Homology and Evolution of the Chaetae in Echiura (Annelida)

Echiura is traditionally regarded as a small phylum of unsegmented spiralian worms. Molecular analyses, however, provide unquestionable evidence that Echiura are derived annelids that lost segmentation. Like annelids, echiurans possess chaetae, a single ventral pair in all species and one or two additional caudal hemi-circles of chaetae in two subgroups, but their evolutionary origin and affiliation to annelid chaetae are unresolved. Since annelids possess segmental pairs of dorsal (notopodial) and ventral (neuropodial) chaetae that are arranged in a row, the ventral chaetae in Echiura either represent a single or a paired neuropodial group of chaetae, while the caudal circle may represent fused rows of chaetae. In annelids, chaetogenesis is generally restricted to the ventral part of the notopodial chaetal sac and to the dorsal part of the neuropodial chaetal sac. We used the exact position of the chaetal formation site in the echiuran species, Thalassema thalassemum (Pallas, 1766) and Echiurus echiurus (Pallas, 1767), to test different hypotheses of the evolution of echiurid chaetae. As in annelids, a single chaetoblast is responsible for chaetogenesis in both species. Each chaeta of the ventral pair arises from its own chaetal sac and possesses a lateral formation site, evidencing that the pair of ventral chaetae in Echiura is homologous to a pair of neuropodia that fused on the ventral side, while the notopodia were reduced. Both caudal hemi-circles of chaetae in Echiurus echiurus are composed of several individual chaetal sacs, each with its own formative site. This finding argues against a homology of these hemi-circles of chaetae and annelids’ rows of chaetae and leads to the hypothesis that the caudal chaetal rings evolved once within the Echiura by multiplication of ventral chaetae.     

Comparison of Invasive Blood Pressure Measurements from the Caudal Ventral Artery and the Femoral Artery in Male Adult SD and Wistar Rats

Background and Purpose

Studies have suggested that the caudal ventral artery is a potential site for continuous arterial blood pressure monitoring in rats. However, the agreement of mean arterial pressure values between the femoral artery and the caudal ventral artery has not been investigated. This study was performed to identify whether the caudal ventral artery could be safely used for continuous blood pressure monitoring as an alternative site to the femoral artery.

Methods

Rats were randomized into four groups: Sprague Dawley rats under normothermia; Wistar rats under normothermia; Sprague Dawley rats under hypothermia; Wistar rats under hypothermia. Each rat underwent simultaneous monitoring of blood pressure using femoral artery and caudal ventral artery catheterization during a stable hemodynamic state and three periods of acute severe hemodynamic changes. The effects of rat strain, rectal temperature, experimental time course and hemodynamic factors on pressure gradients, the concordance of mean arterial pressure values between the femoral artery and the caudal ventral artery, and the rates of distal ischemia after surgery were determined.

Results

There was a significant difference in the rate of distal ischemia between femoral and caudal ventral arteries after catheterization (25% vs 5%, P<0.05). The overall mean gradient and the mean gradient under a steady hemodynamic state were 4.9±3.7 mm Hg and 5.5±2.5 mm Hg, respectively. The limits of agreement (bias±1.96 SD) were (−2.5 mm Hg, 12.3 mm Hg) and (-0.5 mm Hg, 10.5 mm Hg), respectively. Although the concordance decreased during the first 30 sec of each period of severe hemodynamic changes, the degree of agreement was acceptable regardless of the effects of rat strain and rectal temperature.

Conclusions

Based on the degree of agreement and the safety of catheterization, the caudal ventral artery may be a preferred site for continuous arterial blood pressure monitoring without acute severe hemodynamic changes.     

Caudal Papillae in Romanomermis culicivorax

Distribution of caudal papillae in adult Romanomermis culicivorax was determined by scanning electron microscopy. Ninety eight caudal papillae, each containing one pore, were present in males but absent in females. Papillae were arranged in three longitudinal rows, one ventral, two ventrolateral; the middle ventral row bifurcated anterior to the spicule. The appearance of the papillae was different anterior and posterior to the spicule. The role of the caudal papillae in mediating copulatory behavior was discussed.     

