Ultrastructure of the Genital Organs in the Interstitial Syllid Petitia amphophthalma (Annelida,Polychaeta)

Abstract The gonochoristic syllid Petitia amphophthalma is one of the truly interstitial polychaetes. P. amphophthalma does not show any epitokous modifications at maturity such as those that usually occur in syllids. The reproductive structures are unique: the male genital organs consist of a seminal vesicle in chaetigers 6–10, subdivided into a dorsal part tightly filled with spermatozoa and a ventral part with contents in different stages of spermatogenesis, one pair of sperm ducts and conspicuous gland cells situated in chaetigers 10 and 11. Their glandular secretions are discharged into the sperm duct together with those of other types of gland cells that form the duct. The oocytes develop freely within the body cavity of the females. Each of the fertile segments possesses a paired oviduct ending in a large ciliated funnel. Sperm ducts and oviducts are probably modifications of excretory organs; nephridia are absent in segments where gonoducts occur. A direct sperm transfer by lytic opening of the integument of the female and internal fertilization are inferred. Copyright © 1996 Published by Elsevier Science Ltd on behalf of the Royal Swedish Academy of Sciences     

Phylogenetic affinities of the Flabelligeridae (Annelida, Polychaeta)

Cirratuliformia includes Acrocirridae, Cirratulidae, Ctenodrilidae, Flabelligeridae, Flotidae and Sternaspidae. The phylogenetic affinities have not been settled due to a limited availability of type or non-type material and the relationship between acrocirrids and flabelligerids have been problematical. In our study, the type material of all type species for all flabelligerid, and most acrocirrid genera have been studied and the morphological features have been used in a phylogenetic analysis. The results indicate that Acrocirridae, Ctenodrilidae, Fauveliopsidae, Flabelligeridae and Flotidae are monophyletic and that Sternaspidae falls within Cirratulidae; however, the latter conclusion might be reversed through increased taxon-sampling. The flabelligerid genera Brada, Flabelligera, Pherusa and Stylarioides each consists of several monophyletic groups and may be split. Conversely, Bradiella includes Diversibranchius, and the pelagic Buskiella includes Flota. The generic affinities of Poeobius remain uncertain, collecting better materials may resolve this issue.     

Anatomy and ultrastructure of ventral pharyngeal organs and their phylogenetic importance in Polychaeta (Annelida)

Summary A comparative anatomical and ultrastructural study of ventral pharyngeal organs (pharyngeal bulbs) was carried out in two species of the Dinophilidae: Dinophilus gyrociliatus and Trilobodrilus axi. Special attention was paid to the fine structure of the stomodeal epithelium, cuticle, glands, muscles, and myoepithelial junctions. The differences between the species are very slight. The pharyngeal organ of the Dinophilidae is characterized by the following features: solid muscle bulbus made up of muscle cells only, bulbus muscle cells with two myofilament systems crossing at an angle of about 90°, gap junctions between these muscle cells, bulbus projects into a pharyngeal sac and bears rostrally a specific epithelium and cuticle, no bulbus glands, no investing (= sagittal) muscles, specific cuticle ultrastructure, cilia of ascending oesophagus with asymmetric tips, specific structure and position of salivary gland openings. The phylogenetic importance of these structures is discussed. Some of these characters are clearly autapomorphic features of the Dinophilidae and no common derived structures to other families with a ventral pharyngeal organ are present. Therefore, it is most likely that the dinophilid pharyngeal organ evolved independently. These findings do not agree with the hypothesis of the unity of the archiannelid families (Polygordiidae, Protodrilidae, Saccocirridae, Nerillidae, Dinophilidae, and Diurodrilidae) established on the basis of an assumed structural similarity of their ventral pharyngeal organs.Abbreviations bb basal body - bep bulbus epithelium - bl basal lamina - bm bulbus muscle - c cilium - cc coelenchyme cell - cm circular muscle - cr caudal rootlet - cu cuticle - dblm dorsal bulbus longitudinal muscle - dlm dorsal longitudinal muscle - dsn dorsal stomatogastric nerve - dy dyad - el electron-dense layer - fl fibrous layer - fi filaments - g Golgi apparatus - gl gland cell - hv homogeneous vesicle - l lipid droplet - la external lamina - lal lamellar layer - ll lower lip - lm longitudinal muscle - ly lysosome - m mitochondrion - mo mouth opening - mt microtubule - mv microvillus - mvp microvillar process - n nucleus - nu nucleolus - oes oesophagus - pcom preoral commissure - phf pharyngeal fold - phl pharyngeal lumen - phs pharyngeal sac - pms peripheral myofilament system - r rootletlike structure - rer rough endoplasmic reticulum - rr rostral rootlet - s sarcoplasmic reticulum - sc salivary canal - scom suboesophageal commissure - sd septate desmosome - ser smooth endoplasmic reticulum - sg secretory granule - sgl salivary gland - sn stomatogastric nerve - st stomach - step stomodeal epithelium - tep transitional epithelium - tf tonofilaments - va vacuole - vlm ventral longitudinal muscle - vsn ventral stomatogastric nerve - z z-element - za zonula adherens     

