Animal Complexity, Segmentation, Annelids, and Arthropods

Vocabulary flashcards covering segmentation, evolutionary traits, and classes within the phyla Annelida and Arthropoda from the lecture.

Segmentation

The repetition of anatomically identical units that can be added to and modified to serve different purposes as animals evolve.

Synapomorphy

A shared derived trait that sets one group of animals apart from its ancestors and from other groups that came from the same ancestors.

Plesiomorphy

A very basic trait shared by animals with a common ancestry.

Chaetae

Little bristles on the body of an annelid that provide traction and help it move through dirt.

Annelida

The earliest phylum among today's animal phyla to display segmentation, named from the Greek for 'little rings', which includes leeches, earthworms, and lugworms.

Oligochaetes

A class within Annelida consisting of earthworms, named for having few chaetae, which digest soil and enrich it with nitrogen, calcium, magnesium, and phosphorus.

Hirudinea

A class within Annelida consisting of leeches, characterized by powerful suckers on both the anterior and posterior ends of their bodies.

Polychaetes

A class within Annelida made up of mostly marine species that are characterized by having many chaetae.

Arthropoda

A phylum of segmented animals with hard chitin exoskeletons and paired, jointed appendages, whose name means 'jointed feet'.

Chitin

A tough carbohydrate chemically similar to plant cellulose that makes up the hard outer exoskeleton of arthropods.

Cheliceriformes

A subphylum of Arthropoda named for long fang-like pincers ('arm-lips'), characterized by simple eyes with one lens and a lack of antennae.

Cephalothorax

A body region composed of a head segment and a thorax segment fused together, present in arachnids and some crustaceans.

Myriapoda

A subphylum of terrestrial arthropods ('many feet') characterized by antennae and jaw-like mandibles, including millipedes and centipedes.

Hexapoda

A subphylum of arthropods ('six feet') consisting mostly of insects, defined by three-part bodies, three pairs of thoracic legs, compound eyes, and two antennae.

Meganeura

An ancient giant insect from the Carboniferous period, about $320 \text{ million}$ years ago, that resembled a dragonfly with a two-foot wingspan.

Partial Metamorphosis

A process of insect growth where young nymphs resemble miniature adults and undergo molts to grow larger without radically altering their form.

Complete Metamorphosis

A process of insect development unique to certain species where the organism completely changes shape through distinct larva, pupa, and adult stages.

Crustacea

A subphylum of primarily aquatic arthropods referred to as 'insects of the sea', including crabs, lobsters, shrimp, and barnacles.