Histological changes in the epidermis of the subdigital lamellae of Anolis carolinensis during the shedding cycle

The characteristic anoline climbing organ consists of a number of lamellar scales, on whose outer scale surface are numerous keratinized setae which contact the substrate. These setae are derived from the Oberhautchen of the epidermal generation, and as such are renewed and shed periodically along with the rest of the epidermal material. The histological development of the setae is described, and modifications of the surrounding elements are noted. The relative lengths of the setae and their congregation to form a pad unit poses certain mechanical problems during morphogenesis, simply in terms of accommodation between the functional outer epidermal generation and dermal core of each lamella. Regression of the dermal core and a distal migration of some cells permits accommodation within the lamella for the distal aspect of the Oberhautchen layer, or free margin. Additionally, changes in the gross shape of the lamella occur throughout the sloughing cycle, and a swelling of the cells of the lacunar tissue results in a gap between the stratum corneum of inner and outer epidermal generations. There is a considerable amount of variation in mitotic activity between the germinal layers of opposite sides of the lamella.     

The structure of anoline (Reptilia: Dactyloidae: Anolis) toe pads in relation to substratum conformity

Adhesive toe pads of geckos house modified components of vascular and/or connective tissues that promote conformity of the setal fields with the locomotor substratum. Similar modifications have been claimed for the digits of Anolis, but evidence for them is not compelling. Angiographic and histological investigations of Anolis failed to identify any evidence of either an intralamellar vascular reticular network or a central sinus. Instead, their vascularity more closely resembles that of lizards in general than that of pad‐bearing geckos. The loose connective tissue of the toe pads likely contributes to their general pliability and flexibility, promoting localized compliance with the substratum. Through the shedding cycle, the lamellae change shape as the replacing setae elongate. The outer epidermal generation lacunar cells on the inner lamellar faces simultaneously hypertrophy, providing for compatibility between overlapping lamellae, enabling reciprocity between them. This contributes to continuing compliance of the setal fields with the substratum. Overall, digital structure and attachment and release kinematics of the toe pads of Anolis are very similar to those of geckos exhibiting an incipient adhesive mechanism. Both lack major anatomical specializations for promoting conformity of the setae with the locomotor substratum beyond those of the seta‐bearing portions of the epidermis.     

Morphogenesis of the digital pad lamellae in the embryo of the lizard Anolis lineatopus

The present study in the embryo of the lizard Anolis lineatopus describes the modality of cell proliferation responsible for the morphogenesis of the digital pad lamellae and of the epidermal stratification. After tritiated thymidine and 5-bromodeoxy-uridine administration, autoradiographic and immunocytochemical methods have been used. The lamellae originate as long, slightly slanted, undulations of the epidermis of fingers and toes. At an early stage, the epidermis consists of an outer periderm and a basal layer. Cell hypertrophy, and the prevalent cell proliferation in the longer side of the undulation with respect to the shorter side, generate the surface of the outer lamella. Under the peridermis, a shedding complex, composed by clear and oberhautchen layers, is formed and later determines the first intraepidermal shed. The first subperidermal layer derived from the basal layer is a clear layer and the first shed epidermis in the embryo is represented by periderm and clear layer. The heavily granulated clear layer in Anolis lineatopus represents the first epidermal layer produced in the embryonic epidermis, and is connected with the process of shedding. The spinulae of the underlying oberhautchen in the outer scale surface become long setae which grow toward the upper clear layer. Under the shedding complex a β-layer is produced. Autoradiographical study shows that the radioactivity stays in the basal layer for about 4 days before cells move to upper layers. At 6–8 days post-injection labelled cells are visible in the differentiated clear, oberhautchen and β-layers. Under the β-layer differentiating mesos cells are visible before the embryo hatches.     

