Lecture 7+8 (BIO-2040)

What is a second cavity

a internal cavity surrounding the gut that provides a “tube inside a tube” arrangement to the body.

Acloemates

Animals that lack a secondary cavity. The space is filled with a mesodermal parenchyma (flatworms)

Pseudo-Coelmates

Animals with a secondary cavity that is not entirely lines with mesoderm. (round worms)

• mesoderm doesnt cover the endoderm

Coelmates

animals with a true coelom between endoderm and ectoderm. fully lines with mesoderm. (all other bilateral animals)

characteristics of pseudo-coelomates

• most have a pseudo-coelom

• most have an external cuticle

• most have adhesive glands

Nematode excretion

by diffusion and excretory ducts. no proto-nephridia

Nematode

free-living or parasitic. have a thick cuticle and pseudo-coelom, which is visible at the adult stage. >15,000 species on soil, freshwater and seafloor

Nematode Digestive system

Open and complete

Nematode Nervous system

some cephalization and with nerve ring and dorsal and ventral cords

Asearis Lumbricodes

• 1 host parasite of human small intestine

• 25% of humans infected

Trichinella spirallis

• multiple-host parasites

• Adults colonize the intestine, and newborns migrate through the blood to colonize in other organs

Radial Cleavage

Uniform division ending in symmetric blastomeres

Spiral Cleavage

Non-uniform division ending in asymmetric blastomeres

Entero-coelous

by formation of mesodermal pouches

Schyzo-coelous

by the proliferation of mesoderm cells and subsequent splitting

Deuterostome

blastopore becomes the anus first

Protostome

blastopore becomes mouth first

Segmented worms or Annelids

metameric body forms: repitition of systems in each segment, about 15,000 species

Annelids feeding

complete digestive system (with anus). feeding strategy depends on life history

Annelids excretion

by metanephridia on each segment. They collect residuals from the blood and dispose of them directly outside the body.

metanephridia

organs that filter waste from the body cavity

Annelids nervous system

Complexity depends on activity: dorsal brain and ventral cord. One ganglion per segement

Ganglion

clusters of nerve cells

Oligochaete

• lack parapodia, simple prostomium

• no visible sensory organs, uniform segments

Oligochaete food capture

• all deposit feeders

• no proboscis/jaws/palps/etc.

Oligochaete Reproduction

• hermaphroditic species

• practice cross-copulation

• gonads in clitellium

• a cacoon with eggs in formed

Hyrudinea

• no setae

• low diversity

• predatory or eco-parasites

• has several hosts

• external parasite

Hyrudinea segemtation

partially lost (external but not internal)

Hyrudinea food capture

use of suckers for attachment and then suck blood or tissue from host

Hyrudinea locomotion

use of suckers

Hyrudinea reproduction

• hermaphroditic species

• cross-copulation (internal)

• there is a clitellum and a cacoon

Polychaeta

• with parapodia (unjointed appendages)

• With acicular (chitin rods) and setae

Errant mobility

moves a lot

Sedentary mobility

moves very little

pelagic habitat

lives in the water

benthic habitat

lives in the seafloor

Suspension feeders

filter water

deposit feeders

eat sediment

predatory species

proboscis with jaws

Polychaeta sensory organs

• better developed in errant/predatory

• palps, tentacles, eyespots, etc.

Polychaeta reproduction

• external fertilization (different sexes)

• no clitellum

Polychaeta larva

Trochophore