3 arthropod lineages that emerged in the cambrian
Trilobites, chelicerates, crustaceans
when did arthropods arise?
most likely in the precambrian.
x are speculated to be the first arthropod group moving to land, followed by
myriapods, followed by insects.
Why might we say that myriapods gave rise to insects?
because Myriapods are speculated to be the first group moving to land, followed by the insects.
Two schools of thought on how insects arose
1. insects arose from myriapods 2. insects arose from a small crustacean form. Unresolved.
The now extinct trilobites arose
in the Late precambrian to cambrian
This subphylum contains a group of extinct marine arthropods
Ranged in size from a few millimeters up to 75 centimeters
Members of subphylum Trilobita had a body divided into three parts
1. cephalon (head) a single plate made up of several fused segments 2. thorax (a number of segments hinged together) 3. pygidium (tail), also segmented, but like the head, fused together into a single plate.
Even the early derived arthropods like trilobites demonstrated
Even at the time of trilobites, these were present
Extensive fossil record suggests that an early adaptation of the exoskeleton was
Defensive behavior exhibited by trilobites
In their day, x were extremely diverse and already demonstrating a wide variety of segment and appendage modifications
Number of segments and appendages in each tagma varies by
Cephalothorax of x segments in Chelicerata
6 segments. 1 pr. chelicerae, 1 pr. pedipalps. 4 pr walking legs.
Cephalothorax of x segments in Crustacea
13 segments. 2 pr. antennae, 1 pr. mandibles, 2 pr. maxillae, 3 pr. maxillipeds, 5 pr. walking legs(1st pair modified as chelipeds)
Describe uniramous vs. biramous appendages
Appendages are either uniramous (one branch) or biramous (two branches, ancestral characteristic of Crustacea only)
Mouthparts are either chelicerae (characteristic of Chelicerata!) or mandibles (in myriapoda, Crustacea, Hexapoda; collectively, the "mandibulates"
Myriapoda, crustacea, Hexapoda
Both x and x serve as primary feeding structure in arthropods but each is derived from the appendages of different segments.
chelicerae and mandibles.
X are more "claw' like, while x are more typically "jaw" like and more variably modified or specialized depending on the group
Basically, in arthropods, what are now x were once simply legs and feet
feeding appendages - chelicerae and mandibles.
Subphylum Crustacea - 1. Most are x, some x and x 2. head has x pairs of antennae 3. mouthparts are x 4. appendages are primitively x 5. body divided into x tagmata.
1. Most are marine, some terrestrial and freshwater 2. Head has 2 pairs of antennae 3. Mouthparts are "jaws" = mandibles and maxillae 4. appendages are primitively biramous (have 2 major branches) 5. Body divided into 2 tagmata, the cephalothorax and abdomen.
Often called "insects" of the sea
distinguishing character of Crustacea
2nd pair of antennae
In Crustaceans, what appendages are on the cephalothorax?
2 pairs of antenna, mandibles, 1st and 2nd maxillae, 3 pairs of maxillipeds, 5 pairs of walking legs.
Crustacean abdomen has what appendages?
usually 6 segments, 1-5 have swimmeret pairs, last segment has pair of uropods and a telson
Crustaceans often covered with a
Exoskeleton in crustaceans is not x and high in x content
not waxy but high in calcium content.
Crustacean x are modified 1st pair of walking legs of thorax and consist of one movable and one unmovable "finger"
In subphylum Crustacea, x appendages are primitive
True biramous appendages consist of x with 2 branches, known as the x and x that arise from it. What is often attached to medial end of some appendages?
.True biramous appendages consist of basal protopod (coxa + basis) with two branches, the exopod and endopod. Gills often attached to the medial end of some (particularly thoracic) appendages.
The cheliped is/is not biramous
is not (it is secondarily uniramous, since the branches do not arise from the protopod.
Class Branchiopoda is in what subphylum?
sea monkeys and water fleas, marine and freshwater, important zooplankton.
Subphylum Crustacea includes 3 classes
Branchiopoda, Maxillopoda, Malacostraca.
Class Branchiopoda means
4 orders in Class Branchiopoda
Anostraca, Notostraca, Cladocera, Conchostraca.
Flattened, leaf like legs (phyllopodia) that function for respiration as well as feeding and locomotion. 4 orders.
