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3-18-05 Prostostomia: Ecdysozoa Major Phyla: 1. Nematoda – round worms 2. Arthropoda – crabs, insects spiders Alternate taxonomy: 4 major lineages Taditional Taxonomy: Phylum: Class: (trilobites –extinct) Arachnida Phylum Arthropoda (spiders, scorpions, mites) Diplopoda Trilobita Chelicerata (jaw-like chelicerae, no antennae, simple eyes) (millipedes) Chilopoda Uniramia (centipedes) (jaw-like mandibles, 1 pair antennae, complex eyes) Insecta (insects) Crustacea Crustacea (Crabs, lobsters, (jaw-like mandibles, 2 pairs antennae, crayfish, shrimps) complex eyes) SuperPhylum Arthropoda • Diplopoda • Millipedes; 2 pairs of walking legs on each segment. – Feed on decaying leaves and plant matter. – Possibly among the earliest land animals. Fig. 33.31a • Chilopoda • Centipedes – Terrestrial carnivores. – Head has a pair of antennae and 3 pairs of appendages modified as mouthparts including jawlike mandibles – 1 pair of walking legs per trunk segment – Venom in claws of anterior trunk segments • Insecta = hexapoda • Greatest species diversity among animals. • ~ 26 orders. • All terrestrial habitats (even beetles in moss beds in Antarctica); some freshwater, few marine, and lots flying insects. • Oldest insect fossil – Devonian (~400 mya) • Reasons for insect diversity: - evolution of wing/flight escape predators, dispersal to new habitats, etc. - diversification of mouth parts for feeding on plants; - plants and insects adaptive radiation seemed to parallel each other beginning about 100 mya and continued until about 50 mya. Insects probably played a major role in (caused ?) the angiosperm radiation because of specific role as pollinators. Major Orders of Insects Order # spp. Examples Large impact on humans Insect Anatomy Fig. 33.33 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Insect digestion and excretion • Digestive system – complete; specialized organs with discrete functions. • Malpighian tubules – remove nitrogenous waste from hemolymph in form of uric acid; reabsorption of H2O by intestinal hind gut. •Insect respiration • Respiration . by a chitin-lined tracheal system blue – air is carried from spiracles directly to the cells • Insect Reproduction • Separate sexes. • Metamorphosis is central to insect development. – Incomplete metamorphosis: eg. grasshoppers, cockroach; young resemble smaller adults. – Complete metamorphosis: eg. butterfly, flies; larval stages look different from adults and food source different. Morphology changes completely during pupal stage and emerge as adults. Fig. 33.34 Control of Moulting and Metamorphosis • Role of Ecdysone and Juvenile Hormone. • Overhead • Crustacea • ~ 40,000 species; almost all aquatic. – A few terrestrial or semi-terrestrial. • Crustaceans include lobsters, crabs, crayfish, shrimp, and barnacles. • Appendages specialized on segments: - Claws, mouth parts, walking legs, swimming legs. - Can regenerate lost appendages during molting. Fig. 33.35 • Crustacean physiology • Respiration: - small species, across cuticle. - large species: across gills. • Open circulatory system • Excretion: nitrogenous wastes mostly NH3, by diffusion from modified coelomoducts called antennal or maxillary glands. • Reproduction: mostly separate sexes (barnacles are hemaphrodite) – Males use a specialized pair of appendages to transfer sperm to the female’s reproductive pore. – Most aquatic species have several larval stages. • Major Crustacean Orders • Isopods - ~ 10,000 species, largest groups of crustaceans. • Copepods - small; important in aquatic ecosystems; eat phytoplantons; eaten by large animals (fish). • Decapods – 10 walking legs (5 pairs); lobsters, crabs, crayfish, shrimps. 3 additional anterior pairs of appendages form mouth parts. - cephalothorax covered by carapace. • Mysidiacea: - mysid shrimps. Eg. Krill, planktonic, reaching about 3 cm long. – major food source for whales; also used for agricultural fertilizer. • Cirripedia: - barnacles – sessile crustacean on intertidal rocks and whales. – parts of cuticle hardened by calcium carbonate. – Filter feed by extending long thoracic appendages. Deuterostomia: Echinodermata Echinoderm introduction • Echinoderms are invertebrates, but sister taxon to Phylum Chordata, which includes the vertebrates. • Have deuterostome embryo characteristics: radial cleavage, coelom develops from archenteron, and anus formed from blastopore. • This classification based on developmental features supported by molecular systematics. Echinoderm characteristics • Sessile or slow-moving. • The internal and external parts of the animal radiate from the center, often as 5 spokes. • A thin skin covers an endoskeleton of calcareous plates. • Unique to echinoderms is the water vascular system, a network of hydraulic canals branching into extensions called tube feet – function in locomotion, feeding, and gas exchange. • Separate sexes– fertilization external. • Larvae – bilateral symmetry. • Adult radial appearance - result of a secondary adaptation to a sessile lifestyle. Sea urchin larva (bilateral symmetry) • Echinoderm diversity • ~7,000 species, all marine. • 6 classes: – Asteroidea (sea stars) – Ophiuroidea (brittle stars) – Echinoidea (sea urchins and sand dollars) – Crinoidea (sea lilies and feather stars) – Holothuroidea (sea cucumbers) – Concentricycloidea (sea daisies) • Asteroidea - Sea stars; five arms (sometimes more) radiating from a central disk. • The undersides of the arms have rows of tube feet. – Each can act like a suction disk that is controlled by hydraulic and muscular action. • Predators; scavenger eaters. Sea stars feeding on Antarctic Weddell seal pup carcass Fig. 33.38 • Ophiuroidea - Brittle stars. – – – – distinct central disk; long, flexible arms. Tube feet lack suckers. They move by serpentine lashing of their arms. Some species are suspension-feeders and others are scavengers or predators. Fig. 33.37c Antarctic brittle star Astrotoma agassizii • Echinoidea - Sea urchins and sand dollars – No arms; but have 5 rows of tube feet for locomotion. – Sea urchins also move by pivoting their long spines. – The mouth of urchin ringed by complex jawlike structures adapted for eating seaweed and other foods. – Urchins roughly - Sand dollars, flattened spherical. disk. Fig. 33.37d • Crinoidea • • • • Sea lilies; attached to the substratum by stalks. Feather stars; crawl using their long, flexible arms. Both use arms for suspension-feeding. Crinoids show very conservative evolution. – Fossilized sea lilies from 500 million years ago could pass for modern members of the class. Sea lily Feathery star on sponge • Holothuroidea - Sea cucumbers. • Look different from other echinoderms. – No spines, – Little or no hard endoskeleton. – Oral-aboral axis is elongated. • BUT – have 5 rows of tube feet. – Some tube feet around the mouth function as feeding tentacles for suspension-feeding or deposit feeding Fig. 33.37f • When did segmentation evolve? X XX X X X X X • When did segmentation evolve? • Three hypotheses: •Which hypothesis do you think is most parsimonious? CHAPTER 34 VERTEBRATE EVOLUTION AND DIVERSITY • Phylum Chordata Fig. 34.1 • Phylum Chordata • 3 Subphyla: • Subphyla Urochordata and Cephalochordata: no cranium, no backbone “invertebrates” • Subphylum Craniata (text calls it a Clade) : Class Myxini – Hagfish; elemental cranium, no backbone. Class Cephalaspidomorphi – Lamprey; cranium, partial backbone. Subplylum Vertebrata – fused cranium; complete backbone. 4 unifying anatomical features of chordates • Notochord • Dorsal hollow nerve cord Fig. 34.2 •Pharyngeal slits •Muscular, postanal tail. 3. Pharyngeal gill slits and arches. - connect the pharynx to the outside. - filter device for suspension-feeding in invertebrate chordates. - modified in higher vertebrates for gas exchange, jaw support, hearing. 4. Muscular post-anal tail - contains chevron-shaped muscle blocks. - propulsive force in aquatic species. Early gill arch structures in human embryo Urochordata – tunicates, ascidians (sea squirts) • Mostly sessile marine animals, some pelagic (salps). Some colonial, others solitary. tunicate tunicates Filter feeders • Only pharyngeal slits obvious in adult urochordate. • All chordate characteristics evident in larval forms. Tunicate “tadpole” larva Fig. 34.3c Cephalochordata – lancelets or amphioxus • Closely resemble the idealized chordate. • The notochord, dorsal nerve cord, numerous gill slits, and postanal tail, all present in adult. Filter feeder Evolutionary relationships • • Molecular evidence: cephalochordates are closest relatives to vertebrates and urochordates are the next closest. The evolution of vertebrates from invertebrates probably occurred in 2 stages: -- 1st: an ancestral cephalochordate evolved from an organism resembling a modern urochordate larva; paedogenesis - the precocious development of sexual maturity in a larva (the adult lancelet resembles a well developed tunicate larva). -- 2nd: vertebrate evolved from a cephalochordate. Fossil evidence in the early Cambrium (535 mya) show intermediate fossil forms. • Several recent fossil finds in China provide support for the second stage, from cephalochordate to vertebrate. – They appear to be “missing links” between groups. – Features that appear in these fossils include a more elaborate brain, eyes, a cranium, and hardened structures (“denticles”) in the pharynx that may have functioned somewhat like teeth. – These fossils push the vertebrate origins to Cambrian explosion. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 34.5