A longstanding entomological problem finally solved? Head morphology of Nannochorista (Mecoptera,Insecta) and possible phylogenetic implications

External and internal head structures of Nannochorista species were examined and described in detail. The characters are discussed with regard to their functional and phylogenetic implications. The structure of the mouthparts indicates that adults of Nannochorista feed on fluids. The loss of the mandibular muscles and the precerebral pharyngeal dilators are presumptive autapomorphies of the genus. A possible clade comprising Nannomecoptera, Siphonaptera and Diptera is supported by the presence of a labral food channel, the absence of the galea, a sheath for the paired mouthparts formed by the labium, very strongly developed labial palp muscles and cibarial dilators, and the presence of a well‐defined postcerebral pharyngeal pumping chamber. Closer affinities of Nannomecoptera with Diptera are suggested by the presence of a unique sensorial groove on the third maxillary palpomere. Further potential synapomorphies are the presence of a frontal apodeme and a primarily lamelliform mandible without teeth. The presence of a salivary channel on the laciniae and a subdivided labrum are shared derived features of Nannochorista and Siphonaptera. A derived condition present in Mecoptera including Boreidae but excluding Nannochoristidae is the secretion with a strongly developed intrinsic muscle of the salivary duct. The loss of the lateral labral retractor, the cranial muscle of the cardo, and of two of the three premental retractors, and the absence of transverse epipharyngeal muscles are potential autapomorphies of Antliophora. The formation of a maxillolabial complex is a possible synapomorphy of Hymenoptera and Mecopterida.     

Head morphology of <Emphasis Type="Italic">Osmylus fulvicephalus</Emphasis> (Osmylidae,Neuroptera) and its phylogenetic implications

External and internal head structures of Osmylus fulvicephalus were examined and described in detail. Exo- and endoskeleton, musculature, elements of the central nervous system and tracheae are compared to conditions found in other groups of Neuropterida and other endopterygote lineages. Thirty-six adult cephalic characters were compiled, combined in a datamatrix with 64 characters of the larval head, and analysed cladistically. Mainly because many data on adults remain missing, most branches in the cladogram are mostly or exclusively supported by larval features. The shortening of the mesal mandibular wall and the resulting anterior shift of the adductor tendon possibly constitute an adult groundplan apomorphy of Neuropterida. Raphidioptera and Megaloptera share distinct prognathism and the presence of a sclerotised gula. However, the orthognathous head and the absence of a gula resulted as autapomorphies of Neuroptera in our analyses. Further potential autapomorphies are the asymmetry of the mandibles as well as the respective presence of dorsolateral furrows on the head capsule, of a shovel-like extension on the ventral mandibular cutting edge, and of a row of stiff hairs on the mandible’s ventral surface. The systematic affinities of Osmylidae remain ambiguous. Osmylus is mainly characterised by plesiomorphic features of the adult head such as a complete endoskeleton, long filiform antennae, largely unmodified orthopteroid mouthparts, and particularly the nearly complete set of muscles. The placement with a clade also comprising Hemerobiidae and Chrysopidae is poorly supported. The presence of a dense vestiture of long microtrichia on the distal galeomere resulted as a synapomorphy of the three families. An apparent plesiomorphy preserved in Osmylus but absent in all other groups of Neuroptera is the presence of well developed ocelli. The present study underlines the severe shortage of detailed morphological data on the adults. Intensive study of adult structures is required for a solid reconstruction of the phylogeny of Neuropterida, especially of the hemerobiform lineage of Neuroptera.     

Head morphology of Caurinus (Boreidae, Mecoptera) and its phylogenetic implications

