Which class of vertebrates has cartilaginous endoskeletons?
Chondrichthyes, such as sharks and rays, have a cartilaginous endoskeleton.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Vertebrata - Amphibia and Reptilia
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Which of the following groups has an endoskeleton composed of calcareous ossicles?
Echinoderms have an endoskeleton made of calcareous ossicles, which provides support and protection.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Phylum Mollusca and Echinodermata
Endoskeleton of echinoderms is made of
Echinoderm endoskeleton is mesodermal, not epidermal exoskeleton, composed of stereom, a distinctive porous three-dimensional lattice of calcium carbonate predominantly as calcite with small magnesium carbonate. Mesenchymal sclerocytes secrete interconnected ossicles forming articulated arms in sea stars, rigid test with fused plates in sea urchins, and scattered spicules in sea cucumbers. Thin epidermis covers ossicles, spines articulate via muscles. This calcareous construction provides protection, muscle attachment for tube feet and support, contrasting with chitinous arthropod cuticle and siliceous sponge spicules, thus serving as diagnostic phylum character for Echinodermata identification.
Ref: NCERT Class 11 Biology, Chapter 4: Animal Kingdom – Echinodermata; Brusca & Brusca, Invertebrates, 3rd ed., Chapter 21