Epidermal fine structure of the toe tips of Sphaerodactylus cinereus (Reptilia, Gekkonidae)

This paper deals with epidermal structures of the sphaerodactyline gecko Sphaerodactylus cinereus : adhesive pads, cutaneous sensilla and intraepidermal axon terminals.
The adhesive pad is restricted to a single terminal scale and bears approximately 6,000 setae. The setae are complex, hair-like structures which branch and sub-branch up to five times. The terminal ends are shaped like inverted cones. They provide the friction which enables the gecko to walk even on vertical glass-plates.
Cutaneous sensilla of supposed mechanoreceptive function are found in groups of three or four at the anterior free edge of all dorsal and distal scales of the digit. The sensillum consists of a circular platelet in an epidermal depression bordered by an annular furrow and two or three bristles in a central position.
Discoid axon terminals in the digital scales are located between relatively stiff structures: the corneous layers of the epidermis and a layer of tonofibrillar bundles. The axon terminals are hypothesized to be sensitive to the internal pressure depending on hyperextension of the toe.     

Histochemical and ultrastructural analyses of adhesive setae of lizards indicate that they contain lipids in addition to keratins

We studied the distribution of lipid material and organelles in the epidermal layers of toe pads from two species of lizards representing the two main lizard families in which adhesive scansors are found (gekkonids and polychrotids), the dull day gecko, Phelsuma dubia and the green anole, Anolis carolinensis. Although lipids are a conspicuous component of the mesos layer of squamate reptiles and function in reducing cutaneous water loss, their distribution has not been specifically studied in the highly elaborated epidermal surface of adhesive toe pads. We found that, in addition to the typical cutaneous water loss‐resistant mesos and alpha‐layer lipids, the Oberhäutchen (including the setae) on the most exterior layers of the epidermis in P. dubia and A. carolinensis also contain lipid material. We also present detailed histochemical and ultrastructural analyses of the toe pads of P. dubia, which indicate that lipid material is closely associated spatially with maturing setae as they branch during the renewal phase of epidermal regeneration. This lipid material appears associated with the packing of keratin within setae, possibly affecting permeability to water loss in the pad lamella, where the surface area is from 4–60‐fold greater compared with normal scales. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

The structure and development of the digital lamellae of lizards

The epidermal setae and the spinules of the digital lamellae of anoline and gekkonid lizards are shed periodically along with the rest of the outer layer of the skin. These structures are developed within the lamellae prior to ecdysis. The setae are larger and more complicated than the spinules and begin their development first. The setae of Anolis start as aggregations of tonofibrils beneath the plasma membrane of the presumptive Oberhautchen cells. These cells are arranged in rows parallel to the surface, several cell layers beneath the alpha layer of the skin. The developing setae protrude into the clear layer cells as finger-like projections, with the tonofibrils longitudinally oriented in the direction of growth. About 100 setae are formed by each Oberhautchen cells in Anolis. In late development, the clear layer cells lose their cellular contents and when shed along with all distal cells, retain a template of the new setae or spinules. The spinules and setae are formed before the fibrous and alpha layers of the new skin. The fibrous layer, which occurs only on the ventral (outer) layer of the lamellae, and the Oberhautchen with its setae and spinules, is considered the beta layer. The alpha layer, which occurs adjacent to the fibrous layer on the ventral surface and adjacent to the Oberhautchen on the dorsal (inner) surface, is morphologically identical to that of mammalian α keratin. The shed lizard skin consists of the alpha and beta layers as well as the degenerating cells of the outer epidermal generation, and the clear layer. The clear layer that is shed shows the template of the new setae and spinules developed in the new skin layer. The separation of the new from the old skin occurs along the intercellular space between the clear layer cells and the new Oberhautchen. The alpha layer of the skin is not fully keratinized at shedding. The setae of the digital lamellae of lizards represent unique epidermal structures — intracellular keratinized microstructures.     

Tarsal attachment devices of the southern green stink bug Nezara viridula (Heteroptera: Pentatomidae)

Based on analyses with cryo‐scanning and transmission electron microscopy, the present study reports on the morphology and ultrastructure of the attachment structures of the green stinkbug Nezara viridula L. (Heteroptera: Pentatomidae), a cosmopolitan pest of different crops in most areas of the world. In addition, the presence and distribution of large proportions of the elastic protein resilin in these structures was revealed by confocal laser scanning microscopy. The attachment structures of each leg comprise two sclerotised claws, a pair of smooth flexible pulvilli and a hairy adhesive pad located at the ventral side of the basitarsus. No sexual dimorphism is evident. Contact areas of resting individuals on a smooth surface show that N. viridula creates contact to the substrate with the ventral surface of (a) the distal portions of the pulvilli, (b) the setae of the hairy adhesive pad, (c) the two paraempodia representing mechanosensory setae, and (d) the tips of the claws. Each pulvillus is a sac‐like structure formed by complex cuticular layers that vary in their structure and resilin content. The dorsal side consists of sclerotised chitinous material, while the ventral cuticle consists mainly of resilin and shows a very thin epicuticle and a thick exocuticle. The setae of the hairy adhesive pad are pointed and socketed. They exhibit a pronounced longitudinal gradient in the material composition, with large proportions of resilin being present in the setal tips. In most of these setae, especially in those of the distal‐most part of the pad, also a transverse gradient in the material composition is visible.     

