Ultrastructure and histochemistry of the integument of air-breathing polychaetes from mangrove swamps of sumatra

The integument of S.E. Asian air-breathing polychaetes exhibits a variable ultrastructure with regard to cuticle and epithelial cells. The cuticle varies in thickness, contents of regularly arranged collagen fibrils, and structure of the epicuticle. The basal portion of the epithelium is either of smooth outline, or consists of slender processes of the epidermal cells separated by wide intercellular spaces which are invaded by a loose system of glia cells and nerve fibres. Extracellular spaces within the epidermis of the gills of Dendronereides heteropoda are transformed into blood lacunae. The enzyme content of the epithelial cells is relatively low.Supported by the Deutsche Forschungsgemeinschaft (Sto 75/2, We 380/4).     

Feinstruktur des Riechepithels von Chimaera monstrosa (Holocephali)

The epithelia of the olfactory folds of Chimaera monstrosa L. were studied by electron microscope. The greater part of each fold — including the secondary ones — is covered by sensory epithelium, whereas mere ciliary epithelium occurs on the tips of the folds. The olfactory epithelium is composed of ciliary cells, receptor cells, a few supporting cells, and basal cells. Mucous cells are restricted to the ciliary epithelium. As the apical region of the ciliary cells contains numerous vacuoles, including probably mucous substances, they may serve as producers of the superficial olfactory mucous layer. The ciliary basal bodies have two types of rootlets, the structure of which is described. Two morphologically different olfactory receptor cells could be identified: (1) receptors with a single, rod-shaped, free appendage (length 1.5 to 2 μm, diameter 0.1 to 0.5 μm), containing neurotubules, fibril bundles, and vesicles; (2) receptors whose dendrite bears few microvilli (length 2 to 3 μm, diameter 0.06 to 0.08 μm) projecting from a small vesicula olfactoria. Ciliary receptors are absent. The olfactory epithelium also contains sparsely distributed “brush” cells and a very few “giant” cells. Each “brush” cell bears a cluster of up to 250 microvilli (length 5 to 6 μm, diameter 0.1 μm) with 1 or more central tubulus and fibrils, the latter running into the cell body. The apical region of a brush cell contains densely packed mitochondria, which may indicate high metabolic activity; the function of this cell is unknown. The “giant” cell extends from the basal lamella to the epithelial surface. The ultrastructure of this cell does not reveal its special function.     

Über Bau und Funktion der Kiemen und Lungen von Ocypode ceratophthalma (Decapoda: Crustacea)

Electron micrographs reveal great differences between the epithelial linings of gills and lungs in the air-breathing crab Ocypode ceratophthalma. According to the fine structure, the gills have a mainly osmoregulatory function; they exhibit a very active transporting epithelium characterized by a large number of mitochondria, branched microvilli, and basal labyrinth. Blood spaces in the shaft of the gills are lined by podocytes, suggesting ultrafiltration. The lungs are typical respiratory organs, lined by a thin epithelium covered by a thin cuticle.     

Electron microscope study of the digestive system of Strongylocentrotus droebachiensis (Echinodermata: Echinoidea)

The fine structure of esophagus, stomach and intestinal epithelial cells of the sea urchin Strongylocentrotus droebachiensis have been examined. Three types of mucosal cells secreting neutral, acid and sulfated mucopolysaccharides have been found in the esophagus. The modes of origin of different types of mucous granules are described. Storage and zymogen cells have been identified in the stomach epithelium. Storage cells are adapted for intracellular digestion and synthesis of nutritive substance. Zymogen cells are adapted for enzyme synthesis. The columnar cells occur in the intestinal epithelium; they are adapted for nutrient absorption and lipid storage. Digestion in different parts of the digestive tract is considered in context with the ultrastructural and histochemical data obtained. Some problems concerning the relation between intracellular and extracellular digestion are discussed.     

Functional morphology of the larval tentacles of Phragmatopoma californica (Polychaeta: Sabellariidae): composite larval and adult organs of multifunctional significance

Larvae of the sabellariid polychaete Phragmatopoma californica (Fewkes), which were collected in San Diego, California and were competent to metamorphose after 18 to 30 d of development were observed in vivo by videoequipped light microscopy, and the fine structure of the larval tentacles was examined by transmission and scanning electron microscopy. Each tentacle has tufts of at least two types of immotile cilia arranged in dorsolateral and ventrolateral rows, and a ventral groove covered by two types of motile cilia that beat independently of each other. The epidermis is regionalized into glandular, sensory, locomotory, and support cell types and contains four longitudinal bundles of basiepithelial nerve fibers. A layer of connective tissue separates the epidermis and the nerve tracts from obliquely striated muscles that occur within the peritoneum that lines the central coelomic cavities. The peritoneum forms an intact coelomic epithelium that overlies and interdigitates with the muscle cells, with no intervening basal lamina. The muscle cells are considered to be intraperitoneal because they are located above the basal lamina and they lack intercellular junctions with the peritoneal cells. Specialized peritoneal cells form a striated myoepithelial blood vessel that partitions the coelom into medial and lateral cavities. No neuromuscular junctions were found, but both muscular and ciliary movement seem to be under neuronal control. The basiepithelial nerve terminals appear to synapse into the connective tissue layer toward the intraperitoneal muscle. Several similarities in tissue organization are noted between the larval tentacles of P. californica and the tube feet of echinoderms. Observations on the ontogeny, morphology, and behavior of the tentacles suggest that they are multifunctional organs involved in feeding, construction of the juvenile sand tube, locomotion, attachment, and sensory perception during larval and adult lives.     

Investigation of cell proliferation and differentiation in the mantle of <Emphasis Type="Italic">Pinctada </Emphasis><Emphasis Type="Italic">fucata</Emphasis> (Bivalve,Mollusca)

The mantle of the pearl oyster Pinctada fucata was adopted for the proliferation profile study in our work and a proliferation hot spot was found in the outer epithelia of mantle central zone using the BrdU immunohistochemistry method. This result contradicts the previous research that the mantle has numerous growth centers all over the mantle epithelium, with the same proliferation activity throughout the whole mantle outer epithelial cells. This is the first report on the different proliferation features on the whole mantle where Alcian Blue/PAS staining analysis and ultrastructural observation with the aid of transmission electron microscope (TEM) demonstrated distinct features of the epithelium in four different regions of the mantle. Results from the present investigation displayed that in the outer epithelium of the marginal zone in mantle outer fold, organelles such as mitochondria and endoplasmic reticulum (ER) were well-developed and double membrane bounded vesicles were present; in the outer epithelia of mantle central zone, stem-like cells with a high ratio of nucleus to cytoplasm and comparatively undeveloped organelles were detected. Together with the observations of the cell proliferation profile of different regions of the mantle, a hypothetic model for the proliferation and differentiation of the pearl oyster’s mantle is proposed: there exists a proliferation “hot spot” in the outer epithelial cells of central zone and the proliferation ability decreases progressively from this “hot spot” towards the marginal zone; the whole mantle’s differentiation occurs continuously with its growth and the direction is from the proliferation ‘hot spot’ (central zone) towards the marginal zone. Furthermore, another interesting result was found when the proliferation rate was investigated together with the tidal rhythm: the proliferation activity was found to be closely correlated with the tidal rhythm, indicating that the mantle outer epithelia’s proliferation rhythm might be the impetus of the shell’s daily growth bands.     

Histopathological alterations in hepatopancreas of Gafrarium divaricatum exposed to xylene, benzene and gear oil-WSF

Gafrarium divaricatum were exposed to xylene (4.25 and 8.50 mg l(-1)), benzene (4.35 and 8.70 mg l(-1)) and gear oil-WSF (1 and 2%) for 30 days. Chronic exposure of clams to the pollutants resulted in loss of bubbling epithelium, reduction in cytoplasm volume and density, fusion of cell membranes and nuclei forming darkly stained area at basal part of the cells. Disintegration of basement membrane due to damaged epithelial cells, disruption of inner lining of tubule, formation of necrotic spaces, separation of epithelial cells from basement membrane, increase in internal luminar area, complete necrosis of epithelial cells as well as occurrence of cell debris in between the tissue were also observed in the clams due to chronic exposure of the toxicants.     

Studies on reef corals. II. Fine structure of planktonic planula larva of Pocillopora damicornis,with emphasis on the aboral epidermis

Tissue and cellular organization of the planula larva of the reef-coral Pocillopora damicornis are detailed ultrastructurally. Emphasis is placed on fine structure of the aboral (=presumptive calicoblast) epidermis. The pre-settling exploratory behavior of the coral larva is discussed. The aboral epidermis consists of a tall columnar epithelium, made up of a heterogeneous cell population-nematocytes, secretory and mucus cells, and flagellated cells. Basally, the columnar epithelium is modified into complexly interdigitating cellular processes, appearing as a discrete histological layer. A-type granules (Jha and Mackie, 1967) indicate neurosecretory activity. The flagellated cell contains a peculiarly comlex flagellar apparatus, including a new intracellular structure, an electron-opaque fibrous cup. It extends across the entire width of the flagellated cell apically, enveloping the flagellar basal bodies and paired transverse accessory rootlets. The flagellum main basal rootlet passes freely through an opening in the base of the rootlet cup. The flagellated cell is here viewed as a sensory cell, as suggested by the corona of microvilli encircling the flagellum, the bundles of microvilli, and extensive areas of tight junctions with adjacent cells. There is no evidence in the gastrodermis or epidermis of the planktonic larva for pre-settling accumulation of calcareous skeletal material. Vesicles containing a highly oriented fibrous material may represent sites of skeletal organic-matrix precusor buildup.Contribution no. 451. Hawaii Institute of Marine Biology, Kaneohe, Hawaii.     

Cuvierian tubules of the holothuroid Holothuria forskali (Echinodermata): a morphofunctional study

Quiescent Cuvierian tubules of Holothuria forskali (Delle Chiaje, 1823) have a pseudostratified mesothelium made of ciliated cells that cover elongated cells containing lipoproteie granules. Together these cells form conspicuous transversal folds that penetrate the underlaying connective tissue. Circular and longitudinal muscle cells occur under the tips of the mesothelial folds. These cells are presumably myoepithelial cells; they divide the connective tissue into a thin outer layer (where collagen fibers are directed perpendicularly to the tubule long axis) and a thick inner layer (where collagen fibers are arranged in helices parallel to the tubular long axis). Nerve processes are associated with the longitudinal muscles; they also occur between the spirally arranged collagen fibers. A spiral nerve runs along the tubules; it innervates the circular muscles. The tubule lumen is narrow with a highly convoluted limiting epithelium. Epithelial cells are not ciliated; they have basal processes that contain enlarged spherules including mucosubstances and proteins. While having the same diameter as quiescent tubules, elongated tubules have a much thiner wall surrounding an enlarged cylindrical lumen. The mesothelium has no adluminal cells and consists of unfolded granular cells. In contact with a solid surface, granules become a sticky secretion. Longitudinal muscle fibers disintegrate and circular fibers form conspicuous rings along the tubules. Collagen helices still occur, but are considerably elongated and flattened. Inner epithelial cells dissociate from each other and typically lack basal processes and spherules, the latter being secreted into the lumen of elongating tubules. Discharge of Cuvierian tubules results from tubule expulsion and elongation. Tubule expulsion is triggered by the opening of the anus of a contracted holothuroid and results from the rupture of the cloaca with subsequent expulsion of coelomic fluid. Tubule elongation results both from the mechanical stimulation of the tubule sphincter by hydrostatic pressure and the entry of water into the tubule. Mechanical stimulation of the sphincter results in a rapid contraction of the circular muscles that causes the disintegration of adluminal cells, the unfolding of granular cells and the stretching of inner epithelial cells. Entry of water immediately follows sphincter stimulation and complete tubule elongation. Water pressure causes the irreversible elongation of collagen helices, which results both in a considerable thinning of the tubule wall and the formation of enlarged water-filled lumen. It is suggested that slippage of collagen fibers in elongating tubules is nervously mediated.     

An electron-microscope investigation of the cells lining the outer surface of the mantle in some marine molluscs

The ultrastructural details of the cells lining the outer surface of the mantle in Mytilus edulis (L), Cardium edule (L), and Nucula sulcata Bronn. are described. Along the length of the outer mantle fold and the general outer surface of the mantle, the epithelial cells differ, with a progressive reduction in the protein synthetic apparatus and an increase in glycogen, while large numbers of mitochondria are evident in the apical and basal regions.     

Histochemical and ultrastructural characterisation of mantle storage cells in the hydrothermal-vent bivalve Bathymodiolus azoricus

This study reports on two types of storage cells that are present in the mantle connective tissue of the deep-sea mussel Bathymodiolus azoricus. One type corresponds to the adipogranular cells, a kind of storage cell previously described in other bivalves. In these cells extensive regions of the cytoplasm are filled with glycogen deposits and these zones became strongly stained after histochemical (PAS) or ultrastructural detection of polysaccharides. Several lipid droplets and membrane bound granules containing homogeneous electron-dense material are also present in adipogranular cells. A second type of cell contains large lysosomes in addition to numerous lipid droplets, but lacking cytoplasmic glycogen deposits. Due to these characteristics we named them adipolysosomal cells. They can be identified in semi-thin sections stained with PAS reaction because the lysosomes are the only positively stained structures. In the connective tissue of the mantle, some cells containing many lysosomes and a few lipid droplets were also observed. These cells differ from the adipolysosomal cells mainly because they have a reduced amount of lipid reserves, and could be an initial stage in the development of adipolysosomal cells. The vesicular connective tissue cells that in other Mytilidae are specialised in glycogen storage were not detected in B. azoricus. The reserves accumulated in the two types of storage cells described in B. azoricus may be important for the survival of these hydrothermal-vent bivalves if their nutrition is affected by a temporary loss or reduction of endosymbiotic bacteria due to sulphide and/or methane shortage caused by oscillations in vent activity.     

Ultrastructural and cytochemical study on interactions between nutrient storage cells and gametogenesis in the mussel Mytilus edulis

The ultrastructural morphology of storage-cell breakdown and replenishment in Mytilus edulis is described for mussels collected at monthly intervals over a period of one year (September 1981 to October 1982) from a site in Cornwall, England. In addition cytochemical staining reactions at light and electron microscope levels are described for the storage cells and the Sertoli cells. The breakdown of adipogranular (ADG) cell components is believed to be a lysosomally-mediated process of controlled autolysis involving fusion of primary lysosomes with the protein granules. Increasing activity for lysosomal enzymes during ADG cell breakdown is demonstrated using quantitative cytochemistry. The presence of glycogen in vesicular connective tissue (VCT) cells is demonstrated using freeze-dried, formaldehyde-vapour-fixed tissue. The breakdown of VCT cells involves sequestration of glycogen from the central reserve into small cytoplasmic vesicles; subsequent release appears to be mediated by eccrine secretion. The presence of arylsulphatase activity in lysosomes within the peripheral cytoplasm of the VCT cells during the winter months indicates that glycogen breakdown may also be lysosomally mediated. The morphology of the Sertoli cells is described; during the early stages of spermatogenesis they are characterized by the presence of numerous lipid droplets which are depleted as development proceeds. Contact between Sertoli cells and developing spermatogonia is maintained by means of long septate junctions. Following spawning, the well developed lysosomal system is evident in the Sertoli cells and appears to be engaged in intracellular digestion of phagocytosed waste sperm and residual cytoplasm. Resorption of the products of gamete degeneration by the gonoduct epithelial cells is described. During regeneration, VCT cells appear to endocytose material; the ADG cells demonstrate extensive arrays of rough endoplasmic reticulum and are occasionally seen undergoing mitosis. A process involving loss of glycogen vesicles from the mantle epithelial cells by means of apocrine sections is described.     

Surface morphology of dogfish (Scyliorhinus canicula) gill epithelium,and surface morphological changes following treatment with zinc sulphate: A scanning electron microscope study

The surface morphology of the gill epithelium of the dogfish Scyliorhinus canicula L. (collected near Barcelona, Spain, in February–March, 1981) was studied by scanning electron microscopy. Pavement cells exhibited either surface microvilli or microridges, which were randomly distributed on both the primary (afferent and efferent sides and interlamellar spaces) and secondary epithelium. Chloride cell apical regions on the afferent side displayed characteristics closer to freshwater than to marine teleosts: no apical pits were detected; chloride cells displayed longer microvilli than those of adjacent cells. Two morphologically different cell types were identified: a large chloride cell and a smaller cell (probably a chloride cell too), measuring 4 to 7 m and 1 m, respectively, the latter being dominant in the interlamellar spaces. Apart from pavement cells, the mucous cell was the prevalent cell type on the efferent region. The respiratory epithelium consisted of a mozaic of typical epithelial cells; some chloride and mucous cells were present, mainly located at the base of the secondary lamellae. Surface morphological changes were monitored after exposing the dogfish to subacute zinc treatment: 10 ppm Zn (ZnSO₄) for 3 wk. The chloride cell was the only cell type that underwent any modifications: microvilli became longer and tips were swollen following Zn treatment. The results are discussed in relation to a previous study on the effects of zinc sulphate on chloride cell response and heavy metal distribution in excretory organs of the dogfish.     

