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Chapter 16. Phylum Arthropoda
Chapter · December 2016
DOI: 10.1016/B978-0-12-385028-7.00016-0
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306
Thorp and Covich’s Freshwater Invertebrates
Trombidiformes: Prostigmata
Ian M. Smith
Canadian National Collection of Insects, Arachnids and Nematodes, Agriculture and Agri-Food Canada, Ottawa, ON, Canada
David R. Cook
Paradise Valley, AZ, USA
Ilse Bartsch
Forschungsinstitut Senckenberg, Hamburg, Germany
KEY TO PROSTIGMATA COHORTS: LARVAE
1Idiosoma bearing a pair of epimeral pores and lacking urstigmata (Fig. 16.8.7) ..............................................................................................
.......................................................................................... supercohort Eupodides, superfamily Halacaroidea, family Halacaridae [p. 308]
1’Idiosoma bearing paired urstigmata between first two pairs of coxal plates and lacking epimeral pores (Figs. 16.11.4, 13.10, 16, 15.26,
16.41, 17.45, 20.72, 24.100, 32.165, 35.192).....................................................................................................................................................
.................................................... supercohort Anystides, cohort Parasitengonina, subcohorts Hydrachnidiae & Stygothrombiae [p. 312]
Prostigmata Cohorts: Adults
1Idiosoma variously shaped but never vermiform and lacking glandularia (Figs. 16.7.1, 2) ..............................................................................
������������������������������������������������������������������������������������������ supercohort Eupodides, superfamily Halacaroidea, family Halacaridae [p. 308]
1’Idiosoma variously shaped and bearing paired series of well-defined glandularia (Figs. 16.37.200, 38.207, 41.240, 42.244, 63.484) or
vermiform and bearing paired series of stomatoid lyrifissures (Fig. 16.38.204) ...............................................................................................
.................................................... supercohort Anystides, cohort Parasitengonina, subcohorts Hydrachnidiae & Stygothrombiae [p. 312]
Family Halacaridae
Ilse Bartsch
Forschungsinstitut Senckenberg, Hamburg, Germany
INTRODUCTION
Phylum Arthropoda
The Halacaridae (superfamily Halacaroidea) comprises a
large group of aquatic acariform mites ranging from 150–
2000 μm in length. The phylogenetic position of Halacaridae among Acariformes is not well understood, but they
are evidently not closely related to Hydrachnidiae or any
other group of mites with aquatic representatives. Halacarids are primarily marine, and more than 1000 species
have been described from salt water habitats worldwide.
Another 50–60 species occur exclusively, mainly, or at
least regularly, in freshwater (Bartsch, 2009). Formerly,
genera adapted for life in freshwater were classified in the
subfamily Limnohalacarinae Viets, 1927 (Viets, 1927).
In 1933, Viets proposed the family Porohalacaridae for
halacaroid mites with external genital acetabula to include
all freshwater species. This family proved to be a very artificial taxon including several paraphyletic genera whose
members were closely related to marine species with internal genital acetabula classified in the Halacaridae (Newell,
1947; Bartsch, 1989). Currently freshwater species and
genera are assigned to four essentially freshwater subfamilies of Halacaridae, namely Astacopsiphaginae, Limnohalacarinae, Porolohmannellinae, and Ropohalacarinae,
and three mainly marine subfamilies, namely Copidognathinae, Halacarinae, and Lohmannellinae (Viets, 1933;
Bartsch, 1989, 2006).
The first species of freshwater halacarid reported from
North America was the cavernicolous species Hamohalacarus subterraneus Walter, 1931. Newell’s keys to North
American freshwater halacarids (1947, 1959) included
members of six genera. The present work includes ten species representing eight genera that are found exclusively in
freshwater (Bartsch, 2011b).
The known species diversity of freshwater halacarid
mites is substantially lower in the Nearctic, with only ten
described species, than in the Palearctic, with more than 30
described species. All but one of the genera found in the
Nearctic also occur in the Palearctic, and in many cases they
are represented by the same species in both regions. Many
species of freshwater halacarids have broad global distributions spanning several continents (Bartsch, 2007b, 2009).
