Zerconidae

Dorsum (left) and venter of female Prozercon umidicola, from Urhan (2002).

Belongs within: Gamasina.
Contains: Zercon (Zercon).

The Zerconidae are a family of predatory mites known only from the Northern Hemisphere in habitats such as humus, litter, mosses and animal nests. They commonly (but not always) have serrated lateral margins on the dorsal shields and two pairs of large, sclerotised fossae near the posterior margin (Lindquist et al. 2009). Most genera have the peritremal shield free from the ventro-anal shield but the two are connected in the genera Microzercon and Amerozercon. Amerozercon suspiciosus has a long and plumose seta p2 on the venter laterad of the second and third coxae whereas all ventral setae are short and smooth in Microzercon. The peritremal shield ends truncately just behind the fourth coxae in the genera Macrozercon, Mixozercon, Metazercon and Zercon whereas it is more elongate in Parazercon, Mesozercon, Echinozercon and Prozercon (Błaszak 1975).

Zerconids
Published 17 March 2017
Slide-mounted male of Zercon gurensis, copyright Holger Müller.

The animal depicted above is a mite of the Zerconidae, one of the numerous families in the major mite clade known as the Mesostigmata. This family is mostly found in soil habitats such as leaf litter, mosses, decaying vegetation, or occasionally in animal nests (Lindquist et al. 2009). The zerconids are restricted to the Northern Hemisphere and are most diverse in temperate to Arctic regions; those species found in tropical parts of the world are restricted to high altitudes away from the hot lowlands (Ujvári 2012). Like many other Mesostigmata, they have the dorsal surface of the body mostly covered by shields of hardened cuticle. In most zerconids, separate shields cover the front (podonotal) and rear (opisthonotal) sections of the dorsum; the opisthonotal shield wraps around the rear margin of the mite and forms a continuous unit with the ventrianal shield that usually protects most of the underside of the mite behind the legs. Among the most noticeable features of the zerconids are two pairs of large openings near the rear of the opisthonotal shield (the four orange-segment-like structures in the photo above). These represent the openings of secretory glands, but I don’t know if it has been established just what they’re secreting; comparable structures in other mites may secrete pheromones, or defensive chemicals, or oils that prevent debris from sticking to the body. Other features of the zerconids include slender, relatively simple chelicerae that lack the modifications seen in the males of some other Mesostigmata, and peritremes (grooves on the underside of the body that channel air to the openings of the respiratory stigmata) that are relatively short. These peritremes are longer in zerconid nymphs, but become shortened when the mite moults to maturity.

Zerconids are another of those mite groups where the vast majority of what has been written about them relates to their basic taxonomy, with little yet known about their natural history. Several genera of zerconids are recognised, distinguished by features such as the shape of the body’s various shields and the appearance of various setae. The form of their chelicerae indicates that zerconids are predatory like many other Mesostigmata. Because they are mostly found at ground level rather than on vegetation they have not attracted the economic interest of other predatory mites, but those few species that have been observed feeding were chowing down on nematodes. Mating does not appear to have been directly observed in zerconids, but again their anatomy and comparison with other mesostigs allows us to infer that the male fertilises the female by using his chelicerae to pass a spermatophore from his own genital opening on the underside of the body between the legs to hers. Where she then lays her eggs, and how her offspring spend their time to maturity, seem to be questions still awaiting an answer.

Systematics of Zerconidae

Characters (from Lindquist et al. 2009): Female, male and deutonymph with podonotal and opisthonotal shields well developed, rarely secondarily united; those of adult ornamented and extended laterally so as to bear marginal setae along their usually serrated margins; opisthonotal shield of deutonymph and adult fused caudally with ventrianal shield and often with transverse row of four (sometimes three or two) clearly defined fossae near posterior margin. Male without cheliceral sperm-transferring appendages. Palptarsal apotele two-tined. Tritosternum with well-developed laciniae. Male genital opening between coxae II-III; female epigynal shield with one pair of setae, not flanked by setae in soft integument; female and male with broad ventrianal shield; peritremes well developed in deutonymph, often short in adult but rarely reduced to size of stigmata. Genu III and IV each with ten setae, including two posterolaterals on genu III ( 2 2/1, 2/1 2) and one posteroventral on genu IV (2 2/1, 3/1 1).

