Survey of the Phyla- Animalia, Invertebrates The Kingdom Animalia is in the domain Eukarya and in the supergroup Unikonta. They are in the group Opisthkonta with fungi. Both groups have different unicellular organisms that they are their common ancestor. That fact indicates the groups became multicellular organisms independent of one another. Characteristics of the Animal Kingdom 1. Animals are multicellular, heterotrophic, ingestive and eukaryotic. 2. The cells lack cell walls and are held together by structural proteins which are mostly collagen. They have intracellular junctions such as tight junctions, desmosomes and gap junctions. 3. Animal cells have nervous and muscle tissues found only in this kingdom. 4. Most animals have a diploid life cycle with a sperm fertilizing an egg. The zygote undergoes cleavage forming a blastula (hollow ball of cells). The blastula undergoes mass movement of cells to form a gastrula giving rise to three layers of tissue, endoderm, mesoderm and ectoderm. Often there is a larval stage to the animal which is sexually immature. It often will undergo metamorphosis to become an adult.
5. All animals contain both homeotic genes (any of the genes that control the overall body plan of animal by controlling the developmental fate of a group of cells) and homeobox (a 180- nucleotide sequence with a homeotic gene) encoding the part of the protein that binds to the DNA of the genes regulated by the protein. There is an increase in the number of these genes with an increase in the complexity of the animal. The protists most closely related to animals are the choanoflagellates. It is flagellated with a collar to collect food. It will form colonies. Diagramed are the steps thought to have given to evolution of multicellular animals. Other interesting points about animals Embryonic development -Deuterostomes versus protostomes. During development many animals first form a hollow ball of cells or blastula. Afterward that there is a mass movement of the cells called gastrulation. This process results in three layers of tissue being established. Ectoderm-becomes skin and nervous tissue Mesoderm-notochord, lining of coelom, kidneys, muscles and bone and circulatory system Endoderm-interior lining of organs and liver, pancreas, lungs and lining of digestive tract. During this process of gastrulation, the first opening to the gut or archenteron forms. In deuterostomes, this opening becomes the anus but in protostomes it becomes the mouth.
Body plans- Asymmetrical-These animals lack orientation like the sponges. Radial symmetry-The body plan is around an axis and any plane going through the axis will produce opposite halves.
-Bilaterial symmetry The body forms a body in a longitudinal plan that divides the body into two equal but opposite halves. It allows the senses to be concentrated up in one area. Can increase awareness, mobility and predation. -Bilaterial symmetry The body forms a body in a longitudinal plant that divides the body into two equal but opposite halves. Body cavities (coeloms) -Acoelomate-These animals do not have a body cavity like a flat worm or jelly fish -True coelom-The body cavity is lined with tissue derived from the mesoderm. -Pseudocoelom-The body cavity is lined with mesoderm on the outer part and with endoderm on the inside. Round worms have pseudocoeloms.
Clade Parazoa or sponges-Most closely related to colonial choano-flagellates. These protists and animals have a common ancestor. Phylum Porifera 1. Sessile with no specialized tissue i.e. nerves or muscle. 2. Size 1 cm-2 m. Mostly marine species with few freshwater. The body of a sponge has a cavity called a spongocoel. The body is perforated with pores.
Water flows into the pores and into the spongocoel and then out a larger opening called the osculum. There are two layers of cells with a gelatinous layer in between called the mesophyl. The outside of the body is lined with epidermal cells. 3. The pores are lined with cells (porocytes). The inside layer is lined with cells (choanocytes like choanoflagellates ). The flagella of choanocytes beat creating a water current. The choanocyte cell has a collar with a flagella. It also secretes mucus to filter and catch food. There are also amoebocytes which take food from the choanocytes and deliver it to the epidermal cells. 4. Sponges are hermaphrodites. Gametes come from amoebocytes and choanocytes. Eggs reside in the mesohyl and sperm from neighboring sponges fertilize them.
Clade Eumetozoa-Animals with true tissues. Two clades are found in Clade Eumetazoa-Clade Radiata and Clade Bilateria Clade Radiata-Animals with radial symmetry (top and bottom with no head or rear end). Radiata has two tissue layers ectoderm and endoderm and no mesoderm resulting in dipolblastic embryos (no mesoderm). Phylum Cnidaria-Jellyfish and hydra-The basic body plan is a sac with a gastrovascular cavity (GVC). The single opening functions as both the mouth and the anus. Two variations of this body plan-the polyp and medusa. The polyp is a cylinder form that is sessile and adheres to the bottom of the water. The medusa is a "flattened-version of the polyp upside- down". It moves in the water by drifting and contracting its bell shaped body.
