PRELIM.docx

**Summary of the Different Lifestyles Possible in the Two Major Environments, Aquatic** **and Terrestrial, as They Reflect Differences in the Physical Properties of Water and Air** +-----------------------+-----------------------+-----------------------+ | **Property** | **Water**...

**Summary of the Different Lifestyles Possible in the Two Major Environments, Aquatic** **and Terrestrial, as They Reflect Differences in the Physical Properties of Water and Air** +-----------------------+-----------------------+-----------------------+ | **Property** | **Water** | **Air** | +=======================+=======================+=======================+ | Humidity | High: Exposed | Low: | | | respiratory surfaces; | | | | external | Internalized | | | fertilization; | respiratory surfaces; | | | external development; | internal | | | excretion of ammonia | | | | | fertilization; | | | | protected | | | | development; | | | | | | | | excretion of urea and | | | | uric acid | +-----------------------+-----------------------+-----------------------+ | Density | High: | Low: | | | | | | | Rigid skeletal | Rigid skeletal | | | supports unnecessary; | supports necessary; | | | | must | | | filter-feeding | | | | lifestyle possible; | move to find food; | | | external | internal | | | | fertilization; | | | fertilization; | | | | dispersing | sedentary | | | developmental stages | developmental stages | | | \* | | +-----------------------+-----------------------+-----------------------+ | Compressibility | Low: | High: | | | | | | | Transmits pressure | Less effective at | | | changes uniformly | transmitting | | | | | | | and effectively | pressure changes | +-----------------------+-----------------------+-----------------------+ | Specific Heat | High: | Low: | | | | | | | Temperature stability | Wide fluctuations in | | | | ambient temperature | +-----------------------+-----------------------+-----------------------+ | Oxygen solubility | Low: | High: | | | | | | | 5--6 ml O 2 /liter of | 210 ml O 2 /liter of | | | water | air | +-----------------------+-----------------------+-----------------------+ | Viscosity | High: | Low: | | | | | | | Organisms sink | Faster rates of | | | slowly; greater | falling; less | | | frictional | frictional | | | | | | | resistance to | resistance to | | | movement | movement | +-----------------------+-----------------------+-----------------------+ | Rate of oxygen | Low: | High: | | diffusion | | | | | Animal must move (or | (about 10,000 times | | | must move water) | higher than in water) | | | | | | | for gas exchange | | +-----------------------+-----------------------+-----------------------+ | Nutrient content | High: | Low: | | | | | | | Salts and nutrients | No nutrients | | | available through | available via direct | | | absorption | | | | | absorption from air; | | | directly from water | adults supply eggs | | | for all life stages | | | | \* | with all nutrients | | | | and salts needed | | | ; adults | | | | | for development | | | may make minimal | | | | nutrient investment | | | | per egg | | +-----------------------+-----------------------+-----------------------+ | Light-extinction | High: | Low: | | coefficient | | | | | Animals may be far | Animals never far | | | removed from sites | from sites of primary | | | | | | | of surface-water | production | | | primary production | | +-----------------------+-----------------------+-----------------------+ **Summary of the Developmental Characteristics of Idealized Protostomous** **and Deuterostomous Coelomates** +-----------------------+-----------------------+-----------------------+ | **Developmental | **Protostomes** | **Deuterostomes** | | Characteristic** | | | +=======================+=======================+=======================+ | Mouth origin | From blastopore | Never from blastopore | +-----------------------+-----------------------+-----------------------+ | Coelem formation | Schizocoel | Enterocoely | +-----------------------+-----------------------+-----------------------+ | Arrangement of | Variable in number | Generally in three | | coelomic cavities | | pairs | +-----------------------+-----------------------+-----------------------+ | Mesoderm origin | 4d cell (Fig. 2.6n | Other | +-----------------------+-----------------------+-----------------------+ | Cleavage pattern | Spiral, determinate | Radial, indeterminate | +-----------------------+-----------------------+-----------------------+ | Polar-lobe formation | Present in some | Not present in any | | | species | species | +-----------------------+-----------------------+-----------------------+ | Larval ciliary bands | Compound cilia from | Simple cilia, one | | | multiciliated cells | cilium per cell | | | | | | | Downstream particle | Upstream particle | | | capture | capture | +-----------------------+-----------------------+-----------------------+ **Cladistic Analysis: Some Common Terms Defined** 1. **anagenesis**: change occurring within a lineage. 2. **ancestral (primitive) state**: the character state exhibited by the ancestor from which current members of a clade have evolved. **Also called the plesiomorphic state**. 3. **apomorphy**: any derived or specialized character. 4. **autapomorphy**: a derived character possessed by only one descendant of an ancestor, and thus of no use in discerning relationships among other descendants. 5. **Bayesian** **inference**: a statistical technique used to infer the probability that a particular phylogenetic hypothesis is correct. 6. **bootstrapping**: a technique for evaluating the reliability of a branch of a phylogenetic tree by resampling some number of characters from the original data set (with replacement) at random. Each resampling thus creates a new data set, with some values duplicated and others omitted. The bootstrap value given for each branch shows the percentage of resamplings (typically 500--1,000) that recover that branch. For example, in Figure 2.12 , bootstrap values were at least 95% at most branch points, meaning that those branching patterns were recovered in a least 95 of every 100 simulations. 7. **clade**: a group of organisms that includes the most recent common ancestor of all its members and all descendants of that ancestor; every valid clade forms a "monophyletic" group (see monophyletic taxon). 8. **cladogenesis**: the splitting of a single lineage into two or more distinct lineages ( klados = G: twig, or branch). 9. **cladogram**: the pictorial representation of branching sequences that are characterized by particular changes in key morphological or molecular characteristics (character states). 10. **derived** **state**: an altered state, modified from the original, or ancestral condition. Also called the apomorphic state. 11. **homologous** **characters**, **homology**: characters that have the same evolutionary origin from a common ancestor, often coded for by the same genes. Homology is the basis for all decisions about evolutionary relationships among species. 12. **homoplasy**: the independent acquisition of similar characteristics (character states) from different ancestors through convergence or parallelism. Such homoplastic events create the illusion of homology. 13. **jackknifing**: a technique for evaluating the reliability of a branch of a phylogenetic tree by deleting some percentage of information (e.g., base-pair position information) at random and then rerunning the analysis. The jackknife value given for each branch shows the percentage of such resamplings (typically 500--1,000) that recover that branch. 14. **monophyletic** **taxon**: a group of species that evolved from a single ancestor and includes all descendants of that ancestor. By definition, every valid clade must form a monophyletic taxon. 15. **node**: a branching point on a cladogram. 16. **outgroup**: A group of taxa outside the group being studied, used to "root" the tree and imply the direction of evolutionary changes. 17. **paraphyletic** **grouping**: a group of species sharing an immediate ancestor but not including all descendants of that ancestor. 18. **parsimony**: a principle stating that, in the absence of other evidence, one should always accept the least complex scenario. 19. **pleisiomorphy**: any ancestral or primitive character. 20. **polarity**: the direction of evolutionary change. 21. **polyphyletic** **grouping**: an incorrect grouping containing species that descended from two or more different ancestors. Members of polyphyletic groups do not all share the same immediate ancestor. Members of polyphyletic groups may resemble each other because of the independent evolution of similar traits by different ancestors. 