Dr. Forbes' Lectures for Biology 252 DIVERSITY:ANIMAL PROTISTS AND ANIMALS * Most of the 10-50 million spp. of organisms here * All are eukaryotic; recall prokaryote v. eukaryote differences: Differentiating characteristics Prokaryotes Eukaryotes No membrane bound nucleus Nucleus is memb.-limited No mitochondria, plastids, etc. Have them.... No endoplasmic reticulum Have it.... Flagella simple Flagella and cillia of 9+2 type Relatively little DNA 1000x more "Genophore" a DNA ring Chromosomes linear, of DNA + protein Have plasmids (rings of DNA) No plasmids Cell walls of peptidoglycan Cell walls, if present, of cellulose Amitosis Mitosis No meiosis Meiosis Metabolic diversity Structural diversity Small Not so small to really BIG Members of two kingdoms to deal with: PROTISTA (specifically, the "protozoa") and ANIMALIA Characteristics of the "protozoa": * heterotrophic: mostly "ingestive"; some parasitic; some mutualistic * motile: flagella, cilia, pseudopodia * no cell walls; no cellulose * no plastids; no chlorophyll * mostly unicellular; no large colonies.... * usually small; e.g., Anaplasma ~1/6 - 1/10 of a RBC; others barely visible to unaided eye; *Nummulites had 19 cm shell! * emphasis on intracellular specialization * ubiquitous, often numerous; must have water to be active... Classification of protozoa in flux; see text, p. 523. E.g., Giardia, long considered in Ph. Zoomastigophora, now in Ph. Archezoa.... See Table 26. I,. p. 524, for those we'll consider. Ph. Rhizopoda: amoebas, etc.: * unicellular; usually naked, some w/shells * pseudopodia for movement, feeding (but some have flagella in early stages) * chemotactic * no meiosis, no sex; divide by binary fission, w/o appearance of mitotic stages * abundant in soil, aquatic envts. * contractile vacuole in freshwater forms... * most are free-living; Endamoeba histolytica a notable exception.... KINGDOM ANIMALIA General features (compared to protozoa): * multicellular bodies, size microscopic to LARGE * multicellular reproductive structures * small motile sperm, larger nonmotile egg * distinctive developmental stages; see fig. 29.3 * most reproduce sexually, with dominant diploid stage; usually only gametes are haploid * most have cells organized into tissues, tissues into organs, organs into organ systems (but note sponges, cnidarians... * all are heterotrophic - food ingested into a digestive cav ity9 usually an ALIMENTARY CANAL which reflects the TORUS BODY PLAN * digestion usually extracellular... * adults' tissues (when present) derived from 2 or 3 embryonic tissue layers: * ECTODERM: outer lining & derivatives * ENDODERM: inner lining & derivatives * MESODERM: in "Bilateria' only; yields muscle, connective tissue... * symmetry radial in sponges, cnidarians, ctenophores; bilateral in others (or at least basically so ... ); important for locomotion, feeding,, breeding, dispersal, and cephalization .... See fig. 29.2 * most animals have a COELOM (body cavity) that allows room for development of organs related to food processing, reproduction, elimination of wastes... See figs. 29.4, 29.5. Origin of mouth & anus, formation of mesoderm, and formation and nature of coelom provide basis for broad organization of animal phyla into groups. E.g., acoelomates v. coelomates, pseudocoelomates v. eucoelomates, schizocoels v. enterocoels, protostomes v. deuterostomes. FIG. 29.1: STUDY IT DILIGENTLY & OFTEN! Of the ~35 animal phyla currently recognized, we'll consider only 16 (those on fig. 29.1 + one more minor one)... SUBKINGDOM PARAZOA, PHYLUM PORIFERA - SPONGES: * lack true tissues; "cellular grade of construction" * aquatic; mostly (not all) marine * adults sessile, attached * filterfeeders with unique body structure (figs. 29.6, 29.7): note pinacocytes, porocytes, spongocoel, osculum, choanocytes, amoebocytes, mesohyl, spicules.... * feeding effectiveness & surface-mass relations: asconoid, syconoid, and leuconoid body types: [Image] * reproduce both by asexual and sexual processes: * asexual: budding, fragmentation, GEMMULES.... * sexual: most are HERMAPHRODITIC (=MONOECIOUS); sperm released into spongocoel, swept out, drawn into spongocoel of nearby sponge; fertilization produces a free-swimming AMPHIBLASTULA larva that settles, attaches, evaginates, becomes a sponge. [Image] * Classes: * CALCAREA * HEXACTINELLIDA * DEMOSPONGIAE --------------------------------------------------------------------------- SUBKINGDOM EUMETAZOA: ALL