The sensory dorsal organ of crustaceans: Theme and variations

This report presents the results of a scanning electron microscope survey of sensory dorsal organs across a wide range of crustaceans. Sensory dorsal organs are widespread amongst the Crustacea but not ubiquitous. Although many of the organisms surveyed are only distantly related phylogenetically and there is some variation in the appearance of their sensory dorsal organs, a cluster of elements are all or nearly all present. This suggests not only that the sensory dorsal organ appeared very early in crustacean evolution, but that its function requires the elements to be retained in a relatively conservative manner.     

The cuticle of the enigmatic arthropod Phytophilaspis and biomineralization in Cambrian arthropods

Lin, J.‐P., Ivantsov, A.Y. & Briggs, D.E.G. 2011: The cuticle of the enigmatic arthropod Phytophilaspis and biomineralization in Cambrian arthropods. Lethaia, Vol. 44, pp. 344–349. Many non‐trilobite arthropods occur in Cambrian Burgess Shale‐type (BST) biotas, but most of these are preserved in fine‐grained siliciclastics. Only one important occurrence of Cambrian non‐trilobite arthropods, the Sinsk biota (lower Sinsk Formation, Botomian) from the Siberian Platform, has been discovered in carbonates. The chemical compositions of samples of the enigmatic arthropod Phytophilaspis pergamena Ivantsov, 1999 and the co‐occurring trilobite Jakutus primigenius Ivantsov in Ponomarenko, 2005 from this deposit were analysed. The cuticle of P. pergamena is composed of mainly calcium phosphate and differs from the cuticle of J. primigenius, which contains only calcium carbonate. Phosphatized cuticles are rare among large Cambrian arthropods, except for aglaspidids and a few trilobites. Based on recent phylogenetic studies, phosphatization of arthropod cuticle is likely to have evolved several times. □arthropod cuticle, Burgess Shale‐type preservation, fossil‐diagenesis, phosphatization.     

The scolopidial accessory organ in the Jerusalem cricket (Orthoptera: Stenopelmatidae)

Multiple mechanosensory organs form the subgenual organ complex in orthopteroid insects, located in the proximal tibia. In several Ensifera (Orthoptera), a small chordotonal organ, the so-called accessory organ, is the most posterior part of this sensory complex. In order to document the presence of this accessory organ among the Ensifera, the chordotonal sensilla and their innervation in the posterior tibia of two species of Jerusalem crickets (Stenopelmatidae: Stenopelmatus) is described. The sensory structures were stained by axonal tracing. Scolopidial sensilla occur in the posterior subgenual organ and the accessory organ in all leg pairs. The accessory organ contains 10–17 scolopidial sensilla. Both groups of sensilla are commonly spatially separated. However, in few cases neuronal fibres occurred between both organs. The two sensillum groups are considered as separate organs by the general spatial separation and innervation by different nerve branches. A functional role for mechanoreception is considered: since the accessory organ is located closely under the cuticle, sensilla may be suited to detect vibrations transferred over the leg's surface. This study extends the known taxa with an accessory organ, which occurs in several taxa of Ensifera. Comparative neuroanatomy thus suggests that the accessory organ may be conserved at least in Tettigoniidea.     

