Transcript Annelida 2010 - The Bronx High School of Science

“Radiata”
Metazoa
Ancestral colonial
flagellate
Deuterostomia
Eumetazoa
Protostomia
Bilateria
Phylum: Annelida
Nematoda
Nemertea
Rotifera
Arthropoda
Annelida
Mollusca
Platyhelminthes
Chordata
Echinodermata
Brachiopoda
Ectoprocta
Phoronida
Ctenophora
Cnidaria
Porifera
Phylum: Annelida
“segmented worms”
earthworms, bristle worms, leeches
•bilateral symmetry, triploblasts, protostomes,
coelomates
•main advance is segmentation (metamerism)
•body composed of series of fused rings
•segments (and coelom) separated by septa
•repeated structures and organs
Earthworm anatomy
Phylum: Annelida
Class: Oligochaeta
earthworms
•Named for relatively sparse “chaetae” (setae) or
bristles found on eahc segment, made of chitin
•Includes earthworms and some aquatic species
•earthworms eat their way through the soil, extracting
nutrients as soil passes through alimentary canal
•valuable to farmers
•till & aerate soil
•fecal castings improve soil texture
Phylum: Annelida
earthworms, sandworms, leeches
•well-developed complete one-way (mouth to anus)
digestive system, tube within a tube
•mouth- found on protostome (1st segment)
•pharynx- muscular, sucks in soil
•esophagus
•crop- stores food
•gizzard- muscular w/ small stones, grinds food
•intestine- chemical digestion, nutrient absorption
•anus
Phylum: Annelida
Class: Oligochaeta
earthworms
•well-developed excretory system
with repeated structures, two per
segment
•metanephridia (primitive kidney)
•excretory tubule open at both
ends
•network of small blood vessels
closely associated
•nephrostome at one end of tubule
•ciliated funnel collects fluid from
coelom
•excretory pore (nephridiopore) at
other end of tubule
•dilute urine (urea) exits to
outside body
Phylum: Annelida
Class: Oligochaeta
earthworms
•circulatory system
• closed with unidirectional flow of blood
• 5 aortic arches-muscular vessels that pump
blood (“hearts”)
• dorsal blood vessel supplies blood to
posterior
• ventral blood vessel returns blood to anterior
• hemoglobin dissolved in blood increases
capacity to carry oxygen
Phylum: Annelida
Class: Oligochaeta
earthworms
•nervous system
•cerebral ganglia at anterior end comprise brain
•ventral nerve cord runs length of animal
•segmental ganglia originate from ventral nerve
cord, 2 per segment
Phylum: Annelida
Class: Oligochaeta
earthworms
•reproduction
•sexual
•most are hermaphrodites (monoecious)
•clitellum (thick band on epidermis) is site copulation
•sperm transferred from male pore on clitellum
•“cocoon” secreted by clitellum encases
fertilized eggs that develop to juvenile worms
•one mating yields 2 pregnancies in hermaphrodites
Phylum: Annelida
Class: Oligochaeta
earthworms
•locomotion
•circular and longitudinal muscles
•hydrostatic skeleton (fluid filled coelom, cuticle)
•setae on each segment
•chitinous bristles
•embedded in epidermis
•waves of muscular contractions shorten/lengthen
animal
•secrete mucus to lubricate path
Earthworm anatomy
Members of Phylum Annelida
Class Oligochaeta
•means “few setae” (bristles)
•earthworms (Lumbricus terrestris) & relatives
•many terrestrial, some aquatic
Members of Phylum Annelida
Class Polychaeta
•sandworms, bristle worms
•pair of parapodia w/ “many setae” (bristles) per segment
•parapodia are fleshy paddle-like extensions
•highly vascularized for gas exchange
•used as gills & for locomotion
•reproduction
•lack clitellum
•free-swimming trochophore larva
•mostly marine
Members of Phylum Annelida
Class Hirudina
•leeches
•named for “hirudin”, the anti-coagulent
secreted into host
•also secrete anesthetic that prevents
host from feeling attachment
•feed on blood
•historical medical use in bloodletting
•not all bite, many feed on dead or
dying tissues or animals, on open
wounds
•terrestrial and aquatic species
Phylum Annelida:
The Table- selected entries not covered
Cleavage/cells: radial and
determinate; egg is small with
elsewhere
little yolk
Respiratory system: cutaneous breathing; skin must be kept
moist for diffusion of oxygen; in Polychaeta parapodia act as
external “gills”
Relationship to other phyla:
Mollusca- mesoderm origin, larval characteristics,
cleavage pattern
Arthropoda- segmentation, type of cuticle, nervous
system
Chordata- coelom segmentation