Anatomy and ultrastructure of ventral pharyngeal organs and their phylogenetic importance in Polychaeta (Annelida)

Summary Transmission electron microscopic studies were carried out on the ventral pharyngeal organs in Ctenodrilus serratus and Scoloplos armiger. The pharyngeal organs are composed of a muscle bulbus and a tongue-like organ. In both species the muscle bulbus consists of transverse muscle fibres and interstitial cells with voluminous cell bodies and dorsoventral tonofilaments; the investing muscle runs into the tongue-like organ; the nuclei of the investing muscle fibres are located in caudal bulges; salivary glands are not present, but numerous gland cells occur in the bulbus epithelium. The tongue-like organ, however, is formed by lateral folds (C. serratus) or a bridge-like structure (S. armiger). The specific structure of the bulbus muscle is probably a homologous characteristic also occurring in several other polychaete families. The phylogenetic importance of this ventral pharynx is discussed and a hypothesis is suggested to explain the differentiation of certain other ventral pharyngeal organs from this probably primitive type.     

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.     

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.     

Ultrastructure of Presumed Ocelli in Parenterodrilus taenioides (Polychaeta,Protodrilidae) and their Phylogenetic Significance

Abstract Three different types of presumed unpigmented ocelli have been found in the anterior end of Parenterodrilus taenioides, a small gutless interstitial polychaete. The type-1 ocelli are located in the palps and four ocelli have been found along the length of each palp. The type-2 and type-3 ocelli lie close together in the head segment and are located in posterior ganglionic expansions of the brain. There is one pair of the minute type-2 ocelli but at least two pairs of the type-3 organs, which are the largest ocelli. In each ocellus the sensory cells are of the ciliary type and possess two cilia whose plasma membranes branch into numerous microvilli. With the exception of the type-1 ocelli they consist of a sensory cell and a supportive cell. In each ocellus the supportive cell forms a thin cup-shaped envelope around the densely packed ciliary branches. The type-1 ocelli consist of a single cell forming an intracellular vacuole (phaosome) which contains less densely packed microvillus-like structures. In particular, the structure of these ocelli is compared with that in other polychaetes, with special emphasis on the remaining genera of the Protodrilida.     

