).

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1476 J. Stary and W. Block

. . . . . . .

A , 2 0 0 l im , B FIG. 3. Lanceoppla elegantula n.sp., (A) dorsal view of body without legs; (B) ventral view

of body without legs; (C) bothridium and sensillus in lateral view.

Lanceoppia elegantula n.sp. (Figs 3A-C; 4A-D)

Diagnosis Rostrum rounded, seta ta absent, smooth sensillus with distinctly pointed tip, six

pairs of genital setae, lyrifissure iad in apoanal position, setae ad3 in preanal position, three pairs of rounded muscle-scars on prodorsal margin, notogaster without crista, selerotized crest behind each interlammellar seta.

Description Measurements. Length 325.6-375.4/~m, width 168.9-207.6/lm, mean length 351.1 /lm, mean width 190-4/zm, holotype (female) length 375.4/~m, width 200-0/zm. Colour light ochre yellow, cerotegument very thin, body surface smooth without conspicuous sculpture.

Prodorsum (Fig. 3A) with rostrum rounded and entire, smooth rostral setae longer than their mutual distance. Lamellar setae similar in form to rostral setae, but slightly shorter, inserted in central part of prodorsum. Interlamellar setae smooth, fine, same length as lamellar setae, inserted anterior to pair of sclerotized crests. Lamellar ridge situated anterior to bothridium, which disappears in region between bothridium and lamellar setae insertions, anterior of which are three rounded muscle-scars separated from the prodorsal margin by fine lateral ridges. Bothridia with strongly sclerotized cup with aperture directed dorsolaterally. Sensillus with conspicuous slender head, pointed at tip (Fig. 3C), approximately same length as distance between the bothridia. Small, fine exobothridial setae inserted anterolaterally to bothridium.

Notogaster (Fig. 3B) oval, smooth, without conspicuous sculpturing, anterior margin strongly sclerotised. Nine pairs of smooth notogastral setae, approximately similar in length. Setae ta absent. Lyrifissure im located in usual position.

Epimeral region (Fig. 3B), apodeme III absent, epimeres III and IV fused. Epimeres smooth, without conspicuous surface structure. Epimeral setae formula 3-1-3-2. All epimeral setae smooth and fine, lc and 4b longer than the others.

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Oribatid mites of South Georgia 1477

S ¸ r/'

D , loo m , C

FIG. 4. Lanceoppia elegantula n.sp., (A) right leg I in antiaxial view; (B) right leg II in antiaxial view; (C) right leg III in antiaxial view; (D) right leg IV in antiaxial view.

Ventral plates (Fig. 3B), genital plate smaller than anal plate. Six pairs of small, fine genital setae, separated into two groups, anterior ( g l ~ ) near median line and posterior (g5-6). Two pairs of smooth, fine anal setae. Adanal setae ad3 in preanal position, adl in postanal position. Lyrifissure iad in apoanal position, Surface of this region smooth without distinct sculpturing.

Legs (Fig. 4A-D) slender, monodactylous, chaetotactic formulae I 1-4-2(1)-2(2)- 17(2)-1, II 1-3-1(1)-4(1)-11(2)-1, III 2-3-1(1)-2(1)-12(1)-1, IV 2-2-2-2(1)-10-1. Legs without crests or projections.

Types Holotype and two paratypes in ethanol are deposited in the collections of The

Natural History Museum, London and three paratypes in the collections of the British Antarctic Survey, Cambridge, UK.

Material examined South Georgia, above Gull Lake near King Edward Cove, from exposed Festuca

erecta grassland, 20 November 1971, leg. W. Block. Other localities: South Georgia, Moltke Harbour, Royal Bay, east peninsula above German Transit of Venus Expedition huts, sample of pedestal of closed tussock (Poaflabellata), 21 November 1971, leg. W. Block; South Georgia, Moltke Harbour, Royal Bay, east peninsula above German Transit of Venus Expedition huts, moss above beach, 21 November 1971, leg. W. Block.

Remarks The genus Lanceoppia is represented in South America, New Zealand, Queensland

and Java by > 27 species. The most similar species to Lanceoppia elegantula n.sp. is Lanceoppia bicristata (Hammer, 1962), but it differs from the new species by the

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1478 J. Star3~ and W. Block

/

/

/

2oo,m

FIG. 5. Edwardzetes australis n.sp., (A) dorsal view of body without legs; (B) ventral view of body without legs.

slender head of the sensillus and the absence of lateral ridges and rounded muscle-scars on the prodorsum (Hammer, 1962b). Lanceoppia binodosa (Hammer, 1962) has shorter interlamellar and lamellar setae and has no lamellar ridges anterior of the bothridium. Lanceoppia hexapili (Hammer, 1962) has a slender barbed sensillus, notogastral setae of variable length and no sclerotized crests behind the interlammellar setae insertions (Hammer, 1962a). Lanceoppia nodosa (Hammer, 1958) has no lamellar ridges and possesses shorter notogastral, interlamellar and lamellar setae (Hammer, 1958).

Edwardzetes australis n.sp. (Figs 5A-B, 6A-D)

Diagnosis Ribbon-like translamella, six pairs of genital setae, lamellar setae reaching over

rostrum, interlamellar setae coarse, lamellae less than half length of prodorsum.

Description Measurements. Length 781.4-835-6 #m, width 451.8-501.8 #m, mean length 808.5 #m, mean width 476-8 #m, holotype (male) length 781.4 #m, width 451.8/~m. Colour dark brown, cuticle with thin layer or cerotegument.

