Primary Chaetotaxy Research Articles

Unravelling the obscure homology: postembryonic development of chaetotaxic traits in a basal hexapod taxon (Collembola: Tomoceridae)

Abstract Homology assessment is essential for systematic zoology, but for many taxa and traits, precise recognition of homology can be challenging with limited evidence. Tomoceridae is one of the earliest branches in the elongate-bodied springtails (Collembola: Entomobryomorpha), and is among the commonest and best-known families in the class. However, the homology of some important traits is still obscure in this group, including its characteristic chaetotaxic traits. In this study, we conducted the first rigorous homology assessment of chaetotaxy in Tomoceridae based on ontogenetic evidence. The postembryonic development of chaetotaxy was investigated in three species of Tomocerus. The primary chaetotaxy of first instar larvae show high similarity within Tomocerinae. The postembryonic development involves extensive transformations between chaetal types. The continuous dwarfism of primary chaetae during development leads to apparent oligochaetosis in adults. The thoracic bothriotricha are transformed from primary macrochaetae. The sensory chaetotaxy is stable during postembryonic development, and shows interspecific differences mainly on the mesothorax and the fourth abdominal segment. This study will promote the future use of chaetotaxic traits in the taxonomic and phylogenetic studies of Tomoceridae, and will potentially illuminate the early evolution of Entomobryomorpha.

Morphology of larvae and pupae of the genus Autocrates (Coleoptera: Trictenotomidae) and its phylogenetic implications

The trictenotomid genus Autocrates Thomson, 1860 is remarkable for its large and robust adults, but its larval morphology and bionomics have been unknown over the last 160 years. Here, we describe and illustrate in detail the eggs, and also the first and last instar larva and the pupa of Autocrates maqueti Drumont, 2006, based on specimens reared from identified adults collected in South Korea. The first instar larva is very similar to the known trictenotomid larvae of the genus Trictenotoma Gray, 1832, sharing the following features: distinctly flattened and parallel-sided, well-sclerotized head and largely unpigmented postcephalic body, lyre-shaped frontal arms, very short coronal suture, five pairs of stemmata, asymmetrical and tridentate mandibles with mola, simple and apically upturned urogomphi, and absence of longitudinal ridges on the thorax and abdomen. Differences occur in the primary chaetotaxy. The last instar larva is almost identical with Trictenotoma in general appearance, but the longitudinal tergal ridges of Autocrates are much denser and more widely distributed than those of Trictenotoma. Our preliminary assessment of features of immature stages confirms a close relationship of Trictenotomidae with the “salpingid group”, i.e. Salpingidae, Boridae, Pyrochroidae and Pythidae. A sister group relationship with Pythidae is likely. The putative synapomorphy is the subdivision of the ventral element of tergites IX, even though this condition is not visible in the first instars of Autocrates, and quite indistinct (but recognizable) in the last larval stage. The complete mitochondrial genome of A. maqueti is provided. A preliminary phylogenetic analysis of trictenotomid species is presented using two mitochondrial genes (16S and COI). The morphology of eggs and biological information on feeding and oviposition behaviors are also provided with photographs of adults and eggs.

Primary chaetotaxy and morphometry of the head capsule and head appendages of first instar larvae of Chaetarthria bruchi (Coleoptera: Hydrophilidae: Chaetarthriinae: Chaetarthriini) Authors Miguel ARCHANGELSKY Abstract The primary chaetotaxy of the head capsule and head appendages of the larva of Chaetarthria bruchi Balfour-Browne is described for the first time. Morphometric characters derived from the head capsule and mouthparts are included,

The primary chaetotaxy of the head capsule and head appendages of the larva of Chaetarthria bruchi Balfour-Browne is described for the first time. Morphometric characters derived from the head capsule and mouthparts are included, together with detailed illustrations of all characters. Chaetotaxy of C. bruchi is compared with that of C. seminulum (Herbst), the only other Chaetarthriini species for which the chaetotaxy has been described.

