Coelomocytes of Nephtys coeca (Annelida,Polychaeta)

Coelomocytes of Nephtys coeca were studied by transmission electron microscopy. The majority of the coelomocytes were found to be structurally identical with the muscle cells of the body wall. Animals kept under unfavourable conditions tended to have an increased number of coelomocytes and a decreased thickness of the body wall. The muscular coelomocytes, probably released from the body wall, showed various degrees of decomposition, indicating a process of autophagy.     

Influence of the Cerebral Neuroendocrine System on Neutral Lipid Synthesis During Oogenesis in Nereis diversicolor (Annelida Polychaeta)

Summary

After brief incorporation with ³H-glycerol, neutral lipid synthesis is lower in coelomocytes from decerebrated worms than in coelomocytes from control worms, but later this relationship is reversed. The presence of the brain increases the synthesis of neutral lipid, especially triglycerides, by coelomo-cytes maintained in vitro. The release of triglycerides in vitro by previously labelled coelomocytes is also stimulated by cerebral endocrine factors.     

Global diversity of polychaetes (Polychaeta; Annelida) in freshwater

A literature review of Polychaeta (Annelida) including Aphanoneura (the oligochaete-like Aeolosomatidae and Potamodrilidae), living in freshwater yielded 168 species, 70 genera and 24 families representing all of the major polychaete clades, but less than 2% of all species. The best-represented families were, in order, Nereididae, Aeolosomatidae, Sabellidae, Spionidae and Histriobdellidae. Fourteen families were represented by a single species and genus. Regions supporting the highest diversity of freshwater polychaetes were in order, Palaearctic, Neotropical, Oriental, Nearctic, Australasian, and Afrotropical. More than half of all species and genera inhabitat lakes and rivers, followed by lagoons/estuaries, which have a high proportion of euryhaline species, and inland seas. Less common, atypical polychaete habitats include subterranean waters, the hyporheic zone of rivers and plant container habitats (phytotelmata). At least three distinct ecological/historical processes appear to account for the colonisation of continental waters: invasion of a clade prior to the break-up of Gondwana, as in Aphanoneura, Namanereis, Stratiodrilus, and Caobangia; relatively recent stranding of individual species (relicts); and the temporary visitation of euryhaline species. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

The development of the serpulid Pomatoleios kraussii (Annelida, Polychaeta)

The development of Pomatoleios kraussii is extremely similar to that of Pomatoceros triqueter , and is completed under laboratory conditions in 1–3 weeks at 25–27°C. Mature larvae settle and metamorphose preferentially on the shells of adult conspecifics.     

Ultrastructure and mineral composition of serpulid tubes (Polychaeta,Annelida)

We have studied the tube ultrastructure of 44 recent species from 36 serpulid genera. Twelve distinct ultrastructures are identified. Serpulids possess very diverse tube ultrastructures, in contrast with the traditional point of view. Most species show single‐layered tubes, but 34% of these species have between two and four ultrastructurally different layers. Tubes are mostly bimineralic, and are composed of aragonite and calcite; however, one of the polymorphs is always dominant. All the studied single‐layered tubes with a lamello fibrillar tube ultrastructure are exclusively calcitic; prismatic structures, both in regular or irregular orientation, are either calcitic or aragonitic in composition. There is no correlation between tube mineralogy, and ultrastructure, and marine, brackish, and freshwater environments. We find that 47% of the serpulid species studied possess a unique combination of tube structure characters. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 633–650.     

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.     

Unusual granules in the ejaculatory duct of a Microphthalmus species (Polychaeta,Annelida)

Summary The paired prominent ejaculatory ducts of the hermaphroditic polychaete Microphthalmus cf. listensis are surrounded by gland cells the processes of which penetrate the ducts themselves. These cells produce, in separate regions, two different types of spherical granules. Type I is composed of an electron dense and an electron lucent part. Type II granules contain a tubular filament that forms a single or double spiral in the periphery of a more or less unstructured electron dense material. Golgi vesicles give rise to this granule type. During the passage of sperm, these granules are obviously discharged into the lumen of the duct. Here they change form and probably dissolve. Their function is as yet unknown; capacitation of sperm is assumed.     

