Hemichordata - class-XI

Any wormlike invertebrate of the phylum Pentastomida (or subphylum of Arthropoda), having two pairs of hooks at the sides of the mouth: all are parasitic, some in the respiratory tracts of mammals.

Hemichordates are marine invertebrates which are closely related to both chordates and echinoderms. They are deuterostomes which have pharyngeal gill slits and most of them have a dorsal nerve cord and they lack a notochord.

Balanoglossus is a hemichordate. While it is a marine animal, it is not a worm in the traditional sense, and the statement is generally accepted as true in biological contexts regarding its development.

Hemichordates means half chordates. It is a connecting link between non-chordates and chordates as they share some characteristics of both. The chordates have creatine in their energy cycle for the muscle contaction while non-chordates have arginine but the hemichordates have both i.e., creatine as well as arginine.

Protochordates are the animals having a dorsal hollow nerve cord, pharyngeal gill slits, and a notochord. They are usually referred to as the oldest chordates. They mainly include tunicates and cephalochordates. They are bilaterally symmetrical and possess a coelom. They do not have a closed circulatory system or jointed legs.

So, the correct answer is 'Both C  and D'.

Asterias ( star fish) is an example of echinodermata and not protochordata as they have a hard calcium carbonate structure that it uses as their skeleton.

Earthworm is an annelid, hydra is a coelenterate, liverfluke is a platyhelminthes, acorn worm (Balanoglossus, Saccoglossus) is a hemichordate belonging to class Enteropneusta.

Hemichordates consists of a small group of worm-like marine animals with an organ-system level of organization. They are nonchordates. The circulatory system is of open type. The blood flows to a cavity known as hemocoel which bathes the organs directly with oxygen and nutrients and there is no distinction between blood and interstitial fluid. They respire with help of gill slits.

Hemichordates may not always have a cylindrical body, cylindrical body is the main characteristics of nematodes. Rest all are the characteristics of hemichordates.

Protochordates are basically non-vertebrate chordates. They are bilaterally symmetrical and triploblastic animals. They are coelomates and lack a cranium. They are also referred to as acraniates.

Ascidiacea is a class of subphylum urochordata. Rest all  pterobranchiaEg. Rhabdopleura; Enteropneusta Eg. Acorn worms (Balanoglossus, Saccoglossus);planctosphaeroidea Eg. Planctosphaertara pelagica are class of Hemichordata.

Hemichordates, Urochordates, and Cephalochordates are all primitive chordate-related groups that lack true paired appendages (limbs) found in higher vertebrates.

A) Urochordata is a subphylum of the phylum Chordata and is included in protochordata. It does not include Balanoglossus.

In hemichordates and chordates nerve cord is dorsally placed.

Tongue worm Balanoglossus is a Hemichordate. The basic character of Hemichordates is a division of the body into proboscis, collar, and trunk.

Protochordata is included in the phylum Chordata. They possess a single layer of epidermis consisting of long columnar cells. In some cases such as Balanoglossus, these cells are ciliated. The lower layer dermis is absent in Protochordates. Thus, the correct answer is 'Single layered'.

Acorn worm is an any of the soft-bodied invertebrate belonging to phylum Hemichordata.

In Hemichordates, there is a false notochord known as a stomochord.

Hemichordates were earlier a subphylum in the phylum Chordata. Later they were made into a separate phylum.

A) Ventral heart if present, is in non-chordates except Hemichordates.

Chorda dorsalis originates from Latin. Chorda literally means 'sting' and dorsum means 'back'. Hence the answer is 'notochord' because it is the spinal column which is present on the dorsal side of an embryo. The notochord is a common aspect of all Chordates.

Hemichordates do not have a notochord but a false notochord.

Balanoglossus (a hemichordate) is considered a connecting link because it possesses features of both chordates (pharyngeal gill slits, dorsal nerve cord) and non-chordates.

Balanoglossus is a well-known genus belonging to the phylum Hemichordata. Salpa is a urochordate, while Petromyzon and Myxine are cyclostomes (vertebrates).

Acorn worms are the common name for organisms in the class Enteropneusta, which belongs to the phylum Hemichordata.

Statement 'c' is incorrect because Branchiostoma (Amphioxus) belongs to Cephalochordata, not Hemichordata. Statements a, b, and d are biologically accurate.

The proboscis gland (also known as the glomerulus) in Balanoglossus is the primary excretory organ responsible for filtering waste products.

Hemichordates share significant developmental and anatomical similarities with Echinoderms, particularly in their larval stages (e.g., tornaria larva vs. bipinnaria larva).

Balanoglossus is a ciliary feeder that captures food particles from the water or sediment, which is a form of phagotrophic nutrition.

