摘要:

AbstractUnique morphological structures occur near the midgut–hindgut juncture in decapod crustaceans, and neither their fine structure nor function are well understood. In the ghost shrimpLepidophthalmus louisianensis.structures associated with this juncture include an elongate posterior midgut caecum (PMGC) extending into the abdominal hemocoel, a massive swelling of acinar glands encasing the juncture, and a dorso‐lateral valve complex involving cuticularized lumenal surfaces of the anterior hindgut. Vivisection, histological studies (LM, TEM) and paraffin‐carving (SEM) have been applied to reconstruct morphology of these components and characterize constituent tissues. The lumen of the PMGC is lined by very elongate columnar cells underlain by a thin layer of circular muscle. The hemocoelic surface of the PMGC is covered by cells richly endowed with unique lamellar bodies. The acinar glands are composed of multiple rosettes of secretory cells, from which products appear to empty into the anterior extreme of the hindgut. The dorso‐lateral valve complex of the hindgut consists of anterior and posterior components, differing in strength of lumenal ridging and microdentition of the cuticular lining. Unique features of these structures may relate to behavioral, feeding and metabolic adaptations in this obligate fossorial cru

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01241.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe ultrastructure and quantitative distribution of the taste buds (TBs) were studied in the oropharyngeal cavity and in skin from the head of the tench. All TBs are of similar structure, following an orthodox plan: the basal cells (1–2) are the basis of the bud, and vertically elongated gustatory cells and supporting cells span from the basal membrane to the apex where they form a sensory zone (known as the gustatory pore).The basal cells have finger‐like processes pointing towards the nerve plexus. They do not show any hemidesmosomal connections with the basal membrane. Typical afferent synaptic contacts were found only at the basal cells and gustatory cells while no such contacts were found at the supporting cells.The highest concentration of TBs (up to 170 TBs mm2) occurs in the epithelial lining of the distal part of the pharynx, the least (12 TBs mm2) in the epidermis of the distal part of the head. The tops of most TBs protrude above the epithelium but their gustatory pores are slightly sunken, thereby protecting the apical processes of the gustatory cells from mechanical stimulat

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01242.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractMorphometric investigations of the gill apparatus in the small golomyanka,Comephorus dybowskii, revealed a unique structure and a very small gill respiratory area (GRSA) compared with other endemic Cottoidei of Lake Baikal: from 5.5 to about 7 times smaller than in the pelagic waterside sculpins.Cottocomephorus grewingkiandC. inermis, and about 3 times smaller than in groundling deep‐waterCotinella boulengeri.This is an extremely small GRSA considering no accessory respiratory organs are present. Scanning electron microscopic observations revealed numerous chloride cells in the epithelium of golomyanka gill lamellae but not in the sculpin lamellae. Chloride cells probably restrict gas exchange in the lamellae considerably. The results suggest that golomyankas have a small oxygen requiremen

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01243.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA compilation of newly published information on the innervation of the basicranial muscle in the living tufttailLatimeria chalumnaeand data obtained from other craniates, extant as well as extinct, suggest that the coelacanthiform basicranial musculature and the nerve supply which pertains to it are trimetameric in character rather than monometameric, as usually reported. This result supports the available data on the basic composition of the head of craniate animals and gives no support to a recently suggested homology between the tufttail basicranial muscles and the tetrapod retractor bulbi musculature.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01244.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractScanning electron microscopical studies revealed four distinct morphological larva‐types (not instars) ofPriapulus caudatuswhose lorica‐length measured 82–860 μm. The smallest of the larvae are round to oval, have 20 longitudinal ridges, a series of transverse ridges, and have two pairs of laterally situated tubuli near the posterior limits. The second larva‐type is dorsoventrally compressed, has a single dorsal and single unsculptured ventral plate each with a prominent midridge near the anterior limits, three infolded lateral plates with a pair of tubuli near the posterior limits. The third and fourth larva‐types remain dorsoventrally flattened; the third larva‐type has less pronounced sculpturing than the fourth larva‐type and is smaller; two pairs of tubuli are situated as in the previous stage. The number and arrangement of scalids on the introvert and pharyngeal teeth differ according to each of the four larva‐types and are described. The ultrastructure of all organ systems is described. All scalids are sensilla equipped with ciliated receptor cells. The cuticle is similar to the cuticle in the adult and differs fundamentally from the cuticle of larvalHalicryptus.The trunk is richly supplied with sensory structures. Trunk tubuli contain secretory cells. Posteriorly, a gland complex was found which presumably is the precursor of the equivalent gland in postlarvae and adults. The implications of the first larva‐type's structural similarity to the larva ofTubil