Development and differentiation of the eye in Platynereis dumerilii (Annelida,Polychaeta)

The nereid polychaete, Platynereis dumerilii, possess two pairs of post-trochophoral eyes with one vitreous body each. The development of these eyes has first been observed in 2-day-old larvae. Whether the eye anlagen arise from stem cells or from undifferentiated ectodermal tissue was not determined. At first, the anlagen of the anterior and the posterior eyes adjoin each other. They separate in late 3-day-old larvae. The first separated eye complexes consist each of two supporting and two sensory cells. The supporting cells synthesize two different kinds of granules, the pigment granules of the pigment cup and the prospective tubules of the vitreous body. These tubules accumulate in the distal process of the supporting cell. The vitreous body is formed by compartments of the supporting cells filled with the osmiophilic vitreous body tubules. The short, bulbar photosensory processes bear microvilli that emerge into the ocular cavity. At the apex of each sensory cell process, a single cilium (or occasionally two) arises. The sensory cells contain a different kind of pigment granule within their necks at the level of the pigment cup. The rate of eye development and differentiation varies. New supporting cells are added to the rim of the eye cup. They contribute to the periphery of the vitreous body like onion skins, and sensory cells move between supporting cells. The older the individual compartments of the vitreous body are, the more densely packed is their content of vitreous body tubules. Elongation of the sensory and supporting cell processes of the older cells increases the volume of the eye. The eyespots of the trochophore are briefly described as of the two-celled rhabdomeric type with a single basal body with ciliary rootlet.     

Interstitial Dorvilleidae (Annelida, Polychaeta) from Europe, Australia and New Zealand

Four dorvilleid species new to science are described from intertidal and subtidal sandy sediments. For three of them new genera are erected: Coralliotrocha natans gen. et sp.n., Microdorvillea otagensis gen. et sp.n. and Pusillotrocha Åkessoni gen. et sp.n. One species represents the first record of the genus Pettiboneia from Australia, P. australiensis sp.n. Ophryotrocha minuta Levi, 1954 redescribed from Helgoland is transferred to a different genus, Arenotrocha gen.n. The present taxa belong to a morphological series of species with an increasing degree of neoteny in the family Dorvilleidae.     

The origin of yolk in the oocytes of Nereis virens (Annelida,Polychaeta)

Summary Comparative studies have been made of development of the adenohypophysis using the Rathke's pouch (RP)-derived model system. Rathke's pouch with associated mesenchyme and ventral hypothalamus, was microsurgically isolated from 15-day fetal rats and placed in mild trypsin solution. Three variations of donor tissue were isolated and transplanted beneath the kidney capsule of adult hosts: A) pure pouch epithelium; B) pouch epithelium plus mesenchyme; and C) pouch epithelium with mesenchyme and ventral hypothalamus. After 30 days the grafts were isolated and processed for light and electron microscopy. Cell types were characterized by immunostaining as well as by morphological criteria. In group A well differentiated mammotrophs dominated the grafts, many of which were hypertrophied with widely dilated endoplasmic reticulum and Golgi saccules. Mammotrophs, frequently with mitotic figures, were distributed evenly throughout the grafts. Somatotrophs and gonadotrophs were neither abundant nor well differentiated in group A, but were both abundant and more extensively differentiated in groups B and C. Both somatotrophs and gonadotrophs were typically localized at margins of the graft adjacent to connective tissue spaces. Well differentiated mammotrophs were present in groups B and C although there were fewer hypertrophied mammotrophs than in group A; and immunoreaction to prolactin was weaker than in group A.Tumor-like features found in all three groups included some loss of tissue integrity and large, vascular lakes unlined by endothelium.These findings suggest that differentiation of mammotrophs may be inhibited in part by mesenchyme associated with Rathke's pouch, since in the absence thereof these cells become hyperplastic. Conversely, differentiation of somatotrophs and gonadotrophs appears more dependent on these mesenchymal elements for normal development.     

Notes on gamete production in Lanice conchilega (Annelida,Polychaeta, Terebellidae)

Summary

Male and female gametogenesis in Lanice conchilega are described and illustrated as seen by light microscopy. There is no evidence for size-selectivity in the uptake of male gametes by the hypertrophied reproductive nephromixia, since undissociated motile sperm platelets as well as spermatozoa appear to be taken up by the genital funnels, and such funnels show no sexual dimorphism. Maturation of the coelomic oocytes is marked by a change in shape and the appearance of a surface reticulum of ridges.     

Ultrastructure and development of the nephridia in Anaitides mucosa (Annelida,Polychaeta)

Different developmental stages (trochophores, nectochaetae, non-mature and mature adults) of Anaitides mucosa were investigated ultrastructurally. A. mucosa has protonephridia throughout its life; during maturity a ciliated funnel is attached to these organs. The protonephridial duct cells are multiciliated, while the terminal cells are monociliated. The single cilium is surrounded by 14 microvilli which extend into the duct lumen without coming into any contact with the duct cells. Corresponding ultrastructure and development indicate that larval and adult protonephridia are identical in A. mucosa. Differences between various developmental stages can be observed only in the number of cells per protonephridium. A comparison between the funnel cells, the cells of the coelothel and the duct cells reveals that the ciliated funnel is a derivative of the duct. Due to the identical nature of the larval and postlarval protonephridia, such a funnel cannot be a secondary structure. In comparison with the mesodermally derived metanephridial funnel in phoronids it seems likely that the metanephridia of annelids and phoronids evolved convergently.     

