Gland Openings Research Articles

Comparative study of the morphology of the gland opening area among Grassatores harvestmen (Arachnida, Opiliones, Laniatores)

Arachnids of the order Opiliones (harvestmen), which includes around 6000 specìes, have a pair of scent glands that open at the sides of the body, producing substances used as defence. Several types of behavioural, morphological and chemical defensive mechanisms have been identified in the order as a whole, although some of these tactics were restricted to particular groups. Only around 60 species have been studied from this perspective so far, more than half of which belong to the largest harvestman family within the order Laniatores, the Gonyleptidae, and have only recently been studied in an evolutionary perspective, showing the usefulness of defensive characters in taxonomy and evolutionary biology. Within Laniatores, the Grassatores clade includes the Gonyleptidae and 20 additional families, mostly poorly or not previously studied. We describe the morphology of the structures involved in fluid displacement during chemical defence in 15 of these families (data on two additional families are available from the literature) and discuss the evolution of such traits based on an available phylogenetic hypothesis of relationships within Grassatores, using the representatives of Triaenonychidae (a non-Grassatores family of Laniatores) for comparison. We conclude that most non-gonyleptoid Grassatores share (maybe plesiomorphically) a series of characteristics, mostly strongly different from what is observed within the gonyleptoids, and that smaller groups seem to share diagnostic features related to chemical defence, as is the case of stygnids, cosmetids and triaenonychines, and especially of manaosbiids and cranaids, whose defensive morphologies largely resemble those of derived gonyleptids. The following main synapomorphies were detected: (a) Grassatores: the presence of a deep and well-defined descending channel; (b) Samooidea+Zalmoxoidea+Assamioidea+Gonyleptoidea: lateral pegs along the lateral channel; (c) Samooidea+Zalmoxoidea: deep channels forming an H on the dorsal scute; (d) Gonyleptoidea: ozopore cutting dorsally (reversing in Agoristenidae and Stygnidae to a laterally placed oval ozopore), a wide and smooth lateral channel, reversing to a lateral channel whose bottom is covered with either small plates (Agoristenidae) or high tubercles (Stygnidae), and apophyses of coxa II close to or covering the ozopore. Die etwa 6 000 Arten der Opiliones (Weberknechte) besitzen ein Paar Stinkdrüsen, die sich an den beiden Körperseiten öffnen und Sekrete zur Verteidigung abgeben. Verschiedene ethologische, morphologische und chemische Verteidigungsmechanismen sind in der gesamten Gruppe verbreitet, andere sind auf einzelne Teilgruppen beschränkt. Bisher sind unter diesen Gesichtspunkten nur etwa 60 Arten untersucht worden, von denen mehr als die Hälfte zur größten Familie innerhalb der Laniatores gehören, den Gonyleptidae. Sie sind erst kürzlich studiert worden, um die Verwendbarkeit derartiger Schutzmechanismen für Taxonomie und Evolutionsbiologie zu zeigen. Innerhalb der Laniatores enthält der Kladus der Grassatores die Gonyleptidae und 20 weitere Familien, die zumeist nur wenig oder bisher überhaupt noch nicht studiert wurden. Wir beschreiben die Morphologie der Strukturen, die in die Sekretabgabe bei der chemischen Verteidigung involviert sind, für 15 dieser Familien (Daten von zwei weiteren Familien stammen aus der Literatur) und diskutieren ihre Evolution auf der Grundlage von vorhandenen Verwandtschaftshypothesen der Grassatores. Als Vergleich dienen Vertreter der Traenonychidae, einer nicht zu den Grassatores gehörenden Familie der Laniatores. Wir schließen daraus, dass die meisten nicht-gonyleptoiden Grassatores eine Reihe von Merkmalen – vielleicht als Plesiomorphien – miteinander teilen. Sie unterscheiden sich meist stark von denen, die man bei den Gonyleptoiden findet. Kleinere Gruppen stimmen wohl in diagnostischen Abwehrstrukturen überein, was für die Stygniden, Cosmetiden und Triaenonychiden, besonders aber für die Manaosbiiden und die Cranaiden zutrifft, deren Strukturen stark denen der abgeleiteten Gonyleptidae ähneln. Folgende Apomorphien wurden festgestellt: (a) Grassatores: tiefer, deutlicher Ausleitungskanal; (b) Samooidae + Zalmoxoidea + Assaioidea + Gonyleptoidea: seitliche Stifte entlang des seitlichen Kanals; (c) Samooidea + Zalmoxoidea: tiefe Kanäle, die ein H auf dem dorsalen Scutum bilden; (d) Gonyleptoidea: dorsal eingelassener Drüsenporus (dagegen ein lateraler ovaler Porus bei Agoristenidae und Stygnidae), ein breiter und glatter lateraler Kanal im Gegensatz zu einem Kanal, dessen Boden entweder mit kleinen Plättchen (Agoristidae) oder Höckern (Stygnidae) bedeckt ist, und Apophysen an der Coxa II, die nahe am Porus stehen oder diesen bedecken. Figure S1. Matrix of character states plotted on available cladograms showing the relationship among the families of Grassatores (modified from Giribet et al. 2009). Data S1. List of characters. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Structure and phylogenetic significance of the sternum V glands in Trichoptera

