ABSTRACT The unpaired Hatschek' s nephridium is the largest and most anterior of the nephridia in the body of Branchiostoma virginiae. Its single collecting tubule lies on the left side of the notochord along the left anterior aorta. The nephridium extends from the anterior vestibule to a point immediately posterior to the velum where it opens into the endodermal pharynx. Along its length, the collecting tubule gives off clusters of filtration cells (cyrtopodocytes) that radiate from the tubule and enter small urinary capsules of coelomic origin. The capsules lie directly on the wall of the aorta. Filtration-cell perikarya and mesothelial cells comprise the epithelial lining of the capsules. The basal surface of each filtration cell produces podocyte-like pedicels over the wall of the aorta and adjacent connective tissue. Apically, each filtration cell resembles a solenocyte. The apical surface bears a flagellum enclosed in a collar of 10 long microvilli, which are bridged by extracellular matrix. The fla...

Journal of Zoological Systematics and Evolutionary ResearchVolume 21, Issue 3 p. 181-193 Comparative ultrastructure of the bryozoan funiculus: A blood vessel homologue Karen J. Carle, Department of Zoology, Clemson University, Clemson, South Carolina, USA Museum of Comparative Zoology, Harvard University, Cambridge, Ma. 02138.Search for more papers by this authorE. E. Ruppert, Department of Zoology, Clemson University, Clemson, South Carolina, USASearch for more papers by this author Karen J. Carle, Department of Zoology, Clemson University, Clemson, South Carolina, USA Museum of Comparative Zoology, Harvard University, Cambridge, Ma. 02138.Search for more papers by this authorE. E. Ruppert, Department of Zoology, Clemson University, Clemson, South Carolina, USASearch for more papers by this author First published: September 1983 https://doi.org/10.1111/j.1439-0469.1983.tb00286.xCitations: 30 AboutPDF 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 Share a linkShare onEmailFacebookTwitterLinked InRedditWechat Citing Literature Volume21, Issue3September 1983Pages 181-193 RelatedInformation

The present study investigates some aspects of the digestive biology and physiological energetics of the Florida lancelet, Branchiostoma floridae. Florida lancelets are able to remove 47.2–56.9% of the energy from a diet of mixed algae. The respiration rate is 0.100 mL O2 (STPD) h− 1 g− 1 (wet), which estimates a metabolic rate of 0.248 J h− 1, at an average body mass of 0.125 g (wet). Published values of the chlorophyll a concentration in its natural habitat indicate that a 125 mg lancelet would need to filter 0.018–0.031 L h− 1 to remove sufficient food to support its resting metabolism. The filtration rate of lancelets has been reported as 0.138 L h− 1, indicating that the actual filtration rate is 4–7 times greater than the filtration rate needed to meet resting metabolic demands. It appears that lancelets have the potential to be raised in aquaculture, because their absorption efficiency and respiration rate are comparable to suspension-feeding invertebrates that have been successfully aquacultured.

Four chordate characters — dorsal hollow nerve cord, notochord, gill slits, and endostyle — are compared morphologically, molecularly, and functionally with similar structures in hemichordates to assess their putative homologies. The dorsal hollow nerve cord and enteropneust neurocord are probably homoplasies. The neurocord (= collar cord) may be an autapomorphy of Enteropneusta that innervates a unique pair of muscles, the perihemal coelomic muscles. Despite the apparent lack of organ-level homology, chordates and enteropneusts share a common pattern of neurulation that preserves a "contact innervation" between neuro- and myo-epithelia, which may be the primitive deuterostome pattern of neuromuscular innervation. The chordate notochord and hemichordate stomochord are probably homoplasies. Other potential notochord antecedents in hemichordates are examined, but no clear homolog is identified. The comparative morphology of notochords suggests that the "stack-of-coins" developmental stage, retained into adulthood only by cephalochordates, is the plesiomorphic notochord form. Hemichordate and chordate gill slits are probably homologs, but only at the level of simple ciliated circular or oval pores, lacking a skeleton, as occur in adults of Cephalodiscus spp., developmentally in some enteropneusts, and in many urochordates. Functional morphology, I 125 -binding experiments, and genetic data suggest that endostylar function may reside in the entire pharyngeal lining of Enteropneusta and is not restricted to a specialized midline structure as in chordates. A cladistic analysis of Deuterostomia, based partly on homologs discussed in this paper, indicates a sister-taxon relationship between Urochordata and Vertebrata, with Cephalochordata as the plesiomorphic clade.

