Seasonal aspects of the life cycle of solifuges (Arachnida, Solifugae) as compared with pseudoscorpions (Arachnida, Pseudoscorpiones)

Solifuges (order Solifugae) and pseudoscorpions (order Pseudoscorpiones) united into the superorder Haplocnemata (Shultz, 2007) are nevertheless characterized by essential differences both in morphological and biological characters. Analysis of available information on the biology and life cycles of these arachnids revealed a clear difference between the daily rhythms of activity: their presence in solifuges and their absence in pseudoscorpions. However, this concerning the seasonal adaptations in the two orders is not simple since they demonstrate not only differences but also a lot of similarities. All the studied solifuges are characterized by the seasonally timed stenochronous (heterodynamic) type of development which is characteristic of species with uni-, bi-, and semi-voltine development (i.e., to life cycles completed within a year, half a year, and several years), as well as to species combining different forms of voltinism. This type of development is not only prevalent in solifuges (as in pseudoscorpions and other arachnids) but appears to be the only one, since no cases of eurychronous (homodynamic) development have been found in solifuges; whereas pseudoscorpions and other arachnids develop both steno- and eurychronously. The initial ontogenetic stages remain in underground shelters (brood burrows in solifuges and brood chambers in pseudoscorpions). The first nymphal stages (I instar nymphs in solifuges, protonymphs in pseudoscorpions) are embryonized; active life outside the brood burrows starts with II instar nymphs in solifuges and with deutonymphs in pseudoscorpions.     

Dormant stages and their participation in adjustment and regulation of life cycles of harvestmen (Arachnida,Opiliones)

Information on seasonal adaptations in the life cycles of harvestmen (order Opiliones) summarized in this review reveals a great diversity of these arachnids with respect to duration, voltinism, and phenology of their life cycles, as well as to the number and ontogenetic position of the dormant stages required for survival during the winter season and also for synchronizing development with seasonal climate rhythms. Most harvestmen have stenochronous development with univoltine life cycles synchronized by arrest of development in hibernating eggs or (rarely) diapausing nymphs and adults. The number and arrangement of dormant stages represent stable species-specific traits, with some rare cases of interpopulation differences (e.g., in Phalangium opilio). Eurychronous harvestmen exhibit the year-round occurrence of main ontogenetic stages which show equal abilities for either active development or quiescence (depending upon the external factors). Two alternative types of development arrest are common in univoltine opilionids: (1) diapause induced at the early stage of embryogenesis and terminated during cooling (in Opilio parietinus and eleven other species) with transformation into postdiapause quiescence; (2) cold quiescence enforced by low temperatures at the last stage of egg development just before hatching (in Phalangium opilio and four other species). In conclusion, the systems of seasonal adaptations in Opiliones are compared with those in other arachnids, insects, and crustaceans. Some promising directions in the study of seasonal adaptations in opilionid life cycles are suggested.     

Seasonal cycles in stink bugs (Heteroptera,Pentatomidae) from the temperate zone: Diversity and control

