Origin of the trochophora larva

The trochophora larva, which is so well known from the marine plankton, is central to our understanding of the evolution of a large branch of the bilaterians. Two theories for this larval type have been prevalent, the trochaea theory and the theory proposed by Ivanova-Kazas. The embryology, or more precisely the cell-lineage, of these larvae seems to be central for our understanding of their origin, but important details have been missing. According to the trochaea theory, a circumblastoporal ring of blastomeres differentiates to follow the convoluted shape of the conspicuous ciliary bands of the larvae, with prototroch and metatroch around the mouth, forming a filtering system, and telotroch around the anus. According to the Ivanova-Kazas theory, the blastomeres with the ciliary bands develop through specialization of rings of cells of the general ciliation in a lecithotrophic larva. Now, a new cell-lineage study of the gastropod Crepidula has shown that the ring of cells at the edge of the blastopore develops into the band of cells carrying prototroch and metatroch, characteristic of the trochophora. This gives strong support to the trochaea theory.

Drosophila embryonic type II neuroblasts: origin, temporal patterning, and contribution to the adult central complex

ABSTRACTDrosophila neuroblasts are an excellent model for investigating how neuronal diversity is generated. Most brain neuroblasts generate a series of ganglion mother cells (GMCs) that each make two neurons (type I lineage), but sixteen brain neuroblasts generate a series of intermediate neural progenitors (INPs) that each produce 4-6 GMCs and 8-12 neurons (type II lineage). Thus, type II lineages are similar to primate cortical lineages, and may serve as models for understanding cortical expansion. Yet the origin of type II neuroblasts remains mysterious: do they form in the embryo or larva? If they form in the embryo, do their progeny populate the adult central complex, as do the larval type II neuroblast progeny? Here we present molecular and clonal data showing that all type II neuroblasts form in the embryo, produce INPs, and express known temporal transcription factors. Embryonic type II neuroblasts and INPs undergo quiescence, and produce embryonic-born progeny that contribute to the adult central complex. Our results provide a foundation for investigating the development of the central complex, and tools for characterizing early-born neurons in central complex function.

Morphological and molecular characterization of selected species of Hysterothylacium (Nematoda: Raphidascarididae) from marine fish in Iraqi waters

Hysterothylacium species are perhaps the most abundant and diverse group of marine ascaridoids; however, their life cycle and specific identification in larval stages in many parts of the world, particularly in Iraqi marine waters, have not been completely understood. In this study three members of the genus Hysterothylacium collected from Khor Abdulla in Iraq are morphologically described, genetically characterized and their relationship with other closely related taxa are compared and discussed. A new Hysterothylacium larval type in the fourth stage of development is described, and morphological and molecular evidence (based on the sequences of internal transcribed spacers) are provided for its distinction from previously known fourth-stage Hysterothylacium larval types. Based on the sequence data it is suggested that the new larval type, which herein was assigned as Hysterothylacium larval type XVI, is H. persicum which was previously reported from the close proximity in Bandar Abbas, Iran. In addition, two other taxa, including Hysterothylacium larval type XV and H. reliquens, have been found in the present study, for which new hosts are reported. This study provides some insights into the taxonomy and systematics of these parasites, not only in this region but also for similar studies elsewhere.

An additional larval type in the genus Chironomus – the yama-type.

A new larval type in the genus <em>Chironomus</em> is suggested.

Morphometric and molecular descriptions of three new species of Hysterothylacium (Nematoda: Raphidascarididae) from Australian marine fish

Three new species of Hysterothylacium Ward & Magath, 1917, including H. australe, H. kajikiae and H. brucei, from Australian marine fish are described and illustrated by light microscopy followed by genetic characterization of their first and second internal transcribed spacers (ITS-1 and ITS-2, respectively). This is the first study reporting ITS sequence data for adult Hysterothylacium spp. in Australia, which provides an insight into the identification of some of the Hysterothylacium larval types. Alignment of ITS sequences of these species with Hysterothylacium larval types previously reported in Australia showed that fourth-stage Hysterothylacium larval type XI from Seriola lalandi and third-stage Hysterothylacium larval type X from Sphyraene novae-hollandiae are identical with ITS sequences of H. australe, suggesting that these fish are natural intermediate/paratenic hosts of H. australe.

