Exam 1 Flashcards
4 appendage-derived mouthparts
labrum, mandibles, maxillae, labium
Head
a.) 4 appendage-derived mouthparts
(labrum, mandibles, maxillae, labium)
b.) one pair of antennae with 2 musculated
segments
c.) compound eyes and ocelli
Thorax
a.) three pairs of legs (1 pr./segment)
b.) two pairs of wings (usually) (1 pr.
on each of the last two segments)
Abdomen
11 segments
Particular internal organs
tracheal respiratory system
malpighian tubule excretory system
particular embryological characteristics
protosome coelomate
superficial cleavage
epimorphosis
earliest evidence
cambrian fauna - burgess shale in canada and chengjiang in china
cambrian explosion
period from
about 540 to 510 million years ago in which
the earliest forms of modern animal phyla
leave fossils.
What major Phylum of animals is closely
related to arthropods?
- Historical answer, based on morphology:
Annelida (segmented worms). Places
emphasis on presumed synapomorphy of
segmentation
3 modern classes of annelids
Polychaetes - marine
oligochaetes - terrestrial
leeches - freshwater
The Three Modern Classes of Annelids
Polychaetes (marine worms) are the most numerous
annelids and most arthropod-like in appearance
current thinking
major phylum which is closely related to
the Arthropoda is Nematoda (roundworms)!
* The actual important synapomorphy turns out
to be growth by molting! Segmented bodies
with appendages seem to have arisen
several times via convergent evolution!
(Pseudocoeloms, too!)
* Thus, the new zoological grouping,
Ecdysozoa (Animals that molt)
“Pararthropod” Phyla
I. Pentastomida (Tongueworms or
Linguatulids) (= “Five Mouths”)
About 90 spp.; parasites of nasal
passages & lungs of carnivorous
vertebrates, usually reptiles; possess
chitin, molting, segmentation; some have
lobe-like legs with 2 pairs of claws.
(But recent work strongly suggests that
they are modified crustaceans!)
Tardigrada (Water Bears)
(= “Slow Steps”)
~400 spp.; live in aquatic habitats or in
moss/lichens on trees; <1mm in length;
possess chitin, molting; 4 pairs of lobe-like legs
with claws; cuticle plates; hemocoel;
Malpighian tubules.
Unique ability -> cryptobiosis; can
desiccate to only 3% water; able to withstand
570,000 roentgens of radiation in this state!
(human lethal dose = 500)
(Some classify them as arthropods, but the
consensus is that they are a closely-related
sister group to the arthropods plus
onychophorans.)
Onychophora (Velvet Worms) (“Claw
Bearers”)
~80 spp.; tropical forest floor predators
with unique poison “nozzle”; live-bearers; very
ancient group with marine ancestors in Burgess
Shale (540 mya.)
Many arthropod-like traits: chitin; patchy
molting; hemocoel; dorsal tube heart; tracheal
system; antennae; claws; jaws derived from
legs; internal fertilization (copulation); superficial
cleavage development
Some classify them as arthropods.
Arthropods: Phylum Arthropoda
General Arthropod Traits:
1.) Segmented bodies with paired appendages
2.) Jointed legs
3.) Exoskeleton of chitin + a hardener
4.) Growth by molting
5.) Ventral nerve cord with segmental ganglia
6.) Hemocoel, dorsal tube heart
7.) Fusion of Segments into tagmata (body regions)
Arthropod Subphlya: Trilobita, Chelicerata, Crustacea,
Myriapoda, & Hexapoda (insects and very close relatives)
Trilobita
Lived from ~520-250 mya;
4000 fossil species known;
important marine predators
up to 60 cm long; name
from three apparent
longitudinal “lobes”; 3
tagmata: cephalon, thorax,
pygidium; biramous
appendages (2-branched);
compound eyes; 1 pair
antennae
Chelicerata
No antennae; 2 tagmata (cephalothorax + abdomen); 6
pairs of appendages: chelicerae, pedipalps, and 4 pairs
legs
Classes:
(Extinct: Eurypterida – Sea Scorpions: the largest
arthropods that ever lived.)
A.) Pycnogonida: Sea Spiders (~600 spp.)
B.) Merostomata (Xiphosura): Horseshoe Crabs
(~5 spp.) – But Recent Change!
C.) Arachnida (~60,000 spp.)
Important orders: Araneae (spiders, 35,000 spp.),
Acari (mites & ticks, 25,000 spp.), Opiliones (harvestmen
or “daddy longlegs”, 5,000 spp.), Scorpionida (scorpions,
1,200 spp.)
three Orders of
Arachnids:
Spiders & Mites & scorpions
Crustacea
~30,000 spp.; mostly marine (some freshwater
& terrestrial); ancient group, going back to the
Cambrian Era; 2 pairs of antennae,
mandibles, 2 pairs maxillae, varying number
of legs & other appendages; biramous
appendages; cephalothorax (covered with a
carapace) + abdomen
A diverse group with many classes and
orders
Myriapoda
~13,000 spp.; terrestrial; uniramous
appendages; head independent & freely
movable; 1 pair antennae; mandibles (thus
some combine these with Crustacea and
Hexapoda into a group called Mandibulata);
Two minor classes (Symphyta & Pauropoda)
Two major classes (Chilopoda & Diplopoda)
Chilopoda: Centipedes (“Hundred Legs”)
~8,000 spp.; 1 pair of legs per segment; predators
with poison glands; first pair of legs modified to
serve as poison fangs.
Diplopoda: Millipedes (“Thousand Legs”)
~10,000 species; 2 pairs of legs per apparent
segment; herbivores and detritivores; less
active than centipedes; many have
defensive poisons
Hexapoda
Insects and Relatives
Non-insect Hexapods:
Class Entognatha (“Jaws Inside”)
Order Collembola: Springtails
Order Diplura: Diplurans
Order Protura: Proturans
All are soil-dwelling, omnivorous.
