Spermatozoon of the freshwater rotifer Brachionus calyciflorus (Rotifera,Monogononta): Advances in morphological and ultrastructural studies

The morphological and ultrastructural features of the spermatozoon in Brachionus calyciflorus are described using light, fluorescence and transmission electron microscopy (TEM). The mature spermatozoon, which appears to be thread-like, is composed of a slightly expanded anterior of cell body region and a flagellum region without acrosome. The cell body region and flagellum region are respectively 16–27 μm and 20–33 μm in length (n = 60). The spermatozoon is characterized by a mass of dense tubular materials, which occupy most of the cell. Some mitochondria are distributed around the nuclear region in the anterior of the cell body region, while in the posterior portion of cell body, the chromatin often contains a single lobated nucleus arranged at the center of cell. The flagellum contains the classic axoneme (9 × 2 + 2) and possesses lateral undulating membrane. Mature B. calyciflorus males have no germ cell stages earlier than the spermatids in the testis. TEM examination reveals rigid rods as well as predominant typical spermatozoon in the testis. Observations, based on successive photographs and videos, enabled a first-time recording of the unique inverted movement of the spermatozoon, which indicated that the movement of the spermatozoon is driven by the flagellum. Our study also provides further supplementary insights into the phylogenetic systematics of the Rotifera.     

Morphological and ultrastructural characterization of the alimentary canal in Japanese wax scale (Ceroplastes japonicus Green)

The morphology and ultrastructure of the alimentary canal in the adult female of the Japanese wax scale, Ceroplastes japonicus Green (Hemiptera: Coccoidea: Coccidae), was investigated using light microscopy, scanning electron microscopy and transmission electron microscopy. The results showed that the foregut was subdivided into a sclerotized pharynx and an oesophagus. A pair of salivary glands attached in the middle of the foregut. The loop-shaped midgut was narrow and longer than the foregut and its inner wall lined with a thick layer of epithelia. The hindgut was divided into a narrower ileum and a broader rectum, with the well-developed filter chamber enclosed in the anterior rectum. Malpighian tubules consisted of two brownish-yellow moniliform tubules with pores, approximately 1 μm in diameter, scattered on the outer surface and many spherical crystals inside the tubules.     

等节跳虫表皮和小眼表面超微结构的观察：（弹尾目：等节跳科）

本文报道了弹尾目Collembola等节跳科Isotomidae11种跳虫表皮和小眼表面超微结构的观察,发现该超微结构具有明显种属特异性,可作为物种鉴定的重要分类性状;对其研究,还有助于生物进化、亲缘关系及生态适应等的探索。     

Structure and composition of calcareous sponge spicules: a review and comparison to structurally related biominerals

Since the early 19th century, the skeletons of calcareous sponges (Porifera: Calcarea) with their mineralized spicules have been investigated for their morphologies, structures, and mineralogical and organic compositions. These biomineral spicules, up to about 10 mm in size, with one to four rays called actines, have various specific shapes and consist mainly of magnesium-calcite: in only one case has an additional phase of stabilized amorphous CaCO₃ (ACC) been discovered. The spicules are invariably covered by a thin organic sheath and display a number of intriguing properties. Despite their complex morphologies and rounded surfaces without flat crystal faces they behave largely as single crystal individuals of calcite, and to some degree crystallographic orientation is related to morphology. Despite their single-crystalline nature, most spicules show nearly isotropic fracture behaviour, not typical for calcite crystals, indicating enhanced fracture resistance. These unusual morphological and mechanical properties are the result of their mechanism of growth. Each spicule is formed by specialized cells (sclerocytes) that supply mineral ions or particles associated by organic macromolecules to extracellular cavities, where assembly and crystallization in alignment with an initial seed crystal (nucleus) takes place. As a result of discontinuous mineral deposition, cross-sections of larger spicules display concentric layering that mantles a central calcitic rod. On a smaller scale, the entire spicule displays a ‘nano-cluster’ structure with crystallographically aligned and putatively semicoherent crystal domains as well as a dispersed organic matrix intercalated between domain boundaries. This ultrastructure dissipates mechanical stress and deflects propagating fractures. Additionally, this nano-cluster construction, probably induced by intercalated organic substances, enables the formation of complex crystal morphologies independent of crystal faces. In this review, the current knowledge about the structure, composition, and formation of calcareous sponge spicules is summarised and discussed. Comparisons of calcareous sponge spicules with the amorphous silica spicules of sponges of the classes Hexactinellida and Demospongiae, as well as with calcitic skeletal elements of echinoderms are drawn. Despite the variety of poriferan spicule mineralogy and the distant phylogenetic relationship between sponges and echinoderms, all of these biominerals share similarities regarding their nano-scale construction. Furthermore, echinoderm skeletal elements resemble calcareous sponge spicules in that they represent magnesium-bearing calcite single-crystals with extremely complex morphologies.     