Abstract Lancelets are filter feeding, fish-like, marine chordates that resemble anchovies. Although they are widely distributed in coastal areas of the U.S.A., especially in the Southeast, and have been used as a food source in other countries, the only nutritional analysis of lancelets was performed in 1941 on preserved specimens. We report nutritional data on freshly processed lancelets, including a proximate analysis, fatty acid profile, and amino acid profile. These data are preliminary because of the limited number of samples and time periods of collection, but they are important because no similar data exist for this potential food resource. Moisture composed 88.9% of the sample, protein 9.4%, ash 1.3%, and fat 0.7%. Carbohydrates, as estimated by subtraction from the total, are absent. Cholesterol was only 18.3 mg per 100 g sample. Omega-3 fatty acids composed 30% of total fatty acids or 0.58 g per 100 g sample of whole lancelets. The fatty acid profile reveals some similarities to that of vertebrate fishes as well as to invertebrate shellfish, but also reflects the unique nature of lancelets. An uncommon omega-3 fatty acid, 22:5, is prevalent in the lancelet profile in addition to 22:6 and 20:5. The fatty acid data also suggest that the diet of lancelets is diverse, consisting of phytoplankton and zooplankton. The amino acid profile, with glutamic acid, aspartic acid, and glycine as the most common residues, reflects the preponderance of muscle and collagen and the absence of cartilage and bone.

Lancelets of the genus Branchiostoma (amphioxus) are widespread and locally abundant filter-feeding animals in shallow coastal waters of the south-eastern US (up to 5000 ind/m2) and in temperate and tropical seas worldwide (up to 9000 ind/m2). Lancelets are consumed by bottom-dwelling fish and humans. As part of a larger project to aquaculture lancelets, an experiment was conducted to determine the range of diameters of suspended particles filtered and ingested by the Florida lancelet, Branchiostoma floridae (Chordata: Cephalochordata). After a period of starvation, animals were exposed to a suspension of tracer particles of seven different diameters (range 90–0.062 μm) and the protein, ferritin (0.012 μm) and their faeces were examined subsequently for the presence or absence of tracer. Particles ranging from 90–0.062 μm, but not ferritin, were filtered and ingested. Many of the 90 μm diameter particles, however, were excluded from entering the body by the oral cirri. Under experimental conditions, B. floridae filters and ingests particles in the range of ∼100–0.062 μm (microplankton to colloidal particles). This result suggests that the lancelet diet, like that of appendicularians, includes microbial as well as phytoplankton production.

Classical anatomical investigations of the spengelid enteropneust Schizocardium brasiliense suggested that the hypobranchial ridge in the ventral midline of the pharynx is a homolog of the chordate endostyle. A re-investigation of pharyngeal anatomy and histology of S. brasiliense does not support this homology. instead, the dorsal epibranchial ridge of the pharynx of S. brasiliense provides anatomical and histological correspondences with the ventral endostyle of chordates. The potential homology of a dorsal structure in Enteropneusta with a ventral one in Chordata is consistent with a recent evolutionary model for dorsal-ventral axis inversion in the evolution of chordates. Accepting this homology requires rejecting homology between the enteropneust stomochord and neurocord (collar cord) and the chordate notochord and nerve cord, respectively, but suggests a homology between the enteropneust ventral nerve cord and the chordate neural tube. We propose that functional inversion of the dorsal-ventral body axis occurred in the vertebrate clade and that the ancestor of the vertebrates lacked dorsal-ventral axis preference, as illustrated by the functional biology of protochordates. Moreover, body axis shifts may have occurred elsewhere in deuterostomes, particularly in the evolution of Echinodermata and Ascidiacea.

Introduction: Microscopic Anatomy of the Notochord, Heterochrony, and Chordate Evolution (E. Ruppert). Hemichordata (J. Benito & F. Pardos). Chaetognatha (G. Shinn). Urochordata: Ascidiacea (P. Burighel & R. Cloney). Cephalichordata (Acrania) (E. Ruppert). Indexes.

