Asymmetry is a type of body plan in which an organism lacks any axes of symmetry and cannot
be bisected along a plane of symmetry.
Radial symmetry is a form of body organization in which it is possible to cut through the middle
of an organism and obtain two equal halves. Examples include starfish and jellyfish.
Bilateral symmetry is a type of symmetry exhibited in an organism where an imaginary line is
drawn through it, and the two resulting parts are mirror images of each other. Some examples of
animals are humans and butterflies.
Sessile: This term defines immovable living things and those that cannot move from one place to
another. Many sponges and corals are sessile members.
Cephalization is the resting place of the peripheral nerves and the sense organs at the anterior or
head part of an organism. This is true since it is one of the features of bilaterally symmetric
animals.
Protostome: A taxon of animals whose mouth is derived from the blastopore of the embryonic
stage. Some of them include molluscs, annelids, and arthropods.
Deuterostome: A group of animals in which the anus is the primary embryonic opening, and the
mouth comes into existence later. Some examples are Echinoderms and chordates.
Sponges are small, Bottom-dwelling animals with leaky bodies lacking actual tissues and organs.
Porifierns are animals that belong to the species.
Collar cells: These cells, also called choanocytes, are found lining the inner chamber of a sponge.
They contain flagella that help filter water as it passes through the sponge.
Filter feeders: Filter feeders are predominantly animals that pump water through an intricate
filtering system, with the help of which they eat solids within the water and some species of
food. Sponges are an example.
Hermaphroditic: Organisms that contain parts for both reproduction by males and females.
Some sponges and other invertebrates reproduce sexually: they are hermaphrodites.
Spicules: The spicular structures in sponges that offer them support and or give them repelling
force against predators. It can be made of silica, calcium carbonate, or spongin fibrils. These
tests are of great use to archaeologists in preparing their samples for carbon dating and in dating
pottery as the zircon and lead clocks do in the dating of rocks.
Cnidarians are a large group of water animals related to jellyfish, corals, and sea anemones.
They have radial symmetry, a rather basic body plan, and a gastrovascular cavity.
Cnidocytes are the cells within cnidarians that, when mature, enclose the content of
nematocysts, which are used in self-defence or in capturing food.
Nematocyst: A cellular structure within the cnidocytes, a nematocyst is composed of a coiled
filiform style used for piercing toxins into prey or enemies.
Gastrovascular cavity: A digestive cavity with a single orifice which acts at the same time as a
mouth and anus present in Cnidarians and Flatworms.
Polyp: Refers to the asexual and colonial polyps of a cnidarian which are tubular although
immotile with the mouth and tentacles at one end of the colony and the basal disc at the other.
Some of them are – corals and sea anemones.
Medusa: The 'float', independent life-cycle stage of a cnidarian with only the bell and hanging
tentacles. Examples include jellyfish.
Flatworms are invertebrates with a bilaterally symmetric body plan, no particular structure like
circulatory or respiratory systems, and a flat body. They fall under the class grouping of the
phylum Platyhelminthes.
Tapeworms: Helminths, which are ecto-symbiotic in the digestive system of the vertebrates
only. It is a flatworm, the most extended, ribbon-like structure of multiple segments called
proglottids.
Scolex: That part of the tapeworm which is directed forward and provided with hooks and
suckers for anchorage to the interior lining of the host's intestine.
Proglottids are the individual parts that comprise the body of tapeworms, whose hosts or sections
have reproductive organs.
Flukes are a group of parasitic flatworms that cause infection in different hosts, including
humans. They are classified under the class Trematoda.
Rotifers are aquatic animals whose bodies have a ring of cilia at the anterior end, which is used
for feeding and locomotion. They are ranked in the phylum Rotifera.
Molluscs are one of the largest groupings of animal species that do not possess a backbone and
have a soft, slug-like body cavity. These animals include snails, clams, squids, and many others.
Visceral mass: The central mass of the inside of a mollusc's body with many significant organs.
Mantle: A considerable portion of the mollusc can produce the shell part and contains a chamber
for breathing and discharging.
Gastropods: a group of molluscs with only one shell that may be spiralled and a muscular
structure called a foot ending with one or two tentacles.
Cephalopods are a class of molluscs that includes animals like octopuses, squids, and cuttlefish.
Both females and males have bony heads, large orbits, and tentacles.
Bivalves: A group of water animals more commonly known as shellfishes, such as the clam,
oyster, mussel and the like. They have a two-part shell hinged and feed by drawing water
through their mouths.
Annelids are segmented worms that belong to the Phylum Annelida, which also includes
earthworms and leeches. Segmentation, jointed appendages, and coelom are significant
characteristics of Arthropods.
Roundworms, also known as nematodes, are unsegmented worms with round, cylindrical
bodies, complete digestive systems, and pseudocolour. They belong to the phylum Nematoda.
Arthropods are classmate animals with body-covered bodies and outer solid skin. The body is
divided into segments, and the li and limbs are joined. These may include insects, scorpions, and
other small animals such as crustaceans.
Crustaceans are a subphylum within the phylum Arthropoda that consists of crabs, lobsters,
shrimp, and related animals. They are characterized by a tough external skeleton and two
antennae.
Insects: Insects are a class of arthropods with three segments in their body: head, thorax, and
abdomen. They possess six legs and typically one or two wings. Some examples include beetles,
butterflies, and ants.
Metamorphosis is a development process that an insect passes through from the egg stage
through the larval stage, to the pupal stage, and finally to the adult stage, where the insect may
have totally transformed in morphology and physiology.
Arachnids are a group of invertebrate animals, including spiders, scorpions, ticks, and mites.
Most have eight legs and a two-regimented body; some have two half-moon-shaped parts, the
cephalothorax and abdomen.
