The mitochondrial genome of Priapulus caudatus Lamarck (Priapulida: Priapulidae)

We sequenced and annotated the complete mitochondrial (mt) genome of the priapulid Priapulus caudatus in order to provide a source of phylogenetic characters including an assessment of gene order arrangement. The genome was 14,919 bp in its entirety with few, short non-coding regions. A number of protein-coding and tRNA genes overlapped, making the genome relatively compact. The gene order was: cox1, cox2, trnK, trnD, atp8, atp6, cox3, trnG, nad3, trnA, trnR, trnN, rrnS, trnV, rrnL, trnL(yaa), trnL(nag), nad1, -trnS(nga), -cob, -nad6, trnP, -trnT, nad4L, nad4, trnH, nad5, trnF, -trnE, -trnS(nct), trnI, -trnQ, trnM, nad2, trnW, -trnC, -trnY; where '-' indicates genes transcribed on the opposite strand. The gene order, although unique amongst Metazoa, shared the greatest number of gene boundaries and the longest contiguous fragments with the chelicerate Limulus polyphemus. The mt genomes of these taxa differed only by a single inversion of 18 contiguous genes bounded by rrnS and trnS(nct). Other arthropods and nematodes shared fewer gene boundaries but considerably more than the most similar non-ecdysozoan.     

Ultrastructure of erythrocytes and leucocytes of Priapulus caudatus (de Lamarck) (Priapulida)

The marine priapulid Priapulus caudatus has a voluminous body cavity filled with a blood-like fluid containing erythrocytes and leucocytes (amoebocytes). The hematocrit of animals weighing 0.5–14 gm was 2–10%. The erythrocytes contain a hemerythrin blood pigment. The structure of the coelomocytes was studied by light and electron microscopy. The erythrocytes are nucleated and contain marginal bands, vacuoles and occasionally crystals. The cytoplasm has few organelles. The leucocytes are amoeboid motile cells, the cytoplasm of which contains numerous organelles. The most conspicuous of these are oval particles, probably representing developmental stages of lysosomes. Most of these organelles contain tubules stretching from one pole to another. In the hind part of the animal, certain tissues, primarily the posterior warts contain large numbers of coelomocytes. The histological picture is complicated, showing some resemblance to the lymphoepithelial tissues of vertebrates.     

Amoebocytes in the Lining of the Body Cavity and Mesenteries of Priapulus caudatus (Priapulida)

Nuclei associated with membranes lining the body cavity in Priapulus caudatus are shown by electron microscopy to be the nuclei of amoebocytes. The membranes themselves are not cellular and do not constitute a peritoneum. Mesenteries, present in the body cavity, also are not cellular; amoebocytes occasionally are found within them. These findings weaken the idea that priapulids are coelomates, although unequivocal proof that priapulids are pseudocoelomates would require a fine structural study of the early developmental stages.     

Ultrastructure of a Coccidium (Apicomplexa: Sporozoea: Coccidia) in Priapulus caudatus (Priapulida)1

Stages in the life cycle of a coccidium are described from the intestine of Priapulus caudatus Lamarck, 1816. Meronts, merozoites, microgamonts, microgametes, and walled and unwalled macrogametes were seen in intestinal cells. Meronts were about 8 μm long and 3–7 μm wide and produced up to seven merozoites. Free merozoites were about 9 μm long and 4 μm wide and contained about 43 subpellicular microtubules that terminated in the outer polar ring. Microgamonts were up to 23 μm long and 7 μm wide and usually were delimited by a single membrane. Microgametes were about 5 μm long, exclusive of the two flagella, about 2 μm wide, and contained a nucleus that was not uniformly dense. Macrogametes, about 6 μm in diameter, had a nucleus largely without dense chromatin. The oocyst wall formed around intracellular macrogametes to a thickness of 0.2–0.5 μm as thin, osmiophilic elements that became arranged in reticular and tubular layers. Wall-forming bodies were not seen, but fine filaments may participate in wall formation, as these were found between the outer membrane of the pellicle and the nearest wall elements. Microgametes and walled macrogametes were delivered to the lumen of the host intestine during apocrine secretion or excretion by the intestinal cells. Fertilization may occur in the intestinal lumen. Unsporulated ovoid oocysts, 18–27 μm long and 10–14 μm wide, with a 3 μm micropyle and a wall 0.6–0.7 μm thick, were passed from the host.     