Primordial germ cells (PGCs) are described from the gonad of c. 2 cm juvenile Branchiostoma virginiae; early oocytes (c. 10 microm) and enlarging, previtellogenic oocytes (c. 35 microm) are described from the ovary of c. 5 cm adults. The germinal epithelium of the juvenile gonad and adult ovary is composed of both germinal and somatic cells. In the juvenile, somatic cells retain contact with the basal lamina of the germinal epithelium though their perikarya may be displaced towards the lumen; the germinal epithelium is, therefore, a simple but pseudostratified epithelium. In the adult ovary, somatic cells may lose contact with the basal lamina and the epithelium appears to become stratified. PGCs and oocytes are identified as germ cells by the presence of nuage. PGCs and oocytes are polarised epithelial cells. They rest on a basal lamina, extend apically towards a lumen, form adhering junctions with neighbouring cells, and exhibit apical-basal polarity. PGCs and early oocytes have an apical flagellum with an associated basal body, accessory centriole, and one or more striated rootlet fibres. The flagellum is surrounded by a collar of microvilli. Once oocytes begin to enlarge and bulge basally into the connective tissue layer, the flagellum is lost, but the basal bodies and ciliary rootlets are present at the apex of 35 microm oocytes. Similarities of the oogenic pattern in cephalochordates and echinoderms indicate that the establishment of egg polarity in deuterostomes is influenced by the polarity of the germinal epithelium.

The viviparous holothuroid Synaptula hydriformis, a simultaneous hermaphrodite, broods its young in the coelom and releases young year round. Both eggs and sperms develop asynchronously in the two short gonadal tubules that are suspended in the coelomic cavity. Sperms are released into the tubule, but eggs are not. Each gonadal tubule consists of pin outer peritoneum composed of flagellated epithelial cells, muscles, and nerves; an inner germinal epithelium of germinal and somatic cells; and a middle connective-tissue (hemal) compartment bounded by the basal laminas of the peritoneum and germinal epithelium. Spermatogonia and oogonia are flagellated epithelial cells that retain epithelial polarity throughout gametogenesis. During spermatogenesis, spermatocytes emerge towards the lumen from the germinal epithelium and sperms enter the lumen apex (tail) first. Supportive and phagocytic interstitial cells are associated with spermatocytes. During oogenesis, oocytes submerge basally into the hemal sinus and carry the epithelial basal lamina ahead of them. The oocyte apex, however, maintains adhering junctions with somatic (follicle) cells and bears a flagellum, at least into the vitellogenic phase. Full-grown oocytes are enclosed in basal lamina, except apically, where an apical protuberance forms. The apical protuberance is a region of ooplasm, devoid of yolk and rich in microtubules, that terminates apically in an extensive junction between the oolemma and follicle cells of the germinal epithelium. The oogenic pattern of S. hydriformis indicates that the apical-basal polarity of the oocyte becomes the animal-vegetal polarity of the egg, which in turn, becomes the anterior-posterior axis of the larva. Homologous oogenic patterns occur in crinoids and ophiuroids, but not asteroids and echinoids. An outgroup analysis of echinoderm oogenic patterns with those of Cephalochordata and Cnidaria suggests that the pattern common to holothuroids, crinoids, and ophiuroids is plesiomorphic to echinoderms and, in general form, to deuterostome metazoans.

The primordial germ cells (PGCs) of a recently metamorphosed juvenile Synaptula hydriformis occur with somatic cells in the germinal epithelium of the gonad. As part of the epithelium, PGCs rest on a basal lamina, extend apically towards a lumen, are joined to other cells of the epithelium via apicolateral junctions, and express apical-basal polarity. Each PGC has an apical flagellum that is surrounded by a collar of microvilli. The apicolateral junctions of PGCs consist of apical adhering and subapical septate junctions. Hemidesmosomes attach the PGCs to the basal lamina. Although the somatic cells form an incomplete layer over the PGCs, both the PGCs and somatic cells remain exposed to the apical lumen and retain contact with the basal lamina. The peritoneum is the outermost layer of the gonad and faces the perivisceral coelom. The epithelial-cell characteristics expressed by cells of the peritoneum are identical to those of the germinal epithelium. PGCs of S. hydriformis are epithelial flagellated-collar cells and express the apical-basal polarity that is typical of epithelial cells. The apical-basal polarity of the oocyte, animal-vegetal axis of full-grown eggs, and anterior-posterior axis of larvae and adults are all in correspondence. Thus the polarity of the germinal epithelium may determine the primary body axis of the next generation.

