Analyzing Unionicola Phylogeny I: The Genus

Malcolm F. Vidrine and Dale D. Edwards

The detailed analyses that involves the content in this work is provided in our book entitled Mites of Freshwater Mollusks (Edwards and Vidrine 2013—the book is out of print, but copies are available at several locations online (and if you need a digital copy, we will be happy to send one via email in a Dropbox® account)). Our goal here is to provide a short discussion that is simple and easy to translate internationally.

Mites commonly occurring in freshwater mollusks and sponges are diverse and in many ways poorly understood. One group, Unionicola (Unionicolidae: Unionicolinae), has however received considerable attention. While molecular phylogenetic analysis is at its infancy, several morphological studies, including the genus-wide analyses by us (Edwards and Vidrine 2013), have been conducted. Three major studies (Edwards and Vidrine 2006, Edwards et al. 2010 and Wu et al. 2009, 2012) initiated the re-evaluation of the phylogeny of the genus, but these studies were limited to 8-11 subgenera each. The genus contains 57 subgenera, with approximately more than half of both the subgenera and the species known to be associated with mollusks—a rather unusual lifestyle.

Some basic questions and our answers (in red) based upon the trees:

Does the genus Unionicola appear to be a single evolutionary unit (clade)? Yes

Do the subgeneric categories as established reflect the implied phylogeny of the analyses? Yes

Are the mollusk mites represented as a separate phylogenetic unit/group? Yes

Do biogeographic range distributions of the mites appear to support or refute the findings of the analyses? Support

Do host range distributions of the mites appear to support or refute the findings of the analyses? Support

Do behavioral range distributions, e.g., mantle mites vs gill mites, of the mites appear to support or refute the findings of the analyses? Support

Our understanding of the evolutionary relationships among Unionicola water mites is limited and has largely been derived from morphology-based classifications among members that comprise the group. For example, Vidrine (1996b) suggested that sponge-associated mites of the subgenus Hexatax (formerly Unionicola) represent the least-derived taxon within the genus—interestingly, Wilsonatax also appears to be morphologically similar to some Neumania species (see the comparative plates provided in the 2 previous pieces on the site). Morphologically, these mites closely resemble species of free-swimming species from the genus Neumania (Unionicolidae: Pionatacinae). Vidrine (1996b) subsequently identified twenty groupings of Unionicola subgenera based on sets of shared morphological and life-history characters. Despite these rather broad assessments of unionicoline systematics, the evolutionary history of the genus has not been adequately tested using phylogenetic approaches (Edwards and Vidrine 2013).

Addressing evolutionary relationships among Unionicola mites based on morphological criteria is not without its challenges, given that so few characters historically have been used to diagnose the genus and its subgenera (Cook, 1974). Also, a cursory glance at the taxonomic studies involving Unionicola mites suggests that a limited number of characters are available for phylogenetic inference. It should, however, be noted that there have been no previous attempts to diagnose subgenera and species using a large number of morphological characters and to subsequently address patterns of variability of these characters across taxa. We recently went through the taxonomic literature for Unionicola mites and generated 158 characters (157 morphological characters and one life history character) that could be used to estimate evolutionary relationships among the currently named subgenera (N=57) that comprise the genus, especially relationships between free-swimming taxa and those that have adopted symbiotic lifestyles (Edwards and Vidrine 2013).

A tree based on the Bayesian analysis of morphological data of Unionicola subgenera is presented in Figure 1. Although posterior

probability values do indicate strong support for most of the clades involving terminal taxa, many deeper branches presented in this tree are weakly supported. In general, the Bayesian tree suggests that most of the free-swimming Unionicola subgenera are a distinct radiation. Although the tree recognizes multiple clades of free-swimming mites, there appears to be no distinct relationship between he taxa that comprise these clades and their geographic distribution. The tree also shows several lineages of free-swimming mites forming a basal grade with the molluscan mites. Mollusk mites appear to represent a monophyletic grouping and are divided into two major clades, with Australian gill mite subgenera along with gill mites from South America and North America forming one clade and Unionicola mantle mites and gill mites from Africa, Eurasia, and North America forming the other. Two species of gill mites (U. anodontae and U. botswaniana) from the subgenus Iridinicola appear to be sister taxa to the mantle mites. This latter group of mites appears to represent the most derived lineage within the genus (Edwards and Vidrine 2013).

