Biol 1309 Echinoderms & Chordates 1 But first a few words about Development Blastula- zygote first develops into a hollow ball of cells Deuterostome - mouth second Protostome - mouth first Cleavage - describes early cell divisions in relationship with an axis Coelom - cavity contains digestive etc Enterocoely - process (in deuterostomes) that forms coeom - mesoderm forms as evaginations of the developed gut that pinch off 2 1
3 So what is a Protostome? Mouth First Three major groups: Ecdysozoa (arthropods, nematodes) Platyzoa (platyhelminthes, rotifers) Lophotrochozoa (molluscs, annelids) 4 2
So then what is a deuterostome? Distinguished by embryonic development: the first opening (the blastopore) becomes the anus (in protostomes it becomes the mouth) Also known as enterocoelomates because their coelom develops through enterocoely. 5 The 4 Existing Deuterostome Phyla: Phylum Chordata (vertebrates) Phylum Echinodermata (sea urchins, sea cucumbers, sea stars...) Phylum Hemichordata (acorn worms) Phylum Xenoturbellida (only 2 species of worm-like animals) 6 3
Echinoderms! Means tough skin : Spiny skin that covers endoskeleton made of calcium plates. water vascular system hydraulic fluid-filled tube system (and tube feet!) used for movement. five-part symmetry (pentaradial) around a central disc with a central mouth. Includes: crinoids (feather stars, sea lilies) sea stars brittle stars sea cucumbers. 7 Echinoderms- so many kinds of spiney skins! 8 4
Onward - to the Chordates! 9 10 5
11 What is a Chordate? Share four common characteristics At some point in their lives, chordates have: 1. Stiff, rod-like notochord running down the back (serves as a skeleton) 2. Hollow dorsal nerve cord 3. Pharyngeal slits (in throat region) 4. Muscular postanal tail 12 6
13 Additional Chordate Traits Bilateral symmetry Have coeloms Most develop an extensive endoskeleton (cartilage or bone) 14 7
15 CEPHALOCHORDATA: Common Name: Lancelets. Small fish-like chordates retain all four chordate characteristics throughout their lives. (Consider these guys to be invertebrate chordates.) 16 8
UROCHORDATA: Common name: sea squirts Their tadpole-like larvae have the four chordate characteristics. As adults, most of these characteristics are lost when adults settle down to filter feed. 17 Hagfishes + Vertebrates. These animals have a skull. Includes: hagfishes, lampreys, cartilaginous fishes, bony fishes, amphibians, reptiles (including birds), and mammals. CRANIATES: 18 9
VERTEBRATES: Lampreys + gnathostomes. These animals have a vertebral column (spine) made of repeating vertebrae. The notochord is replaced or surrounded by the vertebral column. They also have more extensive skulls plus other characteristics, such as kidneys. The vertebrates include lampreys, cartilaginous fishes, bony fishes, amphibians, reptiles (including birds), and mammals. 19 GNATHOSTOMES: These animals have jaws and paired appendages (fins or limbs). Include: cartilaginous fishes, bony fishes, amphibians, reptiles (including birds), and mammals. An important advancement for this group was jaws, allowing biting teeth to evolve. 20 10
TETRAPODS: Four limbs Modified for life on land. Limbs have common pattern: humerus, radius, ulna, wrist/ankle bones, bones of feet and finger bones. Include amphibians, reptiles (including birds), and mammals. 21 Limbs 22 11
Amniotes: Amniotic egg Include the reptiles (including birds) and mammals. 23 Egg Power! The amniotic egg usually has a shell that protects the developing embryo inside. The amniotic egg creates a little "pond" for the embryo to develop within. Allowed amniotes to reproduce on land, away from water. 24 12
The Amniote Egg Four extraembryonic membranes: (1) Amnion (produces amniotic fluid to cushion the developing embryo) (2) Chorion (allows gas exchange) (3) Allantois- (stores embryo metabolic wastes) 4) Yolk sac (supplies embryo with nutrients (yolk) 25 26 13
HAGFISHES Craniates without vertebral column. Look somewhat like eels, with elongated bodies. Scavengers that feed on dead or dying invertebrates and fishes. Produce slime when threatened. 27 Parasitic jawless fishes. Lamprey can grab onto live prey with suckerlike mouth and use tongue to rasp away flesh. Although most are aguatic, there are some marine species that must spawn in fresh water. LAMPREYS 28 14
Hagfishes Slime! 29 Lampreys 30 15
Cartilagenous Fishes Internal skeletons mainly of cartilage. Presence of pointed or cone-shaped scales (called placoid scales). A major evolutionary advance- development of jaws ( allow biting or crushing prey) The scales of cartilaginous fishes (called denticles) similar to the structure of their teeth, complete with enamel and dentin. One evolutionary possibility is that denticles lead to the development of teeth within the jaw. 31 Cartilagenous Fishes (cont.) Developed two sets of paired fins: pectoral fins (front) and pelvic fins (back) provides stability, support and maneuverability Includes: sharks, rays and skates. Their bodies (like most fishes) are more dense than water, so they tend to sink. 32 16
Bony Fishes More different species than any other group of chordates. Developed internal skeleton made of bone (much stronger than cartilage) Because the ancestor of bony fishes apparently lived in stagnant, fresh-water pond environments, adaptation that evolved in ancestral bony fish was the lung. Modern bony fish have swim bladders, derived from the ancestral lung. This gas-filled internal structure allows a fish to maintain its position in the water without expending a great deal of energy. 33 Bony Fishes (cont.) Majority have fins that are supported by slender rods or rays (often called the ray-finned fishes). Some of the bony-fishes have fleshy, lobed fins that are supported by skeletal elements of bone. Ancestral lobe-finned fishes gave rise to amphibians. Modern-day lobed-finned fishes include the coelacanth and lungfishes in Australia, Africa, and South America. 34 17
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