Rhopalia: These are modified tentacles, hence known as tentaculocysts. Four par-radial and four inter-radial rhopalia (Fig. 20.20) are present in the eight marginal notches.
What is the structure of the sense organs of Aurelia?
The sense organs of Aurelia are the tentaculocysts or rhopalia. The rhopalia are located around the bell margin between lappets. Each rhopalium is flanked by a pair of rhopalial lappets. They are housed in a little hollow club-shaped structure and is covered by a hood (Fig. 1.41).
What is the function of rhopalium in Aurelia?
Rhopalium. In Aurelia they lie in marginal indententions around the bell and are flanked by rhopalial lappets. Specialized structures to sense light ( ocelli) and perceive gravity ( statoliths) are usually present. They also control the pace of swimming-muscle contraction.
How many ocelli are in a rhopalium?
For example, cubozoan rhopalia contain two pairs of laterally located ocelli on the aboral side of the rhopalium (Skogh et al. 2006), which do not have clearly homologous counterparts in scyphozoan rhopalia.
What are the characteristics of a rhopalia?
Rhopalia are unique to the medusoid forms of Cnidarians and are best studied in Scyphozoa, within the genus Aurelia, which exhibits the most typical arrangement and structure of rhopalia in marginal indentations around the skirt of the bell which are flanked by rhopalial lappets.
Which generation is represented by the adult Aurelia?
Where does A. aurita live?
What is the edge of an umbrella?
How many equidistant notches are there in an umbrella?
How many gonads does an A. aurita have?
Which muscle band is found on the subumbrella?
Where is the subgenital pit located?
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An Example of Phylum Cnidaria: Aurelia - Biology Discussion
ADVERTISEMENTS: In this article we will discuss about Aurelia:- 1. Structure of Aurelia 2. Sense Organs of Aurelia 3. Histology 4. Life History. Structure of Aurelia: Adult Aurelia represents medusoid stage. It has the typical form of a medusa (Fig. 12.18). But the concave and convex sides of the umbrella are more pronounced. The edge […]
Aurelia Aurita: Habitat, Nutrition and Life History (With Diagram)
ADVERTISEMENTS: In this article we will discuss about Aurelia Aurita:-1. Habit, Habitat and Structure of Aurelia Aurita 2. Histology of Aurelia Aurita 3. Nematocysts 5. Musculature 6. Circulation 7. Nutrition 8. Respiration and Excretion 9. Nervous System 10. Sense Organs 11. Reproductive System 12. Development and Life History 13. Metamorphosis of Ephyra 14. Alternation of […]
Which generation is represented by the adult Aurelia?
The sexual generation being represented by the adult Aurelia and the asexual generation by the hydra-tuba and scyphistoma. But instead of the medusa being developed as a bud on a branched colony as in Obelia, it is formed by the metamorphosis of an ephyra, developed as one of several transverse segments of a polyp (scyphistoma).
Where does A. aurita live?
A. aurita is a cosmopolitan jelly fish. It occurs in the warm and temperate seas and lives in coastal waters singly or in large shoals. It is generally seen floating with the water current or swimming feebly by the contractile movement of its body.
What is the edge of an umbrella?
Between the pairs of lappets the edge of the umbrella is provided with numerous closely set marginal tentacles. A narrow region of the umbrella, close to the edge, is very thin and flexible. This is the velarium bearing the marginal notches and the fringe of marginal tentacles. The velarium, quite unlike the true velum of the medusa of Obelia, contains gastro-dermal canals.
How many equidistant notches are there in an umbrella?
The outline of the umbrella is somewhat circular, but is broken by eight equidistant notches, each bearing a pair of delicate sense organs, the marginal lappets or rhopalial lappets. At the centre of two rhopalial lappets is present the rhopalium covered by a hood.
How many gonads does an A. aurita have?