307
Phylum Arthropoda
TERMINOLOGY AND MORPHOLOGY
Adult halacarids exhibit the basic acarine body plan with
an idiosoma bearing four pairs of legs and a gnathosoma
bearing the palps and chelicerae (Figs. 16.7.1, 4). The
idiosoma is oblong and slightly to strongly flattened dorsoventrally. Freshwater halacarids have a body length
between 150 and 600 μm, with the notable exception of
Astacopsiphagus parasiticus Viets, 1931, a poorly known
species found in the gill chambers of an ­
Australian
decapod crustacean that may reach a length of 2000 μm
(Viets, 1931).
The idiosomal dorsum typically bears smooth, reticulate
or foveate plates including unpaired anterior and posterior
plates and a pair of ocular plates that may be reduced or
absent (Fig. 16.10.1). The dorsal integument usually bears
serial arrangements of six pairs of idiosomatic setae and five
pairs of gland pores, although the numbers may be reduced
in some species and supernumerary setae may be present in
others. The dorsal as well as ventral plates may be divided,
reduced, or enlarged and fused to a dorsal or ventral shield.
The idiosomal venter bears an anterior epimeral plate
formed by the fusion of epimera I and II, a pair of posterior epimeral plates formed by fusion of epimera III and
IV, and a genital or genitoanal plate formed by fusion of
the genital and anal plates. Epimeral pores may be present or absent. The genital plate bearing the genital opening
(Fig. 16.7.4) is sexually dimorphic, with females typically having a larger genital opening and a lower number
of setae around the genital opening than males. Internal to
the genital opening females have an ovipositor and males
have an elaborate spermatopositor, both of which are visible
through the genital plate.
The gnathosoma consists of the gnathosomal base, rostrum, palps, and chelicerae. There are two pairs of maxillary
setae, with one pair inserted on the gnathosomal base and the
other on the rostrum, or with both pairs inserted on the rostrum. The four segmented palps are inserted either laterally or
dorsally on the gnathosomal base. The first and third palpal
segments are relatively short compared to the longer second
segment (Fig. 16.7.3). The chelicerae are elongate and typically bear a terminal claw, but in some genera are styliform.
The first and second pairs of legs are directed anteriorly
and the third and fourth pairs are directed posteriorly. The
legs have six segments, namely the trochanter, basifemur,
telofemur, genu, tibia, and tarsus (Figs. 16.7.1, 4). The tarsi
bear paired claws terminally. The leg segments bear arrays
of setae of various lengths, thicknesses and form (smooth,
plumose or pectinate).
Halacarid mites are usually found in small numbers and
apparently play relatively minor roles in freshwater communities compared to Hydrachnidiae and Oribatida. Halacarids differ from other freshwater mites by the following
combination of character states: idiosomal plates present
but relatively weakly sclerotized, epimeral plates present;
first and second legs directed anteriorly and third and fourth
legs directed posteriorly; idiosomal dorsum bearing no
more than five pairs of gland pores and seven pairs of setae;
palps four segmented; and legs six segmented.
Most species of freshwater halacarids have a life history
with one larval and two nymphal stages in addition to the
adult. Larvae are smaller than adults and have three pairs
of five-segmented legs. They also differ from adults in the
shape and size of the dorsal and ventral idiosomal plates
(Figs. 16.8.5, 7; cf. Figs. 16.12.6, 8), the lack of a genital plate, the invariable presence of paired epimeral pores,
incomplete setation of the ventral idiosomal plates and
legs, and often in the relative lengths of the leg segments
(Figs. 16.8.11, 12). The shape and setation of the larval
gnathosoma is similar to that of adults (Figs. 16.8.9, 10)
(Bartsch, 2007a, 2011a).
Larvae often can be associated with adults of the same
species using the shape and setation of the tarsi and their
claws, the shape of the gnathosoma, and the arrangement of
setae and gland pores on the dorsum.
Protonymphs are characterized by four pairs of legs,
with the first three pairs six-segmented and the fourth pair
five-segmented. They exhibit epimeral pores in species that
retain these structures as adults, but have them reduced in
size or absent in other species. Protonymphs have a relatively small genital plate bearing only one pair of genital
acetabula and exhibit incomplete chaetotaxy of the idiosoma and legs.
Deutonymphs have four pairs of six-segmented legs.
Their dorsal and ventral idiosomal plates are slightly
smaller than those of adults and are always separate from
one another. The numbers of setae on the idiosoma and leg
segments are often similar to those in the adults.
MATERIAL PREPARATION
AND PRESERVATION
Halacarid mites should be preserved and stored in 70%
ethanol. Fixatives such as Formalin make the mites difficult
to clear.
