Development and metamorphosis of the feeding apparatus of the stone crab,Menippe mercenaria (brachyura,xanthidae)

Analysis of the feeding apparatus of the stone crab, Menippe mercenaria (Brachyura, Xanthidae), has demonstrated that substantial internal and external morphological alterations occur at metamorphosis and suggests that the mastication of food shifts from the mandibles to the gastric mill at that time. These changes correspond to the changes in environment and diet that take place at metamorphosis, when the previously planktotrophic larvae begin benthic life. A detailed account of the structure and development of the mandibles is presented. The mandibles of all zoeal stages are similar: The incisor process has a series of teeth and denticles and the prominent molar process appears to be well adapted for grinding food. Megalopal mandibles are transitional but have the form that is typical of all subsequent stages: The expanded incisor process is rounded and toothless and the molar process is less prominent and has lost its grinding denticles. The cardiac stomach of the zoeal stages has no gastric mill; the medial and lateral teeth of the mill first appear in the megalopa. A very simple procedure is described for preparing larval mandibles for scanning electron microscopy using the molted exoskeletons from larval rearing experiments.     

Foregut morphology and ontogeny of the spider crab Maja brachydactyla (Brachyura,Majoidea, Majidae)

We describe the morphology of the foregut of the spider crab Maja brachydactyla Balss, 1922, from first larval stage to adult, with detailed stage‐specific documentation using light and scanning electron microscopy. A total of 40 ossicles have been identified in the foregut of adults of M. brachydactyla using Alizarin‐Red staining. The morphological pattern of the ossicles and gastric mill is very similar to other Majoidea species with only a few variations. The foregut of the zoeae stages appeared as a small and simple cavity, with a cardio‐pyloric valve that separates the stomach into cardiac and pyloric regions. The pyloric filter is present from the first zoea, in contrast to the brachyuran species which have an extended larval development. Calcified structures have been identified in the cardio‐pyloric valve and pyloric region of the zoeal stages. The most significant changes in foregut morphology take place after the metamorphosis from ZII to megalopa, including the occurrence of the gastric mill. In the megalopa stage, the foregut ossicles are recognizable by their organization and general morphology, but are different from the adult phase in shape and number. Moreover, the gastric teeth show important differences: the cusps of the lateral teeth are sharp (no molariform); the dorsal tooth have a small, dentate cusp (not a well‐developed quadrangular cusp); and the accessory teeth are composed of one sharp peak (instead of four sharp peaks). The gastric mill ontogeny from megalopa to adult reveals intermediate morphologies during the earlier juvenile stages. The relationship between gastric mill structures with food preferences and their contribution to the brachyuran phylogeny are briefly discussed. J. Morphol. 276:1109–1122, 2015. © 2015 Wiley Periodicals, Inc.     

Ontogeny of gut morphology in the white shrimp Penaeus setiferus (Decapoda,Penaeidae)

Ontogeny of the gut in Penaeus setiferus was investigated by reconstruction of serial sections examined by light microscopy. Development of the gut into the adult form is protracted over several weeks beyond metamorphosis in steps that may be directly related to the unique postlarval life history of Penaeus. The gastric mill is lacking in larval stages of P. setiferus. In protozoeal stages Z₁-Z₃, the pyloric ampullae are blind sacs that do not communicate with the midgut. The gland filter first appears in mysis stage M₂. The gastric mill in early postlarval (PL) stages consists of poorly chitinized lobes with flexible setae. By PL₂₁ the ossicles of the gastric mill are rigid and setae are replaced by spine-like denticles, but even by PL₃₅ the gastric mill is neither as massive nor heavily chitinized as in adults. During the mysis stages and early PL stages, the hepatopancreas communicates freely with both the foregut and the midgut trunk. By PL₃₅ the hepatopancreatic ducts are essentially isolated from the remainder of the midgut by foregut ossicles. The midgut in Z₁ consists of two pairs of simple caeca and the midgut trunk. During larval growth, each of the lateral midgut caeca develops into a number of lobes. After metamorphosis these lobes begin to ramify into small-diameter tubules, and by PL₃₅ have completely ramified into the hepatopancreas of adults. From M₁ to PL₄, the anterior midgut caeca decrease in absolute size and become a single anterior diverticulum. The posterior midgut diverticulum first appears in PL₂₁ as a simple sac and thereafter increases in size and complexity.     