22. **saturation**: a situation in which the gene sequences being compared have experienced so many base-pair substitutions that the phylogenetic signal is largely lost. 23. **sister** **groups**: two groups of animals descended from the same immediate ancestor. 24. **synapomorphy**: a derived character that is shared by the most recent common ancestor and by two or more descendants of that ancestor. In cladistic methodology, synapomorphies define clades; that is, they determine which species (or other groups) are most closely related to each other. Essentially, synapomorphies are homologous characters that define clades. 25. **taxon**: any named group of organisms, such as jellyfish or sea urchins or slippershell snails (Crepidula fornicata ); plural = **taxa**. **Protist** **Kingdom Chromista** **The Alveolata** - All members possess flattened membranous sacs (alveoli) beneath the outer cell membrane. - The mitochondrial cristae are tubular, as in most other eukaryotes. - Blepharisma, Didinium, Euplotes, Folliculina, Paramecium, Stentor, Stylonychia, Tetrahymena, Tintinopsis, Tokophyra, Vorticella. The ciliates, about 3,500 described species. **Phylum Dinozoa (= Dinoflagellata)** - Alexandrium (= Protogonyaulax), Amphidinium, Ceratium, Dinophysis, Gonyaulax, Gymnodimium, Noctiluca, Perkinsus, Prorocentrum, Pyrocystis, Zooanthella. The dinoflagellates. - Extant species, about 2,000. **Phylum Apicomplexa** - Babesia, Diplospora, Eimeria, Gigaductus, Gregarina, Haplo sporidium, Monocystis, Paramyxa, Plasmodium, Sarcocystis, Toxoplasma. - A highly diverse group of parasites, largely restricted to invertebrate hosts. About 6,000 species. **The Rhizaria** - This is a tremendously diverse group of protozoans defined exclusively by molecular characteristics. - It includes non-photosynthetic amoebae, amoeboflagellates, and a very large number of zooflagellate species of great abundance and probable ecological importance, particularly in soil and freshwater habitats. - Most have tubular mitochondrial cristae (as do the alveolates and many other eukaryotes). **Phylum Foraminifera** Allogramia, Ammonia, Elphidium, Globigerina, Spirillina. - The foraminiferans, most of which secrete calcium carbonate tests. - Pseudopodia protrude through numerous pores. - Most forams are microscopic, but individuals in some species can exceed 2 cm in diameter. - In marine habitats shallower than about 2,000 meters (at greater depths calcium carbonate solubilizes readily) they form the sediments known as Globigerina ooze. - A small number of foraminiferan species are planktonic, occurring at concentrations of about 1 individual per liter of seawater. Some species form symbiotic relationships with algae (zooxanthellae), similar to those formed by reef-building corals and some other invertebrate metazoans. - Forams have left an extensive fossil record; species composition can be used to date ancient sediments. - In addition, the ratio of 18 O to 16 O in ancient shells of some species is used to determine past climate changes. **Phylum Radiolaria** - All members possess radiating microtubular supports, called axopodia. - Acanthodesmia, Heliodiscus, Hexacontium, Astrosphaera, Spumella, Staurolonche, Triplecta. Another group of small (about 30--250 μm) marine predators, subdivided into spherical forms (Spumellaria) and nonspherical forms (Nassellaria). - Polycystines may be solitary or colonial. Unlike phaeodareans, many polycystine species harbor algal symbionts. The skeleton is composed of silica, providing an extensive fossil record. Formerly grouped with Phaeodarea as radiolarians. - Acanthocolla, Acanthometra, Acanthospira, Acanthostaurus, Heliolithium, Stauracon. - All are marine and free-living micropredators, with a skeleton of - Formerly grouped with phaeodarea and polycystines, with which they share the presence of axopodia, it now appears that axopodia may have been independently acquired in the ancestors of these groups. - Aulacantha, Aulosphaera, Castenella, Gymnosphaera, Phaeodina. - These microscopic predators secrete ornate shells of biogenic opal, and range in size from about 50 to 250 μm. - They are entirely marine, living to depths of at least 8,000 m, and were previously placed in the Radiolaria. Little is yet known