A new genus and species of Dorvilleidae (Annelida, Polychaeta) from Bermuda, with a phylogenetic analysis of Dorvilleidae, Iphitimidae and Dinophilidae

Neotenotrocha sterreri gen. et sp. n. is described from Bermuda. It is a gonochoristic. interstitial polychaete exhibiting sexual dimorphism. The maximum length of males is only 140 μm. while females may be up to 255 μm long. They are thus the smallest polychactes known to contain a mature ovary. The new species is referred to the polychaete family Dorvilleidae, primarily due to the presence of a etenognath jaw apparatus. In almost all external characters the new form is strongly reduced. lacking parapodia, setae, antennae, and palps, whereas larval characters such as trochae and a neurotroch are retained in adults. In the light of earlier literature on phylogeny within Dorvilleidae and the likelihood that Iphitimidae and Dinophilidae are closely affiliated with the latter family, the unique combination of characters in Neotenotrocha is of special interest. A phylogenetic analysis of all apparently valid genera in the three families leads to the hypothesis that Dinophilidae and Iphitimidae represent monophyletic and paraphyletic subgroups. respectively, within Dorvilleidae. Accordingly. the definition of Dorvilleidae is emended and a key to the genera provided. The species Ougia macilenta (Oug, 1978) is referred to Parougia Wolf. 1986 and the generic status of Meiodorvillea apalpata Jumars. 1974 and Protodorvillea gaspeensis Pettibone. 1961 is discussed. Some remarks on the applicability of concepts such as neoteny and progenesis in the characterisation of interstitial dorvilleids are included. On the basis of the cladogram mid these considerations. it is hypothesized that this group may have originated in the single evolutionary event.     

Ultrastructure of pigmented eyes in Dorvilleidae (Annelida,Errantia, Eunicida) and their importance for understanding the evolution of eyes in polychaetes

Among polychaetes, the errant forms are the only group known so far possessing true multicellular eyes in adults which are preceded by bicellular larval eyes in many species. Most likely, two pairs of such eyes showing a specific structure belong to the ground pattern of Errantia = Aciculata. However, these eyes have primarily been investigated in only two subgroups of Errantia, but data on the third main taxon, Eunicida, are available for only two taxa. In the present investigation, the eyes in two additional species of Eunicida, the dorvilleids Protodorvillea kefersteini and Schistomeringos neglecta, were studied. In P. kefersteini, usually described as possessing one pair of small eyes, two pairs could be detected, whereas in S. neglecta only one pair was found. Each eye is made up of rhabdomeric photoreceptor cells, pigment cells and unpigmented supportive cells. Lenses or vitreous bodies are absent. From their structure most likely all eyes represent adult eyes and even the small anterior eyes in P. kefersteini structurally resemble miniaturized adult eyes. Neither persisting larval eyes nor unpigmented rhabdomeric ocelli were found in the two species. The observations in Dorvilleidae confirm the hypothesis of a common origin of adult eyes in Errantia.     

Foraging and mobility in three species of Aciculata (Annelida: Polychaeta).

Aspects of feeding, such as food capture and ingestion, as well as mobility of the polychaetes Eurythoe complanata, Marphysa formosa and Diopatra aciculata, from S?o Sebasti?o Channel (S?o Sebasti?o, state of S?o Paulo) were observed in laboratory conditions. Eurythoe complanata, a carnivorous species, fed exclusively on pieces of fish with the aid of strong muscular retractable lips, and detected the presence of food by chemical stimuli. Diopatra aciculata, an omnivorous species, captured and ingested different kinds of food with the aid of its jaws, generating a flow of water through its tube by which it detects the presence of food and oxygenates its gills. Marphysa formosa also used its jaws to bite and lacerate food. These species showed greater or lesser degrees of intolerance to light.     

Ultrastructure and functional morphology of the female reproductive organs inProtodrilus (Polychaeta,Annelida)

The morphology and function of the female reproductive organs in 6Protodrilus species are investigated by light- and transmission electron microscopy. Possible ways in which spermatozoa may enter the female coelom after leaving the spermatophore are discussed for species with and without special female reception organs. Only femaleP. rubropharyngeus andP. flavocapitatus have “dorsal organs” for spermatophore reception. The structure and function of these organs are described, as well as those of the oviduct found in 3 of the species investigated. The possible phylogenetic origin of gonoducts and different modes of oviposition within the genus are discussed. Finally, the high taxonomic significance of female traits such as dorsal organs, oviducts, cocoon glands and lateral ciliary rows in this genus is stressed.     

