Invertebrates: ecdysozoans & deuterostomes

Question 1

Phylum Nematoda

Answer 1

Roundworms, pseudocoelomates, only recently classed as ecdysozoans
- Cylindrical bodies covered with a tough outer
collagenous cuticle
- To grow, shed old cuticle & secrete larger one

Question 2

Nematode features

Answer 2

• Complete digestive tract but no circulatory system;
  fluid in pseudocoelom transports nutrients
• Sexual reproduction
• Separate sexes, hermaphrodites or both, with
  internal fertilization
• Can self fertilize
• Zygotes are resistant to harsh conditions
• Abundant in moist soil & decomposing organic
  matter
• Eggs and early larval stages resistant to stress
• Locomotion caused by contraction of longitudinal
  muscles

Question 3

Caenorhabditis elegans

Answer 3

• Shares many of the same biological structures and
  processes with more complex organisms
• Short time to reproductive maturity (2-3 days), a
  two-week life span
• Detailed knowledge of its genetics and the function
  of each of its 959 cells
• Model for aging to workings of the nervous system

Question 4

Who won the nobel prize for medicine in 2002 and why?

Answer 4

Sydney Brenner, John Sulston & Robert Hovitz for mapping the fates of cells from embryo through to adult
- Found that generation of new cells is coupled to
programmed cell death

Question 5

Who won the nobel prize for medicine in 2006 and why?

Answer 5

Andrew Z. Fire & Craig C. Mello for discovering that double-stranded RNA triggers suppression of gene activity in a homology-dependent manner in 1998, a process named RNA interference (RNAi)

Question 6

Parasitic nematodes

Answer 6

Many species are important agricultural pests that attack plant roots
- Over 50 species, including various pinworms and
hookworms, parasitize humans
- Trichinella spiralis encysts in a variety of tissues,
including skeletal muscle, causing trichinosis
- From eating undercooked meat with juvenile
worms encysted in muscle tissue

Question 7

How do trichinella’s infect their host’s muscles?

Answer 7

• Able to bypass their host’s immune system
• Control expression of genes in muscle that make
  cells elastic enough to house worms
• Parasitized muscle undergoes angiogenesis
  (growth of new blood vessels) to bathe the worm
  with oxygen & nutrients

Question 8

Phylum onychophora

Answer 8

• Thought to be the first animals on land
• Peripatus - The Velvet Worm

Question 9

Phylum Arthropoda

Answer 9

• A billion billion (10^8) arthropods living on earth
• Represented in nearly all habitats
• By species diversity, distribution, and sheer
  numbers, arthropods are the most successful
  animals phylum

Question 10

Key anatomical features of Arthropods

Answer 10

• Segmented body
• Hard exoskeleton
• Jointed appendages

Question 11

Tagma

Answer 11

Specialized grouping of segments with common function:
- Head
- Thorax
- Abdomen
- Specialization of appendages for variety of
functions, permitting efficient division of labor
among regions

Question 12

Is appendage specialization an inherited or evolved characteristic?

Answer 12

Appendage specialization seems to be an evolved characteristic since ancient arthropods like Trilobites show little variation segment-to-segment

Question 13

How does the evolution of segmentation change depending on if you use a morphological or molecular phylogeny?

Answer 13

Morphology-based
- Arthropods and annelids are grouped because
they have segmented bodies
Molecular phylogeny
- Arthropods and annelids are not closely related

Question 14

What are the three main hypotheses for the evolution of segmentation?

Answer 14

Hypothesis 1: Three origins of segmentation (most
parsimonious hypothesis)
Hypothesis 2: Two origins of segmentation
Hypothesis 3: One origin of segmentation

Question 15

The arthropod exoskeleton

Answer 15

Body completely covered by the exoskeleton, a cuticle made from layered protein & chitin
- The exoskeleton protects & provides points of
attachment for muscles
- It is thick & inflexible in some regions, such as
claws, and thin & flexible in others, such as joints
- The exoskeleton is strong & relatively
impermeable, allowing terrestrial adaptation
- To grow, an arthropod must molt its old
exoskeleton (ecdysis)
- Then secreted a larger one, leaving the animal
temporarily vulnerable

Question 16

What are the four main subphyla of arthropods?

