Food Groove Research Articles

Phylogenetic position of Bohemiacinctus gen. nov. (Echinodermata, Cincta) from the Cambrian of Bohemia: implications for macroevolution and the role of taxon sampling in palaeobiological systematics

Abstract‘Asturicystis’ havliceki Fatka & Kordule from the middle Cambrian of Bohemia (Czech Republic) is re‐described based on its type material. Several features, including the extension of the food grooves and presence of ventral swellings suggest that ‘A.’ havliceki does not belong to Asturicystis, and is placed in the new genus Bohemiacinctus. To ascertain the phylogenetic position of Bohemiacinctus havliceki, we conducted Bayesian fossil tip‐dating and parsimony‐based phylogenetic analyses of 24 species spanning all major groups of cinctan higher taxa. Results show a high degree of congruence between tree topologies recovered by both tip‐dated and parsimony‐based analyses. Both methods indicate B. havliceki is phylogenetically distant from Asturicystis and is most likely to be an early representative of the family Sucocystidae. Overall, our phylogeny is broadly similar to previous estimates of cinctan relationships, including a more conventional phylogenetic position of controversial taxa such as Protocinctus. These results point to the sensitivity of small clades such as cinctans to taxon sampling effects, and highlights the importance of taxonomy and accurate morphological character descriptions in phylogenetic analyses of fossil taxa.

Pentaradiate diploporites (Echinodermata) from the Spanish Middle Ordovician and their taxonomic significance

New Middle Ordovician specimens of pentaradiate diploporite blastozoans from the southern Central Iberian Zone, Spain, show that Oretanocalix is an aristocystitid diploporite with five ambulacra; all other aristocystitid genera have 2?4 ambulacra. The laterally elongate oral frame is composed of eight plates, with five, facet-bearing, circumorals (COO) and three, non-facet-bearing, periorals (POO). This necessitates a new interpretation of the aristocystitid oral area and diagnosis of the family Aristocystitidae. Previous interpretations assumed four COO and four POO. Weathered examples lack oral cover plates and show that plates CO1 and CO4, which support ambulacra D and B, respectively, do not reach the inner margin of the peristome. They also reveal abundant diplopores, which were covered by a thin epistereom in life. Diplopores grew at plate sutures and were incorporated into both adjacent plates as the plates enlarged. Oretanocalix julioi n. sp. extends the stratigraphic range of Oretanocalix back to the basal Dobrotivian ?low in the Upper Darriwilian. The genus Batalleria is a sphaeronitid diploporite with food grooves that branched within the peristome. The branching pattern reflects Lovén’s law and is: AR, BL, CR, DL, ER, where A?E denote Carpenter’s ambulacra and L (left) and R (right) denote on which side of the ambulacrum the first branch lies. Each branch leaves the peristome by a separate ambulacral orifice. No other sphaeronitids have food grooves that branch within the peristome and all other sphaeronitids have one ambulacral orifice per ambulacrum. Thus, a new diagnosis of sphaeronitids is necessary.

Transport of symbiont-encoded cellulases from the gill to the gut of shipworms via the enigmatic ducts of Deshayes: a 174-year mystery solved

Shipworms (Bivalvia, Teredinidae) are the principal consumers of wood in marine environments. Like most wood-eating organisms, they digest wood with the aid of cellulolytic enzymes supplied by symbiotic bacteria. However, in shipworms the symbiotic bacteria are not found in the digestive system. Instead, they are located intracellularly in the gland of Deshayes, a specialized tissue found within the gills. It has been independently demonstrated that symbiont-encoded cellulolytic enzymes are present in the digestive systems and gills of two shipworm species, Bankia setacea and Lyrodus pedicellatus, confirming that these enzymes are transported from the gills to the lumen of the gut. However, the mechanism of enzyme transport from gill to gut remains incompletely understood. Recently, a mechanism was proposed by which enzymes are transported within bacterial cells that are expelled from the gill and transported to the mouth by ciliary action of the branchial or food grooves. Here we use in situ immunohistochemical methods to provide evidence for a different mechanism in the shipworm B. setacea, in which cellulolytic enzymes are transported via the ducts of Deshayes, enigmatic structures first described 174 years ago, but whose function have remained unexplained.

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

BackgroundShipworms 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.ResultsThrough 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.ConclusionBased 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.

A new species and comparative morphology of Philippine sea biscuits (Echinoidea: Clypeaster/).