Reliable identification of halacarid mites requires microscopic examination. Specimens can be examined in a drop
of glycerine, but for species level identification must be
cleared and slide-mounted. Halacarids are typically cleared
in pepsin or lactic acid and gentle warming (40–50 °C) may
facilitate the process. The gnathosoma is then removed
using a sharp needle and the body contents are squeezed out
with help of gentle pressure using a blunt needle.
Cleared specimens can be mounted for study and permanent storage in glycerine jelly or Hyrax. After initial
Phylum Arthropoda
Chapter | 16
308
hardening of the mounting medium, the coverslip should
be ringed using a standard microscopical sealing agent.
Berlese’s medium, modified Hoyer’s fluid, polyvinyl lactophenol, or glycerine can be used for temporary mounts.
Specimens cleared in lactic acid must be rinsed to prevent
formation of crystals in the mounting medium. Staining
Thorp and Covich’s Freshwater Invertebrates
with chlorazol black often facilitates the interpretation of
morphological structures in over-cleared specimens.
Mounting specimens between two cover slips is recommended to facilitate examination of both dorsal and ventral
surfaces. These preparations can be stored in metal slide
frames or attached to a glass slide using a drop of glycerine.
KEYS TO HALACARIDAE
Arachnida: Acari: Halacaridae: Genera and Species
1Gnathosoma relatively wide, only 0.9–1.8 times longer than wide and little more than one-third as long as idiosoma (Figs.16.7.1, 4); integument pale in colour and with brown or green spots indicating gut contents and eye pigment visible through integument ............................2
1’Gnathosoma relatively slender, 2.5 times longer than wide and about half as long as idiosoma (Figs. 16.8.8, 10); integument violet or pink
in colour ....................................................................................................................................... Porolohmannella violacea (Kramer, 1879)
[Canada: Alberta, British Columbia, Manitoba, Newfoundland, Northwest Territories, Ontario, Quebec. USA: New Hampshire, New York,
Rhode Island]
2(1)Palps inserted laterally on gnathosoma and in ventral view with most of first segment visible (Fig. 16.9.13); genital acetabula borne on
genital sclerites in females (Fig. 16.9.16) and on genital plate immediately posterior to genital opening in known males ...........................3
2’Palps inserted dorsally on gnathosoma and in ventral view with first segment almost entirely invisible (Figs. 16.7.1, 4); genital acetabula
borne on genital plate, posterior, lateral, or anterior to genital opening in females and males (Figs. 16.7.4, 9.24) ........................................5
3(2)Idiosoma anterior margin arched or truncate (Figs. 16.7.1, 9.14); first leg with tarsus lateral fossary membrane not enlarged and with tarsus
bearing one ventral seta and pair of parambulacral setae (Fig. 16.9.15) ........................................................................................................ 4
3’Idiosoma anterior margin with a frontal spine (Fig. 16.9.16); first leg with tarsus lateral fossary membrane enlarged to about twice height
of dorsomedial membrane (Fig. 16.9.17, arrow) and with tarsus bearing one ventromedial spiniform seta, two ventral setae, and pair of
parambulacral setae ................................................................................................................ Lobohalacarus weberi (Romijn & Viets, 1924)
[Canada: British Columbia, New Brunswick, Newfoundland, Ontario, Quebec. USA: Alabama, Arizona, California, Colorado, Georgia,
Illinois, New Hampshire, New Mexico, New York, North Carolina, Rhode Island, Tennessee, Virginia]
4(3)Ocular plates with conspicuous cornea and black eye spots (Fig. 16.9.14) ........................................... Porohalacarus alpinus (Thor, 1910)
[Canada: Ontario, Quebec. USA: New Hampshire, Rhode Island]
4’Ocular plates reduced to delicate sclerites (Fig. 16.9.19) lacking eye spots .............................. Ropohalacarus uniscutatus (Bartsch, 1982)
[USA: New York, Rhode Island]
5(2)First leg with telofemur and tibia cylindrical and less than twice as long as genu (Figs. 16.9.21, 23) ...........................................................6
5’First leg with telofemur and tibia clavate and more than three times as long as very short genu (Fig. 16.9.20) ..............................................
