Feeding behaviour of a new worm (Priapulida) from the Sirius Passet Lagerstätte (Cambrian Series 2, Stage 3) of North Greenland (Laurentia)

Singuuriqia simoni gen. et sp. nov. represents the first record of a priapulid worm from the Sirius Passet Lagerstätte (Cambrian Series 2, Stage 3) of North Greenland (Laurentia). It is defined by an unusually broad, longitudinally folded, foregut which tapers through the pharynx towards the anterior mouth; posteriorly, the same longitudinal folding is evident in the narrow gut. The slender, smooth, trunk in the unique specimen passes anteriorly into an oval proboscis which culminates in a smooth, extensible, pharynx with pharyngeal teeth. The capacity for substantial expansion of the foregut permitted rapid ingestion of food prior to digestion at leisure. Cololites suggest both carnivorous and deposit feeding behaviour, indicating that Singuuriqia, like the present day Priapulus, was probably omnivorous.     

The embryonic development of the temnocephalid flatworms Craspedella pedum and Diceratocephala boschmai

We have analyzed the embryonic development of the temnocephalid flatworms Craspedella pedum and Diceratocephala boschmai, using a combination of fuchsin-labeled whole-mount preparation, histology, and transmission electron microscopy. Following the staging system recently introduced for another flatworm species (Mesostoma lingua), we can distinguish eight morphologically defined stages. Temnocephalids produce eggs of the neoophoran type in which a small oocyte is surrounded by a layer of yolk cells. Cleavage takes place in the center of the yolk mass (stages 1-2) and results in an irregular, multilayered disc of mesenchymal cells that moves to the future ventral egg pole (stage 3). Organ primordia, including those of the brain, pharynx, male genital apparatus, sucker, and epidermis "crystallize" within this disc without undergoing gastrulation movements (stage 4). An invagination of the epidermal primordium pushes the embryo back into the center of the yolk ("embryonic invagination"). As a result, organogenesis begins while the embryo is invaginated (stage 5). The brain differentiates into an outer cortex of cell bodies that surround a central neuropile. Precursor cells of the epidermis, pharynx, and protonephridia become organized into epithelia. During stage 6, the embryonic primordium everts back to the surface, where organogenesis and cell differentiation continues. Epidermal cells fuse into a syncytium that expands around the yolk. Myoblasts initially do not spread out in the way epidermal cells do; they remain concentrated in two narrow, longitudinal bands that extend along the sides of the embryo. Three pairs of axon tracts extending posteriorly from the brain follow the bands of myoblasts. Stages 7 and 8 are characterized by the appearance of eye pigmentation, brain condensation, and the formation of tentacles and a sucker that bud out from the epidermis of the anterior and posterior end, respectively. Comparison of morphogenesis in temnocephalids with observations in other flatworm taxa suggests a phylotypic stage for this phylum of invertebrates.     

Fine Structure of the Head and Cervical Region of Ceramonema carinatum (Chromadorida: Ceramonematidae)

Structure of the head and cervical region of Ceramonema carinatum (Chromadorida: Ceramonematidae) was described from transmission electron microscopy of serial transverse and longitudinal sections of two females. An unbroken massive cortical layer encompasses the head, except where three thin liplets surround the mouth. A large flask-shaped buccal cavity, with simpler less dense cuticle identical with that of the pharynx, abuts the body cuticle just within the mouth. Myoepithelial ceils constituting the buccal and pharyngeal regions were described. Sixteen head sensilla, the amphids, and dorsal and ventral internal sensilla were identified and described, each with associated sheath and socket cells. Ultrasturcture of the head was compared with that of other nematodes. Arrangement of sensilla resembled that of Monhysterida and Rhabditida with some significant variations, such as prominent longitudinally arranged intracellular organelles containing many microtubules associated with the amphids. The buccal cavity was almost entirely pharyngeal in character. A well-developed system of structural fibrils and abundant hemidesmosomes were notable features.     