The paper reviews the diversity of seasonal cycles known in stink bugs (Heteroptera, Pentatomidae) from the temperate zone and is based on the data of 43 pentatomid species studied in detail up to date (Saulich and Musolin, 2011). All the seasonal cycles realized by pentatomids in the temperate zone can be divided into two large groups: univoltine and multivoltine cycles. In univoltine cycles, only one generation is annually realized. However, univoltinism of a particular species or population can be ensured by different mechanisms: its control can be endogenous (involving an obligate diapause) or exogenous (environmental, involving a facultative diapause). Furthermore, endogenously controlled univoltine seasonal cycles can include obligate embryonic (egg) diapause (e.g., Picromerus bidens and Apateticus cynicus), obligate nymphal diapause (e.g., Pentatoma rufipes) or obligate adult (reproductive) diapause (e.g., Palomena prasina, Palomena angulosa, and Menida scotti). Exogenously controlled seasonal cycles are more flexible. Many species that are multivoltine in the subtropical or warm temperate zones are univoltine further polewards. In this case, their univoltinism is controlled exogenously, or environmentally. The mechanism often involves such seasonal adaptations as photoperiodic response of facultative winter diapause induction with a high thermal optimum (e.g., Arma custos and Dybowskyia reticulata) or a high critical threshold of winter diapause induction response (e.g., Graphosoma lineatum). The seasonal cycles of some species include not only winter diapause (hibernation) but also summer diapause (aestivation). The diapausing stage can be the same (e.g., Nezara antennata has facultative adult winter and summer diapauses) or different (e.g., Picromerus bidens survives winter in obligate embryonic diapause and spends the hottest period of summer in facultative adult aestivation). All the multivoltine cycles follow the same general pattern, with one, two, or even more directly breeding generation(s) followed by a generation that enters winter diapause. However, this sequence may be complicated by incorporation of specific seasonal adaptations such as aestivation, migrations, different forms of seasonal polyphenism or polymorphism (e.g., seasonal changes of body color), etc. Many stink bugs demonstrate geographic clines of voltinism, producing several generations in the subtropical regions (environmentally controlled multivoltine development) and two or only one generation(s) polewards (environmentally controlled bi- or univoltinism). However, some species demonstrate a strictly bivoltine seasonal cycle: they always produce two annual generations, each with either winter or summer diapause. An example is Nezara antennata which produces two generations and enters facultative winter and summer diapauses. Semivoltine seasonal cycles last more than one year. They are not very rare among insects and are known in true bugs, but have not yet been recorded among pentatomids. Examples of different seasonal cycles are described and discussed in detail. Further discussion is focused on the ecological importance of photoperiodic and thermal responses in cases of natural or artificial dispersal of pentatomids beyond their original ranges. The phytophagous Nezara viridula and the predatory Podisus maculiventris and Perillus bioculatus are used as examples. An attempt is made to compare the phylogeny of Pentatomidae and distribution of realized patterns of their seasonal development. However, it is concluded that reconstruction of phylogenetic relationships cannot yet provide a sufficient basis for prediction of realized seasonal cycles. It is suggested that the terms uni-, bi-, multi-, and semivoltinism should refer to populations rather than species, since the realized patterns of seasonal development often differ between the northern and southern populations of the same broadly distributed species.     

Seasonal cycles of noctuid moths of the subfamily Plusiinae (Lepidoptera,Noctuidae) of the Palaearctic: Diversity and environmental control

Analysis of data on seasonal development of noctuid moths of the subfamily Plusiinae shows that the control of their seasonal cycles is poorly understood. At the same time, the available data demonstrate considerable diversity of the seasonal patterns of Plusiinae species from different regions. The homodynamic type of seasonal development has been found in Trichoplusia ni and Ctenoplusia agnata of the tribe Argyrogrammatini and in Autographa gamma of the Plusiini. The seasonal development of these southern noctuids is accompanied by regular interzonal migrations of flying adults. When spreading northwards, they can produce a different number of annual generations, depending on the local climatic conditions, and establish temporary local populations whose longevity is limited by the available thermal resources. Adults of some species may fly back southwards, but it is more likely that individuals from temporary local populations cannot survive long winters and are destined to die. The heterodynamic type of seasonal cycles allows insects to survive in the regions with pronounced seasonality of climate. This type of seasonal development includes univoltine, multivoltine, and semivoltine seasonal cycles. Univoltine seasonal cycles with obligate diapause are known in Autographa buraetica, A. excelsa, and Syngrapha ain (Plusiini). Diapause provides tolerance to both low temperatures and a prolonged period when food is unavailable. In Syngrapha ottolenguii (Plusiini), the same result is achieved by inclusion of two photoperiodically controlled diapauses (winter larval and summer adult ones) into the life cycle. The semivoltine seasonal cycle has been reported in only one species of Plusiinae, namely Syngrapha devergens. Larvae of this moth overwinter twice before pupation. Multivoltinism is common in the tribe Plusiini. Depending on the latitude, different species of this tribe can produce up to four generations per year and overwinter as middle-instar larvae in the state of facultative diapause. However, the characteristics of diapause vary substantially between the species: diapause can be deep and stable (as in Diachrysia chrysitis, Plusiini) or unstable and thus not ensuring successful overwintering and steady population growth (as in Macdunnoughia confusa, Plusiini). The seasonal adaptations known in Plusiinae include migrations, winter and summer diapauses, photoperiodic control of larval growth rates, and seasonal polyphenism of larval body coloration. In general, seasonal adaptations of Plusiinae are determined by local environmental conditions and only loosely associated with the systematic position of particular taxa. Only the tribe Abrostolini stands apart from other taxa of Plusiinae: moths of this tribe differ not only in morphology but also in peculiarities of their seasonal development, because all the species of this tribe overwinter as pupae and their seasonal cycles are therefore different from those of the rest of Plusiinae.     