Some species exists as polyps and others as medusas and others will have both forms in their life cycles. Both forms have two layers of tissue with a gelatinous layer of material in between called the mesoglea. Surrounding the mouth of these animals are a ring of tentacles.
These tentacles have stinging cells called cnidocyte cells. These cells have poisonous, little dart like structures called nematocysts. No muscles but cell will bundles of contractile fibers.
There is also nerve net that can detect stimuli causing the organism to react. The gastrovascular cavity has specialized cells that release digestive enzymes to aid in digestion. Class Hydrozoa-(Portuguese man-of-war, hydras, some corals). Mostly marine. Both medusa and polyp forms present. Polyp form usually colonial. Class Scypphozoa-(jellies, sea nettles). All marine. Polyp form greatly reduced. Medusa form up to 2 m in diameter. Class Cubozoa-(box jellies,and sea wasp) All marine. Polyp form greatly reduced. Medusa forms a box like shape with complex eyes and potent venom. Class Anthozoa-(sea anemones, most corals, and sea fans). Medusa stage completely absent sessile, many colonial.
Phylum Ctenophora-Superficially looks like cnidarian medusas. These are the comb-jellies. Small and sperical or ovoid. 8 rows of comblike plates fused cilia. Clade Bilateria- These animals have bilateral symmetry. Gives animals dorsal and ventral side as well as an anterior (head) and posterior (tail) end. Cephalization is the movement of sensory organs to the anterior end. The anterior end is first to encounter danger, food and other important stimuli. This clade divides up three smaller clades, Deuterostomia, Lophotrochozoa, Ecdysozoa The first clade are the deuterostomes. The deuterostomes are characterizied by their embryonic development and formation of a deuterostome.
The second clade are the lophotrochozoans either has a lophophore (a crown of ciliated tentacles function in feeding) or the development of a trochophore larva. The third clade is Ecydysozoa. These are animals that form an exoskeleton or thick cuticle. As the animals grow they molt or shed their outer covering (ecdysis).
Clade Lophotrochozoa Phylum Platyhelminthes: Flatworms a. Have gastrovascular cavity with pharynx as mouth on ventral side b. Acoelomates c. Nervous system is a pair of ventral nerve cords. Can have eye spots on anterior end that responds to light. In the anterior region one can find a ganglion. d. Nitrogenous wastes removed by a “flame cell” system Four Classes found in this phylum
Class Tubellaria-Mosly free-living, most marine, few terrestrial, predators, scavengers; body surface ciliated. Class Mongenea- Marine and freshwater parasites on external surfaces of fish. Class Trematoda- Flukes are parasites of vertebrates. Complicated life history witn intermediate host. Class Cestodea-Tapeworms with scolex. No head or digestive system. Complicated life history.
Phylum Rotifera-Rotifers have pseudocoelomates, jaws, crowns of cilia and a complete digestive tract. Complete digestive tract allows for individual organs and processing of food differently for maximum extraction of nutrients. While many rotifers are smaller than single-celled protista, they are much more complicated than even flat worms. Some reproduction in some species is parthenogenesis. Phylum Ectoprocta- called moss animals because they resemble moss. Most species are marine and are small and form colonies. Most of the colony is enclosed in a hard skeleton with the lophophores that extend through the pores when feeding.
Both phyla have lophophores
Phylum Brachiopods-Look like clams but stand up vertically. Called lampshells. Attach to bottom by a stalk. The shells are opened slightly to allow water to flow through lophophores. Phylum Nemertea-Ribbon worms seem to be acoelmate but contain a fluid filled proboscis sac which is derived from a true coelom. A proboscis is a long retractable hollow tube at the anterior end. Used to probe enviroment, capture Phylum Mollusca-Soft-bodied animals with shells. This phylum includes snails, slugs oysters, clams octopuses and squid. Most are marine with some fresh-water and terrestrial species. They have three main parts: -Muscular foot for locomotion -Visceral mass that contains most of the internal organs. -A mantle, which is a heavy fold of tissue that surrounds the visceral
mass and secretes the shell. Many will contain a radula or rasping tongue to scrap food from surfaces. Some species are monoecious while others are dioecious. Gonads are located in the viceral mass. It is possible that mollusks evolved before annelids because they lack segmentation or from an annelid like ancestor as they both have trochophore larva. Most have open circulatory systems with a heart. Structures for gas exchange. Ventral nerve chords with sensory organs. Class Polyplacophora-This class includes chitons. They have an oval shape with eight dorsal plate. The cling to rocks with foot a suction cup. They have a radula to gather food. Class Gastropoda-Snails and slugs. Largest class, mostly marine. Torsion occurs during development-Uneven growth in viceral mass causes the mass to rotate 180 degrees putting the anus above the head. Body protected by a conical shell. (absent in slugs and nudibrances). Aquatic species have gills but terrestrial species use the mantel for gas exchange.
