Evolution of cave Axiokebuita and Speleobregma (Scalibregmatidae,Annelida)

The evolutionary history of Axiokebuita and Speleobregma, two poorly known lineages of annelids exclusive from deep‐sea or marine caves but always from crevicular habitats, is explored here. Speleobregma lanzaroteum Bertelsen, 1986, and Axiokebuita cavernicola sp. n. are described from anchialine and marine caves of the Canary Islands using light and electron microscopy. Speleobregma lanzaroteum is previously known only from a single specimen from the water column of an anchialine cave in Lanzarote. Emended diagnosis, details on the ciliary patterns and behavioural observations are provided based on newly collected material and in situ observations. Axiokebuita cavernicola sp. n. is found in Pleistocene gravel deposits in a shallow water marine cave in Tenerife (Canary Islands). The new species is characterized by the presence of dorsal ciliary bands and short knob‐like neuropodial cirri from segment two. The porosity and permeability of the gravelly environment of A. cavernicola sp. n. are shown to be equivalent to the water column or crevices of Speleobregma and other Axiokebuita spp. Phylogenetic analyses of five gene fragments and 44 terminals using maximum‐likelihood and Bayesian methods support a derived position of A. cavernicola sp. n. within Axiokebuita and confirm a sister‐group relationship of Axiokebuita with Speleobregma with high nodal support. The Axiokebuita–Speleobregma clade is morphologically characterized by a globular pygidium with adhesive glands and ventral ungrooved ciliated palps. Our results support two independent cave colonization events, favoured by the preadaptation of the members of Axiokebuita–Speleobregma lineage to crevicular habitats.     

Evolution of cave suspension feeding in Protodrilidae (Annelida)

Protodrilidae belongs in a lineage that until now entirely consisted of deposit‐feeding, highly adapted interstitial annelids. Except for a pair of anterior palps, all protodrilids lack appendages, parapodia and chaetae; and have slender bodies adapted to glide between the sand grains by ciliary motion. The first exception to these characteristics is Megadrilus pelagicus n. sp. inhabiting the water column of the anchialine La Corona cave system in Lanzarote. Its morphology and evolutionary history are here investigated by combining observations from in vivo video recordings and advanced microscopy with phylogenetic analyses. Our studies revealed a unique pelagic, suspension feeding behaviour attained by its long ciliated palps in combination with an autopomorphic dorsal ciliated keel and several longitudinal and transverse ciliary bands. Phylogenetic analyses recovered Megadrilus pelagicus n. sp. nested within Protodrilidae indicating that its unique traits are derived within the family. These traits are traced in the tree topologies in correlation to cave colonization. The evolution of these traits can be functionally explained by the different demands of a pelagic suspension feeding strategy compared to the ancestral deposit‐feeding guild of the family. The origin of this suspension feeding strategy was presumably favoured by the partial isolation of the anchialine ecosystem, connected to the sea only through the highly porous volcanic subterranean bedrock. This crevicular connection limits the amount of predators and turbulence in the cave, but allows continuous water flow into the system carrying organic particles, which is the main source of food when photosynthetic primary production does not occur and sedimentation is limited. These conditions may select for pelagic suspension feeding as the most feasible life‐strategy in anchialine caves, which the dominance of pelagic, suspension feeding crustaceans and annelids in anchialine cave assemblages may also reflect. For species of ancestrally deposit‐feeding lineages entering the cave system, such as the annelid families Protodrilidae and Nerillidae, an adaptive‐shift from interstitial to crevicular habitats seemingly correlates with dramatic morphological changes and speciation. The dramatic changes observed in these primarily interstitial lineages compared to their relatives, point to alternative adaptive evolutionary pathways related to ecological fitness contrary to the previously proposed theories focusing on geological or stochastic processes.     