Cryptic species within currently accepted species, e. g., U. hoesei, U. arcuata and U. minor, may well exemplify the nature of species taxa in the genus. With molecular analyses, we are on the verge of beginning to understand not only the true diversity within the genus but also the nature of the coevolution of mollusks and mites.

Many of the subgenera are sorted based upon the female genital field structures. Van Reed prepared this plate in order to show the variety of female genital fields in the genus. Female genital field morphology accounted for the first 20 character states in the list (see below).

Plate 1: female genital fields by category.

Figure 8.3. Bayesian tree based on 158 morphological characters for representative species from 53 subgenera of Unionicola mites. Subgeneric designations for each of the representative species are indicated in parentheses. *Temporarily assigned to this subgenus pending reassignment. Figure from Edwards and Vidrine (2013).

Separations denoted by letters

A. The separation between Neumania and Unionicola.B. The separation between free-swimming mites and mollusk-

associated mites.C. Mollusk-associated mites: gill mites from Australia, South America

and North America separated from mites from other regions of the world.

D. Mollusk-associated mites: mantle mites separated from gill mites.E. Mollusk-associated mites: gill mites from Africa, Europe, Asia and

North America.

Comments

1. Unfortunately, Unionicolopsis, Downesatax, Polyatacides and Ferradasatax were not in the final analysis.

2. Curryatax does not have enough information—the original description lacks details except for drawing of weird pedipalps—unfortunately little is learned from its presence in the tree. It may have been more logical to not use it in the final analysis.

3. Unionicola (Wilsonatax) poirrieri is near the base of the tree and close to Neumania. Members of the subgenus Hexatax (namely U. laurentiana group, which includes U. crassipes and U. affinis) are next to break out. These mites are considered to possess the basic or relict body plan of the ancestral Unionicola.

4. Ampullariatax (snail mites are indeed close to Vidrineatax in morphology). Little is known about these mites. We suspect they are mantle mites, but they are indeed divergent in this tree. Female genital fields have many acetabula and resemble those of females of the subgenus Polyatacides. In this case, they group with free-swimming mites. Davidsatax and Conroyatax are also divergent and as such provide little information in this tree.

5. Free-swimming mites are displayed in 20 clades—many of these represent named subgenera. Hexatax appears within several groups as many species currently placed in that subgenus are sufficiently different to be awarded status as new subgenera.

6. With the break-up of Pangaea some 250 mya, the mollusk-associated mites are already established as a clade and as a lifestyle. This large group of more than 130 species is marked at the separation labelled B.

7. The mollusk-associated mites are divided into guilds: mantle mites including the mussel and snail mites and gill mites. In the tree, the mantle mites, a diverse group, is however separated from the gill mites in the separation labelled D.

8. The mollusk-associated mites that are considered gill mites are divided into at least 2 distinctive groups labelled C and E—this separation involves both geographic-isolation and host-isolation. The geographic isolation is noted within the table below.

9. Whereas the mollusk-associated mites will be discussed in a later piece, we want to mark groupings of free-swimming mites evident in this tree: Wilsonatax Hexatax s. s. (e. g., U. laurentiana-crassipes-affinis group) Bakeratax, Bassatax, Cookatax and Everittatax. Australionicola, Heteratax, Poundsatax, Crameratax,

Gledhillatax, Crowellatax and Lundbladatax. Armatax, Edwardsatax, Lasalleatax, Mitchellatax and Giselatax.

10. Unfortunately, too few species were used in the analysis of the free-swimming mites to make many generalizations. Further, many of the subgenera have few described species.

Figure 8.2 Bayesian tree based on 158 morphological characters for representative species from 53 subgenera of Unionicola mites. Numbers above branches represent posterior probability values. Letters indicate notable clades: A=free-swimming mites; B=Mollusk mites; C=Australian, South American, and North American gill mites; D=mantle mites; E=African, Eurasian, and North American gill mites. Abbreviations in parentheses: FS=free-swimming mites; G=gill mites; M=mantle mites; NA=North America; SA=South America; AFR=Africa; AUSTR=Australia. Figure from Edwards and Vidrine (2013).