I investigated the sternum V gland in 38 families of Trichoptera, and found it to be present in 25 of these. I found that the gland is generally present in Annulipalpia, except Dipseudopsidae, and in Spicipalpia. It is widespread in Plenitentoria, while it is often absent in Brevitentoria, especially in males. The opening is slit-like and U or crescent-shaped. There is significant variation in the cuticular structures associated with the opening ranging from no apparent modification, over scaly patches to elaborate protuberances. Gland opening muscles are associated with the gland in all families except Psychomyiidae, and are divided into 2 distinct types: One originating on the front edge of sternum VI found in Philopotamidae, Rhyacophilidae, Glossosomatidae and Hydroptilidae; and 1 originating on the cuticle of sternum V found in all other trichopterans. The shape of the gland reservoir is variable, from round periform to reniform, elongate or compartmentalised. Muscle fibres are often associated with the reservoir, but are notably absent in Limnephilidae. I mapped characters based on gland structures on a phylogeny of Trichoptera, and discuss the results. The sternum V gland provides potentially important characters from the superorder to the species level. I discuss 2 cases where characters from the sternum V gland may solve existing phylogenetic and taxonomic puzzles: Delimitation of Dipseudopsidae versus Polycentropodidae and the relationships among the hydropsychid subfamilies.

Dissecting Microscope Study of the Gastric Mucosa: Capillary Picture visualized by India Ink Infusion and Gland Opening Pattern,

Dissecting Microscope Study of the Gastric Mucosa: Capillary Picture visualized by India Ink Infusion and Gland Opening Pattern,

Systematic position of Umbellozetes Krivolutskiy, 1969 (Acari: Oribatida) in light of the ontogeny of Umbellozetes slaveki n. sp.

On the basis of adult morphology the oribatid mite genus Umbellozetes has been included in the family Tegoribatidae (Achipterioidea) since its original description. Juveniles of this family and other Achipterioidea have plicate cuticle and lack a humeral organ, but the ontogeny of Umbellozetes has been unknown. Herein, we use specimens of all instars to propose and describe Umbellozetes slaveki n. sp. from Central Mongolia. Juveniles of U. slaveki have smooth cuticle, a humeral organ in nymphs, and a dark pigmented macrosclerite around the opisthonotal gland opening, all of which are typical traits of Ceratozetidae, rather than Tegoribatidae. The adult of U. slaveki lack also a posterior notogastral tectum and has long and thin solenidia on legs that is typical for Ceratozetidae. Based on these and other morphological characters, we propose and support the transfer of Umbellozetes to trichoribatinae Ceratozetidae.

Six new species of Prozercon Sellnick, 1943 (Acari, Mesostigmata, Zerconidae) from Greece, with remarks on the genus

The taxonomic histroy of the genus Prozercon Sellnick, 1943 is summarised. A diagnosis of the genus is given, with remarks on variability of certain characters. The genus Rafas Błaszak, 1979b, which was defined earlier on the basis of its divided sternal shield, is proposed as junior synonym of Prozercon, which results in the following new combinations: P. bisternalis (Błaszak, 1979b) comb. nov. and P. blaszaki (Urhan & Ayyildiz, 1996d) comb. nov. Prozercon changbaiensis Bei et al., 2002 is transferred to Mesozercon Błaszak, 1976 as Mesozercon changbaiensis (Bei et al., 2002) comb. nov., on the basis of the presence of the adgenital gland openings and ventrianal setae ZV1. Prozercon willmanni Schweizer, 1948 was synonymised earlier with a former variety of P. kochi Sellnick, 1944, but is here regarded as a valid species since there are several important characters distinguishing the two species. Prozercon masani Moraza, 2006 is proposed as junior synonym of P. cambriensis Skorupski & Luxton, 1996 since no convincing differences exist between the two species. Six new species, P. achaeanus sp. nov., P. bulbiferus sp. nov., P. dramaensis sp. nov., P. graceus sp. nov., P. morazae sp. nov. and P. norae sp. nov., are described from Greece, and P. carpathofimbriatus and P. carsticus are recorded for the first time from the country. Detailed descriptions of the female and the previously unknown deutonymph are of P. yavuzi Urhan, 1998a also presented, as the Greek specimens differ from the Turkish ones by important characters. A key to the known species of Prozercon is provided.