In class Branchiopoda - "no shell" brine and fairy shrimp, no carapace.
tadpole shrimp in Class Branchiopoda. Carapace covers cephalothorax but not abdomen.
Of class Branchiopoda = water fleas, carapace covers all but head.
Of class Branchiopoda = clam shrimp; carapace encloses entire body.
With the exception of Cladocera, notice that all name suffixes of Class Branchiopoda order refer to
shell - ostraca, which is really the carapace and describes the form it takes.
Subphylum Crustacea - class maxillopoda - Subclass Ostracoda.
have a bivalved carapace. Marine and freshwater, reduced number of appendages.
x have a bivalve carapace but is distinguishable from the branchiopods with similar coverage by carapace
ostracod carapace is x vs. enclosing carapace of branchiopods
Distinguishing characters of subclass ostracoda?
reduced # of appendages and appendages not feathery/gill like (lifestyle/feeding habits are also quite different.
Subphylum Crustacea=Class Maxillopoda - Subclass Copepoda - 1. mainly x, some x and x. 2. Usually is the most abundant animal in the x 3. Has a x eye
1. Mainly marine, some freshwater and terrestrial (mosses) 2. Usually the most abundant animal in the plankton 3. median eye
One distinguishing character of this subclass is the median eye.
Very important group at base of food chain
Very abundant x serves as food to many others
What is the big deal about the egg sacs of subclass Copepoda?
Characteristic egg sacs carried at end of thorax.
Subphylum Crustacea - Class Maxillopoda - Subclass Cirripedia 1. what organisms? 2. x and x as adults 3. feed with modified appendages called x 4. x form settles and attaches to substrate by head.
1. Acorn barnacles and gooseneck barnacles. 2. marine and sessile as adults 3. feed with modified appendages called cirri 4. larval form settles and attaches to substrate by head.
In adult form appear very "un-crustacean" like
Subclass Cirripedia (the barnacles)
X larva demonstrates crustacean characteristics, but as adult is sessile with numerous segments/tagmata very reduced.
Subclass cirripedia often form x and are x with a long extendable penis to reach neighbors
form dense mats, hermaphroditic with long extendable penis to reach neighbors.
One of the few arthropods that is monoecious, cross fertilization via long penis that can reach out to other individuals in clumped populations
Largest class of Crustacea
Subphylum Crustacea-Class Malacostraca 1. largest class of x. 2. Marine/freshwater/or terrestrial? 3. diverse? 4. Malacostraca means?
1. Largest class of Crustacea 2. can be either marine/freshwater/or terrestrial. 3. very diverse 4. Malacostraca - "soft" shell.
Largest and most diverse crustacean group
Includes the more familiar "shellfish" (e.g crabs, lobsters, shrimp)
Mostly marine and freshwater, but some terrestrial forms that typically require moist habitats, e.g. isopods (still have gills for respiration)
4 orders in Class Malacostraca
1.Order Isopoda 2. Order amphipoda 3. Order Euphausiacea 4. Order Decapoda
"equal foot" - Class Malacostraca - no carapace, dorso-ventrally flattened; abdominal appendages w/gills.
"both sides foot" - In Class Malacostraca- no carapace; laterally compressed; thoracic gills
"Krill" - Class Malacostraca - important and very abundant plankton; bioluminescent.
"ten foot" - Class Malacostraca - 5 pr. of walking legs, 1st often chelate (pincers); crabs, lobsters, crayfish, true shrimp. Most diverse of the orders of Malacostraca.
"Both sides foot"
5 pr. of walking legs, 1st often chelata (pincers)
Order Decapoda, crabs, lobsters, crayfish
Crustacean life cycle
1. egg 2. Nauplius 3. Protozoea 4. Mysis 5. Postlarval stage 6. Adult - Crustaceans undergo a metamorphosis change - nauplius larva is a crustacean characteristic, but post-napliar stages are group specific and variable, even "alien-like"
"old" wing form in which wings remain extended out, cannot be folded over the body.
"New" wing form includes the most familiar types of insects.
Clade Entognatha includes
Protura, Collembola, Diplura, Thysaura,
Clade Neoptera includes
Orthopterodea, Hemipterodea, Holometabola
Hexapoda (a clade) includes what three smaller clades?
Entognatha, and then Insecta (Paleoptera and Neoptera)
Paleoptera and Neoptera