Vascularization of the telencephalic choroid plexus of a ganoid fish [Acipenser ruthenus (L.)

The vascularization of the telencephalic choroid plexus of the sterlet Acipenser ruthenus, a ganoid fish, was examined by vascular corrosion casting and by light and transmission electron microscopy. The arterial supply is from the dorsal mesencephalic artery via: 1) the ventral choroidal arteries (left and right); 2) the dorsal choroidal arteries (left and right); 3) the caudal choroidal arteries (left and right); 4) the ventral arteries of the dorsal sac; and, from the olfactory arteries, via 5) the rostral choroidal arteries. The venous drainage is mainly through a single main choroidal vein that can take various courses either directly to the anterior cardinal vein or via the middle cerebral vein to the anterior cardinal vein. To a lesser extent, the plexus is drained via the lateral telencephalic veins and the ventral vein of the dorsal sac to the middle cerebral vein. By angioarchitecture and form, the plexus can be subdivided into five distinct parts: the surface network, the median folds, the large lateral folds, the small lateral folds, and the area common to the bottom of the dorsal sac and the telencephalic plexus. Diameters of terminal vessels as measured from vascular corrosion casts and from paraplast, semithin, and ultrathin sections were never less than 10 micron. It is suggested that the different areas in one plexus may have different functions with respect to secretion and absorption of cerebrospinal fluid.     

Living on the Edge: Settlement Patterns by the Symbiotic Barnacle Xenobalanus globicipitis on Small Cetaceans

The highly specialized coronulid barnacle Xenobalanus globicipitis attaches exclusively on cetaceans worldwide, but little is known about the factors that drive the microhabitat patterns on its hosts. We investigate this issue based on data on occurrence, abundance, distribution, orientation, and size of X. globicipitis collected from 242 striped dolphins (Stenella coeruleoalba) that were stranded along the Mediterranean coast of Spain. Barnacles exclusively infested the fins, particularly along the trailing edge. Occurrence, abundance, and density of X. globicipitis were significantly higher, and barnacles were significantly larger, on the caudal fin than on the flippers and dorsal fin. Barnacles were found more frequently and in greater numbers on the dorsal rather than ventral side of the caudal fin and on the central third of dorsal and ventral fluke surfaces. Nearly all examined individuals attached with their cirral fan oriented opposite to the fluke edge. We suggest that X. globicipitis may chemically recognize dolphins as a substratum, but fins, particularly the flukes, are passively selected because of creation of vortices that increase contact of cyprids with skin and early survival of these larvae at the corresponding sites. Cyprids could actively select the trailing edge and orient with the cirri facing the main direction of flow. Attachment on the dorsal side of the flukes is likely associated with asymmetrical oscillation of the caudal fin, and the main presence on the central segment of the flukes could be related to suitable water flow conditions generated by fluke performance for both settlement and nutrient filtration.     

The composition of the caudal skeleton of teleosts (Actinopterygil: Osteichthyes)

The diural caudal skeleton of teleostean actinopterygians develops phylogeneticaily and ontogenetically from a polyural skeleton. The reduction of the polyural anlage to four, three, two or fewer centra in the adult caudal skeleton takes different pathways in different genera (e.g. compare Elops and Albula) and groups of teleosts. As a result, ural centra are not homologous throughout the teleosts. By numbering the ural centra in a homocercal tail in polyural fashion, one can demonstrate these and the following differences. The ventral elements (hypurals) always occur in sequential series, whereas the dorsal elements (epurals and uroneurals) may alter like the ural centra. The number of epurals, five or four in fossil primitive teleosts, is reduced in other primitive and advanced teleosts, but the same epurals are not always lost. The number of uroneurals, seven in fossil teleosts, is reduced in living teleosts, but it has not been demonstrated that the first uroneural is always derived from the neural arch of the same ural centrum. The landmark in the homocercal tail is the preural centrum I which can be identified by (1) bifurcation of the caudal artery and vein in its ventral element, the parhypural, (2) its position directly caudal to the preural centrum (PU2) which supports the lowermost principal caudal ray with its haemal spine, (3) carrying the third hypaxial element ventral to the course of arteria and vena pinnalis, and (4) by carrying the first haemal spine (parhypural) below the dorsal end of the ventral cartilage plate. The study of the development of the vertebral column reveals that teleosts have different patterns of centrum formation. A vertebral centrum is a complete or partial ring of mineralized, cartilaginous or bony material surrounding at least the lateral sides of the notochord. A vertebral centrum may be formed by arcocentrum alone, or arcocentral arcualia and chordacentrum, or arco-, chorda- and autocentrum, or arcocentral arcualia and autocentrum. This preliminary research demonstrates that a detailed ontogenetic interpretation of the vertebral centra and of the caudal skeleton of different teleosts may be useful tools for further interpretations of teleostean interrelationships.     

Cell communication with the neural plate is required for induction of neural markers by BMP inhibition: evidence for homeogenetic induction and implications for Xenopus animal cap and chick explant assays

In Xenopus, the animal cap is very sensitive to BMP antagonists, which result in neuralization. In chick, however, only cells at the border of the neural plate can be neuralized by BMP inhibition. Here we compare the two systems. BMP antagonists can induce neural plate border markers in both ventral Xenopus epidermis and non-neural chick epiblast. However, BMP antagonism can only neuralize ectodermal cells when the BMP-inhibited cells form a continuous trail connecting them to the neural plate or its border, suggesting that homeogenetic neuralizing factors can only travel between BMP-inhibited cells. Xenopus animal cap explants contain cells fated to contribute to the neural plate border and even to the anterior neural plate, explaining why they are so easily neuralized by BMP-inhibition. Furthermore, chick explants isolated from embryonic epiblast behave like Xenopus animal caps and express border markers. We propose that the animal cap assay in Xenopus and explant assays in the chick are unsuitable for studying instructive signals in neural induction.     

Structure and Role of the Renette Cell and Caudal Glands in the Nematode Sphaerolaimus gracilis (Monhysterida)

Ultrastructure of the renette cell and caudal glands was studied in the free-living aquatic nematode Sphaerolaimus gracilis. The renette cell occurred posterior to the esophageal-intestinal junction and opened through an ampulla to a ventral pore behind the nerve ring. The caudal gland system of the tail consisted of two gland cells opening through separate pores and 2 to 3 other gland cells of a different type opening through a common pore. The renette cell and the two caudal gland cells were similar and both contained secretory granules, 0.5-1.5 μm in diameter. The material released attached the nematode to the substrate. The renette ampulla was surrounded by a specialized cell, the ampulla cell, which had characteristics of myoepithelium. A plug or valve structure connected to the ampulla cell may regulate the output of the secretory material. The ampulla cell is able to contract and thus is probably under direct neuronal control. Other cells in the renette ampulla region of body cavity were termed supporting cells. Living, cold-relaxed nematodes were attached to sediment particles in the renette pore region and at the tail tip. Release from sediment particles was mechanical at the renette cell discharge site but appeared to be chemical at the caudal gland. In behavioral experiments, nematodes in a water current had the ability to release a thread from the caudal glands while maintaining contact with a sediment particle attached to the tail end. If the thread was strong enough, it also could be used to change location. Nematodes anchored by the thread from the caudal glands to a sediment particle could float in water currents until they attached themselves to another sediment particle with the help of secretions from the renette cells.     

A new species of sublittoral marine gastrotrich, Lepidodasys ligni sp. n. (Macrodasyida,Lepidodasyidae), from the Atlantic coast of Florida

A new species of Lepidodasys is described from sublittoral sandy sediments off the Atlantic coast of Florida. Lepidodasys ligni sp. n. is a small species (≤ 450 µm) with a crossed-helical pattern of small, non-keeled, non-imbricated scales on the dorsal and lateral body surfaces, two columns of ventral, interciliary scales that form a herringbone pattern, and a series of anterior, lateral, dorsal and posterior adhesive tubes. Similar to Lepidodasys castoroides from the Faroe Islands, the new species possesses a caudal constriction that demarcates the posterior end containing the caudal organ. The frontal organ lies within the posterior constriction, which is heavily invested with somatic circular muscles. These muscles are also present throughout the trunk and represent a novel condition for species of Lepidodasys,which were previously considered to lack somatic circular muscles. Posterior of the caudal constriction is a large, barrel-shaped caudal organ that is wrapped in a series of interdigitating, spindle-shaped, incomplete circular muscle fibers. The caudal organ contains a sclerotized central canal, but the absence of distal cuticular endpieces distinguishes the new species from its morphologically similar congener, Lepidodasys castoroides.     

Morphology and function of the dorsal sound producing scales in the tail of Teratoscincus scincus (Reptilia; Gekkonidae)

The tail of Teratoscincus scincus has dorsal scales that have tubercles on their dorsal and ventral surfaces. Sounds are produced when these rub past each other as the excited animal moves its tail. The relative movement of scales is intensified by caudal torsion. The frequencies of the sounds cover a range from 9 to 25 kops and thus, differ from those produced during vocalizations.     

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.     

Intramedullary projections of the rostral nucleus of the solitary tract in the rat: gustatory influences on autonomic output

The efferent connections of the rostral nucleus of the solitary tract (NTS) in the rat were studied by anterograde transport of Phaseolus vulgaris leucoagglutinin. Rostral to the injection site, fibers travel through the rostral parvocellular reticular formation and deflect medially or laterally around the motor trigeminal nucleus, giving off few terminals in these nuclei and terminate in the parabrachial nucleus. Moderate projections to the peritrigeminal zone, including the intertrigeminal nucleus and the dorsal subcoeruleus nucleus, were observed. Caudally to the injection site, dense innervations from the rostral nucleus of the solitary tract were detected in the parvocellular reticular formation ventral and caudal to the injection site and in the intermediate and ventral medullary reticular formation. The rostral central and ventral subdivisions of the NTS up to the level where the nucleus of the solitary tract abuts the fourth ventricle and the hypoglossal nucleus, receive moderate input from the rostral nucleus of the solitary tract. In general, the projections from the rostral nucleus of the solitary tract were bilateral with an ipsilateral predominance. The caudal part of the nucleus of the solitary tract, the dorsal motor nucleus of the vagus and the facial nucleus were not labeled. It is concluded that medullary rNTS projections participate in oral motor behavior and autonomic control of abdominal organs.     

Distribution of the renal vein in the kidney of the dromedary (Camelus dromedarius)

The venous drainage of the kidney of the one-humped camel (Camelus dromedarius) was studied in 17 kidneys of male and female adult animals. Injection of latex, plastoid as well as radiopaque substance (40% barium sulfate) were used to follow the distribution of the renal vein through the kidney tissue. The renal vein of the camel is unique as it gives off vv. interlobares I which drain the ventral half of the kidney, in addition to large cranial and caudal stem vessels from which vv. interlobares I of the dorsal surface branch. The general pattern of distribution of the renal vein in the camel's kidney resembles, more or less, that of the other domestic animals.     

Effect of venipuncture site on hematologic and serum biochemical parameters in marginated tortoise (Testudo marginata)

Blood samples were obtained from the dorsal coccygeal vein and the brachial vein of five adult (four females and one male) and two subadult males of marginated tortoise (Testudo marginata) and hematologic and biochemical parameters were compared. Significant differences were found for red blood cell count, hematocrit, hemoglobin concentration, total proteins, uric acid, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, alkaline phosphatase, calcium, and phosphorus, which were greater in the brachial vein samples. Hemodilution due to lymph was observed when collecting blood from the dorsal coccygeal vein, and it is thought to be the cause of the differences found. This research documented that the brachial vein is a more reliable and consistent venipuncture site than dorsal coccygeal vein in marginated tortoise.     