REMAINING PHYLA WE CONSIDER.... THE "RADIATA": Phylum Cnidaria - Jellyfishes & Relatives * radially symmetrical; nerve net (i.e., no brain...) * aquatic, mostly marine... * sessile and attached..., or free-swimming... * carnivorous; digestion first extracellular, then intracellular * "tissue grade of construction"; lack of organs * distinctive body plan: double-walled sac; either a polyp (vase-like, sessile) or medusa (bell-like, free-swimming); i.e., dimorphic life history (see below...) [Image] * body wall of 3 basic layers: * EPIDERMIS * GASTRODERMIS, * MESOGLEA (varies...) * high degree of cellular specialization; note cnidocytes, nematocysts, epitheliomuscular cells... * hydrostatic skeleton... * asexual reproduction includes budding, fragmentation... * sexual reproduction (most dioecious): a "typical pattern" - zygote > planula > polyp (incl. strobila, scyphistoma) > medusa...but there are many variations CLASSES: * Hydrozoa - solitary or colonial, varied life histories * Scyphozoa - jellyfishes... * Anthozoa - corals, sea anemones, etc.; polyps only * Note importance of coral reefs , atolls, re biodiversity, etc. The "Radiata":Phylum Ctenophora comb jellies, sea walnuts * about 50 species, all pelagic, marine * derived from a medusoid ancestor * biradial symmetry, jelly-like mesoglea, translucent (29.12) * possess two tentacles; move by 8 ciliated bands (comb rows) * predators, capturing prey by means of colloblasts (adhesive cells; one sp. has nematocysts) * all are hermaphroditic (monoecious) --------------------------------------------------------------------------- ALL REMAINING PHYLA ARE THE,"BILATERIA" bilateral symmetry; triploblastic; organ grade of construction Phylum Platyhelminthes - flatworms; ~ 20K spp. * considered to be the most primitive of the Bilateria * acoelomate * dorsoventrally flattened, vermiform * gastrovascular cavity, either simple or complex * excretory structures are flame cells (= protonephridia) * moderate cephalization; cerebral ganglia, eyespots, auricles * "ladder-like" arrangement of nerve cords, branches * move by cilia &/or contractions/undulations of body * sperm unique: biflagellated, with 9+1 structure * usually hermaphroditic (some notable exceptions... * life cycles often complex (e.g., fig. 29.15... * four classes: I: Class Turbellaria - turbellarians (29.13-14) * one group (archoophorans) considered to be the most primitive, structurally, of the Bilateria... * marine (most), freshwater, moist land habitats * predaceous, scavengers, grazers; a few parasitic * mucus important; smooths substrate, captures prey * digestion first extracellular, completed intracellularly * some contain mutualistic algae * possess rhabdoids - epidermal structures - similar to nematocysts; some acquire nematocysts from hydroids * reproduce by fission, regeneration, or sexually * hermaphroditic, but cross-fertilize; life cycle ~ simple II & III: Classes Monogenea & Trematoda - flukes (29.15) * obligate parasites, most of them internal * oral sucker (surrounds mouth) & ventral sucker * simple forked gastrovascular cavity * digestion initially extracellular, fmally intracellular * reproduction involves asexual, sexual stages; most are hermaphroditic (but note Schistoma spp.) * complex life cycles; definitive host a vertebrate, first intermediate host a snail: [Image] * salmon-poisoning: carnivore ingests fish harboring metacercariae of Goniobasis silicula, which may harbor the rickettsia Neorickettsia helminthica, which causes salmon-poisoning IV: Class Cestoda - tapeworms (29.16) * highly specialized obligate parasites, usually in gut * unique head (scolex) bears hooks &/or suckers * rest of body is a series of proglottids (the strobila) continually generated from posterior end of scolex and of increasing sexual maturity and age posteriorly * size varies from nearly microscopic to ~ 20 m in length * no gastrovascular cavity;absorb host's digested nutrients * life cycles vary; typically, involve an intermediate host that harbors a bladderworm larval stage.... [Image] PHYLUM NEMERTEA - ribbon worms, or proboscis worms (29.17) * phylogenetic position controversial... * mostly marine (one genus in freshwater); to 2 m long, * acoelomate, vermiform, dorsoventrally flattened, ciliated; some have rhabdites * ladder-like arrangement of nervous system * have protonephridia * unique proboscis, hydraulically-operated capture device * simple circulatory system; some have rbc & Hb, thus have a blood vascular system... * complete digestive tract; protostomous Thus, the nemerteans seem to be intermediate between the acoelomate bilateria and the remaining protostomous phyla. PHYLUM ROTIFERA - rotifers (fig. 29.18) * with the roundworms (next) and several other phyla (e.g., Acanthocephala), are pseudocoelomate, protostomous * common and abundant in freshwater; a few marine spp. * small (0.05-2.0 mm); most ~ size of ciliated protozoa * complete digestive tract (like everything else to come...) * pseudocoelomic fluid provides hydrostatic skeleton, internal transport system (body movements move fluid...) * protonephridia as excretory structures * distinctive structures: corona (ciliated...),mastax, "foot" * reproduction is sexual or parthenogenetic, producing only females, while other parthenogenetic species produce fast-hatching diploid eggs (amictic eggs),which develop only into females, or haploid eggs (mictic eggs) which either develop parthenogenetically into males or, if fertilized, into dormant eggs which eventually hatch into females. An adaptation to uncertainties of life in temporary ponds, etc. PHYLUM NEMATODA - roundworms (fig. 29.19) * protostomous, pseudocoelomate, unsegmented, vermiform * complete digestive tract * body covered with cuticle... * longitudinally-arranged muscles * pseudocoelomic fluid provides internal transport * nearly all are dioecious & have internal fertilization; females may produce more than 100,000 fertilized eggs/day * exceptionally diverse and abundant; ubiquitous... * size from < 1 mm to > 1 m * includes many important parasites of plants and animals The "annelid/arthropod/mollusc superphylum" - the major protostomous, eucoelomate, schizocoelomate phyla: fig 29.4-5 --------------------------------------------------------------------------- Phylum Mollusca - mollusks * >50,000 species known * most species are marine, but widely distributed; include some that can live with dry exterior (land, snails).... * unique body plan: foot, visceral mass, mantle; also the mantle cavity, which encloses gills, anus, excretory pores (see figs . 29.20, 29.22, 29.25); calcareous shell is typical * gas exchange by gills, lungs, mantle, or body surface * excretion by 1 or 2 kidneys (metanephridia) * special feeding structure is the radula (fig. 29.20) * schizocoelom, typically reduced to a small space, the hemocoel, around the heart * blood vascular system is open (note limitations and, the exception, Class Cephalopoda...) * most are dioecious, but many snails are monoecious * many marine species have a trochophore larva which is also typical of marine annelids and some other protostomes; others have a derived larva called a veliger; some develop directly [Image] * lack metameric segmentation.... * Classes (only 4 of the 8): * Polyplacophora: chitons; all marine, with 8 dorsal plates; common intertidal animals; graze on algae * Gastropoda: > 40K spp., incl. snails, slugs; broad ecological distribution; torsion in snails; "lung".... * Bivalvia: clams, etc.; shell of 2 halves; filter-feeders; no radula; cephalization obscure; ~ sedentary.... * Cephalopoda: squids, octopuses, nautilus; largest & most intelligent of invertebrates! Predaceous. Foot -> siphon + tentacles + part of head; shell reduced, internal (except nautilus); squids fast, pelagic; octopus benthic; eyes convergent with vertebrate eyes.... Digression 1: Some minor phyla: Three lophophorate phyla: * Phoronida (tube-dwelling, worm-like, marine); * Bryozoa ("moss animals"; tiny, colonial, mostly marine with some reef-builders - fig. 29.27); and * Brachiopoda (lamp shells; shell with dorsal, ventral halves, attached by stalk, all marine; note Lingula....) The position of the lophophorates now thought to be closer to protostomes (molecular evidence), despite coelom devel't. Lophophore is their feeding structure.... Digression 2: Kinds of similarity and their significance: * Homoplasy: similarity in appearance only; examples.... * Analogy: similarity in function; examples.... * Homology: similarity based on common body of genetic information; examples.... Understand these concepts and their implications!!! Phylum Annelida - segmented worms * protostomous, schizocoelous,, etc.; most are vermiform * body has both longitudinally and circularly arranged muscles (note implications for movement ... ) * have homonomous metameric segmentation... * 1 pair of metanephridia per body segment, each with a