The jelly like transparent umbrella shaped body has four, red or purple horse-shoe shaped gonads on its upper surface and form long and narrow oral lobes hanging downwards from lower surface. The circular body of A. aurita measures about 90 mm in diameter.
Which muscle band is found on the subumbrella?
The broad circular muscle band on the sub-umbrella surface is very strongly built and is known as coronal muscle. Longitudinal muscles are present in the tentacles, manubrium and oral arms. The coronal muscle helps Aurelia in its swimming movements, during which the ex-umbrella surface is kept upwards.
Where is the subgenital pit located?
At a short distance from the mouth, at each inter-radial area , there is a somewhat circular aperture leading into a shallow pouch, the sub-genital pit (Fig. 1.39B). It lies immediately beneath one of the gonads. The sub-genital pits are not connected with the reproductive system. Gonads are four in number, situated at the floor of the gastric pouches.
Rhopalial Ocelli
Cubozoa rhoplaial structures and ocelli are the most complex of Cnidarians, and resemble the image-forming eyes of squids, octopuses and vertebrates.
Sources
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External links
"The Jellyfish homepage". University of New South Wales. Archived from the original on 2004-06-12.
Who provided Aurelia material?
Acknowledgements We thank Mike Schaadt and Kiersten Darrow of the Cabrillo Marine aquarium, San Pedro, CA, for providing us with the Aurelia material, and Dr. Thomas Leitz for providing us with the anti-GLWamide antibody. We also thank an anonymous reviewer for helpful comments on the earlier version of the manuscript. This work was supported by the UCLA Edwin W. Pauley fellowship (to N.N.) and the NASA Astrobiology Institute. Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which per- mits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
What is the nervous system in Aurelia sp.1?
Abstract We examined the development of the nervous system in the rhopalium, a medusa-specific sensory structure, in Aurelia sp.1 (Cnidaria, Scyphozoa) using confocal microscopy. The rhopalial nervous system appears primarily ectodermal and contains neurons immunoreactive to antibodies against tyrosinated tubulin, taurine, GLWa- mide, and FMRFamide. The rhopalial nervous system develops in an ordered manner: the presumptive gravity- sensing organ, consisting of the lithocyst and the touch plate, differentiates first; the “marginal center,” which controls swimming activity, second; and finally, the ocelli, the presumptive photoreceptors. At least seven bilaterally arranged neuronal clusters consisting of sensory and ganglion cells and their neuronal processes became evident in the rhopalium during metamorphosis to the medusa stage. Our analysis provides an anatomical framework for future gene expression and experimental studies of devel- opment and functions of scyphozoan rhopalia. Keywords Cnidaria.Scyphozoa.Rhopalia. Nervoussystemdevelopment.Medusa Introduction Sensory structures, defined as distinct multicellular parts of an organism that function to perceive sensory stimuli, are ubiquitous in Metazoa. Examples range from morphologi- cally highly complex-lensed eyes of vertebrates, cephalo- pods, and cubozoan medusae to a morphologically simple but functionally sophisticated feeding chamber of sponges [see Jacobs et al. (2007) for further description of sponge sensory structures]. We know much about the development of sensory organs in a few bilaterian model organisms (e.g., Drosophila and Mus), but our knowledge of sensory structure development in non-model organisms, especially the non-bilaterian metazoans, has advanced relatively little. For instance, although gravity-sensing organs and eyes can be found in cnidarian medusae (Horridge 1969;Martin 2002), the developmental pathway by which these structures are generated remains largely unexplored [but see Kozmik et al. (2003), Bebenek et al. (2004), and Stierwald et al. (2004) for recent developmental genetic efforts]. Detailed knowl- edge of sensory structure development from a diverse array of metazoan species is indispensable for better understanding of the evolution of senses in Metazoa. In this paper, we examined the development of cnidarian sensory structures, rhopalia, in the scyphozoan jellyfish Aurelia. Phylogenetically, cnidarians are the likely sister group to bilaterians (Medina et al. 2001; Wallberg et al. 2004; but see Schierwater et al. 2009 for a contrary view) and consist
Which stage of the rhopalium is the oral distal group?
