Ultrastructure of the introvert and associated structures of the larvae of Halicryptus spinulosus (Priapulida)

Summary Based on new SEM and TEM observations, the arrangement and ultrastructure of the scalids and adhesive tubuli of the larvae of Halicryptus spinulosus are described. The scalids are arranged in 25 longitudinal rows. Transversally they form seven circlets which alternate. The first circlet consists of 8 and the second of 9 scalids. All following circlets consist of three subrings with 8+8+9 scalids each. New scalids develop in a sub frontal growing zone posterior to the second circlet. The ultrastructure of all different receptor cells and sense organs of the scalids is described. Whereas the receptor cell type 1 occurs in nearly all scalids, the verticalrootlet receptor is restricted to the first circlet, the basal receptor to the second and the coiled-cilium receptor to the third and fourth circlet. Based on these new data, the scalid arrangement and the equipment with different receptor cells can be postulated for the ground pattern of the priapulid larvae. Also the larval development, moulting and the structure of the cuticle are discussed in comparison with the Kinorhyncha and Loricifera.     

Ultrastructural Investigation of the Integument of Tubiluchus philippinensis (Priapulida, Tubiluchidae)

The integument of Tubiluchus philippinensis van der Land, 1984 has been investigated by means of scanning and transmission electron microscopy. The ultrastructure of the cuticle corresponds principally to what has been found in Priapulidae. The tumuli are mere cuticular thickenings. Setae, tubuli, flosculi and scalids are receptor organs. Tubuli additionally serve a second function: they produce a secretion. The male genital area is equipped with various receptor organs, the internal morphology of which has been described. All receptor cells are characterized by apical cilia, which may be surrounded by a circlet of microvilli. They sometimes bear a rather complicated rootlet apparatus.     

Variation in number and differentiation of the abdominal infrared receptors in the Australian 'fire-beetle' Merimna atrata (Coleoptera, Buprestidae)

Most individuals of the Australian ‘fire-beetle’ Merimna atrata have two pairs of IR receptors which are located ventrolaterally on the second and third abdominal sternite. An IR receptor consists of a specialized IR absorbing area, which is innervated by a neural complex. This complex contains one thermoreceptive multipolar neuron with a unique terminal dendritic mass (TDM) and two scolopidia and was termed ‘sensory complex’. However, also individuals with one pair of IR receptors on the second sternite and beetles with three pairs on the second, third, and fourth sternites were found. Additionally, beetles having one or two pairs of IR receptors may have preliminary stages of IR receptors on the third and fourth sternite, respectively. We found two kinds of preliminary stages, both of which are characterized by a much less pronounced absorbing area. In all five abdominal sternites segmental nerves are attached to the cuticle with a neural complex. Investigation of complexes of non-IR sternites suggests that the sensory cells inside the sensory complex of an IR receptor have developed from common internal stretch receptors. From our results it can be hypothesized that the IR sensory system in Merimna atrata has not yet reached a stage, which can be regarded as evolutionary stable.     

Microscopic anatomy and ultrastructure of the introvert of Priapulus caudatus and P. tuberculatospinosus (Priapulida)

Introverts of Priapulus caudatus and P. tuberculatospinosus bear 25 rows of scalids, as well as 8 spines and scattered papillae in the region the circumoral lip. These, as well as the first ring of pharyngeal teeth in P. tuberculatospinosus, are sensory organs. Although superficially they differ between species, they are all characterized by apical and/or subapical openings which are located on tiny cuticular tubules. All sensory organs contain cilia bearing bipolar receptor cells. The 8 sensory spines situated between the circumoral area and the beginning of the scalids are ultrastructurally similar to the scalids. The introvert and pharyngeal body walls, and associated muscles are described. © 1994 Wiley-Liss, Inc.     