Sipunculus nudus is a large sipunculan that burrows actively in porous marine sands. The body surface is folded into approximately 30 longitudinal ridges that extend along the length of the trunk and introvert. A dermal canal lies beneath each of the ridges and circulates coelomic fluid and hemerythrocytes to within a few micrometers of the body surface. Coelomic fluid enters and leaves the dermal canals through pores leading from the trunk coelom and hows unidirectionally at approximately 0.7 mm/s from posterior to anterior. The flow is generated by cilia on peritoneal cells lining the canals. The volume of the canals is approximately 8% of the total coelomic volume.We suggest that sipunculan species fall into three functional categories based on the body region or regions used for environmental gas exchange. ''Tentacle breathers,'' such as species of Themiste, bore into rocks or micro-oxic sediments and extend their numerous tentacles into the water, Dissolved,eases are transported between the tentacular and trunk coelomic cavities via well-developed contractile vessels. ''Tentacle and introvert breathers,'' such as species of Aspidosiphonidae and Phascolosomatidae, lodge the trunk region of the body in the substratum and extend an elongated, thin-walled introvert and tentacles into the water. Their contractile vessels are usually simple unbranched tubes. ''Integumentary breathers,'' such as Sipunculus nudus and other species of Sipunculidae, have integumentary specializations for gas exchange across the entire body surface, but usually small tentacles and often weakly developed contractile vessels.

research.This is particularly true for invertebrate organisms because: 1) they are extremely diverse in form and function across taxa and across life stages (e.g.,

The structure and function of the captaculum in Graptacme calamus were studied using light microscopy, videomicrography, and transmission electron microscopy. Graptacme calamus utilizes a longitudinal ciliary band to transport small food particles along the outstretched filament. The head of the captaculum, which bears the alveolar indentation, contains a large ganglion, at least three types of gland cells, circular and longitudinal muscles, and connective tissue. It is likely that gland 1 secretes mucus which is used in the transport of food particles and that gland 2 secretes material which promotes adhesion of the alveolus to the substratum. The function of gland 3 is unknown. Critical observation of the captaculum surface revealed that the cilia of the alveolar region have truncated tips unlike those found on other regions of the captaculum. These alveolar cilia probably aid in the distribution of adhesive substance and in adhesion.

The primitive form of the vertebrate nephron consists of a vascular filtration surface overlain with podocytes, a specialized coelomic cavity to receive the ultrafiltrate, and a tubule for modification to final urine. Although previously thought to be unique to the vertebrates, this design is now known to be widespread among invertebrates, including most of the protochordates, and especially their larvae. Goodrich's rejection of the homology of invertebrate nephridia and the vertebrate nephron, based on a lack of germ-layer correspondence, is shown to be either unsupported by facts or logically dubious. Comparative morphology of adult and larval invertebrates suggests that filtration excretory organs, as protonephridia and metanephridial systems, evolved in the lineage to the bilaterally symmetrical animals and each consisted minimally of a filtration cell, a urinary compartment, and tubule joined to the exterior. Invertebrate metanephridial systems and protonephridia are discussed as homologous structures composed of homologous cells (podocytes, terminal cells; also nephrocytes). The ontogenetic and phylogenetic distribution of nephridia is correlated with body design, especially body size.

The spongy body of Davidaster rubiginosa, D. discoidea, and Comactinia meridionalis, is an axial haemal plexus consisting of two structurally similar, but positionally distinct, regions: an oral circumesophageal part and an aboral part which lies lateral to the axial organ. The axial organ is a large axial blood vessel which is infiltrated by hollow cellular tubes lined with monociliated epithelial cells. The spongy body plexus is a tangle of small blood vessels overlain by podocytes and myocytes. The spongy body and the axial organ are situated in the axial coelom, which is confluent with the perivisceral coelom, the water vascular system, and the parietal canals. The parietal canals open to the exterior via ciliated tegmenal ducts and surface pores. The crinoid spongy body is morphologically similar to the axial gland of asteroids, ophiuroids, and echinoids (AOE). Although the axial glands of these three classes of echinoderms are mutually homologous structures, the homology of the crinoid spongy body and the AOE axial gland is questionable because of differences in organization and developmental origin. Alternatively, the crinoid spongy body may be homologous to asteroid gastric haemal tufts, which are podocyte-covered blood vessels suspended in the perivisceral coelom. The functional organization of the spongy body suggests a filtration nephridium and predicts an excretory function. An alternative hypothesis is that the spongy body is a site of nutrient transfer from the blood vascular system to the perivisceral coelom.