Fine structure of the male reproductive system in two species ofHaplognathia sterrer (Gnathostomulida,Filospermoidea)

Summary The structure of the male reproductive systems of two species ofHaplognathia cf.lyra andH. cf.rosacea was described. The structure of the testes and the anterior portions of the sperm ducts in both species was found to be similar. However, considerable species differences were found between the structures of the glands and muscles associated with the reproductive systems. These were more elaborate inH. cf.lyra than inH. cf.rosacea. The former species possessed an H-shaped sperm duct gland, three distinct groups of penis muscles and a penis with two cell types and with a lumen. The latter species had paired sperm duct glands, no specialized penis muscles and a penis with only one cell type and without a detectable lumen. No open gonopore was observed in either species. The sperm presumably exit through a ventral tissue connection observed connecting the penis and the ventral epidermis. These findings were discussed in the light of Mainitz's (1977) theory concerning the primitive penis type within the Gnathostomulida.Abbreviations ap anterior-posterior penis muscles - bm basement membrane - csd common sperm duct - dl dorsal lumen of the penis - dp dorsal gland cells of the penis - dv dorsoventral muscles anterior to the penis - dw sperm duct wall cell - e epidermis - ex exit cell - g intestine - gl gut lumen - n nerve - p penis - sd sperm duct - sdg sperm duct gland - tw testes wall cell - vl ventral lumen of the penis - vp ventral gland cells of the penis This project was supported by NSF grant #GB 42211 (R.M. Rieger P.I.). The line drawings have been executed after our design by Ms. Linda McVay     

Fine structure and histochemistry of the epidermis of the fish Monopterus cuchia

An attempt is made to correlate fine structure with the histochemical reactions of the epidermis in the synbranchiform fish Monopterus cuchia. Three sources of mucus are identified. Superficial epithelial cells produce weakly acidic glycoprotein which is secreted at the surface as the external mucous layer or cuticle. Numerous large unicellular mucous glands have a secretion which is strongly acidic and sulphated, although the basal and peripheral parts of these cells, which contain most of the rough endoplasmic reticulum, react strongly for neutral glycoprotein; Golgi cisternae appear to be involved in a change of histochemical reaction from neutral to strongly acidic as the secretion is formed. A second, slender, type of mucous gland cell, not previously reported, gives a weaker reaction for sulphated acidic glycoprotein and has cytoplasm with numerous Golgi cisternae and free ribosomes, producing electron–dense secreted drops. Sacciform cells, with a protein–aceous secretion, have a characteristic fine structure with membranous "bubbles" at the surface of the cytoplasm. Ionocytes, sensor) cells and intrusive leucocytes have been identified in the epidermis.     

Fine structure of sacciform cells in the epidermis of the brown trout, Salmo trutta

The fine structure of a cell type in the epidermis of brown trout, Salmo trutta L., is described. Its cytological features are compared with those of other sacciform cells reported in several species of teleost fish. This cell type also has a highly electron-dense cytoplasm with numerous Golgi systems and extensive rough endoplasmic reticulum. However, surrounding the large central vacuole there are no peripheral vesicles—'bubbles'—which are characteristic features in non-salmonid teleosts. Instead of these, in the vacuole there are cytoplasmic intrusions of circular cross-sections forming a mesh in the cortical zone. Inside these intrusions there are granules which are interpreted as ribosomes trapped by fusion of the vacuole and reticulum membranes. The way in which the secretion is released into the lumen of the central vacuole is discussed. It is suggested that this proteinaceous material does not pass through the Golgi system, but flows directly from endoplasmic cisternae to the vacuole.     

The fine structure of spiral ciliary receptors in Gnathostomulida

Summary The fine structure of the spiral ciliary receptor of three gnathostomulid species is described. Each receptor bears a single cilium — with 9+2 axoneme, basal body and accessory centriole — rolled up in an internal cavity. Spherical and annular cavities are construed as two different types of spiral ciliary receptor. Relations to presumptive photoreceptors in other lower Bilateria and considerations of possible function of these gnathostomulid receptors are discussed.     