The longitudinal visceral musculature of Drosophila melanogaster persists through metamorphosis

The larval gut of Drosophila is coated with visceral muscles of mesodermal origin. In the midgut region this musculature comprises circular and longitudinal fibres. The complete visceral musculature is described to be removed during metamorphosis and to be replaced by a newly differentiated imaginal tissue resembling the morphology of the larval musculature. However, progenitors of this imaginal visceral musculature have never been detected prior to differentiation. Here I present results indicating that the longitudinal visceral musculature of the midgut completely persists through metamorphosis. Single cells expressing green fluorescent protein (GFP) as a marker were transplanted at the blastoderm stage. All clones contributing to the longitudinal visceral musculature detected in third instar larvae were recovered after metamorphosis in adult flies. Further evidence for the persistence of the larval visceral musculature was obtained from the P[Gal4] insertion line 5053A. It expresses GAL4 specifically in the longitudinal visceral muscles of the midgut of all developmental stages to the adult fly beginning at the end of embryogenesis. By using GFP as a reporter, it was possible to follow these cells through the entire metamorphosis. Although the muscles undergo dramatic morphological changes including the loss of their contractile system, no evidence for a replacement of the larval visceral musculature by imaginal precursor cells was detected.     

Ultrastructural changes in the connective tissue of the gastric region during the metamorphosis of Xenopus laevis

Development of the gastric connective tissue of Xenopus laevis during metamorphosis was investigated by electron microscopy. Throughout the larval period to stage 60, the layer of connective tissue underlying the gastric epithelium consists of immature fibroblasts surrounded by a sparse extracellular matrix. At the beginning of the transition from the larval to the adult epithelial form, at about stage 60, extensive changes occur in the connective tissue. The number of cells suddenly increses and different cell types appear. Numerous contacts between epithelial and connective tissue cells are established through random gaps in the thickened basal lamina. During stages 62–63, just after the beginning of the morphogenesis of adult-type glands, the basal lamina lining the glandular epithelium becomes thinner, and the number of contacts decreases rapidly except near the tips of the glands. After the glandular cells begin to produce zymogen granules at stage 64, contacts become rare. From stage 63, when the muscularis mucosae develops, until the completion of metamorphosis, the connective tissue consists mainly of typical fibroblasts. Outside the muscularis mucosae, the fibroblasts of the lamina propria are aligned in parallel with the curvature of the glands. These observations indicate that developmental changes in the connective tissue are closely related spatiotemporally to those of the epithelial transition from larval to adult form during metamorphic climax. Although some changes are similar to those in the intestine (Ishizuya-Oka and Shimozawa, '87b), others are specific to the gastric region, which suggests that connective tissue may have a role in organ-specific differentiation of the gastric epithelium.     

Morphological chimeras of larvae and adults in a hydrozoan--insights into the control of pattern formation and morphogenesis

In the marine hydroid Hydractinia echinata, metamorphosis transforms the spindle-shaped larva into a primary polyp. It bears a hypostome with a ring of tentacles at its apical end, a gastric region in the middle and stolons at the base. In nature, metamorphosis is induced in response to external stimuli provided by bacteria. These stimuli can be replaced by artificial inducers, one of which is heat shock. Among heat shock treated stages are those undergoing complete metamorphosis but also specimens forming chimeras of different developmental stages. In the chimeric larvae, the posterior is transformed into the apical hypostome of the adult polyp while the anterior part of the larva persists as larval tissue. After transverse sectioning, these stage chimeras regenerate the missing body parts with respect to the nature of the tissue at the wound surface. This shows that the decision to make larva or polyp morphology depends not on the majority of the tissue in the original body section, but on stage specificity within the regenerating animal part. Single cells can escape from this general rule, since RFamide nerve cells which usually differentiate in polyp tissue appear in regenerated larval tails of sectioned stage chimeras. The results indicate that the pattern-forming system of the larva and of the adult have features in common. The primary signals controlling patterning along the anterior-posterior axis in larvae and the apical-basal axis in polyps arethus likelyto be the same while the interpretation of these primary signals by the individual cells changes during metamorphosis.     