Phenoptosis in arthropods and immortality of social insects

In general, there are no drastic differences in phenoptosis patterns in plant and animal organisms. However, there are some specific features characteristic for insects and other arthropods: 1) their development includes metamorphosis with different biochemical laws at consecutive developmental stages; 2) arthropods can reduce or stop development and aging when in a state of diapause or temporal cold immobility; 3) their life cycle often correlates with seasonal changes of surroundings; 4) polymorphism is widespread — conspecifics differ by their lifespans and phenoptosis features; 5) lifespan-related sexual dimorphism is common; 6) significant situational plasticity of life cycle organization is an important feature; for example, the German wasp (Paravespula germanica) is obligatorily univoltine in the temperate zone, while in tropical regions its lifespan increases and leads to repeated reproduction; 7) life cycles of closely related species may differ significantly, for example, in contrast to German wasp, some tropical hornets (Vespa) have only one reproduction period. Surprisingly, many insect species have been shown to be subjected to gradual aging and phenoptosis, like the highest mammals. However, queens of social insects and some long-lived arachnids can apparently be considered non-aging organisms. In some species, lifespan is limited to one season, while others live much longer or shorter. Cases of one-time reproduction are rather rare. Aphagia is common in insects (over 10,000 species). Cannibalism is an important mortality factor in insects as well as in spiders. In social insects, which exist only in colonies (families), the lifetime of a colony can be virtually unlimited. However, in case of some species the developmental cycle and death of a colony after its completion are predetermined. Most likely, natural selection in insects does not lengthen individual lifespan, but favors increase in reproduction efficiency based on fast succession of generations leading to increased evolvability.     

Typology of life cycles of ground beetles (Coleoptera,Carabidae) in Western Palaearctic

An original classification of the life cycles of ground beetles from Western Palaearctic is proposed. The classification is based on a combination of five criteria: duration, number of generations per season, phenology of reproduction, stability, and repeatability of reproduction. According to the individual lifespan, the cycles are subdivided into annual and biennial ones. The annual life cycles may be uni-and bivoltine, whereas biennial ones are always univoltine. By the time of reproduction, winter-spring, spring, spring-summer, early summer, summer, late summer, summer-autumnal, autumnal, autumn-winter, winter, and aseasonal species are distinguished. The biennial and bivoltine cycles may be of both facultative and obligate nature. Species living only one season and having a continuous reproductive period are designated as semelparous, while those breeding during two or more years or having several distinct periods of reproduction in one season, as iteroparous. By now, 30 variants of life cycles in Carabidae from western Palaearctic have been established. Repeated similarly directed modifications of the life cycle may produce essentially different seasonal rhythms in some individuals. In this case, two subpopulation groups usually appear within the population. Under the most unfavorable conditions, these groups become practically isolated and hibernate at different ontogenetic stages. The individual development in each of these groups takes two years with the same seasonal rhythm. Among the types considered, only obligate-bivoltine life cycles are always polyvariant, but annual univoltine and obligate-biennial ones are always univariant. The facultative-bivoltine and biennial life cycles may be realized as uni-and polyvariant ones, depending on the environmental conditions.     

Biology of Allothrombium pulvinum Ewing (Acari: Trombidiidae) in West Mazandran, Iran

Allothrombium pulvinum Ewing is a common natural enemy of aphids and other arthropods in Iran. It is univoltine in Iran. The eggs hatch in spring, nymphs emerge in early summer and adults appear in autumn. Larvae are ectoparasites of aphids whereas deutonymphs and adults are free-living predators of aphids and spider mites. Adults hibernate in the soil and in cracks of tree trunks during winter. When spring comes, females lay eggs in the soil, on the soil surface and on weeds. Phytoseius plumifer (Phytoseiidae) was observed to be phoretic on deutonymphs of A. pulvinum on nettle trees (Celtis australis). In the laboratory, development from the egg to adult stage takes at least 107 days at 25±1°C. Soil is not essential for female oviposition. High humidity is the most important factor for oviposition and development in A. pulvinum.     

