Review sheet 5             Biology 4900 – Behavior          James Adams and Kristen Sanders

Invertebrates -- Arthropods

Non Insect Arthropods

            The classification of the phylum Arthropoda has been considered to contain 4-5 subphyla for a long time, though as time has passed, our understanding of the relationships between these:

Trilobita (extinct)
Chelicerata -- this includes several different classes, including Horseshoe Crabs, Arachnids (spiders, mites, ticks, scorpions), the unusual Sea Spiders (Pycnogonida), and a bunch of other cool organisms.
Myriapoda -- this includes the well-known centipedes and millipedes, and the less well known pauropods and symphylans.
Crustacea -- this large group includes a number of very well-known marine organisms (crabs, shrimp, lobsters, barnacles), the widespread copepods, and the aquatic/terrestrial isopods.
Hexapoda -- this is the insects, and the small soil-dwelling Protura, Collembola and Diplura

Many earlier studies promoted the idea that hexapods were most closely related to myriapods. However, the most recent studies involving molecular/DNA comparisons suggest that hexapods are actually not only closely related to crustaceans, but that the Crustacea are paraphyletic when hexapods are excluded (see the link to "newest understanding of arthropod relationships" on my website).  The authors of the paper at the indicated link suggest that the Crustacea and Hexapoda should be combined into the Pancrustacea.

Next, we’ll do a quick overview of mating systems, as this will apply not only here, but in insects, other groups we’ve already talked about, and most vertebrates.  Important concepts include:  monogamy, polygamy (polygyny, polyandry, and promiscuity), parthenogenesis

Chelicerates: named for the pincher or fang-like mouthparts (chelicerae)
            Many of these are predatory, and some are venomous, and we will look at the feeding behaviors/predatory avoidance of several groups (sea spiders, spiders [see pg. 271, box 8.1], scorpions, uropygids, camel spiders). Additionally, we will look at spawning behavior/mating behavior in horseshoe crabs and jumping spiders (also see pg. 270, and 333 [sexual suicide]). We’ll further discuss mate guarding and male parental care in harvestmen (daddy-longlegs, see pgs. 327 and 425), and different mating systems (polyandry in pseudoscorpions boosting reproductive success in females, for instance, pg. 372). Some groups are also parasitic, like ticks.

            We will look at feeding behavior/predatory defense in both millipedes and centipedes.  Be aware that millipedes are largely herbivorous or detritivorous, whereas centipedes are active hunters, with large ones being able to kill vertebrates.

            Crabs and lobsters are familiar to everyone – we’ll discuss these and the freshwater crayfish as well. We will discuss a bit about mate signaling, and fitness components indicated by claw size (see pg. 293); different morphs in sponge isopod males (pg. 321); and (female defense) polygyny in marine amphipods (pg. 381). We’ll also show prey capture videos for snapping (pistol) shrimp and mantis “shrimp”, and then filter-feeding by barnacles. There are other groups of crustaceans that include much smaller organisms (copepods, ostracods, decapods, amphipods) that make up much of the zooplankton in the seas. In the terrestrial environment, we can find terrestrial crabs, hermit crabs and isopods (woodlice – pillbugs), though in all cases these species are found close to water or in moist environments.