- Animal phylogeny:
Know the basic family tree of animals
as currently understood.
- Animal phyla:
Know the various animals phyla and their characteristics, as follows:
- Porifera: sponges, organized as a single tissue, with numerous pores and many sharp spicules.
- Cnidaria: radially symmetrical animals with two tissue layers (ectoderm and endoderm),
separated by a jelly-like mesoglea; and an all-purpose gastrovascular cavity with a
single opening (mouth). Tentacles surround mouth and have stinging cells (cnidocytes)
containing stingers (nematocysts).
- Class Hydrozoa: Life cycle includes both asexual polyps (solitary or colonial) and
sexually reproducing medusae (usually small).
- Class Scyphozoa: Solitary "jellyfish" with dominant medusa stage.
- Class Anthozoa: Sea anemones and corals, with polyp stage (solitary or colonial) dominant; no medusa.
- Ctenophora ("comb jellies"): Marine anmimals with biradial symmetry, 2 large tentacles,
and 8 comb-like rows of cilia.
- Platyhelminthes (flatworms): Bilaterally symmetrical, triploblastic animals with a flat body but no
coelom; dorsal and ventral surfaces differ; no circulatory system. Sense organs and brain are
concentrated at anterior end (cephalization) to form a head. A single all-purpose
gastrovascular cavity, as in Cnidaria; single opening (mouth) also functions as anus.
- Class Turbellaria: Mostly free-living; digestive tract and sense organs
still present; mouth often in middle of ventral surface.
- Class Trematoda: Small, parasitic worms (flukes) with small, oval
bodies; digestive tract simple; mouth at anterior end.
- Class Cestoda: Highly degenerate internal parasites (tapeworms)
that have lost their digestive tract, nervous system, and sense organs.
- Small, acoelomate phyla related to flatworms: Mesozoa, Acoela, Gnathostomulida
- Rhynchocoela or Nemertea: "Proboscis worms" with a
long, stick-like proboscis or "evert" that can be withdrawn by
turning it inside out.
- NOTE: The phyla listed below as Rotifera through Pogonophora all belong to the Lophotrochozoa.
- Rotifera: Rotifers, with a wheel-like crown of cilia at one end.
- Acanthocephala: Spiny-headed, parasitic worms.
- Four bottom-dwelling phyla with ciliated lophophores and simple U-shaped digestive systems:
- Phoronida: Tube-dwelling worms with a lophophore surrounding the mouth.
- Bryozoa ("moss animals"): Small, aquatic animals living in colonies; a large, successful group.
- Brachiopoda: Two-part shell with unequal upper and lower valves; long fossil record.
- Entoprocta: A small group of sessile (attached) animals related to the previous 3 phyla.
- Mollusca: Animals with a true coelom, usually bearing a calcium carbonate shell secreted by a mantle
that is withdrawn at one end to form a mantle cavity. Primitive mollusks and snails creep on a
muscular foot and use a tongue-like radula with embedded teeth to scrape encrusted algae
from rock surfaces. This phylum includes:
- Class Monoplacophora: Primitive mollusks, with a simple dome-shaped shell.
- Class Gastropoda (snails and slugs): Body usually undergoes asymmetrical torsion so that
one-piece (univalve) shell is usually coiled; well-developed head, nervous system and sense organs.
- Class Polyplacophora (chitons): Flattened body, with shell divided into overlapping plates.
- Class Bivalvia or Pelecypoda (clams, etc.): Body usually symmetrical, narrowly compressed from side to side. Two-piece
(bivalve) shell, with head and sense organs poorly developed. Muscular foot hatchet-shaped
(flattened side-to-side), often used in burrowing.
- Class Scaphopoda (tusk-shells): Small mollusks with tusk-like shells.
- Class Cephalopoda (octopuses, squids, nautiloids, etc.):
Body usually symmetrical. One-piece shell is symmetrically curved or coiled
in median plane, or often lost. Most species are actively swimming predators.
Head very well-developed, with sense organs (especially eyes), brain, and
beak. Muscular foot subdivided into numerous tentacles.
Body doubled over, with mantle cavity (originally rear) tucked beneath head
and opening forward. Frequent "ink glands" that secrete dark, inky fluid to confuse predators.
- Annelida: Segmented worms, with true coelom, outer covering of chitin, and most internal organs
segmentally arranged. This phylum includes:
- Class Polychaeta: Largest group, mostly marine. Sense organs and nervous
system highly developed; several setae (bristles) per segment.
- Class Oligochaeta (earthworms): Poorly developed head; only one pair of
setae per segment. Important to soil because their digestive wastes leave
behind soil nutrients and their tunnels let air reach plant roots.
