Post-larval Instars Research Articles

The missing metamorphosis: DNA barcoding reveals that Allotanaupodoidea larvae are strikingly similar to post-larval stages</p >

Parasitengona is a diverse group of Prostigmata, including mites with life cycles that include important morphological changes between larva and deutonymph, an evolutionary novelty not shared by its closely related taxa (Halacaridae, Pezidade or Anystidae). Allotanaupodoidea is a superfamily of Parasitengona, known solely by the post-larval instars, that differs from the remaining Parasitengona mainly due to the lack of trichobothria in the prodorsal shield. Allotanaupodoidea has a single family Allotanaupodidae with six species distributed in two subfamilies, Allotanaupodinae Zhang & Fan, 2007 and Paratanaupodinae Zhang & Fan, 2007, with one and two genera, respectively. In the present study, we describe the larva of Allotanaupodus winksi Zhang & Fan, 2007 from New Zealand associated with the deutonymph by means of cytochrome oxidase I barcoding. The description reveals a remarkable resemblance between larval and post larval specimens of A. winksi, a condition approached among Parasitengona only by Calyptostomatidae.

Epimorphic development in tropical shallow-water Nymphonidae (Arthropoda: Pycnogonida) revealed by fluorescence imaging

BackgroundExtant lineages of sea spiders (Pycnogonida) exhibit different types of development. Most commonly, pycnogonids hatch as a minute, feeding protonymphon larva with subsequent anamorphic development. However, especially in cold water habitats at higher latitudes and in the deep sea, some taxa have large, lecithotrophic larvae, or even undergo extended embryonic development with significantly advanced postlarval hatching stages. Similar biogeographic trends are observed in other marine invertebrates, often referred to as “Thorson’s rule”.ResultsTo expand our knowledge on the developmental diversity in the most speciose pycnogonid genus Nymphon, we studied the developmental stages of the two tropical representatives N. floridanum and N. micronesicum., We compared classical scanning electron microscopy with fluorescence-based approaches to determine which imaging strategy is better suited for the ethanol-fixed material available. Both species show epimorphic development and hatch as an advanced, lecithotrophic postlarval instar possessing the anlagen of all body segments. Leg pairs 1–3 show a considerable degree of differentiation at hatching, but their proximal regions remain coiled and hidden under the cuticle of the hatching instar. The adult palp and oviger are not anteceded by three-articled larval limbs, but differentiate directly from non-articulated limb buds during postembryonic development.ConclusionsFluorescence imaging yielded more reliable morphological data than classical scanning electron microscopy, being the method of choice for maximal information gain from rare and fragile sea spider samples fixed in high-percentage ethanol. The discovery of epimorphic development with lecithotrophic postlarval instars in two small Nymphon species from tropical shallow-water habitats challenges the notion that this developmental pathway represents an exclusive cold-water adaptation in Nymphonidae. Instead, close phylogenetic affinities to the likewise more direct-developing Callipallenidae hint at a common evolutionary origin of this trait in the clade Nymphonoidea (Callipallenidae + Nymphonidae). The lack of functional palpal and ovigeral larval limbs in callipallenids and postlarval hatchers among nymphonids may be a derived character of Nymphonoidea. To further test this hypothesis, a stable and well-resolved phylogenetic backbone for Nymphonoidea is key.

Two new species of Caeculisoma (Trombidiformes: Erythraeidae) from Madagascar

Two new species of Caeculisoma are described and illustrated/photographed based on post-larval instars from Madagascar. Caeculisoma banari n. sp. has two different types of setae on dorsal idiosoma whereas C. madagascarensis n. sp. has one type of dorsal idiosomal setae but two different sizes. Details of different characters are presented in photographs and tables.