The Cambrian origin of the circulatory system of crustaceans

The carapace of Recent crustaceans such as myodocope ostracodes and phyllocarids is pervaded with well-developed anastomosing sinuses conveying hemolymph from the metabolizing organs to the dorsal heart. The inner lamella cuticle, which separates the sinuses from seawater, is thin enough to allow gaseous diffusion (e.g., O₂ uptake) over its surface. Comparable radiating and/or anastomosing features, of possible vascular origin, are herein recognized in several possible Crustacea from the Cambrian: cambriid, svealutiid, hipponicharionid and beyrichonid Bradoriida and in Carnarvonia from the middle Cambrian Burgess Shale. The vascular network is basically the same in these groups, consisting of sinuses radiating from supposed adductorial areas or from inferred areas of dorsal attachment of the body. The integumental (carapace sinuses) and branchial (gills) systems of respiration in crustaceans and crustacean-like animals were probably already differentiated by the middle Cambrian. The oldest record of probable integumental circulation is in the bradoriid Petrianna from the early Cambrian of Greenland. Similar circulatory systems may be represented by radiating ridges on the cephalon of other Cambrian arthropod groups such as the arachnomorphs ( Burgessia ) and trilobites ( Naraioa ) and may also be manifest in the carapaces of Ordovician-Devonian leperditicope ostracodes. Organs on the thoracopods of Cambrian supposed crustaceans, such as Canadaspis , resemble the foliaceous thoracic gills of Recent nebaliid phyllocarids and therefore may have served the same (respiratory) function.     

Embryogenesis of the dipluran Lepidocampa weberi Oudemans (hexapoda: diplura, campodeidae): formation of dorsal organ and related phenomena

The developmental changes of embryonic membranes of a dipluran Lepidocampa weberi, with special reference to dorsal organ formation, are described in detail by light, scanning, and transmission electron microscopies. Newly differentiated germ band and serosa secrete the blastodermic cuticle at the entire egg surface beneath the chorion. Soon after, the serosal cells start to move dorsad. All the serosal cells finally concentrate at the dorsal side of the egg and form the dorsal organ. During their concentration, the serosal cells attenuate their cytoplasm to form filaments. The extensive area from which the serosa has receded is occupied by a second embryonic membrane, the amnion, which originates from the embryonic margin. The embryo and newly emerged amnion then secrete three fine cuticular layers, "cuticular lamellae I, II, and III," above which the filaments of the (developing) dorsal organ are situated. With the progression of definitive dorsal closure, the amnion reduces its extension, the dorsal organ is incorporated into the body cavity of the embryo, and the amnion and dorsal organ finally degenerate.The dorsal organ of diplurans is formed by the concentration of whole serosal cells, while that of collembolans is formed by the direct differentiation of a part of serosal cells. However, the dorsal organs of diplurans and collembolans closely resemble each other in major aspects, including that of ultrastructural features, and there is no doubt regarding their homology. The amnion, which has been regarded as being a characteristic of Ectognatha, also develops in the Diplura. This might suggest a closer affinity between the Diplura and Ectognatha than previously believed.     

A rare non‐trilobite artiopodan from the Guzhangian (Cambrian Series 3) Weeks Formation Konservat‐Lagerstätte in Utah,USA

We describe a weakly biomineralized non‐trilobite artiopodan arthropod from the Guzhangian Weeks Formation of Utah. Falcatamacaris bellua gen. et sp. nov. is typified by a thin calcitic cuticle, broad cephalon without eyes or dorsal ecdysial sutures, an elongate trunk with distinctively sickle‐shaped pleural spines and a long tailspine with a bifurcate termination. The precise affinities of Falcatamacaris gen. nov. are problematic due to the presence of unique features within Artiopoda, such as the peculiar morphology of the pleural and posterior regions of the trunk. Possible affinities with aglaspidid‐like arthropods and concilitergans are discussed based on the possession of 11 trunk tergites, edge‐to‐edge articulations and overall body spinosity. The new taxon highlights the importance of the Weeks Formation Konservat‐Lagerstätte for further understanding the diversity of extinct arthropod groups in the upper Cambrian.     

