Diplopoda Millipedes; 2 pairs of walking legs on each segment. –Feed on decaying leaves and plant matter. –Possibly among the earliest land animals. Fig a
Chilopoda Centipedes –Terrestrial carnivores. –Head has a pair of antennae and 3 pairs of appendages modified as mouthparts including jaw- like 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 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 H 2 O by intestinal hind gut.
. Insect respiration Respiration by a chitin-lined tracheal system blue –air is carried from spiracles directly to the cells
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 Insect Reproduction Separate sexes.
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
Crustacean physiology Respiration: - small species, across cuticle. - large species: across gills. Open circulatory system Excretion: nitrogenous wastes mostly NH 3, 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). Decapod s – 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.
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 introduction
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. Echinoderm characteristics Sea urchin larva (bilateral symmetry)
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. Fig Sea stars feeding on Antarctic Weddell seal pup carcass
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 c 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 d
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 f
When did segmentation evolve? XX X X XX XX
When did segmentation evolve? Three hypotheses: Which hypothesis do you think is most parsimonious?
CHAPTER 34 VERTEBRATE EVOLUTION AND DIVERSITY
Fig 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.
Notochord Dorsal hollow nerve cord 4 unifying anatomical features of chordates Fig 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. Early gill arch structures in human embryo 4. Muscular post-anal tail - contains chevron-shaped muscle blocks. - propulsive force in aquatic species.
Only pharyngeal slits obvious in adult urochordate. All chordate characteristics evident in larval forms. Fig. 34.3c Tunicate “tadpole” larva
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: -- 1 st : 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) nd : vertebrate evolved from a cephalochordate. Fossil evidence in the early Cambrium (535 mya) show intermediate fossil forms.