the segmented worms - Welcome to RCSD segmented worms . Phylum Annelida • Annelida from the Latin...
Transcript of the segmented worms - Welcome to RCSD segmented worms . Phylum Annelida • Annelida from the Latin...
Phylum Annelida • Annelida from the Latin word annelus meaning “little ring”
• All are segmented worms • Approximately 15,000 species
including earthworms, freshwater worms, leeches, and marine worms
Annelida Characteristics
Triploblastic- 3 cell layers
Cephalization
Bilateral Symmetry
Highest level of organization: organs
Eucoelomate
Body Cavity Eucoelomate
Have a “true” body cavity that is completely surrounded by mesoderm
ectoderm
mesoderm
endoderm
coelom
Gut
Annelid Characteristics the coelom
ectoderm • is a closed, fluid filled cavity that surrounds the gut • the fluid within acts as a circulatory system (blood) • tissue membranes (mesenteries) suspend organs in the coelom
Annelida Characteristics Metamerism
The body is made up of a series of repeating, coordinated segments called metameres that are separated from one another by septa.
• Each metamere contains sets of repeating organs
e.g. gut, blood vessels, nerve cord, excretory organs
Annelid Characteristics • Two part head consisting of
o Prostomium: fleshy lobe that overhangs the mouth
o Peristomium: first body segment
• Annuli: circular rings • Pygidium: the last segment; where the anus is • Clitellum: reproductive structure
annuli
Annelida Characteristics Nervous system
• 2 cerebral ganglia • a ventral nerve cord with 2 ganglia per metamere.
• In some species, sensory organs such as eyes, palps, and tentacles have arisen (palps are appendages that may or may not be covered in cilia that help the worm find and pull in food)
Annelida Characteristics Locomotion
• both longitudinal and circular muscles which allow them to “wiggle”
• most have setae (chitonous bristles secreted by the epidermis) that aid in locomotion and burrowing
Skeletal System • fluid in coelom acts as a hydrostatic skeleton
Annelid Characteristics
Gas exchange • mainly by diffusion through skin • Class Polychaeta often has specialized structures for gas exchange (e.g. parapodia, gills)
Annelid Characteristics
• unidirectional • regional specialization (digestive organs)
Digestive System
Circulatory System • closed circulatory system composed of blood vessels (some of which are contractile and act as “hearts”) • some circulation is also accomplished by the coelomic fluid
Annelid Characteristics
• excretion is accomplished by organs called nephridia (singular nephridium)
• sexual
Excretion
Reproduction
Class Polychaeta
• All marine • This class contains 2/3 of all known Annelids • Common species are clamworms, sandworms, and lugworms • have a well developed head with specialized sense organs
Class Polychaeta
• Commonly called “bristle worms” • Have many setae (chitonous bristles secreted by the epidermis)
(Poly = many, chaeta= setae) • These setae are arranged in bundles on paddle-like appendages called parapodia
setae
Class Polychaeta
Tagmatization (tagmosis)
• the fusion and specialization of formerly metameric segments
Class Polychaeta Reproduction
• Usually dioecious (separate male and female) • No permanent sex organs; gametes are shed into coelom where they stay until time for fertilization • Fertilization is usually external in water • Indirect development à trocophore larvae swims around until it grows into adult form by adding segments
Ecology • Polychaetes often have effective defense strategies:
• some have tubes to hide in • some have vicious jaws • some have modified “stinging” setae
a fireworm
Ecology
• Some Polychaetes have a mutualistic relationship with their host
• for example, many scaleworms are found near, or in the mouth, of brittlestars, starfish, and sea urchins. • The scaleworm eats its host’s leftovers and with its vicious jaws, it will attack any predator trying to eat it’s host.
Class Oligochaeta
• Habitats: terrestrial, freshwater, and marine • Have few setae (Oligo = few, chaeta = setae)
Class Oligochaeta
What do earthworms eat?
• Usually feed on detritus (decaying organic matter)
• Depends on habitat, but they can feed on… Ø Dead leaves and plant roots Ø Living things such as other worms,
bacteria, and fungi Ø Decomposing remains of other animals
Class Oligochaeta Do earthworms eat dirt?
• Yes and No. • Earthworms consume dirt as they burrow, so yes they do swallow it. • HOWEVER, they do not get nutrients from the dirt. Their nutrients come from decaying plant and animal remains that are in the dirt.
Class Oligochaeta • Earthworms have specialized digestive
system to obtain the maximum amount of nutrients out of the detritus.
• Example: pharynx, crop, gizzard, etc.
Class Oligochaeta Reproduction
• Usually monoecious • Still have to have a partner. • Cross-fertilize by exchanging sperm
clitellum
testis
Ecology
• Earthworms are essential soil aerators, meaning they allow air to enter the soil. • Mix the soil with their tunnels. • Worm feces are great plant food = fertilizer!
Class Hirudinea • Includes leeches • usually freshwater but there are some marine and terrestrial species • no septa between metameres • no setae or parapodia • have 2 suckers
Class Hirudinea • usually have a fixed number of segments (34) • each metamere consists of several annuli (think accordion)
1 metamere
annuli
Class Hirudinea Locomotion
Lack septa between metameres, so they are incapable of moving like Oligochaetes.
Instead, they use their anterior and posterior suckers to move.
Ecology • Although some leeches are parasitic blood suckers (can be temporary or permanent), many are predators.