CH3: Animal Classification (LAB ACT)
Background: Animals have been traditionally classified into phyla. The animal kingdom is divided into at least 36 phyla. This number includes 27 minor and 9 major phyla. Each phylum is distinguished by its structural and functional characteristics that are distinct from other animal groups. Additional minor phyla in the animal kingdom are the following: phylum Loricifera, discovered in 1983; Cycliophora, discovered in 1995; and the Micrognathozoa, discovered in Greenland in 2000. Most of the animals have been discovered during the times of Aristotle and Linnaeus. Major animal groups can be classified as either acoelomate (i.e., without cavity) or coelomate
Phylum | Approximate number of species | Representatives |
Porifera | 8,000 | Barrel sponge, Venus’ flower basket |
Cnidaria | 11,000 | Hydra, Jellyfish, Hard and soft corals, Sea Anemones |
Platyhelminthes | 20,000 | Planaria, Tapeworm, Blood fluke, and Liver fluke |
Nematoda | 25,000 | Ascaris, filarial worms, pinworms, and hookworms |
Mollusca | 110, 000 | Clams, snails, oysters, squids, octopuses |
Annelida | 16,000 | Nereis worms, Eunice worms, tube worms. Earthworms, leeches, fan worms, and other polychaetes |
Arthropoda | 1,000,000 | Insects, crustaceans, spiders, horseshoes crabs, scorpions, millipedes, and centipedes |
Echinodermata | 7,000 | Sea urchins, sea stars, sea lilies, sand dollars, sea cucumbers, and brittle stars |
Chordata | 45,000 | Amphioxus, hagfishes, teleosts, amphibians, reptiles, birds, and mammals |
Phylum Porifera – The general characteristics of this phylum include the following: (1) Asymmetrical body and is pierced with thousands of pores, or ostia; (2) It consists of three main cell types: pinacocytes, mesenchyme cells, and choanocytes; (3) No tissues and organs; and (4) It has a central cavity that is filled with water during filter feeding
Phylum Cnidaria – The general characteristics of this phylum include the following: (1) Radially symmetrical body; (2) Diploblastic tissue level of organization; (3) Two main body layers separated by the mesoglea, a jelly-like layer; and (4) it has specialized cells called cnidocytes used in defense, feeding, and attachment.
Phylum Platyhelminthes – These animals have similar free-swimming larvae called a trochophore and feeding structures made of hollow tentacles called a lophophore; hence, these two groups fall under lophotrochozoan. The general characteristics of this phylum include the following: (1) They are triploblastic, acoelomate, and bilaterally symmetrical; (2) They may be free-living or parasites; (3) The body has a soft covering with or without cilia; and (4) Their body is dorsoventrally flattened without any segments and appears like a leaf
Phylum Nematoda – Nematodes, also called roundworms, are the most abundant and diverse of all the worms. The general characteristics of this phylum include the following: (1) Triploblastic, bilateral, vermiform (resembling a worm in shape; long and slender), unsegmented, pseudocoelomate; (2) Body round in cross section and covered by a layered collagenous cuticle; molting usually accompanies growth in juveniles; and (3) Complete digestive tract; mouth usually surrounded by lips bearing sense organs
Phylum Mollusca – Unlike flatworms, mollusks, and other bilateral animals have a complete digestive tract. They have two openings: the mouth and the anus, found on opposite ends. This group is composed of different-looking members (i.e., oyster, squid, and octopus). The following are the general characteristics of this phylum: (1) Ventral side of the body has a soft muscular foot; (2) On the dorsal side, there is a visceral hump containing the main digestive organs and protected by a shell; (3) Most mollusks have a rasping tongue-like radula for feeding; (4) They have a mantle cavity where gills or ctenidia for respiration or filter feeding is found; (5) majority have lost all traces of metameric segmentation; and (6) there is a trochophore larva (small, free-swimming, and ciliated larva) during development
Phylum Annelida – Members of this phylum show a lot of similarity with each other, unlike the mollusks, which are very different in forms. They are all segmented. Each segment contains parts of the digestive tract, nerve cord, and blood vessels that carry blood to all parts of the body. The following are the common features of this phylum: (1) Metamerism; (2) Segments are separated by sheet-like septa; (3) In most annelids, each segment bears bristle-like chaetae; (3) They possess nephridia for excretion and osmoregulation; (4) typically there is a trochophore larva during development.
Phylum Arthropoda – Arthropods are the most diverse and abundant of all the animals on earth. They can be found almost anywhere. Arthropods are covered by chitinous exoskeleton that protects and supports the tissues. Their joint-appendages became very important adaptation during their evolution. The appendages have several uses, like jumping, walking, alighting, chewing, and sensation. Their body also has segmentation like annelids, which allows mobility, but the segments are not separated by septa. Some groups have compound eyes for vision
Phylum Echinodermata – Echinoderms are on the same evolutionary branch as chordates; they are deuterostomic animals, meaning the origin of the anus is the blastopore. Adult echinoderms are usually slow-moving and with radial type of symmetry. They are known for their internal skeleton made up of interlocking calcium-based plates called ossicles. Their skin contains calcareous ossicles and spines.
Phylum Chordata – This phylum is composed of three groups. One group includes all the animals with backbones or vertebrates. The other two groups are tunicates and lancelets; they are sometimes called invertebrates since they do not have a vertebral column. They have notochord for support. The tunicates are also called urochordates and include both sessile and free-swimming animals such as sea squirts. Lancelets or cephalochordates are usually found along the sandy areas of the ocean where they filter food.