expression appears at the prephyra III stage. Thus, the oral- distal group of sensory cells constitutes a structure with similar morphological, molecular, and developmental char- acteristics to the touch plate. On the basis of these parallels, it could be speculated that this structure may also be touch- plate-like in function; the oral-distal group of sensory cells may constitute another mechanosensory organ of the rhopalium. As the rhopalium grows, the oral-distal sensory cells continue to increase in number and occupy the terminal regionoftherhopaliuminadult(SupplementaryFig.1,C,C′). These sensory cells could be sensitive to local bending or stretching of the epithelium that might occur in this region due to the weight of the lithocyst upon tilting of the medusa, aiding in the gravity-sensing function of rhopalia. In addition, stimulus could occur via contact with (food) particles in the water column, which could facilitate the feeding or escape response in ephyrae by eliciting the con- traction of the rhopalar arms. The function(s) of the newly identified putative mechanosensory structure, as well as of the touch plate and the pigment-spot ocellus (see below), will need to be experimentally verified in future studies. Anatomical location of the “marginal center” Removal of all rhopalia in Aurelia causes cessation of the swimming contraction, but one rhopalium is sufficient to restore the activity (Romanes 1885), suggesting that rhopalia act as pacemakers for regular swimming contrac- tions. The region of pacemaker activity that generates periodic electrical impulses into the MNN to control swimming contraction is called the “marginal center” (Passano 1982). The exact anatomical location of the marginal center is, however, unclear. Passano (1973) claimed that pacemaker output was observed from the rhopalia whose “outer half” was excised, suggesting that the pacemaker may reside in the “inner” half of the rhopalium. In addition, the marginal center likely receives neuronal input from the sensory system of the rhopalia (as discussed above), as well as from the DNN, and sends output via the MNN (reviewed in Lesh-Laurie and Suchy 1991). Thus, the marginal center must be able to commu- nicate with neurons originating from these surrounding nervous systems. Our data show that neuronal connections between the rhopalial nervous system and the MNN develop via lateral projection of tyrTub-IR axons away from the base of the rhopalium (prephyra III), and this is correlated with the onset of the pacemaker activity (i.e., swimming contractions) of the marginal center. This reasoning constrains the marginal center to the cells in the basal region of the rhopalium (e.g., oral-proximal neurons) that can communicate with the DNN, as well as with the sensory cells in the rhopalia, and also generate regular electrical impulses into the MNN via the tyrTub-IR axons at the base of the rhopalium. Structure, function, and development of the ocelli As described, development of presumptive photoreceptors occurs after liberation of ephyrae from strobilae. Differen- tiation of the pigment-cup ocellus has been correlated with the development of behavioral responses to light stimuli (Yoshida and Yoshino 1980). In addition, intramembranous particles (IMPs; presumed to represent the photosensory proteins, rhodopsins) of the microvillar and ciliary mem- branes of the sensory cells of the pigment-cup ocellus, revealed by the freeze fracture technique, were similar in size and density to IMPs in photoreceptive membranes of differentiated photoreceptor cells of Bilateria (Takasu and Yoshida 1984). Thus, sensory cells in the pigment-cup ocellus are likely to be photosensitive. In contrast, the size and density of IMPs in the microvillar and ciliary membranes of ectodermal pigment cells in the pigment- spot ocellus do not resemble those from known photore- ceptor cells, suggesting that they may not be photosensory (Takasu and Yoshida 1984). However, these pigmented cells show FMRFamide-like expression with neurites extending at the base and have long cilia (up to 50 µm) with bulbous tips forming likely apical sensory apparatuses. This strongly indicates that the pigment-spot ocellus contains cells that are sensory if not photo-sensory. A mass of knobbed, long cilia in the space created by the depression of the pigment-spot epithelium might be effective in sensing the chemical environment if a water flow can be circulated in the depression (perhaps by ciliary action). The formation of depression of sensory epithelium, often called the sensory pit, is a typical structure of chemosensory organs in marine invertebrates (Brusca and Brusca 2003); the pigment-spot “ocellus” could potentially act as a chemosensory organ. Evolutionary considerations Homology of scyphozoan rhopalia with staurozoan rhopa- lioids and cubozoan rhopalia is inferred based largely on the position and ontogenetic origin. They are arranged in the perradial and interradial positions at the bell margin and are derived ontogenetically from polyp tentacles (Thiel 1966). The most recent molecular phylogenetic study suggests that the phylogenetic relationship among cnidar- ians is [Anthozoa, (Staurozoa, (Hydrozoa, (Scyphozoa, Cubozoa)))] (Collins et al. 2006). If this is the case, the last common ancestor of Medusozoa likely had rhopalioid/ rhopalium-like structures presumably derived from the polyp tentacles in the perradial and interradial positions. This raises the possibility that hydrozoan marginal sensory
What is the late ephyra stage?
