Ultrastructure of gill bars of Branchiostoma lanceolatum with special reference to gill skeleton and blood vessels (Cephalochordata)

Summary The skeletal rods of the gill bars of Branchiostoma have been examined histochemically and electron microscopically. The rods are composed of 15-nm thick filaments which are interconnected by 10-nm thick and 15-nm long cross-linkages. The filaments appear to consist of structural proteins that are totally different from the proteins of the collagen fibrils. The cross-linkages between the filaments consist of acid mucopolysaccharides, and probably include chondroitin sulphate. The fine structure of blood vessels in the gill bars has been studied in uninjected specimens and in those intravascularly injected with either india ink or horseradish peroxidase. Blood vessels surrounded by basal laminae of delimiting epithelia or simply surrounded by connective tissue material are present in the gill bars. Very characteristic blood cells are normally found in these vessels. Furthermore, when either india ink or horseradish peroxidase is injected via the aorta and the endostylar vessel, irregular slitlike channels can be seen in the connective tissue. These channels are in open connection with the blood vessels and are thus a part of the vascular system.Supported by a grant from the Danish Natural Science Research Council     

The Oral Papilla of the Lancelet Larva (Branchiostoma lanceolatum) (Cephalochordata)

The oral papilla is a prominent larval organ in the lancelet, which develops early during ontogenesis and disappears completely at metamorphosis. Electron microscopic studies indicated that the prevailing theories of its function are unlikely. Its cells lack the cytological characteristics of sensory or mucus producing cells, and the organ is not equipped with a tuft of flagella. It was not possible to reveal the function of the papilla, but its cells seem to be involved in a pronounced substance transport through the basal cell membrane as well as in the cytoplasm. Apical specializations indicate exo- or endocytotic activity and vesicles imply some exchange also between papilla cells and the sea water.     

The Wheel Organ and Hatschek's Groove in the Lancelet,Branchiostoma lanceolatum (Cephalochordata)

The wheel organ is a specialized epithelium in the roof and sides of the adult lancelet oral cavity. It borders the oral epithelium proper, separated by a thin strip of margin cells which are not ciliated but contain a few large dense-cored vesicles apically. The wheel organ cells are tall and strongly ciliated and have dark, heterochromatin-rich nuclei. Dorsally, and slightly paramedially, the organ is further specialized, forming the so-called Hatschek's groove (pit), which consists of two ciliated cell types. The first type synthesizes a dense granular material, the granules being approximately 95 nm in diameter. This is stored basally and apparently it is also released through the basal cell membrane into the blood cavities. The cells at the bottom of Hatschek's groove have peculiar rod-shaped apical cellular regions. Each cell bears one tall cilium surrounded by microvilli and it is apparently involved in the production of secretory material into the groove. It is evident that the histology, and probably also the function, of the wheel organ and its groove is much more complex than hitherto believed.     

The myosepta in Branchiostoma lanceolatum (Cephalochordata): 3D reconstruction and microanatomy

Zoomorphology - Myosepta have been subject to comparative and evolutionary studies in aquatic groups of the Craniata, because they are likely to play a role in transmission of muscular forces to...     

The ultrastructure of the blood vessels of Branchiostoma lanceolatum (Pallas) (Cephalochordata)

Summary The ultrastructure of the blood vessels in the caudal region of Branchiostoma is described in specimens injected with indian ink. None of the vessels have endothelial cells delimiting the luminal surface. The vessels are delimited either by dense connective tissue or by the characteristic basement lamella underneath the basal lamina of the myocoelic epithelium. It is proposed that the main blood flow in the caudal region follows different pathways depending on the activity of the animal. During swimming the muscle activity of the caudal muscles may have the effect that more blood flows from the aorta to the myoseptal plexi and is drained to the caudal vessel. In the resting animal it is possible that the blood flow through the myosepta is insignificant, and that the caudal blood flow is more or less restricted to the direct connections between the aorta and the caudal vessel: the dorsoventral anastomosis and the segmental connecting vessels.Supported by a grant from the Danish Natural Science Research Council     

The ultrastructure of the blood vessels of Branchiostoma lanceolatum (Pallas) (Cephalochordata)