Appendix 6 (from Edwards and Vidrine 2013)

METHODS USED TO CONSTRUCT PHYLOGENETIC TREES AMONG

1) UNIONICOLA MITES AND 2) UNIONICOLA MOLLUSK MITES

Ingroup and Outgroup Taxa

Fifty-three of the 57 currently recognized Unionicola subgenera were used as terminal taxa to construct a morphological phylogeny for the genus, and were, in most cases, represented by their type species (Figures 8.2 and 8.3). Morphological data for mites from 30 subgenera were used to estimate the phylogeny among Unionicola mollusk mites (Figures 8.4 and 8.5). Seven of these subgenera are monotypic, thus a single species served as terminal taxa for these subgenera. Eight of the subgenera are relatively speciose, containing five or more (10.4+2.9SE, range=5-29) described species. For these subgenera, we used a minimum of four species for phylogenetic inference. The remaining 16 subgenera are represented by 2 to 4 species. In most instances, data from all species assigned to these subgenera were included in the analysis. Three subgenera of Unionicola (Downesatax. Ferradasatax and Polyatacides) were not included in this study because many of the character states of mites from these taxa were difficult to characterize. The water mite genus Neumania (Unionicolidae: Pionatacinae) was assigned as the outgroup taxon and was used to root the analysis. The subfamily Pionatacinae represents the sister taxon of the Unionicolinae. Mites of the genus Neumania are morphologically similar to the least-derived subgenus (e.g., Hexatax) of Unionicola (Vidrine 1996b) and a morphologically-based tree generated by Proctor and Wilkinson (2001) indicates that the genus Neumania is the sister taxon to mites of the genus Unionicola.

Character choice and coding

The character matrix used to construct the Unionicola tree (N=61 species from 53 subgenera) was comprised of 158 characters (156 morphological characters and 2 life history characters), whereas the mollusk-mite tree (N=90 species from 30 subgenera) was estimated based on 139 characters (137 morphological characters and 2 life history characters). These character state matrices are not provided here, but have been made available online:

1) Unionicola mite matrix: http://www.evansville.edu/majors/biology/downloads/Unionicola_character_matrix.pdf

2) Unionicola mollusk mite matrix: http://www.evansville.edu/majors/biology/downloads/Mollusk_character_Matrix.pdf .

Some of the characters that were used to reconstruct evolutionary relationships among Unionicola mites were based on those used either by Edwards and Vidrine (2006) or Wu et al., (2009) to address evolutionary relationships among mussel mites of North America and China, respectively. Additional characters, along with their states, were generated by reviewing the taxonomic literature for Unionicola, especially that which provided diagnoses of the genus and its subgenera, including Cook (1974), Vidrine (1980a, 1986e, 1996c and in this work). The characters (see the list provided below) used for phylogenetic reconstruction of Unionicola mites were based on features of female genital fields, male genital fields, pedipalps, pedipalp clawlets, venters with coxal plates, walking legs, tarsal claws, dorsums with plates, sexual dimorphisms of legs, body size, host associations and oviposition sites. Character states for Neumania, the outgroup taxon, were primarily obtained from descriptions by Cook (1974) and from specimens of Neumania sp. in Vidrine’s collection (see previous piece on this site). We used two methods for coding character differences in our morphological and life history data, following the recommendations of Strong and Lipscomb (1999): 1) binary coding with inapplicable scenarios treated as “?”, and 2) ordered multistate character coding where absences were treated as a separate character. The sequence of states in binary code or transformation series were left unordered because it was, in many cases, difficult to determine a nested (ordered) set of synapomorphies based on outgroup comparison.

List of Characters and Character States

Female genital fields

1. Female genital field with sclerotized acetabular plates containing acetabula: 0=yes; 1=no.

2. Number of pairs of acetabular plates: 0=absent; 1=2 pairs; 2=1 pair; 3=1 pair with sutures suggesting the presence of 2 pairs.

