Answer: Option B. -> Water canal system is a unique feature of echinoderms.
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B
Water vascular system is a unique feature of echinoderms, while water canal system is typically found in sponges (Phylum Porifera). Nematocysts or stinging cells are cells that help in defence in cnidarians. Nephridia are excretory organs found in annelids. Phylum Porifera includes sponges, which are exclusively marine.

Answer: Option C. -> 1 - Scoliodon, 2 - Pristis, 3 - Carcharodon, 4 - Trygon            
:
C
The images are those of the following cartilaginous fishes:
1. Scoliodonhas an elongated, spindle-shaped, body tapered at the ends. The trunk and tail are laterally compressed, while the head region is dorsoventrally compressed.Itis commonly known as dogfish, and is a type of shark.
2. Pristisis commonly known as sawfish. It ischaracterised by a long, narrow, flattened rostrum, or nose extension, lined with sharp transverse teeth, arranged so as to resemble a saw, and hence, the name.
3. Carcharodon, known as the great white shark,isknown to prey upon a variety of other marine animals, including fish and seabirds.It is alsoranked among the top predators in having the most recorded shark bite incidents on humans.
4.Trygon, commonly known as stingray,has a diamond-shaped pectoral findisc slightly wider than long, and a whip-like tail with upper and lower fin folds. A stinging spine is present on the tail, equipped with a venomgland at its base.

Answer: Option A. -> a - diploblastic, b - triploblastic
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A
A germ layer is a group of cells in an embryo, that interact with each other as the embryo develops and contribute to the formation of all organs and tissues. All animals, except sponges (sponges exhibit cellular level of organisation), form two or three germ layers. The germ layersdevelop early in embryonic life. Thus, based on the number of embryonic germ layers, organisms are categorised as diploblastic and triploblastic. Diploblastic organisms are those in which the embryonic stage includes just two layers - the ectoderm and the endoderm, from which the fully functional organism develops. A gelatinous substance called mesoglea fills the space between them. Triploblastic organisms are those which possess three germinal layers during embryonic development - the ectoderm, mesoderm and the endoderm, each of which gives rise to the various parts of the fully developed organism.

Answer: Option B. -> Sponges
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B
Protozoans belong to Kingdom Protista and not to Animalia. In the Animal Kingdom, sponges are the only group of animals that exhibit cellular level of organisation. They are thus, grouped under sub-kingdom Parazoa.

Answer: Option C. -> Sea urchin
:
C
Thewater vascular systemis a hydraulicsystem typically used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration. Sea anemone and sea pen are cnidarians, while sea horse is a fish.

Answer: Option B. -> Acoelomates
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B
Platyhelminths are acoelomates, which means that they do not have a body cavity. The space between organs is filled with parenchymatous connective tissue called mesenchyme, leaving no space for a true coelom. The dorsoventrally flattened shape of flatworms is also an indication of their acoelomate nature.

Answer: Option D. -> All of these
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D
In amphibians, the alimentary canal, urinary and reproductive tracts open into a common chamber called cloaca which opens to the exterior.

Answer: Option A. -> Both [A] and [R] are true and [R] is the correct explanation of [A]
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A
Many cnidarians exhibit metagenesis or alternation of generations. Obeliais a good example of this. The life history of Obelia includes both asexual and sexual generations that alternate with each other to complete the life cycle. The sedentary polyp is a colonial form, that alternates with the free-swimming medusa phase. The polyp colony reproduces by asexual budding. The medusa buds get detached from the parent colony, and become free-swimming sexual forms that carry ova and sperms in their respective gonads, and release them into the water. They then fertiliseto form a zygote, which later morphs into a blastula, then a ciliated swimming larva called a planula. The planula eventually attaches to a substrate and gradually develops into a polyp colony.

Answer: Option C. -> (i) Acorn worm, (ii) Hemichordata, (iii) Tornaria, (iv) Echinodermata
:
C
Acorn worm (Balanoglossus), belonging to the Phylum Hemichordata, is said to be the connecting link between the non-chordates and chordates. This is because it possesses certain characters found in chordates, in addition to many of its invertebrate features.The larval form of hemichordates is called tornaria, which resembles the bipinnaria larva of echinoderms.

Answer: Option A. -> Hagfish 
:
A
Sub-phylum Vertebrata is classified into two divisions based on the presence or absence of jaws - Agnatha and Gnathostomata. The former includes the jawless vertebrates while the latter includes the jawed forms. Division Agnatha includes just one class - Cyclostomata. Examples of this jawless class are lamprey and hagfish. Fishes are jawed, and are grouped under division Gnathostomata. Jellyfish is an invertebrate that is classified under Phylum Cnidaria.