Class Bivalvia-contains clams, oysters mussels and scallops. These have a shell divided into two parts. Held together by two adductor muscles. When open, the foot may be extended for motility or anchorage. Siphons are used to move water over the gills. Most are filter feeders. Head is absent and so is radula. Class Cephalopods-Squids, octopuses, and nautiluses. Agile carnivores. Use a beak to crush prey. Mantel covers visceral mass. The shell is either reduced, internal/or absent. Squid swim backwards by drawing water into the mantle and firing the water in a stream through the excurrent siphon. Directions can be changed by pointing the siphon in different directions. A giant squid may reach 17 m longs and weigh 2 tons. Phylum Annelida -Presence of a true coelom and segmentation are two big advances in this phylum. True coelom allows for -development of complex organ systems -protect internal structures -permits internal organs to function separately from the body wall muscles -serve as a hydroskeleton The body of annelids are divided up into many sections separated by a septa. With the exception of certain parts most of the sections are identical to one another. Digestion- -complete digestive tract phaynyx->esophagus->crop->gizzard->intestine
Closed circulatory system with hemoglobin is present -Main dorsal and ventral vessels connected by longitudinal vessels -Five pair of hearts many vessels in the skin permit gas exchange. Marine annelids have gills for each body section. -Excretory system-For each section there is a pair of metanephrida to remove waste from the coelomic fluid. They have an external opening to the outside. -Reproduction-Hermaphrodites with cross fertilization. Two earthworms will exchange sperm and store it temporarily. The clitellum secretes a smooth mucous cocoon which slides long the worm picking up its eggs and stored sperm for fertilization. The cocoon slips of the worm and the embryos develop inside the cocoon. -Movement involves coordinating longitudinal and circular muscles in each segment with the fluid filled coelom functioning as a hydrostatic skeleton. Similar to peristalic waves. Class Oligochaeta-Earthworms and some aquatic species. Important for breaking down and fertilizing soil. Importantin farming. Class Polychaeta-Mostly marine species. Some are plankton, some crawl on ocean floor, others live in tubes. Each segment has a parapodia which are highly vascularize for gas exchange and motion. Class Hirudinea-Majority are frewater with some terrestrial
Many are carnivorous and others are external parasites feeding on blood. - Blade like jaw splits the skin or drills a hole into the skin. The third clade in the bilaterial clade is Clade Ecydysozoa, which secretes and molts of an outer covering (ecdysis). Contains 8 phyla. Two most successful is Phylum Nematoda and Phylum Arthropoda. Based on molecular DNA sequencing. Phylum Nematoda-Round worms. These are nonsegmented pseudocoelomates. A tough cuticle or exoskeleton covers the body which the worm will periodically shed. Molecular genetics puts its relationship closer to the arthropods than the annelids. -Complete digestive tract. -No circulatory system, fluid in the pseudocoelom is used to deliver food. Many are parasites and pest of animals and many attack the roots of plants. Pin worms and hook worms are nematodes. Trichinella spiralis causes trichinosis in humans. Caused by eating undercooked pork with juvenile worms encysted in the muscle tissue. These develop into adults that burrow into the human intestinal wall and invades other organs.
Phylum Arthropoda –Most successful animal phyla. Greatest variety of species and more in terms of numbers than any other animal phyla. Arthropods are covered by a cuticle or an exoskeleton constructed of layers of protein and chitin.
This can be thin and flexible for the joints and thick and hard for other parts. -Provide protection and points of attachment for muscles to move appendages. -Impermeable to water -It must be shed to the animal to grow and a new one secreted. Circulation- -Open circulatory system with hemolymph present. Dorsal blood vessel with one way valves and pores (ostia). The blood enters the vessel and hearts pull the blood forward. The blood moves through the hemocoel are sinuses which are different from the true coelom. The true coelom is reduced in adult arthropods. -Gas exchange -is varied because the arthropods are found in many different environments. Include gills in aquatic species, tracheal systems in insects and book lungs in spiders. Digestive tract is complete with specialized organs. i.e. Grasshopper -Specialized appendages for mouth -Foregut and midgut has gastric ceca to secrete digestive enzymes -Malpighian tubules between midgut and hindgut act like kidneys to reclaim salts and water and to put nitogenous wastes into the hindgut Nervous system is extremely well developed with two ventral nerve cords and extensive cephalization with many sensory structures clustered at the anterior end. Sense organs include eyes, olfactory receptors and tactile receptors. Main Lines- Trilobites-Extinct class but important. Extensive segmented but little appendage specialization. Evolutionary trend in arthropods is to fuse segments and have fewer segments and specialization of appendages to form antennae, wings, mouth parts and so forth. specialize appendages. Subphylum Chelicerforms-have a feeding appendage called a chelircerae. Has a cephalorthorax and posterior abdomen. Some specialization with appendages.Ex. Horseshoe crab, arachnids like spiders, scorpions, ticks and mites. Subphylum Myriapoda-Worm-like arthropods are segments with number of walking legs. Millipedes have two pair of legs/segment and are nonpoisonous detritus eaters. Centipedes have one pair of walking legs per segment and are poisonous carnivores. Subphylum Hexapoda-Body with head, thorax and abdomen. 3 pairs of legs and modified mouth parts Ex insects and springtails Subphylum Crustacea-Body with 2-3 parts. Antennae present and chewing mouth parts. 3 or more pairs of legs. Ex crabs, lobsters and shrimp.