about their precise roles in marine food webs. None harbor algal symbionts. **The Heterokonta** **Phylum Stramenopiles** - The "heliozoans" Actinosphaerium, Actinophyrs. There is a growing belief that heliozoans are polyphyletic and that Heliozoa should be abandoned as a formal category. Many "heliozoans" are now in the class Actinophyridae. **The opalinids (class Opalinata)** - Opalina, Proteromonas. Flagellated protozoans known mostly from the intestines of reptiles, fishes, frogs, and other cold-blooded vertebrates. **Kingdom Protozoa** **The Amoebozoa** - Most members have branching ("ramicristate"), tubular mitochondria. - Includes the naked amoebae (gymnamoebae; e.g., Acanthamoeba, Amoeba, Chaos, Entamoeba), mostly free-living individuals with lobose pseudopodia, although some species are obligate pathogens of humans and other animals. - Usually without flagellated stages in the life cycle. Concentrations of up to 4,200 amoebae per cubic centimeter of sand have been reported from intertidal beaches. **The arcellanids** - Arcella, Difflugia, Pentagonia. This group contains about 75% of all shelled amoebae, which protrude their pseudopodia through a single opening on the test. **The xenophyophoreans** - Aschemonella, Homogammina, Psammetta. All are deepwater (500--8,000+ meters depth) marine amoeboid protozoans that cement foreign particles into large tests, up to 25 cm long. - They are among the largest known protists. For many years they were thought to be either foraminiferans or sponges. - About 50 described species. **Phylum Mastigamoididae** - Mastigamoeba, Mastigella. All individuals have amoeboid bodies, in some cases exhibiting functional pseudopodia, with the addition of one or more flagella. - Marine and freshwater. None have mitochondria or Golgi bodies, but this seems to be a secondary loss rather than the primitive condition. - Mastigamoebae are especially common in stagnant water rich in organic matter. **Phylum Eumycetozoa** - Prostelium, Echinostelium, Dictyostelium. The cellular and acellular slime molds, commonly found among decaying vegetation. **The Excavata** - These protozoans all possess disc-shaped mitochondrial cristae, and most members also have a deep, ventral feeding groove, after which the group is named (Excavata, as in "excavation"). **Phylum Parabasala** - These flagellates are mostly symbiotic, living in hosts ranging from humans to termites and wood roaches. - Instead of mitochondria, they possess hydrogenosomes, which may have been derived from mitochondria or may reflect an ancient, independent symbiotic incorporation. **Class Trichomonadida** - Dientamoeba, Trichomonas **Class Hypermastigia** - Holomastigotes, Lophomonas, Trichonympha, Spironympha. - All are intestinal symbionts oftermites, cockroaches, and woodroaches, with each individual bearing hundreds to thousands of flagella. **Phylum Euglenozoa** **Class Euglenida** **Order Euglenia---Euglena, Peranema, Ploeotia** - Most of the approximately 1,000 species are photosynthetic, but some are parasitic and some feed on particulate food. Euglinids are mostly found in freshwater habitats, although some species occupy marine or brackish waters. **Order Kinetoplastea--- Bodo, Leishmania,** **Leptomonas, Trypanosoma**. - This group of flagellates (one to two flagella per individual) includes free-living, symbiotic, and parasitic species. - Parasitic species infect animals, flowering plants, and other protozoans. - All members have a prominent body of massed DNA within the mitochondrion called a kinetoplast, and a unique microtubular cytoskeleton. - A number of trypanosome species infect and debilitate, or kill, humans, livestock, and a variety of other mammals. Leishmania does similar harm by causing massive skin lesions: At least 400,000 people in 67 countries contract leishmaniasis each year. **Phylum Heterolobsea** - Naegleria, Percolomonas, Vahlkampfia. **The diplomonads** - Enteromonas, Giardia, Spironucleus, Trigomonas. - A coherent group of flagellates of uncertain affiliation. - Individuals lack mitochondria. Widely believed to derive from amitochondrial ancestors, these flagellates, it now appears, have in fact lost mitochondria secondarily. Most species are intestinal symbionts, although some species are free-living. **The oxymonads** - Oxymonas, Polymastimastix, Pyrsonympha. Another