Serotonergic, sensory modifications in the apical ganglion during development to metamorphic competence in larvae of the dendronotid nudibranchsMelibe leoninaandTritonia diomedea

2008 ◽  
Vol 71 (12) ◽  
pp. 863-869 ◽  
Author(s):  
Stephen C. Kempf
Keyword(s):  
Apical Ganglion

The Median Tentacle of the Larva of Lingula Anatina (Brachiopoda) From Queensland, Australia

1996 ◽  
Vol 44 (4) ◽  
pp. 355 ◽  
Author(s):  
C Lüter
Keyword(s):  
Extracellular Matrix ◽  
Nervous System ◽  
Contact Region ◽  
Single Cells ◽  
Muscle Cells ◽  
Proximal Part ◽  
Sensory Organ ◽  
Continuous Transition ◽  
Apical Ganglion

The median tentacle of the larvae of Lingula anatina has been investigated in order to obtain information about the morphological implications of its function and its relation to the paired tentacles of the larval lophophore. The median tentacle is a larval sensory organ with apical, intraepidermal collar receptors and a basiepidermal nervous system (apical ganglion). The monociliated muscle cells in the median tentacle form a compact musculature; where cilia emanate from the single cells, small compartments surrounded by three epithelial muscle cells can be observed. The number of cavities corresponds with the number of muscle cells. In the proximal part of the median tentacle these muscle cells build a continuous transition to the muscle cells in the paired tentacles; an extracellular matrix could not be found in the contact-region between both muscular systems. Because of this continuity the muscle cells in the median tentacle must be regarded as part of the mesosome. The unpaired median tentacle is restricted to the larvae of all species of the Lingulida and Discinida within the inarticulate brachiopods and is lacking in all other brachiopod larvae. Because it is also unknown in Phoronida, it could be regarded as a synapomorphic characteristic of the supraspecific taxa Lingulida and Discinida.

scholarly journals How to make a protostome

2012 ◽  
Vol 26 (1) ◽  
pp. 25 ◽  
Author(s):  
Claus Nielsen
Keyword(s):  
Adult Stage ◽  
Morphological Evolution ◽  
Anterior Part ◽  
Nerve Ring ◽  
Cerebral Ganglia ◽  
New Information ◽  
Planktotrophic Larvae ◽  
Living Organisms ◽  
Almost All ◽  
Apical Ganglion

The origin and radiation of the major metazoan groups can be elucidated by phylogenomic studies, but morphological evolution must be inferred from embryology and morphology of living organisms. According to the trochaea theory, protostomes are derived from a holoplanktonic gastraea with a circumblastoporal ring of downstream-collecting compound cilia (archaeotroch) and a nervous system comprising an apical ganglion and a circumblastoporal nerve ring. The pelago-benthic life cycle evolved through the addition of a benthic adult stage, with lateral blastopore closure creating a tube-shaped gut. The archaeotroch became differentiated as prototroch, metatroch and telotroch in the (trochophora) larva, but was lost in the adult. The apical ganglion was lost in the adult, as in all neuralians. Paired cerebral ganglia developed from the first micromere quartet. The circumblastoporal nerve became differentiated into a pair of ventral nerve cords with loops around mouth (the anterior part of the blastopore) and anus. Almost all new information about morphology and embryology fits the trochaea theory. The predicted presence of a perioral loop of the blastoporal nerve ring has now been demonstrated in two annelids. Alternative ‘intercalation theories’ propose that planktotrophic larvae evolved many times from direct-developing ancestors, but this finds no support from considerations of adaptation.

Hemichordate Nervous System

2018 ◽  
Author(s):  
Norio Miyamoto ◽  
Hiroshi Wada
Keyword(s):  
Nervous System ◽  
Nerve Cord ◽  
The Body ◽  
Model Organisms ◽  
Lateral Side ◽  
Essential Information ◽  
System P ◽  
The Brain ◽  
Nerve Cords ◽  
Apical Ganglion

Hemichordates are marine invertebrates consisting of two distinct groups: the solitary enteropneusts and the colonial pterobranchs. Hemichordates are phylogenetically a sister group to echinoderm composing Ambulacraria. The adult morphology of hemichordates shares some features with chordates. For that reason, hemichordates have been considered key organisms to understand the evolution of deuterostomes and the origin of the chordate body plan. The nervous system of hemichordates is also important in the discussion of the origin of centralized nervous systems. However, unlike other deuterostomes, such as echinoderms and chordates, information on the nervous system of hemichordates is limited. Recent improvements in the accessibility of embryos, development of functional tools, and genomic resources from several model organisms have provided essential information on the nervous system organization and neurogenesis in hemichordates. The comparison of the nervous system between hemichordates and other bilaterians helps to elucidate the origin of the chordate central nervous system. Extant hemichordates are divided into two groups: enteropneusts and pterobranchs. The nervous system of adult enteropneusts consists of nerve cords and the basiepidermal nerve net. The two nerve cords run along the dorsal and ventral midlines. The dorsal nerve cord forms a tubular structure in the collar region. The two nerve cords are connected through the prebranchial nerve ring. The larval nervous system of enteropneusts develops along the ciliary band and there is a ganglion at the anterior end of the body called the apical ganglion. A pair of pigmented eyespots is situated at the lateral side of the apical ganglion. The adult nervous system of pterobranchs is basiepidermal and there are several condensations of plexuses. The most prominent one is the brain, located at the base of the tentaculated arms. From the brain, small fibers radiate and enter tentaculated arms to form a tentacle nerve in each. There is a basiepidermal nerve cord in the ventral midline of the trunk.

Catecholamine-containing, serotonin-like, and FMRFamide-like immunoreactive neurons and processes in the nervous system of the early actinotroch larva of Phoronis vancouverensis (Phoronida): distribution and development

1990 ◽  
Vol 68 (7) ◽  
pp. 1525-1536 ◽  
Author(s):  
Anders Hay-Schmidt
Keyword(s):  
Nervous System ◽  
Glyoxylic Acid ◽  
Ventral Side ◽  
Ciliary Band ◽  
The Future ◽  
Apical Ganglion

The distribution and development of neurons and nerve processes containing the putative neurotransmitters catecholamines (CA), serotonin-like immunoreactivity (5-HT-ir), and FMRFamide-like immunoreactivity (FMRFamide-ir) have been investigated by means of glyoxylic acid induced fluorescence in CA and antibodies against 5-HT and FMRFamide in the 0- to 6-tentacle actinotroch larvae of Phoronis vancouverensis Pixell, 1912. CA and 5-HT-ir were observed in the apical ganglion at all stages (beginning at the early 0-tentacle stage); FMRFamide-ir appeared first at the late 0-tentacle stage. The CA-containing cells are located in a ring at the periphery of the apical ganglion, whereas the 5-HT-immunoreactive cells form a U-shaped area in the centre of the epistome. In late 0-tentacle stages, CA, 5-HT-ir, and FMRFamide-ir are found in processes along the future ciliary band of the tentacles and the margin of the epistome. At the 2-tentacle stage, processes are observed in the apical ganglion extending from the neuropil towards the tentacles and the margin of the epistome. At the 4- to 6-tentacle stage, processes loosely concentrated in large bundles are found along the epistome margin projecting on the ventral side of the mesosome towards the tentacles (CA, 5-HT-ir, and FMRFamide-ir), extending from the apical ganglion towards the tentacles (5-HT-ir and FMRFamide-ir), along the ciliary band of the tentacles (CA, 5-HT-ir, and FMRFamide-ir), and along the posterior ciliary band (CA, 5-HT-ir, and FMRFamide-ir).

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