Necromenic life style of Histiostoma polypori (Acari: Histiostomatidae)

Histiostoma polypori (Histiostomatidae, Astigmata) is associated with the earwig Forficula auricularia, which has an interesting brood behavior: the adult earwig female cares for her eggs and stays with the N2 and N3 nymphs in the nest. Deutonymphs of H. polypori only leave the female earwig to develop on dead earwig N2 and N3 nymphs. The newly molted deutonymphs attach to live earwig N3 nymphs. The earwig’s cleaning behavior displaces the deutonymphs to the exuvial suture, around the area between cephalon and prothorax. From there, deutonymphs switch from one earwig stage to the following, always occupying that region. Histiostoma polypori obviously has a necromenic life style, that is, it ascends a carrier organism and develops on the carrier’s cadavers. Necromeny within the Histiostomatidae presumably derived at least twice convergently from phoretic transport.     

The annual pattern of reproduction of Talitrus saltator (Crustacea: Amphipoda: Talitridae)

The reproductive cycle and breeding biology of Talitrus saltator (Montagu), a supralittoral talitrid amphipod, were investigated over a 15 month period on a sandy beach in the Isle of Man. The species is shown to have an annual, univoltine reproductive cycle with a period of high reproductive activity between May and late August. Two generations are present throughout most of the year and the life spans of female and male T. saltator were calculated to be approximately 18 months and 21 months respectively. Initial juvenile growth was rapid, juveniles attaining sexual differentiation within three to four months of hatching. Juvenile growth rates averaged 5–5 mm in 100 days decreasing to 1–3 mm in 100 days after sexual differentiation at around 8.0 mm.
The relative brood size of incubating females was shown to be dependent on at least two factors, the length of the female and the stage of embryological development of the brood.
It is suggested that photoperiod is the major exogenous factor controlling gonadal maturation and the duration of reproductive activity in T. saltator.     

Life cycles and nymphal feeding of Isoperla morenica Tierno de Figueroa and Luzón-Ortega, 2011 and Brachyptera vera cordubensis Berthélemy and Baena, 1984 (Plecoptera: Perlodidae and Taeniopterygidae) in a Mediterranean stream (Spain)

Some aspects of the biology of two endemic Iberian stonefly species, Isoperla morenica Tierno de Figueroa and Luzón-Ortega, 2011 and Brachyptera vera cordubensis Berthélemy and Baena, 1984, were studied in a temporary stream from Sierra Morena (Southern Spain). Isoperla morenica shows a univoltine fast seasonal life cycle, with nymphs growing from November to April. After oviposition, eggs remain in a dormant state in the riverbed until the following autumn when the river water flows again. Nymphal diet is mainly composed of detritus in small individuals (they behave as gatherer–collectors) but when larger, they become predators. Brachyptera vera cordubensis also shows a univoltine fast seasonal life cycle, from November to March. Nymphs behave mainly as gatherer–collector and no significant ontogenetic changes in diet were detected. Male and female nymphs do not show differences in feeding in this species. Data obtained were compared with the previously known information on both species in another stream from the same mountain range as well as for other related species, and some differences in both aspects, mainly on feeding habits, could be detected.     

Studies on the development biology of Tropilaelaps clareae Delfinado and Baker (Acarina: Laelapidae) vis a vis the threshold stage in the life cycle of Apis mellifera Linn. (Hymenoptera: Apidae).

The biology of the parasitic mite Tropilaelaps clareae Delfinado and Baker (Acarina: Laelapidae) was studied with a view to identify the time of invasion of the mite into the honey bee (Apis mellifera) brood and the threshold stage in the life cycle of the host. Honey bee brood was sequentially sampled on day 0, 4, 8, 12, 16 and 20 of development. Adult T. clareae infested the 8-day larva shortly before its cell was capped. The larvac, protonymphs, deutonymphs and adults of T. clareae were all found parasitising bright red eyed pupae during day 16 of brood development. This was identified as the most parasitised stage in the life cycle of the host. The mite developed from egg to adult in about 8 days.     

Live cycles,drift, and standing stocks of some stoneflies (Insecta: Plecoptera) from streams in Minnesota,U.S.A.

From analyses of monthly length frequency distributions of stonefly (Plecoptera) nymphs from stream riffles, two types of univoltine life cycles (Hynes 1961, classification) were observed: slow seasonal forIsoperla transmarina, Isoperla signata, Isogenoides olivaceus, andAllocapnia rickerii, and fast seasonal forProstoia similis. The Perlodidae stoneflies (Isoperla andIsogenoides) showed greatest propensities to drift near the end of their life cycles. Drift rates of the other two species of stoneflies were correlated to standing stock estimates.     

