11 Phylum Annelida Flashcards
Mostly a free living group of an estimated 15,000 species, found all around the world, in our soil, in rivers and even in the deepest part of the ocean.
Phylum Annelida
(annelus) means
’’ little rings”
Level of complexity of phylum annelida.
Organ-system grade
- Segmented worms: displays a metameric body plan
- 15,000 species
- Worldwide distribution. 1 class is chiefly marine, the rest are freshwater
and terrestrial. - Most free-living, some symbiotic, some ectoparasitic
- Bilaterally symmetrical, often with distinct head
- Triploblastic
Phylum Annelida
External Body Plan:
2 head portion
segmented body portion
epidermis
Head Portion (2 parts)
prostomium
peristomium
Part of 1st segment. It is in front of (but does not include) the mouth, usually a small lip-like extension over the mouth. Sometimes bear sensory palps or tentacles.
Prostomium
1st TRUE body segment. Directly behind prostomium and contains the mouth.
Predatory/parasitic forms may contain jaws or teeth
peristomium
Body is divided into similar segments
metameres
externally marked by circular rings in between each metamere.
annuli
The terminal/last portion; also bears the anus
Pygidium
Epithelium secretes thin outer layer of cuticle made of collagen.
Epidermis
Tiny bristles made of chitin found in epidermis.
Setae
Short and needle-like in earthworms
(Class Oligochaeta)
Long and hair-like in polychaetes
( class polychaetes)
Absent in leeches
(Class Hirudinida)
(allowing lengthening/shortening of body)
inner longitudinal
(allowing increase/decrease in
diameter)
outer circular
– has a true body cavity
Eucoelomate
hence, eu- means
“true”
-coelom means
“cavity”
holds organs in place
peritoneum
acts like an expanding storage compartment. Absent in some earthworms.
crop
– strong, muscular organ. For grounding food and minerals.
gizzard
the “hearts”, usually 5 pairs. Pumps blood to the 2 main blood vessels
Aortic Arches
(blood is contained and circulates the body within vessels)
closed type Circulatory system
which branched off from the major vessels, are found in each segment
transverse vessels
2 major blood vessels
Dorsal blood vessel and Ventral
blood vessel
present around the pharynx, and connected to ventral nerve cord
cerebral ganglia
primitive “kidney” but better than protonephridia (meta- means “higher”)
Metanephridia
terminal opening where waste and water is excreted out the body; Found near the ventral row of setae in each segment
Nephridiopore
Some from Class Polychaeta can asexually reproduce by
fission and fragmentation/budding
Earthworm (Class Oligochaeta) and Leeches (Class Hirudinida)
are:
monoecious
a thickened glandular, nonsegmented section of body wall near the head in
earthworms and leeches that functions in the storage of eggs
clitellum
Class Polycheata are:
dioecious
(poly =_______ + chaite=________)
many, long hair
Largest class of annelids (>10,000 species)
* Mostly marine, some freshwater
* Has a distinct head
* Mostly live under rocks, coral crevices, or in abandoned shells; Some burrow into mud or sand and build
their own tubes
* Important in marine food chain (eaten by fish, crustaceans, hydroids, etc.)
* Some members are sedentary/sessile, some are errant (free-moving)
CLASS POLYCHAETA
may have eyes, tentacles, and sensory palps.
Prostomium
Peristomium may bear setae around mouth or have chitinous teeth or jaws
Peristomium
sexually immature
“atokes”
sexually mature
“Epitokes”
Only class of Annelida with a larval form, called a
trocophore
(oligus = _____ + chaite = ______)
“few, long hair
Setae is less numerous than polychaetes and only found on the ventral surface of the first several segments
* Head indistinct/absent (but still display cephalization)
* Number of segments are variable
* Scavengers, feeding on decaying organic matter and
vegetation
CLASS OLIGOCHAETA
Male genital ducts are found in
segment 15
Female genital pores are found in
segment 14
Sperm from mate is received and stored in 2 pairs of
seminal vesicles in
segment 9 and 10
When mating, worms bring their anterio-ventral surfaces
together and held together by mucus secreted by the
clitellum
mucus will form a
cocoon
Setae are absent
* Aquatic; predominantly freshwater, few marine, some moist terrestrials
* More abundant in tropical regions
* Almost flattened dorsoventally
* Known ectoparasites of carnivores and small invertebrates
CLASS HIRUDINIDA
are considered the “true” leeches
CLASS HIRUDINIDA
(for cutting through skin in order to feed on blood)
Chitinous jaws/cutting plates
used for locomotion (instead of setae)
anterior and posterior suckers
sperm is transferred by a
spermatophore that penetrates the skin of their mate (called
hypodermic impregnation
This is the largest class of Annelida that is exclusively marine.
Polychaeta
This refers to the body segment containing the mouth.
Peristomium
The members of this class do not have setae.
Hirudinida
How do leeches move around?
using suckers