3. Acetabular plates appressed medially into a concise field: 0=no; 1=yes; 2=no, but plates appear to be derived (from ancestors with medially appressed plates).

4. Sclerotization of acetabular plates: 0=obviously sclerotized; 1=weakly sclerotized (well sclerotized only along the medial margins of the plates); 2=not sclerotized.

5. Genital field with obvious medial setae: 0=yes; 1=no.

6. Genital field with medial flaps: 0=no; 1=yes.

7. Number of pairs of acetabula on genital plates: 0=3-7; 1=8-12; 2=13-20; 3=>20.

8. Arrangement of acetabula on genital plates: 0=spread out evenly across the genital plates; 1=in clusters, except along the medial flaps; 2=in a line along the lateral margin of the genital plates.

9. Acetabula all the same size: 0=yes; 1=no.

10. Medial flaps in genital field: 0=absent; 1=present but inconspicuous; 2=present and conspicuous.

11. Location of medial flaps in genital field: 0=positioned centrally; 1=positioned anteriorly; 2=positioned posteriorly; ?=inapplicable, medial flaps absent.

12. Medial flaps modified into a spine-like, chitinized projection: 0=no; 1=yes, for those with 2 acetabular plates; 2=yes, on anterior acetabular plates only for those with 4 plates; ?=inapplicable, medial flaps absent.

13. Type of setae on the medial flaps: 0=no spinous setae; 1=at least one pair of spinous setae; ?=inapplicable, medial flaps absent.

14. Characteristics of medial setae on flaps on acetabular plates: 0=only hairlike setae found on acetabular flaps; 1=only spinous setae found on acetabular flaps; 2=a mixture of hair-like and spinous setae found on acetabular flaps; ?=inapplicable, medial flaps absent.

15. Arrangement of seta in the anterior acetabular plate: 0=arranged in a row of 4 setae on the medial edge of flaps; 1=not arranged in a row of 4 setae on the medial edge of flaps; ?=inapplicable, no anterior plates present.

16. Medial flaps on acetabular plates: 0=small medial flaps with setae on 4 plates (as in Hexatax); 1=long medial flaps with setae on 4 plates (as in Hyricola); 2=flaps not as described above; ?= inapplicable, no flaps present.

17. Types of medial setae on acetabular plates (or on anterior acetabular plates if 4 plates are present): 0=hairlike; 1=thickened; 2=spinous; 3=mix of various setae, ?=inapplicable, medial setae absent.

18. Female genital field wider than it is long: 0=no; 1=yes but <3 times as wide as long; 2=yes, >3 times as wide as long).

19. Acetabula confined to acetabular plates: 0=no; 1=yes.

20. Female genital field with 4 near equal plates: 0=no; 1=yes, each with <7 pairs of acetabula; 2=yes, each with 7 or more pairs of acetabula.

21. Posterior glandularia (one on either side of genital field) on obvious cuplike structures: 0=yes; 1=reduced to very small to inconspicuous but still present; 2=absent.

Male genital fields

22. Male genital field with sclerotized acetabular plate(s) containing acetabula: 0=yes; 1=no.*

23. Sclerotization of acetabular plates: 0=obviously sclerotized; 1=weakly sclerotized (well sclerotized only along at least one of the margins of the plates); 2=not sclerotized.

24. Genital field with obvious medial setae: 0=yes; 1=no.

25. Number of pairs of acetabula: 0=3-7; 1=8-12; 2=13-20; 3=>20.

26. Arrangement of acetabula: 0=spread out evenly across the genital field; 1=in clusters; 2=in a line along the lateral margin of the genital field.

27. Acetabula all the same size: 0=yes; 1=no.

28. Location of the gonopore in the genital field: 0=central; 1=anterior; 2=posterior; 3=on the dorsum.

29. Male genital field wider than it is long: 0=no; 1=yes, <3 times as wide as long; 2=yes >3 times as wide as long).

30. Acetabula confined to acetabular plates: 0=no; 1=yes.

31. Male genital field extending onto the dorsum: 0=no; 1=yes.

32. Male genital field with 1 obvious seta or spine/side/plate: 0=no; 1=yes, in center of genital field; 2=yes, displaced posteriorly.