Morphology and chaetotaxy of Neotropical Haliplus larvae (Coleoptera: Haliplidae)

Larvae of 2 Neotropical species of Haliplus Latreille, 1802 ( H. indistinctus Zimmermann, 1928 and H. subseriatus Zimmermann, 1921) are described and illustrated including detailed morphometric and chaetotaxic analyses of the cephalic capsule, head appendages, and legs. Except for the legs, this is the first treatment of larval primary chaetotaxy for the family Haliplidae. The larvae studied herein have 10 abdominal segments, with segment X forking into 2 caudal projections, 1 pretarsal claw, a clasping device on prothoracic legs, and numerous short tracheal gills on the body, characteristics typically found in haliplid larvae. Regarding primary chaetotaxy, they are characterized by the absence of several setae and pores which are commonly present among other families of Hydradephaga, namely seta FR6 on the frontoclypeus, seta PA16 on the parietal, setae AN2 and AN3 and pore ANg on the antenna, setae MX13 and MX14 on the maxilla, and seta CO6 on the coxa. Mandibular seta MN2 is also strongly developed as compared to other hydradephagans. The larvae of the 2 described species can be separated by comparing the distance from the base of segment X to the point at which it forks into caudal projections.

Description of the first larval instar of <i>Broscus crassimargo</i> Wollaston, 1865 (Carabidae: Broscini) and notes about the presence of the species in the mesovoid shallow substratum of La Gomera (Canary Islands, Spain)

The first larval instar of the ground beetle Broscus crassimargoWollaston, 1865 endemic to La Gomera (Canary Islands, Spain) is described. This is the first comprehensive study of the primary chaetotaxy of the three tagmata ever carried out in larvae of Broscini, being also accompanied by a detailed iconography. The implications of the results of this chaetotaxy analysis are discussed in relation to the possible origin of Broscini within Carabidae. Comments on the ecological determinants for its remarkable presence in the mesovoid shallow substratum are given, analysing the differences between La Gomera and other Canary islands where samplings in the same subterranean habitat have been carried out.

Larval morphology and analysis of primary chaetotaxy in the genusSuphis Aubé, 1836 (Coleoptera: Noteridae).

The three larval instars of Suphis cimicoides Aubé, 1837 are described and illustrated, including morphometric and chaetotaxic analyses of the cephalic capsule, head appendages, legs, last abdominal segment and urogomphus. A preliminary ground plan of primary chaetotaxy for noterid larvae is presented for the first time, based on the species described herein and examination of larvae of the genera Hydrocanthus Say, 1823 and Suphisellus Crotch, 1873. This ground plan is compared with previous systems proposed for other adephagan families. Larvae of Noteridae can be distinguished from those of other families of Hydradephaga by the following combination of characters: (1) antennomere 3 with a rugged area on distal portion; (2) abdominal segment VIII with a U-shaped wavy membranous area ventrally; (3) absence of pore FRd; and (4) presence of seta AB16. Several sensilla present in noterid larvae (notably setae TR2 and TA1 and pores PAl, PAm, COd, TRb and FEb) are absent in larvae of Meruidae. On the contrary, parietal seta PA5 is present in Meruidae but absent in Noteridae. The presence of pore COc in Noteridae may indicate that this family has retained the ancestral condition found only in Carabidae. On the other hand, the absence of setae FE7, FE8, FE9 and FE10 in Noteridae is similar to the condition found in Carabidae, Gyrinidae and Meruidae.

Description of the Egg and First-Instar Larva ofScotobius pilulariusGermar, 1823 (Coleoptera: Tenebrionidae: Scotobiini), and Analysis of Larval Primary Chaetotaxy

Larval morphology of the New World tenebrionid genus Scotobius Germar is studied based on a description of the first instar of S. pilularius Germar, with emphasis on chaetotaxic analysis of the cephalic capsule, head appendages, legs, and thoracic and abdominal segments. This represents the first description of a larva of Scotobius, and the first detailed treatment of the larval primary chaetotaxy pattern of a tenebrionid. A short description and photographs of the eggs are also provided, which are deposited individually and agglutinate small substrate particles. As remarkable characteristics of the studied larvae, the sclerome is a simple oval structure, the tergum IX is acuminate posteriorly, the segment X is extremely small and almost completely concealed by the sternum IX, and prothoracic legs are somewhat more robust than the meso- and metathoracic pairs, which is generally the case in soil-dwelling larvae. Some discussion is provided on a long-standing controversy regarding homology and terminology of the last leg segments in coleopteran larvae.