Light Microscopical and Ultrastructural Organization of Muscles of Priapulus caudatus (Priapulida) and Their Responses to Drugs, with Phylogenetic Remarks

The muscle fibres of the marine invertebrate Priapulus caudatus (Priapulida) are obliquely striated. Thin and thick filaments and characteristic dyad structures were recognized. The ultrastructural organization shows more resemblances with that of arthropod muscles than with that of annelids or molluscs. Pharmacological studies show that the muscles are provided with primitive C 16 type of acetylcholine receptors. Tubocurarine, succinylcholine and decamethonium do not block the effect of acetylcholine but potentiate this. This remarkable response may be due to inhibition of choline esterase. No distinct structural or functional differences were observed between somatic and visceral muscles, but the rectum showed evidence of the presence of unspecific amine receptors. The pharmacological responses resemble in the main those known from various simply organized invertebrate phyla. The priapulids, as suggested by Lang in 1953, may te survivors of a very ancient animal group.     

The surface of Priapulus caudatus (Lamarck, 1816)

A scanning electron microscope study of the surface of Priapulus caudatus is presented. Both adults and larvae have been studied. The pharynx, circumoral region, collar, proboscis, trunk, caudal appendage, and larval lorica are described.     

Allozymes characterize sibling species of bipolar Priapulida (Priapulus,Priapulopsis)

Electrophoretic polymorphism of glucosephosphate isomerase (Gpi^*) and phosphoglucomutase (Pgm ^*) polymorphisms were assayed in the bipolardisjunct species pairsPriapulus caudatus/P. tuberculatospinosus andPriapulopsis bicaudatus/Priapulopsis australis (phylum Priapulida). Numbers of genotypes fromGpi ^* alleles and 14Pgm ^* alleles generally did not show deviations from Hardy-Weinberg expectations in composite populations sampled over geographic distances up to 500 km linearly measured. This genetic pattern suggests efficient population cohesion in a phylum where pelagic larvae have not been observed. Sibling species in generaPriapulus orPriapulopsis from northern and southern polar seas did not share identical allozyme alleles.     

Ultrastructure of the introvert and associated structures of the larvae of Halicryptus spinulosus (Priapulida)

Summary Based on new SEM and TEM observations, the arrangement and ultrastructure of the scalids and adhesive tubuli of the larvae of Halicryptus spinulosus are described. The scalids are arranged in 25 longitudinal rows. Transversally they form seven circlets which alternate. The first circlet consists of 8 and the second of 9 scalids. All following circlets consist of three subrings with 8+8+9 scalids each. New scalids develop in a sub frontal growing zone posterior to the second circlet. The ultrastructure of all different receptor cells and sense organs of the scalids is described. Whereas the receptor cell type 1 occurs in nearly all scalids, the verticalrootlet receptor is restricted to the first circlet, the basal receptor to the second and the coiled-cilium receptor to the third and fourth circlet. Based on these new data, the scalid arrangement and the equipment with different receptor cells can be postulated for the ground pattern of the priapulid larvae. Also the larval development, moulting and the structure of the cuticle are discussed in comparison with the Kinorhyncha and Loricifera.     

Deuterostomic Development in the Protostome Priapulus caudatus

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Highlights? In the protostome P. caudatus, the blastopore forms the anus (deuterostomy) ? The hindgut markers brachyury and cdx are expressed in the blastopore and in the anus ? The foregut markers foxA and gsc are detected in the mouth, but not in the blastopore ? Results favor deuterostomy in ecdysozoan, protostome, and bilaterian ancestors     

The larval nervous system of the penis worm Priapulus caudatus (Ecdysozoa)

The origin and extreme diversification of the animal nervous system is a central question in biology. While most of the attention has traditionally been paid to those lineages with highly elaborated nervous systems (e.g. arthropods, vertebrates, annelids), only the study of the vast animal diversity can deliver a comprehensive view of the evolutionary history of this organ system. In this regard, the phylogenetic position and apparently conservative molecular, morphological and embryological features of priapulid worms (Priapulida) place this animal lineage as a key to understanding the evolution of the Ecdysozoa (i.e. arthropods and nematodes). In this study, we characterize the nervous system of the hatching larva and first lorica larva of the priapulid worm Priapulus caudatus by immunolabelling against acetylated and tyrosinated tubulin, pCaMKII, serotonin and FMRFamide. Our results show that a circumoral brain and an unpaired ventral nerve with a caudal ganglion characterize the central nervous system of hatching embryos. After the first moult, the larva attains some adult features: a neck ganglion, an introvert plexus, and conspicuous secondary longitudinal neurites. Our study delivers a neuroanatomical framework for future embryological studies in priapulid worms, and helps illuminate the course of nervous system evolution in the Ecdysozoa.     