Origins of segmentation- Traditional classification suggests that arthropods evolved from annelids based on the superficial similarities between annelids and centipedes/millipedes but molecular evidence shows this not to be the case. Segmentation is found in all three major clades of the bilarterial clade- Lophotrochozoa-annelids Ecdysozoa-arthodpods Deuterostomia-chordates However, in each of these clades there are also phyla that are not segmented. Segmentation occurs during the development of the embryo. During the course of development part of the embryo are sectioned off or blocked-out into regions where certain body parts will develop.
For example each bilateral animal has a particular linear arrangement of anatomical features along its anterior (head) to posterior axis. Eyes for example are located at the anterior end of the animal. Differential expression of various regulatory gene that code for transcription factors play a key role in the blocking-out of anterior--- ->posterior anatomy in the developing embryo. The gene of the Hox complex determine what organs will develop in each segment. For example, differential expression of various Hox genes along the embryo of lobster cause antennae to develop on certain segment and walking legs to develop on other segments. But even in non- segmented animals, such as flatworms, Hox genes determine where certain organs, such as eyes, develop along the animal's length. In fact, sponges have at least one Hox gene and cnidarian such as jellies have several. In a cnidarian, for example, expression of a Hox gene determines where tentacles will develop in the embryo.
It can be concluded that the original Hox gene originated prior to bilateral symmetry. The mechanism for the development of segmented bodies in certain animal phyla is a variation on a basic regulatory scheme that dates back to the first animals. An increase in the number of Hox genes through gene duplication and mutations, along with adaptation of Hox gene function for development of segmented bodies, made it possible for a great diversity. Clade Deuterostomia- Deuterostomes have- 1. Coelom from archenteron surrounded by mesodermal tissue. 2. Formation of the mouth at the opposite that of the anus which developed from blastopore.
Clade Deuterostomia- contains Phylum Echinodermata and Phylum Chordata Phylum Echinodermata- Echinoderms with a water vascular system and secondary radial anatomy. Sessile or slow moving animals. The appendages are in multiples of five that radiate out from a central disc and there is a thin skin over hard calcareous plates. -Water vascular system. This contains a networks of hydraulic canals branching into extensive structures called tube feet that function in locomotion, feeding and gas exchange.
There are about 7000 species of echinoderms. The six recognized classes are: 1. Class Asteroidea -includes the sea stars which have five or more arms extending from a central disc. They have tube feet on the undersurface of the arms with suction cups at the end of each tube foot. They are predators that attach tube feet to the prey and the arms of the wrap around the prey 2. Class Ophiuroidea contains the brittle stars which differ from sea stars with smaller central discs and longer more flexible arms that have no suckers on their tube feet 3. Class Echinoidea contains sea urchins and sand dollars. Sea urchins are spherical while sand dollars are flattened. These echinoideans lack arms but have five rows of tube feet and muscles. that pivot their spines for locomotion. They have a complex jaw like structure used for feeding on seaweeds and other food
4. Class Crinoidea contains the sea lilies which are sessile, living attached to substratum by stalks. A few are motile and use their arms for a crawling form of locomotion. The arms circle the mouth and are used in feeding. 5. Class Holothuroidea contains sea cucumbers which have little resemblance to other echinoderms as they lack spines and the hard endoskeleton is reduced. Their body is elongated. These species do possess five rows of tube feet, a part of the unique water vascular system and some tube feet around the mouth have developed into feeding tentacles. 6. Class Concentricycloidea contains the sea dasies which are small (less than 1 cm), disc shaped marine animals. They live in deep water and do not possess arms. The tube feet are located around disc margin with water vascular system consisting of two concetric ring canals.