Fine structure of the ciliated epidermis on the tentacles ofOwenia fusiformis (Polychaeta,Oweniidae)

Summary The ultrastructure of the epithelium on the oral surface of the tentacles ofOwenia fusiformis has been studied by light and electron microscopy. Unspecialized monociliated cells are the dominant cell type of the epithelium; however, biciliated epidermal cells, monociliated mucous cells and non-ciliated cells are also present. In all of the ciliated cells each cilium is provided with a diplosomal basal body and two striated rootlets. The cytological features of this unspecialized epithelium strongly resemble those of similar epithelia in the Phoronida, Brachiopoda and Hemichordata. So far,O. fusiformis is the only polychaete known to possess an unspecialized monociliated epidermis. Other characters ofOwenia are also mentioned. The relationship between the nervous system and the epidermal cells on the tentacles is examined. It is proposed thatOwenia should assume an important role in discussions of the phylogeny of the Polychaeta.I wish to thank Dr. R.M. Rieger for his inspiration and guidance during the course of this study. Ms. Wilma Hanton provided technical assistance for the electron microscopy. This work was supported by NSF Grant # GB-42211 to R.M. Rieger     

A new species of Myriochele (Polychaeta, Oweniidae) from Antarctica, with considerations on the Antarctic oweniids

A new species of Oweniidae from the Ross Sea (Antarctica) is described and compared with the remaining species of the genus Myriochele from the Antarctic seas. The authors also discuss the difficulty of detecting the shape of uncini (considered as an important diagnostic character) by optical microscopy; they propose a key to Antarctic Oweniidae based on characters easier to observe than uncini. Received: 14 October 1997 / Accepted: 16 December 1997     

High abundance of Myriochele fragilis Nilsen & Holthe, 1985 (Polychaeta: Oweniidae) in the deep sea of the Eastern Mediterranean

An exceptionally high abundance of Myriochele fragilis Nilsen & Holthe, 1985 (Polychaeta: Oweniidae) is reported for the Ierapetra Basin in the Eastern Mediterranean Sea from depths of 4159 and 4260 m, representing the first record outside the Norwegian and Arctic Sea and extending the depth range by more than 1600 m. Specimens are described and compared to closely related species.     

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.     

Setal Structure, Functions and Interrelationships in Spirorbidae (Polychaeta, Sedentaria)

Typical thoracic setae are composed of longitudinally arranged cylinders ending as teeth at the oblique distal surface. Most thoracic 'blades' are rounded in cross section and show bilateral asymmetry. Some have teeth in oblique rows ("cross striations") on the side adjoining the tube wall. Sickle setae found posteriorly on the thorax have distal portions like abdominal setae. These are flat, each composed mainly of a palisade of spatulate units. On one side cylindrical elements may also be present, in patterns which are characteristic of some taxa. Uncini are made of rows (sometimes single) of shorter cylindrical elements with hooked ends pointing anteriorly. Anterior thoracic hooks are usually blunt, but pointed in the genus Janua. The collar setae assist withdrawal into the tube, the abdominal setae help with emergence, whilst other thoracic setae act as distance pieces, pushing the body to anchor the thoracic uncini against the opposite wall. The other uncini are brought into use by the prehensile abdomen. The flaccid ends of the sickle setae are readily lost in some taxa and their development or loss may reflect unimportant variations in strength of the adjacent abdominal field. Fin and blade setae are not very different from simple setae and the natural grouping of the genera into subfamilies shows that changes from one form of collar seta to another have occurred independently several times.     

Genetic Structure of PILEOLARIA PSEUDOMILITARIS (Polychaeta: Spirorbidae)

The genetic structure of Pileolaria pseudomilitaris was studied by means of gene-diversity analysis of allozyme frequencies. At an esterase locus, most of the gene diversity was due to subdivision of the population into colonies and subpopulations separated by less than 100 meters. Gene frequencies at a phosphoglucose isomerase locus were similar over many kilometers, but differed between two habitat types. Differences between colonies are attributed to drift and founder effect; similarities over greater distances are attributed to similar selection pressures. A mathematical appendix details the method of gene diversity analysis for a multi-leveled, hierarchically subdivided population.     