A new species of clypeasterid sea biscuit, Clypeaster brigitteae n. sp., is described from material collected in the Philippines at depths between 100 and 200 m. The new taxon increases the number of Clypeaster species recorded from the Philippines to nine, representing nearly a quarter of the world's diversity of the genus. Other Philippine species include: C. annandalei Koehler, 1922; C. fervens Koehler, 1922; C. humilis (Leske, 1778); C. japonicus Döderlein, 1885; C. latissimus (Lamarck, 1816); C. pateriformis Mortensen, 1948; C. reticulatus (Linnaeus, 1758); and C. virescens Döderlein, 1885. Using type material where available, each of these species is compared and contrasted with C. brigitteae n. sp. in tables consisting of new data derived from general test shape and size, petal structure, food grooves, plate architecture, internal structure, and morphology of spines, pedicellariae, and tube feet.

Potential evolutionary trade‐off between feeding and stability in Cambrian cinctan echinoderms

AbstractReconstructing the function and behaviour of extinct groups of echinoderms is problematic because there are no modern analogues for their aberrant body plans. Cinctans, an enigmatic group of Cambrian echinoderms, exemplify this problem: their asymmetrical body plan differentiates them from all living species. Here, we used computational fluid dynamics to analyse the functional performance of cinctans without assuming an extant comparative model. Three‐dimensional models of six species from across cinctan phylogeny were used in computer simulations of water flow. The results demonstrate that cinctans with strongly flattened bodies produced much less drag than species characterized by dorsal protuberances or swellings, suggesting the former were more stable on the seafloor. However, unlike the flattened forms, cinctans with high‐relief bodies were able to passively direct flow towards the mouth and associated food grooves, indicating that they were capable of more efficient feeding on particles suspended in the water. This study provides evidence of a previously unknown evolutionary trade‐off between feeding and stability in Cambrian cinctan echinoderms.

Opposed bands of cilia in the nonfeeding larvae of the serpulid annelid Salmacina tribranchiata

AbstractThe nonfeeding planktonic larvae of marine invertebrates typically lack larval feeding structures. One puzzling exception to this generalization is the annelid clade Sabellidae, in which nonfeeding larvae possess ciliary bands (specifically, food groove and metatroch) that, to the best of our knowledge, have no function other than in feeding. Nishi and Yamasu (1992b, Bulletin of the College of Sciences, University of the Ryukyus, 54, 107–121) published a scanning electron micrograph showing that nonfeeding larvae of the serpulid annelid Salmacina dysteri also possess food groove and metatrochal cilia. Here I demonstrate that nonfeeding larvae of Salmacina tribranchiata also bear ciliary bands identifiable as food groove and metatroch by position. High‐speed video of ciliary beat patterns shows that, together with the prototrochal cilia, these bands function in an opposed band system. The presence of feeding structures in nonfeeding annelid larvae is thus more widely distributed than previously recognized. The presence of feeding structures may make evolutionary transitions to planktotrophy more likely, and may underlie an inferred origin of larval feeding in the common ancestor of one of the two major clades of serpulid annelids, Serpulinae.

Uptake and Retention of Nanoplastics in Quagga Mussels.

Here, a set of experiments to assess the feasibility of using an invasive and widespread freshwater mussel (Dreissena rostrformis bugensis) as a sentinel species for nanoplastic detection is reported. Under laboratory experimental conditions, mussels ingest and retain fluorescent polystyrene (PS) beads with carboxylic acid (—COOH) termination over a size range of 200–2000 nm. The number of beads the mussels ingested is quantified using fluorescence spectroscopy and the location of the beads in the mussels is imaged using fluorescence microscopy. PS beads of similar size (1000–2000 nm) to mussels' preferred food are trafficked in the ciliated food grooves of the gills. Beads of all sizes are observed in the mussels' digestive tracts, indicating that the mussels do not efficiently reject the beads as unwanted foreign material, regardless of size. Fluorescence microscopy shows all sizes of beads are concentrated in the siphons and are retained there for longer than one month postexposure. Combined atomic force microscopy–infrared spectroscopy and photothermal infrared spectroscopy are used to locate, image, and chemically identify the beads in the mussel siphons. In sum, these experiments demonstrate the potential for using mussels, specifically their siphons, to monitor environmental accumulation of aquatic nanoplastics.

