Characterisation of the enzyme transport path between shipworms and their bacterial symbionts

Background Shipworms are marine xylophagus bivalve molluscs, which can live on a diet solely of wood due to their ability to produce plant cell wall-degrading enzymes. Bacterial carbohydrate-active enzymes (CAZymes), synthesised by endosymbionts living in specialised shipworm cells called bacteriocytes and located in the animal’s gills, play an important role in wood digestion in shipworms. However, the main site of lignocellulose digestion within these wood-boring molluscs, which contains both endogenous lignocellulolytic enzymes and prokaryotic enzymes, is the caecum, and the mechanism by which bacterial enzymes reach the distant caecum lumen has remained so far mysterious. Here, we provide a characterisation of the path through which bacterial CAZymes produced in the gills of the shipworm Lyrodus pedicellatus reach the distant caecum to contribute to the digestion of wood. Results Through a combination of transcriptomics, proteomics, X-ray microtomography, electron microscopy studies and in vitro biochemical characterisation, we show that wood-digesting enzymes produced by symbiotic bacteria are localised not only in the gills, but also in the lumen of the food groove, a stream of mucus secreted by gill cells that carries food particles trapped by filter feeding to the mouth. Bacterial CAZymes are also present in the crystalline style and in the caecum of their shipworm host, suggesting a unique pathway by which enzymes involved in a symbiotic interaction are transported to their site of action. Finally, we characterise in vitro four new bacterial glycosyl hydrolases and a lytic polysaccharide monooxygenase identified in our transcriptomic and proteomic analyses as some of the major bacterial enzymes involved in this unusual biological system. Conclusion Based on our data, we propose that bacteria and their enzymes are transported from the gills along the food groove to the shipworm’s mouth and digestive tract, where they aid in wood digestion.

New insights concerning homology of the oral region and ambulacral system plating of pentaradial echinoderms

Universal elemental homology (UEH) underpins recent understanding of peristomial and ambulacral elemental homology of pentaradiate echinoderms by providing a uniform set of terminology to construct phylogenetic characters. Variation in the expression of these elements provides evidence for phylogenetic relationships. Two nonhomologous sets of plates border the peristome and are associated with two nonhomologous sets of floor plates forming the ambulacral food groove. Some edrioasteroid-grade and eocrinoid-grade echinoderms have ambulacral systems formed from oral frame plates and adradial floor plates, whereas most blastozoans and crinoids bear oral plates and abradial floor plates. These plates are expressed in a variety of ways among echinoderms, but nearly all can be reconciled with the underlying model. Arguments against UEH are methodologically flawed and confuse many terms and interpretations.

Morphologic and systematic revision of the solute Maennilia estonica (Homoiostelea, Echinodermata) from the Upper Ordovician of Estonia

Maennilia estonica Rozhnov and Jefferies was first described as a stem-chordate but restudy shows it is an unusually large homoiostelean echinoderm. Its feeding structure, an erect ambulacrum, extending exothecally from the peristomial frame plates, bears a large internal tunnel that opens directly into the body cavity. This type of feeding appendage is now recognized to be unique to homoiosteles. It bears no evidence for water vascular system impressions adjacent to its food groove. The theca has poorly developed marginal plates and a narrow rim that, in contrast to some other homoiosteles, does not extend over either lower or upper thecal face. Maennilia appears to have inhabited the deeper portions of a near-shore environment in limey muds adjacent to a linear zone of bryozoan and microbial bioherms.

A new arthropod Jugatacaris agilis n. gen. n. sp. from the Early Cambrian Chengjiang biota, South China

A new arthropod Jugatacaris agilis n. gen. n. sp. with excellent soft anatomy is reported from the Early Cambrian Chengjiang biota. Its “bivalved” carapace with a dorsal fin-like fusion is distinct from those of other Cambrian arthropods. A pair of stalked eyes and a prominent median eye protrudes the carapace anteriorly. The cephalon, attaching to the carapace through the lateral adductor muscles at maxillary segment, bears an antennule, antenna and mandible. The trunk is comprised of a large number of segments (varying from 55 to 65), two-thirds of which is covered by the carapace. Each segment, except for the posterior three to five, carries a pair of uniform biramous appendages. The endopodite is composed of 30 podomeres and a terminal claw. The oar-shaped exopododite is fringed with filaments and distally bears a broad setiferous lobe. Trunk terminates with a conical telson and a pair of broad furcal rami serving as steering devices. Internal features like gonad and gut have also been found. The presence of the food groove combined with other morphological features indicates that Jugatacaris was a filter feeder. The appendages design associated with the overall body-plan supports the view that Jugatacaris is a crustaceanomorph. The accurate phylogenic assessment will remain the subject of debate until more information becomes available.