Summary The ultrastructure of the blood vessels of Branchiostoma has been studied using selected characteristic vessels as examples. It is shown that the vessels are a part of the original blastocoelic cavity and are delimited either by the basal laminae of adjacent epithelia or by connective tissue developed in the blastocoelic space. A brief account of the kinds of connective tissue is given. The observed contractility of some vessels depends on two types of contractile filaments situated in the basal part of the surrounding coelomic epithelia. Amoebocytelike cells are present in the blood. They may sometimes lie in contact with the wall of the vessels or with each other, but never form a typical endothelium with junctional complexes and a basal lamina of its own. Actually, there is no endothelium in any part of the vascular system. It is suggested that the term endothelium should be reserved for a closed cellular lining (with junctions) on the luminal side of the vessel wall, standing on a basal lamina of its own and forming a barrier for the exchange between blood and surrounding tissue. It is concluded that the principal structure of the vascular system of Branchiostoma is different from that of vertebrates, but the same as that of other coelomate invertebrates. The blood vessels in these animals are typically delimited directly by a basal lamina secreted by epithelia (epidermal, coelomic or intestinal) lying peripheral to this lamina, and a true endothelium is not present (with a few questionable exceptions).Abbreviations ac atrial cavity - ace atrial epithelium - ao aorta - ap atrial plexus - ax axon bundle - bc blood cell - bl basal lamina - bl ₁ basal lamina of intestinal epithelium - bl ₂ basal lamina of visceral coelomic epithelium - bl ₃ basal lamina of parietal coelomic epithelium - bl ₄ basal lamina of atrial epithelium - bll basement lamella - cf contractile filaments - co coelomic cavity - coe coelomic epithelium - coe _p parietal coelomic epithelium - coe _v visceral coelomic epithelium - ct dense connective tissue - dv longitudinal dorsal vessel - ep epidermis - epe epipharyngeal groove epithelium - epg epipharyngeal groove - fb fibroblast (?) - fi collagen fiber - fl fibril layer - go gonad - hd hemidesmosome - ie intestinal epithelium - in intestine proper - ip intestinal plexus - iv afferent intestinal vessel - ld liver diverticulum - lu vascular lumen - me myocoelic epithelium - ml muscle lamella - mp myoseptal plexus - ms myoseptum - my myomer - myc myocoelic cavity - nc notochord - ns notochordal sheath - ph pharynx - suc subchordal coelom - sv subintestinal vessel - svv segmental ventral vessel - vv longitudinal ventral vessel Supported by a grant from the Danish Natural Science Research Council     

The fine structure of lamellate cells in the brain of amphioxus (Branchiostoma lanceolatum,Cephalochordata)

Summary The lamellate cells of amphioxus have round nuclei, and cytoplasm with many mitochondria and a large amount of glycogen. Each of these cells projects a highly modified, branched cilium into the central canal, where it characteristically forms lamellar structures. Primary branches and secondary lamellae often contain accessory microtubules that are not derived from the axonema. The functional and evolutionary significance of this cell type is discussed in relation to the ciliary photoreceptors found in other chordates.This work is dedicated to Professor A. Carrato, Universidad Complutense, on the occasion of his 80th birthday     

Vergleichende histophysiologische Tracer-Untersuchungen an verschiedenen Organsystemen von Branchiostoma lanceolatum (Cephalochordata) und Brachydanio rerio (Teleostei)

Zusammenfassung In vergleichend autoradiographischen Untersuchungen wurde der Einbau von percutan applizierten 3H-Uridin, 3H-Histidin und 3H-Glucose in die wichtigsten Organsysteme (Epidermis, ZNS, Muskeln, Chorda, Leber, Kiemendarm, Darm) von Branchiostoma lanceolatum (Acranier) und Brachydanio rerio (Teleosteer) nach Inkorporationszeiten von 11 min bis zu 7 Tagen verfolgt. Der Stoffwechsel der markierten Substanzen in den einzelnen morphologisch miteinander zu homologisierenden Organen war bei den beiden Spezies sehr ähnlich, bei Branchiostoma allerdings (mit Ausnahme des ZNS) 4–5mal stärker als bei Brachydanio. Bei dem letzteren wurde außerdem eine zeitliche Verzögerung in der Tracer-Aufnahme (lag-Phase) beobachtet. Insbesondere der ZNS-Stoffwechsel von Acraniern zeigte ähnliche Charakteristika wie der von Vertebraten: Verbleib des Hauptanteils der neusynthetisierten RNS im Perikaryon, axonalen Protein-Transport, Vorwiegen der Glykogensynthese in den Nervenfaserendformationen. Allerdings fanden sich im ZNS von Branchiostoma niedrigere Stoffwechselraten als im ZNS von Brachydanio.