Chaetotaxy of first-instar Campylothorax sabanus (Wray), and description of three new Campylothorax species from Hispaniola (Collembola, Paronellidae)

ABSTRACTThe dorsal chaetotaxy of adult Campylothorax species is considerably reduced, making homology determinations difficult. Previous studies demonstrated that homology of the adult chaetotaxy can be established by analysis of the primary chaetotaxy of first-instar larvae. The goals of the present study are to provide a description of the complete dorsal chaetotaxy of first-instar C. sabanus (Wray, 1953) in order to evaluate the homology of elements recently proposed for adult Campylothorax, to evaluate new morphological characters useful to diagnose species, and to report on the species of Campylothorax on the Greater Antillean island of Hispaniola. As a result of the analysis of primary chaetotaxy it is concluded that: (1) on thorax (Th.) 2 chaeta p4 is incorporated (as a multiplet) into the p3 complex, whereas the latero-external microchaeta corresponds to p6e; (2) on abdomen (Abd.) 3 the lateral mesochaetae belong to series 7 (i.e., a7, m7 and p7); (3) on Abd. 4 the inner macrochaetae correspond to A3, A5, A6, B3, B4, and B5, the inner posterior bothriotrix, corresponds to B6, whereas T6 is displaced laterally towards row D. Aspects of the chaetotaxy that remain unclear are the identity of chaetae along the inner margin of the eyes, and the homology of the two anterior macrochaetae on Th. 3. New morphological characters useful in species diagnosis revealed by comparative analysis are the number of head macrochaetae in series S, number of meso- and metathoracic macrochaetae and number and identity of latero-external macrochaetae on the fourth abdominal segment. Analysis of Campylothorax from Hispaniola reveals the presence of four species: C. cubanus Gruia, 1983 previously known only from Cuba, and three species new to science – C. notidanus sp. nov., C. hexosetosus sp. nov. and C. dominicanus sp. nov.

New insight into the systematics of Tomoceridae (Hexapoda, Collembola) by integrating molecular and morphological evidence

Tomoceridae is common but among the most problematic groups of Collembola. Its position within Collembola and the relationships within the family remain obscure. This also extends to the generic division of the subfamily Tomocerinae that remains controversial. This study examines these issues by integrating both molecular and morphological evidence. Our molecular phylogeny based on rDNA sequences supports the monophyly of Tomoceridae and the sister relationship between Tomocerinae and Lepidophorellinae. Reconstructions and tree topology tests constraining monophyly did not resolve the relationships between Tomoceridae and other collembolan groups. We also examined the morphology of the first instar (primary) larvae, which has significant phylogenetic value among higher Collembola. Mapping primary chaetotaxy onto our molecular phylogeny provided further evidence for the unique position of Tomoceridae within Entomobryomorpha and Collembola. The monophyly and subfamilial classification within Tomoceridae were validated here, whereas its position among Collembola will need further studies in a broader consideration across the major collembolan orders. Within Tomocerinae, the monophyly of Pogonognathellus was demonstrated, but the status of Tomocerus and Tomocerina is still to be resolved.