Revision of Pseudonereis (Polychaeta, Nereididae)

A taxonomic revision of Pseudonereis (Polychaeta, Nereididae) shows that some of the described taxa are very similar in most morphological characteristics. The revision includes all ten taxa considered valid, and are redescribed from type material. Lectotypes are designated for Pseudonereis anomala Gravier, 1901, Pseudonereis noodti (Hartmann-Schröder, 1962) and Pseudonereis trimaculata Horst, 1924. The widely geographically distributed and well-known P. gallapagensis Kinberg, 1865 and P. variegata ( Grube, 1857 ) show striking morphological resemblance to less well-known taxa with similar distribution. Paragnath variation in populations of P. anomala is discussed relating to its geographical distribution. Pseudonereis trimaculata is recorded from Australia for the first time. Taxa belonging to Pseudonereis are predominantly tropical and subtropical. A cladistic analysis using parsimony is included to test for monophyly of Pseudonereis . A monophyletic clade including all Pseudonereis taxa is given low bootstrap support. This clade is supported by the synapomorphies: presence of paragnaths in closely spaced comb-like rows on the maxillary ring on the pharynx, and presence of p-bar paragnaths in Areas II–IV and VII–VIII. Several of the included taxa share the shield-shaped paragnath in Area VI, which serves to distinguish Pseudonereis spp. from Perinereis spp. Paragnaths of the type p-bars and shield-shaped bar is described for the first time; the latter character is different from the smooth bar-shaped paragnaths in Area VI as has previously been described in these taxa.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 145–176.     

A correlative study of experimentally changed first cleavage and Janus development in the trunk of Platynereis dumerilii (Annelida,Polychaeta)

Summary Among zygotes of Platynereis dumerilii treated with cytochalasin B (CCB) prior to first cleavage, a wide variety of developmental effects were observed. One effect is a delay in the first cleavage. Treated embryos may skip the first or even more than one cleavage cycle and become multinucleated. Once these eggs start cleaving their cleavage plane takes the same position as in synchronously fertilized controls. Accordingly, the first cleavage in embryos having skipped the first normal cleavage cycle is meridional and equal, but their second cleavage is equatorial as in the third cleavage in controls. None of the embryos that were observed to skip early cleavages showed normal organogenesis, but developed into vesicle-shaped embryos with little cytological differentiation. Another effect of CCB treatment is altered blastomere size in those embryos which begin cleaving in synchrony with controls. While the majority of treated embryos followed a normal cleavage pattern, i.e. they cleaved at the right time and inequally, some of them cleaved equally or almost equally (adequally). Most of these embryos showed cleavage defects in subsequent cleavage cycles and became abnormal vesicle-shaped embryos. However, some of these embryos cleaving on schedule and equally or adequally developed into juvenile worms showing complete duplication of urites and parapodial rows (0.3% of all treated eggs) and are described as Janus duplicitates. This means that the occurrence of duplicitates and geometrically altered first cleavage patterns are correlated phenomena. The character and origin of the duplications and the consequences for dorsoventral polarity are discussed.     

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.     

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.     

Structure of the prostomial appendages and the central nervous system in the Protodrilida (Polychaeta)

Summary The prostomial appendages and the central nervous system have been investigated by electron microscopy in Protodriloides chaetifer, P. symbioticus, Protodrilus haurakiensis, P. oculifer, P. ciliatus, P. helgolandicus, P. adhaerens, Saccocirrus krusadensis and S. papillocereus. The tentacles are highly developed, mobile sensory structures and consist of cuticle, epidermis, a different number of intraepithelial nerves, a small blind-ending blood vessel and a bundle of longitudinal muscle fibres. An internal canal is only present in Protodrilus and Saccocirrus species. On the tentacles seven types of sensory cells have been found including different multiciliated and uniciliated sensory cells with cilia penetrating the cuticle, sensory cells with non-penetrative cilia, phaosomes and basal ciliated sensory cells. The latter are described for the first time in polychaetes. From the specific pattern of innervation by up to five nerves originating close to the brain from the dorsal and ventral roots of the circumoesophageal connectives it is evident that the prostomial appendages represent palps. In the palps the nerve fibres form neuroneuronal, myoneuronal and epithelioneuronal synapses. The brain also gives rise to the stomatogastric nerves and various dorsal nerves. The palp canals are separated from the surrounding tissue by a prominent extracellular matrix. The wall is formed by muscle cells. The centre is usually completely filled with the cell bodies of these muscle fibres and large coelenchyme-like cells. These cells move freely in the canals and they are very likely the structural basis for the hydroskeletal function of the canals. The canals are completely separated from other body cavities and fluid is probably driven into the canals from the blood vascular system via podocytes located in a specific zone in the prostomium. In particular, the structure of the central nervous system with its nerves, the pattern of innervation of the palps and the palp canal system are compared with those of other polychaetes with special emphasis to the Spionida, the taxon presumed to include the sister group of the Protodrilida.     