TEM studies on the lattice organs of cirripede cypris larvae (Crustacea, Thecostraca, Cirripedia)

 Lattice organs consist of five pairs of sensory organs situated on the dorsal carapace in cypris larvae of the Crustacea Cirripedia. The lattice organs in cypris larvae of Trypetesa lampas (Acrothoracica) and Peltogaster paguri (Rhizocephala) represent the two main types found in cirripedes, but only minor differences exist at the TEM level. Each lattice organ is innervated by two bipolar, primary receptor cells. The inner dendritic segment of each receptor cell carries two outer dendritic segments. The outer dendritic segments contain modified cilia with a short ciliary segment (9×2+0 structure). Two sheath cells envelop the dendrite except for the distal ends of the outer dendritic segments. This distal end enters a cavity in the carapace cuticle and reaches a terminal pore situated at the far end of the cavity. The cuticle above the cavity is modified. In both species the epicuticle is partly perforated by numerous small pores and the underlying exocuticle is much thinner and less electron dense than the regular exocuticle. Lattice organs very probably have a chemosensory function and are homologous with the sensory dorsal organ of other crustacean taxa. Accepted: 18 August 1998     

Digestive system and feeding mode in Cambrian naraoiid arthropods

The function of the digestive system of naraoiid arthropods is interpreted in the light of new observations on Early Cambrian specimens from China and detailed comparisons with Recent crustaceans and other arthropods. In naraoiids, paired tubular diverticulae ending as blind caeca are present along the entire midgut, and are interpreted as sites for the secretion of digestive enzymes. Naraoia bears one pair of long, ramifying, distensible diverticulae, possibly used for both food storage and digestion as suggested by Recent analogues (e.g. branchiuran and isopod crustaceans and limulids). Naraoiids were probably epibenthic scavengers/predators rather than mud-eaters. They were either opportunistic intermittent feeders ( Naraoia ) or more regular feeders ( Misszhouia ). The mud-fills of the alimentary canals are likely to be artefacts due to taphonomic and weathering processes or, less likely, to sediment ingestion by animals trapped alive in turbiditic flows. The case study of naraoiid arthropods adds to other fossil evidence supporting the idea that predation played a key role in the Early Cambrian food-webs and that organs adapted for this purpose had already reached a high level of diversity and anatomical sophistication.     

The structure of a hair mechanoreceptor in the antennule of crayfish (Crustacea)

Summary In this study we examine the fine structure of mechanosensory hairs in the antennule of crayfish. The sensory hair is a stiff shaft with feather-like filaments. The hair's base is a large expansion of membrane which allows the hair shaft to deflect. The sensory transducing elements are located far from the hair, but are coupled mechanically with the hair shaft by a fine extracellular chorda. The sensory element is a type of scolopidium which consists of a scolopale cell and three sensory cells with a 9 + 0 type ciliary process.This type of scolopidium is characteristic of the chordotonal organ that has no cuticular structure on the surface of the exoskeleton. In this crustacean hair receptor, the deflection of the cuticular hair is transmitted through the chorda to the scolopidium which is a tension-sensitive transducer. The present study reveals that the mechanosensory hair of decapod crustaceans is a chordotonal organ accompanied by a cuticular hair structure. We also discuss comparative aspects of cuticular and subcuticular chordotonal organs in arthropods.     

Fine Structure of Cephalic Sense Organs in Meloidogyne incognita Males

Amphids, and the cephalic and labial papillae of Meloidogyne incognita males were examined in detail by electron microscopy. Each amphid basically consists of an amphidial gland, a nerve bundle and an amphidial duct. The gland is a broad microvillous organ with a narrow anterior process, which is closely associated with the amphidial duct. A posterior process of the gland contains secretory organelles and proceeds along the esophagus with the lateral cephalic nerve bundle. The nerve bundle penetrates the broad portion of the gland and, subsequently, individual nerve processes (dendrites) separate from one another, thus forming the sensilla pouch which is enveloped by the gland. Anterior to the pouch, the dendrites converge as they enter and eventually terminate in the amphidial duct. The external opening of the duct is a broad slit which separates the cheek, the outermost part of the lateral lip, from the remainder of the lip region. M. incognita males have six inner labial papillae and four outer cephalic papillae which are each innervated by two and one cilia, respectively. In labial papillae, the cilia appear to terminate at the base of a pore opening, whereas in cephalic papillae each cilium terminates beneath the labial cuticle.     