Phylogenetic Placement of the GenusSternhydrus(Coleoptera: Dytiscidae: Cybistrini) Based on Larval Morphology, With Description ofS. atratus

The phylogenetic relationships of the Australasian diving beetle genus Sternhydrus Brinck, 1945 were studied based on a cladistic analysis of 16 taxa and 112 morphological larval characters. Larvae of S. atratus (F., 1801) were described and illustrated in detail with particular emphasis on morphometry and chaetotaxy. Primary chaetotaxy were unknown for the genus. The results supported the inclusion of Sternhydrus in a clade of Australian Cybistrini genera along with Onychohydrus Schaum and White, 1847 and Spencerhydrus Sharp, 1882 based on four synapomorphies: presence of additional pores on antennomere 1, tibial seta TI7 short and spine-like, and urogomphi longer than broad, included in the nonsclerotized ventrodistal area surrounding the anus. A sister group relationship of Sternhydrus and Onychohydrus is suggested by two synapomorphies: lateral projections of frontoclypeus serrate, and row of additional anteroventral setae on meso- and metatarsus composed of several thin setae of variable length. The genus Sternhydrus is characterized by two autapomorphies: presence of both spine-like and hair-like additional setae on the ventral surface of the femur, and absence of primary pores on the urogomphus.

First instar tibiotarsal chaetotaxy supports the Entomobryidae and Symphypleona (Collembola) forming a cluster in a phylogenetic tree.

Tibiotarsi, particularly their chaetotaxy, vary from species to orders in Collembola. Symphypleona, Poduromorpha and Isotomidae have been shown to possess characteristic patterns of tibiotarsal chaetotaxy, but the patterns in Entomobryoidea and Tomoceroidea, where a strong plurichaetosis is the rule, remains undocumented. The tibiotarsal chaetotaxy of first instars of 11 species of the main Entomobryidae subfamilies is described here for the first time. A basic pattern of five whorls with eight chaetae per whorl was found to occur in all examined species of Entomobryidae, with limited variations in the distal and proximal whorls. This pattern is similar to that of Symphypleona. Two hypotheses appear possible according to existing phylogenies, making it difficult to determine whether this obvious homology in tibiotarsal chaetotaxy is a plesiomorphy, which appeared independently in both superfamilies, or is a synapomorphy. We conclude that the primary chaetotaxy of tibiotarsus appears to be of high taxonomical value at suprafamilial but not at generic or tribal level.

Larval morphology of the genus Hydrocassis Fairmaire (Coleoptera: Hydrophilidae)

The larval morphology of the genus Hydrocassis Fairmaire, 1878 is described on the basis of three species of the genus: second instar of Hydrocassis jengi Satô, 1998, all instars of Hydrocassis lacustris (Sharp, 1884) and second and third instars of Hydrocassis uncinata Ji et Schödl, 1998; the former two belong to the Hydrocassis scapulata species group and the latter to the Hydrocassis scaphoides species group. Primary chaetotaxy of the larval head of Hydrocassis is described based on the first instar larvae of H. lacustris. Larval morphology of all genera of Sperchopsini with known larvae is summarized based on descriptions and figures from the literature, which are compared with Hydrocassis: larval morphology of Hydrocassis is similar to that of Sperchopsis, and the presumably closely related genus Ametor is distinguishable from Hydrocassis by characters of larval morphology. A key to the Sperchopsini genera on the basis of larval characters is provided.

A Description of the First Instar ofMatus ovatus(Coleoptera: Dytiscidae)

The first instar of Matus ovatus Leech is described and illustrated. The analysis of the primary chaetotaxy of legs, head, and last abdominal segment of M. ovatus revealed no significant differences between this species and the previously described M. bicarinatus. Undescribed primary anatomical features of the tribe Matini presented herein include (1) a tentative identification of anterior tentorial pits and fragments of the anterior tentorial arms, (2) anterior protergal modifications and chaetotaxy, and (3) complete sclerotization of the seventh abdominal segment. Differences in mandibular morphology permit identification of first instars of M. ovatus and M. bicarinatus in the eastern United States.