Eine neueOphryotrocha-Art (Polychaeta,Eunicidae) aus Japan

Zusammenfassung 1. Ein japanischer Vertreter der kosmopolitischen PolychaetengattungOphryotrocha, O. notoglandulata n. sp., wird beschrieben.2.O. notoglandulata n. sp. ist eng mitO. labronica Bacci &La Greca verwandt.3. Besonderes Artmerkmal sind sternförmige Drüsenfelder auf den Dorsalflächen der hinteren 6–12 Segmente.4. Die neue Art ist getrenntgeschlechtlich.5. Das Geschlechtsverhältnis schwankt stark von Gelege zu Gelege. Im Mittel beträgt es 1,5:1.6.O. notoglandulata n. sp. ist mitO. labronica nicht kreuzbar.

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A newOphryotrocha species (polychaeta, eunicidae) from Japan

A new Japanese species ofOphryotrocha is described. It is characterized by oblong cells forming star-shaped glands of unknown function on the 6th to 12th of the youngest segments.Ophryotrocha notoglandulata n. sp. is closely related toOphryotrocha labronica Bacci &La Greca; both have the same chromosome number (2 n=6). The new species is gonochoristic with a sex ratio of approximately 1.5:1. In mass culture as well as in couples, no mutual influence on sex determination was found. It is impossible to obtain hybrids betweenO. labronica and the new species.

     

Phylogenetic relationships within Nephtyidae (Polychaeta,Annelida)

Ravara, A., Wiklund, H., Cunha, M. R. & Pleijel, F. (2010). Phylogenetic relationships within Nephtyidae (Polychaeta, Annelida). —Zoologica Scripta, 39, 394–405. We present the first phylogeny of nephtyids, a common, soft‐bottom living polychaete family comprising five genera and over 100 species. Characters used to distinguish nephtyid genera are a matter of controversy and considerable confusion remains as to the generic delineations. The phylogeny is estimated with molecular data from the mitochondrial genes cytochrome oxidase I and 16S rDNA, the nuclear genes 18S rDNA and 28S rDNA and morphological data. The results reveal two well‐supported major clades, corresponding in part to the two main genera of the family, Aglaophamus and Nephtys. The species Nephtys pulchra and Nephtys australiensis are transferred to Aglaophamus, and new diagnoses for the genera are provided. Dentinephtys is synonymized with Nephtys, and Nephtys cornuta is sister to the remaining nephtyids and is referred to the new genus Bipalponephtys, together with Nephtys danida and Micronephthys neotena. Micronephthys is sister to Nephtys and Inermonephtys is of uncertain position.     

Giant pelagic larvae of Phyllodocidae (Polychaeta,Annelida)

The microscopic anatomy of giant pelagic larvae of Phyllodocidae was studied using routine histological, SEM, and TEM techniques. The larvae consist of two distinct regions: a large spherical trochophore measuring up to 2 mm in diameter and a posterior, long (up to 10 mm length), narrow rudiment of the adult body with up to 120 segments. The larvae have an unusual mixture of larval and adult features, including a very complex, well-developed brain and ganglia in the ventral nerve cord, and only a single pair of protonephridia located in the hyposphere of the trochophore. A muscular pharynx is not developed. The intestinal wall, especially in the trochophore region, consists of endodermal cells containing considerable nutritive material in the form of yolk-like globular inclusions. The digestive tract of all larvae was empty. The position of the frontal sensory organ and the prototroch, the structure of the parapodia and setae, and the three pairs of tentacular cirri dictate inclusion of the larvae in the family Phyllodocidae. The relatively enormous size and unusual pattern of development of the adult body may be adaptations for a long pelagic life and rapid settlement of the species, which inhabits slopes of islands and underwater mounts located far apart. J. Morphol. 238:93–107, 1998. © 1998 Wiley-Liss, Inc.     

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.