Surface structures of the antennular flagella of the hermit crab Pagurus alaskensis (Benedict): A light and scanning electron microscopy study

The surface structures of the antennular flagella of Pagurus alaskensis are described in detail. Attention is directed towards the surface morphology of two types of possible sensilla: (1) exoskeletal pores (1.0–3.0 μm in diameter); (2) setae of various kinds. In addition, small (0.1–0.2 μm) pits occur in the exoskeleton which are not considered to be sensory in function. The exoskeletal pores are found at fairly specific locations on both the inner and outer flagella, particularly on the short segments of the outer flagella. Neither the inner nor the outer flagella are bilaterally symmetrical with respect to their setal armature. On the outer flagellum six groups of setae may be distinguished: lateralmesial; dorsal; ventral; accessory; aesthetasc; setae of the distal segment. On the inner flagellum setae of the mesial and lateral rows form distinctive groups. The morphology, orientation and locations of all the flagellar setae are defined and where possible the numbers of the various morphological types within the specific setal groups are given. It is noteworthy that many setal types have obvious apical pores and yet no pores could be found in the chemoreceptive aesthetasc setae. The functions of the various setae are discussed in relation to their topographical position and to existing electrophysiological and behavioral data. Some suggestions are made about future experiments to demonstrate the central connections of specific sensilla or groups of sensilla and to show their significance in the whole animal.     

Viscoelastic features of adhesive setae of the tokay gecko (<Emphasis Type="Italic">Gekko gecko</Emphasis> L.)

Deformations of particular setae of adhesive toe pad of the tokay gecko were investigated by atomic-force microscopy. The effective elastic modulus of the investigated setae varying within 0.34–19 GPa, a pronounced hysteresis was observed during reversible bending of setae. The hysteresis-related energy losses may be as high as 98% of the total bending work. The pronounced viscous features of the setae contradict the hypothesis of dynamic self-cleaning of the gecko adhesive cover, according to which the setae are considered as absolutely elastic cantilever beams.     

Comparative morphology of pretarsal scopulae in eleven spider families

Many wandering spiders bear attachment pads (scopulae) on their tarsi, consisting of hierarchically-branching adhesive setae. Amongst spider families and even species, these show remarkable differences in morphology. Using scanning electron microscopy, the scopula microstructure of sixteen spider species was described, with the focus on pretarsal scopulae (claw tufts). Area and shape of the claw tuft, seta and setule density, as well as seta and spatula dimensions were analysed and compared. Claw tufts of the majority of species studied show a similar gradient in size and shape from anterior to posterior legs: the dimension of pads increases, while setal density decreases. Commonly, there is also a gradient of both the seta and spatula size within the claw tuft: Setae become larger from the proximal to the distal part of the pad, and spatulae size increases in the same direction at the level of individual seta. Often, different hierarchical levels of claw tuft organisation are differently expressed in different species: Species with lower setal density usually have broader setae. Smaller spatula size often implicates higher setule density. Evolutionary and ecological aspects of the scopula origin are discussed.     

Ultrastructure of aesthetasc innervation and external morphology of the lateral antennule setae of the spiny lobster Panulirus interruptus (Randall)

Summary Six types of setae and one type of cuticular depression were examined on the lateral antennule of the spiny lobster Panulirus interruptus using scanning electron microscopy. The organization and ultrastructure of the innervation of the most numerous setal type, the aesthetasc, were investigated using light-and transmission electron microscopy.Each aesthetasc is innervated by approximately 300 bipolar neurons whose sensory dendrites penetrate the hair and extend toward the tip, and whose axons project towards the central nervous system. The neuronal somata and two types of glia form a cluster within the antennular lumen. The inner sheath-cell somata encircle the dendritic tract distal to the sensory somata. These cells appear to extend distal processes which wrap the dendritic tract to the base of the aesthetasc. Elongate outer sheath cells are interposed between the glia-wrapped dendritic tract and the hypodermis which underlies the antennule cuticle. A continuous investment of neural lamella separates the hypodermis, the entire cluster of somata, and sensillar nerve from the antennule lumen. The organization of the neuronal somata and their association with outer and inner sheath cells in this marine species appear similar to those of crustaceans from freshwater and terrestrial habitats.     

