AP Biology
  Notes InvertIII

Phylum Nematoda: Roundworms are nonsegmented pseudocoelomates covered by tough cuticles

·        Roundworms are found in most aquatic habitats, wet soil, 
  moist tissues of plants, and the body fluids and tissues 
  of animals. There are 90,000 described species, and perhaps
   ten times that number actually exist. They range in size from
   less than 1 mm to more than a meter.

·        The cylindrical bodies of roundworms are covered with
  a tough exoskeleton, the cuticle. As the worm grows, it 
  periodically sheds its old cuticle and secretes a new, 
  larger one.

·        They have a complete digestive tract and use the fluid
   in their pseudocoelom to transport nutrients since they
    lack a circulatory system.

·        Nematodes usually engage in sexual reproduction. The
  sexes are separate in most species and fertilization is internal.
  Females may lay 100,000 or more fertilized eggs per day that
   produce resistant zygotes.

·        The nematodes also include many species that are important 
  agricultural pests that attack plant roots. Other species parasitize
  animals.

·        Over 50 nematode species, including various pinworms and 
  hookworms, parasitize humans. Trichinella spiralis causes 
  trichinosis when the nematode worms encyst in a variety of 
  human organs, including skeletal muscle.

Arthropods are segmented coelomates with exoskeletons and jointed appendages

·        Nearly a million arthropod species have been described - two out 
  of every three organisms known are arthropods.   This phylum is
   represented in nearly all habitats in the biosphere.

·        On the criteria of species diversity, distribution, and
  sheer numbers, arthropods must be regarded as the 
  most successful animal phylum. The diversity and 
   success of arthropods are largely due to three
  features: body segmentation, a hard exoskeleton, 
  and jointed appendages.

·        The body of an arthropod is completely covered by the
   cuticle, an exoskeleton constructed from layers of protein 
   and chitin. The exoskeleton protects the animal and provides
   points of attachment for the muscles that move appendages.

·        The exoskeleton of arthropods is strong and relatively impermeable
   to water. In order to grow, an arthropod must molt (ecdysis) its old 
  exoskeleton and secrete a larger one, a process that leaves the animal 
  temporarily vulnerable to predators and other dangers.

·        Arthropods have well-developed sense organs, including eyes for 
  vision, olfactory receptors for smell, and antennae for touch and smell.
  Most sense organs are located at the anterior end of the animal, 
  showing extensive cephalization.

·        Arthropods have an open circulatory system in which hemolymph 
  fluid is propelled by a heart through short arteries into sinuses (the hemocoel)
  surrounding tissues and organs. Hemolymph returns to the 
  heart through valved pores.   .

·        Arthropods have evolved a variety of specialized organs for
  gas exchange. Most aquatic species have gills with thin feathery 
  extensions that have an extensive surface area in contact with water.  

Candidate phyla

·        Trilobites (all extinct.)

·        Chelicerates (horseshoe crabs, scorpions, ticks, spiders,
   and the extinct eurypterids). clawlike feeding appendages,
   lack sensory antennae most have simple eyes
  (eyes with a single lens)

·        Uniramians (centipedes, millipedes, and insects). 
   jawlike mandibles, pair of compound eyes  
  (multifaceted eyes with many separate focusing elements)
  pair of antennae

·        Crustaceans (crabs, lobsters, shrimps, barnacles, and many others).
   jawlike mandibles, pair of compound eyes (multifaceted eyes with many 
   separate focusing elements),  two pairs of antennae

 Chelicerates have an anterior cephalothorax and a posterior abdomen.                        

·        Their appendages are more specialized than those of trilobites,
  and the most anterior appendages are modified as chelicerae 
  (pincers or fangs).

·        Only four marine species, including the  horseshoe crab, survive today. The
 bulk of modern chelicerates are
 terrestrial and belong to the class Arachnida. The arachnid cephalothorax
 has six pairs of appendages. There are 
  four pairs of walking legs. A pair of pedipalps function in sensing or feeding.

        ·        In most spiders, gas exchange is 
          carried out by book lungs. These are
          stacked plates contained in an internal
          chamber. The  plates present an extensive
          surface area, enhancing exchange 
         of gases between the hemolymph and air.

Uniramians

·        Millipedes (class Diplopoda) are wormlike with two pairs 
  of walking legs on each of their many segments. They eat 
  decaying leaves and plant matter. They may have been 
  among the earliest land animals.

·        Centipedes (class Chilopoda) are terrestrial carnivores.
  The head has a pair of antennae and three pairs of appendages
   modified as mouth parts, including the jaw-like mandibles. Each 
  segment in the trunk region has one pair of walking legs. Centipedes 
  have poison claws on the anterior most trunk segment that paralyzes 
  prey and aids in defense.

