Transcript Animals II

-Hox-genes. Homeobox-containing in structure (contain
common modules of DNA sequences) and homeotic in
function (regulatory genes that function in the
development of body form).
-Animals probably evolved
from a colonial, flagellated
protist “choanoflagellate”
that lived over 700 MYA in
the Precambrian era.
-There are about 35 phyla of animals, most of
them marine, totaling over one million species.
-Embryonic development.
Mitotic cell divisions
Multicellular stage
mesoderm, diploblastic, triploblastic, enterocoely,
schizocoely, fate of the blastopore
Cells relatively
unspecialized.
Loose
coordination of
cells.
Specialized
and integrated
cells.
Parts radiate
from center.
Top (oral) and
bottom
(aboral). No
head, rear,
left, right.
Ectoderm and
endoderm
Central axis. Top
(dorsal), bottom
(ventral), anterior,
posterior, left, right.
Ectoderm,
endoderm, and
mesoderm
No space
between
digestive
tract and
body wall.
schizocoely
enterocoely
Fluid filled
space between
digestive tract
and body wall.
Crown of
ciliated tentacles
used for
feeding.
Phylogenetic tree of animals based on nucleotide sequencing in
the small subunit ribosomal RNA
Coelom
development
happened early and
the acoelomate
condition represents
the loss of the
coelom
Combine
animals with
lophophore
with animals
with a
trocophore
larval stage.
Name: secrete
external
skeletons,
molt.
Most animal phyla originated in a brief span of
geological time.
About 40 million years (about 565-525 MYA) during the late
Precambrian and early Cambrian.
-Ediacarian diversity (Precambric).
First solid evidence. Limited animal diversity. 565-543 MYA.
-Cambrian explosion (Precambric).
Rapid diversification of phyla. 543-525 MYA. Hypotheses:
Ecology- Emergence of predator-prey relationships.
Geology- e.g. atmospheric O2 to support more active metabolism.
Genetics- Evolution of the Hox complex of regulatory genes.
Hypotheses are not mutually-exclusive.
Not one but three Cambrian explosions?
Bilateria: Lophotrochozoa, Ecdysozoa, Deuterostomia.
SUMMARY
•Animals are eukaryotes, multicellular, heterotrophs
lacking cell walls but possessing unique intercellular
junctions, nervous and muscle tissues, and Hox genes.
•The diversity of animal phyla has been studied by
looking at body plan and embryonic development and at
Small Subunit-rRNA.
•Both types of phylogenetic trees are similar in deepest
branches and deuterostomes.
•Trees differ in protostomes.
- Ecdysozoans & Lophotrochozans
•Most animal phyla originated in a brief span of
geological time (40 million years) in the Cambrian
explosion. 543-525 MYA
Multicellularity,
even if loosely
coordinated,
allows sponges
to draw food
from their
surroundings
into their body:
choanocytes
(unique in the
animal
kingdom).
Phylum Porifera “pore bearer”: sponges
-Sessile (permanently attached).
-Without true tissues (cells relatively unspecialized).
~9,000 spp., most of them marine. Height: <1 cm to 2 m.
-Body resembles a sac perforated with holes.
-No true tissues, yet cells sense and react to changes.
-Central cavity (spongocoel), large opening (osculum).
-Outer epidermal cells, internal choanocytes (“collar cells).
-Mesohyl (gelatinous region), amoebocytes.
-Skeletal fibers: spicules (CaCO3 or silica) or spongin.
-Suspension-feeders (collect food particles from water passed
through a food-trapping mechanism).
Tissues allow
for different
cells to take
different roles:
cnidocytes,
unique in the
animal
kingdom, and
extracellular
digestion by
gastrodermis
allow food
larger than
individual
cells.
Phylum Cnidaria “nettle”: cnidarians
-Over 10,000 species, most marine. Diameter up to 2 m.
-Sac w/ gastrovascular cavity (central digestive compartment with one opening).
-Muscles and nerves simple, with little central control.
-Hydra, jellies, corals, anemones, sea fans, Portuguese man-of-war.
-Sessile polyp (adhere by aboral end), floating medusa (oral end
downward).
-Two cell layers: epidermis (outer, protection), gastrodermis (inner,
digestion). Gelatinous layer of mesoglea between them.
-Carnivores, tentacles around the mouth capture prey.
-Tentacles armed with cnidocytes: defense and capture of prey.
-Food partially digested in gastrovascular cavity, but outside cells
(extracellular digestion), fragments then ingested by the cells for
intracellular digestion.
Radial
symmetry:
detection and
response to
stimuli equally
from all
directions .
Phylum Ctenophora “comb bearer”: comb jellies
Eight rows of comblike plates composed of fused cilia, used
for locomotion.
Diameter: 1 to 10 cm.
Bilateral symmetry:
allows
encephalization and
high levels of
specialization in the
form of organs
Phylum Platyhelminthes “flat worm”
-Over 20,000 spp., in marine, freshwater, and damp terrestrial habitats.
-Length: <1 mm to over 20 m.
-A thin body between dorsal and ventral surfaces, NO coelom.
-Bilateral symmetry.
-Flatworms, trematodes, tapeworms.
-Carnivores, scavengers (eat dead animals), parasites.
-Spill digestive juices on food, pharynx (muscular chamber ending in
mouth) sucks food pieces into gastrovascular cavity for more digestion.
-Clusters of nerve cells (ganglia) near the head and longitudinal nerve
cords constitute a simple central nervous system.
-Eyespots detect lights.
Color: serves
as a
hydrostatic
skeleton
against which
the muscles
can work,
making
movement
more efficient
than in
acoelomates.
Phylum Rotifera- “wheel bearer”: rotifers
-Crown of cilia that draws a vortex of water into the mouth.
-Size: 0.5 to 2 mm.
-Pseudocoelom.
-Have a complete digestive tract.
Many evolutionary
trends that become
fully developed in
more derived
animals make their
first appearance in
ribbon worms,
such as complete
digestive tract.
Phylum Nemertea- “Nemertes”: ribbon worms
~900 spp., most marine, few in freshwater and damp soil.
-Length: <1 mm to 30 m.
-Similar to flatworms, but have a small fluid-filled sac that might be a
primitive coelom and is shaped like a thread or a ribbon.
-Carnivores, extensible
proboscis (a long, muscular
tube to capture prey).
-Simplest animals with a
complete digestive tract.
-Several ganglia and small
eyes in the head end and two
lateral nerve cords and a middorsal nerve cord that run
down the body.
Three phyla have a
feeding structure
called a lophophore.
Phylum Bryozoa- “moss animal”: moss animals
~5,000 spp., most marine. Length: usually <0.5 mm.
-Coelom.
-Colonial, superficially resemble mosses.
-Colony encased in a hard exoskeleton with pores, one lophophore
extends out through each pore.
-Lophophore is a horseshoe-shaped
or circular fold of the body wall
bearing ciliated tentacles that
surround the mouth.
-Suspension-feeders.
-U-shaped digestive tract.
Phylum Phoronida- “Phoronis”: phoronids
-Only about 15 species of these tube-dwelling marine worms. Length: 1 mm to 50 cm.
-Coelom, lophophore.
-Suspension-feeders.
-U-shaped digestive tract.
Phylum Brachiopoda- “arm foot”: lamp shells
~330 species, most marine. Length: 1 mm to 9 cm.
-Attached by stalk, resemble clams but shell halves dorsal & ventral.
-Coelom, lophophore.
-Suspension-feeders, U-shaped digestive tract.
A generalized body
paln can become
highly specialized
within a phylum.
Phylum Mollusca “soft”: molluscs
-Over 150,000 species in eight classes; most marine, but several in
freshwater and some on land. Length: <1 mm to 21 m or so.
-Soft body protected in most by a hard shell made of calcium carbonate.
-Well-developed muscles to move the animal or anchor the body.
-Nervous system developed at various levels.
Gastropoda: snails, slugs
Bivalvia:
clams,
oysters,
mussels,
scallops
Polyplacophora:
chitons
Cephalopoda: octopus,
squid, nautilus
Three main parts: foot (usually used for movement), a visceral mass
(contains most of the internal organs), and a mantle (a fold of tissue that
drapes over the visceral mass and secretes the shell).
In many the mantle
extends to produce a
water-filled chamber, the
mantle cavity, which
houses the anus and gills
(portions of the mantle
that increase surface area
for gas exchange,
making it more
efficient).
Filter-feeders, grazers
that feed on algae or
carnivores that capture
prey. Most use a strap
like rasping organ
called a radula to scrape
food.
Segmetation allows a
high degree of
specialization of body
regions (groups of
segments can be
modified for different
functions).
Phylum Annelida “little rings”: segemented worms
~15,000 species in three classes; marine, freshwater and damp soil.
-Length: <1 mm to over 3 m.
-Body & organs segmented (not digestive tract), resemble fused rings.
-Internally, segments divided by partitions called septa.
-Circular muscles around each segment provide movement.
-Front segments contain sense organs and a well-developed brain.
Most groups have
setae, bristles of
chitin that help
anchor the worms
during locomotion.
Segmentation:
having a body built
from repeated units
(segments) allows a
more precise control
of the development
and function of
individual segments
or groups of
segments.
Polychaeta
-Most marine.
-Well-developed head.
-Each segment usually has
fleshy, paddlelike flaps
(parapodia) bearing many
setae.
-Filter feeders or carnivores.
-Tube-dwelling and freeliving.
Oligochaeta
-Terrestrial and freshwater.
-Reduced head.
-No parapodia, a few setae
present.
-Eat detritus, aerating and
improving soil texture.
-Internal fertilization and
development and the use of
skin as a respiratory organ
have assisted in the
exploitation of terrestrial
environments.
SUMMARY
General characteristics of reviewed phyla.
Reproduction from lab notes.
Important evolutionary trends in body plan:
-Multicellularity: Porifera.
-True tissues: Cnidaria.
-Bilateral symmetry: Platyhelminthes.
-Coelom: reduced or absent in some species
These trends helped animals adapt to different
environments or exploit the same environment in a
different manner.