33. Male genital field with 2 obvious setae or spines/side/plate: 0=no; 1=yes, in center of genital field; 2=yes, located anteriorly; 3=yes, located posteriorly.

34. Number of setae on male genital field: 0=># (for numerous); 1=<# (for few (not numerous) and inconspicuous).

35. Arrangement of acetabula such that at least one acetabulum is out of linear arrangement if acetabula are in a line: 0—no, 1—yes, ?=inapplicable (acetabular arrangement not in a row or scattered).

36. Arrangement of acetabula: 0=not in a line along the margin of the plates, but spread out in the field; 1=in a line.

37. Male genital field with obvious sutures on plates on either side: 0=no; 1=yes.

Pedipalps and clawlets and chaetotaxy

38. Female pedipalps: 0=greater than half the length of the idiosoma;1=greater than one-quarter the length of the idiosoma; 2=less than one-quarter the length of the idiosoma.

39. Female palpal tarsus with ventral swelling containing setae: 0=no; 1=yes.

40. Female pedipalps swollen at the base (femur segment noticeably wider than other segments): 0=no; 1=yes.

41. Pedipalps sexually dimorphic: 0=no; 1=yes.

42. Shape of pedipalps: 0=subcylindrical; 1=dorsoventrally flattened.

43. Female longest palpal tarsal clawlet: 0=shorter than length of tarsus; 1=longer than length of tarsus.

44. Female palp tarsus longer than tibia: 0=no; 1=yes.

45. Female palpal tarsus greater than half the length of tibia: 0=yes; 1=no.

46. Female pedipalp tarsus tapered distally (toward a point) with clawlets not prominent: 0=yes; 1= no.

47. Female pedipalp clawlets (2 most obvious) near equal in size: 0=yes; 1=no; 2=only one clawlet present.

48. Female number of obvious tarsal clawlets: 0=3-4; 1=2; 2=1; 3=reduced to chitinous pustules.

49. Female palpal tibia with large, dorsal extension: 0=no; 1=yes.*

50. Female palpal tibia with a ventral protrusion containing setae: 0=yes; 1=no.

51. Female palpal tarsus fist-shaped (e.g., thicker distally than proximally): 0=no; 1=yes.*

52. Female at least one tarsal clawlet >2X length of tarsus: 0=no; 1=yes.

53. Chelicera fused medially: 0=yes; 1=no.*

54. Male pedipalp with large clawlike (sicklelike) clawlet much longer than tarsus: 0=no; 1=yes.*

Venter, coxal plate shapes and projections

55. Shapes of male and female coxal plates similar: 0=yes; 1=no.

56. Shape of posterior coxal group (coxal plates III and IV): 0=boxlike; 1=pointed posteriorly; 2=rounded posteriorly; 3=posterior border indistinct.

57. Female coxal plates fused into groups: 0=4 groups; 1=3 groups; 2=2 groups; 3=I group.

58. Male coxal plates fused into groups: 0=4 groups; 1=3 groups; 2=2 groups; 3=I group.

59. Female coxal plate anterior group (coxal plates I and II) with posterior projection: 0=yes; 1=no.

60. Female coxal plate posterior group (coxal plates III and IV) with posterior projection: 0=yes; 1=no.

61. Posterior projection of coxal plate anterior group (coxal plates I and II): 0= extending beyond the coxal plate III and IV suture; 1= extending to the suture between coxal plate III and IV; 2=extending to coxal plate III; ?=inapplicable, posterior projection absent.

62. Complete suture between coxal plates III and IV: 0=yes; 1= no.

63. Knob-like extensions on medial coxal plate I: 0=present; 1=absent.

64. Coxal plates groups with tooth-like lateral projections: 0=yes; 1=no.

65. Female medial edges of coxal plates III and/or IV apparent and well-sclerotized and not fused to the other posterior coxal plate group: 0=no; 1=yes.

66. Coxal plate IV elongated (>2x length of coxal plate III): 0=no; 1=yes.

67. Lateral gap between coxal plates III and IV: 0=no; 1=yes. 68. Chitinous anterior extension on coxal plate III: 0=absent; 1=present.