Occurrence ofTerranovalarval types (Nematoda: Anisakidae) in Australian marine fish with comments on their specific identities

Pseudoterranovosis is a well-known human disease caused by anisakid larvae belonging to the genusPseudoterranova. Human infection occurs after consuming infected fish. Hence the presence ofPseudoterranovalarvae in the flesh of the fish can cause serious losses and problems for the seafood, fishing and fisheries industries. The accurate identification ofPseudoterranovalarvae in fish is important, but challenging because the larval stages of a number of different genera, includingPseudoterranova,TerranovaandPulchrascaris, look similar and cannot be differentiated from each other using morphological criteria, hence they are all referred to asTerranovalarval type. Given thatTerranovalarval types in seafood are not necessarilyPseudoterranovaand may not be dangerous, the aim of the present study was to investigate the occurrence ofTerranovalarval types in Australian marine fish and to determine their specific identity. A total of 137 fish belonging to 45 species were examined.Terranovalarval types were found in 13 species, some of which were popular edible fish in Australia. The sequences of the first and second internal transcribed spacers (ITS-1 and ITS-2 respectively) of theTerranovalarvae in the present study showed a high degree of similarity suggesting that they all belong to the same species. Due to the lack of a comparable sequence data of a well identified adult in the GenBank database the specific identity ofTerranovalarval type in the present study remains unknown. The sequence of the ITS regions of theTerranovalarval type in the present study and those ofPseudoterranovaspp. available in GenBank are significantly different, suggesting that larvae found in the present study do not belong to the genusPseudoterranova, which is zoonotic. This study does not rule out the presence ofPseudoterranovalarvae in Australian fish asPseudoterranova decipiens Ehas been reported in adult form from seals in Antarctica and it is known that they have seasonal presence in Australian southern coasts. The genetic distinction ofTerranovalarval type in the present study fromPseudoterranovaspp. along with the presence of more species of elasmobranchs in Australian waters (definitive hosts ofTerranovaspp. andPulchrascarisspp.) than seals (definitive hosts ofPseudoterranovaspp.) suggest thatTerranovalarval type in the present study belong to either genusTerranovaorPulchrascaris, which are not known to cause disease in humans. The present study provides essential information that could be helpful to identify AustralianTerranovalarval types in future studies. Examination and characterisation of further specimens, especially adults ofTerranovaandPulchrascaris, is necessary to fully elucidate the identity of these larvae.

Morphology of a new blister beetle (Coleoptera, Meloidae) larval type challenges the evolutionary trends of phoresy-related characters in the genus Meloe

The discovery of some specimens of a new first instar larval type in blister beetles, collected in Iran on Anthophora bees, confirms the existence of repetitive and parallel trends in morphological specialization to phoresy in distinct lineages of Meloidae and in particular in the subfamily Meloinae. The new Iranian larva, herein described and illustrated, shows several characters and a peculiar phoretic strategy that closely parallel that of the Meloe subgenus Lampromeloe, with similar modifications of the fronto-clypeal setae into strong lanceolate spines used to pierce the intersegmental membranes of the bees. Both parallel and shared derived evolution of these characters seem possible. The coexistence in this larva of characters in both primitive and derived state is of particular interest in order to analyse the different rates and trends of evolution of phoretic adaptations. A morphological comparison (SEM) of this new meloine larva (incertae sedis), tentatively assignable to Meloe, with the M. (Lampromeloe) larvae is carried out in order to discuss the evolutionary implications of its placement in Lampromeloe, and the relative characters that would support it, vs other possible alternative scenarios.