Margolisianum bulbosum n. gen., n. sp. (Nematoda: Philometridae) from the southern flounder, Paralichthys lethostigma (Pisces: Bothidae), in Mississippi Sound, USA

A new species of a philometrid nematode, Margolisianum bulbosum, is described from the subcutaneous tissue in the mouth (larvigerous females), head (males, ovigerous, and larvigerous females), and eye (preovigerous females) of the southern flounder, Paralichthys lethostigma, from Mississippi Sound. It is placed in a new genus diagnosed by the combination of 8 large, paired but separate cephalic papillae; no inner cephalic papillae; an esophagus with a separate, muscular anterior bulb; a prominent mononuclear esophageal gland; and variable, irregularly distributed cuticular bosses in the females, as well as a vestigial rectum, particularly in larvigerous females. Some female specimens exhibit rows of lateral grooves and longitudinal ridges near the posterior end. Males have 2 small slightly subequal spicules, a barbed gubernaculum, 4 pairs of small cephalic papillae, and a bipartite hypodermal extension within a membranous cuticle on the posterior end. Males, ovigerous females, and larvigerous females appear to be present year round in this sporadic infection in Mississippi.     

Hatching and earliest larval stages of the priapulid worm Priapulus caudatus

Abstract. Here we describe the hatching and morphology of the earliest larval stages of the priapulid worm Priapulus caudatus for the first time. The hatching larva differs considerably from previously described larvae not only in its general body shape but also in its lack of a proper lorica including the typical lorica tubuli. Furthermore, no mouth opening or pharyngeal teeth have formed as yet, and the number and arrangement of scalids differ from that of later larvae. The hatching larva molts and emerges as the first lorica larva. This larva partially resembles earlier described lorica larvae, but there are a number of important differences; the first lorica larva is smaller, and the mouth opening as well as pharyngeal teeth are still yet to form. The second lorica larva is equipped with four rings of pharyngeal teeth; it shows striking similarity to the previously described larva of P. caudatus , i.e., the larva-type 2 , only differing in the scalid pattern. We conclude that the first two larval stages of P. caudatus have not been described previously. We suggest that discrepancies between the earliest lorica larvae described here and in earlier publications might depend on sub-speciation or ecophenotypic modification of larvae collected from different localities. Our findings highlight the importance of studying the development of non-model organisms such as priapulids under controlled laboratory conditions.     

维螨属2新种记述(蜱螨亚纲:中气门目:维螨科)

记述维螨属2新种:河南维螨Veigaia henanensis sp.nov.和福建维螨Veigaia fujianensis sp.nov.     

An ultrastructural analysis of the cuticle,epidermis and esophageal epithelium of Eisenia foetida (Oligochaeta)

The epidermis of Eisenia is covered by a cuticle and rests on a basement lamella. The cuticle, which is resistant to a variety of enzymes, is composed of non-striated, bundles of probable collagen fibers that are orthogonally oriented and are embedded in a proteoglycan matrix. The basement lamella consists of striated collagen fibers with a 560 Å major periodicity. Proximity and morphology suggest that the epidermis may contribute to both the cuticle and the basement lamella — that is, the single tissue may synthesize at least two types of collagen. The epidermis is a pseudostratified epithelium containing three major cell types (columnar, basal and gland) and a rare fourth type with apical cilia. The esophagus is lined by a simple cuticulated epithelium composed predominantly of a single cell type, which resembles the epidermal columnar cell. Rare gland cells occur in the esophageal epithelium, but basal cells are lacking.     

Tubuläre intranukleäre Einschlußkörper beiLinaria vulgaris,L. alpina (Scrophulariaceae) undIncarvillea variabilis (Bignoniaceae)

The epidermal nuclei of the ovary inLinaria vulgaris andL. alpina, and the nuclei in leaves ofIncarvillea variabilis often contain crystalloid, tubular inclusions. The tubuli in bothLinaria species have an average diameter of 200 Å with a width of 70 Å in the clear and are arranged in a higly organized manner: Parallel tubuli form layers which build up a crystal lattice. There are three directions of tubuli in each inclusion: In each layer they are aligned in an angle of 60° to those of the next, so that the tubuli of the fourth layer are in the same direction as those of the first one. InIncarvillea the tubuli (each with an average diameter of 220 Å, and 70 Å width in the clear) also exhibit compact packing, but their arrangement is not so highly ordered as inLinaria.