Homology & Serial Homology
You should be very familiar with the concept of
homology: similarity of structure between
species due to descent from a common
ancestor possessing that structure.
But with the segmented bodies of arthropods,
there is a second kind of homology, Serial
Homology. This is the similarity of structures
on different segments of the same animal,
due to divergence from a common ancestral
segmental structure (example: legs,
mouthparts of insects).
Insect Evolution (Simplified)
How Can One Study Insect Evolution/Phylogenetic
Relationships?
1.) Fossils: relatively poor record, but fossils are
sometimes found in sediments from lakes and
streams, coal, volcanic ash, and amber.
2.) Biogeographic Analyses (Studies of “disjunct”
ranges of certain insect taxa, for example from
Africa and South America, were among the earliest
evidence for “continental drift”).
3.) Comparative Method (Anatomy, Behavior)
4.) DNA Analyses/Genomics
From What Type of Arthropod
Did the Hexapods Descend?
There are two competing hypotheses:
1.) Uniramia (Atelocerata or Tracheata):
Considers the Myriapods to be the sister
group, emphasizing common possession of
single-branched appendages, Malpighian
tubules, and trachea.
2.) Pancrustacea: Considers one group of
Crustaceans to be the sister group (some
have placed Crustacea as sister group to
the Uniramia because of shared mandible
mouthparts, thus Mandibulata).
The Pancrustacea hypothesis is supported by
molecular analyses, developmental patterns, and some anatomical evidence (compound eyes, nervous system). It is the current majority position, gaining support. If correct, it means that the “shared traits” supporting the Uniramia
hypothesis must be the result of convergent evolution!
So –> Insects
Which Crustaceans are the sister group?
Two suggestions: Malacostraca (lobsters, etc.) or a member of
a group including Branchiopoda (fairy shrimps,
cladocerans) and two obscure groups, Remipedia &
Cephalocarida (see Fig. 8.1) - molecular & paleontological
evidence support the latter suggestion.
Major Stages in Insect Evolution
I. The first unambiguous fossils of hexapods
(springtails) date to about 380 mya, with the first
fossils of true insects (silverfish-like) shortly
thereafter (~376 mya)(During the Devonian
Period). These first insects were Apterygota
(primitively wingless insects, “ones without
wings”). There are two modern Apterygote
orders.
II. The second stage entailed the evolution of
wings. We will discuss theories on the origins of
wings later. The first wings to evolve could not
be folded; insects with this kind of wings are
called Paleoptera (“ancient wings”
springtials/bristletails & silverfish
Mayfly:
one type of Paleopteran insect
Diversification of Paleopterans was extensive in the
Carboniferous Period (approximately 360 to 290 mya). A number of orders evolved that do not survive today (especially a group of 5 orders known collectively as the Paleodictyopterida); there are two existing Paleopteran orders (Ephemeroptera - mayflies - and Odonata - dragonflies & damselflies). Protodonata (Meganisoptera) achieved tremendous size. (See Fig. 8.3, Box 8.2.)
III. The next stage in insect evolution entailed the evolution of wings that could be folded and aligned out of the way along the dorsal surface when not being used. All the remaining orders show this kind of wing and are referred to as Neoptera (“new wings”). Neopteran insects first show up in the late Carboniferous Period but diversified tremendously in the Permian (~299 to 250 mya).
Yellow-winged Grasshopper, showing Neopteran wings
Yellow-winged Grasshopper, showing Neopteran wings
The fourth and last major phase of insect evolution
The fourth and last major phase of insect evolution entailed the evolution of “complete metamorphosis”. Instead of a juvenile that looked like a non-sexually-mature, wingless version of the adult, a new “larva” stage evolved, followed by
a transforming “pupa” stage leading to the adult. The larva and adult often have completely different habitats and feeding modes. These first appear in the late Carboniferous and expand throughout the Permian but radiate explosively in the Mesozoic Era: they now comprise >90% of insect species.
Previous Neopteran insects with “gradual metamorphosis” are called Exopterygotes (ones with wings outside); the new type of insects are called Endopterygotes (ones with wings
inside).
Hypotheses about the evolution of complete metamorphosis
will be discussed later.
Exopterygota
gradual metamorphosis
Endopterygota
complete metamorphosis
Then disaster struck…
At the end of the Permian Period, about 250
million years ago, the greatest of all the
Earth’s “mass extinctions” occurred - over
90% of all species on Earth went extinct,
including several whole orders of the early
insects. Today’s insects are the surviving
orders, and new orders descended from
them.
The “Latest Models” in Insect
Evolution
Although about 8 orders died out in the end-Permian
mass extinction, members of all four major insect
groups survived and subsequently radiated
explosively. The most recent major types to appear,
during the Cretaceous Period (145-65 mya) are:
Moths, Termites, Ants, Butterflies, Bees, Fleas, Lice
What major evolutionary/co-evolutionary factors are
suggested by these new groups of insects?
External Anatomy: General and Head
Insects possess an Exoskeleton comprised of
the Cuticle (Figure 2.1).
The materials of which the cuticle is made are
primarily Chitin (Figure 2.2) and a complex
mixture of Cuticular Proteins.
The non-cellular cuticle plus the underlying
Epidermis of cells collectively are referred to
as the Integument.
Arthrodial Membrane
The external surface of an insect’s body includes
areas of hardened plates (Sclerites) between which
there may be softer, flexible membranous areas
(Arthrodial Membrane).
Sclerites
The external surface of an insect’s body includes
areas of hardened plates (Sclerites)
