Chambered chaetae in nereidiform polychaetes (Annelida)

The nereidiform polychaete taxa Chrysopetalidae, Hesionidae and Nereididae are characterized by the presence of chambered chaetae. The medullae (inner part) of all examined annelid chaetae are provided with internal longitudinal canals, but in these taxa there are additional thin, transverse walls (diaphragms), giving the chaetae a barred or chambered appearance in light microscopy. We investigate this structure in chrysopetalids, hesionids, nereidids, with light, scanning and transmission electron microscopy and compare it to phyllodocids and syllids, which are outside this clade. We conclude that chambered chaetae likely constitute an synapomorphy for chrysopetalids, hesionids and nereidids, although further study are required of some aphroditids and nephtyids.     

On the Innervation and Homologues of the Anterior End Appendages of the Eunicea (Polychaeta), with a Tentative Outline of the Fundamental Constitution of the Cephalic Nervous System of the Polychaetes

Earlier papers dealing with the architecture of the cephalic nervous system of the Eunicea were studied. Thereby, a re-investigation appeared necessary: the existing literature proved insufficient for detailed comparisons with other polychaete families and many earlier statements and conclusions turned out to be quite contradictory, especially as concerns the homologues of the anterior end appendages. In the present paper, the microanatomy of the brain and the innervation of, inter alia, the antennae, the nuchal organs and the alimentary canal of Hyalinoecia tubicola, Nothria conchylega, Eunice norvegica and E. pennata are described. The results are summarized in schematic diagrams and tables and compared with corresponding observations in other polychaete families. Thereby, some earlier opinions about the morphological value of the cephalic appendages of the Eunicea are strengthened while others are rejected. On the basis of the present observations and earlier results arrived at by the present author, and as an object for future discussion and criticism, a diagram of the fundamental constitution of the cephalic nervous system of the Polychaeta is tentatively outlined.     

On the Anatomy of the Central Nervous System of Phyllodocidae (Polychaeta) and the Phylogeny of Phyllodocid Genera: a New Alternative

A reinvestigation of the central nervous system of the Phyllodocidae appeared necessary as the existing literature proved insufficient for detailed comparisons with other polychaete families. Many earlier opinions turned out to be quite contradictory, especially as concerns the morphological value of the anterior end appendages. In the present paper the microanatomy of the brain and the anterior ventral cord, as well as the innervation of, inter alia, the cephalic appendages, the nuchal organs and the alimentary canal of Eulalia viridis (main object of study), Eumida sanguinea, Pterocirrus macroceros, Sige fusigera, Eteone picta, E. foliosa, Phyllodoce groenlandica, P. longipes, P. mucosa, Paranaitis wahlbergi, Notophyllum foliosum and Nereiphylla lutea are described. The results are summarized in schematic diagrams and compared with corresponding observations on other polychaete families. Thereby, some earlier opinions about the nature of the cephalic appendages of the Phyllodocidae are strengthened while others are rejected. Most significantly, it is concluded that the so-called ventrolateral antennae of phyllodocids are homologous with the palps of other polychaetes and the median antenna found in certain genera is homologous with the nuchal papilla found in most other genera of the family. These partly new or revised characters and character states formed the basis for a reconsideration of earlier ideas about the phylogeny of the Phyllodocidae: a new alternative.     

Development of the mouthparts in embryos of Haplothrips verbasci (Osborn) (Insecta,Thysanoptera, Phlaeothripidae)