CH3: Animal Classification (LAB ACT)
Background: Animals have been traditionally classified into phyla. The animal kingdom is divided into at least 36 phyla. This number includes 27 minor and 9 major phyla. Each phylum is distinguished by its structural and functional characteristics that are distinct from other animal groups. Additional minor phyla in the animal kingdom are the following: phylum Loricifera, discovered in 1983; Cycliophora, discovered in 1995; and the Micrognathozoa, discovered in Greenland in 2000. Most of the animals have been discovered during the times of Aristotle and Linnaeus. Major animal groups can be classified as either acoelomate (i.e., without cavity) or coelomate
Phylum | Approximate number of species | Representatives |
Porifera | 8,000 | Barrel sponge, Venus’ flower basket |
Cnidaria | 11,000 | Hydra, Jellyfish, Hard and soft corals, Sea Anemones |
Platyhelminthes | 20,000 | Planaria, Tapeworm, Blood fluke, and Liver fluke |
Nematoda | 25,000 | Ascaris, filarial worms, pinworms, and hookworms |
Mollusca | 110, 000 | Clams, snails, oysters, squids, octopuses |
Annelida | 16,000 | Nereis worms, Eunice worms, tube worms. Earthworms, leeches, fan worms, and other polychaetes |
Arthropoda | 1,000,000 | Insects, crustaceans, spiders, horseshoes crabs, scorpions, millipedes, and centipedes |
Echinodermata | 7,000 | Sea urchins, sea stars, sea lilies, sand dollars, sea cucumbers, and brittle stars |
Chordata | 45,000 | Amphioxus, hagfishes, teleosts, amphibians, reptiles, birds, and mammals |
Phylum Porifera – The general characteristics of this phylum include the following: (1) Asymmetrical body and is pierced with thousands of pores, or ostia; (2) It consists of three main cell types: pinacocytes, mesenchyme cells, and choanocytes; (3) No tissues and organs; and (4) It has a central cavity that is filled with water during filter feeding
Phylum Cnidaria – The general characteristics of this phylum include the following: (1) Radially symmetrical body; (2) Diploblastic tissue level of organization; (3) Two main body layers separated by the mesoglea, a jelly-like layer; and (4) it has specialized cells called cnidocytes used in defense, feeding, and attachment.
Phylum Platyhelminthes – These animals have similar free-swimming larvae called a trochophore and feeding structures made of hollow tentacles called a lophophore; hence, these two groups fall under lophotrochozoan. The general characteristics of this phylum include the following: (1) They are triploblastic, acoelomate, and bilaterally symmetrical; (2) They may be free-living or parasites; (3) The body has a soft covering with or without cilia; and (4) Their body is dorsoventrally flattened without any segments and appears like a leaf
Phylum Nematoda – Nematodes, also called roundworms, are the most abundant and diverse of all the worms. The general characteristics of this phylum include the following: (1) Triploblastic, bilateral, vermiform (resembling a worm in shape; long and slender), unsegmented, pseudocoelomate; (2) Body round in cross section and covered by a layered collagenous cuticle; molting usually accompanies growth in juveniles; and (3) Complete digestive tract; mouth usually surrounded by lips bearing sense organs
Phylum Mollusca – Unlike flatworms, mollusks, and other bilateral animals have a complete digestive tract. They have two openings: the mouth and the anus, found on opposite ends. This group is composed of different-looking members (i.e., oyster, squid, and octopus). The following are the general characteristics of this phylum: (1) Ventral side of the body has a soft muscular foot; (2) On the dorsal side, there is a visceral hump containing the main digestive organs and protected by a shell; (3) Most mollusks have a rasping tongue-like radula for feeding; (4) They have a mantle cavity where gills or ctenidia for respiration or filter feeding is found; (5) majority have lost all traces of metameric segmentation; and (6) there is a trochophore larva (small, free-swimming, and ciliated larva) during development
Phylum Annelida – Members of this phylum show a lot of similarity with each other, unlike the mollusks, which are very different in forms. They are all segmented. Each segment contains parts of the digestive tract, nerve cord, and blood vessels that carry blood to all parts of the body. The following are the common features of this phylum: (1) Metamerism; (2) Segments are separated by sheet-like septa; (3) In most annelids, each segment bears bristle-like chaetae; (3) They possess nephridia for excretion and osmoregulation; (4) typically there is a trochophore larva during development.
Phylum Arthropoda – Arthropods are the most diverse and abundant of all the animals on earth. They can be found almost anywhere. Arthropods are covered by chitinous exoskeleton that protects and supports the tissues. Their joint-appendages became very important adaptation during their evolution. The appendages have several uses, like jumping, walking, alighting, chewing, and sensation. Their body also has segmentation like annelids, which allows mobility, but the segments are not separated by septa. Some groups have compound eyes for vision
Phylum Echinodermata – Echinoderms are on the same evolutionary branch as chordates; they are deuterostomic animals, meaning the origin of the anus is the blastopore. Adult echinoderms are usually slow-moving and with radial type of symmetry. They are known for their internal skeleton made up of interlocking calcium-based plates called ossicles. Their skin contains calcareous ossicles and spines.
Phylum Chordata – This phylum is composed of three groups. One group includes all the animals with backbones or vertebrates. The other two groups are tunicates and lancelets; they are sometimes called invertebrates since they do not have a vertebral column. They have notochord for support. The tunicates are also called urochordates and include both sessile and free-swimming animals such as sea squirts. Lancelets or cephalochordates are usually found along the sandy areas of the ocean where they filter food.