Integrative taxonomy demonstrates the unexpected synonymy between two predatory mite species: Cydnodromus idaeus and C. picanus (Acari:Phytoseiidae)

Species of the mite family Phytoseiidae are well known as predators of mite pests all over the world. Their identification is thus of great interest for biological control. The specimens examined in this study belong to the species Cydnodromus idaeus (described from Brazil) and C. picanus (described from Chile). They were collected together on the same plant in Argentina. These species are mainly differentiated by the presence/absence of the dorsal solenostomes (gland openings) gd2. Some morphometric differences were observed between the Argentinian specimens and the type material of C. idaeus and C. picanus; however, they were not sufficient to support a species separation. Morphological and molecular analyses with two mtDNA (12S rRNA, CytB) and a nuclear DNA (ITS) marker showed no difference between Argentinian specimens with and without the solenostome gd2. Also, molecular differentiation between these latter specimens, C. picanus and C. idaeus, was very low, suggesting that all these individuals belong to the same species. Biological experiments confirm these results, as 75% of the progeny resulting from females with gd2 had gd2 present whereas all the descendants resulting from the females without gd2 had gd2 present too. The presence/absence of this solenostome seems thus to be variable within a species and cannot be used diagnostically. We conclude that all specimens from Argentina belong to C. idaeus and that C. picanus is a junior synonym of C. idaeus. The present results were unexpected as the presence/absence of solenostomes is used in Phytoseiidae identification keys and as one of a suite of diagnostic characters for discriminating between species. The consequences of these findings for the taxonomy of Phytoseiidae are discussed.

Scanning electron microscopic study of the tongue in the rainbow lorikeet (Trichoglossus haematodus)

The dorsal lingual surfaces of rainbow lorikeet (Trichoglossus haematodus) were examined by scanning electron microscopy. Macroscopically, the tongue of the rainbow lorikeet has a finger-like shape. Three parts are distinguished in the dorsal surface of the tongue: the apex, body, and root of the tongue. The apex of the tongue has numerous processes inclined toward medial side from lateral side. These processes are rod-like structure and smooth surfaces. Many grooves are observed in both lateral sides of the lingual body. A large opening of the lingual gland exists in central part of the lingual root and some large openings of the lingual glands exist in both lateral sides of the lingual root.

Investigations on the conjunctival goblet cells and on the characteristics of glands associated with the eye in the guinea pig

To investigate the distribution and density of conjunctival goblet cells (GC) and to study the anatomy and microscopic characteristics of glands associated with the eye in the guinea pig. Twenty-five guinea pigs were used. Meibomian gland openings were counted using biomicroscopy. Conjunctiva, eyelids and glands were embedded in glycol methacrylate and paraffin. Sections were stained with hematoxylin and eosin (H&E), periodic acid Schiff's reaction (PAS) and Alcian blue (AB). Highest GC densities were found in the bulbar and palpebral region of the nasal conjunctiva (GC index: 13.7-16.4%). Lowest GC densities (GC index: 0.0-1.0%) were found in 3/4 limbal regions (nasal and temporal upper eyelid, temporal lower eyelid). Guinea pigs have 27.1±3.0 (mean±SD) meibomian gland openings in the upper lid and 25.7±2.3 in the lower lid. Difference between upper and lower lid was significant (P=0.037). Two subconjunctival sebaceous glands occur temporal to each eye. The Harderian gland is very large. In the lacrimal gland three different cell types were distinguished both according to the cell structure and histochemical staining. Goblet cell densities are lower in guinea pigs than in dogs and horses. Positive staining with PAS and AB could be an indication that mucins are produced in the lacrimal gland. If so, they may contribute to the mucin layer of the tear film. Both the extraordinarily large Harderian gland and the subconjunctival sebaceous glands produce lipids and may contribute to the lipid layer of the tear film.

