Organic coatings and ontogenetic particle selection in Streblospio benedicti Webster (Spionidae: Polychaeta)

Surface deposit feeders select food particles based upon characteristics including size, texture, specific gravity, and organic coatings. Spionid polychaetes feed at the sediment-water interface using a pair of ciliated palps and switch between surface deposit feeding and suspension feeding primarily as a function of water flow. Juveniles and adults of some spionid species have different stable isotopic carbon signals, indicating the ingestion of different food sources and potentially the ability to differentiate organic cues ontogenetically. In the present study, the feeding responses of juvenile and adult Streblospio benedicti Webster to seven organic coatings bound to glass microbeads were tested using five amino acids and two carbohydrates. Coated versus uncoated particles were presented in equal proportions based upon surface area. Juveniles and adults were highly selective for all seven types of organically coated beads—87.1% of all beads ingested were organically coated beads. For two of the organic coatings, there were ontogenetic differences; juveniles were more selective of threonine and adults were more selective of proline. These differences may result in ontogenetic diet shifts that allow maximization of energy and/or essential nutrients during critical early life-history stages. Particle selection in tentaculate surface deposit feeders is generally thought to occur primarily during particle contact and transport to the mouth, and is typically characterized as a passive process. Active particle selection at the site of the everted pharynx was observed and quantified for S. benedicti. Organically coated particles represented 50% of the ambient experimental treatment, 64.4% of the particles transported along the palp after contact, and 81.8% of the particles ingested after pharyngeal rejection behavior. Of the beads reaching the pharynx, 26.9% were rejected by ciliary sorting on the pharynx before ingestion, and 81.8% of the rejected beads at the site of the pharynx were uncoated. Our study demonstrates that microphagous feeders that generally handle food particles in bulk are capable of significant levels of active selection for organically coated particles.     

Palp morphology in two species of Prionospio (Polychaeta: Spionidae)

The palp morphology of Prionospio fallax Söderström, 1920 from Sweden and Prionospio cf. saldanha Day, 1961 from Thailand was examined with a scanning electron microscope. Prionospio fallax was also studied in vivo using light-microscopy. Both species have grooved feeding palps, adorned with up to five ciliary characters: frontal cilia, transverse ciliary bands (or bandlets), latero-frontal cirri, lateral cilia and randomly distributed non-motile cirri. All, except the frontal cilia and non-motile cirri, are asymmetrically arranged relative to the long axis of the palps. Prionospio fallax possesses transverse bandlets and the other four groups, while P. cf. saldanha has transverse bands (consisting of several contiguous bandlets), frontal cilia and some randomly scattered cirri. Asymmetrical palp ciliation was previously only known in Marenzelleria viridis (Verril, 1873) and the genus Scolelepis Blainville, 1828. The newly recognised transverse ciliary bands and bandlets are considered to be homologous with the transverse ciliary rows found basally on the palps of Paraprionospio pinnata (Ehlers, 1901). This multistate character (named transverse cilia) may prove useful in elucidating the phylogeny of the Prionospio-complex of genera.     

Sediment-associated cues for larval settlement of the infaunal spionid polychaetes Polydora cornuta and Streblospio benedicti

Do patchy distribution patterns of infaunal polychaetes result from active site selection of larvae influenced by sediment-associated microbial cues? This hypothesis was tested with still-water laboratory settlement assays revealing the acceptance or rejection of polychaete larvae to qualitatively different sediments. Laboratory brood cultures of the spionid polychaetes Polydora cornuta and Streblospio benedicti yielded a sufficient number of larvae with planktotrophic development for bioassays. High settlement rates (75-95%) of test larvae were observed in response to natural sediment. Sterilization of natural sediment significantly decreased settlement of P. cornuta (25-55%) while combustion of sediment significantly decreased the settlement rate in both species (5-50%). Differences in settlement responses to sediments treated by sterilization or combustion most likely resulted from a variety of factors such as modified sediment fabric, grain size distribution and quantity of adsorbed organic matter. To experimentally address the potential role of microorganisms and microbial metabolites as mediators of larval settlement, ashed sediment was inoculated with viable microorganisms obtained from natural sediment. In both polychaete species, this treatment significantly increased larval settlement in comparison to the control of ashed sediment indicating that larval settlement was at least partially mediated by the presence of microorganisms associated with sediment.     