Life history of the gulf darter,Etheostoma swaini (Pisces: Percidae)

Synopsis Etheostoma swaini, the gulf darter, was collected from the Black Creek drainage in southern Mississippi (February 1978 – April 1979). The gulf darter generally inhabits small- to moderate-size creeks and occurs over a sand or sandy mud bottom, often in association with aquatic vegetation or a layer of organic debris. Larval dipterans were the most important food items, both numerically and volumetrically. Chironomids were found in 71–100% of the stomachs in all except the unusual March 16 collection. The length frequency distribution and the scale annuli analysis indicated there were three year-classes present in the population at any one time. Fifty-one percent of the specimens taken were less than 12 months old. During the mid-February to late March spawning season gulf darters were most often collected over clean gravel or gravelsand substrates. Laboratory observations suggest that the female burrows into the gravel where the demersal, adhesive eggs are deposited. Female gulf darters significantly outnumbered males at a ratio of 59:41.     

Grain-size controls on the occurrence of bioturbation

Grain size and grain-size related stresses impart a significant influence on the ichnological character of marginal-marine deposits. This is evident on the New Brunswick coastline of the Bay of Fundy, Canada, where three coarse-grained marginal-marine deposits are studied to assess grain-size controls on the occurrence and type of bioturbation. Firm mud and sand substrates exhibit the greatest diversity and density of bioturbation (i.e., bioturbation intensity). The types of organisms colonizing sands and firm-mud substrates are variable; however, the resultant trace assemblages are similar. Thixotropic muds exhibit significantly reduced trace diversity and density relative to firm mud, reflecting the additional stress placed on the organisms by the relatively soupy consistency of the sediment. A significant change in the trace assemblage occurs when sediment caliber passes the gradational sand—fine gravel boundary.Four main conclusions can be drawn from this study. First, for mixed sand and gravel, fine gravel, and coarse-gravel deposits, the degree of bioturbation (diversity ^? density) decreases more rapidly onshore (across the intertidal zone) than is noted in sand or mud deposits. Second, there is a decrease in the degree of bioturbation with increasing grain size for substrates composed of sand-sized and larger clasts. Third, burrows in gravels tend to be lined and/or robust, likely to maintain a stable environment within the burrow. Fourth, in coarse-gravel substrates or substrates with a significant component of coarse gravel, burrows are developed between the clasts and tend to be more permanent structures (than those developed in sand or mud), which are generally continuously occupied.The degree of burrowing noted in these modern gravel deposits contrasts with the relative paucity of biogenic structures reported in conglomerates preserved in the rock record. Based on the intensity of burrowing observed in the gravels, we hypothesize that ancient marginal-marine conglomerates are likely bioturbated, but that these burrows are likely distorted during burial and compaction.     

Experimental analysis of the ‘Paarkultureffekt’ in the protandric polychaete, Ophryotrocha puerilis Clap. Mecz.

Female Ophyrotrocha puerilis Clap. Mecz. were coupled. Certain parts of the prostomium and of the pygidium in one or both partners of a couple were amputated in order to prove that they are responsible for the mutual influence which partners normally exert on their sexual differentiation. The results demonstrate that the palps and the ventrolateral prostomial cirri are the transmitters and the ciliated lateral pits on the prostomium the receivers of the mutual influence. The antennae and the pygidial cirri are not necessary as far as the ‘Paarkultureffekt’ is concerned. The nature of the stimulus is still unknown. At the present stage of these investigations, the favoured conception is of a pheromone transmitted during the contact of the partners.     

Morphology of anterior regeneration in two spionid polychaete species: implications for feeding efficiency