<==ZerconidaeS58
    |--SyskenozerconJM91
    |--Paleozercon cavernicolusLKW09
    |--Eurozercon pacificusML98
    |--Aquilonozercon desuetusML98
    |--RafasML98
    |--Halozercon Wiśniewski, Karg & Hirschmann 1992ML98
    |    `--*H. karacholana Wiśniewski, Karg & Hirschmann 1992ML98
    |--Aspar Halašková 1977FH93
    |    `--A. anisotrichus Halašková 1977FH93
    |--Bakeras Błaszak 1984FH93
    |    `--B. opiparus Błaszak 1984FH93
    |--Bledas Halašková 1977FH93
    |    `--B. hesperius Halašková 1977FH93
    |--Caurozercon Halašková 1977FH93
    |    `--C. duplex Halašková 1977FH93
    |--Cosmozercon Błaszak 1981FH93
    |    `--C. setosus Błaszak 1981FH93
    |--Krantzas Błaszak 1981FH93
    |    `--K. mirificus Błaszak 1981FH93
    |--Lindquistas Błaszak 1981FH93
    |    `--L. amythetes Błaszak 1981FH93
    |--Macrozercon Błaszak 1975B75
    |    `--*M. praecipuus (Sellnick 1958) [=Prozercon praecipuus]B75
    |--Monozercon Błaszak 1984FH93
    |    `--M. aciculatus Błaszak 1984FH93
    |--Amerozercon Halašková 1969KA90
    |    `--*A. suspiciosus Halašková 1969B75
    |--‘Allozercon’ Błaszak 1984 non Vitzthum 1924FH93
    |    `--A. pulcher Błaszak 1984FH93
    |--Hypozercon Błaszak 1981FH93
    |    `--H. macleani Błaszak 1981FH93
    |--Parhozercon Błaszak 1981FH93
    |    `--P. medialis Błaszak 1981FH93
    |--Mesozercon Błaszak 1975B75
    |    `--*M. coreanus Błaszak 1975B75
    |--Metazercon Błaszak 1975B75
    |    `--*M. athiasae Błaszak 1975B75
    |--Mixozercon Halašková 1963FH93
    |    |--M. sellnicki Schweizer 1948B75 [=Zercon sellnickiS58]
    |    `--M. stellifer (Aoki 1964) [=Prozercon stellifer]FH93
    |--Echinozercon Błaszak 1975B75
    |    |--*E. orientalis Błaszak 1975B75
    |    `--E. americanus Błaszak 1983FH93
    |--Microzercon Błaszak 1975B75
    |    |--*M. californicus (Sellnick 1958) [=Prozercon californicus]B75
    |    `--M. krantzi Błaszak 1980FH93
    |--Parazercon Trägårdh 1931 [incl. Trizerconoides Jacot 1938]S58
    |    |--*P. sarekensis Willmann 1939B75 [=Zercon sarekensisS58]
    |    `--P. radiatus (Berlese 1904)S58 (see below for synonymy)
    |--Skeironozercon Halašková 1977KA90
    |    |--S. embersoni Halašková 1977FH93
    |    `--S. tricavus Błaszak 1983FH93
    |--Prozercon Sellnick 1943B75
    |    |  i. s.: P. aristatus Athias-Henriot 1961A64
    |    |         P. columbiatus (Berlese 1914)A64 [=Zercon columbianusS58]
    |    |         P. kochi Sellnick 1944A64 (see below for synonymy)
    |    |         P. ornatus (Berlese 1914)A64 [=Zercon ornatusS58]
    |    |         P. plumatusB75
    |    |--P. (Prozercon)U02
    |    |    |--*P. (P.) fimbriatus (Koch 1839) [=Zercon fimbriatus]S58
    |    |    |--P. (P.) denizliensis Urhan 2002U02
    |    |    `--P. (P.) tragardhi Halbert 1923U02
    |    `--P. (Plumatozercon)U02
    |         |--P. (P.) orhani Urhan & Ayyildiz 1996U02
    |         `--P. (P.) umidicola Urhan 2002U02
    `--Zercon Koch 1836 [incl. Triangulozercon Jacot 1938]S58
         |  i. s.: Z. affinisT05
         |         Z. beleviensis Urhan 2002U02
         |         Z. bulgaricus Balogh 1961B61
         |         Z. canadensis Halašková 1977FH93
         |         Z. capillatus Berlese 1914S58
         |         Z. carolinensis Halašková 1969FH93
         |         Z. clairae Halašková 1977FH93
         |         Z. comatus Halašková 1969FH93
         |         Z. crinitus Berlese 1920S58
         |         Z. diessenhofeneri Schweizer 1961S61
         |         Z. farrieri Halašková 1969FH93
         |         Z. foveolatus Halaskova 1969U01
         |         Z. guttulatus Athias-Henriot 1961U02
         |         Z. hammerae Sellnick 1960FH93
         |         Z. helveticus Schweizer 1961S61
         |         Z. insolitus Halašková 1969FH93
         |         Z. jurassicus Schweizer 1961S61
         |         Z. kevani Halašková 1977FH93
         |         Z. lepurus Błaszak 1979U01
         |         Z. lindquisti Halašková 1977FH93
         |         Z. lindrothi Lundqvist & Johnston 1985U02
         |         Z. lischanni Schweizer 1961S61
         |         Z. lundbecki Trägårdh 1906FH93
         |         Z. michaeli Halašková 1977FH93
         |         Z. nemoralis Urhan 2001U01
         |         Z. nivalis Schweizer 1961S61
         |         Z. nortoni Błaszak 1980FH93
         |         Z. ovalis Balan 1972U01
         |         Z. pinicolaM96
         |         Z. quadricrinus Berlese 1916S58
         |         Z. salmani Urhan 2002U02
         |         Z. septemporus Urhan 2001U01
         |         Z. shcherbakae Balan 1994U02
         |         Z. suecicus Sellnick 1944S61
         |--Z. (Zercon)S58
         `--Z. (Zerconella Willmann 1953)S58
              `--Z. (*Z.) leitnerae Willmann 1953S58

