Protonephridial organs in Myzostoma cirriferum (Myzostomida)

Myzostoma cirriferum Leuckart, 1836 possesses five paired, serially arranged, blindending nephridial organs which are described for the first time. Ultrastructural investigations reveal that each nephridium is composed of three terminal cells and one tubular cell that forms the emission tubule. The central lumen of the individual terminal cells contains six to nine flagella, each of which is surrounded regularly by cytoplasmic rods arranged in parallel. Weir-like fenestrations in the peripheral wall of the terminal cells make up the connection between the central lumina and the extracellular space around the nephridial organ. The canal of the emission tubule possesses cilia, microvilli and cytoplasmic structures, suggesting involvement of this cell with active transport and storage. It opens into the cuticle at the ventral surface of the animal.     

Integument and epidermal sensory structures of Myzostoma cirriferum (Myzostomida)

Summary The fine structure of the integument of Myzostoma cirriferum is described with special attention to the integument sensory areas. Hypotheses about the function and a functional model of these are proposed. The integument consists of an external pseudostratified epithelium with cuticle (the epidermis) covering a parenchymo-muscular layer (the dermis). The dermis includes two types of cells: muscular fibers of the double obliquely striated type and parenchymal cells. Differences occur in the epidermis, which consists either of a large non-innervated myoepithelial area (viz. the regular epidermis). or of several rather localized sensory-secretory areas associated with discrete nerve proceses (viz. the sensory epidermis). The regular epidermis is made up of three types of cell: covering cells, ciliated cells and myoepithelial cells. The sensory epidermis shows small or marked structural variations from the regular epidermis. Small variations occur in the cirri, the buccal papilla, the body margin, the parapodia and the parapodial folds where nerve processes insinuate between epidermal cells. They are thought to be mechanoreceptor sites that could give information on the structural variations of the host's integument and participate in the recognition of individuals of the same species. The sensory epidermis differs markedly from the regular eidermis in the four pairs of lateral organs. Each lateral organ consists of a villous and ciliated dome-like central part, surrounded by a peripheral fold. The epidermis of the fold's inner part (viz. the part facing the central dome) is made up of secretory cells, while that of the fold's outer part is similar to the regular epidermis. The epidermis of the dome includes vacuolar cells, sensory cells and a different type of secretory cell. Lateral organs are presumed to be both chemoreceptors and mechanoreceptors. They could allow the myzostomids to recognize the host's integument and prevent them from shifting on the surrounding inhospitable substrate.     

Immunohistochemical investigations of Myzostoma cirriferum and Mesomyzostoma cf. katoi (Myzostomida,Annelida) with implications for the evolution of the myzostomid body plan

Although part of the annelid radiation, Myzostomida exhibit a highly specialized body plan that lacks many typical annelid characters. Their annelid ancestry is evident from their trochophora-like larvae, adult myoanatomy and parts of the nervous system, whereas segmentation is considered at best to be incomplete in myzostomids. We analyzed the morphology of two myzostomid species, the ectocommensal Myzostoma cirriferum and the endoparasitic Mesomyzostoma cf. katoi using a broad set of fluorescent markers to reveal the degree of segmentation in myzostomids. We used immunocytochemical and classical fluorescent staining methods combined with confocal laser-scanning microscopy to visualize tissues labeled with antibodies directed against classical invertebrate neurotransmitters (serotonin, dopamine, FMRFamide), synapsin, which labels nerve cell terminals, and the marker phalloidin–rhodamine which binds F-actin in muscle. Our data provide a broad body of additional evidence for the segmented origin of Myzostomida. It becomes apparent that the adult nervous system of M. cirriferum exhibits signs of pseudoradial symmetry with repetitive patterns of putative FMRFamide, serotonin and dopamine-like immunoreactivity. An analysis of the staining patterns in juvenile M. cirriferum yielded evidence for positional changes, as well as additions and reductions of neuronal structures during development. Interestingly, the neuroanatomy and myoanatomy of Mesomyzostoma cf. katoi indicate further reductions of neuronal and myoanatomical patterns in this species. Notably this taxon shows a presumably secondarily evolved cylindrical and strictly bilateral morphology, which is supposed to have evolved from a flat, disk-shaped Myzostoma-like ancestor with an underlying pseudoradial symmetry.     