New species and records of Scissurellidae and Anatomidae from the Americas (Mollusca: Gastropoda: Vetigastropoda)

New Scissurellidae and Anatomidae from the geographic and political Americas are described, with many long-standing misidentifications being corrected, and some comparisons to described species complementing the contribution. Sinezona kayae n. sp., previously mis-identified as the South African Sin. insignis, and Sin. hawaiiensis n. sp. without a selenizone, are described from Hawaii. Sinezona carolarum n. sp. is added to the Panamic province with a more depressed shell than the more common Sin. rimuloides (Carpenter, 1865), and a proportionally shorter selenizone. Coronadoa demisispira n. sp. from the Panamic and northeastern Pacific provinces is the third species in the genus, living sympatrically in the southern range of C. simonsae Bartsch, 1946. The new species is characterized by a shell with lower profile and a wider umbilicus. Anatoma alternatisculpta n. sp. from the Caribbean is most similar to A. proxima (Dall, 1927), but has conspicuously different sculpture on shoulder and base. Anatoma plicatazona n. sp. from the Caribbean has markedly upturned keels of the selenizone. Anatoma disciformis (Golikov & Sirenko, 1980) is reported from Alaska and illustrated for the first time by SEM. Thieleella kelseyi (Dall, 1905) is resurrected for what has previously been misidentified as the European Anatoma crispata (Fleming, 1828) in the northeastern Pacific, with a neotype designated, as the holotype is missing. Thieleella peruviana n. sp. from Peru is similar to T. kelseyi but has a taller shell and differs in the morphology of lateral tooth 5 of the radula. Thieleella bathypacifica n. sp. from the Panamic province is a deep-water species (2500 m), and known from a single specimen only. The species shows a marked angulation on teleoconch I at the spiral cord in the position of the selenizone; additionally it has a radula with marginal teeth showing a distinct posterior food groove. The bodies of two species (T. kelseyi, T. peruviana) were examined by SEM. An accessory cephalic tentacle between the anterior most epipodial tentacle and the eye stalk was encountered. The epipodial sense organ is recognized for the first time in Anatomidae, and the presence of bursicles on the gill is confirmed.

Development of the tentacles and food groove in the jellyfish Aurelia aurita (Cnidaria: Scyphozoa)

The development of the tentacle-bearing part of the rim of the jellyfish Aurelia aurita is described. The newly liberated ephyra lacks appendages at the bell rim between the rhopalial arms (null stage). The next stage (bump stage) has a subumbrellar bump near the rim. The bump then forms a tongue process (tongue stage) on its adoral side. The aboral part of the bump becomes the primordium of the tentacle. The tongue process elongates and spreads circumferentially, finally melding with the lappets of the rhopalial arms. Next the tongue process develops a groove that spreads laterally. The epithelium of the groove becomes glandular and serves as a food groove where particulate matter such as plankton is concentrated and undergoes the initial phase of digestion. The "upper" side of the split tongue process becomes the floor of the tentacle chambers, while the "lower" side becomes the pseudovelarium. The growth and differentiation zone for the medusa's rim is at the junction of the tentaculate part of the rim with the rhopalial region. It is here that tentacle buds form, followed by intertentacular lappets (partitions).

Microanatomy of the bell rim of Aurelia aurita (Cnidaria: Scyphozoa)

The bell rim of Aurelia aurita is described in detail. This medusa has usually eight marginal sensory complexes and many tentacle chambers, the latter made up of a roof, sides (lappets), and a floor. The sole contents of a tentacle chamber are a few bladelike tentacle bases. The distal tentacle is narrow and moniliform and grooved on the adoral side with a folded sheet of muscle fibers on the deep side. Between the underside of the tentacle chamber's floor and a more adoral circumferential flange (pseudovelarium) lies a ciliated food groove lined with a thick amuscular epithelium containing ordinary surface cells, mucous cells, and presumed digestive cells. The subumbrella is bilayered, with an outer epithelial layer that sends thin cytoplasmic sheets to the mesoglea; deeper is a layer of myocytes each with a striated circular myofibril. Towards the periphery, and before the pseudovelarium, is a rim of smooth radial myocytes overlaid with an epithelial layer. The adoral side of the pseudovelarium has smooth radial epitheliomuscular cells. Where the pseudovelarium attaches to the subumbrella, neuromuscular cords traverse the mesoglea to join the adoral side of the tentacles. Along the food groove and midway between rhopalia is a pocket in the pseudovelarium, the food pouch, which collects plankton. The pararhopalial region of the rim is different in that the floor of the tentacle chamber is short or absent; a modified intertentacular partition can sometimes form a protuberance on the aboral side of the pseudovelarium; and the pseudovelarium takes a right-angled turn outwards near the rhopalium to form the thin part of the rhopalial hood. This type of rim is specialized for the concentration and, perhaps, the early digestion of plankton.