Preliminary assessement of the estrogenic potential of Apuleia leiocarpa (Vogel) J.F. Macbr., Fabaceae, Platypodium elegans Vogel, Fabaceae, and Brosimum guianense (Aubl.) Huber, Moraceae, on the wistar rat reproductive system

Um grupo de primatas da espécie Alouatta guariba foi estudado em seu habitat natural na Mata Atlântica, onde foi observada uma drástica redução populacional dessa espécie. Suspeita-se que essa redução se deve à inibição da fertilidade das fêmeas devido ao consumo de Apuleia leiocarpa (Vogel) J.F. Macbr., Fabaceae, Platypodium elegans Vogel, Fabaceae e Brosimum guianense (Aubl.) Huber, Moraceae. Estudos fitoquímicos indicaram a presença de cumarinas, especialmente em B. guianense e P. elegans, cujo efeito adverso no desenvolvimento de folículos ovarianos foi previamente relatado em ratas. Este trabalho investiga a atividade estrogênica dessas plantas no útero e vagina utilizando ratas castradas como modelo experimental. Ratas Wistar pubescentes castradas foram tratadas por cinco dias com os extratos hidroalcoólicos de A. leiocarpa, P. elegans and B. guianense (50 mg/rata). Foram analisados os seguintes parâmetros: peso de útero e hipófise, cornificação e abertura vaginal. Os resultados preliminares obtidos mostraram que a administração dos extratos não alterou significativamente as variáveis analisadas, indicando, indiretamente, a ausência de efeito estrogênico no sistema reprodutor das ratas tratadas com as plantas citadas. Esses dados sugerem que o consumo dessas plantas não está relacionado com a redução populacional observada no grupo de primatas da espécie A. guariba.

Mesothelae have venom glands

Although venom glands were described for the Mesothelae many years ago (Bristowe & Millot 1933), a more recent monograph (Haupt 2003) denied the existence of such glands in the Mesothelae. Our morphological studies of nine different species of Liphistius demonstrated the presence of venom gland openings on the cheliceral fangs in all of these species. Also, we observed a small venom gland in the anterior portion of the cheliceral basal segment. The possibility that venom glands may be lacking in adult males is discussed. The presence of venom glands in the Mesothelae indicates that this is a plesiomorphic character of all Araneae.

Integumentary “rosette‐like structures” in Microcoryphia and Zygentoma (Insecta): SEM morphological and topographic surveys

Abstract“Rosette‐like structures” (RS) were found previously on integument of different body regions of Microcoryphia and Zygentoma. Their putative functions, either as sensilla or as openings of epidermal glands, are still not clear. This study was carried out as the initial descriptive stage of a special investigation of RS. For the first time, the morphology and topography of RS in nine species of wingless insects, including enigmatic silverfish Tricholepidion gertschi, were examined specially by means of scanning electron microscopy. Rosette‐like structures were found in all studied species except for an atelurid Nipponatelura shirozui. They were numerous, mainly on the unscaled body appendages. Solitary RS were distributed randomly on most surfaces of the insect body, except for the antennal flagellum of all studied representatives and the caudalia of zygentomans where RS were arranged among rows of bristles and sensillae. Some of clustered RS were closely positioned to joints or articular membranes. The female genital appendages exhibited quite a peculiar pattern of RS distribution. The RS were tentatively categorized into five basic morphological types. There is considerable variation in morphology of RS among members of the Microcoryphia, which probably reflects functional heterogeneity of RS. On the contrary, RS of zygentomans mainly belong to one morphological type, whereas another one of RS‐types was found in T. gertschi only. The homologization between highly variable RS in Microcoryphia and morphologically uniform those in Zygentoma currently seems to be unfeasible.

Surface Morphology of the Emu (Dromaius novaehollandiae) Tongue

Despite numerous morphological studies on the avian tongue, very little meaningful information is currently available on the surface features of this organ using scanning electron microscopy (SEM). The only SEM description of a ratite tongue is that of the ostrich, although the descriptions are brief and superficial. This SEM study of the emu tongue confirms and compliments the comprehensive macroscopic and histological data available for this commercially important species. The tongues of five emus were fixed, cut into blocks representing the dorsum, ventrum and root and routinely processed for SEM. Three morphologically distinguishable surface types (desquamating, non-desquamating and lymphoepithelium) related to peculiarities in surface cell shape and status (desquamating or non-desquamating), cell surface modifications and distribution of gland openings, and which showed a regional distribution, could be identified. Three basic types of cell surface modifications (microplicae, microvilli and cilia) were observed, with microvilli and cilia being described for the first time in an avian tongue by SEM. The desquamating surface cells fulfil a mechanical protective function, whereas the microplicae, microvilli and cilia appear to be adaptations for the trapping and spreading of mucus which also fulfils a protective function.

