BIOSCI 106: Lower Arthropod Lab
Modifications
Please read page one with the goal of understanding and
retaining the material. Regarding tagmata, the following illustrations may
help:
Spiders:
At the top of page two, you are comparing
the distinguishing characteristics of annelid worms to the arthropods.
Review the bolded words on page 1 and if they are adaptations new to the
arthropods, enter them on page two into the 1-10 slots.
With regard to the classification of arthropods, zoologists
have been actively debating this issue for 30 years. Recent developmental
and DNA evidence is abundant and should provide some answers within the next
several years. Historically taxonomists fall into two distinct categories:
"the lumpers" and "the splitters." The text implies that the arthropods
should be placed in a larger taxon that would include all of the "molting"
organisms (since most scientists agree that this new adaptation occurred only
once). Within this taxon, there would be four current (living) arthropod phyla.
For purposes of this lab, we will use the classification presented in the lab
book. However, just be aware that it could just have easily been:
Phylum Arthropoda
Subphylum Trilobata
Subphylum Chelicerata
Subphylum Myriapoda
Class Chilopoda
Class Diplopoda
Subphylum Crustacea
Subphylum Hexopoda or Insecta
Subphylum Trilobata Fossil Picture:
Page 3--Subphylum Chelicerata
Chitinous exoskeleton of tarantula (hollow on inside):
Chelicerae (fangs) of tarantula are folded ventrally
under cephalothorax when not in use and extended anteriorly during
feeding and when making a "threat" display:
Bottom of page 3--sun scorpions (or solpugids)
Dorsal and lateral pictures of the sun scorpion's primitive
mouthparts (all the better for holding, mashing, and slurping the juices of
their prey):
Page 4--Picture of the dorsal side of the horseshoe crab:
Picture of the ventral side of the horseshoe crab (Limulus
sp):
Pincer-like chelicerae of the horseshoe crab are the first
pair of appendages. Recall that all chelicerates do not have antennae.
Page 5--Class Arachnida (Read the distinguishing
characteristics and note them in the appropriate place on page 11 (summary
sheet). You may also want to review the distinguishing characteristics shared by
all chelicerates (on pg 3).
When spiders walk, they alternately touch first one and then
the other spinerette to the ground or substrate, each time attaching their web.
Note the spinnerets at the end of the abdomen:
From
what you have learned so far, does the tarantula have antennae? The four
pairs of longer legs are the walking legs. The two shorter
leg-like structures near the folded fangs are the pedipalps, leg-like
appendages modified as sensory and reproductive structures. During
mating, the male must collect sperm from his genital opening with his
pedipalp and then while keeping the female calm and involved in mating
(and not eating him!), transfer it to her genital pore with a pedipalp.
The arachnid plastomount will be out in lab and you will note
that generally arachnids have four pair of walking legs.
Blurry tick picture (middle of page5).
Note the four pair of walking legs. The head has chelicerae and lacks
antennae. Be sure to check out the slide of the tick in lab or when keying out
the unknowns.
Then enjoy the following images:
Note four pair of walking legs, two shorter pedipalps used to
transfer sperm to the female and for sensory purposes, the two chelicerae
(fangs) for injecting vemon (digestive enzymes) into the prey, and at the end of
the organism, the spinnerettes.
Note chelicerae (fangs), pedipalps and walking legs
Page 6, Anatomy and
Dissection of the Crayfish (most of you have done this during the Mollusca/Echinodermata
lab. The following pictures may help to nudge your memory.
Whole crayfish (3
pictures):
Beautiful picture below,
but the diamond shaped heart is missing from the top of the head, just behind
the eyes. Gills (feathery structures)are barely visible on the far side:
Heart on top, gills below to the top left:
From your reading and
these pictures, you should be able to complete the table on page 8.
Page 9 Begins our
discussion of the arthropods that lack fangs, but have chewing mouthparts called
mandibles.
Class Chilopoda--the
centipedes. Note the head with one pair of antennae and the elongate body
with more than 15 pair of walking legs. In the second picture, observe the
mandibles in the form of maxillipeds that function as both pincers and poison
claws.
Bottom of page 5--Class
Diplopoda, the millipedes:
Note the elongate bodies
with most segments having two pair of walking legs. Their head has one
pair of antennae and their mandibles are specialized for chewing decaying
matter, hence they are not predators like the centipedes although some tropical
species are dangerous.
