PRINCIPLES OF ZOOLOGY
LAB # 5 (Supplement)
(Written and provided by Dr. Olson, Professor Emeritus)
PHYLUM: ARTHROPODA ("non-insect arthropods")
LAB. MAN: EXERCISE #13-A; Read pages 203-206.
#14-A; Read/Do pages 211-218.
#15-A: Read pages 225-227.
TEXT: CHAPTER #18: Pages 378-384
#19: Pages 389-399
#20: Pages 411-414
Arthropods are likely to have evolved from annelid-like ancestors. Supporting evidence centers around metamerism, or distinct body segmentation, that occurs in both these groups.
The PHYLUM: ARTHROPODA is the largest in the animal kingdom and includes more than three-fourths of all known animals! As a group, arthropods are found in most ecological habitats and are highly adaptable. Many are "beneficial" to man (especially as a food source, or as pollinators) while others represent a "threat" to man’s well-being (especially as disease vectors).
A small, closely-related and interesting group known as the "velvet worms" (PHYLUM: ONYCHOPHORA) is believed, by some, to represent a "connecting link"between the annelids and the arthropods because "velvet worms" possess both annelid and arthropod features, in addition to some of their own. The small, caterpillar-like organism known as Peripatus is the classic representative of this phylum. SEE DEMONSTRATION SPECIMEN. READ PAGE 445 IN YOUR TEXTBOOK.
MAJOR ARTHROPOD CHARACTERISTICS:
1. EXOSKELETON MADE OF CHITIN:
a. The chitinous exoskeleton is frequently cited as the major reason for arthropod success because it provides (1) structural support, (2) an impermeable surface for prevention of water loss, and (3) a system of levers for muscle attachment for movement/locomotion.
b. Also, possession of an exoskeleton necessitated a variety of adaptations to allow arthropods to live and grow within their secreted, non-living, and rigid "shell". These adaptations include (1) flexibility at joints for better locomotion, (2) highly specialized external sensory structures, (3) modifications for gas exchange, and (4) ecdysis (molting) to allow increase in size.
2. METAMERISM (segmentation):
a. The arthropod body is composed of a series of well-defined segments (somites). Many segments are highly-specialized (and thus are not "all alike" as in the annelids).
b. The segmented body of most arthropods is subdivided into distinct regions (tagma): (1) Head (sensory and food intake). (2) Thorax (locomotion) (3) Abdomen (visceral functions). Insects possess all three tagma while most other arthropods possess a cephalothorax (fused head and thorax) and an abdomen.
3. SEGMENTED (jointed) APPENDAGES:
a. This feature gives the phylum its name (arthros = "jointed"; pod = "foot").
b. Jointed, flexible appendages allow more efficient locomotion and greater specialization to perform various life functions.
4. METAMORPHOSIS:
a. This is a complex process usually involving a distinct "change of body form" during the life cycle between the egg and the adult stage.
b. Metamorphosis involves ecdysis (molting of exoskeleton) and contributes to arthropod success through reduced competition within a species because immature and adult forms are often very different in their morphology, preferred habitat, and food habits. Thus, members of a species often don’t "compete" among themselves.
GENERAL ARTHROPOD TAXONOMY: (modified for this lab)
PHYLUM: ARTHROPODA
SUBPHYLUM: TRILOBITA ("trilobites") (Text: 378)
a. Extinct (over 200 million years). Known only from fossils.
b. Were primitive, marine arthropods with a distinctly 3-lobed body.
c. Possessed paired, bi-ramous (2-branched) appendages on most body segments. Trilobite appendages are considered to be the "prototype" for modern arthropod appendages.
SUBPHYLUM: CHELICERATA ("chelicerates") ((Text: 378)
a. Includes: "horseshoe crabs", "crabs", "sea spiders", "spiders", "scorpions", "ticks", and "mites".
b. Mouthparts consist of a modified 1st pair called chelicerae and a modified 2nd pair called pedipalps. (NOTE: mandibles lacking)
c. Most have 2 body regions (cephalothorax and abdomen).
d. 8 legs (4 pairs).
e. 0 antennae.
CLASS: MEROSTOMATA ("horseshoe crabs") (Text: 378)
-Marine arthropods with a prominent cephalothorax covered by a carapace bearing compound eyes.
-The abdomen features flattened, leaf-like book gills on its ventral surface and has a long tail-like telson at its posterior end.
CLASS: PYCNOGONIDA ("sea spiders") (Text: 379)
-Marine, spider-like, bottom-dwelling (benthic) arthropods.
-Abdomen greatly reduced in size (most of digestive and reproductive systems are housed in their legs).
-Males often with an extra pair of legs called ovigers which carry eggs.
CLASS: ARACHNIDA ("arachnids") (Text: 380)
-Includes "spiders", "scorpions", "ticks", and "mites".
-This is the most varied/diverse class of arthropods.
-Members possess many specialized/unusual features.