- Class Hirudinea (leeches): Mostly blood-sucking external parasites that live in fresh water.
- Several smaller phyla related to the Annelida:
- Sipunculida: Marine worms with tentacles around the mouth.
- Echiurida: Sausage-shaped worms with a tube-like extension
in front of the mouth.
- Chaetognatha: Arrow worms, with dart-shaped bodies, abundant
in marine plankton.
- Gastrotricha: Gastrotrichs.
- Pogonophora: Deep-sea tube-dwelling worms.
- NOTE: The phyla listed below as Nematoda through Arthropoda all belong to the Ecdysozoa.
- Nematoda (roundworms): Small worms with tapering ends, very abundant in many environments.
Some are free-living,
but many are parasitic on plants or animals.
- Gordiacea or Nematomorpha: Very long, thin "horsehair worms."
- Cephalorhyncha: Small, marine worm-like parasites with a proboscis, covered with spines,
that can either be withdrawn or turned inside out and everted.
- Pentastomida: Endoparasites inside vertebrates, with 2 pairs of short, degenerate legs armed with claws.
- Tardigrada: Tiny "water bears," with 8 short legs ending in claws.
- Onychophora: An ancient group (Cambrian to Recent), closely
related to arthropod ancestors. Segmented, wormlike body. Numerous short feet
(1 per segment), ending in claws. Feet around mouth function in seizing and
tearing food.
- Arthropoda: Animals with a tough exoskeleton, often strengthened by calcium salts, and jointed legs
with movable joints between rigid segments. Metamerism (segmental organization), but segments
differ very much regionally. Mouthparts often derived from legs. Open circulatory system. Several
anterior segments commonly coalesced into a head. Nervous system reminiscent of annelids, with
ventral nerve cord, esophageal ring, and dorsal brain. Included groups:
- Trilobites: Extinct, marine arthropods with numerous similar
biramous (two-branched) appendages, each with a leg-like part and
a feathery gill. Body divided into cephalon (head), thorax,
and pygidium. May be ancestral to other arthropods (but experts
disagree on this). Flat-bottomed shape shows that most trilobites were
bottom-dwellers.
- Crustacea: A largely marine group of arthropods, breathing by gills.
Always two pairs of antennae. First post-oral segment has a pair of
mandibles. Appendages biramous (two-branched), as in trilobites.
Includes lobsters, crabs, shrimp, barnacles, and many other species.
- Chelicerate groups: Originally marine arthropods, but one large
group successfully invaded land environments. No antennae are present.
First 2 pairs of appendages include a pair of chelicerae (piercing
structures that may be used to inject venom) and a pair of pedipalps
which may hold prey while the chelicerae pierce them. Many chelicerates
are predators. Body usually divided into cephalothorax and abdomen (except
in mites). Includes Pycnogonida (sea spiders), Xiphosura
(horseshoe crabs), and Arachnida (scorpions, spiders, mites, etc.).
- Uniramous "myriapods": Arthropods with elongate, worm-like
bodies and many pairs of legs. Includes centipedes (Chilopoda),
millipedes (Diplopoda), and two other groups (Pauropoda,
Symphyla) allied to insects. All myriapods have similarities that
they share with insects: a single pair of antennae; a pair of mandibles;
uniramous appendages (having only a single branch); respiration
using a tracheal system of air-tubes. Habitats usually terrestrial,
often hiding beneath rocks and rotting logs.
- Insects: The largest and most successful group of arthropods,
including about 75% of all species in the entire animal kingdom.
Mandibles, uniramous appendages, and tracheal systems as in myriapods.
Division of the body into three portions: head (containing antennae,
mouth, and compound eyes), thorax (typically with three pairs of walking
legs and two pairs of wings), and abdomen or 7 or more segments
(containing reproductive structures).
- Evolutionary advances (and degeneracies):
Be familiar with the major
evolutionary advances within the animal kingdom,
and the advantages that each one confers.
Examples include:
- Gastrulation, and organization into multiple tissue types (in two germ layers initially, then three).
- Bilateral symmetry and cephalization
- Complete ("assembly-line") digestive system
- Degeneracy resulting from parasitism
- Evolution of a body cavity
- Evolution of ciliated bands that serve different functions (lophophore, ciliated larvae, etc.)
- Evolution of a resistant cuticle, and the need for molting (and molting hormones)
- Differences between protostomes and deuterostomes
- Notochord, segmental muscles, dorsal hollow nerve cord, and gill slits
- Amniote (cleidoic) eggs
- Homeothermy; parental care and feeding
- VOCABULARY TO KNOW:
Animalia: Kingdom of multicellular organisms that develop from a hollow ball of cells (blastula);
motility usually present at some life stages or in certain cells.
Blastula: An early embryo consisting of a hollow ball of cells.
Blastocoel: The hollow cavity inside the blastula.
Gastrula: A 2- or 3-layered embryo derived from a blastula by tucking-in (invagination).
Archenteron: The inside cavity ("primitive gut") of a gastrula.
Blastopore: The entrance to the archenteron from the outside.
Diploblastic: Containing 2 germ layers (ectoderm and endoderm), as in Cnidaria.
Triploblastic: Containing 3 germ layers (ectoderm, mesoderm, and endoderm), as in Bilateria.
Ectoderm: Outermost germ layer, giving rise to outer epidermis and in many cases also to nervous system.
Mesoderm: Middle germ layer, giving rise to muscles, bones (when present), kidneys,
reproductive organs, and most connective tissues.
Endoderm: Innermost germ layer, giving rise to inner lining of the gut (also to lungs, liver, pancreas, etc.).
Tissue: A group of similar cells and their products, built together (structurally integrated) and
working together (functionally integrated).
Spicules: Sharp needles or more complex shapes embedded within sponges, functioning in support and
as a defense against predators.
Mesoglea: Jelly-like layer between ectoderm and endoderm in Cnidaria.
Polyp: Cnidarian body form with the mouth directed upward, mesoglea thin, animal usually attached
(as in corals).
Medusa: free-swimming "jellyfish" body form some Cnidaria, with thick mesoglea;
mouth directed downward.
Bilateria: Major group of phyla containing all triploblastic animals with bilateral symmetry.
Radial symmetry: Structure that looks the same when viewed from any angle around a circle.
Biradial symmetry: Symmetry of a 2-armed pinwheel, looking the same if rotated 180 degrees.
Bilateral symmetry: Structure in which the right half is a mirror image of the left half; symmetry
across a central (median) plane.
Cephalization: Building of a head by concentration of sensory structures, etc., at the forward end.
Protostome: Animals whose embryos exhibit spiral, determinate cleavage and whose blastopore
forms the future mouth.
Deuterostome: Animals whose embryos exhibit radial, indeterminate cleavage and whose blastopore
is located near the future hind end, with the mouth forming secondarily at the opposite (front) end.
Radial cleavage: Embryonic cell division producing, in the 3rd cleavage, four smaller cells directly
atop four larger cells.
Spiral cleavage: Asymmetrical cell division in the 3rd embryonic cleavage, producing four smaller
cells staggered between the tops of four larger cells.
Determinate cleavage: Cleavage in which embryonic fate is determined early, so that a cell on the
right loses the ability to form structures on the left.
Indeterminate cleavage: Cleavage in which embryonic fate is determined late, so that cells experimentally
isolated from early embryos are still able to form structures both right and left, front and rear, etc.
Pseudocoel: A body cavity, lined with multiple germ layers, derived from a persistent blastocoel cavity.
Coelom: A body cavity lined entirely with mesoderm.
Enterocoel: A true coelom formed by outpouching of the gut (as in starfish).
Schizocoel: A true coelom formed within the mesoderm by splitting (as in mammals).
Lophotrochozoa: A large and diverse group of phyla characterized by ciliated bands, present
either in "trochophore" larval stages or as a feeding structure (lophophore); includes Mollusca,
Bryozoa, Annelida, and many smaller phyla.
Trochophore: A larval stage using bands of cilia for motility.
Lophophore: A suspension-feeding organ made up multiple ciliated tentacles.
Cuticle: A hardened, chemically resistant outer body covering.
Ecdysis (molting): Shedding of the cuticle and growing a new, larger cuticle after the body rapidly enlarges.
Ecdysone: Hormone that controls molting and associated changes in behavior and development.
Ecdysozoa: A group of phyla that undergo ecdysis, including Nematoda, Arthropoda, etc.
Filter feeding (=suspension feeding): Feeding by filtering small, suspended food particles from the water.
Mantle: An epidermal layer that secretes a calcium carbonate shell in mollusks.
Mantle cavity: Cavity formed by withdrawal of the mantle cavity (primitively at the posterior end);
it contains the anus and gills.
Radula: A tongue-like scraping organ with embedded teeth, used by mollusks for feeding.
Metamerism: Division of the body into numerous similar segments.
Biramous: Two-branched.
Uniramous: One-branched.
:
** Also the animal phyla and classes listed above. **
- MORE DETAILS are contained in the following outlines:
21.Sponge 22.Flatworm
23.VideoHighlights 25.Protostomes
27.Ecdysozoa 26.Lophotrochozoa
28.Form/Function 29.Deuterostomes
- THIS GUIDE will continue to be revised.
It is still tentative.
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