Ultrastructural analysis of spermiogenesis in the Eastern Fence Lizard,Sceloporus undulatus (Squamata: Phrynosomatidae)

Studies on reptilian sperm morphology have shown that variation exists at various taxonomic levels but studies on the ontogeny of variation are rare. Sperm development follows a generalized bauplan that includes acrosome development, nuclear condensation and elongation, and flagellar development. However, minute differences can be observed such as the presence/absence of manchette microtubules, structural organization during nuclear condensation, and presence/absence of a nuclear lacuna. The purpose of this investigation was to examine sperm development within the Sceloporus genus. The process begins with the development of an acrosomal complex from Golgi vesicles followed by nuclear condensation and elongation, which results in the presence of a nuclear lacuna. As the acrosomal complex differentiates, flagellar development commences with elongation of the distal centriole. Spermatid development culminates in a mature spermatid with a highly differentiated acrosomal complex, a condensed nucleus with a nuclear lacuna, and a differentiated flagellum. Although the overall developmental pattern is consistent with other squamate species, minute differences are observed, even within the same genus. For example there is variation in the presence/absence of an endoplasmic reticulum complex during acrosome development, presence/absence of a nuclear lacuna, and presence/absence of manchette microtubules within the three species of Sceloporus studied to date. Future studies concerning sperm morphology in closely related species will aid in our understanding of variation in sperm development and may prove to be useful in testing phylogenetic and evolutionary hypotheses.     

The vegetative arctic freshwater green alga Zygnema is insensitive to experimental UV exposure

The physiological performance and ultrastructural integrity of the vegetative freshwater green alga Zygnema sp., growing under ambient polar day solar radiation and after exposure to experimentally low radiation, but with high UVR:PAR ratio were investigated. In the laboratory, algae were exposed to low photosynthetic active radiation (PAR = P, 400–700 nm, 20 μmol m⁻² s⁻¹), PAR + UV-A = PA (320–400 nm, 4.00 W m⁻² = UV-A) and PAR + UV-A + UV-B = PAB (280–320 nm, 0.42 W m⁻² = UV-B) for 24 h at 7 °C. Photosynthetic performance and ultrastructure of ambient solar radiation-exposed (field control) and experimentally treated Zygnema samples were assessed using chlorophyll fluorescence, and transmission electron microscopy (TEM). No significant treatment effect was observed in the photosynthesis–irradiance curve parameters. Exclusion of the UV-B spectrum in the laboratory treatment caused significantly lower effective photosynthetic quantum yield compared to samples exposed to the whole radiation spectrum. TEM revealed no obvious differences in the ultrastructure of field control and laboratory P-, PA- and PAB-exposed samples. Substantial amounts of lipid bodies, visualized by Sudan IV staining, were observed in all samples. Chloroplasts contained numerous plastoglobules. Organelles like mitochondria, Golgi bodies and the nucleus remained unaffected by the radiation exposures. Zygnema is well adapted to ambient solar radiation, enabling the alga to cope with experimental UV exposure and it is expected to persist in a scenario with enhanced UV radiation caused by stratospheric ozone depletion.     