coherent group of flagellates of uncertain affiliation. - All species are intestinal symbionts of termites and woodeating roaches, with one species (Monocercomonoides) also living in vertebrate guts. **The Opisthokonta** - This recently established group contains the true fungi and their protozoan relatives, and the multicellular animals (including humans) with their protist relatives. All opisthokonts have a posterior ( opistho = G: behind) flagellum (kont = G: flagellum) in some part of the life cycle. **The choanoflagellates (phylum Choanomonada)** - Acanthoeca, Codosiga, Diaphanoeca, Monosiga, Proterospongia. - Free-living protozoans with a single flagellum surrounded by a basket-like collar composed of siliceous filaments. - Many species form colonies, from which both metazoans and fungi may have evolved. **Phylum Fungi** **Phylum Microsporidia** - Buxtehudea, Loma, Metchnikovella, Microfilum, Nosema. - Gene sequence data indicate that microsporidians are degenerate fungi. If so, their lack of mitochondria reflects a secondary loss from ancestors that had them. The members of one genus (Metchnikovella) all are intracellular parasites of gregarine protozoans (phylum Apicomplexa). **The Myxozoans** - Chloromyxum, Myxidium. Molecular data now show that the members of this group, which are all parasitic, mostly in fishes, are highly degenerate metazoans, probably most closely related to jellyfish and other cnidarians. **Porifera** **Taxonomic Summary** Phylum Porifera---the sponges Class Calcarea Class Demospongiae Class Hexactinellida---the glass sponges Class Homoscleromorpha Phylum Placozoa  **Subkingdom Parazoa** **Phylum Porifera** **Class Demospongiae** - This class contains more than 90% of all existing sponge species, including all freshwater species. - Support elements are never calcareous; they are instead composed of silica, spongin, or both, apparently along with chitin. - All members are of leuconoid construction. - Species show a variety of forms---thin and encrusting, erect and branching, multilobed, spherical, tubular---and a single individual may exceed 2 m in diameter. - There are 65 families, containing about 7,000 species. **Family Clionidae** - Cliona. Boring sponges: Marine sponges that excavate burrows in calcareous material, such as mollusc shells and coral. Etching chemicals are released at the tips of specialized surface cells; these secretions dissolve only the edges of calcareous chips, which then fall to the seafloor, contributing up to 40% of the reef sediment in some places. Species in this family are distributed from shallow water to depths exceeding 2,100 m. **Family Spongiidae** - Spongia, Hippospongia. All commercial sponges come from these two genera. All species in this family are marine. They live in all waters, from the tropics to the arctic and Antarctic. **Family Haliclonidae** - Haliclona. Members of this family are among the most commonly found and widely distributed of all shallow-water sponges, although some species reach depths of nearly 2,500 m. **Family Halichondriidae** - Halichondria. These encrusting, marine sponges are common in shallow water. **Family Clathriidae** - Microciona. The first experiments on sponge regeneration were performed on Microciona prolifera during the early 1900s. **Family Callyspongiidae** - Callyspongia. - The species in this group are common in shallow tropical oceans. Species may be upright, encrusting, branching, tubular, or vase-shaped; some are massive. **Family Spongillidae** - Spongilla, Eunapius, Ephydatia, Heteromeyenia. - This widespread group contains most of the approximately 300 freshwater sponge species, which usually encrust solid surfaces in ponds, streams, rivers, and lakes. An individual sponge may exceed 1 m in diameter. - A few species are found in brackish (i.e., slightly salty) waters. Ephydatia is the best-studied sponge genus in the world. **Family Geodidae** - Geodia. These are large cold-water sponges, up to 50 cm in diameter and weighing up to 24 kg. - They are especially common in deep Norwegian fjords. **Family Lubomirskiidae** - This group contains freshwater species restricted to Lake Baikal in Siberia. None of these species produce gemmules. **Family Mycalidae** *Mycale* **Family Cladorhizidae** - Asbestopluma, Cladorhiza. - These are mostly deep-sea sponges, living to depths as great as 8,840 m, although one species now has been found in a shallow-water Mediterranean cave. - Unlike other sponges, these animals lack choanocytes and internal water canal systems. They apparently feed as carnivores, passively entrapping small crustaceans that swim by, and may also gain nutrients from the activities of symbiotic bacteria **Class Calcarea** - All species are marine and have spicules exclusively composed of calcium carbonate. Species in this class may have asconoid, syconoid, or leuconoid grades of construction. There are 16 families. **Family Leucosoleniidae** - Leucosolenia. All members of this family are marine, asconoid, and contained in a single genus. - Species are found from the intertidal zone to depths exceeding 2,400 m. **Family Grantiidae** - Grantia (= Scypha ). Species are all marine. Members of this family are distributed from the intertidal zone to depths of about 2,200 m. **The Sclerosponges** - Acanthochaetetes, Astrosclera, Stromatospongia. - Most sclerosponges live in deep water on coral reefs or in caves, crevices, or tunnels within the reefs. - All species are of leuconoid complexity. The body is supported by a thick layer of calcium carbonate in addition to spicules of silica and fibers of spongin, giving rise to the common name "coralline sponges." - Recent morphological and molecular analyses suggest that sclerosponge species do not have a common, unique origin; members of the former class Sclerospongiae are currently placed within either the Calcarea or the Demospongiae. **Class Hexactinellida---the glass sponges** - Skeletal supports of all species are composed of six-sided spicules of silica and chitin; many spicules are fused to form long, thin, glasslike strands. - The epithelial and "choanocyte" tissues are syncytial. There are 16 families. **Family Euplectellidae** - Euplectella ---Venus's flower basket. Individual sponges often harbor a single pair of shrimps, one of each sex, that enter the sponge when small and reach reproductive adulthood imprisoned together within the spongocoel. - The species in this family are found at depths ranging from 100 m to over 5,200 m. **Class Homoscleromorpha** **Family Oscarellidae** - Oscarella, Plakina. The 84 members of this class were formerly contained within the Demospongiae. - All species are marine. Two families. **Family Plakinidae** - Corticium, Plakina, Plakortis. These unusual sponges have no supporting skeleton, lacking both spicules and spongin fibers. Along with one other family (the Oscarellidae, above), these sponges were formerly members of the Demospongiae. **Placozoa** - Defining Characteristic: - Small, - multicellular, - amorphous, - mobile, - animals lacking a body cavity, digestive system, and nervous system - and composed of two layers of ciliated epithelial cells with a layer of multinucleated contractile cells in between. **Introduction** Although only a single placozoan species has been described, Trichoplax adhaerens recent findings of surprisingly high amounts of 16S mitochondrial rDNA sequence diversity among individuals suggest that the phylum may contain more than a dozen species. Trichoplax has been collected from marine aquariums and from shallow-water tropical and subtropical marine habitats around the world. Although placozoans have been known since 1883, their biology and ecology are poorly understood. The animals are collected by submerging glass microscope slides in the field for one or two weeks, and then examining the slides in the laboratory; their natural habitat is unknown. Indeed, the animals might even be parasitic in some unknown hosts, so that we may be looking at only the free-living portion of the life cycle. **General Characteristics** - Like sponges, placozoans have no front or back and no right or left, and lack organs and tissues. - There is no digestive system, no nervous system, and no true musculature. - Placozoans, like sponges, additionally lack specialized sensory structures and, as with sponges, cells that are artificially dissociated will reaggregate to re-form a functioning animal. - However, unlike sponges, placozoans are fully mobile. - They are apparently planktonic for part of their lives, because they collect on microscope slides suspended in the