Paedomorphosis and sexuality in Eulohmanniidae (Acari, Oribatida): surprising diversity in a relictual family of oribatid mites

The distinctive oribatid mite family Eulohmanniidae has been known almost exclusively from the type species of Eulohmannia, E. ribagai (Berlese, 1910), which is widely distributed in the northern Hemisphere where it inhabits fine humus, typically beneath forest litter and moss. We describe the morphological ontogeny of E. ribagai based primarily on material from New York—supported by specimens from Canada, Europe, and Asia—and correct errors in the literature. Ancillary biological notes relate to phenology, feeding biology, and reproduction; most important is the discovery of apparent sexual populations in the Pacific Northwest in this otherwise thelytokous (‘parthenogenetic’) species. Feeding seems to be preceded by secretion of a thick globule that captures food particles in the ventriculus, but this needs verification. Related nomenclatural actions include the clarification of purported synonyms and the proposal of species-rank for E. ribagai bifurcata Fujikawa. The latter was described as having several traits, including the purported presence of opisthonotal glands, that a study of type specimens show to reflect errors of observation or interpretation. A new diagnosis of Eulohmannia is informed also by preliminary observations on two as-yet undescribed species from Asia, one of which is apparently sexual, and the other paedomorphic in being monodactylous. We propose a new genus, Paedolohmannia n. gen., with P. metzi n. sp. as type, based on type material from Oregon, USA and additional material from California and Washington. The paraprocts of this species are formed by the adanal segment in all post-larval instars; it is only the second unequivocal example in Oribatida of the anal segment failing to appear during anamorphic development. This species also appears to be sexual, so it is unlikely that thelytoky was an ancestral trait of the family. Based on new information, the diagnosis for Eulohmanniidae is adjusted and expanded. Published inferences on the relationships of the family with other members of the paraphyletic infraorder Mixonomata, variously based on morphological and molecular methods, are reviewed and found inconsistent. While properly considered a relictual taxon, Eulohmanniidae is more diverse than previously thought, with the northeast Palaearctic and northwest Nearctic being regions especially deserving of more thorough sampling and genetic analysis.

Correspondence of larval and postlarval instars in two species of the subgenus Zaracarus (Acari: Erythraeidae: Erythraeus) established with laboratory rearing.

Laboratory rearing of two mite species, Erythraeus (Zaracarus) budapestensis Fain Ripka, 1998 collected in Turkey and E. (Z.) rupestris (Linnaeus, 1758) sampled in Germany, allowed establishing the correspondence of their larval and postlarval instars. Erythraeus (Z.) iranicus Saboori Akrami, 2001 syn. nov. is considered a new subjective junior synonym of E. (Z.) budapestensis. Erythraeus (Z.) eleonorae Haitlinger, 1987 syn. nov. and E. (Z.) didonae Haitlinger, 2000 syn. nov. are synonymized with E. (Z.) rupestris. Data on the life history, parasitic associations and habitats are provided, and the status of currently recognized subgenera of Erythraeus is discussed.

<p class="Body"><strong>Integrating phylogeny, ontogeny and systematics of the mite family Smarididae (Prostigmata, Parasitengona): Classification, identification key, and description of new taxa</strong></p>

Unlike most terrestrial parasitengone mites (chiggers, erythraeids), known mostly from parasitic and easy-to-collect larvae, smaridid systematics are mainly based on the post larval instar. Larvae are rarely collected, and their biology and host associations are virtually unknown. Here we infer phylogenetic relationships of Smarididae based on 50 morphological characters using both larval and post larval instars, including data on the larval morphology of Trichosmaris obtained through rearing. The subfamily Smaridinae, as currently understood, was recovered paraphyletic: the genus Smaris was rendered as basal smaridid lineage, while the genus Fessonia (Smaridinae) was sister to Hirstiosomatinae, albeit with moderate support. Our analysis suggests that the genus Surasmaris Southcott, 1995 is a junior synonym of Trichosmaris Southcott, 1963 (syn. nov.), and two Sphaerotarsus species should be placed into Hirstiosoma: Hirstiosoma baenai (Mayoral & Barranco, 2017) comb. nov., Hirstiosoma quercus (Yazdanpanah, Saboori & Hakimitabar, 2016) comb. nov. Sphaerotarsus monticolus Southcott, 1997 and S. leptopilus were recovered as independent lineages, and hence, a new genus Southcottiana gen. nov. is proposed to include Southcottiana monticola comb. nov (Southcott, 1997). We describe two new species, Trichosmaris paulensis sp. nov. (adults, larvae) and T. calcarensis sp. nov. (larva), and present the first description of larval T. dispar, the type species of Trichosmaris, previously known only from post larval instars. Based on the above results, we give a key to larval genera of Smarididae and a key to species of Trichosmaris (larval and postlarval instars).