Adhesive organs of the gastrotricha

Summary Adhesive organs of 17 gastrotrich species of the order Macrodasyida and 2 species of the order Chaetonotida (Chaetonotida-Paucitubulatina) can be seen by transmission electron microscopy to comprise two gland cell types. These cells are morphologically similar to viscid and releasing glands of the Turbellaria and so are identified by these same names; the adhesive system in these gastrotrichs is therefore called a duo-gland system considered at least functionally comparable to the duo-gland organs of turbellarians. The two gland cell types project their necks through tubiform extensions of the animal's cuticle. Some adhesive tubules have only one of each gland type; others, even in the same species, may have two viscid and one releasing glands; and compound organs such as posterior footlike appendages may have three and four viscid glands and one releasing gland per tubule. Gland cells in some species have fibers, evidently cytoskeletal in function. The adhesive tubules are quite similar in all of these species and provide few characters for determining within-group relationships of the gastrotrichs. The duo-gland system of the Gastrotricha is probably not homologous with that of the Turbellaria.Abbreviations Used in Figures cu cuticle - ep epidermal cell - f fiber - la lateral adhesive organ - m muscle - pa posterior adhesive organ - rg releasing gland - sc sensory cilium - scb sensory cell body - vg viscid gland This research was supported by NSF grants DEB-77-06058 (S. Tyler, P.I.) and GB 42211 (R.M. Rieger, P.I.)     

Scent gland apparatus in the Western conifer seed bug Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae)

The coreid Leptoglossus occidentalis is a Nearctic bug responsible for severe seed losses to pine orchards. When disturbed, adults and nymphs emit a defensive secretion deemed an allomone. Here we describe the gross morphology of the scent gland apparatus and the related evaporatory structures in nymphs and adults of L. occidentalis, through light microscopy and scanning electron microscopy. Adults of both sexes possess a metathoracic scent gland complex (MTG) including a central orange‐yellow reservoir and a pair of white lateral glands, connected by ducts to the reservoir. The MTG belongs to the diastomian type, with two ostioles located on the metathorax associated with a microsculptured cuticular accumulation area, i.e. evaporatory area, which can prevent the spread of the secretion on to non‐evaporative cuticle and increase scent fluid evaporation. A high number of male‐specific sternal gland pores were observed. These pores and associated glands are likely the source of an attractant pheromone, which could be extremely useful in monitoring and combating this invasive pest. In nymphs, MTG is replaced by two dorsal abdominal scent glands (DAGs) located between the 4th and the 6th urotergites. DAGs are reddish cuticle‐lined sacs with gland cells forming the gland wall; the scent substances are released through two orifices lying on the mid‐dorsal abdominal line between urotergites IV–V and V–VI. Also in nymphs, peculiar cuticular evaporatory areas surround both orifices.     

On the Distribution of the Crustacean Dorsal Organ

An oval, dorsal organ, variously bearing four minute pits around a central pore and/or encircled by a cuticular border, has been reported for the cephalic region of various groups of living and fossil crustaceans. Although varying somewhat in location and in size, the organ appears basically uniform in organization in at least two of the major crustacean taxa: Branchiopoda (especially Laevicaudata) and Malacostraca (Decapoda and Syncarida). Little is known about its ultrastructure and function in various groups, and it is likely that the term ‘dorsal organ’ also has been applied to several nonhomologous structures. In particular, the embryonic dorsal organ, reviewed recently by Fioroni (Fioroni, P. 1980.—Zoologische Jahrbücher (Anatomie) 104: 425–465) and apparently functioning in nutrition and ecdysis, is not the topic of this paper; that organ is similar in name and location only and appears in embryonic uniramians, chelicerates, and crustaceans. The function of the dorsal organ in branchiopods is in ion regulation, possibly a secondary modification of the original function in marine crustaceans, which is unknown. In larval decapods, the organ probably functions as a chemo- or mechano-receptor. We review the known occurrence of the crustacean dorsal organ, describe the similarities and differences in structure in various taxa, and review the competing hypotheses concerning its function. Phylogenetic implications are discussed.     