External and internal head structures of Caurinus dectes were examined and described in detail. The features are compared to conditions found in other groups of Antliophora. Caurinus is obviously crucial for the reconstruction of the mecopteran and antliophoran groundplan. It displays a remarkable series of plesiomorphic character states such as a complete clypeolabral suture, the presence of M. hypopharyngomandibularis (M. 13) and M. frontohypopharyngalis (M. 41), a subdivided clypeus, a short head without rostrum, a dorsal tentorial arm attached to the head capsule, the absence of a cranial dilator of the antenna, and large mandibles with a well developed apical tooth, two distinct subapical teeth, and a basal molar part. The first three plesiomorphic features render potential autapomorphies of Mecoptera in the traditional sense invalid. Autapomorphies of Caurinus are the distinctly flattened labrum, the absence of the labroepipharyngeal muscle, the very large size of M. 13, the strongly enlarged penultimate palpomeres, the partition of M. 41, the very strongly developed precerebral sucking chamber, strongly curved optic lobes, the presence of a large protocerebral extension in the genal region and deep posterior excavations of the protocerebrum. The maxillolabial plate, the absence of cardines as separate structures, the reduction of ocelli, and the origin of maxillary palp muscles on a median ridge or area of the maxillolabial plate are likely autapomorphies of Boreidae. Another potential autapomorphy of the family is the presence of longitudinal furrows on the mandibles. However, they are absent in Boreus. The thick strongly sclerotised, median ridge of the maxillolabial plate, the missing retractibility of the prementum, the absence of extrinsic labial muscles, and the presence of a median ridge on the prepharyngeal roof suggest a clade Boreus + Hesperoboreus. The origin of extrinsic maxillary muscles from the clypeus has probably evolved independently in Boreus and Hesperoboreus, and in Panorpa, respectively. The absence of M. craniolacinialis and the presence of a row of several subapical mandibular teeth are autapomorphies of Boreus. The presence of a specific intrinsic muscle of the salivary duct and a membranous galea enclosing the labrum and mandibular base are derived features shared by Boreidae and Pistillifera (galea absent in Nannochorista, Siphonaptera and Diptera). The loss of M. frontolabralis (M. 8) is a potential apomorphy of Mecoptera incl. Siphonaptera. A sister group relationship between Boreidae and Siphonaptera is not supported by characters of the adult head. Head structures of Siphonaptera are extremely modified in correlation with ectoparasitic habits.     

New evolutionary evidence of Grylloblattida from the Middle Jurassic of Inner Mongolia, north-east China (Insecta, Polyneoptera)

The small modern insect order Grylloblattida has an abundant fossil record during the Late Palaeozoic and the Mesozoicirca. The relationships between these fossil taxa and the modern grylloblattids remain unclear because most of them are based on isolated wings or have poorly preserved body features. Modern grylloblattids are wingless insects. The new grylloblattid family Plesioblattogryllidae fam. nov. is erected for the new genus and species Plesioblattogryllus magnificus gen. nov., sp. nov. , from the Middle Jurassic of north-eastern China. The well-preserved specimen provides further evidence that could support its close relationships with the modern grylloblattids: (1) several very similar head structures, e.g. developed laciniae with inner row of setae, maxillary palps segmented into five, labial palps segmented into three, large labrum, and morphology of antenna; (2) paired eoplantulae on tarsomeres 1–4; (3) long ovipositor and large eggs comparable with those of modern taxa. The new genus has strongly developed mandibles with sharp pointed apical teeth and strong marginal teeth, and strong hook-like fore claws with basal teeth, suggesting it was carnivorous. The major differences between the extinct and extant Grylloblattida, such as the lack of wings, the eyes and ocelli either degenerated or absent, and the thorax degenerated in the modern forms, are probably related to their adaptation to their life under rocks and rock-crawler habits.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 152 , 17–24.     

The accessory lateral eye of a diplopod, Cylindroiulus truncorum (Silvestri, 1896) (Diplopoda: Julidae)

Using electron microscopy we describe an accessory lateral eye for Cylindroiulus, a diplopod. The accessory eye is situated at the cell body rind of the optic lobes, deep inside the head, and is composed of six R-cells; a dioptric apparatus is absent. Comparison reveals that many arthropods possess accessory lateral eyes in addition to the compound eyes or lateral ocelli. Their homology and distribution among the arthropod main lineages is discussed along with characters that may be useful for reconstructing phylogeny.     

Oldest webspinners from the Middle Jurassic of Inner Mongolia,China (Insecta: Embiodea)

The oldest webspinners, Sinembia rossi gen. et sp. nov. and Juraembia ningchengensis gen. et sp. nov. , are described in the new family Sinembiidae fam. nov. from the Middle Jurassic of Inner Mongolia, China. They differ from the Cretaceous and more recent Embiodea in several plesiomorphic characters, namely they have a long ovipositor, three‐segmented cerci, eyes situated on the posterolateral angles of the head, and the prothoracic prescutum is absent: these characters suggest habits that strongly differ from those of the recent taxa. The loss of the ovipositor and the reduction in the number of cerci can no longer be considered as synapomorphies of the ((Embiodea + Zoraptera) + Plecoptera) and (Embiodea + Zoraptera) clades, respectively.     