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01245.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractParaspermatozoa and euspermatozoa of the littorinid gastropodLittoraria (Palustorina) articulataare examined using transmission electron microscopy and light microscopy. In the seminal vesicle, both sperm types occur, either as free cells or organized into spermatozeugmata. It is shown that the elongate (120–140 μm), flagellum‐like component of the paraspermatozoon is in fact a tubular extension of the plasma membrane which encloses granular material but no axonemes or microtubules. This structure, here termed the pseudotrich, shows no evidence of motility and its function remains obscure. The main body region of the paraspermatozoon (length 32–36 μm) contains numerous spherical vesicles, scattered mitochondria, one or two large, rod‐shaped bodies (length 20–24 μm) and a fusiform, granular body (containing DNA; probably a modified nucleus). The rod‐shaped bodies, granular body and surrounding matrix are contained by a common membrane, and are therefore separated from other contents of the paraspermatozoon. In each spermatozeugma, euspermatozoa are attached via the tips of their acrosomes to the paraspermatozoan body at the opposite end to the pseudotrich. Euspermatozoa exhibit a conical acrosomal complex (with axial rod and basal plate), a tubular nucleus sheathing the axoneme, a midpiece (5–6 helical mitochondrial elements sheathing the axoneme), an annulus (with two rings), a glycogen piece and an end piece (total sperm length 268–272 μm). The euspermatozoa ofL. articulataare similar to those of most littorinids and many other caenogastropods. The presence of a pseudotrich in the paraspermatozoon appears to be restricted to the

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01246.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe morphology of the lateral‐line system of the nine‐spined stickleback (Pungitius pungitius) and the three‐spined stickleback (Gasterosteus aculeatus) has been studied. In the nine‐spined stickleback, a preopercular, infraorbital, supraorbital, postotic and peduncular canal can be identified on both sides of the body. Replacement lines are found as a continuation of the preopercular and infraorbital canal. In addition, lines of free neuromasts are found on the mandible and trunk. An accessory line is present above and below the peduncular canal. The presence of both canals and accessory lines on the peduncle suggests that the peduncle in this species has important sensory functions. No canals are found in the three‐spined stickleback. Instead, replacement lines corresponding to the canals can be identified on the head. Accordingly, the lateral‐line system of the three‐spined and the nine‐spined stickleback has a different structure. The lateral‐line system of both species shows signs of specialization but the three‐spined stickleback has a more specialized lateral‐line system than the ni

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01247.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractEchinocardium cordatumis a detritus‐feeder. Its digestive tract has three functional parts: the mucus‐secreting oesophagus where lubrication and sediment compaction occur, the protein‐secreting stomach and gastric caecum where extracellular digestion occurs, and the absorptive non‐secretory siphon, intestine, intestinal caecum and rectum. Each region harbours typical enterocytes. Acinar mucous glands occur in the posterior oesophagus prior to the incurrent aperture of the siphon; their secretions prevent sediment grains from entering the siphon and may be stimulated by epineural nerves running in the connective tissue layer. The siphon is a sucking organ, and its cytological features indicate that it is a site for absorption of dissolved organic matter. Enterocytes of the intestinal caecum show basal specializations, suggesting that it is a site of active exchange between coelom and gut. This caecum contains symbiotic sulphide‐oxidizing bacteria. Collagen fibres are well developed in organs subjected to severe deformations (e.g., oesophagus and siphon); elastic‐like fibres are conspicuous around haemal lacunae and at the attachment areas of gut‐suspending mesenteries. Circular muscles are seen along the whole gut, whereas longitudinal muscles may be absent in areas such as the siphon. The bulky alimentary bolus that occurs in the ascending segments of the gut is transported by peristalsis; the scattered sediment grains that occur in horizontal segments are presumably moved by the contractions of the gut‐suspend

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01248.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY