Phylum Echinodermata and Phylum Chordata

Transcription

1 Phylum Echinodermata and Phylum Chordata Objectives: Differentiate between protostome and deuterostome characteristics. Identify traits of echinoderms. Differentiate between the different Chordate subphyla. Perform a Sea Star dissection. All Animals Are: heterotrophs multicellular eukaryotes are mobile at some stage of life store carbohydrates as glycogen, not starch, as in plants have an early developmental stage called a blastula have RNA (extracellular matrix) Protostomate and Deuterostomate Lineages: Figure 1 Protostome and Deuterostome The names protostome and deuterostome derive from the differing fate of the initial opening of the primitive digestive tract (the archenteron) in an embryo. As illustrated in the following picture, in protostomes, this initial opening develops into the mouth, and an opening that develops later becomes the anus. In deuterostomes, it develops into the anus, and an opening that develops later becomes the mouth. 1

2 Figure 2 (Images from the University of Tennessee at Martin Biology pages) Determinate cleavage is characteristic of protostomes. After the initial cell division the fate of the resulting daughter cells is determined -- these cells can only develop into specific tissues, not the whole organisms. Indeterminate cleavage is characteristics of deuterostomes. After the initial cell division the fate of the resulting daughter cells is not determined -- each has the potential to develop into an entire organism. Sometimes this occurs; resulting individuals are genetically identical (in humans, they are called identical twins). 2 Figure 3 Protostome and deuterostome cleavage differs in other ways 2

3 Figure 4 (Images from the University of Tennessee at Martin Biology pages) Coelom Development: A coelom is a body cavity completely surrounded by mesoderm. The coelom can be used as a hydrostatic skeleton, i.e., for support. It provides an avenue for release of, for example, gametes and excretory waste. It also provides a place for internal organ placement. The coelom can develop via two pathways: In protostomes: blocks of mesoderm hollow out to form the coelom. Deuterostomes; pockets of mesoderm pinch off to form the coelom. Phylum Echinodermata: Starfish, Sea Urchins Tissues: Three distinct tissue layers in embryo, leading to multiple tissue types in adult. Symmetry: Bilateral in the larva, but adults are more or less radially symmetrical (pentaradial, since they have five arms). Body cavity: Coelom Proto/deutero: Deuterostome Digestive tract: Complete digestive tract (mouth at one end and anus at the other). Other features: Body not clearly segmented. Calcareous endoskeleton. Hydrostatic skeleton (water vascular system). Water vascular system. Planktonic larvae. You might not guess it from looking, but the echinoderms are probably our closest relatives outside our own phylum. Key echinoderm features include: Endoskeleton: Much like our own skeleton, the echinoderm skeleton consists of 3

4 Water- vascular system: numerous calcified structures joined by more flexible tissues. A system of water-filled tubes running throughout the animal s body, the water-vascular system functions as an elaborate and flexible hydrostatic skeleton. (Echinoderms therefore have two skeletons: the hard plates of the endoskeleton and the flexible hydrostatic skeleton.) The water-vascular system includes tube feet, which are used by sea stars and other echinoderms to walk and to grab prey items. Coelom: The coelom in echinoderms is large, filling much of the body. The coelom is just a big, fluid-filled space. It s not the water vascular system, which contains water in a closed system of vessels, and it s not the gut, which is smaller and also enclosed. The coelom is the space where the other organs (water vascular system, gut, gonads, etc.) form. Examples: sea urchins, starfish, sea cucumbers: Figure 5: Sea Cucumber Figure 6: Starfish Figure 7 Sea Urchin Water vascular system - system unique to this phylum. Functions in movement, support, respiration, digestion. Decentralized nervous system. Rapid regeneration. Secondary radial symmetry - Larvae are bilaterally symmetrical. Adults are radially symmetrical. 4

5 A tube foot, an extension of the water vascular system of a starfish. The tube feet act like little suction cups which enable to starfish to grasp onto the sediment for movement or to break into bivalves for food. Note that since this is not a muscular system, they will not tire. Figure 8: Tube Foot Major Classes of Echinoderms Sea urchins; class Echinoidea: No arms; spiny body. Detritivores. Sea stars (starfish); class Asteroidea: Five or more arms. Predators. Sea cucumbers; class Holothuroidea: No arms; body often soft. Detritivores Brittle stars; class Ophiuroidea: Five arms with central disk; delicate and thin. Detritivores. 5

6 Phylum Chordata: This is your phylum. The phylum Chordata includes humans and other vertebrates Examples: Sea squirts, lancelets, vertebrates Notochord Pharyngeal Gill Slits Dorsal Hollow Nerve Cord Post Anal Tail Figure 9: Chordate Body Plan Chordate Characteristics Tissues: Symmetry: Body Cavity: Proto/deuterostome: Digestive Tract: Circulatory System: Three well-defined tissue layers in embryo. Bilateral, with cephalization. Coelom Deuterostome: the blastopore formed during gastrulation eventually becomes the anus; the mouth forms later. Complete digestive tract. Closed in vertebrates; open in a few others. Other Important Features: Segmented body; vertebrae, for example. Endoskeleton Notochord: a connective-tissue body stiffener. Dorsal tubular nerve cord forms the brain and spinal cord. Pharyngeal pouches and slits gill related structures that may appear early in development. In addition to forming gills, these structures also develop into jaw bones and other structures in vertebrates. Post anal tail: In many worms, the anus is at the very end of the animal s body; chordates typically have a tail beyond the anus. 6

7 Non- Vertebrate Chordates Subphylum Urochordata - the sea squirts Larval stage possesses all of the chordate characteristics. Most of these characteristics are lost when the larvae undergo metamorphosis and emerge as adults. Adult stage are primarily sessile filter-feeders. Figure 10: Urochordate Subphylum Cephalochordata - the lancelets Possesses all of the chordate characteristics throughout life cycle. Burrow into sand and use mucous-secreting organs to filter-feed. Feeble swimmers Figure 11: Lancelet Vertebrates The vertebrates (phylum Chordata, subphylum Vertebrata) include fish, amphibians, reptiles (including birds) and mammals. All these animals have the basic characteristics of chordates, with some added twists: The anterior region of the dorsal hollow nerve cord expands to become a brain and is encased within a skeletal cranium. Mesodermal blocks develop not only myotomes, but a segmented vertebral column that protects the posterior region of the dorsal nerve cord (spinal cord) and replaces the notochord. The cranium and vertebral column comprise the axial skeleton of vertebrates allowing an elaborate central nervous system and powerful muscle action with a flexible body. The development of a brain has further spurred the development of more sophisticated cephalic sensory organs, especially eyes, nostrils and ears. To support their enhanced homeostasis, vertebrates also have a closed circulatory system with distinctive types of heart and kidneys, and a greater suite of endocrine organs. The notochord, one of the unique defining characteristics of chordates, is a semi-stiff rod of connecting tissue that forms in the embryo and serves to guide the development of the vertebral 7

8 column (backbone) of vertebrates, along with other structures. In your own body, the notochord has mostly disappeared; the only remnants are the cartilaginous disks between your vertebrae. Subphylum Vertebrata Bone - reduction of notochord (vertebral disks) Figure 12: Lamprey Class Chondrichthyes - the cartilaginous fish Examples: sharks, rays, skates Endoskeleton is composed entirely of cartilage. Heterocercal caudal fin Two-chambered heart Numerous rows of teeth Internal fertilization and separate sexes Class Agnatha - the jawless fish (not monophyletic) Examples: lamprey, hagfish No jaws Most are parasitic fish Very diverse group in past. Now, only a few species are still hanging on. Figure 14: Stingray Figure 13: Sand Tiger Shark 8

9 Class Osteichthyes - bony fish (not monophyletic) Figure 15: Scaley Head Figure 16: Seahorse Figure 17: Stickleback Examples: marlin, bass, catfish, angelfish, eels Most diverse group of vertebrates. Paired fins with fin rays of cartilage or bone. Respiration by gills supported by bony gill arches and covered by a common operculum. Swim bladder often present. Two-chambered heart. Sexes separate and fertilization is usually external. Ray-finned fish - most fish possess this fin structure Lobe-finned fish - lung fish, Coelacanth, etc. The lobe-finned fish gave rise to tetrapods Figure 18: Coelocanth Figure 19: Amphibian Class Amphibia - amphibians (not monophyletic) Examples: frogs, salamanders Living skin - must be moist to breathe Lay eggs in water Outcompeted in water (fish) and land (reptiles) 9

10 Figure 20: Reptile Class Reptilia - reptiles (not monophyletic) Examples: lizards, snakes, gators First truly terrestrial animals Amniotic egg Scales (lungs now sole respiratory organ) Modifications of pectoral and pelvic girdles to facilitate movement on land Class Aves - birds (monophyletic) Examples: robin, jays, emu Feathers Warm-blooded (high metabolic rate) Hollow bones Figure 21: Ave Class Mammalia - mammals (monophyletic) Examples: elephant, bats, Al Gore Hair Mammary glands Occlusional teeth Warm-blooded (high metabolic rate) Figure 22: Vampire Bat Figure 23: Deer Mouse Figure 24: Elephant 10

11 Lab Exercise: Observe the preserved specimens for this lab. View the following prepared slides: Amphioxus-or lancelet, a fish-like marine chordate in the invertebrate subphylum Cephalochordata. Starfish arm-note the coelom, tube feet and radial canal (parts of the water vascular system), pyloric ceca (digestive glands), and pedicellaria (pincers on the outer surface of the body). Starfish development Starfish, ray Dissection of a Preserved starfish dissection (separate document) Sources: