Invertebrates: ecdysozoans & deuterostomes Flashcards
Phylum Nematoda
Roundworms, pseudocoelomates, only recently classed as ecdysozoans
- Cylindrical bodies covered with a tough outer
collagenous cuticle
- To grow, shed old cuticle & secrete larger one
Nematode features
- 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
Caenorhabditis elegans
- 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
Who won the nobel prize for medicine in 2002 and why?
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
Who won the nobel prize for medicine in 2006 and why?
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)
Parasitic nematodes
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
How do trichinella’s infect their host’s muscles?
- 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
Phylum onychophora
- Thought to be the first animals on land
- Peripatus - The Velvet Worm
Phylum Arthropoda
- 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
Key anatomical features of Arthropods
- Segmented body
- Hard exoskeleton
- Jointed appendages
Tagma
Specialized grouping of segments with common function:
- Head
- Thorax
- Abdomen
- Specialization of appendages for variety of
functions, permitting efficient division of labor
among regions
Is appendage specialization an inherited or evolved characteristic?
Appendage specialization seems to be an evolved characteristic since ancient arthropods like Trilobites show little variation segment-to-segment
How does the evolution of segmentation change depending on if you use a morphological or molecular phylogeny?
Morphology-based
- Arthropods and annelids are grouped because
they have segmented bodies
Molecular phylogeny
- Arthropods and annelids are not closely related
What are the three main hypotheses for the evolution of segmentation?
Hypothesis 1: Three origins of segmentation (most
parsimonious hypothesis)
Hypothesis 2: Two origins of segmentation
Hypothesis 3: One origin of segmentation
The arthropod exoskeleton
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
What are the four main subphyla of arthropods?
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
Subphylum trilobita
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
Subphylum chelicerata
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