Burrowing of Priapulus caudatus (Vermes) and the significance of the direct peristaltic wave

Priapulus caudatus is an active predatory animal found burrowing in soft mud. It may employ relatively high body fluid pressures during escape reactions (up to 6 kPa recorded) but normal burrowing probably involves much lower pressures (< 2 kPa). Three points d'appui are formed during the burrowing cycle. A characteristic direct peristaltic wave (DPW) occurs at a low pressure stage in each cycle (<0–5 kPa). The DPW is regarded as an adaptation to burrowing in soft mud. Its function appears to be to transfer body wall anteriorily, providing slack, which is used to allow the trunk to extend forward into the cavity vacated by retraction of the large praesoma at the end of each cycle. The circular and longitudinal muscles of the posterior trunk act synergically through most of the burrowing cycle.     

Zur feinstruktur integumentaler bildungen bei priapuliden (Halicryptus spinulosus und Priapulus caudatus)

Zusammentassung Die Integumente der Priapuliden Halicryptus spinulosus und Priapulus caudatus sind ähnlich aufgebaut. Die miteinander verzahnten und über lange septierte Desmosomen verbundenen Epithelzellen tragen apikal eine amorphe, in Abhgngigkeit von der Häutungsphase± geschichtete Kutikula. Ähnliche Kutikulastrukturen finden sich bei Nematoden. Der Panzer der Halicryptus-Larve ist in seiner Ultrastruktur deutlich verschieden von der Kutikula adulter Tiere and zeigt auch keine Übereinstimmung mit dem Panzer der Kinorhynchen.Die epithelialen Stacheln der Art Halicryptus spinulosus enthalten mehrere Sekretzelltypen. Die epithelialen Differenzierungen am Rumpfende von Priapulus caudatus sind durch ihre Ultrastruktur ebenfalls als sezernierende Zellkomplexe gekennzeichnet.Der Feinbau des distalen Anhangsorganes von Priapulus caudatus entspricht der Ultrastruktur von Zellen mit aktivem Ionentransport. AuBerdem ist dieses Organ Träger von Mechanorezeptoren.

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Fine structure of integumental features in priapulids (Halicryptus spinulosus and Priapulus caudatus)

Summary The integuments of the priapulids Halicryptus spinulosus and Priapulus caudatus exhibit a similar ultrastructure. The epithelial cells, the neighbouring lateral plasma membranes of which are frequently highly interdigitated, are connected by long septate desmosomes and are apically covered by an amorphous cuticle. The latter shows a stratification, the pattern of which is dependent on the moulting phase. Similar cuticular structures are to be found in nematodes. The cuticle of the larvae of Halicryptus differs markedly from that of the adult animals and also does not show agreements with the armour of kinorhynchs. It is threelaminated and contains in the middle layer canalicular structures. The epithelial spines of Halicryptus spinulosus contain various types of secretory cells. The epithelial differentiations at the end of the body of Priapulus caudatus also represent, according to their ultrastructure, secretory cells. The fine structure of the appendicular organs of Priapulus caudatus corresponds to that of cells engaged in ion transport. In addition this organ possesses mechanoreceptors. Both priapulids carry, on the integumental papillae and within the epithelium of the body and pharynx, characteristically constructed receptors with an apical cilium surrounded by seven microvilli. They are interpreted to represent mechanoreceptors.

