Chapter 30 Intro to Animals

30.1 what is an animal?

• Animals are share a common ancestor with fungi and choanoflagellates under the Opisthokonta lineage

• They’re also multicellular eukaryotes, heterotrophic, they possess neurons and muscle (except sponges) with the power to move on their own

• The radiation and evolution of animals begun around 550 million years ago during the Cambrian explosion (the rapid diversification of animals’ body type and lineage)

30.2 what key innovations occurred during the origin of animal phyla?

• Key innovations that evolve in animals are multicellular, triploblastic, diploblastic, embryonic tissue layers and muscle, radical symmetry, cephalization and coelom formation

• Multicellular evolved in fungi and animals independently and with animals’ evidence shows that multicellular came about in sponges (porifera) like 700 mya

  • Sponges have specialized feeding cells called choanocytes that help that trap bacteria and organic debris similar to choanoflagellates (fungi). some sponges have an epithelium layer which is a layer of tightly joined cells that cover the interior/exterior surface of an animals essential for the form and function

• Animals can be split up by the number of embryonic germs or tissue layers (the layers that make up diploblast and triploblast) they have which are diploblast (two layer) and triploblast (three layer)

  • Diploblast consist of ectoderm/outer-skin (forms skin and nervous system) and endoderm/inner-skin (forms digestive tract and related organs) connected by mesoglea (gelatinous material that may consist of cells) whereas Triploblast has a mesoderm/middle-skin (forms circulatory system, muscle, and internal structure) included on top of that

• Animals have genes contractile proteins like actin and myosin. Epitheliomuscular cells which are used for movement evolved independently in Ctenophora and Cnidarians, similar to mesodermal muscle cells

• Radical and bilateral are to the two main types of body symmetry whereas radical symmetry has multiple planes of symmetry like Ctenophora, many cnidarians, and some sponges also with some ctenophoras having biradical symmetry which are two planes of symmetry. Bilateral symmetry (two-sided) which evolve later than radical is a single plane of symmetry usually present with a narrow, long body like annelid. also present in all triploblastic lineage.

  • There was evidence of bilateral symmetry internal in cnidarian called sea anemone

  

• Sponges lack nerve cells but possess genes for nerve development and function. Ctenophora and Cnidarian both have nerve net (which is a diffuse arrangement of nerves cells) but Ctenophora also has a cluster of nerves called ganglia

• Bilateral animals range from nerve net into a more complex central nervous system (which has neurons clustered into tracts or ganglia. Cephalization (the formation in animals where mouth and sense organs are clustered or concentrated in the head) contributed to the evolution of the central nervous system

• Some bilateral animals have coelom (which is an internal fluid-filled body cavity that is completely or partially lined with mesoderm)

• Coelomates (have enclosed coelom completely lined with mesoderm tissue, acoelomates (no enclosed coelom), pseudocoelomates (have enclosed coelom partially lined with mesoderm tissue)

• Protostomes (“mouth-first”) are named for the embryonic development where the mouth forms before the anus, while in deuterostomes (“mouth-second”), the anus forms before the mouth.

• Segmentation is the division of the body into a series of similar structures and is a defining characteristic of vertebrates, including fishes, reptiles, amphibians, and mammals.

30.3 what themes occur in the diversification within animal phyla?

• Cephalization led to the concentration of the sensory organs being in the head region to help animals better interact with their environment with senses like sight, hearing, taste, touch, smell and temperature sensing

  • Sensory organ diversification varies in special abilities within different animals allowing species to gather diverse information about food, predators, and mates in the different environments

• Feeding diversification varies in animals with detritivores (feeds on dead organic matter), herbivores (feeds on plants or algae), carnivore (feeds on animals), omnivore (feeds on mixture of plants/algae and animals), and parasites-ectoparasites (feeds on outside of host)/ endoparasites (feeds on inside the host)

• Animals have three types of skeletal systems that allow complex movements; hydrostatic (supports flexible bodies wall with soft tissue and fluid under compression), endoskeletons (supports from rigid structures inside the body, like bones in vertebrates and spicules in sponges), exoskeleton (supports from rigid structures outside the body like external arthropods armor

• Limbs contribute to diversity of movement with out pocket developments of the body wall taking many forms like lobe-like limbs, jointed limbs, tenacles, tube feet, and parapodia

• Reproduction varies from asexual (produced by fission/splitting and budding and parthenogenesis which produces identical offspring without being fertilized) and sexual (produced with meiosis and gamete fusion) with both external fertilization ( eggs and sperms out in the environment, common in aquatic habitat) and Internal fertilization (usually sperm transfer directly into the female’s body)