Ocellar atavism in Coleoptera: plesiomorphy or apomorphy?

Ocelli and ocellus‐like structures on the vertex of the adult head were examined in different representatives of Coleoptera and the presence of these was confirmed for the suborder Polyphaga. The presence of structures, which are likely homologous with ocelli of other insects were confirmed by semi‐thin sectioning in Hydraenidae, Staphylinidae, Derodontidae and Dermestidae. The presence of ocelli is newly recorded for a representative of Scydmaenidae (Nesuthia fijii Franz). The weakly pigmented areas on the vertex of Neopelatops (Leiodidae) lack a lens and associated nervous tissue and are referred to as pseudocelli, which may be present in other groups. The internal structure of Coleopteran ocelli is strongly simplified compared with other groups of Insecta where longitudinal retinula cells are arranged at a right angle to the cuticular surface and enclosed by a sheath of pigment cells. Such a regular arrangement is absent from all beetles examined histologically. A flattened group of cells without a rhabdom and without an enclosing layer of pigment cells is present underneath the cuticular lens. While, the infrastructure of the ocelli is more or less reduced in Coleoptera, the presence of these features in the ground‐plan of Coleoptera is dependent on the confirmation of the presence of ocelli in Archostemata (Jurodidae?) and a robust phylogenetic hypothesis for the order.     

Fine structural organization of the lateral ocelli in two species of Scolopendra (Chilopoda: Pleurostigmophora): an evolutionary evaluation

The lateral ocelli of Scolopendra cingulata and Scolopendra oraniensis were examined by electron microscopy. A pigmented ocellar field with four eyes arranged in a rhomboid configuration is present frontolaterally on both sides of the head. Each lateral ocellus is cup-shaped and consists of a deeply set biconvex corneal lens, which is formed by 230–2,240 cornea-secreting epithelial cells. A crystalline cone is not developed. Two kinds of photoreceptive cells are present in the retinula. 561–1,026 cylindrical retinula cells with circumapically developed microvilli form a large distal rhabdom. Arranged in 13–18 horizontal rings, the distal retinula cells display a multilayered appearance. Each cell layer forms an axial ring of maximally 75 rhabdomeres. In addition, 71–127 club-shaped proximal retinula cells make up uni- or bidirectional rhabdomeres, whose microvilli interdigitate. 150–250 sheath cells are located at the periphery of the eye. Radial sheath cell processes encompass the soma of all retinula cells. Outside the eye cup there are several thin layers of external pigment cells, which not only ensheath the ocelli but also underlie the entire ocellar field, causing its darkly pigmented. The cornea-secreting epithelial cells, sheath cells and external pigment cells form a part of the basal matrix extending around the entire eye cup. Scolopendromorph lateral ocelli differ remarkably with respect to the eyes of other chilopods. The dual type retinula in scolopendromorph eyes supports the hypothesis of its homology with scutigeromorph ommatidia. Other features (e.g. cup-shaped profile of the eye, horizontally multilayered distal retinula cells, interdigitating proximal rhabdomeres, lack of a crystalline cone, presence of external pigment and sheath cells enveloping the entire retinula) do not have any equivalents in scutigeromorph ommatidia and would, therefore, not directly support homology. In fact, most of them (except the external pigment cells) might be interpreted as autapomorphies defining the Pleurostigmophora. Certain structures (e.g. sheath cells, interdigitating proximal rhabdomeres, discontinuous layer of cornea-secreting epithelial cells) are similar to those found in some lithobiid ocelli (e.g. Lithobius). The external pigment cells in Scolopendra species, however, must presently be regarded as an autapomorphy of the Scolopendromorpha.     

The cost of being able to fly in the milkweed-oleander aphid,Aphis nerii (Homoptera: Aphididae)

Summary In the wing dimorphic milkweed-oleander aphid,Aphis nerii, winged aphids begin reproducing about 1.5 days after wingless aphids. The longer maturation period is primarily due to slower development since even adult eclosion by winged aphids takes place after wingless aphids begin reproducing. The delay is not due to a post-eclosion, pre-reproductive flight since, beginning with the fourth instar, larval winged aphids were reared at a density of one per plant and the vast majority were not stimulated to fly under such low-density conditions. Thus, the ability to fly incurs a fitness cost in terms of delayed reproduction, irrespective of whether flight actually occurs. We did not observe a difference between morphs for lifetime fecundity, even though wingless aphids have larger abdomens than winged aphids and for both morphs there is a significant correlation between abdomen width and fecundity. Offspring produced by wingless aphids over the first four days of reproduction are larger than those produced by winged aphids, and the size difference at birth is maintained into adulthood. However, there are no differences in life history traits between these offspring, including maturation period and lifetime fecundity. Thus, reduced body size does not increase the cost of being able to fly, at least under the conditions of these experiments. The cost of being able to fly in this species should favor reduced production of winged individuals in populations that exploit more permanent host plants.     

