List three common characteristics of animals that are not found in other multicellular eukaryotes
- They are multicellular heterotrophs that ingest their food
- Animals are mobile and lack a cell wall
- Many animals have the diploid life cycle, and usually reproduce sexually. Many reproduce sexually and some asexually and some combine both life cycles.
- Muscle and nerve tissues characterize animals
- Animals are monophyletic-meaning both invertebrates (no backbone) and vertebrates (spinal cord, backbone) can trace their ancestry to the same ancestor.
Summarize the colonial flagellate hypothesis as its relates to the origin of animals
- It states that animals are descended from an ancestor that resembled a hollow, spherical colony of flagellated cells.
- The choanoflagellate (collared flagellates) most likely resemble the last unicellular of living animals, and molecular data illustrates that they are the closest living relatives of animals.
- A choanoflagellate is a single cell with a flagellum.
- The transition from colonial flagellates to multicellular animals may have begun by aggregation of a few flagellated cells.
- Individuals cells within the colony may have specialized.
- Two tissue layers may have arisen by infolding of certain cells into a hollow sphere.
- This hypothesis is attractive because of its implications regarding animal symmetry.
Distinguish among the different body plans of animals
There are three types of symmetry (a pattern of similarity that is observed in objects) in the animal kingdom.
- Asymmetry: no particular body shape (e.g., sponge)
- Radial symmetry: two identical halves. describes body parts arranged around an axis, like spokes of a wheel (e.g., starfish). RS animals may be sessile (attached to a substrate or less motile) This symmetry allows the animal to reach out in all directions from one center.
- Bilateral symmetry: definite right and left halves, or complementary halves. Only one longitudinal cut down the center produces mirror halves. Animals tend to be active and to move forward at an anterior end. The localization of the brain and sensory organs at the anterior end is called cephalization.
- The first tissue layers that appear are called germ layers. These give rise to organs and organ systems. Diploblastic – Two tissue layers (ectoderm, endoderm), Triploblastic – Three tissue layers (ectoderm, mesoderm, endoderm)
- Animals have 3 tissue layers that could be protostome or deuterostome
- Cleavage: cell division without cell growth first development event after fertilization.
- Blastula: hollow sphere of cells with an indentation that forms an opening called a blastopore.
- A coelom is a body cavity lines by mesoderm; if the mesoderm lines the cavity completely, it is a true coelom.
Differentiate between protostome and deuterostome development
- Protostomes – First embryonic opening becomes the mouth, The blastopore is associated with the mouth, Spiral cleavage, which cells divide without an increase in size, The fate of cells is fixed-each contributes to development in only one particular way. Coelom forms by a splitting of the mesoderm, which has arisen from cells near the blastopore.
- Deuterostomes – Second embryonic opening becomes the mouth, The blastopore is associated with the anus, Radial cleavage where the new daughter cells sit atop the previous cells, the fate of these cells is indeterminate, Coelom forms by the fusion of mesodermal pouches from the primitive gut
Explain why sponges are considered to be the simplest animals
Sponges have no symmetry, lack true tissues, and have only the cellular level of organization
Discuss how a sponge respires, feeds, and reproduces
- Saclike bodies are perforated by many pores. They have a canal system that allows water to move through their bodies.Beating collar cells (choanocytes) produce currents through pores in the wall into a central cavity and out through the osculum.
- It is a sessile filter feeder. They stay in one place and filter food from the water. Collar cells engulf and digest food particles in food vacuoles.
- Reproduction. Asexually by budding, which can produce large colonies. Fragmentation occurs when sponges are chopped up; each piece can start a complete sponge. They reproduce sexually when eggs and sperm are released into a central cavity; the zygote. develops into a flagellated larvae.
Compare the anatomical features of comb jellies to those of cnidarians, such as hydras
Both have tentacles. Come jellies have long tentacles covered with sticky filaments. Hydras have 4 to 6 tentacles contacting nematocysts that surround the mouth. Both contain jellylike material called mesoglea
List the basic features of lophotrochozoans.
- They are bilaterally symmetrical in at least one stage of development.
- As embryos, they have three germ layers.
- As adults, they have the organ level of organization. . 4. They have a protostome type of development.
- Some have true coelom.
- The two groups of lophotrochozoans are lophophorans (bryozoans, brachiopods, phoronids) and trochozoans (flatworms, rotifers, molluscs, annelids).
Describe the basic anatomy and physiology of a planarian
Planarians live in freshwater habitats. They have a head that is bluntly arrow shaped. The head has auricles that function as sense organs, and it has two light-sensitive eye spots. They have three kinds of muscle layers including an outer circular layer, an inner longitudinal layer, and a diagonal layer. Planarians have excretory organs that function in osmotic regulation and water secretion. They can reproduce sexually and asexually. They are hermaphroditic and practice cross-fertilization. They also reproduce asexually by regeneration. They have undergone cephalization. Their heads have lateral extensions with chemosensory and tactile cells. They have a ladder-type nervous system, and paired ganglia function as a primitive brain.