The velum is a muscular fold found in the pharynx of cephalochordates like Amphioxus (also known as Branchiostoma).

Hemichordates were historically considered a sub-phylum of Chordata, but are now a separate phylum that serves as a link between non-chordate invertebrates and true chordates.

The proboscis gland is the primary excretory organ in Balanoglossus. Protonephridia are not the primary excretory structures in adult hemichordates.

Balanoglossus is known to undergo physiological changes during starvation, including the reduction of body size as it metabolizes its own tissues.

A Protochordate belongs to any two invertebrate subphyla of the phylum Chordata- the Tunicates (sea squirts, salps, etc.) and the Cephalochordates (amphioxus). Like the remaining subphylum of the chordates, the Vertebrata, the protochordate has a hollow dorsal nerve cord, gill slits and a stiff supporting rod, the notochord, the forerunner of the backbone. The protochordate differs chiefly from the vertebrates in not having a backbone. Hence, they have bilateral symmetry, coelom, and a circulatory system. However, they lack jointed appendages

Phylum Hemichordata consists of a small group of worm-like marine animals with an organ-system level of organisation. The body is cylindrical and is composed of an anterior proboscis, a collar, and a long trunk. The circulatory system is of open type. Respiration takes place through gills. The excretory organ is proboscis gland.

Connecting links are good evidences of organic evolution. These There are organisms exhibit intermediate characteristics of two taxonomic groups. Balanoglossus is a connecting link between non-chordates and chordates. Chimaera is a connecting link between cartilaginous and bony fishes. Coelocanth is a connecting link between bony fishes and amphibians. Sphenodon is a connecting link between amphibians and reptiles.

Protochordates are closely related to vertebrates. These lack some of the peculiar characteristics of chordates like the true skull, brain, skeleton. These are invertebrates.

Balanoglossus has some characteristics in common with chordates, such as gill slits and a dorsal nerve cord; however, this species also has a ventral nerve cord and the nerve cords in general are not hollow like most chordates, but instead are solid. Therefore they are nonchordate - protochordate. 

Acorn worms is a hemichordate. They are closely related to echinoderms. They are solitary worm-shaped organisms. They can be traced in burrows and are deposit feeders, but some species are pharyngeal filter feeders.

Hemichordata is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the lower or middle Cambrian and include two main classes: Enteropneusta (acorn worms), and Pterobranchia. 

A) Schizocoel is a type of coelom which is derived by splitting of mesoderm. It is not present in hemichordates.

In hemichordates, the pharyngeal gill slits are located dorsally along the pharynx, which is a characteristic feature of this phylum.

A) Amphioxus is a filter feeder and does not swallow mud.

The body is distinguished into three unequal regions, proboscis, collar and trunk in hemichordates, like Balanoglossus. Hemichordates are most primitive marine chordates, their body is soft and devoid of any skeleton. 

Acorn worms is a hemichordate. They are closely related to echinoderms. They are solitary worm-shaped organisms. They can be traced in burrows and are deposit feeders, but some species are pharyngeal filter feeders. Many are well known for their production and accumulation of various halogenated phenols and pyrroles. 

Acorn worms are unsegmented worms belonging to the phylum Hemichordata. Balanoglossus is an ocean-dwelling acorn worm genus. It is considered to be an evolutionary link between invertebrates and vertebrates.

Balanoglossus is a hemichordate acorn worm. It is the connecting link between invertebrates and vertebrates. It is basically a bottom-dwelling marine worm. It is tubicolous, that is, lives inside U-shaped burrows or tubes in the sand.  In Balanoglossus, the sexes are separate and prominent sexual dimorphism does not exist and fertilization is external, that is, it takes place outside the body of the organism.

Hemichordates are enterocoelous coelomates with radial cleavage. Enterocoelic coelom (enterocoel) develops as mesodermal pouches, arising from the gut of the embryo. 

Balanoglossus is an ocean-dwelling 'acorn worm', genus of Hemichordata. It is an 'evolutionary link' between invertebrates and vertebrates. It has a notochord in the upper part of the body and has no nerve chord. Hence, option B is correct.

A tornaria is the planktonic larva of some species of Hemichordata. Trochophore is the larva of marine annelids and most groups of molluscs.
A tadpole is a larval stage in the life cycle of an amphibian. Ammocoete is the larval stage of lamprey.

Protochordates are the invertebrate members of Chordata and include urochordates (sea squirts) and cephalochordates (amphioxus, lancelets). Cephalochordates are filter feeders that use cilia to generate a current of water and phytoplankton particles into the mouth. 