·        Insects (class Insecta) outnumber all other forms of life combined.

 Flight is one key to the great success of insects.

·        Flying animals can escape many predators, find food and mates, 
  and disperse to new habitats faster than organisms that must crawl 
  on the ground.

·        The internal anatomy of an insect includes several complex organ systems.

·        In the complete digestive system, there are regionally specialized
  organs with discrete functions. Metabolic wastes are removed from
  the hemolymph by Malpighian tubules, outpockets of the 
  digestive tract. Respiration is accomplished by a branched, 
  chitin-lined tracheal system that carries O₂ from the spiracles 
  directly to the cells.

        ·        The insect nervous system consists of a pair of ventral nerve 
          cords with several segmental ganglia. The two chords 
          meet in the head, where the ganglia form 
          several anterior segments are fused into a cerebral
          ganglion (brain).

Metamorphosis is central to insect development.

·        In incomplete metamorphosis (seen in grasshoppers and some other orders), 
 the young resemble adults but are smaller and have different body proportions.  
 Through a series of molts, the young look more and more like adults until it reaches full size.

·        In complete metamorphosis, larval stages specialized for eating and growing 
  change morphology completely during the pupal stage and emerge as adults.  

 Crustaceans remain in marine and freshwater environments.

·      A few crustaceans are terrestrial or semi-terrestrial. Crustaceans include
lobsters, crabs, crayfish, shrimp, and barnacles, among many others. The multiple 
appendages of crustaceans are extensively specialized.

·        For instance, lobsters and crayfish have 19 pairs of appendages, 
  adapted to a variety of tasks. In addition to two pairs of antennae, 
  crustaceans have three or more pairs of mouth parts, including hard mandibles.

·        Walking legs are present on the thorax and other appendages for 
  swimming or reproduction are found on the abdomen.

        ·        Small crustaceans exchange gases across thin areas of the cuticle, 
          but larger species have gills.   The circulatory system is open, with 
          a heat pumping hemolymph into short arteries and then into sinuses
          that bathe the organs. Nitrogenous wastes are excreted by diffusion
          through thin areas of the cuticle, but glands regulate the salt balance
          of the hemolymph.

  Common  Orders

        ·      Isopods, with about 10,000 species, are one of the largest groups 
        of crustaceans. Most are small marine species, but they can be
        abundant at the bottom of deep oceans. They also include the
         land-dwelling pill bugs, or wood lice, that live underneath moist 
         logs and leaves.

        ·      Copepods are among the most numerous of all animals. These small 
        crustaceans are important members of marine and freshwater plankton 
        communities, eating protists and bacteria and being eaten by many fishes.

        ·      Decapods, including lobsters, crayfish, crabs, and shrimp,
        are among the largest crustaceans. The cuticle is hardened 
        with calcium carbonate. The exoskeleton over the cephalothorax 
        forms a shield called the carapace. While most decapods are marine, 
        crayfish live in freshwater and some tropical crabs are terrestrial as adults.

Deuterostomia

 Phylum Echinodermata: Echinoderms have a water vascular system and 
  secondary radial symmetry (radial adults develop by metamorphosis from bilateral larvae)

·        Sea stars and most other echinoderms are sessile, or slow-moving 
  animals. The internal and external parts of the animal radiate from the 
  center, often as five spokes. A thin skin covers an endoskeleton of 
  hard calcareous plates. Most echinoderms are prickly from skeletal 
  bumps and spines that have various functions.

·        Unique to echinoderms is the water vascular system, a network of 
  hydraulic canals branching into extensions called tube feet. These 
  function in locomotion, feeding, and gas exchange.

·        They are divided into six classes:

·        Asteroidea (sea stars) use tube feet to move, move, and capture
prey; feeds on closed bivalves by grasping the bivalve and 
inserting its stomach into the shell; enzymes from digestive 
organs then digest soft body of bivalve in its own shell; 
can regenerate lost limbs and sometimes an entire body from 
a single limb.

·        Ophiuroidea (brittle stars) distinct central disk, long flexible 
arms, move by lashing arms; either scavengers, predators, or 
suspension feeders.

·        Echinoidea (sea urchins and sand dollars) no arms, five rows 
of tube feet for locomotion; sea urchins are spherical, sand dollars 
are flat; eat seaweed and other foods.

·        Crinoidea (sea lilies and feather stars) use arms for suspension feeding; 
show very conservative evolution; fossilized sea lilies from 500 million 
years ago could pass for modern members of that class.

·        Holothuroidea (sea cucumbers) do not look like other echinoderms; 
lack spines, hard endoskeleton reduced, and oral-aboral axis is elongated; 
five rows of tube feet; feet can act as feeding tentacles for suspension- or 
deposit-feeding.

·        Concentricycloidea (sea daisies).