Studies on Pogonophora. 4. Fine structure of the cuticle and epidermis

The fine structure of the integument in several species of Pogonophora has been examined by electron microscopy. The cuticle over the main body is composed of several layers of orthogonally arranged fibres embedded in an amorphous matrix. It is regularly traversed by microvilli from underlying epidermal cells. Toothed bristles of the annuli and setae of the anchor are composed of closely packed fibrous cylinders wrapped in a cortical material. In fine structure the cuticle, setae, toothed bristles (or setae) and setal sacs forming the setae closely resemble the corresponding structures in annelids. The cuticle is maximally thick over the forepart (protosome + mesosome) ; it is very thin and non-fibrous over the surface of the metameric papillae and over extensive areas of post-metameric trunk. The possibilities of a collagenous nature of the cuticle fibres and their mode of secretion by the epidermal cells are discussed. The organization of various cell-types forming the epidermis over the entire animal is examined. Possible functions of these cell-types are discussed. Notable amongst these are 'possible zymogen cells' and some absorptive cells. The intriguing question of nutrition in these gut-less tubiculous animals is re-examined in the light of present observations.     

Fine structure of the epidermis of the mudskipper,Periophthalmus modestus (Gobiidae)

The ultra-structure of the epidermis of the mudskipper,Periophthalmus modestus, was examined by both light and transmission electron microscopies. The epidermis is exceptionally not well endowed with mucous or granular cells. Filament-containing cells occur in three distinct layers of the surface, middle and basal epidermis. The surface layer is further subdivided into two layers, an outermost and less superficial one. Two different cell types were identified in the epidermis. Type I cells are fiat cells in a single stratum. Type II cells are enormous cells, characterized by having a large vacuole in the cytoplasm. The outermost layer is composed of a free surface of Type I cells and numerous microridges covered with a fuzzy, fibrillar substance. The “fuzz” forms a cuticule-like structure, but keratinization as found in terrestrial animals does not occur. The superficial layer contains Type I cells and intraepithelial blood capillaries. When Type I cells become senescent, numerous intercellular spaces are formed in the plasma membranes of adjacent cells, with the senescent cells finally falling off. Just beneath these cells, however, young cells of Type I are always found. The blood capillaries are usually reinforced with young Type I cells. A large volume of oxygen may be absorbed through the skin using the blood capillary network. The middle layer contains several strata of Type II cells. The special corky structure of these cells seems to play an important role in thermal insulation and protection against ultraviolet light in relation to life out of water. However, by comparison with terrestrial animals, the histological design of the epidermis of this goby appears incomplete, so as to reduce desiccation on land, owing to the epidermis lacking a keratinized stratum. The differentiation of the epidermis seems to be an adaptation for a terrestrial habit in this species.     

Fine structural observations on the epidermis

Summary The organization of the wall of epidermal cells in the petiole of species of Apium, Eryngium, Rumex, and Abutilon as well as that of the epidermis of Avena coleoptile has been investigated. The outer and inner tangential walls consist of layers in which the cellulose microfibrils are oriented alternately parallel or transverse to the longitudinal cell axis. This organization resembles that previously described for collenchyma cell walls (Wardrop, 1969; Chafe, 1970). On the radial (anticlinal) walls the orientation of the microfibrils is transverse and these appear continuous with the layers of transverse orientation of the outer and inner tangential walls. Variation in thickness of the outer tangential, and radial, and inner tangential walls appears to result from the variation in thickness of those layers in which the microfibrils have a longitudinal orientation. The extent to which these observations can interpreted in terms of some type of modified multi-net growth is discussed.     

Fine structure of the epidermis of the optic tentacle in a slug, Limax flavus L.

The epidermis at the tip of the optic tentacle in Limax flavus is constructed of columnar epithelial cells, distal processes of nerve cells, and scattered processes of the collar cells. The epithelial cells extend stout microvilli called plasmatic processes by Wright perpendicularly from the free surface. Each plasmic process branches into a few terminal twigs embedded in a fuzzy filamentous substance. Most nerve cells have their nuclei under the basal lamina. The distal processes of these nerve cells reach the free surface and send long microvilli to form the spongy layer under a filamentous covering. At the side surface of the tentacle the epithelial cells are cuboidal or squamous and the neural elements are fewer. Here, no spongy layer is formed; and the collar cell processes are replaced by the lateral cell processes. Peculiar secretion granules are contained in the lateral and collar cell processes as well as in their cell bodies situated beneath the basal lamina.     