Early Cambrian fuxianhuiids from China reveal origin of the gnathobasic protopodite in euarthropods

Euarthropods owe their evolutionary and ecological success to the morphological plasticity of their appendages. Although this variability is partly expressed in the specialization of the protopodite for a feeding function in the post-deutocerebral limbs, the origin of the former structure among Cambrian representatives remains uncertain. Here, we describe Alacaris mirabilis gen. et sp. nov. from the early Cambrian Xiaoshiba Lagerstätte in China, which reveals the proximal organization of fuxianhuiid appendages in exceptional detail. Proximally, the post-deutocerebral limbs possess an antero-posteriorly compressed protopodite with robust spines. The protopodite is attached to an endopod with more than a dozen podomeres, and an oval flap-shaped exopod. The gnathal edges of the protopodites form an axial food groove along the ventral side of the body, indicating a predatory/scavenging autecology. A cladistic analysis indicates that the fuxianhuiid protopodite represents the phylogenetically earliest occurrence of substantial proximal differentiation within stem-group Euarthropoda illuminating the origin of gnathobasic feeding.

Ordovician Paracrinoids from the Baltic: Key Problems of Comparative Morphology of Pelmatozoan Echinoderms

The erect feeding appendages of paracrinoids, brachioles of typical blastozoans and arms of crinoids are morphologically similar in their terminal growth, biserial cover plates, and pinnulation. This is attributed to the inducing effect of the radial ambulacral canal on their growth mode. The uniserial brachioles of Laurentian paracrinoids are homologous to the biserial brachioles of the Baltic Achradocystites and Heckerites, and those of other blastozoans. Based on this assumption, the two Baltic genera, which have a brachiole system plesiomorphic for paracrinoids, and a similar morphology of the theca, are assigned to this class. Brachiolars in brachioles are a new development, homologous to the flooring plates of the food groove and, where present, are the continuations of these plates beyond the theca. The uniserial brachioles of Laurentian paracrinoids evolved from the biserial brachioles as a result of a gradual shift of brachiolars in the neighboring rows and their subsequent fusion in pairs. Brachials in crinoidal arms are a new development that evolved as distal serial growth of radial plates under the induced influence of the incipient radial canals emerging from the closed vestibular cavity, which was an ontogenetic innovation in crinoids. The transformation of a nonorganized small-plated theca into a large-plated, and completely or partly symmetrized theca, or vice versa is possible and results from accelerated or retarded growth of some plate generation in relation to the growth rate of the theca.

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

AbstractUniversal 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.

A new genus of mellitid sand dollar (Echinoidea: Mellitidae) from the eastern Pacific coast of the Americas.

Lanthonia gen. nov. Coppard 2016 is a genus of clypeasteroid sand dollar whose members inhabit shallow, sandy waters from Mexico (including the Gulf of California) to Colombia in the tropical and subtropical eastern Pacific. Lanthonia includes Lanthonia longifissa (Michelin, 1858) and Lanthonia grantii (Mortensen, 1948), with L. longifissa hereby designated as the type species. Both L. longifissa and L. grantii were previously placed in the genus Mellita (L. Agassiz, 1841). However, levels of genetic divergence between a lineage containing L. longifissa and L. grantii and a lineage containing all other species of Mellita, including the type species M. quinquiesperforata (Leske, 1778), indicate genus level differentiation. The systematic interpretation of this group also supports the designation of this new genus as it allows the tree topology to be recovered from the nomenclature and clarifies the historical biogeography of these clades. This has resulted in members of both lineages today being sympatric in the eastern Pacific. Members of Lanthonia are morphologically differentiated from the type species of Mellita and all Pacific Mellita in having very narrow ambulacral regions between the food grooves and the ambulacral lunules on the oral surface, these being very broad in both M. quinquiesperforata and M. notabilis. The dentation of the bidentate pedicellariae also differentiate these genera, with small peripheral teeth present along the edge of the blade in species of Lanthonia and one to three enlarged intersecting teeth present distally in all species of Mellita.

From benthic to pseudoplanktonic life: morphological remodeling of the Triassic crinoid Traumatocrinus and the Jurassic Seirocrinus during habitat change