water, but they seem adapted for gliding across hard substrates on thousands of motile cilia and through coordinated contractions of fiber cells, changing shape markedly, amoeba-style, as they travel. - The animals don't get much larger than 2 mm across in laboratory culture, and individuals collected from the field are even smaller: no more than about 1/10 that size. - They have the smallest nuclear genome of any known animal, at 98 million base pairs. - Placozoans are flat, with two distinct layers of epithelial cells, each layer containing perhaps a thousand or so cells. - As with sponges, the epithelial cells lack a basal lamina. The ventral layer is composed of columnar cells, each bearing a single flagellum. - Associated glandular cells apparently secrete digestive enzymes beneath the animal as it sits atop the algae and protozoans on which it apparently feeds; digestion seems to be entirely extracellular, as there is no mouth and no sign of phagocytosis. - The much thinner, upper layer of the animal bears flagellated cells along with numerous "shiny spheres" that seem to play a role in chemical defense against predators, but no gland cells. - Between the upper and lower cell layers is a fluid-filled space containing a dense network of fibrous cells that may be contractile. - Asexual reproduction---by budding, fragmentation, or binary fission---occurs commonly in the laboratory. - Also, individuals have no difficulty regenerating pieces that are cut off. - Genetic evidence suggests that placozoans also reproduce sexually, although we don't yet know many details. While fertilization has never been seen, some individual placozoans have produced what seem to be embryos; unfortunately, the embryos have never developed beyond 64 cells in the laboratory. - The relationship between placozoans and other metazoans is not clear. Possibly, placozoans are secondarily simplified from more complex animals. - However, some recent studies of mitochondrial genome sequences place placozoans at the very root of the metazoan tree, that is, as the oldest (most basal) group of metazoans. - As support for this scenario, their mitochondrial genome is the largest ever documented, at 43,079 base pairs, - not because of especially complex coding systems, but mostly because it contains numerous intragenic spacers and introns, characteristics shared with the mitochondrial genomes of choanoflagellate protozoans and some fungi. whereas recent studies of the nuclear genome 19 place them as the sister group to (sponges +cnidarians). - It is also possible that placozoans are secondarily simplified from some more complex ancestor. If placozoans are secondarily simplified from more complex animals, then placozoan evolution must reflect loss of the nervous system, and other degenerative events. - Interestingly, the placozoan genome includes genes that code for various transcription factors and signaling genes that are involved in early embryonic development and cell fate determination in most other animals. **Reviewer: Biology of Invertebrates (Chapter 3)** I. General Characteristics of Protists - Eukaryotic organisms, often unicellular. - Found in diverse environments (marine, freshwater, soil). - Can be autotrophic (photosynthesis) or heterotrophic (ingestion/absorption of nutrients). - Reproduce asexually (binary fission, budding) or sexually (conjugation). II\. Protozoan Locomotory Systems - Flagella: Long, whip-like appendages used for swimming (seen in flagellates). - Cilia: Short, hair-like structures that beat in a coordinated manner (common in ciliates). - Pseudopodia: Temporary, amoeba-like extensions of the cell body used for movement and feeding (amoeboid protozoans). III\. Reproduction in Protists Asexual reproduction: - Binary fission: The cell divides into two identical cells. - Budding: A new organism grows from a small outgrowth or bud on the parent organism. Sexual reproduction: - Conjugation: Exchange of genetic material between two protists, primarily seen in ciliates. IV\. Feeding Strategies - Phagocytosis: Engulfing food particles (common in amoebas). - Absorption: Directly absorbing dissolved nutrients (common in parasitic protozoans). - Photosynthesis: Using light to produce energy (phytoflagellates). V. Phyla and Groups of Protists 1\. Amoeboid Protozoans: - Movement: Use pseudopodia for locomotion and engulfing food. - Examples: Amoeba, Foraminifera. - Characteristics: Mostly free-living; some have intricate shells (Foraminifera). - Reproduction: Mostly asexual (binary fission). 