2303ENV Zoology. Lecture week 1: Phylogeny and Classification

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1 Lecture week 1: Phylogeny and Classification 2303ENV Zoology Definition of animals: multicellular, eukaryotic, motile (can move independently and spontaneously), heterotrophic (must ingest other organisms or their products), lack cell walls and produce sperm cells. Body plan of most animals eventually becomes fixed. First appeared about 540Mya ago. First 2 kingdoms (Prokaryota and Eukaryota), then 4 (plants, animals, fungi, unicellular organisms), then 5 (plants, animals, fungi, protists and bacteria) and finally 6 (plants, animals, fungi, protista, eubacteria and archaebacteria). The 4 first are eukaryotic kingdoms, the two last are prokaryotic kingdoms. Prokaryotic cells are smaller and simpler, doesn t not have a nucleus or organelles, the DNA is circular, the reproduction is always asexual etc.. Classical Classification The naming of organisms is called taxonomy, the grouping classification. Relatedness: sharing a common ancestor. Evolutionary history of a species = phylogeny. Many species of tiny parasitic animals have been impossible to classify = incertae sedis (uncertain placement) Based on characters essential to the species (flower structure or embryo form). Molecular phylogeny of life Molecular genetics based on ribosomal RNA and mitochondrial DNA because of their fairly regular evolutionary pace. Diversity of life is much more in the Prokaryota than Eukaryota. Fungi/plants/animals very close to each other and fungi and animals closer to each other than with plants. 3 domains: Bacteria (biggest), Archaea, Eukarya. LUCA (last universal common ancestor) known because the same code is used to pass from DNA to protein in any living things. Most basal organisms are the Archea (closest to LUCA). Archea and Eukaryotes closer than either is to Bacteria. Most of the genetic diversity in Eukarya is among the unicellular Protists. Proto-protists became mitochondria. Cyanobacteria enable photosynthesis and became chloroplasts. Animals The name of the Kingdom is Metazoa (Animalia). Parazoa ( next to animals ) animals without any specific form and without any organised tissues. Eumetazoa ( true animals ) animals with true tissues, organised into two or three layers, and which possess neurons and a blastula in early development. Levels of Classification Life Domain Kingdom Phylum Class Order Family Genus Species About 35/36 Phyla Each level is called a clade. We thought that sponges were the basal animal but should be comb jelly according to molecular genetics.

2 Lecture week 1: Basal animals Sponges (Phylum Porifera) Sponges belong to the Phylum Porifera. They are aquatic animals almost all marine. They feed from suspended particles in the water such as bacteria, but a few also have photosyntethic endosymbionts and a very small number are carnivores and trap and feed on small crustaceans. Sponges have cells lining the body cavity called choanocytes. These cells drive the water through the cavity and out the major opening called osculum. Food is then captured on the inner wall by choanocytes. The pores in the body wall allows water to enter the sponge and are called ostia. The mesohyl in the sponge tissues provide the only skeletal support thanks to collagen fibres. Some sponges also have spicules which provide a skeletal support also. Some cells can directly ingest food particles, others need the help of specialised cells called amoebocytes to distribute them the food. The fossil record of sponges dates back to 580Mya. Even if sponges have a very simple body form, comb jelly are believed to be closer to the basal animals because sponges have become simplified through evolutionary time and then have arisen from more complex and probably more motile predecessors. Trichoplax (Phylum Placozoa) Trichoplax are tiny multicellular creatures with no fixed form, which differ them to amoeba. The species is known to be entirely female as no male genes nor sperm have been found. Orthonectids (Phylum Orthonectida) Very tiny endoparasites of marine invertebrates. They are among the simplest animals known and are eutelic (eutelic= having a fixed number of cells for a given species). They live in the body spaces of various marine invertebrates and cause host castration. Dicyemids (Phylum Rhombozoa) Tiny parasites found in the kidney of squid and octopus. Ii makes the host in difficulty but the effects are still unclear. They are, like orthonectids, eutelic. Lecture week 2: Radiata vs Bilateria & Ctenophora and Cnidaria. Eumetazoa includes organisms with fixed body forms and organ systems. This sub-kingdom is divided into two very unequal groups: Radiata (animals with a radial symmetry) and Bilateria (animals with bilaterial symmetry). Radiata is not really a clade because the two phylum are more distantly related to each other than they are to some bilaterians. They don t share a common ancestor that is closer to them than to any other extant animals. However, the two phyla are united by homoplasy (*analogous but not

3 homologous structures that have similar form or function, but were not present in the last common ancestor of those groups): radial symmetry and simplicity of tissues and structure. Comb jellies (Phylum: Ctenophora) Closest to the basal animal. They are called comb jellies because they swim by means of coordinated beating of usually eight rows of cilia (comb rows). Marine free swimming predatory animals. Distinguished from all other animals by possession of colloblasts: specialised cells that capture prey by squirting glue. Their body is largely a mass of jelly with a single layer of cells on the outside and inside. These layers are two cells deep and are held together by a basement membrane to give them strength. Lack an organised brain but they do have a nervous network allowing them to swim, close their mouth, and retract their tentacles. They feed on small prey. Some ctenophores also specialise in eating other ctenophores. Only 100 to 150 species named. They are economically important because if they are too numerous, they eat the plankton and then fish can t eat it anymore. It is important to control their number in order to control the population of fish in some seas around the world. Phylum: Cnidaria Exclusively aquatic and mostly marine animals, more than recognised species. Their body are made of three layers one cell thick, a mass of jelly-like mesoglea and an inner cell layer also one cell thick. Size from 5mm to 75m long and 2m across the bell. They are distinguished by the possession of cnidocytes on their tentacles, the main type of which are called nematocysts: which are harpoons that inject venom into prey and usually have barbs to keep them embedded in the victims. They are polymorphic and have juvenile (sessile polyp) and adult forms (swimming medusa). Both polyp and medusa have linear differentiation into an oral end and an aboral end. Medusa have their mouth on the underside and polyp on the upper side. Prey are caught on the tentacles and bring to the mouth by contraction of these tentacles. Some big jellyfish swim upwards in the mater column, spread their tentacles and sink to maximise food collection capacity. Nutrients are then absorbed by the cells that line the cavity and diffused to external epidermal or transferred through the mesoglea by mobile mesogleal cells. Some species (mostly corals) host endosymbiotic algae that contribute to their nutrition. All known cnidarian can restore lost tissues and regenerate after fragmentation. Reproduction by fission or sexually:

4 Coral animals and Sea Anemones (Phylum: Cnidaria, Class: Anthozoa) Can move slowly over surfaces. Corals host endosymbiotic algae (zooxanthellae) that contribute to their nutrition. Don t have a medusa phase, thus they are cnidarian polyp capable of sexual reproduction. The polyps have cylindrical body, with a ring of tentacles and mouth at the top. The mouth leads to a gastrovascular cavity which is subdivided into partitions (unique amongst cnidarians). Anemones and some corals are solitary but most corals are colonial. Coral reefs are limited to tropical regions with a maximum depth of 50m, water btw 20 to 28degrees, high salinity, low nutrients and low carbon dioxide level. Hydras (Phylum: Cnidaria, Class: Hydrozoa) May be colonial or solitary. Can dispensed a medusa stage or not. Siphonophores are unique in that the colonial organism is comprised of both polypoid and medusoid individuals, specialised for particular functions. Box jellyfish (Phylum: Cnidaria, Class: Cubozoa) Box jellyfish get their name from their cuboidal shape, with four tentacles (or sets of tentacles) at the corners of a hollow box-shaped bell. They are faster than other jellyfish, a much more developed nervous system and have four eyes. They pursue their prey more like a fish than a jellyfish. Only 36 species are known. They are notorious for their potent venom, and the bow jellyfish Chironex fleckeri is the most lethal jellyfish in the world. In Australia the medusoid jellyfish develop between the coast and the Reef in spring and early summer and then return to the coast to find estuaries in late summer. They swim up estuaries and in fresh water lay eggs that develop into polyps on submerged surfaces. In late winter the polyps produce medusae that wash back to sea. Irukandji are more concern to swimmers in Australia because it is a tiny creature, transparent but with long tentacles. It has venom on the bell as well and several deaths have been attributed to this creature. It is much more common than Chironex fleckeri and the population seems to be increasing. True jellyfish (Phylum: Cnidaria, Class: Scyphozoa) Only marine animals. About 200 species known. Owns tentacles and arms which assist it in feeding. They often possess statocysts and ocelli on the rim of the umbrella (which allows them to detect up and down, and the direction of light and darkness). Jellyfish blooms are thought to be caused by (i) overfishing that has drastically removed the predatory species that feed on medusae, (ii) increases in plankton that were fed on by smaller fish, (iii) increasing warmth of the oceans from global warming and (iv) increasing nutrient loads in nearshore (and pelagic) waters from changes in land-use.

5 Lecture week 2: Bilateria: Acoelomorpha, Xenoturbellida, Chaetognatha & Deuterostomia vs Prostomia. Bilateria: all animals that have bilaterial symmetry and most of which have organ systems. Bilateria is divided in three groups: (1) the uncertainly-placed Acoelomorpha and Xenoturbellida, (2) the Mesozoa and (3) the Nephrozoa. Bilateria is the major group of animals. Typically, bilaterian embryos are triploblastic, having three germ layers: endoderm, mesoderm, and ectoderm. Nearly all are bilaterally symmetrical, at least at some stage of their life Acoelomates: lack body cavities. Acoelomorphs: more advanced and have a couple of well-defined organ systems. Hermaphrodites may be sequential (occur in species in which the individual is born as one sex, but can later change into the opposite sex) or simultaneous (an adult organism that has both male and female sexual organs at the same time). Acoelomorpha: Asexual reproduction can occur by simple fission (e.g. Convolutriloba, species are distinguished by their usual mode of fission in which part of the body attaches to the substrate and is torn away as the animal moves). Statocyst helps them orient to gravity. Xenoturbellida: Worm-like marine animals, inhabiting soft substrates up to 100 m depth in the far northern hemisphere (off Sweden, Scotland and Iceland). Based on molecular analysis they were once thought to be degenerate molluscs, but this was based on food in their gut and not their own tissue: they are often connected with molluscs, and it is speculated that the earliest stages may be endoparasites of some mollusc larvae or parasitoids of mollusc embryos. Chaetognatha: This Phylum (Chaetognatha) is accepted as a nephrozoan, but its placement in either Deuterostomia or Protostomia is doubtful, so it sits outside these clades in incertae sedis. Chaetognatha is an enigmatic Phylum: comparative anatomy and embryology suggest alliance with the Deuterostomes while molecular biology and nervous system layout suggest Protostomes. A credible scenario is that they are close to the basal nephrozoan which split from Protostome line very soon after the Deuterostomes and Protostomes split. They may be found in tidal pools in arctic regions, the tropics, open ocean and the deep sea. Chaetognaths are hermaphrodites, possessing both male and female reproductive organs in their body. Bundles of sperm (spermatophores) are transferred from one individual to another, and fertilized eggs are subsequently released into the sea. They hatch as miniature versions of the adult and no larval stage exists.