The asymmetric “punch and suck” mouthparts of larval Haplothrips verbasci develop from paired appendages in the late, post-anatrepsis embryo similar to those of other insects. Later, the labrum flexes ventrally over the stomodaeum, the right mandibular appendage degenerates, the maxillary appendages divide into inner (lacinial) and outer (stipital) lobes, and the hypopharynx arises from the venters of the mandibular and maxillary segments. All cephalic segments consolidate anteriorly prior to katatrepsis, their appendages flex ventrally, and the labial appendages fuse medially to form the labium and the primordia of the salivary glands and valve. The left mandible and the lacinial lobes of the maxillae invaginate into the head during and after katatrepsis to form the mandibular and maxillary stylet-secreting organs and these later deposit the cuticle of their respective stylets. Cuticle of the mandibular lever is deposited by labral cells at the apex of the mandibular sheath during and after hatching. That of each maxillary lever is secreted simultaneously into the lumen of a ventrally-directed diverticulum developing from stipital cells at the apex of each maxillary sheath. Shortly after katatrepsis, the maxillary and labial palpi originate respectively from cells in the outer wall of each stipital lobe and at the apex of the labium. Muscles of the mouthparts arise after katatrepsis from cephalic mesoderm and are fully-differentiated before cuticle of the mandibular and maxillary levers has been deposited. Gnathal morphogenesis in embryos of H. verbasci resembles that occurring in bug embryos and provides additional evidence that Thysanoptera and Hemiptera evolved from a common psocopteroid stem species having small, paired, biting and chewing mandibles and well developed lacinial stylets.     

Embryogenesis of the damselfly Euphaea yayeyamana Oguma (Insecta: Odonata: Euphaeidae), with special reference to the formation of their larval abdominal “gill‐like” appendages

The acquisition of wings in insects is the most significant subject in considering the diversification and adaptive radiation of insects, that is, the “macro‐evolution” of insects. In the discussion of the origin of insect wings, Palaeoptera has attracted particular attention in phylogenetic and evolutionary studies. In particular, Ephemeroptera have segmental gill‐structures on their abdominal segments during their nymphal stage, and these have been noted in discussions regarding their homology and/or serial homology between wings, gills and appendages. Although Odonata has received little attention in the course of these discussions, there are cases of segmental gill‐like structures on their abdomen in the two families, Euphaeidae and Polythoridae. Under such cirumstances, in this study, the embryological developmental process in Euphaea yayeyamana of Euphaeidae was observed, focusing on the formation process of the gill‐like structures. As a result, it was revealed that four of the seven pairs of gill‐like projection structures started their visible formation within the middle stages of embryonic development, and the remaining three pairs developed during the early stages of post‐embryogenesis. Some joint‐like structures existed in all of the gill‐like projections. It was revealed that muscle tissue was interposed within these protrusions and that all of the projections themselves fully articulated, and that the nervous system was extended into the protrusions. All of the gill‐like projections strongly suggested their homology with the cephalic and thoracic appendages, when we considered them with regard to their serial homology based on the topology of their formation position.     

On the Microanatomy of the Cephalic Nervous System of Nereidae (Polychaeta), with a Preliminary Discussion of Some Earlier Theories on the Segmentation of the Polychaete Brain

Abstract Earlier papers dealing with the microanatomy of the nereid brain have been studied. On this basis a re-investigation of the cephalic nervous system and of the innervation and homologues of the anterior end appendages of these animals appeared necessary: the existing literature proved insufficient for detailed comparisons with other polychaete families and many earlier statements were quite contradictory. In the present paper, the brain commissures and the innervation of, inter alia, the antennae and the palps of Neanthes virens and Nereis pelagica are described. Special attention was paid to the roots of the circum-oesophageal connectives and the ganglia in this part of the nervous system. The results, summarized in schematic diagrams and tables, are compared with corresponding observations in 14 other polychaete families. In a discussion of the architecture of the polychaete nervous system as a phylogenetic instrument, the supposed segmentation of the polychaete brain is questioned and the idea that the configuration of the polychaete nervous system offers support to the cyclomer theory is rejected. Other conclusions concerning the relationships within the Polychaeta are pointed out.     