CHLOROPLAST DEVELOPMENT AND ULTRESTRUCTURE IN THE FRESHWATER RED ALGA BATRACHOSPERMUM1

Chloroplast development and ultrastructure of the freshwater red alga Batrachospermum moniliforme are described. Chloroplasts develop from proplastids which have a double-membraned chloroplast envelope and a parallel double-membraned outer photo-synthetic lamella. Of these 2 double-membraned structures of the proplastid, only the outermost pho-tosynthetic lamella functions in production of further lamellae. The mature chloroplast consists of 2 or more concentric lamellae and a variable number of nonconcentric lamellae. These lamellae are not dense, uninterrupted sheets as described for other red algae, but are largely constructed of tubules, lying side by side, that form interrupted lamellar sheets. The possible physiological significance of lamellar interruptions in providing path-ways for movement of materials in the chloroplast stroma is discussed.     

Fetal development of the segment-specific papillary body in the equine hoof

Fetal development of the unique papillary body and its localized peculiarities in the equine hoof are described based on the study of 51 fetuses, nine newborn foals, and five adult horses. The shape and dimensions of the dermal papillae and lamellae have a formative influence on the structure and physical quality of the corneous hoof capsule with its horn tubules and lamellae. The size and arrangement of these horn structures determine the mechanical quality of hoof horn. Proper horn quality is a prerequisite for the various functions of the hoof capsule, such as protecting the living dermis supporting the hoof capsule, shock absorption, and formation of the suspensory apparatus of the distal phalanx. Development of the segment-specific papillary body is initiated by the increasing mitotic activity of the epidermal cells invaginating the dermal surface, thus forming dermal microridges. These microridges are transformed into single dermal papillae, which are arranged in rows, or enlarged to become primary and secondary dermal lamellae. The formation of a segment-specific papillary body enables the increasing keratinization ratio in the hoof epidermis and the formation of the characteristic tubular and lamellar horn responsible for the special mechanical properties of hoof horn.     

Regeneration of adhesive tail pad scales in the New Zealand gecko (Hoplodactylus maculatus) (Reptilia;Squamata;Lacertilia) can serve as an experimental model to analyze setal formation in lizards generally

During the regeneration of the tail in the arboreal New Zealand gecko (Hoplodactylus maculatus) a new set of tail scales,modified into pads bearing setae 5-20 μm long,is also regenerated.Stages of the formation of these specialized scales from epidermal pegs that invaginate the dermis of the regenerating tail are described on the basis of light and electron microscopic images.Within the pegs a differentiating clear layer interfaces with the spinulae and setae of the Oberh(a)utchen according to a process similar to that described for the digital pads.A layer of clear cytoplasm surrounds the growing tiny setae and eventually comifies around them and their spatular ends,later leaving the new setae free-standing on the epidermal surface.The fresh adhesive pads help the gecko to maintain the prehensile function of its regenerated tail as together with the axial skeleton (made of a cylinder of elastic cartilage) the pads allow the regenerated tail to curl aroundtwigs and small branches just like the original tail.The regeneration of caudal adhesive pads represents an ideal system to study the cellular processes that determine setal formation under normal or experimental manipulation as the progressive phases of the formation of the setae can be sequentially analyzed.     