Legs and tarsal claws and chaetotaxy

69. Male and female leg I similar: 0=yes; 1=no.

70. Female genu of leg I with hairlike setae only: 0=no; 1=yes.

71. Female tibia of leg I with hairlike setae only: 0=no; 1=yes.

72. Female tarsus of leg I straight (not curved, bent, concave or arcuate or swollen at the base): 0=yes; 1=no.

73. Female tibia of leg I straight (not curved, bent, concave or arcuate or swollen at the base): 0=yes; 1=no.

74. Female tibia of leg I longer than genu: 0=no; 1=yes.

75. Female tibia of leg I longer than tarsus: 0=no; 1=yes.

76. Female number of large setae on genu: 0=2pairs; 1=1 pair; 2=0; 3=>2 pairs.

77. Female number of large setae on tibia: 0=2pairs; 1=1 pair; 2=0; 3=>2 pairs.

78. Female leg I with long, large, moveable, blunt setae on raised cuplike structures: 0=no, setae pointed and not raised on cuplike structures; 1=inapplicable; 2=yes; 3=no, setae pointed and raised on cuplike structures, ?=inapplicable, no large, long setae on leg I.

79. Female leg I genu, tibia, and tarsus exclusively with hairlike setae: 0=yes; 1=no.

80. Female leg I with telofemur, genu, and tibia all nearly as wide as long: 0=no; 1=yes.

81. Distal, dorsal, spoonlike setae over tarsal claws: 0=absent; 1= present.

82. Female distal, ventral, blunt setae on tibia of leg I: 0=absent; 1=present, setae smooth; 2=present, setae ornate.

83. Leg I distinctly wider than other walking legs: 0=yes; 1=no.

84. Female leg I with blunt setae on genu and tibia only: 0=no; 1=yes; ?=not applicable

85. Female leg I with one or more rows of at least 4 straight hairlike setae: 0=no; 1=yes, one row; 2=yes, two or more rows.

86. Female leg I longer than length of idiosoma: 0=yes; 1=no.

87. Female leg IV more than 2X length of idiosoma: 0=yes; 1=no.

88. Female leg IV with arcuate tarsus: 0=no; 1=yes.

89. Female leg IV with 2-3 long setae at distal end of genus and tibia: 0=yes; 1=no; 2=23 setae present but obviously reduced in length.

90. Male and female leg III similar: 0=yes; 1=no.

91. Male and female leg IV similar: 0=yes; 1=no.

92. Leg IV of female with conspicuous setae: 0=yes; 1=no.

93. Legs III-IV of both sexes with at least one row of four straight, hairlike setae on the genu and tibia: 0=no; 1=yes.

94. Female leg IV with large, blunt, dorsal, distal spines on telofemur and genu. 0=no; 1=yes.

95. Female leg I with dense, hairlike setae on dorsal surface of genu and tibia: 0=no; 1=yes.

96. Female leg IV with dense, hairlike setae on dorsal surface of telofemur, genu, and tibia: 0=no; 1=yes.

Sexual dimorphism of legs

97. Sexual dimorphism of leg I: 0=leg I of males without 2 large setae on telofemur; 1=Leg I of males with 2 large setae on telofemur.

98. Sexual dimorphism of leg I: 0=leg I equally setose in males and females; 1=leg I noticeably less setose in males than in females.

99. Sexual dimorphism of leg IV: 0=leg IV of males without bundles of setae on genu and tibia; 1=Leg IV of males with bundles of setae on genu and tibia.

100. Sexual dimorphism of leg IV: 0=leg IV of males without bundles of setae on telofemur, genu, and tibia; 1=Leg IV of males with bundles of setae on telofemur, genu, and tibia.

101. Sexual dimorphism of leg IV: 0=leg IV of males without bundles of setae on telofemur and genu; 1=Leg IV of males with bundles of setae on telofemur and genu.

102. Sexual dimorphism of leg IV: 0=leg IV of males without a large, blunt distal dorsal seta on telofemur and genu; 1=Leg IV of males with a large, blunt distal dorsal seta on telofemur and genu.

