Non-chordates are animals that do not possess a notochord, which is a flexible, rod-like structure found in chordates (animals with a backbone or a similar structure). This phylum consists of a small group of worm-like, marine species with an organ-system level of organization. They are the most abundant and diversified of all animals living or extinct.
Members of phylum Porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata and Hemichordata fall under Non-chordates.
The general characteristic features of Non-Chordates are:
Water Vascular System is a unique system of echinoderms which helps mainly in locomotion. It is in fact a modified part of coelom consisting of a system of canals containing sea water and amoeboid corpuscles.
Phylum Echinodermata (Gr., echinos = hedgehog ; derma = skin) is a group of marine invertebrates characterized by radial symmetry, a calcareous endoskeleton, and a water vascular system used for locomotion, feeding, and respiration. Members of this phylum include starfish, sea urchins, sand dollars, and sea cucumbers. They exhibit pentamerous symmetry in adults, have a unique regenerative ability, and possess tube feet for movement and adhesion. Echinoderms are exclusively marine and play essential roles in ocean ecosystems as predators, grazers, and sediment stabilizers.
The “pearl” is literally formed by the mantle epithelium which becomes deposited around any external body or particles; these external particles or body invade in between the shell and mantle in any way.
Pila globosa is a common freshwater apple snail found in ponds, pools, tanks, lakes, marshes, paddy fields and sometimes even in streams and rivers of Northern India except Punjab. Pila is adapted to lead an amphibious life, it is provided with a pulmonary sac for aerial respiration and a gill or ctenidium for aquatic respiration.
Phylum Mollusca (L., mollis = soft) is a major group in the animal kingdom that includes soft-bodied invertebrates, often characterized by a calcareous shell, though not all members possess one. Molluscs exhibit a wide variety of body forms and habitats, ranging from marine to freshwater and terrestrial environments. Key features of this phylum include a muscular foot used for locomotion, a mantle that secretes the shell (if present), and a visceral mass housing the internal organs. The phylum includes diverse classes such as Gastropoda (snails and slugs), Bivalvia (clams and mussels), Cephalopoda (octopuses and squids), and others. Molluscs play important ecological and economic roles, from maintaining marine ecosystems to serving as food for humans.
Peripatus is a connecting link between Annelida and Arthropoda. Peripatus and related animals belong to the Phylum Onychophora, which was conventionally classified with arthropoda as one of its classes. But the modern classification has given to it the status of an independent phylum.
Palaemon (The Freshwater Prawn) is studied in the Indian Universities as a typical representative of the class Crustacea.
Phylum Arthropoda (Gr., arthros = jointed ; podos = foot) is the largest and most diverse group of animals in the animal kingdom, characterized by their segmented bodies, jointed appendages, and exoskeleton made of chitin. This phylum includes insects (e.g., butterflies, beetles), arachnids (e.g., spiders, scorpions), crustaceans (e.g., crabs, lobsters), and myriapods (e.g., centipedes, millipedes). Arthropods play essential ecological roles, such as pollinators, decomposers, and as part of the food web.
Phylum Annelida (L., annelus = little ring or F., anneler = to arrange in rings) is a group of bilaterally symmetrical, coelomate, and segmented animals known commonly as segmented worms. Members of this phylum exhibit a body divided into repeated segments called metameres, which give them structural and functional division. Annelids are triploblastic and possess a true coelom, which is divided by septa, and a closed circulatory system. They have a complete digestive system, a well-developed nervous system with a ventral nerve cord, and excretory structures called nephridia. Respiration occurs through the body surface, gills, or parapodia.
Phylum Aschelminthes (Gr., askes = cavity ; helmins = worm) is a group of bilaterally symmetrical, unsegmented, and pseudocoelomate animals. They are typically characterized by a cylindrical or thread-like body covered with a tough, flexible cuticle. The phylum includes organisms that are predominantly aquatic or parasitic in nature, such as nematodes (roundworms).