The life cycle and drumming behavior of Zealeuctra claasseni (Frison) and Zealeuctra hitei ricker and ross (Plecoptera: Leuctridae) in Texas,USA 1

The life histories of Zealeuctra claasseni (Frison) and Zealeuctra hitei (Ricker and Ross) (Plecoptera: Leuctridae) were determined from observations and sampling on a Red River tributary in Cooke County, and N. Pecan Creek, Wise County, Texas, Dec., 1974‐June, 1978. Both species showed peak emergence when daily temperature was ca. 12°. Emergence was diurnal, with teneral adults and mating pairs found from dawn—late evening. Male‐female drumming signals were successfully recorded for both species. Incubation experiments at simulated stream temperatures indicated rapid embryonic development, so that larvae were visible through the chorion within ca. 4 weeks after deposition. Both species have highly flexible seasonal development patterns. Four types of life cycles seem possible, depending on field conditions: (1) slow univoltine, (2) fast univoltine, (3) slow semivoltine, and (4) fast semivoltine.     

Reinterpretation of Dracochela deprehendor (Arachnida: Pseudoscorpiones) as a stem‐group pseudoscorpion

Abstract: The middle Devonian (Givetian–Eifelian) pseudoscorpion Dracochela deprehendor Schawaller, Shear and Bonamo is redescribed from the type material and an additional palpal fragment. Dracochela differs from extant pseudoscorpions in having numerous spinules on the leg tarsi, the femur at least as long as the patella on the posterior legs, the stem of the arolia thick, most blades of the serrulae only weakly fused and in lacking a spinneret on the chelicera. The blades of the cheliceral rallum are shown to have been arranged in two rows, as in most Heterosphyronida. The cheliceral serrulae are compared with analogous structures in other arachnids (Notostigmata, Opiliones, Palpigradi, Schizomida and Scorpiones), and it is concluded that the panctenal state (all lamellae attached to finger) is plesiomorphic relative to the hemictenal state (apical lamellae raised), which has evolved independently in Heterosphyronida and Neobisioidea. The trichobothriotaxy of the chela of Dracochela is shown to be similar to that of the extant family Pseudotyrannochthoniidae. The growth of the chelal fingers followed the same pattern as that seen in modern pseudoscorpions, with most of the increase in length occurring at the base of the fingers. The family Dracochelidae Schawaller, Shear and Bonamo is treated as a plesion and assigned to the stem‐group of Pseudoscorpiones. The ordinal name Chelonethi Thorell is restricted to crown‐group pseudoscorpions, and the superordinal name Pseudoscorpiones Latreille is adopted for the total‐group (i.e. stem‐group plus Chelonethi).     

Can morphological and behavioral traits predict the foraging and feeding dynamics of social arachnids?

Complex social insect species exhibit task specialization mediated by morphological and behavioral traits. However, evidence of such traits is scarce for other social arthropods. We investigated whether the social pseudoscorpion Paratemnoides nidificator exhibits morphologically and behaviorally specialized individuals in prey capture. We measured body and chela sizes of adult pseudoscorpions and analyzed predation processes. Larger individuals spent more time moving through the colony and foraging than smaller pseudoscorpions. Individuals that captured prey had increased body and absolute chelae sizes. Although larger individuals had relatively small chelae size, they showed a higher probability of prey capture. Larger individuals manipulated prey often, although they fed less than smaller pseudoscorpions. Individuals that initiated captures fed more frequently and for more time than the others. Natural selection might be favoring individuals specialized in foraging and colony protection, allowing smaller and less efficient adults to avoid contact with dangerous prey. To our knowledge, there is incipient information regarding specialized individuals in arachnids, and our results might indicate the emergence of a morphologically specialized group in this species.     

Mayfly production in a Colorado mountain stream: an assessment of methods for synchronous and non-synchronous species

Year-round collections of mayflies (Ephemeroptera) from a Colorado mountain stream allowed critical examination of several methods of calculating production for species with different life cycles. Five of the six numerically dominant species exhibited slow seasonal, univoltine life cycles. Baetis tricaudatus was bivoltine. Two species demonstrated well synchronized development, three species were poorly synchronized and a sixth was intermediate. Mean density and biomass data from each sampling date were used to ascertain the goodness-of-fit of each species to the Allen curve. It is proposed that such information can provide quantitative criteria for identifying species with well synchronized development and thereby determine when it is appropriate to directly apply cohort methods while avoiding time intensive body size (e.g. head width) measurements necessary for size-frequency analyses. In addition, these data demonstrate that species specific production varies with gross changes in elevation.     