Answer 16

Cheliceriformes
- Body having one or two main parts; six pairs of
appendages mostly terrestrial or marine
Myriapoda
- Distinct head bearing antennae and chewing
mouthparts; terrestrial
Hexapoda
- Body divided into head, thorax, and abdomen;
antennae present; three pairs of legs and usually
two pairs of wings; mostly terrestrial
Crustacea
- Body of two or three parts; antennae present;
chewing mouthparts; three or more pairs of legs;
mostly marine and freshwater

Question 17

Subphylum trilobita

Answer 17

Earliest arthropods were common in shallow Paleozoic seas but disappeared in Permian extinctions ~250 MYA
- Pronounced segmentation, but appendages
showed little segmental differentiation
- Trend in arthropod evolution toward fewer, more
specialized segments & appendages

Question 18

Subphylum chelicerata

Answer 18

Anterior cephalothorax, posterior abdomen
- Appendages more specialized than in trilobites, the
most anterior, chelicerae (pincers or fangs)
- Most marine species including all sea scorpions,
extinct today

Question 19

What organism is considered a living fossil?

Answer 19

Horseshoe crabs
- Surviving members of a once rich diversity of cheliceriforms ~450 mya

Question 20

What organisms are considered to be modern chelicerates?

Answer 20

Certain terrestrial organisms in Class Arachnida
- Scorpions
- Spiders
- Ticks
- Mites

Question 21

Arachnid segmentation

Answer 21

Cephalothorax has six pairs of appendages
- Four pairs of walking legs
- A pair of pedipalps function in sensing or feeding
- A pair of chelicerae for feeding

Question 22

Subphylum myriapoda

Answer 22

Among earliest land animals
- Millipedes, class diplopoda, wormlike with two pairs
of walking legs on each of many segments
- Centipedes, class chilopoda, are terrestrial
carnivores, one pair of walking legs on each
segments

Question 23

Subphylum hexapoda

Answer 23

Class insecta
- In species diversity, insects outnumber all other
forms of life combined
- In almost every terrestrial habitat, fresh water, and
air (rare but not absent from the sea)

Question 24

Insect macroevolution

Answer 24

Adaptive radiation in Carboniferous & Permian sparked by:
- Evolution of flight
- Diversification of mouthparts for feeding on
gymnosperms and other Carboniferous plants
Did radiation of flowering plants trigger diversification of insects in Cretaceous & early Tertiary or vice versa?
- Diversity of pollinators & herbivores
- Many examples of plant-insect interactions

Question 25

Evolution of flight

Answer 25

Flight, a key to great success of insects - Escape from predators, find food & mates, disperse to new habitats faster - One or two pairs of wings on dorsal thorax; extensions of cuticle and not true appendages - Evolved to absorb heat, gills, swimming, gliding?

Question 26

Insect development

Answer 26

Two kinds of metamorphosis - Incomplete metamorphosis (hemimetabolous): in grasshoppers & other orders, young resemble adults but smaller, with different body proportions - Through a series of molts, young grow into adults - Complete metamorphosis (holometabolous): specialized larval stages change morphology during pupal stage & emerge as adults

Question 27

What similarity do beetles, flies, ants, bees, and butterflies have with metamorphosis?

Answer 27

- Complete metamorphosis - Have specialized larval stages that look different and often feed differently

Question 28

What similarities do hemiptera and orthoptera's have with metamorphosis?

Answer 28

- Incomplete metamorphosis - Young resemble adults

Question 29

Insect reproduction

Answer 29

Usually sexual, separate males & females - Coloration, sound, or odor bring together opposite sexes at the appropriate time - In most species, sperm cells deposited directly into female at copulation - Females store sperm in spermatheca, sometimes holding enough from one mating to last a lifetime - After mating, females lay their eggs on a food source appropriate for the next generation

Question 30

What is the importance of insects?

Answer 30

Insects affect all other terrestrial organisms - Carriers for many diseases, including malaria, African sleeping sickness, West Nile Virus - Competitors with humans for food and fiber - Billions of dollars spent each year on pesticides to minimize crop losses to insects - Important natural & agricultural pollinators

Question 31

Honeybee decline

Answer 31

Honeybee's are the most economically valuable pollinators of agricultural crops worldwide - Bee pollination involved in 1/3 of US diet - Responsible for 80% of all pollination events - Monetary value of honeybee pollination is $15 billion Colony collapse disorder (CCD) first reported in 2006 38% of estimated 2.3 million colonies lost Characterized by: - Loss of adult bees from colony - Adult bees do not die in close proximity to colony - Colony appears otherwise healthy, food and brood present

Question 32

What are some possible causes of CCD?