The pseudoplanktonic driftwood-attached crinoids Traumatocrinus (late Ladinian—early Carnian) and Seirocrinus (Norian–Toarcian) are compared with their Middle Triassic benthic ancestors of the families Encrinidae and Holocrinidae, respectively. The morphological transformations allow five major adaptations of stalked crinoids for pseudoplanktonic life to be specified within the constraints of the ancestral clades: (1) Lightweight construction to reduce the load of the driftwood, maintaining its buoyancy for as long as possible. This was achieved by pore systems of intercolumnal fossulae and longitudinal tubuli in Traumatocrinus, and by a distally tapering column in Seirocrinus. (2) Peramorphic lengthening of the column to reach plankton-rich water levels (Traumatocrinus and Seirocrinus), and the possibility to make the column flexible or stout by mutable connective tissue (Traumatocrinus). Different column lengths in a colony of Traumatocrinus allowed filtering of a larger water column. (3) Solid and persisting anchoring to the drifting substrate to prevent breakage and detachment from the log by adhesive, anastomosing radicular rootlets in Traumatocrinus and—less successful—in Seirocrinus by a tuft of flexible cirri. (4) Increasing the length of the food grooves to compensate for the disadvantage of drifting along with the plankton by peramorphic augmentation of endotomously branching arms (both forms). (5) Enlargement of the functional cup by intercalation of tegminal or/and pinnular elements (both forms). Exclusively ligamentary (granosyzygial) brachial articulation made the Traumatocrinus crown rather inflexible while Seirocrinus retained the ancestral flexible muscular articulations. A prerequisite for the pseudoplanktonic lifestyle was the availability of large driftwood logs that became available in late Middle Triassic times after the recovery of large gymnosperms. After 50 Ma, the niche of pseudoplanktonic drifting of stalked crinoids was closed in the Middle Jurassic by the rise of shipsworms.

Roveacrinids (Crinoidea) from the mid-Cretaceous of Texas: ontogeny, phylogeny, functional morphology and lifestyle

New material of known roveacrinids from two Cretaceous sites in Texas is described. Upper Albian strata at Saginaw Quarry furnished rich material of Poecilocrinus latealatus and Roveacrinus pyramidalis; for these two forms cups can be combined with primibrachials and secundibrachials. Some cups of Orthogonocrinus apertus are also present. Juvenile cups of these three species demonstrate ontogenetic changes, which are most prominent in P. latealatus. At the adult stage this species has cups with dish-like lateral wings; the first primibrachials have an aboral bowl; axillary second primibrachials and proximal secundibrachials have a wide aboral bowl; and distal brachials carry spines. The arms lack pinnules. A pelagic lifestyle with a mouth-up position is assumed. In contrast, R. pyramidalis has rod-shaped or stick-like brachials without wings, and food grooves are lacking. The less rich lower Cenomanian strata at the Dottie Lynn site provided a number of cups and brachials of Roveacrinus spinosus. In addition, cups of R. peracutus and R. alatus are present. Styracocrinus Peck is considered synonymous with Roveacrinus Douglas. The double cavity in the cups of the various species is discussed; its proposed function as a hydrostatic organ seems conjectural. Two genera of Saccocominae of the Late Jurassic radiation are thought to be ancestors to similar genera of Roveacrinidae first appearing during the Albian radiation. Derivation of Poecilocrinus may be from Saccocoma, Discocrinus and Plotocrinus possibly from Crassicoma. The ancestry of species of Roveacrinus and Orthogonocrinus with conical cups and two distinct body chambers is unclear. The closely similar juvenile cups of Roveacrinus pyramidalis and Poecilocrinus latealatus suggest a common origin despite the widely diverging arm structure. A comparison of Roveacrinus pyramidalis with the Triassic somphocrinid Osteocrinus reveals similar rod-shaped, smooth and tall brachials lacking a distinct food groove. Based on their mass occurrence and wide distribution, species of Osteocrinus species are thought to have been pelagic. This is substantiated by the presence of cups and rod-shaped brachials in Ladinian black shales of southern China. While food of species of Poecilocrinus presumably consisted of coccolithophores and planktonic foraminifera, collection and transport of food particles by Roveacrinus pyramidalis is enigmatic, as is that of Osteocrinus.

Brooding in the Chilean oyster Ostrea chilensis: unexpected complexity in the movements of brooded offspring within the mantle cavity.