A postlarval instar of Phoxichilidium femoratum (Pycnogonida, Phoxichilidiidae) with an exceptional malformation.

Individuals of the marine chelicerate lineage Pycnogonida (sea spiders) show considerable regenerative capabilities after appendage injury or loss. In their natural habitats, especially the long legs of sea spiders are commonly lost and regenerated, as is evidenced by the frequent encounter of specimens with missing or miniature legs. In contrast to this, the collection of individuals with abnormally developed appendages or trunk regions is comparably rare. Here, we studied a remarkable malformation in a postlarval instar of the species Phoxichilidium femoratum (Rathke, 1799) and describe the external morphology and internal organization of the specimen using a combination of fluorescent histochemistry and scanning electron microscopy. The individual completely lacks the last trunk segment with leg pair 4 and the normally penultimate trunk segment bears only a single aberrant appendage resembling an extension of the anteroposterior body axis. Externally, the proximal units of the articulated appendage are unpaired, but further distally a bifurcation into two equally developed leg-like branches is found. Three-dimensional reconstruction of the musculature reveals components of two regular leg muscle sets in several of the proximal articles. This confirms interpretation of the entire appendage as a malformed leg and reveals an externally hidden paired organization along its entire proximodistal axis. To explain the origin of this unique malformation, early pioneering studies on the regenerative potential of pycnogonids are evaluated and (a) an injury-induced partial fusion of the developing limb buds of leg pair 3, as well as (b) irregular leg regeneration following near complete loss of trunk segments 3 and 4 are discussed. Which of the two hypotheses is more realistic remains to be tested by dedicated experimental approaches. These will have to rely on pycnogonid species with established laboratory husbandry in order to overcome the limitations of the few short-term regeneration studies performed to date.

Postembryonic development of Nymphon australe Hodgson, 1902 (Pycnogonida, Nymphonidae) from Antarctica

Developmental modes in pycnogonids are variable, even between congeneric species. Most of our previous knowledge of pycnogonid life history stages is based on morphological descriptions of the larval and those postlarval instars still retained on male ovigers, whereas the free-living instars are largely unknown. In this paper, a combination of morphological and molecular tools is used in order to link those postlarval instars retained on male ovigers to free-living specimens representing putatively later stages in the postembryonic development of a sea spider species. Male specimens of Nymphon australe carrying postembryonic instars were collected from localities off the South Shetland Islands, the Weddell Sea, the Drake Passage, the Bransfield Strait, and the Ross Sea. Three subsequent free-living instars were collected from Drake Passage. Nymphon australe hatch as a postlarval instar with two-articled palps and limb buds of the two first-walking legs. Postlarval instars 1 and 2 (both carried on the ovigers of males), postlarval instars 3 and 4, and a juvenile (all three free living) are all described and illustrated. A molecular phylogenetic based on the cox1 gene links all free-living stages to N. australe populations from the Antarctic Peninsula. The postlarval development of N. australe is discussed here and compared with those known from other pycnogonid species with similar development pathways.

Multi-instar descriptions of cave dwelling Erythraeidae (Trombidiformes: Parasitengona) employing an integrative approach.

The life cycle of Parasitengona includes major morphological changes precluding an instar association based only on the morphology. This makes rearing and/or molecular data necessary to associate the heteromorphic instars. Most of the described species are known from either post larval instars or larva. Following a previous study on Palearctic Erythraeidae, in the present study the instar association was made through an integrative approach including rearing trials and molecular analysis of the cytochrome oxidase I (COI) gene with the Bayesian Generalized Mixed Yule Coalescent (bGMYC) algorithm for species delimitation. Two new cave dwelling Erythraeidae (Trombidiformes: Parasitengona) species are described Lasioerythraeus jessicae sp. nov. and Leptus sidorchukae sp. nov. including all active instars. Additionally, a complete description of the previously unknown adults of Charletonia rocciai Treat Flechtmann, 1979 is provided with notes on the larva and deutonymph. We also demonstrate experimentally that Ch. rocciai larvae are not attached to the same individual host during the entire feeding stage. We discuss the presence of troglomorphisms in Le. sidorchukae sp. nov.; and the distribution of the species.