Parazercon radiatus (Berlese 1904)S58 [=Zercon radiatusS58, *Trizerconoides radiatusS58; incl. T. misgenatus Jacot 1938FH93, Zercon ornatus Trägårdh 1931 non Berlese 1904S58, Parazercon ornatusS58, Z. trigonus Berelese 1904S58, Prozercon trigonusS58]

Prozercon kochi Sellnick 1944A64 [incl. P. kochi var. pluripennatus Sellnick 1944S58, P. willmanni Schweizer 1948S58]

*Type species of generic name indicated

References

[A64] Aoki, J. 1964. Der erste Bericht über die Familie Zerconidae aus Japan (Acarina: Mesostigmata). Pacific Insects 6 (3): 489–493.

[B61] Balogh, J. 1961. Zercon bulgaricus spec. nov. (Mesostigmata, Acari). Folia Entomologica Hungarica (series nova) 14 (29): 433–435.

[B75] Błaszak, C. 1975. A revision of the family Zerconidae (Acari, Mesostigmata) (systematic studies on family Zerconidae—I). Acarologia 17 (4): 553–569.

[FH93] Farrier, M. H., & M. K. Hennessey. 1993. Soil-inhabiting and free-living Mesostigmata (Acari-Parasitiformes) from North America: an annotated checklist with bibliography and index. North Carolina Agricultural Research Service, North Carolina State University, Technical Bulletin 302: i–xvi, 1–408.

[JM91] Johnston, D. E., & M. L. Moraza. 1991. The idiosomal adenotaxy and poroidotaxy of Zerconidae (Mesostigmata: Zerconina). In: Dusbábek, F., & V. Bukva (eds) Modern Acarology: Proceedings of the VIII International Congress of Acarology, held in České Budĕjovice, Czechoslovakia, 6–11 August 1990 vol. 2 pp. 349–356. SPB Academic Publishing: The Hague.

[KA90] Krantz, G. W., & B. D. Ainscough. 1990. Acarina: Mesostigmata (Gamasida). In: Dindal, D. L. (ed.) Soil Biology Guide pp. 583–665. John Wiley & Sones: New York.

[LKW09] Lindquist, E. E., G. W. Krantz & D. E. Walter. 2009. Order Mesostigmata. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3rd ed. pp. 124–232. Texas Tech University Press.

[ML98] Moraza, M. L., & E. E. Lindquist. 1998. Coprozerconidae, a new family of zerconoid mites from North America (Acari: Mesostigmata: Zerconoidea). Acarologia 39: 291–313.

[M96] Munderloh, E. 1996. Gamasina (Mesostigmata) in a dune transect at Spiekeroog (Germany, Lower Saxony). In: Mitchell, R., D. J. Horn, G. R. Needham & W. C. Welbourn (eds) Acarology IX vol. 1. Proceedings pp. 589–594. Ohio Biological Survey: Columbus (Ohio).

[S61] Schweizer, J. 1961. Die Landmilben der Schweiz (Mittelland, Jura und Alpen): Parasitiformes Reuter, mit 246 Arten und Varietäten und 268 meist kombinierten Originalzeichnungen. Denkschriften der Schweizerischen Naturforschenden Gesellschaft [Mémoires de la Société Helvétique des Sciences Naturelles] 84: i–vii, 1–207.

[S58] Sellnick, M. 1958. Die familie Zerconidae Berlese. Acta Zoologica Academiae Scientiarum Hungaricae 3: 313–368.

[T05] Trägårdh, I. 1905. Monographie der arktischen Acariden. In: Römer, F., & F. Schaudinn (eds) Fauna Arctica. Eine Zusammenstellun der arktischen Tierformen, mit besonder Berücksichtigung des Spitzbergen-Gebietes auf Grund der Ergebnisse der Deutschen Expedition in das Nördliche Eismeer im Jahre 1898 vol. 4 pp. 1–78. Gustav Fischer: Jena.

Ujvári, Z. 2012. Draconizercon punctatus gen. et sp. nov., a peculiar zerconid mite (Acari: Mesostigmata: Zerconidae) from Taiwan. Opusc. Zool. Budapest 43 (1): 79–87.

[U01] Urhan, R. 2001. Two new species of the genus Zercon Koch from Turkey (Acari: Gamasida: Zerconidae). Genus 12 (4): 589–597.

[U02] Urhan, R. 2002. New zerconid mites (Acari: Gamasida: Zerconidae) from Turkey. Journal of Natural History 36: 2127–2138.

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