Kingdom Animalia – Nematoda. Phylum nematoda – round worms (~50,000 species, or more?); general characteristics:. Very, very, very, very, very, very, common!!!. One study found 90,000 nematordes in a single rotting apple. Maybe we’ll check this one out for ourselves in next weeks lab !!.
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Phylum nematoda – round worms (~50,000 species, or more?); general characteristics:
Very, very, very, very, very, very, common!!!
One study found 90,000 nematordes in a single rotting apple.
Maybe we’ll check this one out for ourselves in next weeks lab !!
Another study found 236 different species in about 6.7 cc of coastal mud!!
Triploblastic, bilateral, vermiform, un-segmented, pseudocoelomates
Body round in cross section and covered by a layered cuticle; growth in juveniles
usually accompanied by molting
Have complete gut
Have no specialized circulatory or gas exchange structures, and only longitudinal
muscles. Why do you think they need a substrate to live in?
Can be free-living or parasitic
Parasitic example: Heart worms… cool eh?
Whereas cnidarians and platyhelminthes did not have a body cavity (coelom),
nematodes do. It is however a pseudocoelom. All the other animals that we discuss
from now on will have true coelom (including us!). What is the advantage of
having a coelom?
* Note that in this picture, blue represents ectoderm, yellow represents endoderm, and red
represents mesoderm. Green is the mesoglea which is not a true tissue…
Phylum Annelida – segmented worms (~12,000 species) - general characteristics:
Bilaterally symmetrical, segmented worms with a true coelom
Digestive tract complete, usually with regional specializaiton
Closed circulatory system
Nervous system well developed
Marine, terrestrial, and freshwater species exist
Include earthworms, marine polychaetes, and leaches
Evolution of the coelom (body cavity):
Generally speaking, annelids are a very
diverse group, particularly the marine
polychaetes which may have highly
Class Polychaeta – include most of the marine and freshwater annelids… these
worms are often very well developed, having specialized
appendages for feeding and/or swimming called setae or
Class Oligochaeta – earthworms and other similar freshwater annelids.
have no setae or parapodia…
Class Hirudinida – leeches… complex reproductive systems, hermaphroditic, most
most are freshwater or marine (a few are semi-terrestrial).
Ectoparasitic, they can be predaceous or scavenging…
These animals have specialized suckers
to help them attach to their “prey”…
They also produce anesthetics and
anticoagulation chemicals… Why do you
think this is?
Phylum Trdigrada (water bears)
~ 400 – 500 species
Free living or symbiotic, they are
found all over…
Tardigrades are known for their
Anabiosis – state of greatly recuced
metabolic activity during
unfavorable conditions; and
Cryptobiosis – an extreme state of
anabiosis or dormancy where
all external sings of metabolic
activity are missing!!
How tough are they?
check it out…
Tartigrades have recovered from immersion in extremely toxic compounds such as
brine, ether, absolute alcohol, and even liquid helium!!
They have survived temperature ranging from +149 C to –272 C (almost at absolute zero!!)
They have also survived high vacuums, intense ionizing radiation, and long periods with no
Former Soviet zoologists claim that tardigrades survived experiments in outer space!!
In one case, a 120 year old dried moss specimen from a museum was accidentally moistened,
yielding living tardigrades!!! ….. You get the picture….
Phylum Mullusca – snails, slugs, clams, oysters, squids, octopus, etc. (> 50,000 species – maybe up to 100,000??)
Bilaterally symmetrical (or secondarily asymmetrical), coelomate
Well developed organ systems
Have mantle with shell glands that secrete calcareous epidermal spicules,
shell plates, or shells
Have large, well defined muscular foot, often with a flattened creeping sole,
(in squids and octopus, the foot is modified into tentacles / arms.
Generalized mulluscan body:
Class Gastropoda – slugs, snails, and nudibranchs
Not all gastropods have shell (blue). There is a high level of variation amongst different
shells; why do you think this is? How do you think nudibranchs that do not have any
Shells defend themselves?
Most gastropods have a large, fleshy foot which is used for locomoation (green)
Most gastropods have a unique file-like mouth part called the radula (orange).
Herbivorous forms use it for grazing, carnivorous forms have modified it into a drill, or
a harpoon that can inject toxins into their prey.
Most gastropods have gills for gas exchange.
What do you think is the function
of this shell?
How do you think this animal
Chitons also have a large foot (green) that
is used for locomotion and clamping down
on rocks; gills (yellow) for gas exchange;
a shell made up of 7 or 8 individual plates
(blue); and a radula (orange) specialized
for grazing on algae and some encrusting
What do you think is the advantage
of having multiple (7 or 8) shell plates?
Bivalves have two shells, hinged along
One edge, with the animal in between (blue).
Most bivalves use their gills (yellow) for both
gas exchange, as well as for food capture. How
do you think this may work?
The foot (green) of some bivalves is reduced,
While in others, it is specialized for digging.
Here is a picture of a clam.
Bivalves also include mussels, oysters,
Cephalopods – octopus, squids, nautilus, and cuttlefish
Cephalopods have generally modified their
foot (green) into tentacles (arms) that allow them
to manipulate potential prey items, as well as to
move around their environments
Their shells (blue) can be complete and external
(nautilus), reduced and internal (squid), or completely
non-existent (octopus). What is the advantage of each?
Most cephalopods use gills (yellow) for gas exchange,
and have a specialized beak (orange) for tearing
Finally, most cephalopods use jet propulsion
for movement and swimming… and… they
seem to be very good at “solving problems”…