     

Light and electron microscopy studies of the midgut and salivary glands of second and third instars of the horse stomach bot,Gasterophilus intestinalis

A morphological study of the midgut and salivary glands of second and third instars of Gasterophilus intestinalis (De Geer) (Diptera: Oestridae) was conducted by light, scanning and transmission electron microscopy. The midgut is anteriorly delimited by a proventriculus, without caeca, and is composed of posterior foregut and anterior midgut tissue from which a double‐layered peritrophic matrix is produced. The midgut can be divided into anterior, median and posterior regions on the basis of the structural and physiological variations of the columnar cells which occur along its length. Two other types of cell were identified: regenerative cells scattered throughout the columnar cells, and, more rarely, endocrine cells of two structural types (closed and open). Different secretion mechanisms (merocrine, apocrine and microapocrine) occur along the midgut epithelium. Abundant microorganisms are observed in the endoperitrophic space of the anterior midgut. The origin and nature of these microorganisms remain unknown. No structural differences are observed between the second and third instar midguts. The salivary glands of G. intestinalis second and third instars consist of a pair of elongated tubular structures connected to efferent ducts which unite to form a single deferent duct linked dorsally to the pharynx. Several intermediate cells, without cuticle, make the junction with the salivary gland epithelium layer. Cytological characteristics of the gland epithelial cells demonstrate high cellular activity and some structural variations are noticed between the two larval stages.     

EFFECT OF VARIOUS DOSES OF ESTROGEN TO BALB/cCrgl NEONATAL FEMALE MICE ON MAMMARY GROWTH AND BRANCHING AT 5 WEEKS OF AGE

High doses of 17β-estradiol given newborn mice the first 5 days of life had no effect on mammary growth at 3 weeks of age whereas glands measured at 5 weeks of age displayed marked dose-dependent differences in area and branching. The number of duct branches increased significantly as the estrogen dose was raised from the 25 μg threshold to 35 or to 70 μg. Ratios between area and branching remained constant under all experimental conditions. Regional, dose-dependent, differences in gland-pair response were also observed at 5 weeks. Mammary gland pairs differed significantly in several growth parameters. The third gland pair was smaller in area and had fewer branches, but the opposite was true of the second and fourth gland pairs. Systemic injection of high doses of 17β-estradiol into neonates reduced differences in growth parameters between gland pairs.     

TEM studies on the lattice organs of cirripede cypris larvae (Crustacea, Thecostraca, Cirripedia)

 Lattice organs consist of five pairs of sensory organs situated on the dorsal carapace in cypris larvae of the Crustacea Cirripedia. The lattice organs in cypris larvae of Trypetesa lampas (Acrothoracica) and Peltogaster paguri (Rhizocephala) represent the two main types found in cirripedes, but only minor differences exist at the TEM level. Each lattice organ is innervated by two bipolar, primary receptor cells. The inner dendritic segment of each receptor cell carries two outer dendritic segments. The outer dendritic segments contain modified cilia with a short ciliary segment (9×2+0 structure). Two sheath cells envelop the dendrite except for the distal ends of the outer dendritic segments. This distal end enters a cavity in the carapace cuticle and reaches a terminal pore situated at the far end of the cavity. The cuticle above the cavity is modified. In both species the epicuticle is partly perforated by numerous small pores and the underlying exocuticle is much thinner and less electron dense than the regular exocuticle. Lattice organs very probably have a chemosensory function and are homologous with the sensory dorsal organ of other crustacean taxa. Accepted: 18 August 1998     

Ultrastructure of the lycophora larva ofGyrocotyle urna (Cestoda,Gyrocotylidea)

Summary The fine structure of the glands of the lycophora larva ofGyrocotyle urna is described. There are four pairs of different glands which can be differentiated by the ultrastructure of their vesicles, their location and their gland pores. Their cell bodies are located at the transition from the median to the posterior third of the larva. Gland ducts formed by extensions of the gland cells run anteriorly and terminate at the anterior tip of the larva. In the cytoplasm of the terminal duct regions peripheral microtubules are found. The structure and function of the glands inGyrocotyle is discussed with regard to the evolution of cestodes and other Neodermata.     

