Q.87 The animals belonging to which one of the following phyla are characterized by
“segmented body” ?
(A) Annelida
(B) Cnidaria
(C) Echinodermata
(D) Porifera

Annelida is the correct answer (A).

Animals in phylum Annelida are distinctly characterized by a segmented body, divided into repeating units called metameres or somites, separated externally by ring-like grooves (annuli) and internally by septa. This true metameric segmentation enhances flexibility, locomotion, and specialization of organs across segments.​

Option Analysis

Annelida (A): Features a long, cylindrical body with clear external and internal segmentation into numerous segments (up to 600 in some species), each with repeated structures like setae for movement and coelomic compartments. Examples include earthworms and leeches, where segmentation supports burrowing and regeneration.​

Cnidaria (B): Lacks segmentation; exhibits radial symmetry with a simple body wall of two layers (epidermis and gastrodermis) separated by mesoglea, forming polyp or medusa shapes with a central gastrovascular cavity.​

Echinodermata (C): Shows pentaradial symmetry in adults, not linear segmentation; body organized into five ambulacra arms with spiny skin, tube feet, and a water vascular system, lacking repeated segments.​

Porifera (D): Has no segmentation or tissues; body is a porous, asymmetrical aggregation of cells (asconoid, syconoid, or leuconoid forms) with choanocytes lining canals for filter-feeding.​

Phylum Annelida stands out as the phylum with segmented body among animal groups, making it a key topic for CSIR NET Life Sciences aspirants studying invertebrate diversity. This segmentation, or metamerism, divides the body into functional repeats, aiding survival in diverse habitats from soil to oceans.​

Key Features of Segmented Body

• Metameric Division: External rings (annuli) and internal septa create 20–600 somites, each with ganglia, nephridia, and setae.​

• Coelom and Locomotion: Fluid-filled coelom acts as hydrostatic skeleton; circular and longitudinal muscles enable peristaltic movement.​

• Classes: Polychaeta (marine, parapodia), Oligochaeta (earthworms, few setae), Hirudinea (leeches, suckers).​

Why Not Other Phyla?

Cnidaria shows radial, non-segmented forms like jellyfish; Echinodermata has radial arms without linear segments; Porifera lacks organization beyond pores.​

This phylum with segmented body exemplifies evolutionary efficiency, relevant for exams on animal phylogeny and adaptation.​