An electron-microscope study of periostracum formation in some marine bivalves. II. The cells lining the periostracal groove

The histology and ultrastructure of the epithelial cells of the outer and middle mantle folds of the bivalves Mytilus edulis (L), Cardium edule (L), Macoma balthica (L) and Nucula sulcata Bronn are described. The cells lining the inner face of the outer fold exhibit a prominent granular endoplasmic reticulum, and Golgi complexes which are concerned with the elaboration of granules and vesicles eventually incorporated into the periostracum. A gradual reduction in the protein synthetic apparatus occurs towards the tip of the fold. Within the cells, it is proposed that the ovoid inclusion bodies are lysosomes and that they control the rate of secretion. The cells of the middle fold are cuboidal in appearance. Those of M. edulis and N. sulcata exhibit prominent granules, whereas those of C. edule and M. balthica possess vesicles. The cells of M. edulis differ from the others in possessing stout bundles of filaments, which occupy large areas of the cell and constitute a cell web. The cells of the epithelium in all cases do not appear to be implicated in periostracum formation.     

Cortical and endosomal structure of the marine sponge Stelletta grubii

The fine structure of the marine astrophorid sponge Stelletta grubii is described for the first time. The following new data are presented: spongin is present, choanocyte chambers are diplodal, intercellular symbiotic bacteria are numerous and unequally distributed in the cortex and endosome, and collagenous fibril bundles are associated with lophocyte activity and are not elastic fibers. The cortex contains numerous fibril bundles, fewer symbionts, very few cells, and transitional zones with higher archeocyte density near the surface and endosome. Limited phagocytosis of the bacterial symbionts is observed. This species appears to be dioecious and oviparous. These observations suggest that the enigmatic species Chondrosia reniformis is closely related to S. grubii and that it should be placed within or near the astrophorids. The rhizoids of the red alga Phyllophora palmettoides penetrate the sponge tissue without eliciting the development of a structurally specialized contact zone in the sponge matrix or of a limiting epithelium.     

Fine structure of some prosobranch ospharadia

The fine structure of the osphradia of Buccinum undatum 1. three Hawaiian Conus spp., Nassarius reticulatus (L), Nucella lapillus (L) and Littorina littorea (L) was examined. There is a remarkable uniformity in the arrangement of ultrastructural cell types in all the ospharadia investigated. The marginal glandular region is characterised by a single layer of cells, bearing a regular pallisade of microvilli and including two types of mucous cell. The epithelium of the sensory region is several cells deep, and bears a complex layer of microvilli in many orientations. Besides indifferent cells it contains two types of cell bodies of ciliated nerve processes. One type ends at the surface of the sensory region. The other, containing an elaborate array of smooth membranes in the perikaryon, has a process which enters the transitional region between sensory and glandular areas. In the transitional region, specialised cells with motile cilia adjoin the glandular region, and similar, but unciliated cells, containing large pigment granules scattered throughout the cytoplasm, adjoin the sensory region. The distal surface of both cell types is dissected by elefts extending 2 to 3 proximally, then widening into extensive spaces which contain cytoplasmic processes. The ciliated neurites which enter the transitional region end in the spaces at the base of the unciliated transitional cell elefts. It is suggested that the neuroepithelial cell processes, both those distributed over the sensory region and those concentrated in the transitional region, are receptors.     

An electron-microscope investigation into the cuticle and associated tissues of the operculum of some marine serpulids

The fine structure of the opercula of Spirobis borealis Daudin and S. pusilloides Bush, and the primary and secondary operculum of S. granulatus (L) have been examined by electron microscopy. In different regions, the epithelium of the operculum exhibits variations in thickness and fine structure which correspond to transitions from peduncular to opercular wall to opercular plate epithelia. Externally, the peduncle and walls of the operculum are covered by a cuticle which is composed of several layers of fibrils/fibres embedded in an amorphous matrix. It is regularly traversed by microvilli from underlying cells. At the operculum rim, the cuticle changes so that its appearance is thick and solid. It continues across the roof of the operculum as a thin layer overlying a calcareous plate. The secondary operculum of S. granulatus differs from those of the other species in that an internal calcareous plate and solid cuticle line the roof of the operculum. It differs further in possessing an opercular pore. The possibilities are discussed of the cuticle fibrils/fibres of the peduncle and the opercular wall being collagenous in nature, and later being transformed to a solid tanned structure overlying a calcareous plate. The modes of secretion of the cuticle and calcareous plate by underlying cells are also discussed.     