The echinoderm classes Stylophora and Homoiostelea: non Calcichordata

Stylophora and Homoiostelea are the largest classes of the subphylum Homalozoa. They have also been placed in the Calcichordata but that position is herein rejected. Stylophorans are divided into two orders the Cornuta and Ankyroida: cornutes have asymmetrical thecae, aulacophores with stylocones and cover plates over the food groove that open widely; ankyroids have essentially bilaterally symmetrical thecae, aulacophores with styloids and in most the cover plates do not open widely. Epispires, cothurnopores, and lamellipores in cornutes are respiratory structures not atypical of early echinoderms and are only superficially similar to chordate gill slits. The superior and inferior faces of cornute and ankyroid thecae and the aulacophores are homologous. There is no evidence that ‘mitrates’ (most ankyroids) are inverted or their aulacophores(calcichordate tail) have been lost and re-evolved.Homoiosteles are superficially similar to stylophorans: the column or stele resembles the aulacophore and the theca in younger genera develope distinct marginal and somatic plate patterns. The earliest homoiosteles are attached by a holdfast, at least in juvenile stages, and this fixation may have imprinted some morphological features on steles of vagile genera. Earliest homoiosteles share significant characters with coeval species of the eocrinoid Gogia and it serves as outgroup.Cladograms for Stylophora and Homoiostelea were generated by NONA, a phylogenetic program for personal computers.

Eoparisocrinid crinoids from the Middle Ordovician (Galena Group) of northern Iowa and southern Minnesota

Two species of eoparisocrinid crinoids from the Middle Ordovician Galena Group of northern Iowa and southern Minnesota are described, namely Eoparisocrinus crossmani n. sp. and E. grandei n. sp. The post-larval development of Eoparisocrinus crossmani is examined. Crinoid arms grow by addition of new plates at their distal tips in conjunction with calcite deposition on old plates. New branches appear where axillary plates are initiated. Consequently, the growth rates for number of brachials and length of food-gathering system compared to crown volume are much faster than if the animals were isometric. The number of food particles collected is related to the number of food-catching tube-feet, which can be estimated if the length of the arms and height of the covering plates are known. The size of the largest food item is constrained by the food groove width. Thus, food-gathering capacity is the number of food-catching tube-feet multiplied by food groove width. The food-gathering capacity increases more rapidly than if the animal grew isometrically, and the ratio of food-gathering capacity: crown volume only declines slightly over the known growth range. All Ordovician cladid crinoids examined follow nearly identical ontogenetic trajectories. The ecological niche of a stalked crinoid is related to four basic parameters: stem length, food groove width, tube-foot spacing, and branch density. Stem length limits the highest elevation above the seafloor. The column of E. crossmani becomes longer during ontogeny due to the formation of new columnals and height growth of old ones. Consequently, individuals gradually “move up” until the adult elevation of about 50 mm is reached. The growth rates of stem length relative to crown size are slow in the youngest and mature animals but rapid in juveniles. The food grooves become wider throughout growth so that older crinoids ate larger food particles than younger ones. The food groove width increases less rapidly than if the shape were constant, because distal plates and branches are more narrow and have more slender food grooves than proximal plates. Growth curves for food groove width versus stem length and elevation were generated for E. crossmani and other crinoids that commonly occur in the same beds. Together, elevation and food particle size define the main dimensions of the niche. The various taxa are more or less separated by different food groove widths at most comparable elevations. This pattern minimizes ecological overlap and probably competition between the different species. The tube-foot spacing of E. crossmani is constant regardless of size, which suggests that it employed the same type of feeding mechanism throughout post-larval ontogeny. The arm branches of adults gradually become less densely spaced relative to the area of water filtered than in juveniles.