103. Sexual dimorphism of leg IV: 0=leg IV of males without large curved spines at distal end of genu; 1=Leg IV of males with large curved spines at distal end of genu.

104. Sexual dimorphism of leg IV: 0=tibia and tarsus of leg IV of males not grossly modified and tarsal claw obviously visible; 1=tibia and tarsus of leg IV of males grossly modified and tarsal claw not obviously visible.*

105. Sexual dimorphism of leg IV: 0=genu and tibia of leg IV of males without with large blunt spines; 1=genu and tibia of leg IV of males with large blunt spines, tibia noticeably short; 2=genu and tibia of leg IV of males with large blunt spines, tibia elongate.

106. Sexual dimorphism of leg IV: 0=leg IV of males without large blunt distal, dorsal, straight spine on genu; 1=leg IV of males with large blunt distal, dorsal, straight spine on genu.

107. Sexual dimorphism of leg IV: 0=leg IV of males without a series of short blunt serrated setae on ventral side of genu and tibia; 1=leg IV of males with a series of short blunt serrated setae on ventral side of genu and tibia.

108. Sexual dimorphism of leg IV: 0=claws of leg IV of males similar to females or bifid or as on all other legs; 1=claws of leg IV of males simple, whereas trifid on all other legs.*

109. Sexual dimorphism of leg IV: 0=leg IV of males without ventral indentation and stout setae on genu, tibia, and tarsus; 1=leg IV of males with ventral indentation and stout setae on genu, tibia, and tarsus.

110. Sexual dimorphism of leg IV: 0=leg IV of males without stout, curved setae at distal ends of telofemur, genu, and tibia; 1=leg IV of males with stout, curved setae at distal ends of telofemur, genu, and tibia.

111. Sexual dimorphism of leg IV: 0=leg IV of males without stout, ventral setae on telofemur, genu, and tibia; 1=leg IV of males with stout, ventral setae on telofemur, genu, and tibia.

112. Sexual dimorphism of leg IV: 0=leg IV of females without one or more rows of four straight setae on the genu and tibia; 1=leg IV of females with one or more rows of four straight setae on the genu and tibia.

Tarsal claws of walking legs

113. Tarsal claws of males and females similar: 0=yes; 1=no.*

114. All tarsal claws of walking legs: 0=finely bifid at tip; 1=simple; 2=deeply bifid; 3=other than above.

115. All tarsal claws similar: 0=yes; 1=no.

116. Female Tarsal claw of leg I different from those of other walking legs: 0=no; 1=yes, different from 2 other legs; 2=yes, different from one other leg.

117. Dorsal teeth on the tarsal claws pectinate: 0=no; 1=yes.

118. Ventral teeth on the tarsal claws pectinate: 0=no; 1=yes.*

119. Lateral teeth on the tarsal claws pectinate: 0=no; 1=yes.*

120. Tarsal claws noticeably large (at least as long as tarsus is wide at its midpoint): 0=no; 1=yes.

121. Tarsal claw of leg I of females bifid: 0=yes; 1=no.

122. Bifid tarsal claw of Leg I of females with equal prongs: 0=yes; 1=no, dorsal prong as long or longer than ventral prong; 2=no, ventral prong longer than dorsal prong; ?=inapplicable, tarsal claws of leg I not bifid.

123. Tarsal claws of Leg II of females bifid: 0=yes; 1=no.

124. Bifid tarsal claw of Leg II of females with equal prongs: 0=yes; 1=no, dorsal prong as long or longer than ventral prong; 2=no, ventral prong longer than dorsal prong; ?=inapplicable, tarsal claws of leg II not bifid.

125. Tarsal claws of Leg III of females bifid: 0=yes; 1=no.

126. Bifid tarsal claw of Leg III of females with equal prongs: 0=yes; 1=no, dorsal prong as long or longer than ventral prong; 2=no, ventral prong longer than dorsal prong; ?=inapplicable, tarsal claws of leg III not bifid.

