Biomedical subjects

A Garm

Publications and source records attributed to A Garm.

5 recordsLinked to original sources

PubMed2006

Rhopalia are integrated parts of the central nervous system in box jellyfish.

In cubomedusae, the central nervous system (CNS) is found both in the bell (the ring nerve) and in the four eye-bearing sensory structures (the rhopalia). The ring nerve and the rhopalia are connected via the rhopalial stalks and examination of the structure of the rhopalial stalks therefore becomes important when trying to comprehend visual processing. In the present study, the rhopalial stalk of the cubomedusae Tripedalia cystophora has been examined by light microscopy, transmission electron microscopy, and electrophysiology. A major part of the ring nerve is shown to continue into the stalk and to contact the rhopalial neuropil directly. Ultrastructural analysis of synapse distribution in the rhopalial stalk has failed to show any clustering, which indicates that integration of the visual input is probably spread throughout the CNS. Together, the results indicate that cubomedusae have one coherent CNS including the rhopalia. Additionally, a novel gastrodermal nerve has been found in the stalk; this nerve is not involved in visual processing but is likely to be mechanosensory and part of a proprioceptory system.

Animals↗

PubMed2006

Bilaterally symmetrical rhopalial nervous system of the box jellyfish Tripedalia cystophora.

Cubomedusae, or box jellyfish, have the most elaborate visual system of all cnidarians. They have 24 eyes of four morphological types, distributed on four sensory structures called rhopalia. Box jellyfish also display complex, probably visually guided behaviors such as obstacle avoidance and fast directional swimming. Here we describe the strikingly complex and partially bilaterally symmetrical nervous system found in each rhopalium of the box jellyfish, Tripedalia cystophora, and present the rhopalial neuroanatomy in an atlas-like series of drawings. Discrete populations of neurons and commissures connecting the left and the right side along with two populations of nonneuronal cells were visualized using several different histochemical staining techniques and electron microscopy. The number of rhopalial nerve cells and their overall arrangement indicates that visual processing and integration at least partly happen within the rhopalia. The larger of the two nonneuronal cell populations comprises approximately 2,000 likely undifferentiated cells and may support a rapid cell turnover in the rhopalial nervous system.

Animals↗

PubMed2003

Role of maxilla 2 and its setae during feeding in the shrimp Palaemon adspersus (Crustacea: Decapoda).

The movements of the basis of maxilla 2 in Palaemon adspersus were examined using macro-video recordings, and the morphology of its setae was examined using both scanning and transmission electron microscopy. The basis of maxilla 2 performs stereotypical movements in the latero-medial plane and gently touches the food with a frequency of 3-5 Hz. The medial rim of the basis of maxilla 2 carries three types of seta. Type 1 is serrate, type 2 and 3 are serrulate, and type 2 has a prominent terminal pore. Type 2 is innervated by 18-25 sensory cells whose cilia protrude through the terminal pore and are in direct contact with the external environment. The structure of type 2 setae indicates that they are mainly gustatory, although still bimodal due to their innervation by presumed chemosensory and mechanosensory neurons. Distally, the three types of setae have a complex arrangement of the cuticle involving water-filled canals, which may serve to improve flexibility. Type 1 and 3 setae have fewer sensory cells (4-9) but probably also have a bimodal sensory function. The function of type 1 setae is probably to protect type 2 setae, while type 3 setae might serve to groom the ventral side of the basis of maxilla 1.

Animal Structures↗

PubMed2001

Function and functional groupings of the complex mouth apparatus of the squat lobsters Munida sarsi Huus and M. tenuimana G.O. Sars (Crustacea: Decapoda).

Like all other decapods, the anomuran squat lobsters Munida sarsi and M. tenuimana have a mouth apparatus composed of six pairs of mouthparts plus labrum and paragnaths (upper and lower lips). To study the functional significance of this complexity, we examined the mouthparts with scanning electron microscopy and also observed their function directly, under laboratory conditions, using macro-video equipment. No differences were found between the two species. The movement patterns of the mouthparts are described in detail and illustrated as serial drawings. Proceeding from maxillipeds 3 towards the mandibles, the movement pattern gets increasingly stereotypical, with the mandibles performing but a single movement in a medio-lateral plane. From morphology, the mouthparts are subdivided into 20 parts, but from the functional analyses the 20 parts form 8 functional groups: 1, transporting mouthparts (maxilliped 2 endopod and maxilliped 3 endopod); 2, transporting-aligning mouthparts (maxilliped 1 basis); 3, sorting-aligning mouthparts (maxilla 1 basis and maxilla 2 basis); 4, current-generating mouthparts (flagella of maxilliped 2 and maxilliped 3 exopods); 5, cutting-crushing mouthparts (incisor and molar processes, labium, and mandibular palp); 6, ingesting mouthparts (maxilla 1 coxa, maxilla 2 coxa, and maxilliped 1 coxa); 7, respiratory mouthparts (scaphognathite, maxilliped 1 epipod, and maxilliped 2 and maxilliped 3 exopods); and 8, dorso-ventral mouthparts (maxilla 1 endopod, maxilla 2 endopod, maxilliped 1 endopod, and maxilliped 1 exopod). These groupings apply mostly to the processes of food handling and have little significance with respect to grooming. When comparing our results to the literature on other decapods, we found much resemblance to conditions in other anomurans.

Animals↗

PubMed1999

The Sheway project.

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British Columbia↗