Answer 32

- Parasites, mites, and disease loads in the bees and brood - Emergence of new or newly more virulent pathogens - Poor nutrition among adult bees - Lack of genetic diversity and lineage of bees - Level of stress in adult bees (e.g., transportation and confinement of bees, overcrowding, or other environmental or biological stressors) - Chemical residue/contamination in wax, food stores, and/or bees) - A combination of these and/or other factors

Question 33

What has been found to be strongly correlated with CCD?

Answer 33

By comparing microbial sequences derived from CCD and non-CCD colonies, it was found that Israeli acute paralysis virus of bees (IAPV) - IAPV was first described in 2004 in Israel where infected bees presented with shivering wings, progressed to paralysis, and then died

Question 34

Subphylum crustacea

Answer 34

Dominant aquatic arthropod - Most of ~40,000 species live in marine and freshwater environments with a few terrestrial or semi-terrestrial species

Question 35

Class malacostraca - Decapoda

Answer 35

Decapoda (lobster, crayfish, crabs & shrimp) are among largest crustaceans - Cuticle hardened with calcium carbonate - Exoskeleton over cephalothorax forms a shield called carapace - Most marine, crayfish live in freshwater, some tropical crabs are terrestrial as adults Related to decapods, krill are shrimplike planktonic organisms up to 3 cm long - Major food for whales and other ocean predators, now harvested extensively for food & fertilizer

Question 36

Class malacostraca - Isopoda

Answer 36

Isopoda, with ~10,000 spp., one of the largest groups of crustaceans - Most are small marine species, can be abundant at the bottom of deep oceans - Also includes land-dwelling pill bugs, or woodlice, that live underneath moist logs and leaves

Question 37

Class Maxillipoda - copepoda

Answer 37

Subclass Copepoda among the most numerous of all animals - Important members of marine & freshwater plankton communities, eating protists & bacteria & eaten by many fishes

Question 38

Class maxillipoda - cirripedia

Answer 38

Subclass Cirripedia - Barnacles are sessile crustaceans with parts of their cuticle hardened by calcium carbonate - No molting in adults - they strain food from the water by extending an appendage (cirrus)

Question 39

Deuterostomia

Answer 39

Phylum Echinodermata: - Echinoderms have a water vascular system and secondary radial symmetry Phylum Hemichordata: - Chordate characters, echinoderm affinity Phylum Chordata: - The chordates include two invertebrate subphyla and all vertebrates

Question 40

What do sea stars and sea urchins have in common with chordates & vertebrates?

Answer 40

- Echinoderms & chordates share radial cleavage, development of a coelom from archenteron, formation of anus from blastopore, mouth second - "Our Clade" Deuterostomia supported by molecular systematics

Question 41

Phylum Echinodermata

Answer 41

- All echinoderms (~7,000 species) are marine - Sea stars & most echinoderms are sessile or slow, moving by hydraulics not levers - Thin skin over hard endoskeleton of calcareous plates - Echinoderms are sessile and slow moving using by hydraulics not levers - Specialized filtration pore that allows seawater entry and exit - Underside of arms have 5 rows of tube feet - Water vascular system that runs down each arm branching into many tube feet

Question 42

Water vascular system

Answer 42

Unique to echinoderms, the water vascular system is a network of hydraulic canals branching into extensions called tube feet - Tube feet function in locomotion, feeding, and gas exchange - Ampulla squeeze, podium expands, and adhesive chemicals attach foot to substrate. Reverse process to move

Question 43

How do sea stars feed?

Answer 43

Sea stars use tube feet to grasp prey as well as substrate

Question 44

Bilateral and "radial" symmetry

Answer 44

Reproduction by release of sperm and eggs into seawater - Larvae are bilaterally symmetrical but adults are not truly radial - madreporite shifted to one side (pentameral symmetry)

Question 45

Krogh's principle

Answer 45

For such a large number of problems there will be some animal of choice or a few such animals on which it can be most conveniently studied

Question 46

Who won the nobel prize for medicine in 2001 and why?

Answer 46

Leland Hartwell, Tim Hunt & Paul Nurse for identifying key molecules that regulate the cell cycle in all eukaryotic organisms, including yeasts, plants; animals and humans. These fundamental discoveries have a great impact on all aspects of cell growth