CLSM analysis of the phalloidin-stained muscle system in Nerilla antennata, Nerillidium sp. and Trochonerilla mobilis (Polychaeta; Nerillidae)

The entire muscle system of Nerilla antennata, Nerillidium sp. and Trochonerilla mobilis was three-dimensionally reconstructed from whole mounts. In juvenile and adult specimens the F-actin musculature subset was stained with FITC-conjugated phalloidin and visualized with a confocal laser scanning microscope (cLSM). The muscle system shows the following major organization: 1) circular muscles are totally absent in the body wall; 2) the longitudinal muscles are confined in two ventral and two dorsal thick bundles; 3) additional longitudinal muscles are located in the ventro- and dorsomedian axis; 4) three segmental pairs of ventral oblique muscles elongate into the periphery: the main dorsoventral muscles that run along the body side posterior and dorsally and the anterior and posterior oblique parapodial muscles, which contribute to the ventral chaetal sacs; 5) one segmental pair of dorsal oblique parapodial muscles, contributing to the dorsal chaetal sacs; 6) five to seven small dorsoventral muscles per segment; and 7) complex head and pharyngeal musculature. These results support the belief that absence of circular muscles in the polychaete body wall is much more widely distributed than is currently presumed.     

Trochonerilla mobilis gen. et sp.n., a meiofaunal nerillid (Annelida, Polychaeta) from a marine aquarium in Moscow

A nerillid species new to science is described from the marine aquarium system of Moscow Zoo. Trochonerilla mobilis gen. et sp.n. is characterized by eight chaetigerous segments, three antennae, absence of palps, parapodia with two bundles of simple chaetae and pygidium with two anal cirri. In contrast to other eight-segmented nerillids, Trochonerilla mobilis are very active and mobile animals. They are also able to swim through the water column by means of the strong ring of cilia on the first chaetigerous segment. Their geographical origin is unknown.     

Ultrastructure of the Alimentary Canal in Five-Month-Old Pentactulae of the Holothurian Eupentacta fraudatrix

Five-month-old pentactulae (juveniles) of the holothurian Eupentacta fraudatrixpossess a well-developed alimentary canal comprising an esophagus, a stomach, an intestine, and a rectum. The intestine in turn consists of five parts. The esophagus, stomach, and rectum are lined with a cuticular epithelium. The intestinal lining lacks a cuticle and is composed of mainly polyfunctional vesicular enterocytes. Granular enterocytes are less abundant; their cytoplasm contains electron-dense granules, which are probably zymogenic. The gut connective tissue consists of electron-lucent ground substance with collagen fibers and embedded coelomocytes. The gut mesothelium is composed of myoepithelial and peritoneal cells and contains the neurons of the hyponeural nerve plexus.     

Phylogeny of Nerillidae (Polychaeta, Annelida) as inferred from combined 18S rDNA and morphological data

A phylogeny of the meiofaunal polychaete family Nerillidae based on morphological, molecular and combined data is presented here. The data sets comprise nearly complete sequences of 18S rDNA and 40 morphological characters of 17 taxa. Sequences were analyzed simultaneously with the morphological data by direct optimization in the program POY, with a variety of parameter sets (costs of gaps: transversions: transitions). Three outgroups were selected from the major polychaete group Aciculata and one from Scolecida. The 13 nerillid species from 11 genera were monophyletic in all analyses with very high support, and three new apomorphies for Nerillidae are identified. The topology of the ingroup varied according to the various parameter settings. Reducing the number of outgroups to one decreased the variance among the phylogenetic hypotheses. The congruence among these was tested and a parameter set, with equal weights (222) and extension gap weighted 1, yielded minimum incongruence (ILD). Several terminal clades of the combined analysis were highly supported, as well as the position of Leptonerilla prospera as sister terminal to the other nerillids. The evolution of morphological characters such as segment numbers, chaetae, appendages and ciliation are traced and discussed. A regressive pathway within Nerillidae is indicated for several characters, however, generally implying several convergent losses. Numerous genera are shown to require revision. © The Willi Hennig Society 2005.     

Ultrastructure of Chrysopetalid Paleal Chaetae (Annelida,Polychaeta)

Paleal notochaetae belonging to a number of Chrysopetalum species (Chrysopetalidae) were examined by scanning and transmission electron microscopy. Paleae are composed of broad medullary channels stacked with a regular series of horizontal fibrous diaphragms. The medullary part of the palea is surrounded by irregular rows of narrow tubular channels within the chaetal cortex. The origin and function of camerate chaetae is discussed.     

