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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