��������������������������������������������������������������������������������������������������������������������������������������������� Parasoldanellonyx parviscutatus (Walter, 1917)
[USA: Rhode Island]
6(5)First leg with tarsal claws bearing either thick tines or slender tines and a lamellar ventral process (Figs. 16.7.2, 9.25) ..............................7
6’First leg with tarsal claws very slender and with tines very delicate or absent (Fig. 16.9.18) ............................................................. ��������������������������������������������������������������������������������������������������������������������������������������� Hamohalacarus subterraneus Walter, 1931
[USA: Indiana]
7(6)First leg with tarsal claws pectinate and bearing thick tines (Fig. 16.7.2); anal sclerites at least half as large as genital sclerites (Fig. 16.7.4);
genital acetabula borne in posterolateral regions of genital plate ............................................................................... Soldanellonyx [p. 308]
Phylum Arthropoda
7’First leg with tarsal claws bearing slender tines and a lamellar ventral process (Fig. 16.9.25); anal sclerites minute (Fig. 16.9.24,
arrow), much smaller than genital sclerites; genital acetabula borne along lateral margins of genital plate ���������������������������������������
............................................................................................................................................. Limnohalacarus cultellatus Viets, 1940
[USA: Georgia, Wisconsin]
Arachnida: Acari: Halacaridae: Soldanellonyx: Species
1First leg with telofemur 1.7–1.8 times longer than genu and tibia with four ventral spines (Fig. 16.9.23) ....................................................2
Chapter | 16
Phylum Arthropoda
309
1’First leg with telofemur of leg I about 1.3 times longer than genu and tibia with two ventral setae (Fig. 16.9.21) �����������������������������������������
................................................................................................................................................................. Soldanellonyx monardi Walter, 1919
[Canada: British Columbia, New Brunswick, Newfoundland, Ontario, Quebec. USA: Alabama, Arizona, California, Georgia, Indiana,
Missouri, New Hampshire, New York, North Carolina, Oregon, Pennsylvania, Rhode Island, Tennessee, Texas, Virginia]
2(1)First leg ventral spines with blunt or slightly spinose tips; palp with third segment bearing spine near or just proximal to mid-length
.............................................................................................................................................................. Soldanellonyx chappuisi Walter, 1917
[Canada: Nova Scotia, Ontario, Quebec. USA: Colorado, Indiana, North Carolina, Oregon]
2’First leg ventral spines with tapering tips; palp with third segment bearing spine well proximal to mid-length (Fig. 16.9.22) .......................
������������������������������������������������������������������������������������������������������������������������������������������������������������������� Soldanellonyx visurgis Viets, 1959
PLATE 16.07 Figures 1–4: Soldanellonyx monardi Walter, female adult. Fig. 1 dorsum of gnathosoma and idiosoma. Fig. 2 tarsus of first leg, lateral
view. Fig. 3 gnathosoma, lateral view. Fig. 4 venter of gnathosoma and idiosoma.
Phylum Arthropoda
[USA: Arizona, Georgia, New York, Rhode Island]
310
Thorp and Covich’s Freshwater Invertebrates
PLATE 16.08 Figures 5–12: Porolohmannella violacea (Kramer). Fig. 5 larva, dorsum of idiosoma. Fig. 6 female adult, dorsum of idiosoma. Fig. 7
larva, venter of idiosoma. Fig. 8 female adult, venter of gnathosoma and idiosoma. Fig. 9 larva, venter of gnathosoma. Fig. 10 female adult, venter of
gnathosoma. Fig. 11 larva, first leg, medial view. Fig. 12 female adult, first leg, medial view.
REFERENCES
Phylum Arthropoda
Bartsch, I. 1982. Halacariden (Acari) im Süßwasser von Rhode Island,
USA, mit einer Diskussion über Verbreitung und Abstammung der
Halacaridae. Gewässer und Abwässer 68/69: 41–58.
Bartsch, I. 1989. Süsswasserbewohnende Halacariden und ihre Einordnung
in das System der Halacaroidea (Acari). Acarologia 30: 217–239.
Bartsch, I. 2006: 5. Acari: Halacaroidea. Pages 113–157 in: Gerecke, R.
(ed.), Chelicerata: Araneae, Acari I. Süßwasserfauna Mitteleuropas,
7/2-1. Spektrum Elsevier, Heidelberg.
Bartsch, I. 2007a. The freshwater mite Porolohmannella violacea (Kramer,
1879) (Acari: Halacaridae), description of juveniles and females and notes
on development and distribution. Bonner zoologische Beiträge 55: 47–59.