Transdifferentiation in holothurian gut regeneration

It has recently been shown that the whole spectrum of cell types constituting a multicellular organism can be generated from stem cells. Our study provides an example of an alternative mechanism of tissue repair. Injection of distilled water into the coelomic cavity of the holothurian Eupentacta fraudatrix results in the loss of the whole digestive tract, except the cloaca. The new gut reforms from two separate rudiments. One rudiment appears at the anterior end of the body and extends posteriorly. The second rudiment grows anteriorly from the cloaca. In the anterior rudiment, the luminal epithelium (normally derived from endoderm) develops de novo through direct transdifferentiation of the coelomic epithelial cells (mesodermal in origin). In the posterior rudiment, the luminal epithelium originates from the lining epithelium of the cloaca. After 27 days, the two rudiments come into contact and fuse to form a continuous digestive tube lined with a fully differentiated luminal epithelium. Thus in this species, the luminal epithelia of the anterior and posterior gut rudiments develop from two different cell sources-i.e., from the mesodermally derived mesothelium and the endodermally derived epithelium of the cloacal lining, respectively. Our data suggest that differentiated cells of echinoderms are capable of transdifferentiation into other cell types.     

The embryonic development of the flatworm <Emphasis Type="Italic">Macrostomum</Emphasis> sp.

Macrostomid flatworms represent a group of basal bilaterians with primitive developmental and morphological characteristics. The species Macrostomum sp., raised under laboratory conditions, has a short generation time of about 2–3 weeks and produces a large number of eggs year round. Using live observation, histology, electron microscopy and immunohistochemistry we have carried out a developmental analysis of Macrostomum sp. Cleavage (stages 1–2) of this species follows a modified spiral pattern and results in a solid embryonic primordium surrounded by an external yolk layer. During stage 3, cells at the anterior and lateral periphery of the embryo evolve into the somatic primordium which gives rise to the body wall and nervous system. Cells in the center form the large yolk-rich gut primordium. During stage 4, the brain primordium and the pharynx primordium appear as symmetric densities anterior-ventrally within the somatic primordium. Organ differentiation commences during stage 5 when the neurons of the brain primordium extend axons that form a central neuropile, and the outer cell layer of the somatic primordium turns into a ciliated epidermal epithelium. Cilia also appear in the lumen of the pharynx primordium, in the protonephridial system and, slightly later, in the lumen of the gut. Ultrastructurally, these differentiating cells show the hallmarks of platyhelminth epithelia, with a pronounced apical assembly of microfilaments (terminal web) inserting at the zonula adherens, and a wide band of septate junctions underneath the zonula. Terminal web and zonula adherens are particularly well observed in the epidermis. During stage 6, the somatic primordium extends around the surface dorsally and ventrally to form a complete body wall. Muscle precursors extend myofilaments that are organized into a highly regular orthogonal network of circular, diagonal and longitudinal fibers. Neurons of the brain primordium differentiate a commissural neuropile that extends a single pair of ventro-lateral nerve trunks (the main longitudinal cords) posteriorly. The primordial pharynx lumen fuses with the ventral epidermis anteriorly and the gut posteriorly, thereby generating a continuous digestive tract. The embryo adopts its final shape during stages 7 and 8, characterized by the morphallactic lengthening of the body into a U-shaped form and the condensation of the nervous system.Edited by J. Campos-Ortega     

The retinoic acid signaling pathway regulates anterior/posterior patterning in the nerve cord and pharynx of amphioxus,a chordate lacking neural crest

