Transcript Systematics
Systematics Systematics is the science of categorizing organisms into like groups and establishing their relationship relative to each other. Seven major categories are used to classify organisms: kingdom phylum class order family genus species Systematics In case of humans: kingdom: Animalia phylum: Chordata class: Mammalia order: Primates family: genus: Hominidae Homo species: sapiens Note that Homo sapiens is italicized. Another acceptable notation would be to underline the Genus and species… Also note that the first letter of the Genus is capitalized, whereas the species is not. Systematics – Domains and Kingdoms Note that Taxonomies are constantly changing. Part of the reason is new information (mostly based on molecular biology) being discovered about different groups. Here for example, it is suggested that there should be three Domains, each of which would then contain the various Kingdoms. Other suggested changes are occurring at the other taxonomic levels of classification… Systematics –Kingdoms Relationships are not quite as simple as suggested by this figure. Ideally, each branch point is where a new form (i.e. adaptation) has created two distinct forms from a single common ancestor. Kingdom Animalia Animal features: 1. Multicellular 2. Heterotrophic 3. Lack cell walls 4. Motile (at least at some stage of life) 5. Typically can reproduce sexually (although there is a lot of variation) 6. Most can rapidly respond to external stimuli Kingdom Animalia – Phylum Porifera Phylum Porifera – Sponges (9000-10,000 species) General features: Cellular level of organization with no tissues or organs Adults are typically asymmetrical Cells tend to be totipotent Can reproduce sexually or asexually Adults are sessile suspension-feeders; larval stages are motile Skeletal elements, when present, composed of calcium carbonate, silicon dioxide, and/or collagen fibers An ancient group, probably originated from flagellated protist ancestors Kingdom Animalia – Phylum Porifera Sponges are essentially made up of a loose aggregate of cells… You could even pass a sponge through a mesh, and the individual cells would come back together to reform the animal. Kingdom Animalia – Poriferan Body Plan Kingdom Animalia – Poriferan Body Plan Choanocytes (collar cells) produce water flow through the sponge body. Why is water flow such an important part of biology of sponges? Feeding Waste removal Gas exchange Reproduction Kingdom Animalia – Poriferan Body Plan Sponges depend on the water flow for every aspect of their lives. The only way they can get larger is by creating complex series of water canals throughout the body. The different body forms are: A. asconid B. simple syconoid C. complex syconoid D. leuconoid Kingdom Animalia – Poriferan Body Plan - Spicules Sponges use spicules made up of silicon dioxide and calcium carbonate for both structural support as well as for defense against potential predators. Cells called sclerocytes are responsible for producing the spicules. The spicules can have many forms. They vary from one species to the next, and have different shapes, sizes, forms, and make-ups. In addition to the spicules, sponges use layers of the protein collagen for additional structural support. this intercellular matrix is referred to as the spongin. Kingdom Animalia – Porifera Sponge Classification: 1. Class Calcarea Sponges with calcium carbonate spicules. 2. Class Demospongiae – Sponges with siliceous spicules, spongin fibers, or both. Approximately 90% of all poriferans, they include boring sponges, bath sponges, and many other forms… 3. Class Hexactinellida – Deep water sponges with siliceous six-pointed spicules and long siliceous fibers… includes the Genus Euplectella, or the Venus’s flower basket. Kingdom Animalia – Porifera Sponges are often very colorful. Why do you think this is? Kingdom Animalia – Cnidaria corals, sea anemones, jelly fish, box jellies, hydra, sea fans Phylum Cnidaria (~3000 species); general characteristics: Have tissue level of organization, with two tissue layers (diploblastic) Have radial symmetry Have specialized stinging structures called cnidae Have only one opening to the body cavity / digestive cavity Have no head, no centralized nervous system (only a nerve net), no discrete gas exchange, excretory, or circulatory systems Exhibit alternation of asexual polypoid and sexual medusoid generations. Kingdom Animalia – Cnidaria General body forms 2 body forms: Polyp and Medusa 2 tissue layers (diploblastic), ectoderm to the outside (blue), and endoderm to the inside (yellow). The layer in between is just a jelly-like material called the mesoglea (it is not a true tissue) Only one opening to the gastrovascular cavity acts as mouth and anus Kingdom Animalia – Cnidaria General body forms Cnidarians have radial symmetry: Kingdom Animalia – Cnidaria All cnidarians have specialized stinging or adhesive structures called cnidae Discharge acceleration is at 40,000g!!! When triggered, the the cnidocyte cells discharge the cnidae. A specialized form of cnidae called the nematocyst, has a harpoon like structure that enters the flesh of the potential predator or prey, releasing neurotoxins. Need both physical and chemical stimulation to induce release. Why do you think this is? Kingdom Animalia – Cnidaria No matter what the size or shape of the cnidarian, they all have cnidae, and they are all made up of one or more of polyp or medusoid body forms Kingdom Animalia – Cnidaria In general, cnidarians alternate between sexual medusoid and asexual polypoid forms There are a lot of exceptions though… Kingdom Animalia – Cnidarian Classification 1. Class Hydrozoa – Both polyp and medusa present, with both marine and freshwater forms represented. Includes hydra, siphonophora, and the Portuguese man-of-war. Kingdom Animalia – Cnidarian Classification 2. Class Anthozoa – Medusa absent, these are entirely marine cnidaria including corals, sea anemones, sea fans, sea pens, and zoanthids. Kingdom Animalia – Cnidarian Classification 3. Class Scyphozoa - Medusa dominant (although both body forms are present), these are entirely marine cnidaria including the jelly fish. Kingdom Animalia – Cnidarian Classification 4. Class Cubozoa – Meduasa cuboidal in shape, these marine cnidaria include the box jellies. Kingdom Animalia – Cnidarian Diversity Hydra Box jelly Corals Sea pen Jelly fish Zoanthids Sea fan Sea anemone Kingdom Animalia – Symbiosis in Cnidaria Many cnidarians live in symbiosis with unicellular algae… This symbiosis may be the reason for their great success in otherwise nutrient poor waters of the tropics... Kingdom Animalia – Platyhelminthes Phylum Platyhelminthes – flat worms (~20,000 species); general characteristics: Have tissue level of organization, with three tissue layers (triploblastic – with endoderm, ectoderm, and mesoderm) Have bilateral symmetry Have only one opening to the body cavity / digestive cavity Have cephalization (and at least at some stage of their lives, so will all the animals that we’ll discuss from now on). Are hermaphroditic, with complex reproductive systems Can be free-living or parasitic Have great regenerative abilities!!!