Bartsch, I. 2007b. Freshwater Halacaridae (Acari) from New Zealand rivers and lakes, with notes on character variability. Mitteilungen aus
dem Hamburgischen Zoologischen Museum und Institut 104: 73–87.
Bartsch, I. 2009. Checklist of marine and freshwater halacarid mite genera
and species (Halacaridae: Acari) with notes on synonyms, habitats,
distribution and descriptions of the taxa. Zootaxa 1998: 1–170.
Bartsch, I. 2011a. The freshwater halacarid mite Soldanellonyx chappuisi Walter, 1917 (Acari: Halacaridae), character development from
larva to adult and comparison with other halacarids. Entomologische
Mitteilungen aus dem Zoologischen Museum Hamburg 15(184):
223–235.
Bartsch, I. 2011b. North American freshwater Halacaridae (Acari): literature survey and new records. International Journal of Acarology 37:
490–510.
Kramer, P. 1879. Ueber die Milbengattungen Leptognathus Hodge, Raphignathus Dug., Caligonus Koch und die neue Gattung Cryptognathus.
Archiv für Naturgeschichte 45: 142–157.
Newell, I. M. 1947. A systematic and ecological study of the Halacaridae
of eastern North America. Bulletin of the Bingham Oceanographic
Collection 10: 1–232.
Newell, I. M. 1959. Chapter 42: Acari. Pages 1080–1116 in: H.B. Ward,
H.B & G.C. Whipple (eds.), Fresh-water Biology. Second edition.
John Wiley and Sons, New York.
Romijn, G., K.H. Viets. 1924. Neue Milben. Archiv für Naturgeschichte
90: 215–225.
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311
Thor, S. 1910. Die erste norwegische Süßwasserform der Halacariden.
Zoologischer Anzeiger 36: 348–351.
Viets, K. 1927. Die Halacaridae der Nordsee. Zeitschrift für Wissenschaftliche Zoologie 130: 83–173.
Viets, K. 1931. Über eine an Krebskiemen parasitierende Halacaride aus
Australien. Zoologischer Anzeiger 96: 115–120.
Viets, K. 1933. Vierte Mitteilung über Wassermilben aus unterirdischen
Gewässern (Hydrachnellae et Halacaridae, Acari). Zoologischer
Anzeiger 102: 277–288.
Viets, K. 1940. Zwei neue Porohalacaridae (Acari) aus Südamerika. Zoologischer Anzeiger 130: 191–201.
View publication stats
Viets, K. 1959. Die aus dem Einzugsgebiet der Weser bekannten oberirdisch
und unterirdisch lebenden Wassermilben. Veröffentlichungen des Instituts für Meeresforschung in Bremerhaven 6: 303–513.
Walter, C. 1917. Schweizerische Süßwasserformen der Halacariden.
Revue Suisse de Zoologie 25: 411–423.
Walter, C. 1919. Schweizerische Süßwasserformen der Halacariden.
Revue Suisse de Zoologie 27: 235–242.
Walter, C. 1931. Arachnides halacariens. Biospeologica LVI. Campagne spéologique de C. Bolivar et R. Jeannel dans l’Amérique du
Nord (1928). Archives de Zoologie Expérimentale et Générale 71:
375–381.
Phylum Arthropoda
PLATE 16.09 Figures 13–15: Porohalacarus alpinus (Thor), female adult. Fig. 13 venter of gnathosoma. Fig. 14 dorsum of idiosoma. Fig. 15 tarsus of
first leg, lateral view. Figures 16–17: Lobohalacarus weberi (Romijn & Viets), female adult. Fig. 16 venter of idiosoma. Fig. 17 tarsus of first leg, lateral
view. Fig. 18: Hamohalacarus subterraneus Walter, female adult, tarsus of first leg (from Walter, 1931). Fig. 19 Ropohalacarus uniscutatus (Bartsch),
female adult, dorsum of idiosoma. Fig. 20 Parasoldanellonyx parviscutatus (Walter), female adult, first leg, medial view. Fig. 21 Soldanellonyx monardi
Walter, female adult, first leg, medial view. Fig. 22 Soldanellonyx visurgis Viets, female adult, gnathosoma, lateral view. Fig. 23 Soldanellonyx chappuisi
Walter, female adult, first leg, dorsal view. Figures 24–25: Limnohalacarus cultellatus Viets, female adult. Fig. 24 venter of idiosoma. Fig. 25 tarsus of
first leg, lateral view.