Fine structure of the spermatophore and intradermic penetration of sperm cells inMyzostoma cirriferum (Annelida,Myzostomida)

Summary The spermatophore ofMyzostoma cirriferum is a white V-shaped structure up to ca. 500 m long. It is formed by a translucent matrix which includes numerous cysts of two types that are very close together and tend to form interlacing twists. According to their contents, three spermatophoral regions can be distinguished: the body with the horns, the foot and the basal disc. The body-horns region forms the upper part of the spermatophore and extends over ca. 400 m. This region includes mature spermiocysts which are formed by one cyst cell each including one to three groups of rolled up spermatozoons. Features of these cyst cells are their great length (up to 25 m), their euchromatic nuclei each provided with a large nucleolus, their numerous mitochondria and osmiophilic vesicles included in the cytoplasm as well as cytoplasmic remnants of the residual bodies of the spermatids. Spermatozoons appear to be well adapted to the intradermic penetration occurring in this species in that all of them possess nuclei provided with dense nuclear grains, a hairpin-bent flagellum and a microtubular palissade. The spermatophore foot is located just below the body and extends over ca. 90 m. It contains exclusively spermiocysts which include one to three abortive germinal cells. They differ also from the previous cysts by their smaller length (ca. 6–10 m) and their more heterochromatic nuclei. The basal disc is the lower part of the spermatophore. It extends over ca. 10 m and contains electron-dense vesicles in its upper part and vesicles with fibrillar material in its lower part. When mature myzostomids contact each other, a spermatophore is expulsed from one seminal vesicle of the donor myzostomid to the integument of the receiver myzostomid. The vesicles with fibrillar content are the first in contact with the cuticle of the receiver myzostomid. The material they include is supposed to have a histolytic action and to be responsible for the lysis of the cuticle and epidermal cells thus providing a passage for the spermatophore contents. Afterwards, cysts move as a result of the spermatozoons' beating and pass through the receiver's integument. At the time of penetration, cytoplasmic membranes of the cyst cells merge together forming an enormous syncytium extending into the whole receiver's body. This syncytium surrounds the spermatozoons and the abortive germinal cells. The whole process of intradermic penetration (i.e. from the fixation of the spermatophore to its reduction to an empty matrix) lasts from 1–5 h.     

Structure of the nervous system of Myzostoma cirriferum (Annelida) as revealed by immunohistochemistry and cLSM analyses

The nervous systems of juvenile and adult Myzostoma cirriferum Leuckart, 1836, were stained with antisera against 5-HT (5-hydroxytryptamine, serotonin), FMRFamide, and acetylated alpha-tubulin in combination with the indirect fluorescence technique and analyzed by confocal laser scanning microscopy. The central nervous system consists of two small cerebral ganglia, connected by a dorsal commissure, a ventral nerve mass, and a pair of long circumesophageal connectives joining the former to the latter. The two neuropil cords within the ventral nerve mass curve outward and are joined to one another anteriorly and posteriorly. They are connected by 12 commissures, forming a ladder-like system. A single median nerve runs along the midventral axis. In addition to the circumesophageal connectives, 11 peripheral nerves arise from each main cord. The first innervates the anterior body region. The others form five groups of two nerves each, the first and thicker nerve of which is the parapodial nerve, innervating the parapodium and two corresponding cirri. Except for those in the most posterior group, the second nerves innervate the lateral organs and the body periphery. Serotonergic perikarya are arranged in six more or less distinct clusters, the first lying in front of and the other five between the main nerve cords. The distribution pattern of the FMRFamidergic perikarya is less clear and the somata lie between and outside the cords. One pair of dorsolateral longitudinal nerves was visualized by tubulin staining. Peripheral nerves and the commissures, in particular, demonstrate a segmental organization of the nervous system of M. cirriferum. Furthermore, their arrangement indicates that the body consists of six segments, the first of which is identifiable only by the first pair of peripheral nerves, the first two commissures, and the anteriormost ventral ganglion. The nervous system M. cirriferum thus exhibits several structures also found in the basic plan of the polychaete nervous system.     

Locomotion and fine structure of parapodia in <Emphasis Type="Italic">Myzostoma cirriferum</Emphasis> (Myzostomida)

Most myzostomids are ectocommensals of crinoids on which they move freely. Their locomotion is ensured by five pairs of parapodia located laterally below their trunk. Each parapodium in Myzostoma cirriferum is a conical structure that includes a hook-like chaeta, replacement chaetae and an aciculum. Structure and ultrastructure of the myzostomid chaetae are similar to those of polychaetes: they are formed by a chaetoblast, which gives rise to microvilli where chaetal material is assembled on the outer surface. Myzostoma cirriferum walks on its host. It moves the anterior part, the posterior part or the lateral parts forwards but is able to rotate of 180° on itself. Its locomotion entirely depends on parapodial motions and not on trunk movements. Three pairs of muscles are involved in parapodial motions: parapodium flexor and parapodium extensor, aciculum protractor and aciculum retractor, and hook protractor with conjunctor. A functional model is proposed for explaining the global motion of a parapodium in M. cirriferum that may be extended to all ectocommensal myzostomids.     