The Skin Landscape Following Nonoptical Capacitance Imaging

Skin capacitance is an electrical property measurable at the level of the stratum corneum. Values are related to the moisture content of the tissue. Using the silicon image sensor technology, it has recently become possible to measure capacitance at 50 microm intervals on the skin surface. The resulting nonoptical picture corresponds to skin capacitance imaging. This novel tool for dermatologists highlights with precision the hollow skin surface patterns, including dermatoglyphics, the patterns of the shallow skin lines, and wrinkles. The topographic heterogeneity in skin surface hydration is made visible. In addition, the sweat gland and follicular openings are disclosed. Skin disorders induced by surfactants or presenting as hyperkeratotic areas, including some neoplasms, may show typical aspects. It is concluded that skin capacitance imaging brings added value to the clinical assessment performed by dermatologists.

A new termite species (Isoptera: Termitidae: Termitinae: Amitermes) and first record of a Subterranean Termite from the Coastal Desert of South America

At about one hundred species (Scheffrahn & Su 1987), Amitermes, is the second largest genus after Microcerotermes in the subfamily Termitinae. This cosmopolitan genus is found in a wide variety of habitats from rainforests e.g., Amitermes excellens (Silvestri) from Guyana (Emerson 1925) and Amitermes dentatus (Haviland) from Sumatra (Gathorne-Hardy et al. 2001) to deserts, e.g. Amitermes emersoni Light from Coachella, California (Light 1930) and Amitermes desertorum Desneux from Egypt (Sands 1992). Only eight species of Amitermes are known from the Neotropics and only five occur across mainland South America. Soldiers of Amitermes are characterized by a bulbous head capsule and sickle-shaped mandibles, each with a single tooth of various shapes on their inner margins. Soldiers of all species have a large cephalic gland opening to a circular fontanelle on the frons. When confronted by an agonist, the soldier emits a terpenoid secretion which oozes onto setae around and below the fontanelle (Scheffrahn et al. 1983). Herein, is described a new Amitermes from Peru and the first record of a subterranean termite along the Pacific coastal desert of South America.

Scanning Electron Microscopic Study of the Tongue in the Jungle Nightjar (Caprimulgus indicus)

The dorsal lingual surfaces of adult Jungle Nightjar (Caprimulgus indicus) were examined by scanning electron microscopy. Macroscopically, the tongue of the Jungle Nightjar had a spearhead-like shape. Three parts were distinguished in the dorsal surface of the tongue: the apex, body, and root of the tongue. The tip of the tongue was round shape and a median groove is not observed. The dorsal surface of the lingual apex presented a smooth aspect and desquamation of the epithelial cells was observed on the surface of the lingual apex. Small and large conical papillae were observed on the lateral side of the lingual body. There were the giant conical papillae on the lateral side of the lingual body. The conical papillae of the lingual body were inclined toward the posterior of the tongue on the posterior end. Some openings of the lingual glands existed in the lingual root.

A Defensive Behavior ofAcerentulus confinis(Berlese) (Protura: Acerentomidae)

A proturan (Acerentulus confines (Berlese)) was observed and videotaped in an encounter with a springtail (Tomocerina lamellifera (Mills)). Following repeated contacts between the two, the proturan released a sticky exudate when a leg of the springtail came in contact with the proturan's abdomen. The exudate stretched to a 1-mm length before snapping. This exudate emanated from the large gland openings on the eighth abdominal segment. Comparison with the few other videotaped examples of proturan defensive behavior suggests that the exudate is released only after repeated contact between the proturan and another organism.

Two new species of Amnestus from Guatemala, with new records for some other Guatemalan burrower bugs (Hemiptera: Heteroptera: Cydnidae)

In this paper we describe two new species in the genus Amnestus, Amnestus henryi and Amnestus zacki, and we register new localities for 10 species of burrowing bugs for the fauna of Guatemala; two of these species correspond to new records, Amnestus pusio (Stål), and Dallasiellus reflexus Froeschner. We include a brief description of the 28 species known for Guatemala, mentioning old and new records; new species are fully described and illustrated, and drawings of the male genitalia, scent gland opening, fore, and hind legs of males are also presented. A key to separate the 28 Guatemalan species of burrower bugs is provided.