Experimental analysis of the migration and differentiation of neuroblasts of the autonomic nervous system and of neurectodermal mesenchymal derivatives, using a biological cell marking technique

By isotopic and isochronic transplantations of fragments of quail neural tube into chick, it has been previously shown that enteric ganglion cells arise from the “vagal” (somites 1–7) and the “lumbo-sacral” (behind somite 28) levels of the neural crest, while the trunk region (somites 8–28) gives rise to orthosympathetic ganglion chain and adrenomedullary cells. The latter originate precisely from the neural crest corresponding to somites 18–24 (i.e., “adrenomedullary” level of the crest). Heterotopic transplantations of fragments of quail neural tube into chick have been carried out in the present work. When the “adrenomedullary” level of the quail neural tube is grafted into the “vagal” region of a chick, the crest cells colonize the gut and differentiate into enteric ganglia of Auerbach's and Meissner's plexi. If quail cephalic neural crest is transplanted in the “adrenomedullary” level of a chick, quail cells migrate into the suprarenal glands and differentiate into adrenomedullary cells. Mesectodermal cells migrate laterally, and differentiate into cartilage, dermis and connective tissues. Thus it appears that preferential pathways located at precise levels of the embryo lead crest cells to their definitive sites. On the other hand the differentiation of the autonomic neuroblasts is controlled by the environment in which crest cells are localized at the end of their migration. On the contrary, mesenchymal derivatives of the cephalic neural crest appear to be early determined since they differentiate according to their presumptive fate when transplanted into the trunk.     

Position and Delineation of Chrysopetalidae and Hesionidae (Annelida,Polychaeta, Phyllodocida)

Previous studies suggest that the polychaete taxa Hesionidae and Chrysopetalidae may not represent separate groups, that Pilargidae constitute a subgroup within Hesionidae, and that Hesionides and Microphthalmus are highly derived hesionids. Phylogenetic systematic analyses of Phyllodocida and the subgroup Nereidiformia are presented in order to clarify the position and delineation of these taxa. The phyllodocida analysis includes 18 families representing the majority of the taxa in the group, is rooted with Onuphidae, and is based on 42 absent/present coded morphological characters, obtained mainly from literature. All 69 resulting shortest trees include the clade (Chrysopetalidae, Nereididae, Hesionidae), but with either Syllidae, Nautiliniellidae, Pilargidae or (Aphroditiformia, Pisionidae) as sister. In- and outgroup taxon selection for the Nereidiformia study is dictated by the outcome of Phyllodocida analysis, with scores based on examined species of two chrysopetalids, four hesionids, one nereid, one pilargid, one pisionid, one syllid, plus the putative hesionids Hesionides arenaria and Microphthalmus sp. It is based on 46 absent/present coded morphological characters. Two equally parsimonious trees indicate that chrysopetalids and hesionids are well delineated, that pilargids and hesionids are non-overlapping, and that Microphthalmus and Hesionides are not hesionids.     

On the Innervation and Homologues of the Cephalic Appendages of the Aphroditacea (Polychaeta)

Abstract Earlier papers dealing with the innervation and homologues of the anterior end appendages of some aphroditacean families were re-studied. However valuable these earlier works may be, in some respects they proved to be insufficient for detailed comparisons with other polychaete families and some of their statements are quite contradictory. This prompted a re-investigation of the central-most parts of the nervous system of representatives of the families Polynoidae, Sigalionidae, Aphroditidae and Acoetidae. In the present paper, the brain commissures and the innervation of, inter alia, the antennae, the palps and the ommatophores (when present) in Lepidonotus squamatus, Harmothoe longisetis, Leanira (Sthenolepis) tetragona, Laetmonice producta benthaliana, and Panthalis oerstedi are described. Special attention is paid to the much-debated question about the presence or absence of a palp ganglion. The results, summarized in schematic diagrams, are compared with corresponding observations of the brains of, above all, the ‘spiomorphic’ polychaetes. Using the first Remanian criterion for identifying homologies, equivalents in the aphroditacean brain and the central nervous system of ‘sedentary’ families are proposed. By this a broader base is established for the discussion regarding the fundamental constitution of the anterior end of the polychaetes and the structure and homologues of their cephalic appendages.     