黑鸢消化系统形态学的初步研究

对黑鸢消化系统的形态学作了初步的观察与研究,结果表明：黑鸢舌尖钝圆,舌根分叉,叉粘膜上具有尖端指向后方的栉状突;食管宽而扁,无明显可见的嗉囊;肌胃无明显的类角质膜;肠道长是体长2．3倍,小肠较发达,K1275mm,古肠道总长的93．6％,具有不发达的双侧盲肠：胰腺短而厚、并与蛇雌、毛脚鸢的消化系统进行了比较。     

雕鸮消化系统形态学的初步研究

对一只雕消化系统的形态学作了初步的观察与研究,结果表明:雕舌呈鞋底形,舌根分叉,叉粘膜上具有尖端指向后方的栉状突;食管宽而扁,无明显可见的嗉囊;肌胃无明显的类角质膜;肠道长是体长的2.05倍,小肠较发达,长970.5 mm,占肠道总长的75.7%,具有较发达的双侧盲肠。并与蛇雕、毛脚、黑鸢的消化系统进行了比较。     

Functional Morphology of Aztekium ritteri (Cactaceae)

The dwarf globular cactus Aztekium ritteri shows a high degree of surface differentiation. The stem consists of 8–15 ribs, these in turn being sculptured by transverse furrows: compared with a sphere of equal size, the surface/volume ratio is increased by more than 10-fold. At the same time, only 20% of the stem surface is exposed to direct sunlight, 80% lying in the shade of its own body, in a system of furrows and crypts. The exposed areas have few stomata and the epidermal cell walls are notably thickened and cutinised. In addition, these form an exoskeleton by means of a hypodermis containing calcium oxalate crystals while the unexposed cell surface regions, hidden in the furrows, lack xeromorphic characters and calcium oxalate crystals. By far the greatest number of stomata are found in the furrows mostly in deep crypts. When dehydration occurs as a consequence of longer periods of drought, the furrows and crypts close together, thereby reducing transpiration losses. The complicated interlocking nature of the surface architecture of Aztekium is discussed in terms of the functional aspects as an adaptation to an extreme habitat (vertical shale cliffs in Nuevo León, Mexico).     

Comparative Functional Morphology of the Bivalve Excretory System

Combining injection techniques with ultrastructural observations,and relating these findings to the more traditional physiologicaland morphological studies have shed new light onthe excretorymechanisms underlying the processes of ultrafiltration, secretionand reabsorption in some bivalve molluscs. These basic processesare further elucidated by comparing normal excretory tissueswith those in bivalves that have been subjected to stress bypollutants in either the natural environment or under laboratoryexperimentation. The process of ultrafiltration is size andcharge dependent and occurs at the filtration barrier at thebase of the podocytesin the pericardial gland. Primary urinemay be modified by secretion (primarily from the kidney cellsbut also from the podocytes), reabsorbtion in the kidney, andby the addition of hemocytes passing from blood spaces throughthe epithelium into the lumen of the kidney. Numerous concrements(granules, concretions and membranes) that result from lysosomalactivities inthe podocytes, kidney cells and hemocytes alongwith the fluid are excreted into the mantle cavity     

蓝翅希鹛消化系统的初步研究

对6只(3♀,3♂)蓝翅希鹛的消化系统进行了解剖观察,结果表明:蓝翅希鹛的舌成细长三角形,雌、雄舌尖端差异显著:雌鸟舌尖端各有一根长刺毛,而雄鸟无此长刺毛;在舌前端正中央还有一"v"形的凹缺,使舌成二分叉,雌鸟分叉深约2.77 mm,雄鸟为1.63 mm。食道颈胸部分段不明显,食管长18.64~23.55 mm,嗉囊外观不明显。腺胃乳突短而小,分布均匀;肌胃发达,具角质膜。肠道长与体长基本相等,小肠较发达,雌鸟长100.90 mm,占肠道总长90.08%,雄鸟分别为102.52 mm和89.60%;具有双侧盲肠,但不发达,占肠道总长的2.3%~2.8%,右侧盲肠略大于左侧;直肠短,雌鸟仅占肠道8.55%,雄鸟占8.72%。肝为体内最大的消化腺,分左右两叶。胰位于十二指肠袢内,细长形,分二小叶。由消化道特征说明其食性是以食虫为主的杂食性鸟类。     

Feeding Mechanisms and Comparative Functional Morphology of Macrothricidae (Crustacea : Cladocera)

Feeding of the Macrothricidae is accomplished b y two principal methods: active collection of food from the substrate surface and filtration of suspended particles. As differentiated from Ilyocryptus sordidus and Lathonura rectirostris, Ophryoxus gracilis is equipped with the most universal set of limbs allowing catching of food along with filtratory feeding. They are described in detail. Lathonura rectirostris is a highly specialized species, an inhabitant of plant thickets, since i t adapted to feeding on epiphytic algae and particles at the plant surface. Feeding is accomplished only by scraping or catching food by means of complexes of setae of the II pair of limbs. Filtratory feeding and appropriate structures are lacking. The structure and action of the limb apparatus of Ilyocryptus sordidus rule out active catching of food particles.     