Hemichordata is a phylum of marine deuterostome animals. They show characteristics of both Echinoderm and Chordates. They show bilateral symmetry and are triploblastic. Body is unicellular and is composed of epidermis. Body consists of three regions, proboscis, collar and trunk.

Protochordates are closely related to vertebrates. They differ from the chordate by not having a backbone. They are marine worms that share some, but not all of the characteristics of chordates. All living protochordate are strictly marine and are isosmotic with the sea.

Protochordates are closely related to vertebrates. These lack some of the peculiar characteristics of chordates like the true skull, brain, skeleton. These are invertebrates. This group is composed of the phylum Hemichordata and the subphylum Urochordata and Cephalochordata.
So, the correct answer is option D.

Balanoglossus is a hemichordate. The excretory organ in Balanoglossus is glomerulus. This is also known as the proboscis gland. This gland is present in front of the central sinus. The gland projects outward in the proboscis coelom. The gland is comprised of many tube like projections. The tubes are blind at one end. The tubes are formed by the peritoneum. They are present as the covering of buccal diverticulum, central sinus, and heart vesicle. This organism is considered as the link between vertebrates and invertebrates. 

Buccal diverticulum is a short and thick-walled projection which extend forwards through the proboscis stalk into the proboscis coelom. This is a hollow tube like projection. This is a tubular outgrowth from the mouth cavity forward into the proboscis.The wall is composed of a single layer of tall and vacuolated endodermal cell. Hemichordata is known as half chordate because of the buccal diverticulum. The structure resembles like a rudimentary notochord present in the dorsal or back side and supporting axis for primitive vertebrates. 

Early developmental stages of Balanoglossus possess a spacious coelom, lined with peritoneum. It is enterocoeles in origin, as the adult condition is attained, the coelomic epithelium gives rise to the connective tissue and muscle fibers. Hence, the coelomic cavity is obliterated. The coelom as a whole is divided into three parts. These include one cavity in proboscis, (protocoel), two in the collar, (mesocoel) and two in the trunk (metacoel).

A tornania is the planktonic larva of some species of Hemichordata. It is very similar in appearance to the bipinnaria larvae of starfishes, with convoluted bands of cilia running around the body. Hemichordata is a phylum of marine deuterostome animals.

The structure of 'tornaria larva' was first described by J. Muller in 1850. He suspected it to be the larva of starfish. Later, in 1869, Metchinkoff found that it was the larva of Balanoglossus clavigerus. The name tornaria was given to it because of its habitat of rotating in circles.

Protochordates are an informal category of animals (i.e., not a proper taxonomic group). This group has the animals that possess some but not all characteristics of chordates. They have pharyngeal gill slits and a dorsal nerve cord, however, they lack vertebral column and paired appendages.

Hemichordates share some but not all of the typical chordate characteristics and hence, are not true chordates.
There is a rudimentary structure in the collar region, the stomochord, that is similar to a notochord. There is a dorsal nerve cord, in addition to a smaller ventral nerve cord.

Balanoglossus is an ocean-dwelling acorn worm genus. They possess a long protrusible proboscis.
The tentacular apparatus, which is present in some hemichordates is of lysosomal (collar).
Balanoglossus also possess the trunk in which the gonads are present.

Balanoglossus was earlier placed in the group of the Hemichordates. But now like the other doubtful Hemichordates, such as Cephalodiscus and Rhabdopleura, Balanoglossus are now classified under non-chordates after echinoderms. It is because their notochord is doubtful. They have a short notochord which is confined to proboscis and non homologous with that of chordates.

Hemichordata closely relates the Chordates. It contains marine deuterostome animals. They have a tubular structure known as stomochords. Stomochords arise in embryonic development as an out-pocketing from the roof of the embryonic gut anterior to the pharynx. In adults, they extend dorsally from the pharynx into the proboscis and serve to communicate with the oral cavity. Their walls are composed primarily of epithelial cells, but ciliated and glandular cells are also present.Balanoglossus belongs to the Hemichordata phylum. So, it has buccal diverticulum.

Protochordates are closely related to vertebrates. These lack some of the peculiar characteristics of chordates like the true skull, brain, skeleton. These are invertebrates. 
So, the correct answer is option A.

Balanoglossus belongs to subphylum Hemichordata, which have a short notochord present in anterior part of the body but it is only present in the larval stage.

Balanoglossus is an ocean-dwelling acorn worm, it is an "evolutionary link" between invertebrates and vertebrates. It belongs to chordates, phylum Hemichordata and order Enteropneusta.

• Balanoglossus belongs to phylum Hemichordata. They possess notochord (only in the embryonic stage) whereas earthworm, leech, series belongs to phylum Annelida and they do not possess notochord.