Martinssonia elongata gen. et sp.n., a crustacean-like euarthropod from the Upper Cambrian 'Orsten' of Sweden

A tiny arthropod, with five growth stages, is described. Three of the instars are metanauplius-like larvae, having unsegmented bodies and four pairs of appendages. The largest stage, with a length of about 1.5 mm, may still be immature. Its body is divided into three tagmata. The cephalon, including five appendiculate segments, h a projecting forehead with a rostral spine and a small shield with a joint between fourth and fifth segments. Eyes are absent. The trunk is composed of seven annular segments, the anterior two with appendages. The caudal end is a long pleotelson-like segment with the anus on its ventral surface. There are seven pairs of appendages: uniramous antennulae, composed of few tubular podomeres; four pairs of biramous postantennular, almost homeomorphic cephalic appendages; two pairs on the trunk, the anterior pair being similar to the cephalic appendages except for the exopodite, the posterior being much smaller, uniramous and apparently rudimentary. Martinssonia was probably benthic, feeding on detritic particles which it stirred up from the bottom. Besides various crustacean-like features, the new form reveals structures different from Crustacea as well as from all other known arthropodan groups. Martinssonia presumably is a descendant of an euarthropodan group, originating from the crustacean branch long before reaching the eucrustacean level of evolution.     

Fine structure and absorption of ferritin in the digestive organs of Loligo vulgaris and L. Forbesi (Cephalopoda,Teuthoidea)

The digestive organs possibly involved in food absorption in Loligo vulgaris and L. forbesi are the caecum, the intestine, the digestive gland, and the digestive duct appendages. The histology and the fine structure showed that the ciliated organ, the caecal sac, and the intestine are lined with a ciliated epithelium. The ciliary rootlets are particularly well developed in the ciliated organ, apparently in relation to its function of particle collection. Mucous cells are present in the ciliated organ and the intestine. Histologically, the digestive gland appears rather different from that of other cephalopods. However, the fine structure of individual types of squid digestive cell is actually similar to that of comparable organs in other species, and the squid cells undergo the same stages of activity. Digestive cells have a brush border of microvilli, and numerous vacuoles, which sometimes contain “brown bodies.” However, no “boules” (conspicuous protein inclusions of digestive cells in other species) could be identified in their cytoplasm; instead only secretory granules are present. In the digestive duct appendages, numerous membrane infoldings associated with mitochondria are characteristic features of the epithelial cells in all cephalopods. Two unusual features were observed in Loligo: first, the large size of the lipid inclusions in the digestive gland, in the caecal sac, and in the digestive duct appendages; and second, the large number of conspicuous mitochondria with well-developed tubular cristae. When injected into the caecal sac, ferritin molecules can reach the digestive gland and the digestive duct appendages via the digestive ducts, and they are taken up by endocytosis in the digestive cells. Thus, it appears that the digestive gland of Loligo can act as an absorptive organ as it does in other cephalopods.     

The chelifores of sea spiders (Arthropoda,Pycnogonida) are the appendages of the deutocerebral segment

SUMMARY Within the last decade, gene expression patterns and neuro‐anatomical data have led to a new consensus concerning the long‐debated association between anterior limbs and neuromeres in the arthropod head. According to this new view, the first appendage in all extant euarthropods is innervated by the second neuromere, the deutocerebrum, whereas the anterior‐most head region bearing the protocerebrum lacks an appendage. This stands in contrast to the clearly protocerebrally targeted “antennae” of Onychophora and to some evidence for protocerebral limbs in fossil euarthropod representatives. Yet, the latter “frontal appendages” or “primary antennae” have most likely been reduced or lost in the lineage, leading to extant taxa. Surprisingly, a recent neuro‐anatomical study on a pycnogonid challenged this evolutionary scenario, reporting a protocerebral innervation of the first appendages, the chelifores. However, this interpretation was soon after questioned by Hox gene expression data. To re‐evaluate the unresolved controversy, we analyzed neuro‐anatomy and neurogenesis in four pycnogonid species using immunohistochemical techniques. We clearly show the postprotocerebral innervation of the chelifores, which is resolved as the plesiomorphic condition in pycnogonids when evaluated against a recently published comprehensive phylogeny. By providing direct morphological support for the deutocerebral status of the cheliforal ganglia, we reconcile morphological and gene expression data and argue for a corresponding position between the anterior‐most appendages in all extant euarthropods. Consequently, other structures have to be scrutinized to illuminate the fate of a presumptive protocerebral appendage in recent euarthropods. The labrum and the “frontal filaments” of some crustaceans are possible candidates for this approach.     