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Für die Überlassung eines Arbeitsplatzes im Institut far Pharmakognosie Kiel danke ich Herrn Prof. Dr. D. Frohne. Alit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Image analysis of the burrowing mechanisms of Polyphysia crassa (Annelida: Polychaeta) and Priapulus cudatus (Priapulida)

The burrowing mechanisms of two soft-bodied marine invertebrates, Polyphysia crassa (Annelida: Polychaeta) and Priapulus caudatus (Priapulida) were re-examined and extended utilizing computer image analysis. Predetermined points on sequential photographs of animals burrowing in methylcellulose (an artificial medium of high transparency) were digitized and stored as x, y coordinates from which were calculated segment length, width, and volume in addition to producing real and straightened images of the animal on a plotter. Both species are adapted to soft substrata and both utilize a direct peristaltic wave to advance the body into a cavity or loosened area formed by anterior structures. Polyphysia displaces and loosens the substratum with lateral scraping movements of its anterior six segments (the head region) while Priapulus makes a large cavity anteriorly by the forceful eversion and dilation of the praesoma. Unlike Priapulus, Polyphysia utilizes a different method of locomotion when moving on the mud surface as opposed to burrowing, the former involving two direct peristaltic waves at a time and negligible internal pressures resulting in nearly continuous advance. However when burrowing, Polyphysia , like Priapulus , utilizes a single direct peristaltic wave alternating with phasic pressure pulses which advance the animal in step-wise fashion.     

Microscopic anatomy and ultrastructure of the stomach of Porcellio scaber (Crustacea,Isopoda)

Summary From the micromorphological viewpoint, the stomach is by far the most complicated part of the digestive tract of Porcellio scaber. All parts are shown in electron micrographs. The simplest inner surface of the stomach is the dorsal part, which has an unpaired flap directed posteriorly (lamella dorsalis). The lateral walls carry the lateralia, superolateralia and lamellae annulares. The most complicated region of the stomach is the ventral surface with its anterior primary filter, the adjacent masticatory areas, the posterior secondary filter on the lateral sides of the inferomedianum and the inferolateralia. Ingested food can be filtered twice: first on the primary filter and then on the secondary filter. The digestive fluid secreted in the midgut glands can be conveyed on the same route as the filtrate of the gastric juice, but in the other direction. The posterior part of the stomach is wrapped by a ring-shaped fold of the anterior hindgut, thus making seven epithelia closely apposed to each other.     

Electron microscopical localization of chitin in the cuticle of Halicryptus spinulosus and Priapulus caudatus (Priapulida) using gold-labelled wheat germ agglutinin: phylogenetic implications for the evolution of the cuticle within the Nemathelminthes

 The ultrastructure of the cuticle of adult and larval Priapulus caudatus and Halicryptus spinulosus is investigated and new features of cuticle formation during moulting are described. For the localization of chitin by TEM wheat germ agglutinin coupled to colloidal gold was used as a marker. Proteinaceous layers of the cuticle are revealed by digestion with pronase. The cuticle of larval and adult specimens of both species consists of three main layers: the outer, very thin, electron-dense epicuticle, the electron-dense exocuticle and the fibrillar, electron-lucent endocuticle. Depending on the body region, the exocuticle comprises two or three sublayers. The endocuticle can be subdivided into two sublayers as well. In strengthened parts such as the teeth, the endocuticle becomes sclerotized and appears electron-dense. Only all endocuticular layers show an intense labelling with wheat germ agglutinin-gold conjugates in all investigated specimens. Additional weak labelling is observed in the exocuticle III layer of the larval lorica of P. caudatus. All other cuticular layers remain unlabelled. Chitinase dissolves the unsclerotized endocuticular layers almost completely, but also exocuticle II and partly the loricate exocuticle III. The epicuticle, the homogeneous exocuticle I and the sclerotized endocuticle are not affected by chitinase. The labelling is completely prevented in all layers after incubation with chitinase. Pronase dissolves all exocuticular layers, but not evenly. The presumably sclerotized regions of exocuticle I are not affected as well as the complete epicuticle and the endocuticle. All cuticular features of the Priapulida are compared with the cuticle of each high-ranked taxon within the Nemathelminthes with special regard to the occurrence of chitin. Based on this out-group comparison it can be concluded that: (1) a two-layered cuticle with a trilaminate epicuticle and a proteinaceous basal layer represents an autapomorphic feature of the Nemathelminthes, (2) the stem species of the Cycloneuralia have already evolved an additional basal chitinous layer, (3) such a three-layered cuticle is maintained as a plesiomophy in the ground pattern of the Scalidophora and (4) in the Nematoida, the chitinous basal layer is replaced by a collagenous one at least in the adults; the synthesis of chitin is restricted to early developmental phases or the pharyngeal cuticle. Accepted: 12 March 1998     

