Protostomes: Ecdysozoa (Nematodes and Arthropods)

A set of vocabulary flashcards defining key groups, biological structures, and developmental processes of Ecdysozoans (Nematodes and Arthropods) based on lecture notes.

Ecdysozoa

A group of protostome animals characterized by the ability to molt their external cuticle, a process known as ecdysis.

Ecdysis

The process of shedding or molting an external cuticle and replacing it with a larger one to allow for growth, which evolved approximately $500$ million years ago.

Protostomes

Triploblastic animals where the blastopore formed during gastrulation develops into the mouth first.

Deuterostomes

Triploblastic animals where the blastopore formed during gastrulation develops into the anus first, or 'mouth second.'

Triploblastic

Animals possessing three germ layers: the ectoderm, endoderm, and mesoderm.

Kinorhynchs

Commonly known as 'mud dragons,' these are marine or brackish water Ecdysozoans that are usually less than $1\,mm$ in size.

Loriciferans

Commonly known as 'armoured bears,' these marine Ecdysozoans live in sediments and are usually less than $1\,mm$ in size.

Priapulids

Known as 'penis worms,' these are marine predators with a toothed, muscular pharynx that burrow in soft sediments and can grow up to $15\,cm$.

Nematoda

Commonly called roundworms, these thread-like organisms are unsegmented, vermiform, and possess a multi-layered cuticle.

Pseudocoelomate

An organism possessing a fluid-filled body cavity that is not derived from the mesoderm, located between the mesoderm and the endoderm.

Hydrostatic skeleton

A structural system in nematodes and tardigrades where a fluid-filled body cavity under pressure provides shape and facilitates locomotion.

Complete digestive tract

A continuous digestive tube with a separate mouth and anus, allowing for one-way food movement and specialized regional functions.

Ascaris lumbricoides

An intestinal roundworm parasite that infects approximately $1 \times 10^9$ people worldwide, with larvae developing in the lungs.

Caenorhabditis elegans

A model organism in genetics and developmental biology that is transparent, matures in $3$ days, and has a fixed number of somatic cells ($959$) and neurons ($302$).

Nematomorpha

Commonly known as 'horsehair worms' or 'hairsnakes,' these are parasites that reach up to $2\,m$ in length and lack a mouth as adults.

Tardigrada

Commonly known as 'water bears' or 'moss piglets,' these are small organisms with fleshy, unjointed legs that can enter a dormant 'tun state' to survive extreme conditions.

Onychophora

Commonly known as 'velvet worms,' these are tropical predators with paired, unjointed legs that hunt by squirting a sticky secretion onto prey.

Arthropoda

An ultra-diverse group of Ecdysozoans characterized by a segmented body, hard chitinous exoskeleton, and paired, jointed appendages.

Chitin

A waterproof polysaccharide found in the hard exoskeleton of arthropods that provides protection and prevents desiccation.

Tagmata

Specialized body regions, such as the head, thorax, and abdomen, formed by the grouping or fusion of segments.

Cephalothorax

A tagma formed by the fusion of the head (cephalon) and the thorax, found in chelicerates and some crustaceans.

Trilobites

An extinct group of early marine arthropods from the Paleozoic era that possessed one pair of appendages per segment and left an abundant fossil record.

Chelicerates

A group of arthropods, including spiders and scorpions, that possess two tagmata, four pairs of walking legs, and lack antennae and jaws.

Chelicerae

Modified appendages in chelicerates, such as the fangs in spiders, used for capturing prey or injecting venom.

Pedipalps

A pair of appendages in arachnids used for sensory purposes, reproduction in males, or as pincers in scorpions.

Mandibulates

A group of arthropods, including insects, crustaceans, and myriapods, characterized by the presence of antennae and mandibles for chewing.

Chilopoda

Centipedes; terrestrial mandibulates with one pair of legs per segment and poisonous fangs for capturing prey.

Diplopoda

Millipedes; terrestrial mandibulates with two pairs of legs per segment (due to fused segments) that scavenge on decaying plant material.

Hexapoda

The largest group of arthropods, characterized by having six legs ($3$ pairs) and three tagmata: head, thorax, and abdomen.

Incomplete metamorphosis

A type of insect development where changes between life stages are gradual and the young resemble the adults.

Complete metamorphosis

A type of insect development where changes are dramatic, with no resemblance between the juvenile (larva), pupa, and adult stages.