Summarize the steps in the life cycles of Schistosoma and Taenia.
The Schistosoma life cycle starts with the larvae penetrating the skin of a human, the primary host, and mature in the liver. Adult worms live and copulate in blood vessels of the human gut. Eggs migrate into the digestive tract and are passed in feces. Ciliated larvae hatch in water and enter a snail, the secondary host. In the snail, a mother sporocyst encloses many developing daughter sporocysts. Daughter sporocysts enclose many developing larvae. This larvae break out of daughter sporocysts, escape the snail, and enter water.
The Taenia life cycle starts with the primary host ingesting meat containing bladder worms. The bladder worm attaches to human intestines where it matures into a tapeworm. As the tapeworm grows, proglottids mature, and eventually fill with the eggs. Eggs leave the primary host in feces, which may contaminate water or vegetation. Livestock may ingest the eggs, becoming a secondary host as each larvae becomes a bladder worm encysted in muscle. Rare or uncooked meat from secondary hosts contains many bladder worms.
Identify morphological features of molluscs
Molluscs have a three part body plan. This includes the visceral mass, the mantle, and the foot. The visceral mass contains internal organs, the mantle may secrete shell and/or contribute to the development of lungs or gills, and the foot is a muscle adapted for locomotion, attachment, or food capture. Molluscs have a nervous system that consists of several ganglia connected by nerve cords. Their true coelom is reduced and is largely limited to the region around the heart. Their hearts pump hemolymph through vessels into hemocoel.
Identify morphological features of bivalves
Bivalves have shells that have two hinged parts closed by powerful muscles. They don’t have a head or radula. They have little cephalization and an open circulatory system. Their ciliated gills hang down within the mantle cavity. Beating of the cilia causes water to enter the mantle cavity. Bivalves are filter feeders, meaning that they capture tiny food particles suspended in water. In freshwater clams, the sexes are separate, fertilization is internal, and specialized larvae are released from the clam.
Identify morphological features of rotifers
Rotifers are trochozoans that are abundant in freshwater. Marine and terrestrial forms exist. have a crown cilia known as a corona that resembles a rotating wheel This causes a rotating motion. It serves as both an organ of locomotion and aids direction of food to mouth. They can desiccate during harsh conditions and remain dormant for lengthy periods of time.
Identify morphological features of annelids
Annelids have segmented partitions, or septa, that divide the coelom which acts as a hydrostatic skeleton. Annelids have a specialized digestive tract, a closed circulatory system, and a ventral solid nerve cord. Most of them are marine. They have setae (bristles) that help in movement. Most annelids are marine polychaetes. Their setae are in bundles on parapodia. Clam worms are predators. They have sex organs only during the breeding season.
Identify the characteristics unique to ecdysozoans.
The ecdysozoans are a group of protostomes and include roundworms and arthropods, which periodically shed their outer covering. Ecdysis, where the name ecdysozoan comes from, means “stripping off”. They construct an outer covering called a cuticle. It protects and supports the animals, and it is shed by molting. The ecdysozoans have evolved separate sexes.
Compare the anatomical features of roundworms and arthropods.
Roundworms are nonsegmented, generally colorless worms. They contain a pseudocoelom, a false body that cavity that is incompletely lined by mesoderm. It provides a space for internal organs and can serve as a hydrostatic skeleton.
Arthropods have rigid, jointed exoskeleton composed of chitin. They must molt as they grow. They are segmented, but some segments are fused into regions. They have a head, thorax, and abdomen. They have a well-developed nervous system including a brain and ventral nerve cord and simple or compound eyes. They have a variety of respiratory organs including gills, book lungs, and tracheae.
Roundworms and arthropods have some type of skeleton, and both of them are either unsegmented or have segments that are fused together. They are ecdysozoans that periodically shed their outer covering
Describe the five characteristics responsible for the success of the arthropods
- Arthropods have a rigid exoskeleton with freely movable jointed appendages. The exoskeleton is a strong but flexible outer covering composed mainly of chitin, a strong nitrogenous polysaccharide. The exoskeleton serves for protection, attachment for muscles, locomotion, and prevention of desiccation.
- Segmentation can be observed because each segment has a pair of jointed appendages, although some segments of arthropods have fused into regions (head, thorax, abdomen). Jointed appendages are hollow tubes moved by muscle. The appendages are modified for food gathering, reproduction, and locomotion. Some appendages associated with sensory structures are used for tactile purposes.