Evaluation of the pair-culture effect inOphryotrocha puerilis (Polychaeta: Dorvilleidae). I. Pair-culture effect and sex ratio

Pairs and larger groups of femaleOphryotrocha puerilis puerilis were formed from formerly isolated specimens. Neither the diameter of the oocytes present in the coelomic fluid nor the number of setigerous segments (ss) of the partners of a newly formed pair allow us to predict which one of the two animals will exhibit sex reversal. Amputation of the palps showed that these ventrolateral appendages of the prostomium are not responsible for the transmission of the mutual influence which is exerted during the pair-culture effect. Isolated females do not produce egg masses but keep their oocytes in the body cavity until they are eventually resorbed. The shedding of oocytes in one of the females of a newly formed pair was formerly considered to be the first step in the pair-culture effect. The present results demonstrate that egg laying in these cases is unspecific and due rather to the end of isolation than to specific interactions with the partner. In groups consisting of up to 50 animals the sex ratio oscillates around 1:1. The presence of primary males does not influence the sex ratio of adult specimens, although these males are capable of fertilizing egg masses produced by adult females. As a result, a high percentage of both young and old males are found in densely populated bowls. The significance of the pair-culture effect in natural populations is discussed in the light of these findings.     

Phylogenetic relationships and evolution of Orbiniidae (Annelida, Polychaeta) based on molecular data

The phylogenetic relationships of orbiniid taxa were reconstructed based on sequence data of the mitochondrial 16S rRNA and nuclear 18S rRNA genes. Both genes were analysed separately and in combination using maximum likelihood, Bayesian inference and maximum parsimony. Regardless of the method used, a clade consisting of the investigated Orbiniidae, Methanoaricia dendrobranchiata and Questa was strongly supported by the 18S dataset. The analysis of the combined dataset suggests inclusion of M. dendrobranchiata within the Orbiniidae with close relationships to species of Orbinia and Phylo, rather than as a sister taxon to all other orbiniids. Evidence is given for the paraphyletic status of Leitoscoloplos , Naineris , Orbinia , Phylo and Scoloplos , which represent the most species-rich genera of the Orbiniidae. It is thus reasoned that the morphological characters presently used for genus diagnosis are not informative for cladistic analysis. No support is found for the hypothesis that taxa of the Protoariciinae represent juveniles of Orbiniinae. Instead, in the case of Protoaricia oerstedi , strong support for a progenetic origin is found.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 144 , 59−73.     

Ultrastructure of Nuchal Organs in Polychaetes (Annelida) — New Results and Review

Nuchal organs are epidermal sensory structures present in most polychaetes. They are situated at the posterior edge of the prostomium and may extend posteriorly onto the peristomium. Although there is considerable external variation, they all consist of ciliated supporting cells, bipolar primary sensory cells and retractor muscles. They are innervated directly from the brain by paired nerves. The sensory cells are usually monociliated; their sensory processes lie in subcuticular spaces, the olfactory chambers. Structural variability is to be observed in the location of the sensory cells, the course of the nuchal nerve, position of nuchal ganglia as well as in cytological features of sensory and supporting cells. These differences provide useful characters for phylogenetic considerations to establish supraspecific taxa within the phylogenetic system of the Annelida. Special emphasis is laid on the problem of whether the nuchal organs represent an autapomorphy of the Polychaeta or the Annelida and thus whether the lack of nuchal organs in Clitellata is primary or secondary. As is discussed, the probability of a loss of the nuchal organs in Clitellata is higher, which favours the second hypothesis: that nuchal organs are part of the ground pattern of the Annelida and very likely are an autapomorphy of this group.     

