Hemichordata balanoglossus. Phylum Hemichordata: Characteristics, Classification, Examples 2022-10-11
Hemichordata is a phylum of marine invertebrates that includes the acorn worms and the pterobranchs. The acorn worms, also known as enteropneusts, are worm-like animals with a simple, tubular body and a simple digestive system. They are named after the acorn-shaped proboscis, or feeding organ, that protrudes from the front of their body. The pterobranchs, on the other hand, are small, colonial animals that live in tubes and have a more complex anatomy.
One well-known member of the hemichordata phylum is the acorn worm Balanoglossus. Balanoglossus is a burrowing animal that lives in soft sediments at the bottom of the ocean. It has a long, slender body with a series of gill slits along the sides and a simple digestive system. The front part of its body is modified into a proboscis, which it uses to filter small particles from the water for food.
Balanoglossus is an important organism in the study of evolutionary biology because it is thought to be a transitional form between invertebrates and vertebrates. It has many features that are found in both groups, such as a notochord (a flexible rod that provides support and movement), a hollow nerve cord, and pharyngeal gill slits (which are used for respiration and feeding). These features suggest that Balanoglossus may have evolved from a common ancestor with the vertebrates.
Despite its importance in evolutionary studies, little is known about the biology and ecology of Balanoglossus. It is found in shallow, tropical waters, but very little is known about its behavior or reproductive habits. Further research on this fascinating animal could help us understand the early evolution of vertebrates and the relationships between different groups of animals.
In which group is Balanoglossus classified?
Chordates do not have the body and coelomic regions corresponding to those of hemichordates. Balanoglossus and allied forms have phylogenetic importance. Nephridia are excretory organs in molluscs. The greatest and the most convincing resemblance lies in the method of formation and arrangement of coelomic cavities. What are the basic chordate characters? Since the hemichordates arose from the ancestral line after the divergence of the ancient Echinodermata but before the rise of true chordates, they are often called prechordates.
Hemichordata: Characters and Classification (With Diagram)
The post-anal tail in juvenile enteropneusts, which is a relic of the stalk of pterobranch ancestor. Modern workers of hemichordates do not accept this idea and have raised many objections: 1. Mouth appears by invagination in the position of the groove. It is called tornaria larva. Hemichordata has 130 known species, and many more are being discovered, particularly in the deep water.
Digestive System of Balanoglossus (Hemichordata)
Balanoglossus is a deuterostome, which is similar to Ascidian or marine squirts in that it has branch openings or gill slits. The details of the branchial apparatus having tongue bars, M-shaped skeletal rods and synapticula are exactly like those of Amphioxus. But they have only one character of Chordata, i. They are the typical Acorn Worms. The close affinities of Hemichordata, Echinodermata and Chordata, etc.
ADW: Balanoglossus: CLASSIFICATION
Ans: The two common characteristics between chordates and hemichordates are the presence of tubular nerve cords and pharyngeal slits. The embryo has reached the 16-cell stage once the fourth division has happened. The trunk coelom is separated from the collar coelom by a collar-trunk septum. At the same time, the Palaeoscolecida share a number of char- acters with the lobopod-bearing Cambrian ecdysozoans, the Xenusia. The sperm swim and seek out the eggs, which it is believed they detect chemically. The body elongates and is distinguished into proboscis, collar and trunk by the appearance of two constrictions, and the trunk region is elongated. The chief link between the hemichordates and chordates lies in the pharynx and its gill-clefts.
Balanoglossus: Habitat, Development and Affinities
Phylum Hemichordata involves marine deuterostome animals and is related to chordates. There are certain resemblances between the nervous system of hemichordates and chordates, such as its position, and formation of the dorsal nerve cord from the dorsal epidermis, and the collar cord which often has a neuropore and is comparable with the brain of vertebrates. The four vegetal blastomeres split evenly but unequally, resulting in four large macromeres and four smaller micromeres. The zooids of the genus Rhabdopleura are constantly linked to the remainder of the colony through a stolon system. Filter feeders have mucous secreting glands and cilia on their proboscis. Hemichordates are usually vermiform, solitary, or colonial enterocoelous coelomate animals with an intra-epidermal nervous system and a pre-oral with or without gill-slits and without typical nephridia. The coelomic cavities of collar are completely cut off from the proboscis cavity.
Phylum Hemichordata: Characteristics, Classification, Examples
The first part of body is called the Protosome, which is modified as proboscis and that gives the Hemichordates their common name of Acorn Worms. Balanoglossus is a sluggish animal and the proboscis is the most active part of the body. The proboscis is a muscular, ciliated organ that helps animals move around and gather and transfer food particles. It is also used as an organ of locomotion, much in the way a snail uses its foot — both for movement inside and outside the burrow. Alimentary Canal The alimentary canal in Balanoglossus is a complete and straight tube running between the mouth and anus. They have an offensive odour.
Affinities of Balanoglossus
They are small animals, ranging in size from 1 to 12 millimetres in length. Reproductive System of Balanoglossus: The sexes are separate and often differ in shape and colour. But now it is placed as a separate phylum under non-chordata. The anterior prosome, intermediate mesosome, and posterior metasome are the three sections of the anteroposterior axis. To the right of the hydropore lies a pulsating heart vesicle which develops in the later stages of tornaria larva.
Affinities of Hemichordata with Chordates, Annelids & Echinoderms
The collar coelom is greatly obliterated by the collar musculature and connective tissue. Hemichordates have traditionally been thought to evolve in two ways: directly and indirectly. The larva of Hemichordata and Annelida also differ in the following ways: i Nephridia present in trochophore larva are absent in tornaria larva. A respiratory current is created by the beating of lateral cilia on the sides of the gill bars. Development is direct without a free- swimming tornaria larva. The alimentary canal has the same shape and the same divisions into foregut, stomach, and intestine in hemichordate and echinoderm larvae.