禾谷缢管蚜复眼外部形态的扫描电镜观察

【目的】通过比较禾谷缢管蚜Rhopalosiphum padi两种生活史(全周期型和不全周期型)及5种蚜型(有翅孤雌蚜、无翅孤雌蚜、雄蚜、雌性蚜和产雌性母)成蚜复眼外部形态,分析了其视觉能力差异,为进一步探索禾谷缢管蚜生殖转换及寄主搜寻机制提供参考。【方法】利用扫描电镜技术,观察全周期型和不全周期型禾谷缢管蚜无翅孤雌蚜及其低温短日照(12℃, 光周期8L∶16D)诱导条件下全周期型所产5种蚜型成蚜的复眼外部形态。【结果】禾谷缢管蚜成蚜复眼着生于头部触角基部,呈卵圆形,小眼间无感觉毛。全周期型和不全周期型禾谷缢管蚜无翅孤雌蚜的复眼大小(长轴直径及短轴直径)、复眼弧高、小眼数量和小眼直径均没有显著差异。而这5个复眼指标在低温短日照诱导全周期型禾谷缢管蚜产生的5种蚜型的成蚜中均存在显著性差异,其中,雄蚜、有翅孤雌蚜和产雌性母的复眼区域较大,小眼数量较多;雌性蚜的复眼区域最小,小眼数量也最少。【结论】综合以上指标结果,推测5种蚜型的视觉能力由大到小是：雄蚜＞有翅孤雌蚜＞产雌性母＞无翅孤雌蚜＞雌性蚜。复眼和小眼的这些差异可能与禾谷缢管蚜生殖转换及寄主搜寻存在一定的联系。     

Phylogenetic analysis of Adephaga (Coleoptera) based on characters of the larval head

Abstract. Characters of the head of adephagan larvae were examined and analysed phylogenetically. A labrum which is completely fused to the clypeofrons and the presence of a closed prepharyngeal tube are autapomorphies of Adephaga. Partial reduction of the fossa maxillaris, cardo and stipes forming a functional unit, the immobilization of the lacinia, attachment of M. craniolacinialis to the lateral stipital wall, and loss of one stipitopalpal muscle, are considered autapomorphies of Adephaga excluding Gyrinidae. Complete reduction of the fossa maxillaris and the presence of M. craniostipitalis medialis are possible autapomorphies of Adephaga excluding Gyrinidae and Haliplidae. The presence of caudal tentorial arms, insertion of the galea on the mesal side of palpomere I, and absence of the lacinia are considered synapomorphies of Trachypachidae and Dytiscoidea (Noteridae, Amphizoidae, Hygrobiidae, Dytiscidae). The presence of a slender, elongated process of the head capsule, which articulates with a corresponding socket of the cardo, is a possible autapomorphy of Dytiscoidea. The sinuate frontal sutures, distinctly protruding prementum, shortened M. craniostipitalis medialis, and absence of M. submentopraementalis are considered autapomorphies of Geadephaga excluding Trachypachidae. The presence of a regular row of hairs along the anterior hypopharyngeal margin is a possible autapomorphy of Geadephaga excluding Trachypachidae and Rhysodidae. Improvement of the hypopharyngeal filter apparatus suggests the monophyly of Anisochaeta. Presence of a penicillum and partial reduction of the lacinia are possible autapomorphies of Anisochaeta excluding Omophronini. Larvae of Cychrini, Carabini, Nebriini and Notiophilini are characterized by a strongly developed, cone-shaped hypodon. Postocular and cervical ridges, crosswise arrangement of antennal muscles, and a completely flattened hypopharynx are considered autapomorphies of Caraboidea Limbata.     

Queen polymorphism in the North American harvester ant,Ephebomyrmex imberbiculus

Summary In the North American harvester antEphebomyrmex imberbiculus, in addition to dealate queens, wingless female reproductives occur that have greatly reduced ocelli and thoracic sutures (intermorphic queens). Both queen types are equivalent in function, and do not differ in ovarian morphology. Colonies may contain several inseminated and egg-laying intermorphic queens. We discuss queen polymorphism in respect to the biology of this desert-dwelling species.     