Ultrastructure of introvert and pharynx of Halicryptus spinulosus (priapulida)

The introvert of Halicryptus spinulosus bears three kinds of sensilla: buccal papillae, ordinary scalids, and dentoscalids. They are all characterized by bipolar monociliary receptor cells. The former two have apical openings at which the sensory cilia are in close contact with the ambient sea water. The pharyngeal teeth are composed of slender epithelial cells the tips of which are devoid of organelles and a thick cuticle. The anatomy of the muscle arrangement of the pharynx is described. Glands occur at the junction of the pharynx and midgut.     

Histological organization of the intestine in the crayfish Procambarus clarkii

Six longitudinal ridges span the length of the intestine in the crayfish Procambarus clarkii. A simple columnar epithelium with tetralaminar cuticle lines the lumen. Folds of the epithelium overlie a dense irregular connective tissue packed with mixed acinar (alveolar) glands. Mucous secretions are probably involved with formation and lubrication of faecal strings; neither the nature nor the role of the serous secretions is immediately apparent. Aggregations of cells with large cytoplasmic vacuoles, called bladder cells, appear in the subepithelial connective tissue near the tops of the intestinal ridges. The bladder cells are suitably positioned to bolster the integrity of the ridges. Striated muscle of the intestine occurs in inner longitudinal and outer circular layers. The inner longitudinal layer consists of six strips, with one strip associated with the base of each intestinal ridge. The outer circular layer is essentially complete, but there are periodic apertures in this layer on the left and right sides of the intestine, providing nerves and haemolymph vessels with access to the interior of the gut. Based on histological features, and consistent with reports on other crayfish, we conclude that the intestine of P. clarkii has a proctodeal (ectodermal) origin.     

The function of forks: Isotelus‐type hypostomes and trilobite feeding

Hegna, T.A. 2010: The function of forks: Isotelus‐type hypostomes and trilobite feeding. Lethaia, Vol. 43, pp. 411–419. Despite previous investigations, the function of the forked morphology of asaphid trilobite hypostomes is enigmatic. The focus of this study is the large and robust forked hypostome of the largest known genus of trilobite, Isotelus, and the independently‐derived forked hypostome of Hypodicranotus, the longest hypostome relative to body size of any trilobite. Although the trilobite hypostome is analogous to the labrum in other arthropods, forked hypostomes lack an obvious modern functional counterpart. The Isotelus hypostome is distinguished from other trilobite hypostomes by closely‐spaced terrace ridges on a greatly thickened inner surface of the forked posterior margin, with the scarp of the terrace facing antero‐ventrally. This is compatible with a grinding function, suggesting possible limb differentiation to complement this structure. The inner face of the tine (one of the two, prominent, sub‐parallel posterior projections) is also unique in that it has a microstructure which is evident in section, running perpendicular to the surface. Macropredatory and filter‐feeder roles are ruled out, and previous characterizations of the hypostome as knife‐like or serrated are rejected. Its function is incompatible with that of other non‐asaphid trilobites with forked hypostomes, like the remopleuridid Hypodicranotus, which lack similar terrace ridges and thickened inner‐edge cuticle. □Arthropoda, Asaphida, ecology, functional morphology, Trilobita.     

Ultrastructure of Gonionchus australis (Xyalidae,Nematoda)

Observations are reported on the ultrastructure of the buccal cavity, body cuticle, spermatids, spermatozoa, male genitalia, and caudal glands of Gonionchus australis. The buccal cuticle is a continuation of the pharyngeal cuticle. Anteriorly it is secreted by arcade tissue and overlaps the mouth rim; laterally it forms longitudinal tooth ridges. The non-annulated cephalic cuticle differs sharply from the remainder of the body wall cuticle. The cortical and basal zones become much thinner, while a largely structureless, lucent median zone expands to fill the bulk of the lips and lip flaps. Spermatids possess fibrous bodies, multimembrane organelles, mitochondria, and compact chromatin. The spermatozoa of G. australis resemble those of most other nematodes by the absence of the nuclear envelope and presence of fibrous bodies, mitochondria, and compact chromafin. The ejaculatory duct possesses microvilli. Two ejaculatory glands lie beside the duct. Two neurons are located within each spicule and each part of the paired gubernaculum. Caudal gland nuclei are large, with dispersed chromatin. The ducts of all three caudal glands are filled with secretory vesicles.