Cloning and expression of xP1-L, a new marker gene for larval surface mucous cells of tadpole stomach in Xenopus laevis

The amphibian gastrointestinal tract is remodeled from a larval-type to an adult-type during metamorphosis. In the present study, we examined the products of subtractive hybridization between tadpole and frog stomach cDNAs of Xenopus laevis in order to identify genes expressed specifically in the larval stomach epithelium. A new gene homologous to xP1 was obtained and named xP1-L. In the genome database of Silurana tropicalis, we found a homologue of xP1-L and named it stP1-L. RT-PCR showed that the expression of xP1-L was detected in stage 41/42 tadpoles. In addition, in situ hybridization showed that xP1-L was localized to surface mucous cells of the larval stomach. The H(+)/K(+)-ATPase beta subunit, a marker gene for manicotto gland cells in the tadpole stomach, was also detected at the same time. However, adult marker genes such as xP1 for surface mucous cells and pepsinogen C (PgC) for oxynticopeptic cells were not expressed in the tadpole stages. The expression of xP1-L gradually decreased towards the metamorphic climax and disappeared after stage 61 when larval-type gastric epithelium is replaced by adult-type. We found that xP1-L was never expressed in surface mucous cells of the adult-type stomach, and xP1, instead of xP1-L, was expressed. During T3-induced metamorphosis, xP1-L expression decreased in the same manner as during natural metamorphosis. Thus, xP1-L is a useful marker for larval surface mucous cells in tadpole stomach. This is the first demonstration of a marker gene specific for the surface mucous cells of the larval stomach.     

Lepidopteran larval midgut during prepupal instar: digestion or self-digestion?

Programmed cell death (PCD) is crucial in body restructuring during metamorphosis of holometabolous insects (those that have a pupal stage between the final larval and adult stages). Besides apoptosis, an increasing body of evidence indicates that in several insect species programmed autophagy also plays a key role in these developmental processes. We have recently characterized the midgut replacement process in Heliothis virescens larva, during the prepupal phase, responsible for the formation of a new pupal midgut. We found that the elimination of the old larval midgut epithelium is obtained by a combination of apoptotic and autophagic events. In particular, autophagic PCD completely digests decaying tissues, and provides nutrients that are rapidly absorbed by the newly formed epithelium, which is apparently functional at this early stage. The presence of both apoptosis and autophagy in the replacement of midgut cells in Lepidoptera offers the opportunity to investigate the functional peculiarities of these PCD modalities and if they share any molecular mechanism, which may account for possible cross-talk between them.     

Digestive anatomy of Halella azteca (Crustacea,Amphipoda)

The digestive tract of the freshwater amphipod Hyalella azteca is a straight but differentiated tube consisting of foregut, midgut, and hindgut divisions. The foregut is subdivided into a tubular esophagus, a cardiac stomach, and a pyloric stomach. The cuticular lining of the cardiac stomach is elaborated into a set of food-crushing plates and ossicles, the gastric mill, while the pyloric cuticle forms a complex straining and pressing mechanism. Nine caeca arise from the midgut, seven anteriorly and two posteriorly. Four of the anterior caeca, the hepatopancreatic caeca, are believed to be the primary sites of digestion and absorption. The remaining caeca may be absorptive, secretory, or both. The much-folded hindgut wall is capable of great distention by extrinsic muscle action for water intake to aid in flushing fecal material out of the anus; such action also may stimulate antiperistalsis by intrinsic rectal muscles.     

FMRFamide-related peptides in the gut of Locusta migratoria L.: a comprehensive map and developmental profile

The gut tissues and associated nervous system of the African migratory locust, Locusta migratoria, were found to contain FMRFamide-like immunoreactive (FLI) material throughout the five larval instars and 2 weeks into the adult stage in both males and females. FMRFamide-like immunoreactivity associated with the locust gut was described using camera lucida techniques. FMRFamide-like immunoreactivity is observed in the frontal connectives, recurrent nerve, and oesophageal nerves; projections from the ingluvial ganglion onto the anterior midgut, and from the proctodeal nerve onto the hindgut and posterior midgut; in the neuropils of the frontal ganglion, hypocerebral ganglion and ingluvial ganglia; 30 cell bodies in the frontal ganglion; multipolar sensory cells on the foregut; and endocrine-like cells in the gastric caecae and midgut. Radioimmunoassay (RIA) was used to determine the quantities of FLI material in foreguts, gastric caecae, anterior and posterior midguts, and hindgut of first-fifth instar larvae, 1-3- and 14-17-day male and female adult locusts. As expected, as the tissue size (assessed by total protein content) increases, so does the amount of FLI material in each tissue. Normalizing for tissue size reveals significant differences in FLI content among the stages for each tissue tested. Reversed phase-high pressure liquid chromatography (RP-HPLC) followed by RIA has identified four groups of FLI fractions present in the gut, and different members of these groups are present in the various gut tissues.     