-Most arachnids are predaceous on other arthropods; Some are "harmful" to man (bite, sting, transmit diseases).
SUBPHYLUM: CRUSTACEA ("crustaceans") (Text: 390)
a. Includes "crayfishes", "lobsters", "shrimp", "crabs", "barnacles", etc.
b. Mouthparts include mandibles (1 pair) and maxillae (2 pairs).
(NOTE: No chelicerae or pedipalps).
c. 2 body regions (cephalothorax and abdomen).
d. Most paired appendages in crustaceans (like crayfish) are biramous, occur in a linear series along the body, and are of a common ancestral origin (from trilobites). For these reasons, crustacean (crayfish) appendages are a good example of serial homology.
e. 2 pairs of antennae (only arthropods with 2 pairs).
f. Crayfishes possess green glands (=antennal glands) for excretion.
SUBPHYLUM: UNIRAMIA ("uniramians") (Text: 412)
a. Includes "centipedes", "millipedes", and "insects".
b. Mouthparts include mandibles (1 pair) and maxillae (1 pair).
(NOTE: No chelicerae or pedipalps)
c. 2 body regions (head and trunk) in centipedes and millipedes.
d. 3 body regions (head, thorax, abdomen) in insects.
e. Appendages are uniramous (un-branched, or not forked).
f. 1 pair of antennae (only living arthropods with 1 pair).
CLASS: CHILOPODA ("centipedes") (Text: 412)
-Body dorso-ventrally flattened (in cross-section view).
-1 pair of appendages per segment; Appendages relatively long.
-1st pair of appendages modified into poison claws.
-Are predaceous and poisonous.
CLASS: DIPLOPODA ("millipedes") (Text: 412)
-Body cylindrical (in cross-section view).
-2 pairs of appendages per segment; Appendages relatively short.
-No poison claws; Are herbivorous (plant feeders).
CLASS: INSECTA ("insects") (Text: 414)
-The largest class of arthropods by far!
- Insects will be more closely considered in lab # 6 (next week)
OBSERVE / STUDY DEMONSTRATION MATERIALS:
"Trilobites"
Phylum?
Subphylum?
Why are they called trilobites?
Where did trilobites live before they became extinct? How long have they been extinct?
What is a biramous appendage? Can you name the 3 basic parts of a typical one?
**Observe trilobite demonstration materials.
"Horseshoe crabs"
Phylum?
Subphylum?
Class?
What are chelicerae and pedipalps?
Where do horseshoe crabs normally live and what do they usually eat?
What are the carapace, book gills, and telson?
**Observe horseshoe-crab demonstration materials.
"Sea spiders:
Phylum?
Subphylum?
Class?
Where do sea spiders live and what do they eat?
What is so unusual about the abdomen of a sea spider?
What are ovigers, which sex usually has them, and what is their purpose?
**Observe sea-spider demonstration materials.
"Spiders"
Phylum?
Subphylum?
Class?
What are the pedicel, book lungs, and spinnerets?
Do a spider’s poison glands connect to its chelicerae or to its pedipalps?
**Observe spider demonstration materials.
"Scorpions"
Phylum?
Subphylum?
Class?
Should all scorpions be considered as deadly/dangerous? Do any live in Arkansas?
How do scorpions "grasp" and then "sting" their prey?
**Observe scorpion demonstration materials.
"Ticks and Mites"
Phylum?
Subphylum?
Class?
How many body regions (tagma) do these arthropods possess?
What is the capitulum of a tick or mite?
In Arkansas, ticks in the genus Dermacentor can transmit a disease called __?__ (abbreviation = RMSF) to man.
Is a "chigger" the larval stage of a tick, or of a mite?
**Observe tick / mite demonstration materials.
"Crustaceans"
Phylum?
Subphylum?
How many pairs of antennae do crustaceans possess?
Do crustaceans possess chelicerae/pedipalps, or do they have mandibles/maxillae?
How can you tell if a crayfish is a male or a female?
**DO CRAYFISH DISSECTION. FOLLOW INSTRUCTIONS IN LAB MANUAL (beginning on page 212). Also, study Fig’s. 14-1, 14-2, 14-3, and 14-4.
Know the structures / terms seen in heavy print on pages 212-218 in lab manual.
**Observe crustacean demonstration materials.
"Centipedes"
Phylum?
Subphylum?
Class?
Are centipedes poisonous? Are they all dangerous to man? What do they normally eat?
Is the centipede body cylindrical or dorso-ventrally flattened (in cross-section view)?
How many pairs of legs do centipedes possess on each body segment?
**Observe centipede demonstration materials.
"Millipedes"
Phylum?
Subphylum?
Class?
Are millipedes poisonous? What do they normally eat?
Is the millipede body cylindrical or dorso-ventrally flattened (in cross-section view)?
How many pairs of legs do millipedes possess on each body segment?
**Observe millipede demonstration materials