Prodorsum (Fig. 5A), rostrum rounded without distinct incision or similar structure, barbed rostral setae inserted on small projections, approximately as long as distance between their insertions. Lamellae short, < 0.5 length of prodorsum and with conspicuous ribbon-like translamella. Lamellar setae long, barbed, overlapping the rostrum for 0-33 of their length. Interlamellar setae long, barbed and distinctly longer than lamellar setae. Tutoria well-developed on each side of prodorsum, extending posteriorly to bothridium. Bothridium cup-shaped with sharp inner projection. Sensillus smooth with short, slender stem and clavate head.

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Oribatid mites of South Georgia 1479

r

FIG. 6. Edwardzetes australis n.sp., (A) right leg I in antiaxial view; (B) right leg II in antiaxial view; (C) right leg IV in antiaxial view; (D) right leg III in antiaxial view.

Notogaster (Fig. 5A) comparatively long, generally smooth and with weak striations on pteromorphae. Ten pairs of smooth notogastral setae, four pairs of areae porosae, Aa the largest, A1-2 smaller and A3 the smallest. G la and fissurae im in usual position. Pteromorphae large with smooth margins.

Epimeral region (Fig. 5B) smooth with four pairs of apodemata, epimeral setae formula 3-1-2-2, all short, fine and smooth. Well developed discidium reaching epimera III with sharp custodium on the tip.

Ventral plates (Fig. 5B) smooth, genital plates rounded with six pairs of minute, smooth genital setae. Larger anal plate with two pairs short anal setae, three pairs of smooth, short adanal setae. Lyrifissure iad in apoanal position.

Legs (Fig. 6A-D) tridactylous, robust. Leg chaetotactic formulae I 1-4-2(1)-4(2)- 20(2)-3, II 1-4-3(1)-5(1)-16(2)-3, III 1-2-1(1)-3(1)-15-3, IV 1-2-2-2(1)-12-3. Femora I, III and IV with .ventral crests, femora II, genua I and II with anterior, tooth-like projection.

Types Holotype in ethanol is deposited in the collections of The Natural History Museum,

London and one paratype in the collections of the British Antarctic Survey, Cambridge, UK.

Material examined South Georgia, Maiviken, near cave on beach, in lichen on peat overlying a cliff,

15 November 1971, leg. W. Block. Other localities: South Georgia, above Gull Lake near King Edward Cove, from exposed Festuca erecta grassland, 20 November 1971, leg. W. Block.

Remarks The new species together with Edwardzetes elongatus Wallwork, 1966 have

characters intermediate between the genera Edwardzetes Berlese, 1914 and Jugatala

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1480 J. Star2~ and W. Block

Ewing, 1913. The genus Edwardzetes has five genital setae and is without translamella, whilst the genus Jugatala has pteromorphae connected by a transverse bridge covering the bothridium and the basal part of the sensillus. The most closely related species is Edwardzetes elongatus Wallwork, 1966, which differs from the new species by the absence of ribbon-shaped translamella, shorter lamellar setae and smooth interlamellar setae (Wallwork, 1966). Two other Neotropical species, Edwardzetes dentifer Hammer, 1962 and Edwardzetes andicola Hammer, 1958, have five pairs of genital setae but they do not have a translamella. Two species of the genus Jugatala Ewing, 1913 are recorded from the Neotropical Region: Jugatala armata Hammer, 1958, which does not have ribbon-shaped translamella and Jugatala montana Hammer, 1961 which has a conspicuously longer cuspis on each lamella (Hammer, 1958, 1961, 1962a).

Discussion The 21 species of oribatid mites found in the present study, together with 10

additional species previously recorded (Wallwork, 1966, 1970, 1972), provides a total of 31 species for South Georgia.

The oribatid mite fauna of South Georgia consists of three zoogeographical elements: endemic species, South American or Neotropical species and circum-Antarc- tic species (Wallwork, 1966, 1969). Wallwork (1972) reported the following proportions of these three elements in the South Georgian fauna: endemic 31%, South American 38% and Antarctic 31%, but he stated that the three zoogeographical elements cannot always be clearly defined. From the present results, it is clear that endemism is on the same level (nine species, i.e. 29% of the total species). Ten of the South Georgian species (32%) are distributed in the Neotropical region, mainly in Tierra del Fuego, southern Chile, south Argentina and the Andes Mountains. The smaller, but not insignificant, number of semicosmopolitan species (three species, 10% of the total) may reflect the long period of geographical isolation of South Georgia, or they may have been introduced by human activities. The remainder of the oribatid fauna (nine species, 29% of the total) are species with circum sub-Antarctic or Antarctic distribution.

These results confirm Wallwork's findings (1972), but differences in the distribution of certain species are recognised. For example, Edwardzetes elongatus Wallwork andAntarcticola georgiae Wallwork belong at present to the Neotropical and the sub-Antarctic elements respectively; they are not endemic to South Georgia. For an explanation of the origin and present-day composition of the oribatid fauna of South Georgia it will be necessary to study fossil mites from the sub-Antarctic islands and from the Antarctic continent. Also, the possible mechanisms of transport and migration of oribatids need to be investigated. The composition of oribatid communities in the nests of sea birds and in decaying drifted tree trunks around the Southern Ocean may be helpful here. In addition, ecophysiological data on the resistance of these small arthropods to desiccation and to salt water immersion will he required before an explanation of the present-day composition of Antarctic oribatid mite fauna can be advanced.

Acknowledgements The support of the British Council and the British Antarctic Survey (BAS) in

providing travel funds to allow JS to work in Cambridge is much appreciated. The use of the collections in the Data and Resource Centre of the BAS Terrestrial and Freshwater

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Life Sciences Divis ion is grateful ly acknowledged . The manuscr ip t was improved by the construct ive comments o f two anonymous reviewers.

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