On the Microanatomy of the Supraoesophageal Ganglion of Some Amphinomids (Polychaeta Errantia), with Further Discussion of the Innervation and Homologues of the Polychaete Palps

Earlier papers dealing with the anatomy of the amphinomid brain were studied. Discrepancies in the studied works prompted a re-investigation of the central nervous system of these animals. In this paper the brain commissures, the clusters of ganglion cells and the innervation of the antennae, the palps and the nuchal organs of Eurythoe complanata, Amphinome rostrata, Pherecardia striata, and Notopygos variabilis are described in some detail. The brain of Hermodice carunculata is studied more cursorily. The results, summarized in schematic diagrams, are compared with corresponding observations of the brains of ‘spiomorphic’ and ‘serpulimorphic’ polychaetes and to information given by earlier authors about structures in the Nereidiformia and Aphroditiformia. Using the major Remanian criteria for identifying homologies, equivalents in the amphinomid brain and the central nervous systems of some ‘sedentary’ and ‘errant’ families are proposed. As a consequence, some earlier opinions about the morphological value of the cephalic appendages of the amphinomids are strengthened while others are rejected. The necessity of further investigations of the polycheaete nervous system is emphasized.     

Morphological and molecular evidence of the phylogeny of Nereidiform polychaetes (Annelida)

The phylogeny of Nereidiformia is assessed in a parsimony analysis of combined morphological and DNA data, with special focus on previously questioned relationships between Chrysopetalidae and Hesionidae, between Pilargidae and Hesionidae, and the affinities of Hesionides and Microphthalmus. A 660 bp segment of the mtDNA cytochrome c oxidase subunit I gene was sequenced for two chrysopetalids, one nereidid, one pilargid, one pisionid, two hesionids, plus the two questionable hesionids Hesionides arenaria and Microphthalmus sp. Phylogenetic resolution was poor for the cytochrome c oxidase subunit I gene data alone, but the combined analysis yielded partially robust topologies, suggesting that nereids are the sister group to chrysopetalids, and that pilargids, Hesionides and Microphthalmus do not belong within the hesionids     

Environmental factors structuring polychaete communities in shallow rocky habitats: role of physical stress versus habitat complexity

Polychaetes inhabiting 12 different hard bottom habitats were studied. A total of 157 species belonging to 32 families were identified. Differences among habitats in polychaete density, species richness, and diversity were analysed, as well as the relationships between these ecological indices and depth range, slope and in-bay/out-bay gradient. A high faunal homogeneity was found: all biotopes were dominated by a low number of eurytopic species. Intertidal habitats and subtidal ones with scarce algal cover were typified by vagile polychaetes (syllids, nereids), while sessile polychaetes (serpulids, sabellids) appeared typically among subtidal large macrophytes, habitats with a calcareous substrate and shaded habitats. Multivariate analyses showed that habitat complexity, determined by physical disturbance, is the main structuring factor for polychaete populations. Biotopes with the highest structural complexity displayed a high number of companion species increasing ecological indices and denoting a well-structured habitat. On the other hand, communities such as those in the upper intertidal, mainly controlled by physical environmental variables, showed a poorer polychaete fauna, dominated by ubiquitous species and a few well-adapted specialists.     