The long-awaited first instar larva of Paussus favieri (Coleoptera: Carabidae: Paussini)

Paussus favieri Fairmaire is one of only two species of the myrmecophilous carabid tribe Paussini known from Europe. Larvae are known from only 10 of the 580 paussine species. As in many beetles with considerably modified later instar larvae, the first instars represent a valuable source of informative characters for taxonomy and phylogenetic analyses (primary chaetotaxy, egg-bursters, etc.). Therefore, the discovery of the first instar larva of P. favieri is particularly important, as it represents only the second species for which this larval stage is known. In this paper we describe the behavior and morphology of the larval first instar of P. favieri (subtribe Paussina of Paussini) and compare it with that of Arthropterus sp. (subtribe Cerapterina), which is the only other 1st instar described in the Paussini. Most surprisingly, we found that the 1st instar of P. favieri lacks a prostheca, which was previously thought to be a synapomorphy of Paussina + Platyrhopalina. Rather, P. favieri has a unique mandibular structure that seems to be functionally analogous to the protheca. It is a long, broadly lanceolate, distinctly flattened structure apparently homologous to the medial mandibular seta (MN2*), which arises from an area behind the cutting edge of mandible. We predict that the function of the protheca and this similar structure in P. favieri are involved in a specialized feeding strategy that may include soliciting trophallaxis from their host ants. We also report some observations of the first instar hatching from the egg, feeding on liquid and a behaviour we interpret as a "calling behavior," all of which were videotaped and posted on the Tree of Life Web Project.

Descriptions of the first-instar larva of the hypogaeic species Neobidessodes limestoneensis (Watts & Humphreys) and of the third-instar larva of Hydroglyphus balkei Hendrich (Coleoptera: Dytiscidae: Bidessini) with phylogenetic considerations

The first-instar larva of Neobidessodes Hendrich & Balke (through the hypogaeic species N. limestoneensis (Watts & Humphreys)) and the third-instar larva of Hydroglyphus Motschulsky (through H. balkei Hendrich) (Dytiscidae: Bidessini) are described and illustrated in detail for the first time, including detailed morphometric and chaetotaxic analyses of the cephalic capsule, head appendages, legs, last abdominal segment and urogomphi. A cladistic analysis including 51 characters and 32 hydroporine taxa is performed, which supports the inclusion of both genera in the tribe Bidessini based on the absence of the primary pore ABc on the last abdominal segment. The third instar of H. balkei is characterized by the absence of secondary setae on the urogomphi and anterior secondary setae on the coxa, and the presence of 8–9 secondary setae on the mesofemur. On the other hand, the first instar of N. limestoneensis bears 14 lamellae clypeales on the anteroventral margin of the nasale. This species has evolved several morphological characters that are probably associated with its hypogaeic existence, including a lightly sclerotized body, relatively longer cephalic capsule and mandibles, a strongly reduced occipital foramen, absence of stemmata, and short claws. However, primary chaetotaxy apparently has remained as a very conservative expression of the phenotype.

Descriptions of larvae of Megadytes (Coleoptera: Dytiscidae: Dytiscinae): The subgenera Trifurcitus and Megadytes s. str., ground plan of chaetotaxy of the genus and phylogenetic analysis

The three larval instars of Megadytes (M.) carcharias Griffini and M. (Trifurcitus) fallax (Aube) are described and illustrated in detail for the first time, with an emphasis on morphometry and chaetotaxy of the cephalic capsule, head appendages, legs, last abdominal segment and urogomphi. The ground plan of chaetotaxy of the genus Megadytes Sharp is described and illustrated based on three of the four recognised subgenera. First-instar larvae of Megadytes are characterised by the presence of a large number of additional sensilla on almost every part of the body. Primary chaetotaxy of the subgenera (Bifurcitus Brinck based on third instar) is very similar, with few differences including (1) shape of the setae on the anterior margin of the frontoclypeus; (2) presence or absence of a ring of multi-branched setae on distal third of mandible; and (3) number of setae on the urogomphus. A cladistic analysis of Dytiscidae, based on 169 larval characters and 34 taxa, indicates that: (1) Trifurcitus Brinck deserves generic status; (2) Cybistrini are not closely related to Hydroporinae; (3) the absence of a galea in Cybistrini is a secondary loss independent of that in Hydroporinae; (4) Cybistrini are well supported by many characters (including several aspects of first-instar chaetotaxy).