Development and sexual dimorphism of branchiae in Streblospio benedicti

The Spionidae is one of the largest and most studied annelid families, but to date, the development and differentiation of post-metamorphic anatomy have not been documented. This study used scanning electron microscopy to examine the development of the branchiae, presumed respiratory organs, in Streblospio benedicti. Branchiae in this species are prominent, paired head structures and first appear around the time of metamorphosis, but do not complete their development until the worm reaches the older juvenile or adult stages. We observed that as the branchiae grew, their overall morphology changed through four different shapes: small bud, tubular, tapered, and, finally, bilimbate. In addition, the abfrontal and frontal surfaces each possessed a unique set of cilia patterns, which we named, and these arose in a particular sequence between the 8- and 35-chaetiger stages. This detailed examination of every stage of branchial development led us to discover that branchia in Streblospio benedicti was a sexually dimorphic organ. Streblospio benedicti is one of approximately eight Spionidae in which there is any type of structural sexual dimorphism, and it is the only species in which sexually dimorphic branchiae are found. The male's frontal surface had four unique cilia patterns, and we hypothesize that those located around the medial protrusion capture and control the release of the spermatophores. This first documentation of a spionid's branchial developmental sequence revealed that not only is this respiratory organ involved in reproduction, but it significantly differentiates after metamorphosis through adulthood.     

Observations of serotonin and FMRFamide-like immunoreactivity in palp sensory structures and the anterior nervous system of spionid polychaetes

Evidence suggests that ciliated sensory structures on the feeding palps of spionid polychaetes may function as chemoreceptors to modulate deposit-feeding activity. To investigate the probable sensory nature of these ciliated cells, we used immunohistochemistry, epi-fluorescence, and confocal laser scanning microscopy to label and image sensory cells, nerves, and their organization relative to the anterior central nervous system in several spionid polychaete species. Antibodies directed against acetylated alphatubulin were used to label the nervous system and detail the innervation of palp sensory cells in all species. In addition, the distribution of serotonin (5-HT) and FMRFamide-like immunoreactivity was compared in the spionid polychaetes Dipolydora quadrilobata and Pygospio elegans. The distribution of serotonin immunoreactivity was also examined in the palps of Polydora cornuta and Streblospio benedicti. Serotonin immunoreactivity was concentrated in cells underlying the food groove of the palps, in the palp nerves, and in the cerebral ganglion. FMRFamide-like immunoreactivity was associated with the cerebral ganglia, nuchal organs and palp nerves, and also with the perikarya of ciliated sensory cells on the palps.     

The benthic invertebrates of the Salton Sea: distribution and seasonal dynamics

The Salton Sea, California's largest inland water body, is an athalassic saline lake with an invertebrate fauna dominated by marine species. The distribution and seasonal dynamics of the benthic macroinvertebrate populations of the Salton Sea were investigated during 1999 in the first survey of the benthos since 1956. Invertebrates were sampled from sediments at depths of 2–12 m, shallow water rocky substrates, and littoral barnacle shell substrates. The macroinvertebrates of the Salton Sea consist of a few invasive, euryhaline species, several of which thrive on different substrates. The principal infaunal organisms are the polychaetes Neanthes succinea Frey & Leuckart and Streblospio benedicti Webster, and the oligochaetes Thalassodrilides gurwitschi Cook, T. belli Hrabe, and an enchytraeid. All but Neanthes are new records for the Sea. Benthic crustacean species are the amphipods Gammarus mucronatus Say, Corophium louisianum Shoemaker, and the barnacle Balanus amphitrite Darwin. Neanthes succinea is the dominant infaunal species on the Sea bottom at depths of 2–12 m. Area-weighted estimates of N. succinea standing stock in September and November 1999 were two orders of magnitude lower than biomass estimated in the same months in 1956. During 1999, population density varied spatially and temporally. Abundance declined greatly in offshore sediments at depths >2 m during spring and summer due to decreasing oxygen levels at the sediment surface, eventually resulting in the absence of Neanthes from all offshore sites >2 m between July and November. In contrast, on shoreline rocky substrate, Neanthes persisted year round, and biomass density increased nearly one order of magnitude between January and November. The rocky shoreline had the highest numbers of invertebrates per unit area, exceeding those reported by other published sources for Neanthes, Gammarus mucronatus, Corophium louisianum, and Balanus amphitrite in marine coastal habitats. The rocky shoreline habitat is highly productive, and is an important refuge during periods of seasonal anoxia for Neanthes and for the other invertebrates that also serve as prey for fish and birds.     

Identification and activity-dependent labeling of peripheral sensory structures on a spionid polychaete

In marine sedimentary habitats, chemoreception is thought to coordinate feeding in many deposit-feeding invertebrates such as polychaetes, snails, and clams. Relatively little is known, however, about the chemosensory structures and mechanism of signal transduction in deposit feeders. Using electron microscopy, confocal laser scanning microscopy (CLSM), and immunohistochemistry, we investigated the structure and function of putative chemosensory cells on the feeding appendages of a deposit-feeding polychaete species, Dipolydora quadrilobata. Tufts of putative sensory cilia were distributed over the prostomium and feeding palps and typically occurred next to pores. Examination of these regions with transmission electron microscopy revealed multiciliated cells with adjacent glandular cells beneath the pores. The sensory cells of prostomium and palps were similar, displaying an abundance of apical mitochondria and relatively short ciliary rootlets. Staining with antiserum against acetylated alpha-tubulin was examined by CLSM, and revealed axonal processes from putative sensory tufts on the palp surface to palp nerves, as well as many free nerve endings. Activity-dependent cell labeling experiments were used to test the sensitivity of putative sensory cells on the palps to an amino acid mixture that elicited feeding in previous behavioral experiments. In static exposures, the number of lateral and abfrontal cells labeled in response to the amino acid mixture was significantly greater than in the controls. Ultrastructural, positional, and now physiological evidence strongly suggests that spionid feeding palps are equipped with sensory cells, at least some of which function as chemoreceptors.     

Spermatogenesis and sperm ultrastructure in three species of polydora and in streblospio benedicti (Polychaeta: Spionidae)

Summary Spermatogenesis was studied at the ultrastructural level in Polydora ligni, P. websteri, P. socialis and Streblospio benedicti. Spermatogonia, spermatocytes, spermatids and mature sperm are described. In all four species, meiosis occurs in the coelom following release of spermatogonia from the gonad. In Polydora spp., chromatin condensation is lamellar with no microtubules present during nuclear elongation. In S. benedicti, chromatin condensation is fibrous with a manchette of microtubules present around the nucleus. In all four species, the acrosome forms from a Golgi-derived vesicle situated at the base of spermatids. The acrosome in Polydora spp. is conical with a distinctive substructure whereas the S. benedicti acrosome is long and spiral. The implantation fossa is short in all species except P. ligni. All four species have elongated sperm heads. The middlepiece as well as the nucleus is elongated in Polydora spp. whereas S. benedicti has a long nucleus but a short middlepiece. Platelet-shaped electron-dense bodies are present throughout the nuclear region and middlepiece of Polydora spp. and the nuclear region of S. benedicti. These membrane-bounded bodies may be energy storage organelles. The use of ultrastructural data in analysis of sibling species complexes is discussed.Contribution Number 203 from Harbor Branch Foundation, Inc.     

Distribution of Streblospio benedicti (Webster, 1879) and Manayunkia aestuarina (Bourne, 1883) (Annelida: Polychaeta) in the Vistula Lagoon of the Baltic Sea

The polychaetes Streblospio benedicti (Webster, 1879) and Manayunkia aestuarina (Bourne, 1883) have been recorded in the Vistula Lagoon of the Baltic Sea since the mid 1990s. The impact that salinity and the necrozooplankton (dead plankton) concentration in the near-bottom layer have on their distributional patterns was studied. The spatial distribution of these polychaetes depends on the water salinity; however, no correlation was found between their abundance and the necrozooplankton concentration. An area of high necrozooplankton concentration was defined for the near-bottom water layer in the central part of the lagoon; its position is mostly determined by the currents. We assume that the sustainable presence of S. benedicti and M. aestuarina is supported by their opportunistic species biology patterns and the lagoon hydrology, even in the last decade of unfavorable water mineralization conditions.     

Studies on the gill ciliation of the American oyster Crassostrea virginica (Gmelin)

Latero-frontal, para-latero-frontal, and frontal ciliary tracts on the gill filaments of Crassostrea virginica (Gmelin) were studied with light microscopy and scanning electron microscopy. Latero-frontal cirri are complex structures composed of varying numbers of paired cilia. The multiple pairs of cilia which constitute a single cirrus are closely appressed for a portion of their length; they then branch laterally from the central axis in a plume-like fashion. Latero-frontal cirri of adjacent gill filaments create a filtration sieve which should be capable of retaining particles smaller than 1 μm in diameter. Para-latero-frontal cilia are short, closely spaced cilia arranged as a staggered row along the frontal side of each tract of latero-frontal cirri. Latero-frontal cirri and para-latero-frontal cilia occur on ordinary, principal, and transitional gill filaments. Frontal ciliary tracts of ordinary filaments are divided into a central, ventrally directed coarse tract, flanked on either side by a dorsally directed fine ciliary tract. The coarse tract is covered by cirri which are comprised of five to eight cilia, while the fine frontal tracts are made up of individually functioning cilia. The frontal ciliary tracts of principal and transitional filaments bear only dorsally directed fine cilia. The unique direction of effective beat of the coarse frontal cirri of ordinary filaments, in combination with the action of fine frontal cilia and the strategic location of mucus producing cells, is used to describe a possible mechanism for the sorting of filtered particles.     