A revision of the Pteridopodinae (Acari: Parasitengonina: Chyzeriidae) with the description of a new genus from South Spain and key to the Pteridopodinae

The subfamily Pteridopodinae (Chyzeriidae) is reviewed and an updated diagnosis is provided for the family and the subfamily. A new genus, Iberochyzeria gen. nov., is described from mites parasitizing Orthoptera (Acrididae) in southern Spain. In addition, a list of species and a diagnosis for the larvae and postlarval instars are provided for each genus of the subfamily, as well as comments about their taxonomic status. Napassenia Haitlinger, 1999 is synonymized with Parawenhoekia Paoli 1937. A key to the species of Pteridopodinae is presented.

Linear intermolt growth in Americamysis bahia (Molenock 1969) (Mysida, Mysidae)

ABSTRACTTwo phases of allometry, prepubertal, and pubertal, are evident in A. bahia, equally dividing the first six instars. Coefficients of variation of the sizes of individuals’ abdomens, carapaces, and standard lengths significantly decrease in intermolt four, suggesting a synchronization of the size at which individuals enter the pubertal phase. Growth in standard length is best expressed over the first six post-larval instars by a quadratic equation, but within instars 85%, or more, of the expansion occurs linearly during the intermolt period, with only about 15% occurring during ecdysis. Estimations of carapace:abdomen allometry indicate an average ratio of 1:1.97 during the intermolt and 1:1.68 during ecdysis. The average molt:intermolt ratio in the carapace expansion is 1:3.16, and in the abdomen, 1:3.71, indicating that proportional growth between the carapace and the abdomen is continuous during both the intermolt and molt phases, but occur at different rates and proportions during the two periods.

Ontogeny of Trimerocephalus lelievrei (Trilobita, Phacopida), a representative of the Late Devonian phacopine paedomorphocline; a morphometric approach

A detailed morphometric approach based on size and on outline analyses has been used on an exceptionally well-preserved assemblage of silicified trilobite exuvia, recovered from a Late Devonian limestone from southeastern Morocco. The material comprises a series of late larval to postlarval growth stages belonging to a single phacopine species, Trimerocephalus lelievrei Cronier and Feist, 1997. Plurimodality of size distribution has allowed us to discriminate postlarval instars. Distinct dimensional classes of isolated parts are obtained using the intertooth distances on the posterior pygidial margin and the internotch distances in the cephalic vincular furrow, which are functionally linked during trilobite enrollment. Morphometric analysis of development permitted demonstration of progressive shape change in agreement with ontogenetic ordination and a comparison of the timing of size and shape changes. The main shape changes appear to occur early in development, and once the adult morphology is obtained, size increases significantly. The growth rate during ontogeny is estimated by analogy with extant deep-sea crustaceans. Exponential size increase resulting from constant duration of intermolt periods may be regarded as a life history strategy to compete in a nutrient-impoverished offshore environment. The particular phacopine mode of molting, which involves the opening of the neck joint after ankylosis of the facial sutures, occurred in Trimerocephalus lelievrei between the first two postlarval instars, later than in its ancestor. Trimerocephalus lelievrei occupies an intermediate position within the phacopine paedomorphocline as indicated by the delayed onset of ankylosis.

New data concerning postembryonic development in Antarctic Ammothea species (Pycnogonida: Ammotheidae)

In this paper, new data on larval and postlarval stages after newly collected and museum-deposited material of six Ammothea species is provided and compared with previously known information. Different developmental stages attached to the ovigerous legs of adult males for each species were found: four stages [protonymphon (Ptn), postlarval instar 1 (PL-1), postlarval instar 2 (PL-2), and postlarval instar 3 (PL-3)] for A. carolinensis; just one (Ptn) for A. clausi and A. minor; three stages (Ptn, PL-1, PL-2) for A. bicorniculata and A. spinosa; and other three (Ptn, PL-2, PL-3) for A. longispina. In the present contribution, the external morphology of each larval and postlarval instar is described, illustrated, and discussed. The larval and postlarval development of Ammothea bicorniculata, A. carolinensis, A. longispina, and A. spinosa is characterized by (1) the eggs hatch as a protonymphon larva; (2) the larvae and subsequent postlarval stages have yolk reserves and a relatively large size (0.5–0.85 mm in length for the protonymphon); (3) the postlarvae remain on the ovigerous legs of males during several moults; (4) the spinning spine is absent; and (5) the development of walking legs is sequential. The protonymphon larva of A. clausi and A. minor is the only stage on the ovigerous legs of males, and this stage is characterized by: (1) there is no yolk reserve and it has a relatively small size (0.22–0.3 mm in length); (2) the spinning spine is present; and (3) all larval appendages have a relatively large size.