Microscopic anatomy and ultrastructure of the digestive system of three Antarctic shrimps (Crustacea: Decapoda: Caridea)

Mandibles and stomachs of three Antarctic shrimp species (Nematocarcinus lanceopes, Notocrangon antarcticus, and Chorismus antarcticus) were investigated by means of scanning electron microscopy. Transmission electron microscopy of the midgut glands was applied to find out the nutritional status of the animals, which contained a broad variety of food items in their stomachs. In contrast to the Antarctic krill, the three carideans possess a dual filter system; primary filters in the cardia and secondary filters in the pyloric chamber. Morphologically, the mandibles and stomachs of the three species vary considerably; however, their food items are similar. We conclude that stomach contents do not really reflect the different modes of life or habitat preferences of the investigated species.     

Microscopic anatomy,functional morphology,and ultrastructure of the stomach of Euphausia superba Dana (Crustacea,Euphausiacea)

Summary Microscopic anatomy, functional morphology, and ultrastructure of the stomach of the antarctic krill Euphausia superba Dana were investigated by means of serial sections, scanning and transmission electron microscopy, and video technique. A separation of the stomach into an anterior part, called cardia, and a posterior part, called pylorus, became evident. Protrusions of the stomach into the midgut form the third region, called the funnel. The interior of the cardia is dominated by the two lateralia, originating from the side walls of the stomach. At their undersurface, they bear the primary filter. It separates the dorsal food channel from the ventral filtration channel, which is divided into two channels by a ventromedian ridge, the anteromedianum. Within the pylorus, the inferolateralia act in sealing the food channel from the filtration channel. In contrast to many other Malacostraca, the inferomedianum bears no secondary filter. During live observations, the stomach of Euphausia superba shows distinct pumping phases. A comparison of the structure of the stomach with data obtained from other Crustacea will lead to a better understanding about the relationships between the Malacostraca.     

Morphology and ultrastructure of the sensory appendages of a kinorhynch introvert

The structure and arrangement of appendages (scalids) on the head of the homalorhagid kinorhynch Kinorhynchus phyllotropis Brown & Higgins, 1983 are named, described and illustrated. In adults of this species, seven rings of external scalids are separated by segment boundary structures from the oral styles and three rings of internal scalids. All of these appendages contain ciliated receptor cells which pass to pores at the scalid tips, and all but the two anterior rings are jointed. All of these appendages are radially arranged in multiples of five, and closely associated with the ten lobed circumoral nerve ring. The most posterior scalid ring consists of fourteen trichoscalids, of which six are longer than the other eight. The six longer trichoscalids are arranged in bilateral symmetry, two to each of the three facets of the body. Similarities between scalid arrangement in Kinorhyncha and Loricifera are discussed.     

Burrowing dynamics and energy cost of transport in the soft-bodied marine invertebrates Polyphysia crassa and Priapulus caudatus

The dynamics and mechanical forces generated during burrowing in Polyphysia crassa (Annelida: Polychaeta) and Priapulus caudatus (Priapulida) were investigated. Both animals live in soft marine muds and burrow by utilizing a direct peristaltic wave alternating with a high internal pressure event which thrusts the anterior part of the body into the substratum. Forces generated during the various phases of a typical burrowing cycle were measured in animals moving beneath the natural substratum at 5±3 °C using electronic transducers and recorder. During 'head' advance Polyphysia generated 0.027 N, and during 'tail' advance 0.020 N, with peak internal pressures averaging 0.95 kPa (= 0.095 N/cm²). Force by Priapulus during head advance and tail advance was 0.081 N and 0.121 N, respectively, with peak internal pressures averaging 2.47 kPa (= 0.247 N/cm²). Polyphysia moves more slowly (0.24 cm/min) than does Priapulus (0.76 cm/min) and expends more energy on mass moved per unit distance. These force measurements during a burrowing cycle were used in place of respirometry as a basis for computation of net cost of transport (NCT) for each animal. NCT for Polyphysia was 635 J kg^-1 m^-1 and for Priapulus was 314Jkg^-1m^-l. Cost of transport for all burrowing animals thus far investigated is high compared to swimming, running and flying. For soft-bodied invertebrates that live an entirely buried existence this high cost must be interpreted in the broader context of the adaptive value of infaunal life, especially protection against predation, and not as simply a means of moving about.