nephrostome (ciliated funnel) draining segment before it * have a closed blood vascular system, with multiple "hearts" derived from main dorsal vessel (note direction of flow) * ubiquitous in aquatic and moist terrestrial habitats * respire through body surface or through "gills" * nervous system organized as 1 pr cerebral ganglia, two ventral nerve cords,, and paired segmental ganglia and nerves; * distinctive structures include setae and parapodia (in marine annelids; homologous with paired lateral appendages in arthropods?) * monoecious or dioecious; trochophore larva (marine spp.) or direct development; some capable of complete regeneration * Classes: * Oligochaeta: earthworms and relatives (fig. 29.28); familiar occupants of moist soils; many pairs of setae; no parapodia; clitellum is prominent; highly significant 46 macrodecomposers"; hermaphroditic, cross-fertilize * Polychaeta: most are marine; pelagic, benthic, sometimes in self-secreted tubes; prominent parapodia, bearing many setae, provide for locomotion, gas exchange; tentacles about mouth,,which in predatory spp. bears chitinous "jaws" and "teeth"; usually dioecious, but lack permanent sex organs; note palolo worm... * Hirudinea: leeches (f. 29.29c); no parapodia or setae; first and last segments, respectively, modified as anterior and posterior suckers, the anterior one encircling the mouth; coelom undivided; most are monoecious, cross-fertilize; clitellum present only in breeding season parasites or carnivores, with "jaws"; note Hirudo medicinalis.... --------------------------------------------------------------------------- Phylum Arthropoda - arthropods. - "most successful animals"... * protostomous, schizocoelous, etc.... * basic body plan as in annelids, but significant modification * schizocoelom reduced to a hemocoel * circulatory system is open...; heart is dorsal * have metameric segmentation, but an important trend is - * segments often grouped into major body regions (tagmata); e.g., head, thorax, & abdomen, or cephalothorax, abdomen * paired, jointed, lateral appendages; primitively l pr/segment but variously reduced, highly specialized (serial homology) * chitinous exoskeleton (chitin + protein, sometimes + CaCO3); must be molted (ecdysis) to allow growth * highly complex arrangement of muscles (made possible by jointed exoskeleton ... ) * gas exchange by body surface, "gills", tracheae, or book lungs; includes most spp. of "dry air" dwellers.... * excretory organs either paired glands (homologous with metanephridia of mollusks) or Malpighian tubules * nearly all dioecious, with permanent sex organs; some are seasonally parthenogenetic * nervous system annelid-like, but sensory and motor capabilities much more complex (e.g., most insects fly) * 4 important evolutionary trends: * reduction in total number of segments * grouping of segments into tagmata * increasing cephalization * specialization of appendages for uses other than locomotion Compare a beetle (highly derived) with centipede or Peripatus Why are arthropods so successful? 1. . Exoskeleton: protection (but note liabilities.... 2. . Segmentation + jointed appendages: many adaptations.... 3. . Superior gas exchange (terrestrial spp.): makes high metabolism possible 4. . Superior sensory systems: visual, acoustic, chemical, mechanical, proprioceptive receptors well-developed 5. . Complex behaviors, both innate and learned.... 6. . Use of diverse resources through metamorphosis: e.g., individuals of a species at different metamorphis stages use different resources, reducing intraspecific competition. As the ultimate example of all these, consider beetles.... Note Peripatus (Ph. Onychophora; fig 29.3 1): long considered to be descended from an ancient common ancestor for Annelida and Arthropoda; however, molecular evidence doesn't support this view; perhaps annelids and arthropods arose independently from an unsegmented protostome close to mollusks, and segmentation developed independently in the two phyla.... Subphyla (4) and some classes of arthropods: *Subphylum Trilobitomorpha - trilobites (fig. 29.32) - common marine animals throughout Paleozoic; vanished during the Permo-Triassic extinction event. Subphylum Cheliceriformes - *eurypterids, horseshoe crabs, spiders, pseudoscorpions, scorpions, harvestmen, ticks, etc. * body organized into cephalothorax and abdomen * six pairs of appendages; first pair are chelicerae; second pair are pedipalps (e.g., pincers of a scorpion); remaining four pairs are walking legs * no mandibles, no antennae, simple eyes * Classes: * Merostomata - *eurypterids, horseshoe crabs * Arachnida - Spiders; predaceous, envenomate prey, ingest liquified tissues; gas exchange by book lungs and unique in use of silk to capture food, etc. (29.35) * Scorpions; also predaceous, with last segment as sting w/venom gland. (29.34a.) * Harvestmen; cephalothorax and abdomen broadly joined. Predominantly scavengers. * Ticks & mites: free-living, parasitic, scavenging, or commensalistic depending on species and stage in life cycle. (29.34b & c.) The next two subphyla are similar in having mandibles, 1-2 pr of antennae, and (usually) a pair of compound eyes. They differ as noted below: Subphylum Uniramia - millipedes, centipedes, insects. * have one pr antennae, * appendages are unbranched (uniramous) * probably evolved on land; note significance of exoskeleton for support, movement, resistance to evaporation; also superior mechanisms for gas exchange, even in dry air * Classes: * Diplopoda - millipedes; terrestrial; head of 3 segments; trunk organized into diplosegments, so appear to have 2 pr legs/segment; scavengers; note chemical defenses, aposematism. (Fig. 29.36a.) * Chilopoda - centipedes; terrestrial; head of 3 segments, trunk segmentation typical; predaceous; use poison claws on anteriormost trunk segment to paralyze prey * Insecta - insects; in - every environment except marine; adult body organized into: * head (3 segments), * thorax (3 segments, each with 1 pr legs; also, thorax typically bears 2 pr of wings), & * abdomen (9-1 1 segments); includes more species than all other taxa combined; see Table 29.1 for some of the major orders, and note variety in body forms, etc. Insects also remarkable for variety in life cycles, from direct development (e.g., silverfish, springtails; the primitive condition) to hemimetabolous metamorphosis ("incomplete metamorphosis"; e.g., grasshoppers, true bugs - go through series of nymph stages) to holometabolous metamorphosis (complete metamorphosis - egg, larva with instars, pupa, adult; e.g., beetles, flies, bees, butterflies - nearly 90% of all insects.) Complete metamorphosis allows individuals of a species to saturate the environment in different stages of life cycle while reducing intraspecific competition, especially among the adults. Subphylum Crustacea - crabs, barnacles, shrimp, etc. (see fig. 29.40). * two pr antennae * appendages are basically branched (biramous) * evolution and greatest diversity in aquatic environments * several small classes; the two main ones are: Maxillopoda - includes ostracods, copepods, and barnacles; ostracods and copepods important in aquatic food chains; barnacles unusual in that the exoskeleton is hardened with calcium carbonate.... Malacostraca - crabs, lobster, isopods, shrimp; esp. remarkable for diversity regional specialization of appendages; hard to overstate importance. The phyla remaining to be discussed are deuterostomous, have radial & indeterminate cleavage, & are enterocoelous. Two minor phyla (Chaetognatha, Hemichordata) & two major ones: Phylum Echinodermata - sea stars/urchins/sea cucumbers, etc. * described as a "noble group especially designed to puzzle the zoologist' (Hyman). Unique array of characteristics.... * secondary radial pentamerous symmetry (but basically bilateral) * lack cephafization; no head or brain! * dermal endoskeleton composed of calcareous plates, typically with spines or bumps, and covered with a thin epidermis * water vascular system, derived from coelom; opens to outside through the madreporite, and extends by means of hydraulic canals into the numerous tube feet * tube feet: food procurement, locomotion, gas exchange * gas exchange also via dermal branchiae * pedicillariae sometimes present... * body not segmented * no specialized excretory organs; circulatory system reduced * exceptional ability to autotomize, regenerate lost parts * dioecious; develop through free-swimming bilateral larval stages; larva of the dipleurula type, which is bilateral * all are marine! * Classes: Asteroidea - sea stars (29.41, 29.42a, b); "typical" echinoderms; predaceous, using tube feet; stomach everted through mouth to envelope, digest prey... Ophiuroidea - brittle stars (29.42c); note distinct central disc, arms don't join each other at disc; move by flailing about with the arms Echinoidea - sea urchins (29.42d), sand