Arthropods Lecture Notes PDF

They are the largest group within the arthropod phylum.  They live in almost every terrestrial habitat and in fresh water, and flying insects fill the air.  Entomology is the scientific study of insects, a branch of zoology is a vast field with many subspecialties, including physiology, ecolog...

They are the largest group within the arthropod phylum.  They live in almost every terrestrial habitat and in fresh water, and flying insects fill the air.  Entomology is the scientific study of insects, a branch of zoology is a vast field with many subspecialties, including physiology, ecology, and taxonomy….etc.  Class Insecta is divided into about 26 orders. Many insects have one or two pairs of wings that emerge from the dorsal side of the thorax.  950,000+ species insects described, about 20,000 new species of all organisms are described each year, most insect species may remain undescribed.  Many adaptations make insects one of the most successful terrestrial animals.  Exoskeleton for water conservation  Tracheal System for gas exchange  Metamorphosis  Many types of mouth parts  Flight Sense organs and specialized Mouthparts  Sense organs: compound eye and antennae Generalized Insect  Organ Modified mouthparts Mouthparts have allowed hexapods to diversify and use different food sources.  The internal anatomy of an hexapod includes several complex organ systems:  In the complete digestive system, there are  regionally specialized organs with separated 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. 3 Kinds of Hexapod Metamorphosis  Ametabolous Metamorphosis – only difference between larvae and adult are size; both are wingless. (case of Silverfish).  Hemimetabolous (incomplete) Metamorphosis – develop from egg to adult has several stages or instars with smaller versions of adults called nymphs. Immature nymphs have no wings or reproductive organs until adult.  Holometabolous Metamorphosis – after hatching from egg, immatures are called larvae (very different body form than adult). After several instars, the last larval molt forms a pupa – undergoes radical body form change.  Protective case may enclose pupal stage:  Moths use silk to make a cocoon. Chrysalis fruit  Butterflies use the larval Chrysalis exoskeleton to make a chrysalis.  Adult emerges from the case very  different in body form – eclosion. Complete or Holometabolous Metamorphosis Chrysalis fruit