Fitness consequences of alternative life histories in water striders,Aquarius remigis (Heteroptera: Gerridae)

Using field and laboratory observations and experiments over 3 years, I investigated whether reproductive trade-offs shape individual life histories in two natural populations of the water strider, Aquarius remigis, in which univoltine and bivoltine life cycles coexist. Both later eclosion dates and food shortages, even after adult eclosion, induced diapause in females, thus deferring reproduction to the following spring. Adult body size was positively affected by food availability during juvenile development. Higher food levels also increased the reproductive output of females, but not their longevity or oviposition period. When compared to spring breeders (univoltine life cycle), direct (summer) breeders (bivoltine life cycle) experienced reduced lifetime egg numbers and longevity, as well as reduced survivorship of their second-summer-generation offspring; these reproductive costs offset, at least in part, the advantage in non-decreasing populations of having two generations per year. Fecundity was correlated with body size, and among summer-generation females direct breeders were larger than non-breeders. The time remaining before the onset of winter and/or the time since adult eclosion augmented cumulative energy uptake, and consequently the lipid reserves and winter survival probability of non-breeding (diapausing) summer adults approaching hibernation. Overwintered spring reproductives died at faster rates than non-reproductive summer individuals despite greater food availability in spring, indicating a mortality cost of reproduction. Body length correlated with absolute and not with proportional lipid content but showed no consistent relationship with survivorship in the field. These results are in agreement with current theory on the evolution of insect voltinism patterns, and further indicate high degrees of life history flexibility (phenotypic plasticity) in the study populations in response to variable environmental factors (notably photoperiod and food availability). This may be related to their location in a geographic transition zone from uni- to bivoltine life cycles.     

Ecology and phenology of cattle ticks in Zambia: Development and survival of free-living stages

A study on development and survival of free-living stages of three important cattle ticks in Zambia,Amblyomma variegatum Fabricus,Boophilus decoloratus Koch, andRhipicephalus appendiculatus Neumann, was carried out to complement studies on seasonal dynamics of parasitic stages.Different instars of engorged ticks were exposed under quasi-natural conditions according to the season in which they occur naturally. Generally, development rates of all stages of the three species were related to temperature, whilst the duration of survival was influenced mainly by rainfall and consequent relative humidity.Observations on the effect of age and climate on the behaviour of ticks on pastures were also made. BothA. variegatum andR. appendiculatus completed only one generation per year. InA. variegatum, engorged females detaching early in the adult season (August to October) undergo morphogenetic diapause. Adults ofR. appendiculatus emerging between August and October enter a period of behavioural diapause before becoming active in December. These mechanisms effectively synchronize the life-cycles of these two univoltine species. The one-host tick,B. decoloratus, is able to complete three to five generations each year with no indication of seasonal synchronization.     

Life cycles and habitats of wisconsin heptageniidae (ephemeroptera)

Detailed studies were made of the life cycles of Heptageniidae known to occur in Wisconsin. 19 species had univoltine cycles while two and possibly a third had bivoltine cycles. Three univoltine species developed in late spring and early summer while the other univoltine species developed in fall, winter and early spring. For three of the univoltine species, eggs hatched both in fall and the following spring. Diagrams of the life cycles of 15 Wisconsin heptageniids are presented, illustrating the different types of life cycles. Also presented are observation on the food and habitats of the nymphs and flight periods of the adults.     

First molecular phylogeny of the major clades of Pseudoscorpiones (Arthropoda: Chelicerata)

The phylogenetic relationships of the major lineages of the arachnid order Pseudoscorpiones are investigated for the first time using molecular sequence data from two nuclear ribosomal genes and one mitochondrial protein-encoding gene. The data were analyzed using a dynamic homology approach with the new program POY v.4 under parsimony as the optimality criterion. The data show monophyly of Pseudoscorpiones as well as many of its superfamilies (Feaelloidea, Chthonioidea, Cheiridioidea and Sternophoroidea), but not for Neobisiodea or Garypoidea. Cheliferoidea was not monophyletic either due to the position of Neochelanops, which grouped with some garypoids. In all the analyses, Feaelloidea constituted the sister group to all other pseudoscorpions; Chthonioidea is the sister group to the remaining families, which constitute the group Iocheirata sensu Harvey--a clade including pseudoscorpions with venom glands within the pedipalpal fingers. This phylogenetic pattern suggests that venom glands evolved just once within this order of arachnids.