The venom gland of queens of Apis mellifera (Hymenoptera, Apidae): morphology and secretory cycle

The venom gland of queens of Apis mellifera was examined through light and transmission electron microscopy and subjected to electrophoretic analyses. Virgin queens exhibited prismatic secretory cells containing large amounts of rough endoplasmic reticulum with dilated cisternae, open secretory spaces, numerous vacuoles and granules scattered in the cytoplasm, and spherical nuclei with numerous nucleoli. The secretion produced was non-refringent under polarized light and the electrophoretic analysis of glandular extracts revealed five main protein bands. In mated queens, the venom gland exhibited a high degree of degeneration. Its secretion was refringent under polarized light and one of the main bands was absent in the electrophoretic pattern obtained. The morphological aspects observed are in agreement with the function of this gland in queens, given that virgin queens use venom in battles for the dominance of the colony, a situation that occurs as soon as they emerge, while fertilized queens rarely use venom.     

Microanatomy and ultrastructure of outer mantle epidermis of the cuttlefish,Sepia esculenta (Cephalopoda: Sepiidae)

This study describes the ultrastructural characteristics of external epidermis of mantle of Sepia esculenta using light and electron microscopy. The epidermis was thicker on the ventral surface than on the dorsal surface, with a higher secretory cell distribution on the ventral surface than on the dorsal surface. The epidermis was a single layer composed of epithelial cells, secretory cells, ciliated cells and neuroglial cells. Epithelial cells were columnar with well-developed microvilli on the free surface, and the microvilli were covered with glycocalyx. The epithelial cells were connected to the neighboring cells by tight junctions and membrane interdigitations of the apico-frontal surface. Well-developed microfilaments were arranged in a vertical direction in the cortical cytoplasm. The secretory cells were categorized into three types (A, B and C) in accordance with the light microscopical characteristics and ultrastructures of the secretory granules. The distribution of these cells was in the following order: Type A > Type B > Type C. SEM observation revealed that the secretory pore size of the Type A secretory cells was approximately 8.6 μm × 12.2 μm. Cytoplasm displayed a red color as the result of Masson's trichrome stain and H–E stain, and contained polygonal granules of approximately 1.2 μm² with a high electron density. The secretory pore size of the Type B secretory cells was approximately 10.1 μm × 12.1 μm. As the results of AB–PAS (pH 2.5) and AF–AB (pH 2.5) reactions, the cytoplasm displayed a red color. The cells contained membrane bounded secretory granules with very low electron density. The secretory pore of the Type C secretory cells was circular shape, and approximately 5.5 μm × 5.5 μm. Cytoplasm was found to be homogeneous under H–E stain and Masson's trichrome stain, and displayed a red color. As the result of AB–PAS (pH 2.5) reaction, the cytoplasm displayed a red color. The electron density of the secretory substance was the highest among the three types of secretory cells. The ciliated cells had a ciliary tuft on the free surface and were distributed throughout the mantle with the exception of the adhesive organs. Neuroglial cells were connected to the basal membrane, epithelial cells, secretory cells and nerve fibers through cytoplasmic process, and contained neurosecretory granules with high electron density within the cytoplasm.     

Temperature induced alterations in the liver of wall lizard (Hemidactylus frenatus): morphological and biochemical parameters

Wall lizards (Hemidactylus frenatus) were adapted to 20, 25, and 30 °C, and the liver was examined using standard transmission electron microscopy (TEM) and biochemical analysis. Peroxisomes were visualized after using the 3,3′-diaminobenzidine (DAB) technique. Catalase, uricase and protein content wsere determined biochemically. The hepatocytes of animals adapted to higher temperature displayed larger lipid inclusions than those of animals adapted to lower temperature. Rough endoplasmic reticulum was better developed in the animals kept at low temperature (20 and 25 °C) than in the animals held at 30 °C. Cytoplasmic crystalline structures were visualized, and better developed in the hepatocytes at 25 °C. Peroxisomes varied with the temperature, being more frequent in the animals kept at 20 °C, while the bigger ones prevailed in the animals kept at 30 °C. The higher catalase activity at higher temperature was correlated to an increase in staining intensity of DAB-incubated peroxisomes as visualized cytochemically in TEM. The biochemical results confirmed the cytochemical reaction observed by TEM. The hepatocytes of the animals at 30 °C showed a reduction in the number of peroxisomes, however, at this temperature the largest peroxisomes with a stronger reaction to DAB and a higher activity of catalase predominate. In contrast, the uricase activity showed no significant variation in relation to adaptation temperature. Overall, these data show the morphological and functional plasticity of hepatocytes to temperature adaptation of H. frenatus.