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Comparative histophysiological investigations of different organs in Branchiostoma lanceolatum (Cephalochordata) and Brachydanio rerio (Teleostei)

Summary Incorporation of 3H-uridine, 3H-histidine and 3H-glucose into some organs (epidermis, CNS, muscles, spinal cord, notochord, liver, gills, intestine) of Branchiostoma lanceolatum (Acrania) and Brachydanio rerio (Teleostei) was investigated by means of comparative autoradiograms following incorporation periods of 11 min to 7 days. The metabolism of the labeled substances in the various homologous organs examined was quite similar, although it was 4 to 5 times higher in Branchiostoma than in Brachydanio; in the latter there was also a delay of tracer incorporation of about 3 hrs, a so-called lag-phase. In particular the metabolism of the CNS of Branchiostoma showed the same characteristics as the CNS of vertebrates, e. g. storage of neuronally synthesized RNA in the neuronal perikarya, axonal flow of proteins, glycogen synthesis in nerve endings. However, metabolic activity of the CNS was lower in Branchiostoma.

Mit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft.     

The Histochemistry and Fine Structure of the Nutritional Reserves in the Fin Rays of a Lancelet,Branchiostoma lanceolatum (Cephalochordata = Acrania)

Abstract Adults of the European lancelet were collected at Banyuls-sur-Mer (Mediterranean France) in mid-spring, shortly before the onset of the breeding season. The dorsal and ventral fin rays were studied by light microscopic histochemistry and by transmission electron microscopy (TEM). Each fin ray is a mass of extracellular material that accumulates beneath the mesothelium of a fin box coelom. The fin ray material is rich in lipids, proteins, and neutral mucopolysaccharides. TEM reveals no lipid droplets in this material, which consists entirely of a packed mass of 15–20 nm granules of medium electron density. It is likely that these granules consist of glycoproteins or glycolipoproteins. Our results are consistent with the proposal of Azariah (1965, Journal of the Marine Biological Association of India 7: 459–661) that lancelet fin rays are nutritional reserves supporting gametogenesis during the breeding season.     

New complete mitochondrial DNA sequence of the lancelet Branchiostoma lanceolatum (Cephalochordata) and the identity of this species' sequences

Three mitochondrial (mt) genes were sequenced for two Atlantic lancelet species, Branchiostoma lanceolatum and B. floridae, to examine a serious discrepancy among previously published results of molecular studies: substantial sequence difference in a nuclear gene vs. virtual identity in the mt genome sequence. The results revealed that three mt genes of B. lanceolatum, collected from Helgoland in the North Sea and Naples in the Mediterranean, were quite diverged from those of B. floridae, collected from Tampa Bay, Florida. Therefore, the previously recognized identity in the mt genome between the two species is attributable to misidentification of materials used. To correct this misleading information, the complete mtDNA sequence of B. lanceolatum was determined for an individual from Helgoland.     

Branchiostoma japonicum and B. belcheri are distinct lancelets (Cephalochordata) in Xiamen waters in China

Lancelets in Xiamen were reported as Branchiostoma belcheri in 1932, and subsequently were believed to comprise a single species. However, recent studies revealed that Xiamen lancelets actually represent two species, B. belcheri and B. japonicum. We observed thousands of lancelets from Xiamen beach to recognize these two species. Our observations showed that at least three morphological characters distinguish them: 1) the rostral fin is slightly round with the end obtuse in B. belcheri but elliptic with the end cuspate in B. japonicum; 2) the number of preanal fin-chambers is more than 80 in B. belcheri but less than 64 in B. japonicum, and the chambers are slender in the former but stout in the latter; 3) the caudal fin of B. belcheri is narrower than that of B. japonicum, and the angle between the dorsal and super-caudal fins, and between preanal and sub-caudal fins, is obtuse in B. belcheri but acute in B. japonicum. We also provide some ecological and distributional evidence to support the conclusion that there are two separate species in Xiamen waters.     

Acrosome reaction in spermatozoa from the amphioxus Branchiostoma belcheri (Cephalochordata, Chordata)

The formation of an acrosomal process at acrosomal exocytosis in spermatozoa of the amphioxus was described in the present report for the first time. A non-reacted acrosome was located in front of the nucleus, where a cup-shaped acrosomal vesicle covered a conical accumulation of subacrosomal material. When naturally spawned spermatozoa were treated with a calcium ionophore, ionomycin, the acrosomal vesicle opened at the apex and an acrosomal process was projected. The process exhibited a filamentous structure. The reaction followed the mode typically seen in marine invertebrates. These observations suggest that the features and function of the acrosome of amphioxus, whose position is on the border between invertebrates and vertebrates, reflect their ecological adaptation and phylogenic position.     