Abstract. In marine soft‐sediment habitats, tissue loss by infuanal invertebrates can provide significant energetic input to higher trophic levels, have substantial impacts on individual behavior, growth, and fecundity, and resulting changes in bioturbation rates can secondarily affect community dynamics. The degree to which a community is affected by such sublethal predation depends in part on whether injured individuals can regenerate and on the speed at which they do so. Previously, we demonstrated differences in the rate of anterior segment and palp regeneration by the spionid polychaetes Pygospio elegans and Dipolydora quadrilobata. The current study examined the morphology of the anterior segment and palp regeneration in these species using scanning electron microscopy (SEM) and indirect immunohistochemistry with confocal laser scanning microscopy at 3, 6, 9, and 12 d post‐ablation. Antibodies for acetylated α‐tubulin and the neural tetrapeptide FMRFamide were used to label the regenerating nervous system. SEM revealed that the morphology of anterior tissue regeneration was similar for both species, but the ciliated food groove tended to form sooner on palps in P. elegans than on those of D. quadrilobata. In both species, palp regeneration and ciliated food groove formation were faster when only palps were removed. A shortened ciliated food groove is likely to reduce particle contact and transport efficiency in suspension and deposit feeding. Regenerating palp nerves were initially visible at 3 d following ablation of palps only, but at 6 d following ablation of five anterior segments. Following ablation of anterior segments, the regenerating nervous system was largely complete by 9 d, nuchal organs were innervated by 6 d, and processes of palp sensory cells were visible at 12 d. Contact chemoreception by sensory cells on the palps may be diminished during the early stages of regeneration, but chemoreception of waterborne cues via the nuchal organ should not.     

Protodrilus (Protodrilidae, Annelida) from the southern and southeastern Brazilian coasts

Protodrilus corderoi, Protodrilus ovarium n. sp. and Protodrilus pythonius n. sp. are reported from beaches in southern and southeastern Brazil and described combining live observations with light and electron scanning microscopy studies. Protodrilus corderoi is redescribed from new collections at the type locality, and a neotype for the species is assigned since the original type material no longer exists. New information on reproductive organs, segmental adhesive glands and unpigmented ciliary receptors as well as morphometrics is provided. Protodrilus ovarium n. sp. and P. pythonius n. sp. are formally described. Protodrilus ovarium n. sp. is diagnosed by the presence of separated lateral organs on segments 7–12, three spermioducts of segments 10–12 and salivary glands in segments 1–9. Protodrilus pythonius n. sp. is defined by the presence of separated lateral organs on segments 7–16, long pygidial lobes and body tapering toward the pygidium. The distribution of the different species in more or less spacious habitats seems to be correlated with their gross morphology. Protodrilus pythonius n. sp., with relatively long and wide body and long palps with ciliary bands, was collected in very coarse sandy sediments at a reflective sheltered beach. Conversely, P. corderoi and P. ovarium n. sp., both possessing more slender bodies with shorter, less ciliated palps, occurred in medium-coarse, well-sorted sediments in the more energetic swash zone of exposed intermediate-reflective beaches. The finding of P. pythonius and P. corderoi in nearby beaches corroborates other studies showing a higher morphological variability among species in different habitats within the same geographical area than among species in the same habitat in different geographical areas.     

Articulation,interlocking devices and enrolment in Monkaspis daulis (Walcott, 1905) from the Guzhangian,middle Cambrian of North China

Monkaspis daulis (Walcott 1905 ) is the first enrolled trilobite to be documented from the Kushan Formation (Guzhangian, Cambrian Series 3) of Northern China. It has a wide pygidium that allowed a sphaeroidal enrolment type to be achieved, covering the cephalon and anterior trunk segments. Monkaspis daulis is micropygous, but the pygidium is proportionally larger than that of many other Cambrian trilobites, and there is a slightly variable number of segments in the trunk. Articulation structures are very well developed through the trunk, but interlocking or coaptative devices are poorly developed with the exception of the terrace lines and a novel structure, a ‘posterior arch’, in the pygidium, which would have prevented shear. The absence of genal spines that would otherwise have inhibited sinking into the mud substrate may have enabled Monkaspis daulis to use the enrolment procedure to excavate a hole in the sediment for taking shelter.     