Fine structure of the ciliated epidermis on the tentacles ofOwenia fusiformis (Polychaeta,Oweniidae)

Summary The ultrastructure of the epithelium on the oral surface of the tentacles ofOwenia fusiformis has been studied by light and electron microscopy. Unspecialized monociliated cells are the dominant cell type of the epithelium; however, biciliated epidermal cells, monociliated mucous cells and non-ciliated cells are also present. In all of the ciliated cells each cilium is provided with a diplosomal basal body and two striated rootlets. The cytological features of this unspecialized epithelium strongly resemble those of similar epithelia in the Phoronida, Brachiopoda and Hemichordata. So far,O. fusiformis is the only polychaete known to possess an unspecialized monociliated epidermis. Other characters ofOwenia are also mentioned. The relationship between the nervous system and the epidermal cells on the tentacles is examined. It is proposed thatOwenia should assume an important role in discussions of the phylogeny of the Polychaeta.I wish to thank Dr. R.M. Rieger for his inspiration and guidance during the course of this study. Ms. Wilma Hanton provided technical assistance for the electron microscopy. This work was supported by NSF Grant # GB-42211 to R.M. Rieger     

The fine structure of protonephridia in Gnathostomulida and their comparison within Bilateria

Summary The fine structure of the protonephridia of Haplognathia rosea (Filospermoidea) and Gnathostomula paradoxa (Bursovaginoidea) is described. Each protonephridium consists of three different cells: (1) a monociliated terminal cell which constitutes the filtration area, (2) a nonciliated canal cell showing a special protonephridial outlet system, and (3) an intraepidermal cell — the nephroporus cell — constituting the nephroporus. The protonephridia are arranged serially. There is no canal system connecting the protonephridial units.Protonephridial characters in other Bilateria are considered. The pattern of characters in the protonephridia in the last common gnathostomulid stem species and presumed apomorphies in the protonephridia of the Gnathostomulida investigated are discussed.Abbreviations used in figures ac acessory centriole - AC additional epidermal cell - bb basal body - bl basal lamina - bm bundle of microvilli - c cilium - cc cilium duct cell - cd cilium duct - cr ciliary rootlet - crs structures resembling ciliary rootlets - di diplosome - ds desmosome - dy dictyosome - f filtration area - g granules - m mitochondrium - mv microvillus - n nucleus - NC nephroporus cell - np nephroporus - oc outlet canal - TC terminal cell - tl tubules of lacunar system     

Indication of an Anal Pore in Gnathostomulida

Two species of Haplognathia (Gnathostomulida, Filospermoidea) were examined by electron microscopy and found to possess a tissue connection between the posterior end of the intestine and the dorsal epidermis. This anal tissue connection is characterized by a thinned out epidermis, interdigitation of epidermal and intestinal cells, and the absence of the basement membrane. An open anal pore was not observed. It is possible that the anal tissue connection of Haplognathia serves as a functional anal pore. The implications of this discovery with respect to the various theories of early Metazoan evolution are discussed.     

Comparative structure of the epidermis in polychaetes (Annelida)

The polychaete epidermis generally consists of a single layer of supportive cells, gland cells and sensory cells. Except for the latter, this paper reviews the recent literature on the annelid epidermis, focussing on the mentioned cell types and the cuticle. The annelid epidermis is compared to that of Sipuncula, Echiura and Myzostomida. Supportive cells predominate in the polychaete epidermis. They show a high structural diversity even within single specimens. Ciliated cells are usually multiciliary and only two cases of monociliary epidermis cells are known. Unambigous epithilio-muscle cells are only described in feeding palps of a Magelona species. Secretory cells release a large number of gland products and some of them are essential for tube secretion. Rather pecularities of the cells and its arrangement within glands than the ultrastructure of the secretions is useful for phylogenetic considerations. One of the main components of the cuticle is collagen. Recent studies indicate that annelid cuticular collagen differs in several aspects from collagen of the connective tissue and might be of interest for systematics.     

Fine structure of the honeybee Z-disc

Z-discs from the dorsal longitudinal indirect flight muscles of the honeybee (Apis mellifera) are perforated with hundreds of triangular-shaped tubes ordered into an hexagonal array. Each tube is surrounded by 80 Å thick rims which incorporate six thin filaments, three from each bordering sarcomere. Although the triangular rims of the tubes are oriented identically in any plane perpendicular to the fibril axis, this orientation changes as the tubes cross the Z-line. The tubes rotate approximately 60 ° about an axis parallel to that of the fibril in passing from one I-Z junction to another.On the basis of filament counting in the A (overlap zone) and I bands of stretched myofibrils, it is concluded that the primary filaments are physically continuous with the Z-lines by material which appears to participate both in the formation of Z-rim substance and the surrounding matrix.Finally, evidence is presented to support the view that filament lattices of adjacent sarcomeres are displaced from one another, so that each thick filament faces the trigonal position of three thick filaments on the other side of the Z-disc.