Cytological study and immunohistochemical location of PSP toxins in foot skin of the ormer, Haliotis tuberculata, from the Galician coast (NW Spain)

The ormer, Haliotis tuberculata Linnaeus, 1758, is able to accumulate paralytic shellfish toxins (PST) in the foot side skin. Epidermal and secretory cells are described separately for the pedal side and sole epithelia, as notable differences have been observed. Melanin and photosynthetic pigment granules in the epidermal cells of the foot side epithelium give this skin its appearance and characteristic color. This epidermis also has abundant secretory cells containing at least three kinds of secretory granules. Conversely, the epidermal cells of foot sole epithelium do not have pigment granules, and the secretory cells are mostly subepithelial. Immunohistochemical reaction against PST (saxitoxin and its derivatives) showed that the toxins are located in specific cells of the foot side epithelium, which are distinct from the epidermal cells. Immunofluorescence also reveals toxins throughout many areas of the mucilage covering the epithelium, suggesting the secretory nature of the cells containing the toxins. These results do not show any apparent relationship between melanin or photosynthetic pigment granules and PST content. PST were not detected in the foot sole epithelium either immunohistochemically or by HPLC. Considering the toxic characteristics of ormers described in previous studies and the results presented here, the authors discuss the role of toxins retained or produced by the foot side epithelium Received: 25 July 2000 / Accepted: 7 November 2000     

Cyclical contributions of the digestive epithelium to faecal pellet formation by the copepod Calanus helgolandicus

Faecal pellet formation within the gut of Stage V and adult females of the copepod Calanus helgolandicus Claus involves (1) cyclical processes of digestion and (2) the contribution of parts of the gut epithelium to the pellets. During an experimental regime in which dim lighting was restricted to day-time and feeding to night-time (17.00 to 09.00 hrs), the copepods responded with cyclical changes in both the quantity of pellets they produced and the fine structure of the contents. During the feeding period, the contents showed changes in the relative amounts of materials originating from disintegrated cells of the digestive epithelium and those derived directly from the ingested food. The vacuolar B-cells of the gut contribute to the content of the pellets and the distal, necrotic N-cells appear to be involved in forming the peritrophic membrane which encloses each pellet. Cells of the gut epithelium which are broken down during feeding are all replaced during the non-feeding period. Other individuals were taken directly from the sea and in these, also, the cells of the gut broke down during feeding and contributed to the faecal pellets. The supply of epithelial cells may limit the duration of the feeding period.     

Physiology of the digestive tract of the sedentary polychaete Terebellides stroemi

The digestive tract of the sedentary polychaete Terebellides stroemi, collected from 88 m depth on the French Catalan Coast, was studied using histological, biochemical, cytological and spectrographic techniques. The ciliated oesophagus possesses a ventral pharyngeal pouch with a muscle bulb. The stomach is divided into two parts, the fore stomach is ciliated, but the hind stomach takes the place of a gizzard with a thick peritrophic membrane and a thick muscle mantle. The digestive gland enters the digestive tract at the boundary of the two stomachal areas; it is comprised of epithelial lamellae with a glandular epithelium. The gland cells contain a spherocrystal secretion with a high calcium and phosphorus content. The cells are also absorbant due to their microvillar brush border and to the storage of glycogen and lipids in the basal epithelium. A biochemical study using the Apizym System confirmed the secretion of enzymes such as phosphatases, esterases and various carbohydrases. Tryptic and chymotryptic enzymes were visualized by biochemical hydrolysis of synthetic substrates. The epithelium of the fore intestine is similar in appearance to the epithelium of the digestive gland, but consists of a single epithelial layer. Hind intestine and rectum are only excretory systems. The presence of this digestive gland does not seem to have been described elsewhere in polychaetes but is similar to the Morren's gland of some oligochaetes. The study was carried out during 1982 and 1983.