  • There’re three embryonic developments which are viviparous (species nourish embryos internally and gives birth to live young like most mammals), oviparous (species deposit fertilized eggs and uses yolk to nourish embryo like most insects and birds), and ovoviviparous (species retain eggs internally, embryo nourish by yolk and gives birth to live young like snakes)

• Many animal life cycles include metamorphosis (which is a drastic change in form from one development stage to another)

  • A direct development is when the young looks similar to adult version just smaller compared to indirect development which involves larvae look radically different from adult, lives in different habitat and eats different food

  30.4 Key Lineage of non-bilateral animal phyla

• Porifera (sponges) are a diverse group of non-symmetry/asymmetry and sessile (in place) that are live in the benthic part of the ocean. They use suspension feeders which filter out the water feeding on the bacteria, archaea, and small protist. they’re also important in the nutrient cycle.

• Ctenophora (comb jellies) are radically symmetric, diploblastic with few found in the benthic, but most are planktonic and predatory and they’re transparent in the water. They use specialized sticky cells called coloblast to capture their prey.

• Cnidarians (jellyfish, corals, anemones, hydroids) are also radically symmetric, diploblastic like Ctenophora and are found from surface of water to benthic parts. They use specialized STINKING cells called cnidocyte to capture their prey. When they sense their prey, they eject barbed, spear-like structure that might contain toxins. Many cnidarians have a life cycle that has both a sessile polyp form that reproduces asexually and a free- floating medusa that produces sexually

DSM Answers

• Movement allows adult animals to find food, find mates, and escape predators. This movement can occur in various modes (burrowing, slithering, swimming, crawling, and running), involves limbs, and is mostly powered by muscles.

• The vast majority of bilaterians are protostomes. The vast majority of animal species are protostomes; however, the largest animals and predators tend to be deuterostomes.

• Jointed limbs are found in vertebrates and arthropods

• An unusual feature of sponges is that they can grow into complete individuals from fragments broken off from an adult. Some sponge cells are totipotent, having the capacity to develop into all of the cells of a complete adult organism.

• The closest living relatives to sponges are choanoflagellates. The most complex choanoflagellates and the simplest sponges feed in the same way; that is, they are suspension feeders.

• One hypothesis is that the evolution of the nervous system and head are tightly linked to bilateral symmetry and that together, these characteristics contributed to the radiation of bilaterians.

• Parasites can be herbivores or carnivores. Both animals and plants can act as hosts from which smaller parasitic organisms can harvest nutrients.

• Traditionally, the morphological interpretation of animal phylogeny related to body plan was from simple acoelomates (without a coelem) to pseudocoelomates to coelomates. Molecular data now suggests acoelomates like nematodes had ancestors with a coelom but that this trait was lost.

• How some jellyfish reproduce (the two stages of the life cycle of some cnidarians) might lead a new biology student to compare cnidarians and plants.

• Deposit feeders are found in a variety of animal lineages, including annelids, echinoderms, and a few chordata. Deposit feeders digest organic material that has been deposited within a substrate or on a surface.

• The major lineages are defined by when certain morphological traits are hypothesized to have originated. The origin of segmentation is one of the most recent events that occurred in several lineages.

• The order of events in a typical animal life cycle is fertilization → embryogenesis → growth → gametogenesis.

• Animals are a monophyletic group. One of their closest relatives is the Fungi group. Both of these groups are heterotrophs, but fungi carry out external digestion in the surrounding environment, and most animals ingest food in a digestive tract.

• One of the adaptive values of metamorphosis is that it reduces competition for food between larvae and adults of the same species. Because larvae and adults feed on different foods in different ways, they do not compete with each other and can specialize to take advantage of available food sources.

• Electric field sensing is found in only few animals rather than being nearly universal in animals. Some aquatic predators, such as sharks, are so sensitive to electric fields that they can detect electrical activity in the muscles of passing prey.

• Heterotrophs occupy the upper levels of food chains in most habitats.

• The feeding method shared by barnacles and baleen whales is suspension feeding. Both barnacles and baleen whales trap suspended particles from the water—usually detritus or plankton, small organisms that drift in the currents.

• The disappearance of most prokaryotic lineages opening up niches for eukaryotes is not hypothesized to have played a key role in animal diversity

• Animals are eukaryotes that share the following traits: Animals are multicellular, they move under their own power, and they eat other organisms.

• Jellyfish and other cnidarians have evolved a cnidocyte, a specialized cell used for prey capture. When cnidocytes sense a fish or other type of prey, the cells forcibly eject a barbed structure that may contain toxins. The barbs hold the prey until it can be brought into the mouth and digested.

• A bilaterally symmetric animal that feeds through predation and carries out asexual reproduction would be an animal with at least one characteristic from a plathyhelminth, a ctenophore, and a poriferan.