Structural mouthpart interaction evolved already in the earliest lineages of insects

In butterflies, bees, flies and true bugs specific mouthparts are in close contact or even fused to enable piercing, sucking or sponging of particular food sources. The common phenomenon behind these mouthpart types is a complex composed of several consecutive mouthparts which structurally interact during food uptake. The single mouthparts are thus only functional in conjunction with other adjacent mouthparts, which is fundamentally different to biting–chewing. It is, however, unclear when structural mouthpart interaction (SMI) evolved since this principle obviously occurred multiple times independently in several extant and extinct winged insect groups. Here, we report a new type of SMI in two of the earliest wingless hexapod lineages—Diplura and Collembola. We found that the mandible and maxilla interact with each other via an articulatory stud at the dorsal side of the maxillary stipes, and they are furthermore supported by structures of the hypopharynx and head capsule. These interactions are crucial stabilizing elements during food uptake. The presence of SMI in these ancestrally wingless insects, and its absence in those crustacean groups probably ancestral to insects, indicates that SMI is a groundplan apomorphy of insects. Our results thus contradict the currently established view of insect mouthpart evolution that biting–chewing mouthparts without any form of SMI are the ancestral configuration. Furthermore, SMIs occur in the earliest insects in a high anatomical variety. SMIs in stemgroup representatives of insects may have triggered efficient exploitation and fast adaptation to new terrestrial food sources much earlier than previously supposed.     

麦长管蚜虫龄鉴别特征

【目的】为明确麦长管蚜Sitobion avenae (Fabricius)虫龄鉴别特征, 达到快速鉴别的目的。【方法】在成像观察的基础上, 测定无翅型和有翅型个体不同虫龄的体长、 体宽、 头壳宽、 触角长、 腹管长和后足胫节长6项指标。【结果】麦长管蚜不同翅型个体的体长、 体宽、 头壳宽、 触角长、 腹管长和后足胫节长在虫龄间均存在显著差异, 其中体长、 体宽、 头壳宽和触角长在相邻虫龄之间重叠程度大, 后足胫节长的重叠百分比极小或无重叠; 除有翅型个体4龄若蚜和成蚜之间存在13.93%的重叠外, 腹管长在不同翅型的其他相邻虫龄之间重叠百分比均极小或无重叠, 说明后足胫节长和腹管长可作为虫龄鉴定的主要特征。翅、 触角和尾片的其他外部形态特征在虫龄间也存在一定差异： 3-4龄有翅型若蚜和成蚜虫个体前胸的膨大程度及其翅的长度明显大于同一龄期的无翅型个体, 可用于蚜虫翅型的分辨以及3-4龄有翅若蚜和成蚜的鉴别; 麦长管蚜1和2龄若蚜触角均为5节, 3-4龄若蚜和成蚜的触角均为6节; 同时, 除了成蚜具有完整的尾片外, 1-4龄若蚜尾片均不发达, 说明触角的节数和尾片的发达程度可作为麦长管蚜不同龄期形态鉴别的辅助特征。【结论】以腹管和后足胫节作为麦长管蚜虫龄鉴别的主要特征, 配合其他辅助特征, 如翅的大小、 触角的节数以及尾片的发达程度等, 可达到快速鉴别不同翅型不同龄期蚜虫的目的。     

Adaptations for nectar‐feeding in the mouthparts of long‐proboscid flies (Nemestrinidae: Prosoeca)

The insects with the longest proboscis in relation to body length are the nectar‐feeding Nemestrinidae. These flies represent important pollinators of the South African flora and feature adaptations to particularly long‐tubed flowers. The present study examined the morphology of the extremely long and slender mouthparts of Nemestrinidae for the first time. The heavily sclerotized tubular proboscis of flies from the genus Prosoeca is highly variable in length. It measures 20–47 mm in length and may exceed double the body length in some individuals. Proximally, the proboscis consists of the labrum–epipharynx unit, the laciniae, the hypopharynx, and the labium. The distal half is composed of the prementum of the labium, which solely forms the food tube. In adaptation to long‐tubed and narrow flowers, the prementum is extremely elongated, bearing the short apical labella that appear only to be able to spread apart slightly during nectar uptake. Moving the proboscis from resting position under the body to a vertical feeding position is accomplished in particular by the movements of the laciniae, which function as a lever arm. Comparisons with the mouthparts of other flower visiting flies provide insights into adaptations to nectar‐feeding from long‐tubed flowers. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Wingless and intermorphic males in the ant <Emphasis Type="Italic">Cardiocondyla venustula</Emphasis>