127. Tarsal claw of leg IV of females bifid: 0=yes; 1=no.

128. Bifid tarsal claw of Leg IV of females with equal prongs: 0=yes; 1=no, dorsal prong as long or longer than ventral prong; 2=no, ventral prong longer than dorsal prong; ?=inapplicable, tarsal claws of leg IV not bifid.

129. Tarsal claw of leg I of females trifid: 0=no; 1=yes.*

130. Tarsal claw of leg IV of females trifid: 0=no; 1=yes.

131. Tarsal claws on at least one leg appearing as an inverted spoon with serrated edge: 0=no; 1=yes.*

132. Tarsal claws of leg I retractable: 0=no; 1=yes.

133. Tarsal claws of first 3 pairs of legs of males obviously bifid, last leg simple: 0=no; 1=yes.*

134. Female tarsal claws of leg I bifid and ‘cartoonish’: 0=no; 1=yes.

Dorsum plates and chaetotaxy

135. Male and female dorsal surfaces/plates similar: 0=yes; 1=no.

136. Male dorsal apodemes apparent: 0=no; 1=yes.

137. Female dorsal apodemes apparent: 0=no; 1=yes.

138. Male dorsal plates obvious: 0=no; 1=yes.

139. Female dorsal plates obvious: 0=no; 1=yes.

140. Male dorsum with 4 small plates in the anterior portion: 0=no; 1=yes.

141. Female dorsum with 4 small plates in the anterior portion: 0=no; 1=yes.

142. Male dorsal plates cover more than half the dorsum or nearly so: 0=no; 1=yes.

143. Female dorsal plates cover more than half the dorsum or nearly so: 0=no; 1=yes.

144. Number of dorsal plates on males: 0=none; 1=1 plate; 2=divided into 2 or more plates.

145. Number of dorsal plates on females: 0=none; 1=1 plate; 2=divided into 2 or more plates.

146. Dorsal plates of males with associated apodemes: 0=no; 1=yes.

147. Dorsal plates of females with associated apodemes: 0=no; 1=yes.

148. Dorsal plates of males with obvious spinous setae: 0=no; 1=yes.

149. Dorsal plates of females with obvious spinous setae: 0=no; 1=yes.

Body size

150. Female Body size: 0=<400µm; 1=400-999µm; 2=1mm-2mm; 3=>2mm.

151. Body white in color: 0=no; 1=yes.

152. Body elongate with a projecting posterior (obvious cauda in males): 0=no; 1=yes.

Larval characters

153. Shape of anal plate of larvae: 0=circular or oval; 1=triangular (wider than long).*

154. Number and location of setae on anal plate of larvae: 0=2 setae arising anterior and two posterior; 1=4 setae arising along posterior edge.*

155. Larvae brown in color or transparent: 0=yes; 1=no.*

156. Larvae with posterior pair of setae arising wide apart (distance equal to the length of a seta): 0=no; 1=yes.*

Host-associations

157. Lifestyle: 0=free-swimming mite; 1=sponge-associated mite; 2=snail-associated mite; 3=mussel-associated mite.

Egg deposition

158. Oviposition: 0=in sponges; 1=in molluscan mantle tissue; 2=in molluscan gill tissue; 3=unknown; ?=inapplicable, free-swimming mite.

Phylogenetic analyses

Characters were analyzed using Bayesian optimality criteria. All analyses treated binary and multistate characters as unweighted and unordered. Bayesian analysis was conducted with default priors and the Markov k model with a gamma (Mk+G) distribution (Lewis 2001) using MrBayes 3.1 (Huelsenbeck and Ronquist 2001; Ronquist and Huelsenbeck 2003). Two analyses ran in parallel each with four chains of five million generations and the posterior distribution was sampled every 5000 generations. We concluded that the analysis had reached stationarity when the average standard deviation of split frequencies was less than 0.01, evidence of chain swapping was sufficient, and the potential scale reduction factors (PSRF) were near one. An appropriate burnin was assessed by a plot of log likelihoods viewed in the program Tracer v1.4 (Rambaut and Drummond 2007) and was discarded before summarizing model parameters and tree statistics using the sump (burnin=500) and sumt (burnin=500) commands in MrBayes.