Neural Complex of Ascidians and Features of Its Structure in Polyclinidae

The structure of the neural complex has been studied under a light microscope in the representatives of 4 genera belonging to the family Polyclinidae. Particular attention was given to the relationships between the ciliary organ, dorsal tube, and neural gland. No dorsal string was found in Polyclinidae. The neural gland is located in the proximal portion of the mediodorsal blood vessel of the branchial sac. This paper discusses probable reasons for the differences in the structure of the neural complex in different ascidians taking into account original data and the existing literature.     

条背萤成虫与幼虫发光器的超微结构观察

对水生萤火虫——条背萤Luciola substriata(Gorham)成虫和幼虫发光器的超微结构进行研究。结果表明,成虫发光器由明显的2层组成:反射层和发光层。反射层由排列紧密的“尿酸囊泡”构成,具有发达的气管结构,对光起反射作用;发光层由大量发光细胞构成,内含典型的发光颗粒、线粒体、内质网及大量糖原,该层通过发光细胞胞质内的生化反应而发光。2层均由非细胞层膜包被,间距25~30μm。发光器腹节由外向内依次为表皮、发光层、反射层和内部细胞层。幼虫发光器球形,由背射层和发光层构成,由非细胞层膜包被。背射层由单层柱状细胞构成,内含大量“尿酸囊泡”。发光层细胞膜相互绞缠,含有2种类型的发光颗粒:“致密”型和“凋亡”型,含有大量的线粒体和无定形颗粒,发光细胞之间分布着大量的气管、微气管及神经末梢,可观察到神经突触。与条背萤相比,陆生种成虫反射层和发光层均无非细胞层膜包被,2层间无明显间距,发光颗粒形状不规则,气管通常形成2分支;陆栖种幼虫发光层形状差异较大,背射层由单层或2~4层细胞构成;相似点在于,成虫发光器都由均由反射层和发光层构成,发光细胞内都含发光颗粒、线粒体及大量糖原,都具有发达的气管结构,发光颗粒相似。幼虫发光器都由背射层和发光层构成,都具有发达的气管和直接的神经支配,发光颗粒相似,都由非细胞层膜包被。     

Fine structure and probable function of ring organs in the mite Histiostoma feroniarum (Acari: Actinotrichida: Acaridida: Histiostomatidae)

Histiostoma feroniarum, like other histiostomatid mites, possesses peculiar ring organs that are visible under the light microscope as ventrally located, characteristic rings of sclerotized cuticle. The ring organ is composed of three elements: a disc of modified cuticle, ring organ cells located underneath the disc, and an "empty" chamber frequently visible between the cuticular disc and the cells. The cuticle of the disc is not perforated and differs from the surrounding unmodified cuticle as revealed by special staining developed for light microscopy and by electron microscopy. The ring organ cells show a polarity, with a practically smooth apical surface and an extremely folded basal membrane. The basal invaginations reach the apical cell portion, where they form tubular canaliculi distributed beneath the apical cell membrane. The cytoplasm contains many mitochondria, which are usually in contact with the cell membrane invaginations. Structurally, the ring organ cells closely resemble the transport cells described in osmoregulatory organs both in water-inhabiting and terrestrial arthropods. Thus, our results support earlier suggestions of an osmoregulatory function performed by sclerotized rings (=ring organs), as an adaptation to aqueous environments. A possible homology with similar organs of other mites is discussed.     