Anthropogenic disturbance and spatial heterogeneity of macrobenthic invertebrate assemblages in coastal lagoons: the study case of Pialassa Baiona (northern Adriatic Sea)

The distribution patterns of macrobenthic invertebrate assemblages at different spatial scales and in relation to natural and anthropogenic disturbance gradients were investigated in the Pialassa Baiona, a eutrophic and polluted brackish coastal lagoon located along the Italian coast of the northern Adriatic Sea. This coastal lagoon shows a complex physiography with several shallow water ponds and channels separated by discontinuous artificial embankments. Environmental variables and macrobenthic invertebrate assemblages showed higher heterogeneity at small spatial scale (i.e. within channels and ponds). Distinction between channels and ponds is only weakly supported by the distribution patterns of macrobenthic assemblages. Depth was the major factor in structuring benthic communities within ponds, while species distributions along the channels were strongly correlated with the anthropogenic disturbance gradient. Anthropogenic disturbance mainly affected species richness, which was inversely correlated with the organic carbon contents in the sediments and the water surface temperature, which is affected by the input of cooling water from two thermal power plants. Some opportunistic species, like the polychaetes Streblospio shrubsolii and Capitella capitata, were more abundant in the southern polluted areas. In particular, the abundance of S. shrubsolii significantly increased with organic carbon contents in the sediments and water surface temperature, while C. capitata was more abundant in the warmed sites and close to sewages. Conversely, the abundance of the amphipod Corophium insidiosum was inversely related to organic carbon contents.     

Factors controlling the distribution of Marenzelleria cf. viridis, Pygospio elegans and Streblospio shrubsoli (Polychaeta: Spionidae) in the southern Baltic Sea, with special attention for the response to an event of hypoxia

The large-scale distribution patterns of the estuarine spionid polychaetes Marenzelleria cf. viridis, Pygospio elegans, and Streblospio shrubsoli were studied in the Pomeranian Bay (southern Baltic Sea) at 20 stations in April 1993 and their relationship with hydrographic factors and sediment composition investigated. The densities of M. cf. viridis and S. shrubsoli decreased rapidly with increasing distance offshore. A corresponding decrease in phytoplankton concentration offshore is suggested as the main cause for the observed spatial patterns. P. elegans was more evenly distributed. At 10 selected stations further samples were collected between April 1993 and July 1996 to study the response of abundance and biomass of the three polychaetes to changes in environmental conditions and to investigate interspecific interactions within the macrofauna. Salinity, pelagic food supply, and sediment parameters did not change. At three of these stations redox potential of the sediment and macrofauna composition were affected by an unusual hypoxic/anoxic event in July/August 1994. All three spionid species were able to survive moderate seasonal hypoxic conditions, but died after exposure to severe anoxia. Special attention was focused on the re-establishment of the spionids. The rate with which M. cf. viridis and P. elegans re-colonised defaunated stations varied between a few weeks and two years. These differences in rate of re-establishment were attributed to the distance from undisturbed recruitment areas, and to the severity of the oxygen deficiency. Increasing densities of P. elegans and S. shrubsoli after the hypoxic event coincided with a reduced abundance of the bivalve Mya arenaria, suggesting a negative interspecific interaction.     

Biodiversity and distribution of polychaetes and molluscs along the Dese estuary (Lagoon of Venice, Italy)

Mollusc and polychaete distribution in the mud flats along the Dese estuary (lagoon of Venice, Italy) was analysed in May, August and October to evaluate taxonomic biodiversity and zonation pattern of soft macrobenthos in an area of the lagoon hardly known from this point of view. Throughout the studied area most of the species were polychaetes, particularly Streblospio shrubsolii (Buchanan), which showed greater abundance from May to October. Molluscs and polychaetes showed a zonation of marine species which colonize brackish environments in the outer and intermediate areas of the estuary and of brackish water species in the inner one. In the outer area different assemblages were attributed to different sediment types. This distribution pattern, put in relation to the distance from the sea, was evident in May and partly blurred in August and October: the assemblages of the inner area of the estuary invaded the intermediated area in August and affected outer area in October because of spreading of the brackish water species S. shrubsolii, which became dominant. The distribution pattern of molluscs and polychaetes can be explained in terms of confinement as the leading factor influencing water quality and dynamics of the ecosystem. It is also needed to be taken into consideration the role played by competition due to different degree of opportunism of the most abundant species.     

