Nervous system of balanoglossus. Affinities of Balanoglossus 2022-10-03
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The nervous system of Balanoglossus, also known as the acorn worm, is a relatively simple yet crucial system that is responsible for coordinating and controlling the various functions and behaviors of the animal.
The acorn worm has a diffuse nervous system, meaning that it lacks a centralized brain and instead has a network of nerve cells distributed throughout its body. This diffuse nervous system is responsible for coordinating sensory information and initiating reflex responses to stimuli.
One of the key components of the acorn worm's nervous system is the pharyngeal nerve ring, which is located in the pharynx region of the body. This nerve ring is composed of a series of interconnected ganglia, or clusters of nerve cells, that receive sensory input from the animal's body and coordinate reflex responses.
In addition to the pharyngeal nerve ring, the acorn worm also has a number of sensory organs that are essential for detecting and responding to stimuli in its environment. These include simple eyespots, which are located on the animal's head and are sensitive to light, as well as sensory tentacles that are used to detect touch and movement.
Overall, the nervous system of Balanoglossus plays a vital role in coordinating the various functions and behaviors of the animal, including movement, digestion, and reproduction. Despite its simplicity, this system is essential for the survival and success of the acorn worm in its natural habitat.
Nervous System of Balanoglossus (With Diagram)
The ventral vessel supplies blood through lacunar plexus to the body wall and alimentary canal. The fibres of sensory epidermal cells synapse with the fibres of nerve cells. The small ovum measures about 0. Affinities of Balanoglossus Enteropneusta, Hemichordata with chordates and non-chordate phyla are as follows: Affinities with Chordata : Bateson 1887 included Hemichordata in phylum Chordata, since then a close relationship has been acknowledged between hemichordates and chordates. Recent workers do not accept the notochordal nature of the buccal diverticulum. The trunk is divisible into three parts, an anterior branchio-genital region, a middle hepatic region, and a posterior abdominal or post-hepatic region.
The cilia in this band are long, powerful and act as chief locomotor organ of tornaria. The mature sperms and ova are discharged outside through the genital pores. Its cilia are short and serve to collect the food. The body elongates and is distinguished into proboscis, collar and trunk by the appearance of two constrictions, and the trunk region is elongated. Derivation of Balanoglossus 2. The mucus, secreted by gland cells, covers the animal and lines its burrow. Within 12-24 hours, an invagination starts in the blastula which deepens to form the archenteron.
Balanoglossus: Habitat, Development and Affinities
The nervous layer becomes thickened along definite strands to form two main nerve cords, one mid-dorsal and the other mid-ventral, which run along the entire length of the trunk. The buccal diverticulum is neither analogous nor homologous with the chordate notochord, histologically it is identical with the wall of the buccal cavity, it is apparently nothing more than a pre-oral extension of the gut. From this plexus an efferent branchial vein is formed. The gonopores are generally located to the lateral external side of the gill-pores in the same branchiogenital groove. The dorsal trunk cord in the collar leaves the epidermis and projects into the collar coelom as the collar cord or neurocord. It is a Y-shaped body and is composed of cartilaginous tissue.
In these genital ridges, gonads are situated. The central mesentery is complete. It is claimed that in some species a few neurosensory cells form photoreceptors sensory to light. The frontal cilia occur within the lining of the pharynx Fig. Most of the blood vascular system is located between the lamellae of the basement membrane and the leaves of the mesentery. There are two sets of muscle fibres— the radial fibres which open the mouth and the sphincter muscles which close it.
One prong of the skeleton is present in the septum and the other lies in the tongue Fig. In this condition, the particles adhere to the mucus secreted by the epidermal glands and are carried towards the mouth. The collar cavity is paired and opens to the exterior by two apertures. Regarding phylogeny, the structural similarities with the different groups demand a link between chordates in one hand, and echinoderms and groups of other invertebrates in other hand. Our mission is to provide an online platform to help students to discuss anything and everything about Zoology.
A lateral pharyngeal vessel appears in the lacunar plexus at the junction of the two pharyngeal regions. The larva now becomes worm-like juvenile Balanoglossus. Pre-larval Development: The pre-larval developmental stages resemble closely that of Branchiostoma. The chief link between the hemichordates and chordates lies in the pharynx and its gill-clefts. Nervous system consists primarily of an epidermal plexus or a layer of nerve cells and nerve fibres lies just below the epidermis.
The ventral vessel continues up to the anus and gives off lacunar networks all along the alimentary canal. Subsequently, the dorsal end of the aperture projects downwards as the tongue-bar Fig. This will help to avoid controversies to a large extent. The mucus, secreted by the proboscis, entangles the sand or other food particles from the surrounding region and the mucus coated particles are pushed directly into the mouth by the action of cilia Fig. Knight Jones 1952 reported that the animal moves in its burrow with the help of cilia present all over the body. The epithelial cells are of tall columnar type and have their nuclei near their broader bases. It then undergoes morphological changes to become an adult.
Reproductive System of Balanoglossus (With Diagram)
Its similarity to chordate nerve cord, formed by the invagination of the nervous ectoderm at the dorsal mid-line, is evident. Again molecular analysis fails to find a homology between the stomochord of hemichordates and notochord of other chordates. Thus, the larva gradually changes into the adult. But the three unique chordate characters are not very pronounced in Balanoglossus. Sense Organs of Balanoglossus : In Balanoglossus, the sense organs are poorly developed.
The vascular system of most hemichordates is like that of annelids with blood flowing anteriorly in the dorsal vessel and posteriorly in the ventral vessels. Dorsolaterally, on each side, the branchial portion of pharynx is perforated by a longitudinal series of numerous U-shaped openings, the gill- slits. The evaginations push the collar-trunk septum into the collar and thus make the collar coelom complicated. The blood flows anteriorly through the dorsal vessel. The food particles and mucus are drawn in through the mouth into the buccal cavity by the action of cilia, aided by the respiratory water current. The size of tornaria larva varies from 1 mm to 3 mm. Nervous system solid except collar nerve cord.