2\. Rhizaria: - Movement: Use thin, filamentous pseudopodia. - Examples: Radiolarians, Foraminifera. - Characteristics: Possess complex, often mineralized shells. - Habitat: Mostly marine environments. 3\. Flagellated Protozoans: Divided into two main groups: Phytoflagellates: - Nutrition: Autotrophic (photosynthetic). - Examples: Euglena, Dinoflagellates. - Reproduction: Mainly asexual (binary fission). Zooflagellates: - Nutrition: Heterotrophic. - Examples: Trypanosoma (causes sleeping sickness), Giardia. - Reproduction: Asexual and sexual reproduction. - Habitats: Free-living, symbiotic, or parasitic. Key Terms and Definitions Eukaryotic: - Organisms with cells that have a membrane-bound nucleus and other organelles. Protists are eukaryotic, unlike prokaryotes (bacteria and archaea). Pseudopodia: - Temporary, arm-like extensions of the cell membrane and cytoplasm used by amoeboid protozoans for movement and engulfing food. Means \"false feet.\" Flagella: - Long, whip-like structures used for locomotion in some protozoans (like zooflagellates and phytoflagellates). Move in a wave-like motion. Cilia: - Short, hair-like structures that cover the cell surface and beat rhythmically to propel the organism through water or move substances around the cell. Binary Fission: - A type of asexual reproduction where a single organism divides into two identical offspring. Common in many protists like amoebas. Phagocytosis: - The process by which a cell engulfs particles or other cells by extending pseudopodia around them. It\'s a feeding method for amoeboid protozoans. Conjugation: - A form of sexual reproduction in some protozoans (especially ciliates) where two individuals exchange genetic material through direct contact, allowing genetic recombination. **Reviewer: Biology of Invertebrates (Chapter 4)** **I. Phylum Porifera (Sponges) General Characteristics:** - Simplest multicellular animals. - Lack true tissues and organs. - Sessile (immobile) and primarily marine. - Filter feeders: Draw water through their bodies to capture food particles. - Body has pores, channels, and chambers that allow water circulation. Morphology: Composed of specialized cells: - Choanocytes (collar cells): Drive water flow and capture food particles. - Amoebocytes: Distribute nutrients and play a role in reproduction. - Porocytes: Form pores for water intake. Skeletal elements: - Spicules: Structural support made of silica or calcium carbonate. - Spongin: Flexible protein fibers in some sponges. Diversity: Sponges show a wide variety of forms: - Asconoid: Simplest structure with a single central cavity (spongocoel). - Syconoid: Intermediate complexity with folded body walls. - Leuconoid: Most complex with many interconnected chambers for water flow. Reproduction and Development: - Asexual reproduction: By budding or fragmentation. - Sexual reproduction: Sponges are hermaphroditic; produce both eggs and sperm. - Fertilization usually occurs internally, and the larvae are free-swimming. **II. Classes of Phylum Porifera:** Class Calcarea: - Sponges with calcium carbonate spicules. - Typically small, found in shallow marine waters. - Have all three body forms (asconoid, syconoid, leuconoid). Class Hexactinellida (Glass Sponges): - Spicules made of silica, often forming intricate glass-like structures. - Mostly found in deep marine environments. - Body typically syconoid or leuconoid in form. Class Demospongiae: - Largest class, including 90% of all sponge species. - Spicules made of silica, or the skeleton may be entirely spongin. - Exclusively leuconoid in form. - Includes freshwater sponges. **III. Phylum Placozoa:** General and Distinguishing Characteristics: - Simplest animal phylum: - Only one known species, Trichoplax adhaerens. Morphology: - Flattened, disk-like body with only a few thousand cells. - Lack specialized tissues and organs, but they move via cilia and absorb nutrients from their environment. Reproduction: - Asexual through fission or budding, but sexual reproduction might occur under certain conditions. Habitat: - Typically found in shallow, tropical waters.