Brooding in invertebrates serves to protect embryos from stressful external conditions by retaining progeny inside the female body, effectively reducing the risk of pelagic stages being exposed to predation or other environmental stressors, but with accompanying changes in pallial fluid characteristics, including reduced oxygen availability. Brooded embryos are usually immobile and often encapsulated, but in some Ostrea species the embryos move freely inside the female pallial cavity in close association with the mother’s gills for as long as eight weeks. We used endoscopic techniques to characterize the circulation pattern of embryos brooded by females of the oyster, Ostrea chilensis. Progeny at embryonic and veliger stages typically circulated in established patterns that included the use of dorsal and ventral food grooves (DFG, VFG) to move anteriorly on the gills. Both embryos and veligers accumulated around the mother’s palps, and remained there until an active maternal countercurrent moved them to the gill inhalant area. Both food grooves were able to move embryos, veligers, and food-particle aggregates anteriorly, but the DFG was more important in progeny transport; early embryos were moved more rapidly than veligers in the DFG. A microcirculation pattern of embryos was apparent when they were moved by gill lamellae: when they were close to the VFG, most embryos lost gill contact and ´´fell´´ down to the DFG. Those that actually reached the DFG moved anteriorly, but others came into contact with the base of the lamellae and again moved towards the VFG. The circulation pattern of the progeny appears well-suited for both cleaning them and directing them posteriorly to an area where there is more oxygen and food than in the palp region. This process for actively circulating progeny involves the feeding structures (gill and palps) and appears to be energetically costly for the female. It also interferes with feeding, which could explain the poor energy balance previously documented for brooding females of this species.

Erratum

PalaeontologyVolume 58, Issue 2 p. 391-391 ErratumFree Access Erratum This article corrects the following: Deciphering the early evolution of echinoderms with Cambrian fossils Samuel Zamora, Imran A. Rahman, Andrew Smith, Volume 57Issue 6Palaeontology pages: 1105-1119 First Published online: November 25, 2014 First published: 05 March 2015 https://doi.org/10.1111/pala.12156AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL In Zamora and Rahman (2014), Figure 3 should have been printed in colour and is reproduced below. The publisher wishes to apologize for this error. Figure 3Open in figure viewerPowerPoint Cambrian spiral echinoderms. A, C, the helicoplacoid Helicoplacus gilberti; A, general view of the theca, with a lateral mouth and three ambulacra, UT TMM 2041TX1a (courtesy of Bryan Wilbur); C, view from the interior of the ambulacral flooring plates, NHMUK EE 5343. B, D, the helicocystoid Helicocystis moroccoensis; B, general view of the theca, with a terminal mouth and five ambulacra, NHMUK EE 15375; D, view from the exterior of food groove associated with floor plates, NHMUK EE 15373. Floor plates are indicated in green. All images are photographs of latex casts whitened with NH4Cl sublimate. Scale bars represent 5 mm (A); 1 mm (B, D); 2 mm (C). Reference Zamora, S. and Rahman, I. A. 2014. Deciphering the early evolution of echinoderms with Cambrian fossils. Palaeontology, 57, 1105– 1119. Volume58, Issue2March 2015Pages 391-391 FiguresReferencesRelatedInformation

Development and larval feeding in the capitellid annelid Notomastus cf. tenuis.

Making inferences about the evolution of larval nutritional mode and feeding mechanisms in annelids requires data on the form and function of the larvae, but such data are lacking for many taxa. Though some capitellid annelids are known or suspected to have planktotrophic larvae, these larvae have not previously been described in sufficient detail to understand how they feed. Here we describe embryos and larvae of the capitellid Notomastus cf. tenuis from San Juan Island, Washington State. Fertilized oocytes average about 58 μm in equivalent spherical diameter. Early embryos undergo spiral cleavage and develop into larvae that feed for about 5 weeks before metamorphosis. Larvae of N. cf. tenuis capture food particles between prototrochal and metatrochal ciliary bands and transport them to the mouth in an intermediate food groove; this arrangement is typical of "opposed band" larval feeding systems. Surprisingly, however, larvae of N. cf. tenuis appeared to have only simple cilia in the prototrochal ciliary band; among planktotrophic larvae of annelids, simple cilia in the prototroch were previously known only from members of Oweniidae. The anteriormost tier of prototrochal cilia in N. cf. tenuis appears to be non-motile; its role in swimming or particle capture is unclear. Like some planktotrophic larvae in the closely related Echiuridae and Opheliidae, larvae of N. cf. tenuis can capture relatively large particles (up to at least 45 μm in diameter), suggesting that they may use an alternative particle capture mechanism in addition to opposed bands of cilia.

Phylogeny of Myzostomida (Annelida) and their relationships with echinoderm hosts.

