Lecture 24 (1) Vocabulary (BIOL211)

This set of vocabulary flashcards covers the diversity and defining characteristics of Ecdysozoans (Nematodes, Arthropods) and Deuterostomes (Echinoderms, Hemichordates, Chordates), including the origins of Vertebrates.

Ecdysozoa

A clade of animals, sister to the Lophotrochozoa, whose bodies are covered by an extracellular cuticle and must undergo molting to grow.

Cuticle

An extracellular layer covering the body of all ecdysozoans used for protection and skeletal support.

Ecdysis

The periodic process of molting or shedding the old cuticle to form a new one, allowing for growth.

Nematoda

A phylum of unitary, pseudocoelomate ecdysozoans that live in damp habitats, feed on fluids, and possess a complete gut.

Caenorhabditis elegans

A critical model system in developmental biology; adults have exactly $959$ somatic cells, the locations and functions of which are well understood.

Cryptobiosis

A state of suspended animation undergone by certain organisms, such as Tardigrades and rotifers, in temporarily wet habitats.

Arthropoda

A phylum containing approximately $1,000,000$ described species (~$75\%$ of all described animals) characterized by a rigid cuticle and jointed appendages.

Hemolymph

The blood-like fluid found in the partially open circulatory systems of arthropods, flowing in spaces between tissues and organs.

Tracheae

Long, narrow tubes in the insect gas exchange system that open at spiracles and deliver oxygen to organs by diffusion.

Chelicerae

One of two pairs of head appendages in chelicerates, modified for grabbing food and sometimes injecting poison.

Pedipalps

A pair of head appendages in chelicerates used to sense or grab food.

Myriapods

A clade of arthropods with two body regions (head and trunk) including centipedes (one pair of legs per segment) and millipedes (two pairs per segment).

Nauplius

A specific larval stage characteristic of the crustacean group within the Pancrustacea clade.

Hemimetabolous development

Also known as incomplete metamorphosis; the larval stages (instars) look like small versions of the adult.

Holometabolous development

Also known as complete metamorphosis; the larva looks very different from the adult and undergoes a dramatic change.

Deuterostomia

A group where embryos undergo radial cleavage, the blastopore becomes the anus, and mesoderm develops from outpocketings of the archenteron.

Hemichordates

Worms with a three-part body plan consisting of a proboscis, collar, and trunk, possessing pharyngeal slits for gas exchange.

Pentaradial symmetry

A secondarily evolved radial symmetry found in adult echinoderms where body parts are arranged in five rays.

Water vascular system

A unique system in echinoderms consisting of fluid-filled tubes like the madreporite and tube feet used for locomotion and feeding.

Chordata

A phylum of bilaterally symmetrical, coelomate, segmented animals defined by a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.

Notochord

A dorsal rod composed of large, fluid-filled cells that acts as a rigid but flexible skeletal element in chordates.

Tunic

A secreted exoskeleton of cellulose-like material found in urochordates, also known as tunicates.

Cranium

An anterior skull with a large brain, a defining feature for the vertebrate lineage.

Cyclostomes

A clade of jawless vertebrates consisting of hagfishes (Myxini) and lampreys (Petromyzontida).

Gnathostomes

A clade encompassing all vertebrates that possess jaws.

Myxini

Commonly known as hagfishes; marine scavengers with a cartilaginous skull, no jaws, and the ability to secrete large amounts of slime.

Petromyzontida

Commonly known as lampreys; vertebrates with a cartilaginous skeleton and larvae called ammocoetes.