The functional morphology of the metapleural gland of the leaf-cutting ant Atta laevigata (Formicidae: Attini)

Given the importance of the metapleural gland in ants, the present study aimed at describing it in minor, media, and major workers of Atta laevigata, focusing their physiology using scanning electron microscopy (SEM), histologic, and histochemical techniques. The results revealed that this gland is paired and located in the metathoracic region, consisted of two portions: secretory and the storage ones. Both portions are connected by extracytoplasmic canaliculi that drain the secretion of each secretory cell they form groups that open into the perforated plate located in the wall of the collecting chamber. The oval-shaped and elongated secretory cells form clusters of approximately 20 cells, bundled together by connective tissue. Each secretory cell connects to the reservoir through a canaliculus divided into an intra- and extracytoplasmic portion. The collecting chamber and the reservoir are internally lined by a single squamous epithelium with a cuticular intima, with folds in the collecting chamber and smooth in the remaining of the reservoir. External muscle layers surrounding the reservoir are observed which aid the release of secretion by the gland opening (one on each side) located in the exoskeleton near coxae of hind legs. Secretory cells were strongly positive for acidic and total lipids, proteins, and acidic polysaccharides, suggesting the glycolipoproteins nature of the final secretion. Morphometrically, the diameter of the reservoir is proportional to body size of minor, media, and major workers. This implies a larger capacity to produce secretion, including antibiotic substances, by the individuals that perform specific tasks within the colony.

Histomorphology of the Proventriculus of three Species of Australian Passerines: Lichmera indistincta, Zosterops lateralis and Poephila guttata

Histomorphology of the proventriculi of nectarivorous, granivorous and omnivorous passerines was studied. The proventriculus consisted of mucosal, submucosal, muscularis and serosal layers. Proventricular wall was thickest in omnivore, thinnest in granivore and intermediate in nectarivore. The openings of mucosal glands had a single spiral-like fold of mucosa in the omnivorous Silvereye, 2-3 spirals in the granivorous Zebra finch and 4-5 spirals in the nectarivorous Brown honeyeater. The mucosal glands were arranged in a uniform row in the wall of the organ and opened individually via a primary duct to the lumen of the proventriculus. The surface epithelial cells of the tunica mucosa contained secretory cells and the proventricular glands contained endocrine, neck and oxynticopeptic cells. The ultrastructural features of the oxynticopeptic cells changed from the oral to the aboral portion of the gland. In the oral region, the cytoplasm presented numerous, smaller (600-900 nm) homogenously dense zymogen secretory vesicles and larger (0.8-2.3 microm) pale floccular, tubular, mucin-like secretory granules, few small mitochondria and RER while in the aboral portion of the gland, the cytoplasm presented numerous, large mitochondria with closely packed cristae, secondary lysosome and infolding of the basal and apical cell membrane. The tunica sub mucosa was thin with occasional large blood vessels. The tunica muscularis consisted of inner longitudinal, middle circular and outer longitudinal layers. The external tunica serosa contained large bundles of myelinated and unmyelinated axons that were possibly branches of the intestinal nerve. The structural adaptations of the proventriculi of these three species to their various diets are discussed.

Morphology of Hydrozetes confervae ( ) and H. parisiensis (Acari: Oribatida: Hydrozetidae), and keys to European species of Hydrozetes Berlese, 1902

Hydrozetes confervae [Schrank, F.P., 1781. Enumeratio insectorum Austriae indigenorum. Augustae Vindeliciorum, 1–552] and Hydrozetes parisiensis [Grandjean, F., 1948. Sur les Hydrozetes (Acariens) de l’Europe occidentale. Bull. Mus. Nat. Hist. nat., Paris, ser. 2(20), 328–335] are common European species of the aquatic oribatid mite family Hydrozetidae, but their external morphology is incompletely known. We describe and illustrate their larvae for the first time, and the nymphs of both species are redescribed and illustrated. Juveniles of the two species differ mainly by the position of gastronotal seta lm in relation to the opisthonotal gland opening ( gla) and by the number of extremely long posterior hysterosomal setae in nymphs. In H. confervae seta lm inserts anteromedial to gla, but posterior to gla in H. parisiensis; nymphs of H. confervae have three pairs of long hysterosomal setae, while H. parisiensis has a larger, but variable number. Separate identification keys for the larvae, nymphs and adults of all known European species of Hydrozetes Berlese, 1902, are presented.