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 of spermiogenesis and spermatozoa in Diurodrilus subterraneus (Polychaeta,Diurodrilidae)

Spermiogenesis in the polychaete species Diurodrilus subterraneus may be divided into six stages. These stages, as well as the ultrastructure of the mature spermatozoa, are described based on TEM studies. The spermatozoa are unusual in having a very large acrosome followed by a region containing the nucleus and several ovoid mitochondria. A secondary acrosomal membrane forms a manchette around the nucleus and mitochondria. In this region, the plasma membrane is modified, with many small, mushroom-shaped cytoplasmic processes, each including filaments. The flagellum may be divided into three sequential regions; the longest, middle one is covered by a helically arranged mucous coat. Spermatozoa of the type described here are unknown among polychaetes but show certain superficial resemblances to those in oligochaetes. The resemblance of the mushroom-shaped bodies to spermatozoal microvilli in certain gnathostomulids is discussed. The phylogenetic relationships of Diurodrilidae are considered on the basis of this new information.     

Nephridial and gonoduct distribution patterns in Nerillidae (Annelida: Polychaeta) examined by tubulin staining and cLSM

The distribution and configuration of nephridia and gonoducts are described for seven species from seven genera of the interstitial polychaete family Nerillidae. The ciliated nephridia and gonoducts were identified by tubulin staining and examined with a confocal laser scanning microscope. The following species of the seven to nine-segmented nerillids were examined: Leptonerilla prospera, Nerilla antennata (nine segments); Nerillidium mediterraneum, Trochonerilla mobilis, Gen. sp. A (eight segments); and Aristonerilla brevis, Paranerilla limicola (seven segments). Two of the examined species are hermaphroditic (N. mediterraneum and Gen. sp. A). Segmented nephridia can be found from the first to the last segment, with a total of two to five pairs. One to three pairs of segmented spermioducts are present in all species. One pair of gonoducts is found in all species, except for P. limicola, where they are absent. Nephridia vary in length from half to almost twice the length of a segment and may be curled up in loops. In A. brevis and P. limicola the nephridia are discontinuously ciliated. The distribution and configuration of spermioducts and gonoducts are also variable, although to a lesser extent. The spermioduct distribution is generally consistent within genera and therefore of systematic significance. Nephridia and gonoducts are never found together in the same segments, and the results indicate that gonoducts and nephridia have developed from the same anlagen. The distribution patterns of nephridia and gonoducts are discussed with respect to segmentation, systematics, and development.     

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 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.     

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     

Ultrastructure of gill epithelial cells of Diopatra neapolitana (Annelida,Polychaeta)

Summary The ultrastructure of gill epidermal cells of Diopatra neapolitana and their relationship with blood spaces are described. The existence of a basal infolding complex, related to the blood spaces, is also reported. A possible involvement of these cells in osmoregulation and ion interchange, apart from their well-known role in respiration, is suggested.Abbreviations bc Blood cell - bi Basal infolding - bl Basal lamina - bs Blood space - ci Cilia - cu Cuticle - db Dense body - EC Epidermal cell - Gc Golgi complex - id Interdigitation - j Junction - m Mitochondria - mv Microvilli - n Nucleus - pv Pinocytotic vesicle - rer Rough endoplasmic reticulum     

Ultrastructure of spermiogenesis and spermatozoa of four Oriopsis species (Sabellinae, Sabellidae, Polychaeta)

The ultrastructure of sperm from four species of Oriopsis is described. Males of Oriopsis bicoloris produce sperm with an elongate nucleus divided into four rods, connected proximally, and four long mitochondria lying along the nucleus. The axoneme runs in the middle of the nuclear and mitochondria1 rods. Oriopsis brevicollaris males have sperm with an elongate nucleus and long midpiece comprised of four mitochondria wrapped around the axoneme. Males of O. mobilis have sperm with an elongate nucleus and long midpiece similar to that of O. brevicollaris , although the midpiece is much longer. Oriopsis dentata males havc sperm with a flattened head, similar to those of mammals, though the midpiece is simple and the axoneme free. The variability of reproductive mechanisms within the Polychaeta is discussed with reference to the elucidation of the function of various sperm morphologies. The implications for the taxonomy and systematics of Oriopsis , and the Sabellidae as a whole, are also discussed. It is concluded that Oriopsis is not monophyletic and examination of reproductive structures in other small sabellids is required. Study on reproduction in the type species, O. armandi , is needed to establish the reproductive method of Oriopsis and so allow revision of this genus.     