Structure of the nephridium in Ophryotrocha puerilis (Polychaeta,Dorvilleidae)

Summary The nephridia of Ophryotrocha puerilis are segmental organs. The nephrostome opens at the posterior margin of a setigerous segment into the coelomic cavity of this segment. The nephridial canal is made up of about 15 cells. These cells form an S-shaped tubule which extends into the following segment. The lumen of the nephridial canal ranges from 2 to 7 m in diameter. The nephropore opens laterally on the ventral surface of the body wall.In cross sections, one, two, or three cells are seen forming the canal. The inner surfaces of the canal cells are of different appearances along the canal. Since no regular pattern of cell distribution was found along the canals of different nephridia it is assumed that changes in cell structure along the canal are due to functional states or properties rather than to anatomically fixed regional differences. The canal cells either show smooth contours or they form brush borders of microvilli or sponge-like inner surfaces with a system of vacuolar canals running through the cytoplasm. Most of the canal cells are filled with various kinds of vesicles. Usually two or three cells contain larger vesicles up to 2.5 m in diameter with more or less electron-dense contents. Some of these vesicles resemble lysosomes. There are at least three bundles of cilia in each canal. In young specimens the number of cilia in one bundle is smaller (10–15) than in adult specimens (60–70). The nephridia do not show sex specific differences. The female nephridia do not function as genital ducts. As judged from the sizes of sperm and nephridia it appears to be possible that sperm are shed via male nephridia.     

Evaluation of the pair-culture effect inOphyryotrocha puerilis (Polychaeta: Dorvilleidae). II. Conditions for the moult of the upper jaw

The conditions for moult of the upper jaw ofOphryotrocha puerilis were determined in isolated individuals and in groups of various sizes. The frequency of formation of the complicated upper jaw in both isolated individuals and in groups varies to a considerable extent. Although formation of the upper jaw and sex reversal normally are associated processes, the relationship of these two processes is not very well understood. Histological investigations at the light microscopic level demonstrate that the dental apparatus is an elaboration of the ectodermal stomodaeum which is considered to be a highly specialized part of the cuticle in the pharyngeal region of the gut.     

Ultrastructure and functional morphology of male genital organs and spermatophore formation inProtodrilus (Polychaeta,Annelida)

Summary The structure and functional morphology of lateral organs and sperm ducts, as well as the mechanisms of spermatophore formation and transfer, are investigated by means of light and electron microscopy in the genusProtodrilus. The sperm ducts are simple, ciliated, intercellular gonoducts with a funnel section surrounded by a thin muscle layer and a tube section opening externally in the anterior region of the lateral organs. No glands are present in the sperm ducts. The lateral organs are formed by long epidermal invaginations enclosing an elongate lumen into which numerous cilia project and a large number of glands open. Five to ten different gland types with strikingly distinctive secretory granules are found in the different species. In addition, special supporting cells, the so-called sponge cells, sensory cells and an underlying nervous tissue are developed in the lateral organs. It is stated that apart from some similarities to the ventral atrium ofNerilla antennata no corresponding organs are known within the Annelida. It is argued that inProtodrilus the spermatophores are formed by the lateral organs as there are a high number of glands opening into the lumen of the organ. The possible origin and genesis of the male gonoducts as well as the mode of spermatophore transfer inProtodrilus is discussed.Abbreviations used in the figures bl basal lamina - cc coelomic cell - ci ciliated cell - cir ciliary root - cr ciliary ring - cu cuticle - cv bs contractile ventral blood sinus - d dissepiment/septum - dbs dorsal blood sinus - es euspermatozoa - f funnel - fi filament - g gut - glo gland openings - lgl lateral organ gland - lm longitudinal muscle - lo lateral organ - lu lumen - mi mitochondrion - mt microtubules - mu muscle - mv microvilli - mvc microvillar crown - n nucleus - ne nervous tissue - o opening - ps paraspermatozoa - rer rough endoplasmatic reticulum - s spermatozoa - sc sponge cell - sg salivary gland - spd sperm duct - spdo sperm duct opening - t tube - tm transverse muscle - vc ventral ciliary band