The effects of sediment type on growth rate and shell allometry in the soft shelled clam Mya arenaria L

Hatchery-reared juvenile Mya arenaria L. were grown for 11 wk in replicated gravel, sand, mud, and pearl net treatments under flow-through sea-water conditions in Maine. Analyses of variance showed significant differences between sediment treatments for final shell length, dry meat weight, chondrophore growth increment, and percent shell weight. Growth of juvenile M. arenaria was more rapid in fine sediments than in coarse sediments or nets.Regression slopes of shell length-shell height and shell length-shell depth varied significantly between sediment treatments. Slower-growing clams from nets and gravel were more globose than clams from sand or mud treatments. Clams grown in sand were longer and narrower than those from mud. Differences in growth rates and shell form were attributed primarily to the physical properties of the substrata, and their effects on the scope for growth of M. arenaria.     

The effects of prey size, predator size, and sediment composition on the rate of predation of the blue crab, Callinectes Sapidus Rathbun, on the hard clam, MercenariaMercenaria (Linné)

Sediment preferences of blue crabs, Callinectes sapidus Rathbun, and predation rates on various size classes of the hard clam, Mercenaria mercenaria (Linné), in a variety of sediment types were studied in the laboratory. Blue crabs of all size classes exhibited a preference for sand, mud, and sand/mud rather than crushed oyster shell or granite gravel. Clams were more vulnerable to predation by crabs in sand and sand/mud than in crushed oyster shell or granite gravel. When crabs were given a choice of clam sizes based on carapace width (CW), small crabs (<75 mm CW) consumed 5- and 10-mm shell length (SL) clams. Medium crabs (75–125 mm CW) preferentially consumed 10-mm SL clams. Large crabs (> 125 mm CW) consumed 10- and 25-mm SL clams equally. Blue crabs did not eat clams that were >40-mm SL.     

General characterization of regeneration in Aeolosoma viride (Annelida,Aeolosomatidae)

Regeneration has long been the focus of scientific interest for its potential to restore lost, damaged, or aged tissues and organs. A wide range of regenerative studies have been conducted on different vertebrate and invertebrate model organisms. Annelids are known for their regenerative capacities, and because of their relatively complex organ systems, they are an ideal organism for regeneration study. Our present work focused on the freshwater annelid Aeolosoma viride, an asexually reproducing annelid capable of regenerating both anteriorly and posteriorly. Even though regenerative ability has been documented in this animal in previous studies, detailed characterization of the process is still unavailable. The objective of this study was to evaluate the regenerative ability of A. viride. We described the sequential morphological events during the process of regeneration, such as wound healing and the formation of blastema, mouth, and pygidium. In order to clarify the capacity and type of regeneration, we conducted a series of observations and experiments using a cell proliferation assay. Massive proliferation and the absence of cell migration indicated that the animal regenerates primarily through epimorphosis. Our study of the epimorphic regenerative process of A. viride provides a clearer picture of the evolutionary origin of regeneration in annelids.     

Caulostrepsis spiralis isp. nov., Miocene grand bay formation of Carriacou (Grenadines,lesser antilles)

A new ichnospecies of Caulostrepsis, namely C. spiralis, is described from the Miocene Grand Bay Formation of Carriacou (Grenadines, Lesser Antilles). It occurs in association with C. cretacea and a common progenitor, most likely a spionid polychaete annelid, was most likely for its production.     

基于物理模型实验的光倒刺鲃生态行为学研究

建立了基于天然河道的物理模型,通过控制实验研究水环境因子对鱼类行为的影响。文中选取了金沙江下游2.6 km河段建立物理模型,以南方水系的经济鱼类光倒刺鲃为研究对象,进行了鱼的行为对底质和流速的响应实验。分析得出,光倒刺鲃对砂卵石底质的选择明显大于其它底质且差异极其显著(P<0.01),光倒刺鲃2龄幼鱼期的喜好流速范围为0.3-0.6 m/s;研究同时发现水流紊动强度对光倒刺鲃行为具有重要影响。该研究结果可以为光倒刺鲃栖息地模型提供参考。     