Cloning and expression of xP1-L,a new marker gene for larval surface mucous cells of tadpole stomach in Xenopus laevis

The amphibian gastrointestinal tract is remodeled from a larval-type to an adult-type during metamorphosis. In the present study, we examined the products of subtractive hybridization between tadpole and frog stomach cDNAs of Xenopus laevis in order to identify genes expressed specifically in the larval stomach epithelium. A new gene homologous to xP1 was obtained and named xP1-L. In the genome database of Silurana tropicalis, we found a homologue of xP1-L and named it stP1-L. RT-PCR showed that the expression of xP1-L was detected in stage 41/42 tadpoles. In addition, in situ hybridization showed that xP1-L was localized to surface mucous cells of the larval stomach. The H⁺/K⁺-ATPase β subunit, a marker gene for manicotto gland cells in the tadpole stomach, was also detected at the same time. However, adult marker genes such as xP1 for surface mucous cells and pepsinogen C (PgC) for oxynticopeptic cells were not expressed in the tadpole stages. The expression of xP1-L gradually decreased towards the metamorphic climax and disappeared after stage 61 when larval-type gastric epithelium is replaced by adult-type. We found that xP1-L was never expressed in surface mucous cells of the adult-type stomach, and xP1, instead of xP1-L, was expressed. During T3-induced metamorphosis, xP1-L expression decreased in the same manner as during natural metamorphosis. Thus, xP1-L is a useful marker for larval surface mucous cells in tadpole stomach. This is the first demonstration of a marker gene specific for the surface mucous cells of the larval stomach.     

黑水虻消化道形态及组织结构的观察

本文比较了不同发育阶段黑水虻Hermetia illucens消化道的形态学差异,掌握了幼虫消化系统的组织学特征。利用体视镜观察黑水虻5龄幼虫、预蛹及成虫的消化道形态,利用光学显微镜和扫描电镜观察幼虫消化道各段(前肠、中肠、后肠)的显微及超微结构。结果表明：黑水虻幼虫及预蛹的消化道均由前肠(食道和前胃)、中肠及后肠组成,从幼虫到成虫,消化道的长度不断缩短。与幼虫和预蛹相比,成虫消化道形态变化明显,前胃消失,出现了嗉囊及胃盲囊,中肠进一步缩短,后肠分化为回肠、结肠和直肠。组织学观察结果显示,幼虫的唾液腺开口于口腔,由膨大的管状腺体和腺管组成。食道由特化为角质刺突的内膜层及发达的肌层组成,其末端延伸至前胃。前胃膨大为球状,包括三层组织结构。根据上皮细胞形态的差异,中肠可分为四个区段。后肠薄,肠腔内褶丰富,肠壁可见数量较多的杆状细菌。马氏管开口于中、后肠交界处,包括4支盲管,管内壁密布微绒毛。黑水虻消化道形态随发育阶段的变化,反映了各阶段摄食及消化生理的差异。幼虫消化道各段具有各自典型的组织学特征,其前、中、后肠可能分别承担了食物接纳与初步消化、消化与吸收以及重吸收功能。本研究结果为进一步了...     

Structure of the stomach cuticle in adult and larvae of the spider crab Maja brachydactyla (Brachyura,Decapoda)

The stomach of decapods is a complex organ with specialized structures that are delimited by a cuticle. The morphology and ontogeny of the stomach are largely described, but few studies have focused on the morphology of its cuticle. This study examined the morphology of the stomach cuticle of cardiac sacs, gastric mill ossicles, cardio-pyloric valve and pyloric filters, and during various stages (zoea I and II, megalopa, first juvenile, and adult) of the common spider crab Maja brachydactyla using dissection, histology and transmission electron microscopy. The results show that cuticle morphology varies among structures (e.g., cardiac sacs, urocardiac ossicle, cardio-pyloric valve, pyloric filters), within a single structure (e.g., different sides of the urocardiac ossicle) and among different life stages. The cuticle during the larval stages is very thin and the different layers (epicuticle, exocuticle, and endocuticle) are infrequently distinguishable by histology. Major changes during larval development regarding cuticle morphology are observed after the molt to megalopa, including the increment in thickness in the gastric mill ossicles and cardio-pyloric valve, and the disappearance of the long thickened setae of the cardio-pyloric valve. The cuticle of all the stomach structures in the adults is thicker than in larval and juvenile stages. The cuticle varies in thickness, differential staining affinity and morphology of the cuticle layers. The structure–function relationship of the cuticle morphology is discussed.     