Melatonin concentrations in the two jugular veins, and relationship with the seasonal reproductive activity in goats

The authors investigated whether melatonin concentrations vary between the two jugular veins and whether absolute (nocturnal) or relative (nocturnal/diurnal ratio) plasma melatonin concentrations are associated with seasonal reproductive activity measured by oestrus or ovulatory activity in Payoya goats. Thirty-two adult Payoya goats were penned under natural photoperiod. Oestrus activity was tested daily using aproned males—twice a week plasma was sampled for progesterone. Melatonin plasma concentrations were studied at each equinox and solstice of the year in jugular samples taken simultaneously by venipuncture. Nocturnal and diurnal plasma melatonin concentrations from each jugular vein were assessed in 3 and 2 plasma samples per goat, respectively, taken at hourly intervals in each period. No differences in melatonin concentrations between the two veins were observed, but there was a significant interaction (P < 0.001) between jugular vein and animal in nocturnal melatonin concentrations. There was no effect of sampling period on melatonin concentrations and the coefficient of correlation between sampling periods was very high. The analyses performed indicated that neither absolute nor relative melatonin concentrations were related with the dates of onset or end of ovulatory/oestrus activity. Therefore, we concluded that in goats (1) melatonin concentrations are highly variable between jugular veins in the same individual but not in the general population, (2) melatonin concentrations are highly repeatable for each individual, and (3) absolute and relative amplitudes of melatonin concentrations are not linked to the seasonal breeding activity in Mediterranean goats.     

Ontogeny of the parietal frill of Triceratops: A preliminary histological analysis

The parietal frill of Triceratops, one of the largest cranial ornamental features known, undergoes extraordinary morphological changes late in ontogeny — progressing from a large, thickened, solid frill to a substantially larger, thin, fenestrated frill. To understand how this structure changed so dramatically we undertook a histological examination of the caudal end of an ontogenetic series of Triceratops parietals. Investigation revealed a histological progression that involved an initial period of non-pathologic hyperostosis, followed by a phase of external (dorsal and ventral sides of the parietal) resorption and border extension, with a conclusive stage hypothesized to be dense fibrous connective tissues mineralized through the process of metaplasia. These fibrous tissues form the caudal end of the mature parietal as well as the epiparietals that fuse to the caudal border of the frill late in ontogeny. Continued resorption near the central parietal regions of the left and right lateral portions of the parietal eventually results in a pair of large circular fenestrae. This progression is somewhat similar to the parietal ontogeny of Centrosaurus.     

Determining the fate of Shh-expressing cells in the diencephalon using a BAC transgenic reporter

The thalamus and prethalamus consist of multiple distinct nuclei and their boundary is demarcated by the zona limitans intrathalamica (ZLI). The development of the primordial thalamus and prethalamus proceed within the caudal diencephalon. Shh has been shown to be essential for diencephalic patterning and regionalization. To understand the role of Shh in the specification of distinct thalamic and prethalamic nuclei, we developed a lineage marker for diencephalic cells expressing Shh by using bacterial artificial chromosome (BAC) transgenesis. A genomic fragment containing ～210 kb of the mouse Shh locus was used to target enhanced green fluorescent protein (eGFP) in transgenic mice. This transgenic BAC reporter faithfully mimicked the pattern of endogenous Shh expression in the caudal diencephalon, including the ZLI. Fate mapping analysis at multiple developmental stages showed that descendents of Shh-expressing progenitor cells derived from ZLI contribute to a population of cells in the ventral lateral geniculate nucleus.     

Sampling Blood from the Lateral Tail Vein of the Rat

Blood samples are commonly obtained in many experimental contexts to measure targets of interest, including hormones, immune factors, growth factors, proteins, and glucose, yet the composition of the blood is dynamically regulated and easily perturbed. One factor that can change the blood composition is the stress response triggered by the sampling procedure, which can contribute to variability in the measures of interest. Here we describe a procedure for blood sampling from the lateral tail vein in the rat. This procedure offers significant advantages over other more commonly used techniques. It permits rapid sampling with minimal pain or invasiveness, without anesthesia or analgesia. Additionally, it can be used to obtain large volume samples (upwards of 1 ml in some rats), and it may be used repeatedly across experimental days. By minimizing the stress response and pain resulting from blood sampling, measures can more accurately reflect the true basal state of the animal, with minimal influence from the sampling procedure itself.