The hierarchical basis of serial homology and evolutionary novelty

Given the pervasiveness of gene sharing in evolution and the extent of homology across the tree of life, why is everything not homologous with everything else? The continuity and overlapping genetic contributions to diverse traits across lineages seem to imply that no discrete determination of homology is possible. Although some argue that the widespread overlap in parts and processes should be acknowledged as “partial” homology, this threatens a broad base of presumed comparative morphological knowledge accepted by most biologists. Following a long scientific tradition, we advocate a strategy of “theoretical articulation” that introduces further distinctions to existing concepts to produce increased contrastive resolution among the labels used to represent biological phenomena. We pursue this strategy by drawing on successful patterns of reasoning from serial homology at the level of gene sequences to generate an enriched characterization of serial homology as a hierarchical, phylogenetic concept. Specifically, we propose that the concept of serial homology should be applied primarily to repeated but developmentally individualized body parts, such as cell types, differentiated body segments, or epidermal appendages. For these characters, a phylogenetic history can be reconstructed, similar to families of paralogous genes, endowing the notion of serial homology with a hierarchical, phylogenetic interpretation. On this basis, we propose a five-fold theoretical classification that permits a more fine-grained mapping of diverse trait-types. This facilitates answering the question of why everything is not homologous with everything else, as well as how novelty is possible given that any new character possesses evolutionary precursors. We illustrate the fecundity of our account by reference to debates over insect wing serial homologs and vertebrate paired appendages.     

Sinohesione genitaliphora gen. et sp. n. (Polychaeta, Hesionidae), an interstitial annelid with unique dimorphous external genital organs

A new hesionid. Sinohesione genitaliphora gen. et sp. n., is described from intertidal sandy sediments of Hainan Island, China. It differs from hitherto known hesionids by the presence of external genital organs in both sexes. In the males there is one pair of sae-like appendages, each bearing a tube-shaped penis, on chaetiger 10. In the females the paired sae-shaped organs are situated on chaetiger 12. Reconstructions of semi- and ultrathin sections show that a long, heavily coiled sperm duct opens at the tip of each penis. The duct opens with a ciliated funnel into a seminal vesicle in chaetiger 9. Prominent gland cells surround the sperm duct for the most part. The female genital organs each have two openings; one of which leads to a blind ending seminal receptacle. The other is the external pore of a ciliated oviduct that originates as an open funnel in the coelom of chaetiger 10. The functional and phylogenetic significance of these structures is discussed.     

Evolutionary aspects of cephalic sensory papillae of the Indo‐Pacific species of Eleotris (Teleostei: Eleotridae)

Eleotris species (Teleostei: Eleotridae) are one of the most common fish in Indo‐Pacific estuaries and insular freshwater streams. In these rivers, they are a sit‐and‐wait predator. They have an amphidromous life cycle, that is adults grow, feed and reproduce in rivers, while larvae have a marine dispersal phase. Larvae recruit back to rivers and settle in stream habitats. Primary characters used to determine Eleotris species are the presence and the disposition of cephalic sensory papillae rows on the operculum and under the eyes as well as scale row numbers. The morphology of these cephalic sensory papillae is of particular importance in this predatory genus as it is generally correlated in fish to predation and feeding. In this paper, we have established a molecular phylogeny of the genus based on the 12 mitochondrial protein‐coding genes to discuss the relationship between Indo‐Pacific Eleotris species. There is a well‐supported dichotomy in the molecular phylogeny, and this separation into two main clades is also morphologically visible, as it reveals a difference in the arrangement of cephalic sensory papillae. Indeed, the phylogeny distinguishes the species with the “open” pattern of the operculum sensory papillae and the species with the “closed” one. This phylogeny thus reflects the morphology of the opercular papillae. The evolution of this character is discussed in terms of the adaptation of the Eleotris genus to life in tropical insular river systems.