Description of the preimaginal stages of Enochrus (Hugoscottia) variegatus (Steinheil, 1869) and E. (Methydrus) vulgaris (Steinheil, 1869) (Coleoptera: Hydrophilidae), with emphasis on larval morphometry and chaetotaxy

The morphology of the preimaginal stages of Enochrus Thomson (Coleoptera: Hydrophilidae) is investigated. Descriptions and detailed illustrations of the egg cases, all three larval instars, and pupae of the Neotropical species E. (Hugoscottia) variegatus (Steinheil, 1869) and E. (Methydrus) vulgaris (Steinheil, 1869) are presented. The larval morphology of these species is studied on the basis of chaetotaxic and morphometric analyses of selected structures (head capsule, head appendages and legs). A key to larval instars of Enochrus is also presented. The larval instars can be separated by means of morphometry and chaetotaxy of the head capsule, cephalic appendages and legs. Several characters common to the five subgenera known as larvae are discussed. The primary chaetotaxy plan for the maxilla is updated on the basis of observations made on Enochrus larvae as well as on additional hydrophilid taxa.

Postembryonic development of the dorsal chaetotaxy in Seira dowlingi (Collembola, Entomobryidae); with an analysis of the diagnostic and phylogenetic significance of primary chaetotaxy in Seira

Postembryonic development of the dorsal chaetotaxy in Seira dowlingi (Collembola, Entomobryidae); with an analysis of the diagnostic and phylogenetic significance of primary chaetotaxy in Seira

Primary chaetotaxy of the larval head capsule and head appendages of the Hydrophilidae (Coleoptera) based on larva of Hydrobius fuscipes (Linnaeus, 1758)

The primary chaetotaxy of the larval head capsule and head appendages of the family Hydrophilidae (Insecta: Coleoptera) is described and illustrated using the larva of Hydrobius fuscipes (Linnaeus, 1758) as a model, and compared with fifteen hydrophilid taxa representing all main taxonomic groups within the family; brief comparative notes with representatives of the families Helophoridae, Spercheidae, Hydrochidae and Histeridae are also provided. Primary chaetotaxic nomenclature is developed for the Hydrophilidae, allowing the use of chaetotaxic characters for phylogenetic studies as well as diagnostic purposes. The study of representatives of the families Helophoridae, Hydrochidae and Spercheidae suggests that this nomenclature can also be effectively applied to other hydrophiloid families. Chaetotaxic nomenclature systems used in larvae of other groups of Coleoptera are briefly reviewed.

Postembryonic development of the dorsal chaetotaxy in Seira dowlingi (Collembola, Entomobryidae); with an analysis of the diagnostic and phylogenetic significance of primary chaetotaxy in Seira

Chaetotaxy is probably the most important character system used to diagnose species in Entomobryidae, but its use in studies of phylogenetic relationships of suprageneric taxa has been hampered by difficulties in identifying the homology of individual setae. Currently there is developmental information for three (Orchesella, Entomobrya sensu lato and Lepidocyrtus sensu lato) of the four largest groups of entomobryids. Seira is the only major genus for which the postembryonic development of the chaetotaxy has not been described. To fill this gap a complete description of the postembryonic development of the dorsal chaetotaxy of Seira dowlingi (Wray, 1953) is presented. Based on this description and by comparisons with up to 96 additional Seira species, it is suggested that the loss of second abdominal segment primary setae m4 and p4 (by transformation into scales during postembryonic development) is the only chaetotaxic character diagnostic for the genus. The posterior botriothricum (homologous to D3) on the fourth abdominal segment is absent only in S. (Afroseira) rowani Yosii, from South Africa. It is suggested that the presence of seta p3 and absence of p4 on the third abdominal segment support a more recent relationship between Seira and Lepidocyrtus/Pseudosinella than between Seira and Entomobrya sensu lato.