Cambrian stem-group annelids and a metameric origin of the annelid head

The oldest fossil annelids come from the Early Cambrian Sirius Passet and Guanshan biotas and Middle Cambrian Burgess Shale. While these are among the best preserved polychaete fossils, their relationship to living taxa is contentious, having been interpreted either as members of extant clades or as a grade outside the crown group. New morphological observations from five Cambrian species include the oldest polychaete with head appendages, a new specimen of Pygocirrus from Sirius Passet, and an undescribed form from the Burgess Shale. We propose that the palps of Canadia are on an anterior segment bearing neuropodia and that the head of Phragmochaeta is formed of a segment bearing biramous parapodia and chaetae. The unusual anatomy of these taxa suggests that the head is not differentiated into a prostomium and peristomium, that palps are derived from a modified parapodium and that the annelid head was originally a parapodium-bearing segment. Canadia, Phragmochaeta and the Marble Canyon annelid share the presence of protective notochaetae, interpreted as a primitive character state subsequently lost in Pygocirrus and Burgessochaeta, in which the head is clearly differentiated from the trunk.     

Caudal and even-skipped in the annelid Platynereis dumerilii and the ancestry of posterior growth

In order to address the question of the conservation of posterior growth mechanisms in bilaterians, we have studied the expression patterns of the orthologues of the genes caudal, even-skipped, and brachyury in the annelid Platynereis dumerilii. Annelids belong to the still poorly studied third large branch of the bilaterians, the lophotrochozoans, and have anatomic and developmental characteristics, such as a segmented body plan, indirect development through a microscopic ciliated larva, and building of the trunk through posterior addition, which are all hypothesized by some authors (including us) to be present already in Urbilateria, the last common ancestor of bilaterians. All three genes are shown to be likely involved in the building of the anteroposterior axis around the slit-like amphistomous blastopore as well as in the patterning of the terminal anus-bearing piece of the body (the pygidium). In addition, caudal and even-skipped are likely involved in the posterior addition of segments. Together with the emerging results on the conservation of segmentation genes, these results reinforce the hypothesis that Urbilateria had a segmented trunk developing through posterior addition.     

Short term dynamics of the dominant annelids in a polyhaline temperate estuary

Weekly sampling over a two year period from a muddy sand bottom in the polyhaline York River, Virginia, U.S.A., clearly identified the pattern of recruitment and survival of the dominant annelid species. Three intermingled recruitment strategies and two survival patterns were observed, ranging from the classic opportunistic life style of mass recruitment over short time periods followed by mass mortality to prolonged recruitment with lower mortality. Qualitatively the annelid assemblage was very similar from year to year with most of the changes being quantitative. Oligochaetes, Tubificoides spp., were the most stable and characteristic members of the annelid assemblage.Contribution No. 1118 of the Virginia Institute of Marine Science     

Zum Aufbau und zur Innervation des Wimperepithels der Bivalvia-Palpen

Zusammenfassung Im Epithel der Palpen vonMytilus edulis, Cyprina islandica, Astarte borealis undMya arenaria dominieren zwei Zelltypen, die sich in den Furchen der Mundlappen gegenüberliegen. Es handelt sich einerseits um schleimproduzierende Zellen, die einen kennzeichnenden Mikrovillussaum tragen, andererseits um zilientragende Zellen, die basal zahlreiche Synapsen besitzen. Die reiche Innervation wird im Zusammenhang mit der Funktion der Palpen diskutiert.

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Fine structure and innervation of the ciliated epithelium of the lamellibranch palps

Summary The epithelium of the palps ofMytilus edulis, Cyprina islandica, Astarte borealis andMya arenaria is dominated by two cell types, which occupy the opposing walls of the furrows in the surface of this organ. They are on the one hand mucus producing cells which are characterized by typical microvilli, and on the other hand ciliated cells which are in direct contact with many synapses at their base. The rich innervation is discussed in connection with the function of the palps.

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Die Untersuchungen wurden mit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft durchgeführt.     