Molecular and morphological evidence of Alvinellidae relationships (Terebelliformia, Polychaeta, Annelida)

In this study we assessed the phylogenetic relationships of the hydrothermal vent polychaete group Alvinellidae, based on parsimony analyses of combined morphological and molecular data. Morphological data were obtained from newly examined specimens and literature information of 16 terminal taxa belonging to Alvinellidae, Ampharetidae, Pectinariidae, Terebellidae, Trichobranchidae, and the outgroups Oweniidae and Sabellidae. Molecular data were based on 28S rRNA from 13 of the 16 morphological terminals (10 previously published sequences plus three new ones). The combined analysis indicated the clades ((Alvinellidae, Trichobranchidae) Pectinariidae) and (Ampharetidae, Terebellidae). Alvinellidae, Ampharetidae and Terebellidae, as currently delineated, are monophyletic. The positions of Trichobranchidae and Pectinariidae contradicted traditional views, and they also had low Bremer support and merit further studies. Well-supported clades included Alvinellidae and Terebellinae. Previous statements that Alvinellidae are either nested within Ampharetidae or the sister to this taxon were not supported. The traditional but here contradicted view that Terebellidae and Trichobranchidae are closely related may be based on plesiomorphic similarities between these two taxa.     

Chaetal arrangement in Orbiniidae (Annelida,Polychaeta) and its significance for systematics

The systematic position of Orbiniidae within Polychaeta is still uncertain. In order to provide additional comparative data, we investigated the chaetal arrangement in this family, which is considered valuable for polychaete systematics. Specimens of Scoloplos armiger, Orbinia latreillii, and Pettibonella multiuncinata were examined by SEM and serial sections analysed by computer aided 3D-reconstructions. The obtained data suggest that the chaetal arrangement of Orbiniidae resembles that of other sedentary polychaetes in only a few respects. Transverse rows are only present in the main, anterior part of the chaetal patches of thoracic neuropods. The position of the formative site indicates homology with the transverse rows of several sedentary polychaete taxa. The chaetal patches thus differ significantly from those known in Apistobranchidae. Independent rows with an own caudal formative site, which run along the caudoventral edge of the chaetal patches, resemble the neuropodial ventral longitudinal rows known in Spionidae and related taxa. The abdominal neuropodia of S. armiger and O. latreillii bear longitudinal rows of chaetae. These are reorientated during ontogenetic chaetiger transformation and become the transverse rows of the thoracic chaetal patches. 3D reconstruction of S. armiger revealed that the notopodial chaetal bundles are organized in rows as well. Notopodia and abdominal neuropodia bear deep reaching supportive chaetae. They are the first chaetae formed during neuropodial development and reside dorsally to the longitudinal row of capillary chaetae. Neither position nor structure indicates homology with the supportive chaetae of other sedentary polychaetes. Spionidae and related taxa are thus the only sedentary polychaetes, which specifically resemble Orbiniidae in certain aspects of their chaetal arrangement. Dedicated to Prof. Dr. Wilfried Westheide on the occasion of his 70th birthday.     

Morphogenesis during asexual reproduction in Pygospio elegans Claparede (Annelida, Polychaeta)

The spionid Pygospio elegans reproduces both asexually and sexually. Using scanning electron and bright field microscopy, we examined morphogenesis following asexual reproduction to determine how "lost" body regions were regenerated after a worm spontaneously divided. Asexual reproduction occurred through transverse fission and divided the parent worm into 2 to 6 fragments (architomy). All fragments retained their original anterior-posterior polarity. Regeneration in all fragments followed a specific series of events: wound healing (day 1); extension of the blastema to generate lost body regions-specifically, the head and thorax for posterior fragments and the tail and pygidium for anterior fragments (days 2-3); segmentation (days 3-6); and differentiation of segment- or region-specific structures (days 4-8). This pattern occurred regardless of where the original division took place. Subsequent growth occurred through addition of terminal setigers anterior to the pygidium followed by differentiation of tail setigers into abdominal setigers, leaving the tail region about 6 to 10 setigers in size. Division rates were compared in worms from three populations in Nova Scotia, Canada. Worms from two populations (Conrad's Beach, Starr's Point) divided more frequently (about 1.2 and 1.3 weeks between divisions, respectively) than worms from Bon Portage Island (3.5 weeks between divisions). Fragments containing the original head (original mouth intact, generally much larger fragment) had a higher survivorship than fragments containing the original tail.