Organ repair and regeneration: An overview

A number of organs have the intrinsic ability to regenerate, a distinctive feature that varies among organisms. Organ regeneration is a process not fully yet understood. However, when its underlying mechanisms are unraveled, it holds tremendous therapeutic potential for humans. In this review, we chose to summarize the repair and regenerative potential of the following organs and organ systems: thymus, adrenal gland, thyroid gland, intestine, lungs, heart, liver, blood vessels, germ cells, nervous system, eye tissues, hair cells, kidney and bladder, skin, hair follicles, pancreas, bone, and cartilage. For each organ, a review of the following is presented: (a) factors, pathways, and cells that are involved in the organ's intrinsic regenerative ability, (b) contribution of exogenous cells – such as progenitor cells, embryonic stem cells, induced pluripotent stem cells, and bone marrow‐, adipose‐ and umbilical cord blood‐derived stem cells – in repairing and regenerating organs in the absence of an innate intrinsic regenerative capability, (c) and the progress made in engineering bio‐artificial scaffolds, tissues, and organs. Organ regeneration is a promising therapy that can alleviate humans from diseases that have not been yet cured. It is also superior to already existing treatments that utilize exogenous sources to substitute for the organ's lost structure and/or function(s). (Part C) 96:1–29, 2012. © 2012 Wiley Periodicals, Inc.     

Ultrastructure of the Juxtaganglionar Organ,a Putative Endocrine Gland Associated with the Cerebral Ganglia of Aplysia juliana

Summary

Electron microscopy was used to examine the morphology of a putative endocrine gland, the juxtaganglionar organ (JO), and its relation to the cerebral ganglia of the hermaphroditic opisthobranch gastropod Aplysia juliana. The JO is a well-vascularized, poorly innervated tissue of glandular cells—rich in mitochondria, lipids, ribosomes, and endoplasmic reticulum, with sparse cilia and membrane-limited secretory granules—within the connective tissue sheath just exterior to the neuronal soma in the dorsal and posterior portions of the cerebral ganglia. The cytology and organization of the JO supports its homology to the dorsal bodies of pulmonate gastropods, which axe endocrine organs known to release one or more female gonadotropic factors.     

Phylogenetic Significance of the Burgess Shale Crustacean Canadaspis

The crustaceans, like the other major living groups of arthropods, have a long evolutionary history. The earliest examples occur in the Cambrian, and fossils of this age are a critical source of evidence of relationships both within the Crustacea, and between the Crustacea and other major arthropod groups. Canadaspis perfecta, from the Middle Cambrian Burgess Shale, is important as one of the oldest well-documented crustaceans. The evidence for reconstructing its remarkable combination of primitive and derived characters is reviewed, and its possible phylogenetic significance re-assessed.     

The Origin of the Crustacea*

Pre-Cambrian metamerically segmented bilaterians that ultimately gave rise to crustaceans probably arose from unsegmented flatworms. The recent suggestion that early arthropods, far from possessing a capacious segmented coelome of the annelid type, may never have had such, is attractive. Crustaceans were probably derived from small, segmented, surface-dwelling non-annelidan marine worms with a haemocoele. Their appendages probably originated as simple outgrowths whose shape was maintained by haemocoelic pressure. Possible routes whereby trunk limbs could have been derived from such rudiments are suggested. Trunk limbs would originally be unsegmented, as in many extant branchiopods and in certain Cambrian crustaceans. The evolution of thoracopodal feeding and some of the factors involved in the differentiation of the cephalic appendages are considered, as is the origin of the nauplius larva and the establishment of its feeding mechanism. Certain features of the cephalic region of the adult reflect changes necessitated as a result of the incorporation of the nauplius into the life cycle. Ontogeny would originally be anamorphic and follow the pattern preserved in its most primitive form in certain extant anostracan branchiopods. A reconstruction of the Ur-crustacean is attempted. Justification for features not previously associated with such a reconstruction, such as locomotory antennae, a relatively short trunk with only a short series of limbs and a limbless posterior region, and unsegmented trunk limbs, is provided by fossil evidence, functional considerations and the situation in primitive extant forms. Crustaceans were evidently not derived from any known arthropod clade. Stem lineage forms probably arose from the same group of pre-crustacean ancestors. While the Crustacea appears to be a monophyletic group, the idea that arthropodization must have occurred more than once and that the Arthropoda is a polyphyletic assemblage is supported, and evidence in favour of this view is cited.