Comparative structure of the epidermis in polychaetes (Annelida)

The polychaete epidermis generally consists of a single layer of supportive cells, gland cells and sensory cells. Except for the latter, this paper reviews the recent literature on the annelid epidermis, focussing on the mentioned cell types and the cuticle. The annelid epidermis is compared to that of Sipuncula, Echiura and Myzostomida. Supportive cells predominate in the polychaete epidermis. They show a high structural diversity even within single specimens. Ciliated cells are usually multiciliary and only two cases of monociliary epidermis cells are known. Unambigous epithilio-muscle cells are only described in feeding palps of a Magelona species. Secretory cells release a large number of gland products and some of them are essential for tube secretion. Rather pecularities of the cells and its arrangement within glands than the ultrastructure of the secretions is useful for phylogenetic considerations. One of the main components of the cuticle is collagen. Recent studies indicate that annelid cuticular collagen differs in several aspects from collagen of the connective tissue and might be of interest for systematics.     

Invertebrate colonization of woody debris in coastal plain streams

We studied colonization dynamics and habitat preferences of macroinvertebrates associated with submerged woody debris in Louisiana coastal plain streams. In an in situ experiment, Branches of magnolia Magnolia grandiflora and water oak Quercus nigra were anchored over sand and gravel substrate at two sites in the Bogue Falaya River, St. Tammany Parish, Louisiana, U.S.A. Branches were removed from the units weekly for 4 weeks and biweekly for 1 month to assess colonization. Invertebrate numbers were highest at weeks three and six on magnolia over gravel habitat, although numbers of the most dominant taxa (Baetidae, Hydropsyche sp., Cernotina sp., Oecetis sp. and Hydroptilia sp.) peaked at different times during the study. Abundances of Hydropsyche sp. and Cernotina sp. were greatest on magnolia branches secured over gravel substrate, whereas Oecetis sp. abundances were greatest on oak branches secured over sand substrate.We also surveyed six streams in southeast Louisiana to examine the relative importance of wood, gravel and sand as substrate for lotic macroinvertebrates. In fall 1997 and spring 1998, we took water samples and measured in situ water quality characteristics at one site on each stream, and then collected submerged wood (surface area about 3051 cm²) and sand and gravel substrate (Surber samples totaling 2800 cm² for each substrate) to determine the density and taxonomic composition of resident macroinvertebrates. Highest numbers of invertebrates were collected in fall and spring from gravel substrate (P=0.0001). Macronychus sp. were more abundant on wood than gravel or sand (P<0.0003) and Hydropsyche sp. was more abundant on fall wood samples (P=0.0001). Analyses of water quality parameters revealed associations between Hydropsyche sp. abundance and potassium (P=0.0070) and specific conductance (P=0.0080), although both parameters exhibited interactions with substrate type (P<0.0144).     

Burrowing behaviour of the softshell clam (Mya arenaria) following erosion and transport

Erosion and transport of juvenile individuals may alter the distribution pattern of intertidal bivalves. The burrowing success of recently transported juvenile softshell clams (Mya arenaria) was studied in a laboratory flume under a wide range of hydrosedimentary environments. Juvenile individuals (5-20 mm) were observed under a simulated 30 min slack tide before initiating the flow for a period of 60 min. Five different free-stream velocities (0, 3, 5, 10 and 24 cm s^− 1) and four sediment types (mud, sandy-mud, sand and gravel) were used. The mean proportion of juvenile clams that initiated (MPI) or completed (MPC) a burial decreased with increasing shell length. Erosion from the sediment was more important in large juveniles suggesting that large juveniles may have more difficulty successfully relocating once transported. The MPI increased with increasing flow speed in experimental runs held at speed < 24 cm s^− 1. This was observed in all sediment types. Most individuals were unable to burrow at 24 cm s^− 1 because they got eroded. The MPC also increased with increasing flow speed in mud, sandy-mud and sand. The MPC's response to flow was more complex in gravel because of a shell length × flow speed interaction effect. Our observations suggest that water movement may induce the burrowing behaviour of recently eroded juvenile clams. Results are discussed in an ecological and aquacultural context.