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.

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.

Poriferans are commonly known as sponges. They are multicellular organisms with cellular level of organization. They are sessile and sedentary in nature. These have an exoskeleton made up of either spongin fibers or calcareous or siliceous spicules. The spicules form the skeleton of the body which provides protection. These spicules are  formed by sclerocyte cells present in the mesenchyme.

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.

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.

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.

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

Non-symbiotic bacteria in the soil and symbiotic bacteria that live in the roots of plants are capable of nitrogen fixation. Bacteria in the genera Clostridium and Azotobacter are non-symbiotic nitrogen-fixing bacteria, while those in the genus Rhizobium are symbiotic bacteria. Pseudomonas species fixes nitrogen under microaerobic conditions in the free-living state and colonizes rice endophytically. Nitrogen fixation in phototrophic bacteria has been found in Rhodospirillum rubrum. 

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.

Nephridium is an excretory organ which functions similarly to a kidney in vertebrates. These are present in paired form in the invertebrates. It is also in amphioxus. It expels wastes from the body cavity to the exterior.

Excretory organs of Amphioxus is the pronephros. The pronephros is the anterior end of this excretory organ, which is developed before the rest to meet the larval needs.

Amphioxus also known as lancelet is a fish-like marine chordate. Unlike vertebrates, the dorsal nerve cord is not protected by bone but by a simpler notochord made up of a cylinder of cells that are closely packed to form a toughened rod. The lancelet notochord, unlike the vertebrate spine, extends into the head and therefore they are placed in subphylum Cephalochordata. Hence, option C is correct.

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. 

Amphioxus are fish-like marine chordates. The notochord is a flexible rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In case of Amphioxus, it is retained in the adults.

Protochordates consists of the organisms that are categorized under subphyla Urochordata and Cephalochordata. Protochordates are also called as Acraniata, due to the lack of head and cranium. These organisms are extremely marine and have small sized bodies. In protochordates, kidneys contain protonephridia, whereas, in euchordates, kidneys contain meso- or metanephridia.

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.

Amphioxus or lancelets comprise approximately of 32 species of fish-like marine chordates. In the lancelet, there is a nerve cord above the notochord, but no cranium or vertebrae or eyes.
So, the correct answer is option A.

The roof of the oral hood in Amphioxus show the presence of Hatschek's pit which is responsible for the secretion of mucus. This mucus secretion helps to entrap food particles present in the water.

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.

Branchiostoma is one of the few living genera of lancelets. They do not have a true head, but merely a mouth adjacent to the gill slits with the slightly enlarged anterior end of the dorsal nerve cord above and in front of them. In Brannchiostoma, the notochord is extended up to the head and is retained throughout its life.

The wheel organ is found in amphioxus, which is a specialized epithelium in the roof and sides of the adult lancelet oral cavity. It borders the oral epithelium proper. The wheel organ cells are tall and strongly ciliated and have dark, heterochromatin-rich nuclei. It draws food through the use of its cilia for digestion. 

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.

Amphioxus also called as lancelets or cephalochordates form one of the three chordate subphyla. Amphioxus possess typical chordate characters, such as a dorsal hollow neural tube and notochord, a ventral gut and a perforated pharynx with gill slits, segmented axial muscles and gonads, a post-anal tail, a pronephric kidney. Hence, option B is correct.

The unpaired 'Hatscheck's nephridium' is the largest and most anterior of the nephridia in the body of the Branchiostoma. It is a single tubule which lies on the left side of the notochord running parallel to the left anterior aorta. It stretches from the anterior vestibule to a point immediately posterior to the velum where it opens into the endodermal pharynx. 

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.