- Arthropods have a well-developed nervous system. Their brain is connected to a ventral solid nerve cord. The head has various sensory organs. They have compound eyes that have many complete visual units, and each collects light independently. The lens of each individual unit focuses the image on the light-sensitive membrane of a few photoreceptors. In simple eyes, a single lens brings the image to focus into many receptors, each receiving a portion of the image. Many arthropods have well-developed touch, smell, taste, balance, and hearing. They display complex behaviors and methods of communication.
- Arthropods use a variety of respiratory organs. Marine forms use gills with vascularized, thin-walled tissue specialized for gas exchange. Terrestrial forms have book lungs (spiders) or air tubes called tracheae (insects) for transporting oxygen directly to cells.
- Metamorphosis is a drastic change in form and physiology that occurs as a larvae becomes an adult. It contributes to the success of arthropods. A larvae eats food and lives in environments different from the adult. This causes competition between the immature and adults of a species to be reduced. This reduction in competition allows more members of the species to exist at one time.
List the two major groups of animals in the Deuterostomia.
Deuterostomes include invertebrate echinoderms and chordates
Identify the major morphological structures of the sea star, an echinoderm.
Sea stars have structures outside of their body wall. Spines from exoskeletal plates offer protection. Pincer-like structures around the bases of spines keep the surface free of small particles. Skin gills are used for respiration. On the oral surface, each arm has a groove lined by tube feet.
Describe how sea stars move, feed, and reproduce.
Sea stars use their tube feet are used to open clams, bivalves, and oysters. Once open, the sea star inverts its cardiac stomach and pushes through the crack, secreting enzymes. Digestion begins externally. It continues in the pyloric stomach using enzymes from the digestive gland found in each arm. Locomotion depends on a water vascular system. Water enters through the sieve plate and passes through a series of canals. Contraction of an ampulla forces water into the tube foot. Expansion and contraction of tube feet allow movement. Echinoderms have no respiratory, excretory, or circulatory system. Sea stars reproduce sexually and asexually. They reproduce asexually by fragmentation. Each fragment can regenerate a whole animal as long as a portion of the central disk is present. Spawning is the sexual reproduction method in echinoderms.
Identify the four basic characteristics of a chordate
- Notochord –Dorsal-supporting rod located below nerve cord-It provides support and is replaced by the vertebral column in vertebrates.
- Dorsal Tubular Nerve Cord–In vertebrates, the spinal cord-Protected by vertebrae–contains a fluid-filled canal-Anterior portion becomes brain in most chordates
- Pharyngeal Pouches–These openings function in feeding, gas exchange, or both-Aquatic vertebrates become gills–Seen only as embryos in most vertebrates–Terrestrial vertebrates modified for various purposes-In humans, the first pair of pouches becomes the auditory tubes.
- Postanal Tail–Extends beyond the anus–In humans, tail disappears in the embryo stage.
Name the two groups of nonvertebrate chordates
Lancelets (Cephalochordates) Sea Squirts (Urochordates)
Describe two features of each of the two groups of non vertebrate chordates
Lancelets (Cephalochordates)
–Shallow marine environments, filter feed partly buried in sandy substrates, they feed on microscopic particles filtered from a constant stream of water that enters the mouths and exits through gill slits into an atrium that opes at the atriopore, segmented muscles, dorsal hollow nerve cord has periodic branches, the notochord extends from head to tail
Sea Squirts (Urochordates)–tunicates--Adults contain a thick outer covering (tunic); an excurrent siphon squirts out water when it is disturbed.–Marine organisms, filter feeders, bilateral symmetry (larvae)– Larvae undergo metamorphosis to develop into sessile adults Water passes into a pharynx and out numerous gill slits, the only characteristics that remain in adults. Many biologists hypothesize that these organisms are directly related to the vertebrates. Larva may have become sexually mature without developing other adult characteristics, and then evolved into a fishlike vertebrate
Describe four characteristics that are unique to vertebrates
- Vertebral column: Replaces the embryonic notochord, It is part of a flexible, strong endoskeleton that is also evidence of segmentation. remnants of the notochord are seen in the invertebrate disks.
- Skull: An anterior component of the main axis of vertebrate endoskeleton; Encloses and protects brain, it encases the brain. High degree of cephalization, Complex sense organs, The ears-equilibrium devices in water-function as sound-wave receivers in land vertebrates.
- Endoskeleton: Living tissue that grows with the animal, Protection for internal organs. Attachment for muscle: permit rapid and efficient movement. Paired appendages characteristic: evolved from pectoral and pelvic fins of fish.
- Internal organs Large coelom and complete digestive tract, Closed circulatory system with blood contained within blood vessels, Respiratory system consisting of gills or lungs: provide proficient gas exchange, Kidneys–Serve as excretory and water: excrete nitrogenous waste and regulate water, regulating organs that regulate water balance in the body, sexes are separate and reproduction is sexual.