The connection between spinal cord and notochord in Amphioxus (Branchiostoma lanceolatum)

Summary Silver impregnation of nerves, histochemical reactions for acetylcholinesterase, and electron microscopy reveal an efferent innervation of the notochord in amphioxus. Extensions of the notochordal lamellae end in groups (the notochordal horns) just below the ventro-lateral surface of the spinal cord where they are opposed to large nerve terminals originating as short collaterals of axons running longitudinally in the nerve cord. This neurochordal junction resembles an ordinary neuro-muscular junction in several respects and is interpreted as a part of the muscular system found in the notochord itself. Acknowledgement. The author is indebted to the staffs at the Marine laboratory in Plymouth and the Biological station at Helgoland for supply of material. The expert advices and criticism of Q. Bone, Ph. D., Plymouth, and Dr. U. Welsch, Kiel, are also greatly appreciated.     

On Branchiostoma californiense (Cephalochordata) from the Gulf of Nicoya estuary, Costa Rica

The cephalochordates are represented by the lancelets, of which species of the genus Branchiostoma are the best known. In recent years, these organisms have been the center of activity of studies focusing on the phylogenetic relationships of the chordates. In 1980, a survey of the benthos at 48 stations in the Gulf of Nicoya estuary, Pacific coast of Costa Rica, yielded 265 specimens of the lancelet Branchiostoma californiense. A total of 48 specimens was also collected at an intertidal flat in the mid upper estuary. Of the 48 subtidal stations, only eight had B. californiense, and these sites all had a sand fraction above 72%. The remaining stations ranged in their sand content from as low as 1% to as high as 92%, with an average of 25.9%, with 29 stations having a sand content lower than 72%. Lower salinities and muddy sediments may limit the distribution of the lancelet further upstream. This information is useful when changes over decades in the ecology of the estuary need to be evaluated against the background of local, regional, and global dynamics.     

Nocturnal behavior and rhythmic period gene expression in a lancelet, Branchiostoma lanceolatum

The authors here present the first anatomical, molecular biological, and ethological data on the organization of the circadian system of a lancelet, Branchiostoma lanceolatum, a close invertebrate relative of vertebrates. B. lanceolatum was found to be a nocturnal animal and, since its rhythmic activity persisted under constant darkness, it also appears to possess an endogenous, circadian oscillator. The authors cloned a homolog of the clock gene Period (Per), which plays a central (inhibitory) role in the biochemical machinery of the circadian oscillators of both vertebrates and protostomians. This gene from B. lanceolatum was designated as amphiPer. Both the sequence of its cDNA and that of the predicted protein are more similar to those of the Per paralogs of vertebrates than to those of the single protostomian Per gene. A strong expression of amphiPer was found in a small cell group in the anterior neural tube. The amphiPer mRNA levels fluctuated in a rhythmic manner, being high early in the day and low late at night. The authors' data suggest a homology of the amphiPer expessing cells to the suprachiasmatic nucleus of vertebrates.     

Spermatozoal Ultrastructure: Evolution and Congruence with a Holomorphological Phylogeny of the Oligochaeta (Annelida)

Plesiomorph characters for the oligochaete spermatozoon are proposed. The chief trends from these plesiomorphies have been elongation of the acrosome and its tube; withdrawal of the primary acrosome vesicle and the axial rod into the acrosome tube and development of a capitulum; development of connectives from the secondary tube to the axial rod (though there is some possibility that the reverse, absence of connectives, is plesiomorph); detorting and shortening of the midpiece (or possibly, again, the reverse) with an increase in numbers of mitochrondria from the plesiomorph four to eight; modification of the base of the tube to form a hen of variable form; and, in one line (lumbricids) flattening of the tip of the nucleus and correspondingly of the limen. Sperm ultrastructure, examined for 9 oligochaete families, corresponds well with taxonomic and phylogenetic groupings recently recognized by the author. However, convergent similarity of the phreodrilid sperm to that of the Lumbricina suggests a corresponding alteration of fertilization biology in the phreodrilids. The results indicate that the Haplotaxidae lie at the base of the opisthopores, though they do not unequivocally contraindicate acceptance of a Haplotaxis-like form as a stem form of the Haplotaxida (opisthopores and Haplotaxidae) and Tubificida. An even more basal position for prosopores, now represented by the Lumbriculida, cannot yet be dismissed.