裸项栉鰕虎鱼消化系统组织形态学观察

目的 研究裸项栉缎虎鱼消化系统的组织形态学.方法 对裸项栉鰕虎鱼进行解剖,并测量和计算肠道系数、食道长度等数据;制作组织切片,采用光镜技术对消化系统的组织器官进行观察分析.结果 裸项栉鰕虎鱼的消化系统由消化管和消化腺组成,其中消化管包括口咽、食道、胃、小肠和大肠等,消化腺包括肝脏和胰腺.咽部上皮和食道上皮为复层扁平上皮,内有较多的杯状细胞和黏液腺,食道肌层为横纹肌.胃上皮为单层柱状上皮,胃底腺主要位于胃体部的固有层中.肠黏膜向肠腔突起形成许多皱襞,肠上皮为单层柱状上皮,上皮中有数量不等的杯状细胞.肠道系数(IC)约为0.30.胃和肠的肌层都为平滑肌.肝细胞中含有丰富的脂滴,在HE染色标本中因脂滴被溶解而呈大小不等的空泡.胰腺包括外分泌部和内分泌部,外分泌部是浆液腺,内分泌部又称胰岛,主要由内分泌细胞组成.结论 裸项栉鰕虎鱼的消化系统组织形态学与其杂食性相适应,本研究可为裸项栉鰕虎鱼的实验动物化提供支持.     

Functional Morphology of the Phallosome in Glossina (Diptera, Glossinidae) and Its Evolutionary Implications

Current views on the phylo-genetjc relations of the three species groups within the genus Glossina are critically reviewed. In respect of the male genitalia, the fusca group is here regarded as more specialized than the morsitans group. The detailed phallosome morphology of G. austeni is compared with that of G. fuscipes , on the basis of their mode of action in living flies. The comparison is extended to fusca group species, using dead material only. The presumed phylogeny of Glossina is presented in outline; the evolution of the genus has involved a progressive invasion of riverine and later of forest habitats, from an original semi-arid grassy woodland habitat.     

Myzostomida: A review of the phylogeny and ultrastructure

Myzostomids are minute, soft-bodied, marine worms associated with echinoderms since the Carboniferous. Due to their long history as host-specific symbionts, they have acquired a highly derived body plan that obscures their phylogenetic affinities to other metazoans. Because certain organs are serially arranged a closer relationship between polychaetes and myzostomids has repeatedly been discussion. We presented here a review on the ultrastructure of myzostomids with the most recent analyses that concern their phylogenetic position. The ultrastructure of the integument, digestive system, excretory system and nervous system are summarized. Unpublished information on the gametogenesis and reproductive systems of myzostomids are also exposed with a view on their reproductive process.     

Functional Morphology of the Olfactory Organ in Spinachia spinachia (L.) (Teleostei,Gasterosteidae)

The functional morphology of the olfactory organ in Spinachia spinachia (L.), which has only a single nare, was studied by light microscopy, scanning electron microscopy, and experimental investigations. It was shown that only the incoming water passes over the olfactory epithelium. The device for ventilating this olfactory organ is an accessory ventilation sac activated by respiratory pressure changes in the buccal cavity. This one-way water current over the olfactory epithelium in a monotrematous olfactory organ was found to be possible because of the morphology of the olfactory organ combined with movements of the lateral wall of the olfactory organ and the nasal tube during respiration. The olfactory epithelium is divided into irregular islets. Both ciliated receptor cells and microvillous receptor cells are present.     

Molecular phylogenetic analyses indicate multiple independent emergences of parasitism in Myzostomida (Protostomia)

The fossil record indicates that Myzostomida, an enigmatic group of marine worms, traditionally considered as annelids, have exhibited a symbiotic relationship with echinoderms, especially crinoids, for nearly 350 million years. All known extant myzostomids are associated with echinoderms and infest their integument, gonads, celom, or digestive system. Using nuclear (18S rDNA) and mitochondrial (16S and COI) DNA sequence data from 37 myzostomid species representing nine genera, we report here the first molecular phylogeny of the Myzostomida and investigate the evolution of their various symbiotic associations. Our analyses indicate that the two orders Proboscidea and Pharyngidea do not constitute natural groupings. Character reconstruction analyses strongly suggest that (1) the ancestor of all extant myzostomids was an ectocommensal that first infested crinoids, and then asteroids and ophiuroids, and (2) parasitism in myzostomids emerged multiple times independently.