dollars; lack arms, move by spines . . .; grazers (sea urchin-sea otter story); sea urchins have unique masticatory apparatus, Aristotle's lantern Crinoidea - sea lilies (29.42e); sedentary or attached; a very ancient group.... Holothuroidea - sea cucumbers (29.42f); no spines; endoskeleton greatly reduced; elongated body; some tube feet specialized as feeding tentacles; unusual regenerative ability.... Read text material on "Cambrian explosion" for general information and perspective. Some major body plans appear in rocks -700 myo; all major plans appeared by -545 mya --------------------------------------------------------------------------- Phylum Chordata - lancets, tunicates, vertebrates; highly diverse in adult forms and habits, but united by having at least some time in their lives - * a notochord - a stiffening but flexible rod dorsal to the gut and ventral to the nerve cord; fulcrum for the * segmentally arranged antagonistic muscles of the trunk and tail, alternating contractions of which provide for movement by lateral undulations, especially of the tail... * a dorsal, hollow nerve cord, derived from dorsal ectoderm and which develops into the brain, spinal cord, nerves * pharyngeal slits, which originally were an adaptation that made filter-feeding more effective and secondarily became useful as well as structures for effective gas exchange * a postanal tail, highly significant in locomotion... * metameric segmentation (but merely convergent with that seen in annelids, arthropods); see fig. 30.4 for examples There are three subphyla, two of which are entirely marine and never develop a bony vertebral column. 1. Subphylum Urochordata - tunicates (30.2); most sessile, attached as adults (30.2a, b); have a free-swimming larva (30.2c). Adults are the ultimate filter-feeders.... The larva is considered by some to represent a living version of a creature that may have been ancestral to cephalochordates & vertebrates through paedogenesis (sexual maturity as an immature form; sometimes carelessly called neoteny, which correctly refers to retention of some immature features by an adult. Examples...) 2. Subphylum Cephalochordata - lancets (30.1, 30.3); burrow near the surface of marine sediments, sands; filterfeeders; typify the primitive chordate plan even as adults; molecular evidence suggests that lancets are the closests relatives of vertebrates. [exclusively marine]. 3. Subphylum Vertebrata - fish, amphibians, reptiles, birds, and mammals; more than 40,000 spp (most of them fish ... ) In addition to the basic chordate features, vertebrates are distinguished by - : * presence of a bony endoskeleton, organized into axial (cranium, ribs, vertebral column) and appendicular (limbs, limb girdles) portions; replaces notochord; bone is secondarily lost in living jawless fishes, cartilaginous fishes; improved locomotor ability, greater body size, more effective foraging, etc. * well-developed cephalization and highly developed nervous system; complex neuromotor, sensory, learning abilities * well-developed endocrine system; esp. important in control of long-term events... * well-developed blood vascular, gas exchange, and excretory systems, high level of activity in foraging, etc. Classification of vertebrates: done in several ways; text uses a "traditional" approach, recognizing one extinct class (*Placodermi - ancient jaws fishes) and 7 classes with living representatives: 1. Agnatha; 2. Chondrichthyes, & 3. Osteichthyes, collectively called fishes (Pisces); and 4. Amphibia, 5. Reptilia, 6. Aves, & 7. Mammalia, collectively called tetrapods (Tetrapoda). Significant adaptive breakthroughs are associated with each of these groups, although not all living species may show them. Major breakthroughs (which are cumulative as shown here) and the group in which they first appear include: * jaws: first appear in *Placodermi, or perhaps in a group of archaic bony fish, the *Acanthodii. (The relationship between these two groups is controversial.) * two pairs of lateral appendages supported by endoskeletal structures: Osteichthyes, specifically a group known as the Sarcopterygii (lobe-finned fishes), ancestral to Amphibia * lungs (or their homologues): Osteichthyes (or perhaps in the placoderms.) The swim bladder seen in many more highly derived bony fish is a modification of the ancestral lung. * lateral appendages with elbow & wrist, knee & ankle joints: Amphibia. Made possible effective