development of a digestive tract enables (3):
- continuous operation
- specialization of gut regions
- sequential food processing
How does a complete digestive tract develop?
- have mesenchymal filopodia which are filaments that pulls up to form either a mouth or anus (from blastopore)
Two ways to develop a digestive tract
- Protostomes (mouth first)
- Deuterostomes (anus first)
What are organisms that are deuterostomes?
Echinoderms, Chordates
Three different body plans with respect to body cavities:
- Coelomate
- Pseudocoelomate
- Acoelomate
Coelomate
coelom = cavity
mesoderm lines the entire cavity as a “peritoneum”
-lining derived from mesoderm
- enclosed body cavity completely lined with mesoderm
Pseudocoelomate
- mesoderm lines the outside of pseudocoel
- ex. Nematoda
Acoelomate
- no body cavity
- solid except digestive space
Two ways to make a coelom
Schizocoely: splits within the mesoderm (protostomes)
Enterocoely: mesoderm forms pockets from guts (deuterostomes)
Which are acoelomate?
flatworms
Which are Pseudocoelomate?
Rotifers, Nematodes
Which are coelomate?
Annelids, Molluscs, Arthropods, Echinoderms, Chordates
Lophotrochozoans
One of the following:
Lophophore: “tuft bearer” = ciliated feeding/gas exchange structure
Trochophore: “wheel-bearer” = a ciliated free-living larval form
Ecdysozoans
- moulting animals
- have an external covering secreted by epidermis that must be shed in order to grow
- growth happens in steps
- vulnerable after moulting
- moulting evolved > 500 million years ago
Nematoda (8)
- ecdysozoans
- multi-layered, flexible cuticle (allows diffusion of gases, must live in moist habitats)
- have a tapered posterior end and blunt anterior end
- Pseudocoelomate
- have longitudinal muscles, move by thrashing
- fluid-filled body cavity (hydrostatic skeleton)
- complete digestive tract
- no respiratory or circulatory system (respiration occurs across their cuticle
Nematoda diversity (4)
- abundant
- terrestrial (moist soil) or aquatic
- free-living (scavengers, predatory) or parasitic
- important for soil
C. Elegans
- major model organism of geneticists, developmetal biologists and neurobiologists
Earthworm
has gizzard (grinding down), also produce enzyme (cellulase)
Cow (4 stomach)
- Rumen (fermentation)
- reticulum (fermentation)
- Omasum
- Abomasum
Some are nematodes are scavengers and predators but some are parasitic
infect protists, plants, animals
Ex. crop damage cause by nematode outbreak
Solution: to not grow those crops for a couple of years because nematodes are highly specialized
Largest nematode
9 m (parasite in placenta of sperm whales)
Hookworm
- common in tropics and subtropics because of moisture
- feed on red blood cells
- worms penetrate skin from foot and moves to abdomen
Annelida (7)
- segmented worms
- Lophotrochozoans
- terrestrial (moist), aquatic
- abundant
- coelomates (hydrostatic skeleton)
- have longitudinal and circular muscles
- have setae “hairs” anchor
Why is segmentation advantageous?
- multiple copies of organs, structures (Ex. Nephridia, parapodia)
- efficient nervous control (response faster, ganglion in each segment)
- increase body size by unit repetition