Distal invaginations and the renewal of cone outer segments in anuran and monkey retinas

Summary Although it is now clear that the outer segments of mature vertebrate cones are regularly renewed, it is not known how a cone outer segment can maintain a tapered shape if its narrower tip is periodically lost by shedding. This problem was addressed by morphological examination of photoreceptors in retinas of anurans (Xenopus laevis) and monkeys (Macaca fascicularis). Light microscopy revealed a marked daily change in the shape of cone outer segments in X. laevis: at light offset they were long and conical, at light onset they had shed their narrow tips, were sharply truncated, and 40% shorter. Electron microscopy revealed previously undescribed fine-structural features in these mature cone outer segments, most notably the presence of many partial membrane infoldings within their distal lamellae. The growth of each of these distal invaginations apparently split 1 pre-existing distal lamella into 2 daughter lamellae of reduced width. The formation of distal invaginations at various heights within a cone outer segment would thus make it longer and narrower. Similar ultrastructural features were also found in cone outer segments of monkey retinas. These findings suggest that during outer segment renewal the tapered shape of mature cone outer segments is maintained via a remodelling process that accompanies the formation of distal invaginations.Portions of this work have been published in abbreviated or preliminary form (Eckmiller 1988, 1989b, c)     

Morphology and distribution of setae on the antennules of the Caribbean spiny lobster Panulirus argus reveal new types of bimodal chemo-mechanosensilla

This study describes the morphology and distribution of setae on the lateral and medial flagella of the antennules of the spiny lobster Panulirus argus in an effort to identify antennular chemoreceptors in addition to the well-studied aesthetasc chemosensilla. Setae were examined using light and electron microscopy, and their distribution on flagellar annuli was analyzed. We identified ten setal types based on external morphology: hooded, plumose, short setuled, long simple, medium simple, short simple, aesthetasc, guard, companion, and asymmetric setae, with the last four types being unique to the "tuft" located on the distal half of the lateral flagellum. The three setal types whose ultrastructure was examined--hooded, long simple, and medium simple setae--had characteristics of bimodal (chemo-mechanoreceptive) sensilla. The antennules have four distinct annular types based on their setal complement, as shown by cluster analysis. This basic distribution of non-tuft setal types is similar for both lateral and medial flagella. Annuli in the tuft region have tuft setal types superimposed on a basic organization of non-tuft setal types. These results show that the antennules possess a diverse set of setae, that these setae have a highly ordered arrangement on the antennules, that at least four (and probably many more) of these setal types are chemosensilla, and suggest that most antennular chemosensilla are bimodally sensitive.     

A scanning electron microscope study of tarsal adhesive setae in the Coleoptera

Scanning electron micrographs of the tarsal adhesive setae of 84 species of beetle are described. These show a vast range of setal structure and distribution.     

Ultrastructural autoradiographic and immunocytochemical analysis of setae formation and keratinization in the digital pads of the gecko Hemidactylus turcicus (Gekkonidae,Reptilia)

The modified subdigital scales of some lizards allow them to climb vertical surfaces. This is due to the action of millions of tiny setae present in the digital pads. Setae are mainly composed of beta-keratin which may have some modality of aggregation similar to that of barbs and barbules of feathers. Keratins and associated proteins are involved in the organization of setae. The formation of setae in the climbing pad lamellae of the gecko Hemidactylus turcicus has been analyzed under the electron microscope after injection of tritiated histidine and immunocytochemistry for a chick scale beta-keratin. Setae are made up of dense and pale filaments, both oriented along the longer axis of setae. Beta-keratin is present in the oberhautchen layer and in the growing setae which are highly modified oberhautchen cells. Most of the immunolabeling concentrated in the central part of setae. This cross-reactivity suggests that some epitopes in chick beta-keratin are also present in gecko setae. Four hours after injection of tritiated histidine, the labeling is localized over setae, in particular in the dense filaments and less in the pale filaments. Some labeling is also seen in the keratinaceous material present in the cytoplasm of clear cells, which are believed to mold setae. The present observations suggest that both beta-keratin and denser matrix proteins, possibly incorporating histidine, are packed into growing setae. These proteins may be mixed to form pale and dense filaments oriented along the longer axis of setae, a pattern resembling that of barb and barbule cells of feathers. The role of matrix material in the orientation of the deposited beta-keratin during setal outgrowth is discussed with the problem of barb and barbule differentiation in avian feathers.     