Amphioxus, the closest living invertebrate relative of the vertebrates, has a notochord, segmental axial musculature, pharyngeal gill slits and dorsal hollow nerve cord, but lacks neural crest. In amphioxus, as in vertebrates, exogenous retinoic acid (RA) posteriorizes the embryo. The mouth and gill slits never form, AmphiPax1, which is normally downregulated where gill slits form, remains upregulated and AmphiHox1 expression shifts anteriorly in the nerve cord. To dissect the role of RA signaling in patterning chordate embryos, we have cloned the single retinoic acid receptor (AmphiRAR), retinoid X receptor (AmphiRXR) and an orphan receptor (AmphiTR2/4) from amphioxus. AmphiTR2/4 inhibits AmphiRAR-AmphiRXR-mediated transactivation in the presence of RA by competing for DR5 or IR7 retinoic acid response elements (RAREs). The 5' untranslated region of AmphiTR2/4 contains an IR7 element, suggesting possible auto- and RA-regulation. The patterns of AmphiTR2/4 and AmphiRAR expression during embryogenesis are largely complementary: AmphiTR2/4 is strongly expressed in the cerebral vesicle (homologous to the diencephalon plus anterior midbrain), while AmphiRAR expression is high in the equivalent of the hindbrain and spinal cord. Similarly, while AmphiTR2/4 is expressed most strongly in the anterior and posterior thirds of the endoderm, the highest AmphiRAR expression is in the middle third. Expression of AmphiRAR is upregulated by exogenous RA and completely downregulated by the RA antagonist BMS009. Moreover, BMS009 expands the pharynx posteriorly; the first three gill slit primordia are elongated and shifted posteriorly, but do not penetrate, and additional, non-penetrating gill slit primordia are induced. Thus, in an organism without neural crest, initiation and penetration of gill slits appear to be separate events mediated by distinct levels of RA signaling in the pharyngeal endoderm. Although these compounds have little effect on levels of AmphiTR2/4 expression, RA shifts pharyngeal expression of AmphiTR2/4 anteriorly, while BMS009 extends it posteriorly. Collectively, our results suggest a model for anteroposterior patterning of the amphioxus nerve cord and pharynx, which is probably applicable to vertebrates as well, in which a low anterior level of AmphiRAR (caused, at least in part, by competitive inhibition by AmphiTR2/4) is necessary for patterning the forebrain and formation of gill slits, the posterior extent of both being set by a sharp increase in the level of AmphiRAR. Supplemental data available on-line     

Functional analysis of a specialized prey processing behavior: winnowing by surfperches (Teleostei: Embiotocidae).

Several surfperches (Embiotocidae), including the black surfperch, Embiotoca jacksoni, exhibit a specialized prey handling behavior known as winnowing, in which ingested food and non-nutritive debris are separated within the oropharyngeal cavity. Prey items are swallowed, and unpalatable material is ejected from the mouth. Winnowing is believed to play an important role in the partitioning of food resources among sympatric embiotocids. We present a mechanistic model for this separative prey processing based on high-speed video analysis, cineradiography, electromyography, and buccal and opercular cavity pressure transducer recording. Winnowing by embiotocids is characterized by premaxillary protrusions repeated cyclically with reduced oral gape. Protrusion is accompanied by depression of the hyoid apparatus and adduction of the opercula. Alternating expansion and contraction of the buccal and opercular cavities generate regular pressure waveforms that indicate bidirectional water flow during processing. Separation of food from debris by Embiotoca jacksoni occurs in three phases. The prey-debris bolus is transported anteriorly and posteriorly within the oropharyngeal cavity and is then sheared by the pharyngeal jaws. Mechanical processing is complemented by the rinsing action of water currents during hydraulic prey transport. The feeding apparatus of Embiotoca jacksoni is functionally versatile, although not obviously specialized relative to that of nonwinnowing surfperches. Protrusion of the premaxillae and depression of the hyoid apparatus are critical to both prey capture and subsequent prey processing. The pharyngeal jaws exhibit kinematic patterns during separation of food from debris distinct from those observed during mastication of uncontaminated prey. This behavioral flexibility facilitates resource partitioning and the coexistence of E. jacksoni in sympatric embiotocid assemblages.     