A novel tissue in an established model system: the <Emphasis Type="Italic">Drosophila</Emphasis> pupal midgut

The Drosophila larval and adult midguts are derived from two populations of endodermal progenitors that separate from each other in the early embryo. As larval midgut cells differentiate into an epithelial layer, adult midgut progenitors (AMPs) remain as small clusters of proliferating, undifferentiated cells attached to the basal surface of the larval gut epithelium. During the first few hours of metamorphosis, AMPs merge into a continuous epithelial tube that overgrows the larval layer and differentiates into the adult midgut; at the same time, the larval midgut degenerates. As shown in this paper, there is a second, transient pupal midgut that develops from the AMPs at the beginning of metamorphosis and that intercalates between the adult and larval midgut epithelia. Cells of the transient pupal midgut form a multilayered tube that exhibits signs of differentiation, in the form of septate junctions and rudimentary apical microvilli. Some cells of the pupal midgut develop as endocrine cells. The pupal midgut remains closely attached to the degenerating larval midgut cells. Along with these cells, pupal midgut cells are sequestered into the lumen where they form the compact “yellow body.” The formation of a pupal midgut has been reported from several other species and may represent a general feature of intestinal metamorphosis in insects.     

The larval alimentary canal of the Antarctic insect, Belgica antarctica

On the Antarctica continent the wingless midge, Belgica antarctica (Diptera, Chironomidae) occurs further south than any other insect. The digestive tract of the larval stage of Belgica that inhabits this extreme environment and feeds in detritus of penguin rookeries has been described for the first time. Ingested food passes through a foregut lumen and into a stomodeal valve representing an intussusception of the foregut into the midgut. A sharp discontinuity in microvillar length occurs at an interface separating relatively long microvilli of the stomodeal midgut region, the site where peritrophic membrane originates, from the midgut epithelium lying posterior to this stomodeal region. Although shapes of cells along the length of this non-stomodeal midgut epithelium are similar, the lengths of their microvilli increase over two orders of magnitude from anterior midgut to posterior midgut. Infoldings of the basal membranes also account for a greatly expanded interface between midgut cells and the hemocoel. The epithelial cells of the hindgut seem to be specialized for exchange of water with their environment, with the anterior two-thirds of the hindgut showing highly convoluted luminal membranes and the posterior third having a highly convoluted basal surface. The lumen of the middle third of the hindgut has a dense population of resident bacteria. Regenerative cells are scattered throughout the larval midgut epithelium. These presumably represent stem cells for the adult midgut, while a ring of cells, marked by a discontinuity in nuclear size at the midgut-hindgut interface, presumably represents stem cells for the adult hindgut.     

Maturation and degeneration of the fat body in the Drosophila larva and pupa as revealed by morphometric analysis

Using morphometric and cytochemical techniques we have described changes taking place in the fat body cells during three different stages of development. The cell number remains constant at about 2200 cells during larval life and then decreases gradually and continuously throughout metamorphosis and the first 3 days of the adult stage until no more cells can be observed. Cell size increases rapidly during the larval period and decreases steadily during metamorphosis and adult stage. The size of the nuclei increases during the larval instars and decreases during the pupal interval. The change in nuclear size is correlated with the amount of DNA present throughout development implying the nuclear DNA is synthesized during the larval period and degraded gradually during metamorphosis. The cell size changes are due in large part to accumulation or loss of reserve substances: lipid droplets, glycogen deposits and protein granules. During metamorphosis the amount of lipid decreases slightly whereas glycogen experiences two loss cycles. The protein granules in the form of lysosomes continue to increase in amount during the first day of metamorphosis because of a short period of massive autophagy. Then the lysosomes decrease in amount throughout the remainder of metamorphosis. The lysosomes stain positively for lipofuscin.     

Electron microscopy of extracellular materials during the development of a sea star,Patiria miniata (Echinodermata: Asteroidea)

The fine structure of conspicuous extracellular materials during the life history of a sea star (Patiria miniata) is described. The outer surface of the developing sea star is covered by two morphologically different cuticles that appear sequentially during ontogeny. The primary cuticle, which is about 120 nm thick and two-layered, is present from mid-blastula through the end of the larval stage. The secondary cuticle, which is about 1 micron thick and three-layered, first appears on the epidermis of the rudiment region of the larva and, after metamorphosis, covers the entire epidermis of the juvenile and adult stages. During ontogeny, there are only two conspicuous gut cuticles: the first lines the newly invaginated archenteron at the start of the gastrula stage, and the second lines the esophagus during the larval stage. A blastocoelic basal lamina first appears at mid-blastula and persists as subectodermal and subendodermal basal laminae. Ruthenium red-positive granules are detectable between the lateral surfaces of adjacent ectodermal cells during part of the gastrula stage; this transient intercellular material may possibly aid in lateral adhesion between cells.