movement on land... * amniotic egg: Reptilia. Amnion made it possible to lay eggs out of water, since the amnion enclosed the "ancestral pond" as well as the developing individual. * endothermy: probably Reptilia. Ability to regulate body temperature metabolically made it possible to live and remain active in thermally hostile environments.... * feathers (Aves) and hair (Mammalia): make endothermy somewhat less expensive.... * vivipary (giving birth to young): has appeared, perhaps independently, in all vertebrate classes except for Agnatha and Aves. Nearly universal in mammals, not uncommon in reptiles, the rule in sharks and their relatives.... Improved matemal care, opportunity to train young, etc. * other important adaptations, neither unanimous nor unique, include indirect & direct development, internal fertilization. See Figure 30.6 for relationships and adaptive breakthroughs among the vertebrates. Consult this figure often! --------------------------------------------------------------------------- Some notes on the classes of vertebrates: Class Agnatha - *ostracoderms, lampreys, hagfishes. Jawless; lampreys & hagfishes have soft cartilaginous skeletons, lack lateral appendages; median fins present. *Ostracoderms, the first vertebrates, had bony skeletons; appeared ~ 510 mya, probably in marine water. Lampreys parasitic, anadromous; hagfishes saprozoic, marine. Many pr gill pouches. Oviparous. *Class Placodermi - archaic jawed (gnathostomous) fishes with at least some bone in their skeletons. One pair pectoral, I pr pelvic appendages + median fins. Mostly marine. Important during Devonian; rapidly replaced by chondrichthyans at end of Devonian. Relationship to bony & cartilaginous fishes unclear. Class Chondrichthyes - cartilaginous fishes [sharks, skates, rays (the elasmobranchs) and ratfishes]. Gnathostomous, with 1 pr each of pectoral & pelvic appendages, + median fins. Skeleton never bony. Teeth not fused to jaws, replaced serially. No lungs or swim bladder. Usually 5 pr gill slits. Fertilization usually internal; ovoviviparous. Isoosmotic with sea water by retention of urea, trimethylamine oxide. Mostly marine. Class Osteichthyes - bony fishes (all have at least some bone in their skeleton.) Gnathostomous, typically with 2 pr lateral fins + median fins (many exceptions). Groups: *Acanthodii (ancestral to other bony fishes?); Sarcopterygii [lungfishes & lobe-finned fishes (ancestral to amphibians)]; & Actinopterygii (ray-finned fishes; most living bony fishes). Gills beneath an operculum. Lungs (primitive) or swim bladder (derived) usually present. Most oviparous. Represented any place that will support a fish! Class Amphibia - frogs, salamanders, apodans; ~4600 extant spp. Gnathostomous; usually 2 pr limbs, each with 2 flexures (elbow/wrist, knee/ankle - the tetrapod limb); adults lack median fins on body. Ectothermic. Epidermis highly permeable to water. Usually with I pr lungs (lacking in plethodontid salamanders); retention of gills considered a persistent larval characteristic. Most are oviparous; usually a larval stage. Note paedogenesis. N-waste ammonia in larvae, urea in adults. Class Reptilia - crocs., turtles, snakes, lizards (& more.... -6000 living spp. Gnathostomous; usually 2 pr limbs (except snakes) of tetrapod design. Living forms ectothermic. Thick, comified epidermis resists movement of water. All respire with lungs, never gills or external surface. Amniote egg! Most oviparous; many in cool environments ovoviviparous or truly viviparous. Incl. ancestors of birds, mammals. N-waste uric acid Class Aves - birds. At least 10,,OOO spp (20K?) Gnathostomous; 2 pr limbs, pectoral pr usually modified as wings. Endothermic; feathers present, -> insulation & more. Epidermis comifted, - resistant to water loss. Respire by lungs; air sacs important in ventilation. Amniote egg. All oviparous (body temp. too high?). Living forms toothless. N-waste is uric acid. Class Mammalia - mammals; - 5000 spp. Gnathostomous; 2 pr limbs (except whales, sirenians). Endothermic; hair present, usually abundant. Epidermis thick, comified. Respire by lungs; muscular diaphragm aids ventilation. Amniote. All but duckbill & echidnas are viviparous; either yolk-sac placenta (marsupials) or chorio-allantoic placenta. Young fed milk. N-waste is urea. --------------------------------------------------------------------------- (Higher directories and ASCII versions: http://www.europa.com/~rsc/biol252/)