Intro to Animal Diversity

• A synapomorphy is a shared derived characteristic which evolved in a common ancestor
• Morphologically, choanoflagellate cells are almost indistinguishable from the collar cells of porifera
• DNA sequence data indicate that choanoflagellates and animals are sister groups
• Animal synapomorphies include the CCD cadherin domain, epithelia, and collagen
• Cadherins are proteins that play key roles in how animal cells attach to one another
• A germ layer is a primary layer of cells that forms at an early stage in the embryo
• The ectoderm is the germ layer carrying the embryo's surface
• The endoderm is the innermost germ layer and lines the developing digestive tube
• Diploblastic animals only have the ectoderm and endoderm
• Triploblastic animals have the ectoderm, endoderm, and mesoderm
• The zygote of an animal undergoes a series of mitotic cell divisions called cleavage
• An eight-celled embryo is formed by 3 rounds of cell division
• Eumetazoa synapomorphies include nerves and at least 2 germ layers
• Bilateria synapomorphies include 3 germ layers, muscles, and bilateral symmetry
• Deuterostomia synapomorphies include radial cleavage, formation of the coelom from the archenteron, and formation of the anus from the blastopore
• Lophotrochozoa synapomorphies include the lophophore feeding structures and trochophore larva structures
• The synapomorphy of ecdysozoa is ecdysis (moulting)
• Cleavage produces a multicellular stage called a blastula, a hollow ball of cells that surround a cavity called the blastocoel
• Most animals undergo gastrulation, a process in which one end of the embryo folds inward, expands and eventually fills the blastocoel producing layers of embryonic tissues
• The endoderm of the archenteron develops into the tissue lining the animal's digestive tract
• The body parts of a radially symmetrical animal are arranged around a single main axis that passes through the center of the animal
• The body parts of a bilaterally symmetrical animal are arranged around two axes of orientation
• In indeterminate cleavage, each cell produced by early cleavage divisions retains the capacity to develop into a complex embryo
• In determinate cleavage, daughter cells are no longer able to produce a complete embryo by themselves
• Porifera lack true tissues and organs. They are sedentary filter feeders that live in fresh and marine waters. Choanocytes generate a water current through the sponge and ingest suspended food. Water is drawn into the spongocoel through pores and out through the osculum. Amoebocytes in the non cellular mesohyl layer play roles in digestion and structure. Most are hermaphrodites
• Cnidaria include a wide range of both sessile and motile forms including jellies, corals, and hydras. They are relatively simple and diploblastic, with a radial body plan. It is a sac with a gastrovascular cavity and a single opening which functions as mouth and anus. They are carnivores that use tentacles armed with cnidocytes to capture prey. They can be polyps or medusas
• Platyhelminthes are flatworms which live in marine, freshwater, and damp terrestrial habitats. They may be free living or parasitic . They are lophotrochozoa and triploblastic acoelomates. They are flattened dorsoventrally and have a gastrovascular cavity. Gas exchange takes place across the surface and protonephridia regulate the osmotic balance.
• Mollusca are lophotrochozoa and includes snails and slugs, oysters and clams, and octopuses and squids. Most are marine though some are fresh water and some are terrestrial. They are soft-bodied animals but most are protected by a hard shell. They have a similar body plan with three main parts: muscular foot, visceral mass, and mantle. They are triploblastic and bilaterally symmetrical. Synapomorphies include the radula, and a ring of ganglia around the oesophagus
• Mollusca include Gastropoda, Bivalvia, and Cephalopoda. Gastropods such as snails have torsion; their anus and mantle is above their head. Bivalvia include clams, oysters, mussels, and scallops, and a have shell divided into two halves. Cephalopoda include squids and octopuses; carnivores with beak-like jaws surrounded by tentacles of their modified foot.
• Annelida are Lophotrochozoa and are triploblastic, coelomate, bilaterally symmetrical protostomes. Their bodies are a series of fused rings. They include earthworms, polychaetes, and leeches.
• Coelomate animals possess coelom between the body wall and digestive tract
• In protostomes, the mouth develops from the primary opening whereas in deuterostomes, the anus develops from the primary opening
• Nematoda are Ecdysozoa and also called roundworms. They are enormously abundant and diverse in the soil and in aquatic habitats. They have a tough cuticle that coats their body which moults as they grow.
• Arthropoda are Ecdysozoa and make up 75% of all known animals. Their body plan consists of a segmented body, hard exoskeleton, and jointed appendages. Their body is completely covered by an exoskeleton which moults as they grow. They have an open circulatory system in which hemolymph is circulated into the spaces surrounding the tissues and organs.
• Hexapoda are a subphyla of arthropoda and are mostly insects which live in almost every terrestrial habitat and in fresh water. Their internal anatomy includes several complex organ systems. Flight is key to their success
• Crustacea is a subphylum of athropoda which includes crabs, lobsters, shrimps, barnacles, and others. Many have specialized appendages and 2 pairs of antennae. Unlike insects, they have appendages on their tail
• Myriapoda is a subphylum of Arthropoda and are all terrestrial. Each segment of a millipede is formed from 2 fused segments and has 2 pairs of legs. They eat decaying leaves and other plant matter. Each segment of a centipede has one pair of legs. They have poison claws on their foremost segment that paralyze prey and aid in defence. They are carnivorous.
• Chelicerata is a subphylum of Arthropoda that includes sea spiders, horse-shoe crabs, scorpions, ticks, mites, and spiders, and also extinct groups such as eurypterids. They are named for claw-like feeding appendages called chelicerae. They lack antennae and most have simple eyes (1 lens)
• Echinodermata are Deuterostomia and include sea stars and other slow-moving marine animals. A thin epidermis covers an endoskeleton of hard calcareous plates. They have a unique water vascular system; a network of hydraulic canals branching into tube feet that function in locomotion, feeding, and gas exchange. Males and females are usually separate
• Chordata are Deuterostomia and all share a set of derived characters; a notochord, a hollow nerve chord, pharyngeal slits or clefts, post anal tail.