Late ephyra (metephyra) stage At the late ephyra stage, or the “metephyra” stage, the pigment-cup ocellus develops further, and the pigment-spot ocellus differentiates. A layer of endodermal pigment cells in the pigment-cup ocellus forms a cup, within which a mass of internalized subepidermal sensory cells is housed (Fig. 3i). Pigment granules are observed on the aboral side of the rhopalium just proximal to the lithocyst (Figs. 1g and 7c), and a new population of FMRFamide-IR epidermal sensory cells occur in this region (Figs. 3i and 7c), indicating that the pigment-spot ocellus is undergoing differentiation at this
Which generation is represented by the adult Aurelia?
The sexual generation being represented by the adult Aurelia and the asexual generation by the hydra-tuba and scyphistoma. But instead of the medusa being developed as a bud on a branched colony as in Obelia, it is formed by the metamorphosis of an ephyra, developed as one of several transverse segments of a polyp (scyphistoma).
Where does A. aurita live?
A. aurita is a cosmopolitan jelly fish. It occurs in the warm and temperate seas and lives in coastal waters singly or in large shoals. It is generally seen floating with the water current or swimming feebly by the contractile movement of its body.
What is the edge of an umbrella?
Between the pairs of lappets the edge of the umbrella is provided with numerous closely set marginal tentacles. A narrow region of the umbrella, close to the edge, is very thin and flexible. This is the velarium bearing the marginal notches and the fringe of marginal tentacles. The velarium, quite unlike the true velum of the medusa of Obelia, contains gastro-dermal canals.
How many equidistant notches are there in an umbrella?
The outline of the umbrella is somewhat circular, but is broken by eight equidistant notches, each bearing a pair of delicate sense organs, the marginal lappets or rhopalial lappets. At the centre of two rhopalial lappets is present the rhopalium covered by a hood.
How many gonads does an A. aurita have?
The jelly like transparent umbrella shaped body has four, red or purple horse-shoe shaped gonads on its upper surface and form long and narrow oral lobes hanging downwards from lower surface. The circular body of A. aurita measures about 90 mm in diameter.
Which muscle band is found on the subumbrella?
The broad circular muscle band on the sub-umbrella surface is very strongly built and is known as coronal muscle. Longitudinal muscles are present in the tentacles, manubrium and oral arms. The coronal muscle helps Aurelia in its swimming movements, during which the ex-umbrella surface is kept upwards.
Where is the subgenital pit located?
At a short distance from the mouth, at each inter-radial area , there is a somewhat circular aperture leading into a shallow pouch, the sub-genital pit (Fig. 1.39B). It lies immediately beneath one of the gonads. The sub-genital pits are not connected with the reproductive system. Gonads are four in number, situated at the floor of the gastric pouches.
