Which polysaccharide is present in the exoskeleton of arthropods?
Chitin is a polysaccharide found in the exoskeleton of arthropods.
Ref: NCERT Class 11 Biology Chapter 9: Biomolecules Proteins and Polysaccharides - Structure and Functions
#invertebrate biology
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Blood of phoronids contains
Phoronid circulatory physiology includes red blood corpuscles containing hemoglobin enabling oxygen storage and transport in often hypoxic burrow environments. Hemoglobin located inside nucleated corpuscles circulating within vascular lumen, not dissolved plasma as in some annelids, giving blood red coloration and high oxygen affinity. Corpuscular packaging improves carrying capacity and buffers pH. Trait parallels vertebrate erythrocytes and some polychaete blood cells considered convergent acquisition in lophophorate lineage enhancing gas exchange. Quantity and binding properties vary between intertidal versus subtidal species reflecting ecological adaptation to oxygen availability and temperature fluctuations experienced daily in habitats with limited circulation.
Ref: Ruppert et al., Invertebrate Zoology, Chapter 16: Phoronida blood corpuscles hemoglobin
Excretory organs of hemichordates are
Excretory apparatus in Hemichordata centers on glomerulus or proboscis gland, a vascular knot of blood vessels projecting into protocoel anterior to stomochord, filtering hemolymph through podocytes to produce urine collected via protocoel pore. Additionally, gill slit region contributes to excretion via branchial epithelium diffusion. Among simplified textbook choices, gill slits region is historically linked to excretory function because filtrate drains near pharyngeal area and wastes diffuse across gill surfaces. Unlike segmented nephridia of annelids, intracellular flame cells of flatworms or Malpighian tubules of insects, hemichordate ultrafiltration via glomerulus illustrates primitive deuterostome arrangement.
Ref: Hickman et al., Integrated Principles of Zoology, 17th ed., Hemichordata Excretion; Brusca & Brusca, Invertebrates
Respiration in Balanoglossus occurs through
Balanoglossus is burrowing enteropneust hemichordate inhabiting intertidal mudflats forming U-shaped mucus-lined tubes. Anterior trunk pharynx bears paired dorsolateral gill pores, up to 100 pairs, each comprising gill slit opening to exterior via branchial sac, similar to chordate pharyngeal slits. Ciliary current drives water from mouth through pharynx, exiting via slits, trapping food particles in mucus and allowing diffusion of oxygen across vascularized branchial lamellae. No tracheae, lungs or specialized skin respiration occur. Slit number increases during growth, illustrating respiratory and feeding dual function and deuterostome heritage shared with cephalochordates.
Ref: NCERT Class 11 Biology, Chapter 4: Hemichordata – Balanoglossus; Campbell Biology, 12th ed., Chapter 34
Hemichordates show which type of coelom?
Hemichordate coelom development is enterocoelous, characteristic of deuterostomes, where coelomic cavities form as outpocketings of archenteron endoderm that pinch off and expand. This yields three successive compartments: protocoel in proboscis, mesocoel in collar and metacoel in trunk, each lined by peritoneal mesothelium. Enterocoely contrasts with schizocoely seen in protostomes where mesodermal bands split, with pseudocoely lacking complete lining and acoely lacking cavity. Presence of enterocoely places hemichordates alongside echinoderms and chordates within Deuterostomia, supporting embryonic cleavage pattern as major phylogenetic criterion in animal systematics.
Ref: Campbell Biology, 12th ed., Chapter 32: Animal Development – Enterocoelom; Barnes et al., Chapter 22