Water balance of the American dog tick, Dermacentor variabilis, throughout its development with comparative observations between field-collected and laboratory-reared ticks

Water balance characteristic data are compiled and determined for each non-fed instar of the American dog tick, Dermacentor variabilis, vector of tularaemia and spotted fever rickettsia, comparing wild-caught and laboratory-colonized populations, to establish how habitat influences D. variabilis dehydration resistance. In contrast to ticks from the field, laboratory-colonized ticks show a progression in percentage body water content from a low of 59% in the egg to a high of 68% in the adult (all instars from the field population have similar values, averaging 63%) and are less tolerant of water stress (2–6% reduction in dehydration tolerance (DT)). We presume that these are colony artefacts as a product of relaxing selective pressure by rearing under optimal conditions of temperature, relative humidity (RH) and host quality. For field-collected and laboratory-colonized populations, larvae survive down to 75–85% RH [critical equilibrium humidity (CEH)], but nymphs and adults require moist air of 85–93% RH, and eggs do not absorb water vapour. Larvae, but not eggs, experience rapid water loss at 30–35°C [critical transition temperature (CTT)], which is 5°C lower than that of post-larval instars. Larvae succumb to dehydration more readily (lower DT limit, eggs have the highest) and are more prone to water loss by having a high net transpiration rate (NTR) as a result of their minute body size and high activation energies for water loss. Comparison of DT with water loss during development for seven tick species reveals that NTR is a species-specific characteristic and species that lose water quickly or slowly as larvae do so for subsequent developmental instars. The CEH, CTT and DT reveal little with regard to habitat suitability and matching a tick to a particular habitat. Ticks operate at the microhabitat, not habitat, level, indicating that ticks can find suitable refuges in many different geographic areas, which accounts for the overlapping distribution of ticks with different NTRs.

Proliferation of red velvet mite Balaustium sp. nr. putmani (Erythraeidae) in Ohio based on water relations of active instars

ABSTRACT Population bursts, numbering in thousands of individuals, are characteristic of red velvet mites, Balaustium sp. nr. putmani, in the springtime in Central Ohio. We determined water-balance characteristics for each of the mobile instars (larva, deutonymph, adult female; males are seemingly absent from this population) to link dehydration tolerance with heightened activity in the same habitat. This mite loses water rapidly: larva > deutonymph > adult. None of these active instars could absorb water vapor, unlike many terrestrial mites, indicating that this mite must imbibe liquid as free water or from food sources to maintain water balance. As a voracious predator, most of the liquid is probably obtained from feeding. Developmentally, larvae are the most sensitive and vulnerable to water stress because of their high net transpiration rate and low dehydration tolerance limit. Additionally, urnulae glands are only present in the post-larval instars; hence, larvae lack the protective waterproofing secretion that is provided by these glands. Deutonymphs and adults are much more resistant to desiccation, are capable of losing approximately 40% of their water content before succumbing to death, and have reduced water loss rates. We concluded that population bursts of B. sp. nr. putmani might be a response to abundance of plant pests in the landscape. Deutonymphs and adults are modified for water conservation and are correspondingly active for longer periods of time. Larvae survive for a brief time, which minimizes their exposure to desiccating habitats, and use the cooler temperatures experienced early in the season, which suppress their high rate of water loss.

Taxonomic Notes onWillmannellaFeider, 1952 (Acari: Actinotrichida: Microtrombidiidae) with Redescription of AdultW. Racovitzai(Feider, 1949) from Hungary

Abstract. Willmannella racovitzai (Feider, 1949) is redescribed based on adults. A male, collected in Hungary has been designated as neotype. Willmannella franzi (Willmann, 1950) is regarded the subjective junior synonym of W. racovitzai. The taxonomy and distribution of the genus are discussed and a key to all species known from postlarval instars is provided.