南海轮盘虫属(单殖吸虫, 分室科) 一新种及一新记录种

记述采自中国南海日本红娘鱼（Lepidotrigla japonica）鳃上的单殖吸虫1新种:红娘鱼轮盘虫（Trochopus lepidotrigla sp.nov.）,以及绿鳍鱼（Chelidonichthys kumu）鳃上的1中国新记录种:戈尔韦轮盘虫（Trochopus gaillimhe Little,1929）。新种红娘鱼轮盘虫以其后吸器上3对锚钩特殊的形态大小而区别于该属的近似种。所有标本均保存于华南师范大学生命科学学院鱼类寄生虫学研究室。     

Ultrastructure of the pharynx of Prorhynchus (Platyhelminthes, Lecithoepitheliata)

The pharynx variabilis of Prorhynchus is strongly muscular, with a small pharyngeal fold and a thin surrounding sheath. There is one row of inner longitudinal musclcs, up to six rows of inner circular muscles, many radial muscles, one row of outer circular and one row of outer longitudinal muscles, with no sphincter muscle groups. Three kinds of secretion, produced in a cluster of gland cell bodies posterior to the pharynx, enter the pharynx wall. They travel anteriorly in ducts and two kinds unite in a common duct just prior to discharging into the anterior region of the pharynx lumen. The perikarya of lumen epithelial cells lie within the pharynx musculature and, at the anterior and posterior margins of the pharynx, external to the pharynx. Bundles of ciliated receptors are numerous at the anterior and posterior constrictions. Similarities in the ultrastructure of flame bulbs of Rhabdocoela and Lecithoepitheliata suggest a relationship between these groups. However, the usefulness of pharynx ultrastructure for platyhelminth phylogeny cannot be assessed until complete ultrastructural studies of various groups of Rhabdocoela have been made.     

Ventilation and the origin of jawed vertebrates: a new mouth

This study investigates the origin of jaws by re-assessing homologies between the oropharyngeal regions of Agnatha and Chondrichthyes. In accordance with classical theory, jaws are interpreted as the most anterior arches of the ventilatory branchial basket. It is proposed that jaws first enlarged for a ventilatory function, i.e. closing the jaws prevented reflux of water through the mouth during forceful expiration. Next, they enlarged further to grasp prey in feeding. As they enlarged, the jaws tilted forward, squeezing the ancestral oral cavity in front of them ('old mouth') into a slit between the jaws and lips. Simultaneously, the anterior part of the pharynx behind the jaws was pulled forward and became a 'new mouth' (the buccal part of the buccopharyngeal cavity of gnathostomes). During the transition to gnamostomes, the premandibular cheeks and lips of the old mouth remained in place, and are represented in ammocoete lampreys, chimaeroids, and sharks. The stages in the evolution of gnathostomes, driven by selection for increasing activity, are modelled as: ancestral vertebrate (with unjointed branchial arches) to early pre-gnathostome (jointed internal arches and stronger ventilation) to late pre-gnadiostome (with mouth-closing, ventilatory 'jaws') to early gnathostome (feeding jaws).     

Ultrastructure of the anterior alimentary tract of a monogenean, Diclidophora merlangi

The anterior alimentary tract of Diclidophora merlangi is composed of a complex series of morphologically distinct epithelia interconnected by septate desmosomes and penetrated by the openings of numerous unicellular glands. The mouth and buccal cavity are lined by an infolding of modified body tegument, distinguished by uniciliate sense receptors, buccal gland openings, and in the buccal region by a dense, spiny appearance. The prepharynx is covered by an irregularly folded epithelium and, for part of its length, by the luminal cytoplasm of the prepharyngeal gland cells. The epithelium is syncytial and pleiomorphic, and regional variation in structure is common. A separate epithelium invests the lips of the pharynx and its free surface is greatly amplified by numerous, dense lamellae of varying dimensions. The lip epithelium is continuous with cytoplasmic processes of cells located external to the pharynx. A further, distinct epithelium borders the pharynx lumen and is composed of discrete cytoplasmic units connected by short septate desmosomes. The oesophagus is lined by a modified caecal epithelium, lacking haematin cells, and, in places, is perforated by the openings of oesophageal gland cells; it is continuous with the syncytial connecting tissue of the gut caeca.     