BackgroundMyzostomids are marine annelids, nearly all of which live symbiotically on or inside echinoderms, chiefly crinoids, and to a lesser extent asteroids and ophiuroids. These symbionts possess a variety of adult body plans and lifestyles. Most described species live freely on the exterior of their hosts as adults (though starting life on the host inside cysts), while other taxa permanently reside in galls, cysts, or within the host’s mouth, digestive system, coelom, or gonads. Myzostomid lifestyles range from stealing incoming food from the host’s food grooves to consuming the host’s tissue directly. Previous molecular studies of myzostomids have had limited sampling with respect to assessing the evolutionary relationships within the group; therefore molecular data from 75 myzostomid taxa were analyzed using maximum likelihood and maximum parsimony methods. To compare relationships of myzostomids with their hosts, a phylogeny was inferred for 53 hosts and a tanglegram constructed with 88 associations.ResultsGall- and some cyst-dwellers were recovered as a clade, while cyst-to-free-living forms were found as a grade including two clades of internal host-eaters (one infecting crinoids and the other asteroids and ophiuroids), mouth/digestive system inhabitants, and other cyst-dwellers. Clades of myzostomids were recovered that associated with asteroids, ophiuroids, and stalked or feather star crinoids. Co-phylogenetic analyses rejected a null-hypothesis of random associations at the global level, but not for individual associations. Event-based analyses relied most upon host-switching and duplication events to reconcile the association history.ConclusionHypotheses were revised concerning the systematics and evolution of Myzostomida, as well their relationships to their hosts. We found two or three transitions between food-stealing and host-eating. Taxa that dwell within the mouth or digestive system and some cyst forms are arguably derived from cyst-to-free-living ancestors – possibly the result of a free-living form moving to the mouth and paedomorphic retention of the juvenile cyst. Phylogenetic conservatism in host use was observed among related myzostomid taxa. This finding suggests that myzostomids (which have a free-living planktonic stage) are limited to one or a few closely related hosts, despite most hosts co-occurring on the same reefs, many within physical contact of each other.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0170-7) contains supplementary material, which is available to authorized users.

Callocystites fresti sp. nov., and the significance of ambulacral branching in the Callocystitidae (Echinodermata, Glyptocystitoida)

Callocystites fresti sp. nov. is characterized by an elongate theca, protuberant periproct and raised ambulacral facets. Ambulacral branching in Callocystites is isotomous, but left‐ and right‐handed branches occur because the ambulacral groove branches in the same direction twice, interrupting the regularly alternating branching to brachioles. Branching in Strobilocystites does not interrupt the alternation of brachioles and lateral food grooves always pass adoral to the first brachiole of each branch. Sphaerocystites branched as in Strobilocystites. Other morphological features suggest Callocystites, Sphaerocystites and Strobilocystites are not closely related. Callocystites has open infra‐lateral and lateral circlets and five ambulacra; Sphaerocystites and Strobilocystites have closed/modified circlets and four ambulacra. In Callocystites and Sphaerocystites the B and D ambulacra differ from the others and they have one hydropore; in Strobilocystites all four ambulacra are the same and the hydropore is double. All three genera have large, globular thecae. Ambulacral branching was a response to increased food‐gathering requirements. The following are phylogenetically informative callocystitid characters: truly open vs closed/modified plate circlets; number of pectinirhombs; number of ambulacra; presence vs absence of the ‘B D different’ pattern of primary brachioles; single vs double hydropore.In echinoderms with five ambulacra in a 2–1–2 pattern ambulacral homologies are unambiguous: the single amb is A (III). In echinoderms without this pattern or with less than five ambulacra the hydropore or a single gonopore is best for orientation. Both always occur in the CD (V‐I) interambulacrum. The position of the periproct is unreliable. Different patterns and numbers of ambulacra in Palaeozoic echinoderms render a single developmental sequence improbable. Cystoids (blastozoans) had radial water vessels in their ambulacra and added new ambulacral plates terminally. Functional morphological considerations suggest tube feet were essential for food gathering. Copyright © 2014 John Wiley & Sons, Ltd.

The gill morphology of the date mussel Lithophaga lithophaga (Bivalvia: Mytilidae)

The purpose of the present research was to study the descriptive anatomy of the gill of the mussel Lithophaga lithophaga. Mussels were collected from 2 sites in Antalya Bay, Turkey. Observations using stereomicroscopy and electron microscopy showed that the gills of L. lithophaga consist of homorhabdic filaments, a characteristic of the mytilids. The lamellae have cavities at their laterals in addition to their prominent ciliary structure on the frontal and lateral surfaces. The latero-frontal cilia extend in pairs, one attached to the other with a membrane and showing a composite structure. The ascending and descending lamellae are fused by fan-like cilia groups and form a food groove at their ventral margins. Scabrous blocks at the abfrontal edges of the ascending lamellae appear to function as food graters. The relatively large food particles captured by the mussel are ground into smaller pieces to be ingested. These morphological features of the gills of L. lithophaga can be used for comparison with those of other congeners or mytilids.