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.     

Ultrastructure of spermiogenesis, sperm, and the spermatheca in Terebrasabella heterouncinata (Polychaeta: Sabellidae: Sabellinae)

Abstract. The sabellid polychaete, Terebrasabella heterouncinata, forms burrows in gastropod shells. It is a small, intratubular brooder that breeds semi‐continuously. It has been shown to self‐fertilize, but its reproductive biology suggests that some form of sperm transfer must occur between individuals. To gain an understanding of its fertilization biology, the ultrastructure of spermiogenesis and the sperm in T. heterouncinata was described, and the animal examined for sperm storage structures. Spermiogenesis occurs in clusters of eight spermatids. The mature sperm has an elongate nucleus and a bilaterally symmetrical acrosome with twisted subacrosomal spaces. The midpiece is short, with three crescent‐shaped mitochondria, and forms a tight sheath around the axoneme. A single spermatheca, which opens on the inner ventral part of the crown near the buccal region, is present. It is a simple blind‐ending duct that runs below the ventral nerve cord and is longer than 100 μm. This is the first record of a single spermatheca in Sabellidae. The shape of the sperm and the presence of a spermatheca confirm that individuals of T. heterouncinata produce ent‐aquasperm and would normally cross‐fertilize.     

Ultrastructure of sperm morphology ofTrilobodrilus axi andT. heideri (Dinophilidae,Polychaeta)

The ultrastructure of the sperm of the dinophilidsTrilobodrilus axi andTrilobodrilus heideri was investigated. The sperms are extremely modified and show an elongated head, middle piece, and tail region, which are overlapping. This condition is a synapomorphous feature for the dinophilids. The sperm structure has to be related to the specialized mode of sperm transfer by hypodermal injection in these species.     

Phylogenetic position of Nerillidae and Aberranta (Polychaeta, Annelida), analysed by direct optimization of combined molecular and morphological data

The phylogenetic position of the most speciose meiofaunal polychaete family, Nerillidae, has remained contentious. Recent hypotheses have generally focused on the fact that Nerillidae shares with Aciculata (a major polychaete subgroup) features such as compound chaetae, ventral buccal organ and short ventrolateral palps. Here we present the first phylogenetic analysis of Aciculata, together with Nerillidae, combining morphological and molecular data. We also include Aberrantidae, previously referred to or placed near to spiomorph polychaetes, but recently referred to Aciculata, possibly close to Nerillidae. The data sets of 24 terminals contain 53 morphological characters and nearly complete sequences of 18S rRNA. The sequences were analysed simultaneously with the morphological data by direct optimization in the program POY with a variety of parameter settings (costs of gaps: transversions: transitions). The various settings resulted in markedly different phylogenetic hypotheses, but on the basis of congruence (ILD) the results of two parameter settings were chosen. In all analyses, the three included nerillid species constituted a monophyletic group. Only two analyses provided fully resolved cladograms. The morphological analysis gave poor resolution and the position of the nerillids was equivocal. The two molecular‐based cladograms (minimizing ILD) were also poorly resolved, but one provided a position for nerillids next to Eunice pennata and Nothria conchilega, from the subgroup Eunicida within Aciculata. The two cladograms of the combined analyses (minimizing ILD) were fully resolved and placed nerillids in a terminal position next to Aberranta sp., within a clade of eunicidan species. The study showed that the analytical conditions for the homology assignment of 18S rRNA strongly influenced the phylogenetic results. The various previous proposals on the phylogenetic position of the Nerillidae are reviewed, some of which are in accordance with the results of the present study.     

Ultrastructure and functional morphology of the protonephridia and segmental fenestrated lacunae inProtodrilus rubropharyngeus (Polychaeta,Protodrilidae)

The protonephridia ofProtodrilus rubropharyngeus are described. They consist of a terminal cell, one nephridiopore cell, and different types of duct cells (proximal, medial, distal) with the duct running intracellularly. Reabsorption takes place in the duct by means of very unique lamellar foldings. An interesting characteristic of the nephridial system inP. rubropharyngeus is the presumed double filtration of the primary urine that occurs in the walls of both the lateral blood lacunae and the terminal cell. The structure of excretory organs in relation to the particular coelomatic conditions found in different groups of polychaetes is discussed.