New buccinator myomucosal island flap: anatomic study and clinical application

The authors studied the vascular anatomy of the buccinator muscle by dissecting fresh cadavers. The anatomy of the buccal branches of the facial artery consistently confirmed the existence of a posterior buccal branch, a few inferior buccal branches, and anterior buccal branches to the posterior, inferior, and anterior portions of the buccinator. The buccal artery and posterior buccal branch anastomose to each other and ramify over the muscle. Several veins originate from the lateral aspect of the muscle, converge into the buccal venous plexus, and drain into the facial vein (from two to four tributaries) or into the pterygoid plexus and the internal maxillary vein (from the buccal vein). These vessels and nerves enter the posterior half of the buccinator posterolaterally. The facial artery and vein are located at variable distances from each other around the oral commissure and the nasal base. Two patterns of buccinator musculomucosal island flaps supplied by these buccal arterial branches are proposed in this article. The buccal musculomucosal neurovascular island flap (posteriorly based), supplied by the buccal artery, its posterior buccal branch, and the long buccal nerve, can be passed through a tunnel under the pterygomandibular ligament for closure of mucosal defects in the palate, pharyngeal sites, the alveolus, and the floor of the mouth. The buccal musculomucosal reversed-flow arterial island flap (superiorly based), supplied by the distal portion of the facial artery through the anterior buccal branches, can be used to close mucosal defects in the anterior hard palate, alveolus, maxillary antrum, nasal floor and septum, lip, and orbit. The authors have used the flaps in 12 patients. There has been no flap necrosis, and results have been satisfactory, both aesthetically and functionally.     

Morphology of a novel glandular epithelium lining the infrabuccal cavity in the ant Monomorium pharaonis (Hymenoptera, Formicidae)

A novel glandular epithelium lining the infrabuccal cavity and anterior pharynx is described in both workers and queens of the pharaoh's ant Monomorium pharaonis. The infrabuccal cavity, connected with the buccal tube, forms a ventral outgrowth of the anterior pharynx, and as such displays the tegumental lining with a cuticle and an epithelial layer. In its dorsal region, the cavity's epithelium reaches a thickness of approx. 11–12 μm in both workers and queens, which is considerably thicker than the epithelium lining the rest of the infrabuccal cavity. Also the possible role of the infrabuccal gland is discussed.     

Fine structure of the Caenorhabditis elegans secretory-excretory system

The secretory-excretory system of C. elegans, reconstructed from serial-section electron micrographs of larvae, is composed of four cells, the nuclei of which are located on the ventral side of the pharynx and adjacent intestine. (1) The pore cell encloses the terminal one-third of the excretory duct which leads to an excretory pore at the ventral midline. (2) The duct cell surrounds the excretory duct with a lamellar membrane from the origin of the duct at the excretory sinus to the pore cell boundary. (3) A large H-shaped excretory cell extends bilateral canals anteriorly and posteriorly nearly the entire length of the worm. The excretory sinus within the cell body joins the lumena of the canals with the origin of the duct. (4) A binucleate, A-shaped gland cell extends bilateral processes anteriorly from cell bodies located just behind the pharynx. These processes are fused at the anterior tip of the cell, where the cell enters the circumpharyngeal nerve ring. The processes are also joined at the anterior edge of the excretory cell body, where the excretory cell and gland are joined to the duct cell at the origin of the duct. Secretory granules may be concentrated in the gland near this secretory-excretory junction. Although the gland cells of all growing developmental stages stain positively with paraldehyde-fuchsin, the gland of the dauer larva stage (a developmentally arrested third-stage larva) does not stain, nor do glands of starved worms of other stages. Dauer larvae uniquely lack secretory granules, and the gland cytoplasm is displaced by a labyrinth of large, transparent spaces. Exit from the dauer stage results in the return of active secretory morphology in fourth-stage larvae.     