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.     

Interference interactions among tube-dwelling polychaetes in a dense infaunal assemblage

Interactions involving contact between the feeding organs of the tube building polychaetes Pseudopolydora paucibranchiata Okuda, Streblospio benedicti Webster, and Fabricia limnicola Hartman were observed through a dissecting microscope and quantified for frequency of occurrence and effects on foraging time and withdrawal. These surface feeding species form a dense intertidal assemblage ( > 100000 individuals · m^?2) and can be readily transferred to the laboratory and observed in undisturbed sediment cores. Interspecific contact with Pseudopolydora often resulted in withdrawal and consequently a 4 to 7% loss of foraging time for individuals of other species, while intraspecific interactions among Pseudopolydora did so rarely. Larger individuals of all three species experience more interaction. The probability and duration of withdrawal due to contact with Pseudopolydora is size dependent in Fabricia and Streblospio: juvenile Fabricia and adult Streblospio show the greatest interference. The observation that Pseudopolydora interferes with individuals of other species more than with conspecifics contradicts the small-scale dispersion of these species as well as previous reports of interference behavior. A possible explanation is the relatively recent coexistence of these three species, two of which were introduced to the eastern Pacific since 1900.     

A new genus of Syllidae (Polychaeta) from Western Australia

During a study carried out on the subfamily Exogoninae (Syllidae) from Australia, several specimens of a new genus and species were found in samples of dead coral substrate from Western Australia. They have long palps, fused except for a terminal notch, long median and two short lateral antennae, a single pair of short tentacular cirri, and short dorsal cirri, somewhat longer than the parapodial lobes. These characters resemble those of the genus Exogone Örsted, 1845. However, all these appendages are articulated. The chaetae are very similar to those of several species of Syllis Lamarck, 1818, having coarse spines on the margin of compound chaetal blades and truncated dorsal simple chaetae. Furthermore, the pharynx begins in chaetiger 3, posterior to the peristomium, as in many species of the genus Syllis; this condition does not occur in any described species of Exogone. The new genus is provisionally proposed to belong to the subfamily Syllinae, although it has some characters typical of the Exogoninae. Examination under the SEM shows another peculiar feature, the nuchal organs are distinctly laterally located. Within the Syllinae, only Paratyposyllis Hartmann-Schröder, 1962 has a single pair of tentacular cirri, but in that genus, the palps are only basally fused.     

Sense organs in polychaetes (Annelida)

Polychaetes possess a wide range of sensory structures. These form sense organs of several kinds, including the appendages of the head region (palps, antennae, tentacular cirri), the appendages of the trunk region and pygidium (parapodial and pygidial cirri), the nuchal organs, the dorsal organs, the lateral organs, the eyes, the photoreceptor-like sense organs, the statocysts, various kinds of pharyngeal papillae as well as structurally peculiar sensory organs of still unknown function and the apical organs of trochophore larvae. Moreover, isolated or clustered sensory cells not obviously associated with other cell types are distributed all over the body. Whereas nuchal organs are typical for polychaetes and are lacking only in a few species, all other kinds of sensory organs are restricted to certain groups of taxa or species. Some have only been described in single species till now. Sensory cells are generally bipolar sensory cells and their cell bodies are either located peripherally within the epidermis or within the central nervous system. These sensory cells are usually ciliated and different types can be disinguished. Structure, function and phylogenetic importance of the sensory structures observed in polychaetes so far are reviewed. For evaluation of the relationships of the higher taxa in Annelida palps, nuchal organs and pigmented ocelli appear to be of special importance.     

The prevalence of non-indigenous species in southern California embayments and their effects on benthic macroinvertebrate communities

The prevalence of non-indigenous species (NIS) in southern California embayments was assessed from 123 Van Veen grab samples collected in nine bays and harbors during the summer of 1998. NIS occurred in all but two samples. They accounted for only 4.3% of the 633 taxa but contributed 27.5% of the abundance. There was no significant difference in the proportion of NIS abundance among ports harboring large vessels, small boat marinas, and areas where boats were not moored. Three species accounted for 92% of the NIS abundance: a spionid polychaete worm Pseudopolydora paucibranchiata, a mytilid bivalve Musculista senhousia, and a semelid bivalve Theora ubrica. The NIS did not appear to have a negative impact at the overall community level since NIS abundance was positively correlated with the abundance and richness of other species. This may be due to biogenic structures built by P. paucibranchiata and M. senhousia that enhance the abundances of other macrofauna.