First Description of the Larva ofTrischidothrombiumFeider, 1952 (Acari: Actinotrichida: Microtrombidiidae)

Trischidothrombium discrepans (Willmann, 1950) is redescribed basing on postlarval instars. The larva of the genus is described for the first time. Data on habitat specificity and phenology of the species as well as on larval developmental time are given. A female, from which larvae were obtained by experimental rearing, has been designated as neotype. The distribution of the genus, hitherto known from Austria and Hungary, is extended for Poland. The phylogenetic position of Trischidothrombium within the Microtrombidiidae is discussed.

Notes on the Taxonomy and Biology of Smarididae (Acari: Prostigmata: Parasitengona)

Abstract. Rearing of larvae from eggs deposited by adults in laboratory proved Pilosoma pluto Southcott, 1961 (based on larva) and Fessonia papillosa (Hermann, 1804) (based on adult) to be conspecific. Clipeosoma, Southcott, 1961 (larva) and Hirstiosoma (Berlese, 1887) (adult) are congeneric. The validity of Hirstiosoma latreillei (Grandjean, 1947) is confirmed, the larva of Hirstiosoma, ampulligera Berlese, 1887 is described for the first time. Data on egg development and nutrition of postlarval instars are provided. Causal reasoning for the exclusion of Phanolophinae from Smarididae is provided.

Prelarva and larva of Opilioacarus (Neocarus) texanus (Chamberlin and Mulaik) (Acari: Opilioacarida) with notes on the patterns of setae and lyrifissures

The prelarva and larva of Opilioacarus (Neocarus) texanus (Chamberlin and Mulaik, 1942) are described based on reared specimens. The larval description focuses on the pattern of setae, lyrifissures, and glands in order to test the hypothesis that these structures can be homologized among larvae of all suborders of the Parasitiformes. The distribution pattern of lyrifissures and setae on the hysterosoma of opilioacarid larvae appears to be the most complete pattern of these structures in the order Parasitiformes, and strongly suggests an ancestral segmental arrangement of the cuticular sensillae and glands. Unlike the condition for the post-larval instars, sensillae (setae and lyrifissures) on the palps, hysterosoma, and legs II-III of the larva can be homologized among larvae in all suborders. Homologies among suborders could not be established for the sensillae and glands of the propodosoma and most segments of legs I.

Assessment of lateral compression of the idiosoma in adult water mites as a taxonomic character and reclassification of Frontipodopsis Walter, Wettina Piersig and some other basal Hygrobatoidea (Acari : Hydrachnida)

Systematists have frequently interpreted lateral compression of the idiosoma in post-larval instars of water mites as a synapomorphy indicating common ancestry. This paper re-examines the evidence to support this assumption and concludes that lateral flattening has occurred independently several times during water mite evolution, and especially often in various basal clades of the superfamily Hygrobatoidea. Reassessment of the phylogenetic relationships of the genera attributed to these clades results in improved understanding of the early evolution and biogeography of hygrobatoid water mites and necessitates redefinition of several clades and significant revision of the family classification. The South African genus Karlvietsia K.O. Viets, 1962 is transferred from the subfamily Frontipodopsinae of the family Aturidae to the Hygrobatidae. The Australian genera Tasmanaxona Cook, 1986, Wheenyella Cook, 1986 and Wheenyoides Harvey, 1990 are also removed from Frontipodopsinae and placed with the genus Wettina Piersig, 1892, here removed from the family Pionidae, in the family Wettinidae Cook, stat. nov. Based on apparent relationship with members of Wettinidae, the South African genus Stormaxonella K.O. Viets, 1962 is transferred from the Aturidae and provisionally placed in the Wettinidae. The clade including the predominately Holarctic genus Lethaxona K.H. Viets, 1932 and the Western Hemisphere genus LethaxonellaCook, 1963 is recognised as the probable sister group of Wettinidae, and these genera are consequently removed from the Aturidae and placed in Lethaxonidae, fam. nov. The genus Frontipodopsis Walter is reassigned from Aturidae to the now monobasic family Frontipodopsidae K.H. Viets, stat. nov. Finally, five new species are described, including Frontipodopsis (Frontipodopsella) sudafricanus, sp. nov., Wettina occidentalis, sp. nov., Karlvietsia simplex, sp. nov., Hygrobates (Hygrobates) gereckei, sp. nov. and Hygrobates (Hygrobatides)frontipodoides, sp. nov., and both Karlvietsia brevipalpis K.O. Viets and K. angustipalpis K.O. Viets are redescribed.