The ant genus Cardiocondyla is characterized by a pronounced male diphenism with wingless fighter males and winged disperser males. Winged males have been lost convergently in at least two species-rich clades. Here, we describe the morphological variability of males of Cardiocondyla venustula from uThukela valley, South Africa. Winged males appear to be absent from this species. However, in addition to wingless (“ergatoid”) males with widely fused thoracic sutures and without ocelli, “intermorphic” males exist that combine the typical morphology of wingless males with characteristics of winged males, e.g., more pronounced thoracic sutures, rudimentary ocelli, and vestigial wings. Similar “intermorphic” males have previously been described from one of several genetically distinct lineages of the Southeast Asian “Cardiocondyla kagutsuchi” complex (Insect. Soc. 52: 274-281, 2005). To determine whether male morphology is associated with distinct clades also in C. venustula, we sequenced a 631 bp fragment of mitochondrial DNA of workers from 13 colonies. We found six haplotypes with a sequence variation of up to 5.7 %. Intermorphic and wingless males did not appear to be associated with a particular of these lineages and within colonies showed the same sequence. Interestingly, two colonies contained workers with different haplotypes, suggesting the occasional migration of queens and/or workers between colonies.     

Head structures of Karoophasma sp. (Hexapoda, Mantophasmatodea) with phylogenetic implications

External and internal head structures of adults of Karoophasma sp. were examined and described. The results are compared with conditions found in other representatives of Mantophasmatodea and members of other lower neopteran groups. The X-shaped apodeme of the frons, the unpigmented oval area enclosed by apical branches of the anterior tentorial arms, the oval sclerotisation at the base of the labrum, the sclerotized rounded apical part of the galea, and the loss of M. labroepipharyngalis are probably autapomorphic for Mantophasmatodea. Plesiomorphic features (groundplan of Neoptera) are the orthognathous condition, the absence of parietal ridges, the absence of a gula, the absence of a 'perforation of the corpotentorium', the multisegmented antennae inserted between the compound eyes, the general arrangement of the mouthparts, the shape and composition of the maxillae and labium, and the nearly complete set of muscles. The presence of a transverse muscle connecting the antennal ampullae is a potential synapomorphy of Orthoptera, Phasmatodea and Dictyoptera. Character states suggesting affinities with Grylloblattodea are the absence of ocelli, the elongation of the corpotentorium, and the very similar mandibles with widely separated bases and completely reduced molae. Whether predacious habits are a synapomorphic feature of Mantophasmatodea and Grylloblattodea is uncertain. The retained orthognathous condition in Mantophasmatodea and Mantodea is likely related with different specialized preying techniques in both groups, i.e. rapid forward pushes of the head–prothorax complex, and the use of raptorial legs, respectively.     

Phylogenetic analysis of Myxophaga (Coleoptera) using larval characters

A phylogenetic parsimony analysis of fifty-four larval characters of Myxophaga (excluding Lepiceridae) resulted in two minimal length cladograms. The monophyly of Torridincolidae, Hydroscaphidae and Microsporidae is supported by several autapomorphies: miniaturization, flattened body with laterally extended tergites, broadened head, scale-like surface structures, broad tentorial bridge, disc-shaped labral sensilla, spiracular gills and pupation in the last larval exuviae. Hydroscaphidae are the sister group of Microsporidae. Larvae of both families are characterized by semi-entognathous mouthparts, tergites with posterior rows of lancet-shaped setae, claws with flattened basal spines and balloon-shaped spiracular gills. The monophyly of all families is supported by autapomorphies. Torridincolidae excluding Delevea is defined as a monophylum by four derived character states: body ovoid, thorax semicircular and as long as abdomen, labral sensilla fused and abdominal sternite IX distinctly reduced and triangular. The monophyly of Torridincolinae (sensu Endrödy-Younga 1997b) is supported by two autapomorphies. The proposed branching pattern suggests that the early representatives of Myxophaga (excluding Lepiceridae) were living in aquatic conditions with a preference for hygropetric habitats. The tendency to live on rocks in running water and miniaturization have played an important role in myxophagan evolution.