Anatomy of the mouthparts and digestive tract during feeding in larvae of the parasitoid wasp Trichogramma australicum Girault (Hymenoptera : Trichogrammatidae)

To aid in the development of artificial diets for mass rearing parasitioids, we investigated the anatomical changes in the digestive tract during feeding behaviour of larval Trichogramma australicum (Hymenoptera : Trichogrammatidae). Larvae begin to feed immediately upon eclosion and feed continuously for 4 h until replete. Feeding is characterised by rhythmic muscle contractions (ca 1 per s) of the pharynx. Contractions of the pharyngeal dilator muscles lift the roof of the lobe-shaped pharynx away from the floor of the chamber, opening the mouth and pumping food into the pharyngeal cavity. Another muscle contraction occurs about 0.5 s later, forcing the bolus of food through the oesophagus and into the midgut. The junction of fore- and midgut is marked by a cardiac valve. The midgut occupies most of the body cavity and is lined with highly vacuolated, flattened cells and a dispersed layer of muscle cells. In the centre of the midgut, food has the appearance of host egg contents. Food near the midgut epithelial cells has a finer, more homogeneous appearance. This change in the physical properties of the gut contents is indicative of the digestion process. In the prepupa, where digestion is complete, the entire gut contents have this appearance. After eclosion, the vitelline membrane remains attached to the posterior end of the larva. We believe this attachment to be adaptive in two ways: (1) to anchor the larva against the movements of its anterior portion, thereby increasing the efficiency of foraging within the egg; and (2) to prevent a free-floating membrane from clogging the mouthparts during ingestion.     

Terrestrial feeding in the Mudskipper Periophthalmus (Pisces: Teleostei): A cineradiographic analysis

Mudskipping gobies (Periophthalminae) are among the most terrestrial of amphibious fishes. Specializations associated with terrestrial prey capture and deglutition have been studied in Periophthalmus koelreuteri by light and X-ray cinematography which permits direct visualization of pharyngeal jaw movement during deglutition. Anatomical specializations of the pharyngeal jaws are described and include depressible teeth, a large ventral process on ceratobranchial five, and muscular modifications.
Multiple terrestrial feedings occur by Periophthalmus without a return to the water, and cineradiography reveals that the buccal cavity is often filled with air during terrestrial excursions in contrast to some previous hypotheses. Transport of the prey into the oesophagus occurs primarily by anteroposterior movement of the upper pharyngeal jaw. The lower pharyngeal jaw plays a limited role in food transport and may serve primarily to hold and position prey. The bite between upper and lower pharyngeal jaws occurs between the anterior teeth, and both jaws are protracted together during raking of food into the oesophagus. Functional specializations correlated with terrestrial feeding include obligatory use of pharyngeal jaws for swallowing even small prey items and positioning of the prey in the pharynx by pharyngeal jaw and hyoid movements alone.
This analysis of terrestrial feeding allows hypotheses of design constraints imposed by the aquatic medium on fishes to be raised and tested.     

Fate of the anterior neural ridge and the morphogenesis of the xenopus forebrain

The fate of the anterior neural ridge was studied by following the relative movements of simultaneous spot applications of DiI and DiO from stage 15 through stage 45. These dye movements were mapped onto the neuroepithelium of the developing brain whose shape was gleaned from whole-mount in situs to neural cell adhesion molecule and dissections of the developing nervous system. The result is a model of the cell movements that drive the morphogenesis of the forebrain. The midanterior ridge moves inside and drops down along the most anterior wall of the neural tube. It then pushes forward a bit, rotates ventrally during forebrain flexing, and gives rise to the chiasmatic ridge and anterior hypothalamus. The midanterior plate drops, forming the floor of the forebrain ventricle, and, keeping its place behind the ridge, it gives rise to the posterior hypothalamus or infundibulum. The midlateral anterior ridge slides into the lateral anterior wall of the neural tube and stretches laterally into the optic stalk and retina, and then rotates into a ventral position. The lateral anterior ridge converges to the most anterior part of the dorsal midline during neural tube closure, then rotates anteriorly, and gives rise to telencephalic structures. Whole-mount bromodeoxyuridine labeling at these stages showed that cell division is widespread and relatively uniform throughout the brain during the late neurula and early tailbud stages, but that during late tailbud stages cell division becomes restricted to specific proliferative zones. We conclude that the early morphogenesis of the brain is carried out largely by choreographed cell movements and that later morphogenesis depends on spatially restricted patterns of cell division. © 1995 John Wiley & Sons, Inc.