Vascular anatomy of the gills in a high energy demand teleost,the skipjack tuna (Katsuwonus pelamis)

Tunas (family: Scombridae, Tribe: Thunnini) exhibit anatomical, physiological, and biochemical adaptations that dramatically increase the ability of their cardiorespiratory systems to transfer oxygen from the water to the tissues. In the present study the vascular anatomy of the skipjack tuna, Katsuwonus pelamis, gill was examined by light and scanning electron microscopic analysis of methyl methacrylate vascular corrosion replicas prepared under physiological pressure. The gill filament contains three distinct blood pathways, respiratory, interlamellar, and nutrient. The respiratory, or arterio-arterial (AA) pathway, is the site of gas exchange and consists of the afferent and efferent filamental arteries (AFA and EFA) and arterioles (ALA and ELA) and the lamellae. Each ALA in the basal filament supplies ten or more lamellae and they anastomose with their neighbor to form a continuous vascular arcade. Four modifications in the lamellar circulation appear to enhance gas exchange efficiency. 1) The ALA deliver blood directly to the outer margin of the lamellae where unstirred boundary layer effects are predicted to be minimal and water PO2 highest. 2) Pillar cells are closely aligned along the outer boundary of the inlet side and the inner boundary of the outlet side of the lamellae to form multiple distributing and receiving blood channels. 3) Elsewhere in the lamella, pillar cells are aligned to form diagonal channels that direct blood from the outer to the inner lamellar margins, thereby reducing vascular resistance. 4) The lamellar sinusoid is especially widened near the efferent end to augment oxygen saturation of blood flowing through the inner margin. These adaptations, plus the presence of a bow-shaped interlamellar septum, and a thinned filament core appear to decrease gill vascular resistance and maximize gas-exchange efficiency. The interlamellar (IL) and nutrient systems originate from post-lamellar vessels and are arterio-venous (AV) pathways. IL vessels form an extensive ladder-like lattice on both sides of the filamental cartilage and are supplied in part by narrow-bore vessels from the medial wall of the EFA. Their function is unknown. Nutrient vessels are formed from the confluence of a myriad of tortuous, narrow-bore vessels arising from the basal region of the EFA and from efferent branchial arteries. They re-enter the filament and eventually drain into the IL system or filamental veins. As these AV pathways are retained despite considerable reduction in filamental tissue, it is evident that they are integral components of other non-respiratory homeostatic activities of the gill.     

Ultrastructure and formation of hooded hooks in Capitella capitata (Annelida, Capitellida)

 The hooded hooks of Capitella capitata are aligned in a transverse row inside each neuro- and notopodial rim of the last thoracic and all abdominal setigers. Each seta consists of a rostrum, a capitium, the spines of which surmount the rostrum, and a long, sigmoid shaft or manubrium, towards which rostrum and capitial spines are curved. A thin hood, complete except for a subapical opening and a short, subrostral cleft, encloses the apical portions of the seta. Generally, the tip of the rostrum extends beyond the hood. The hood consists of an outer and an inner lamella, between which is a compartment loosely filled with fibrillar material. Hooded hooks are generated at the dorsal edge of the neuropodial rim and at the ventral edge of the notopodial rim during the entire life of C. capitata. Chaetogenesis starts in a small compartment surrounded by the basal chaetoblast and four follicle cells. Initially a group of microvilli emanating from the chaetoblast preforms the rostrum. Next, stout microvilli appear adrostrally, each preforming a spine of the capitium. When both structures have been formed, the longitudinal axis of the anlage shifts, because the actin filaments inside the microvilli reorientate and initiate formation of the manubrium. During this initial phase of chaetogenesis the anlage sinks into the chaetoblast, until the latter finally enwraps the anlage, except the tip of the rostrum. The chaetoblast now generates microvilli that face the new setal structures and preform the hood. During further development the microvilli separate into two layers, an inner and an outer one. The inner layer of microvilli merges with the manubrium prior to the outer layer. Addition of setal material occurs between the bases of the microvilli and elongates the manubrium until it extends beyond the epidermal surface. The microvilli, which have continuously been withdrawn from the seta during chaetogenesis, remain in the basal section. Specific morphogenetic and structural correspondence between the hooked setae of species of Maldanomorpha, Psammodrilida and Oweniida, the uncini of species of the Sabellida, Terebellida and Pogonophora, and the hooded hooks of species of Capitellidae justify the hypothesis that all these setae are homologous. This hypothesis implies the existence of a monophyletic group consisting of all polychaetous Annelida with such setae. Accepted: 16 December 1997