Annelids and Arthropods: Structure and Evolution

Prostomium

First segment of annelids' body structure.

Peristomium

Second segment following the prostomium.

Pygidium

Last segment of an annelid's body.

Growth Plate

Structure after pygidium for growth.

Parapodium

Lateral extensions from segments, non-jointed.

Triploblastic

Organism with three germ layers: ectoderm, mesoderm, endoderm.

Closed Circulatory System

Blood contained within vessels, no direct contact.

Ocelli Eyes

Light-sensitive organs for detecting light.

Metanephridia

Excretory organs for ammonia removal.

Hydrostatic Skeleton

Support structure using fluid pressure.

Dorsal Blood Vessel

Main vessel pumping blood anteriorly.

Ventral Blood Vessel

Vessel pumping blood posteriorly.

Clitellum

Band structure secreting cocoons in earthworms.

Monoecious

Organisms having both male and female reproductive organs.

Typhlosole

Fold increasing surface area in earthworm intestines.

Spermathecae

Organs storing sperm for later fertilization.

Subclass Oligochaeta

Class of annelids including earthworms.

Subclass Hirudinea

Class of annelids including leeches.

Hirudin

Anticoagulant secreted by leeches.

Hemocoelic System

Body cavity filled with blood, not segmented.

Ecdysone

Hormone triggering molting in nematodes.

Eutelic

Organisms with a fixed number of cells.

Malpighian Glands

Excretory structures in tardigrades for osmoregulation.

• filters the blood and dumps wastes into the gut for elimination

Lobopod

Jointed appendages in onychophorans.

ecdysozoan clade

- open circulatory system

- must molt to grow

- extensive hemocoel

- heart with openings to hemocoel (ostia)

- spiders use blood pressure to jump

- striated muscle lets things fly

Phylum Nematoda Characteristics

- triploblastic

- unsegmented but with annotations

- All free living live in the water due to permeability of the cuticle

- Body is turgid (limitations in movement)

- Only longitudinal muscles

- eutelic

- Pseudocoelom

- Nonexistent respiratory / excretory systems

- dioecious

- must shed cuticle to grow

Phylum Tardigrade Characteristics

- Loss of heart

- Loss of nephridia

- Eutelic development

Striated muscles

- Hemocoelic body cavity

- Malpighian glands (Osmoregulatory structures)

Phylum Onycophora (velvet worms)

- No blood pigment

- To feed they Shoot glue from slime glands and bite prey injecting material to liquefy prey

- Free living Protostome coelomates

- Slime glands

(Discharge glue that helps digest material through openings in the oral papillae)

Subclass Oligochaeta Characteristics - EARTHWORMS

- Parapodia absent (spiky looking things that help with movement)

- Prostomium is small

- Has typhlosole

- has spermathecae

Crop

- storage of food

gizzard

- grinding of food

Tergum

Dorsal Plate for arthropods

Sternum

Ventral plate for arthropods

Pleuron

holds dorsal and ventral body plates together (flexible)

Resilin

- insect rubber

- inprocuticle

- substance that stores energy and releases efficiently

Arthropod Gut characteristic

- straight, differentiated for special functions

foregut

- ingestion, "chewing", and storage of food, lined with cuticle

midgut

- site of enzyme production, digestion and absorption

hindgut

- function in absorption of water and formation of feces

Arthropod excretory system

1. Malpighian tubules

- filters blood and dumps waste into gut for elimination

2. saccules

- paired, open to the outside of body next to an appendage

- derived from coelom

- filter surrounding blood

Arthropod Digestive system

metamer

“rings” that divides body into segments

hydrostatic skeleton

uses pressure of coelomic fluid as support for movement

heteronomous

some segments are specialized

pereopod

used for walking

Telson

end of abdomen, where the rectum is

Hemocoel

body cavity filled with hemolymph

What type of body cavity is found in nematodes?

Pseudocoelom

What structure provides nematodes with structural support?

Hydrostatic skeleton

What is the composition of the nematode cuticle and a second character shared with one other phylum?

 Multilayered collagen fibers that must be shed to grow

How is nematode development characterized in terms of cell division?

Eutely, where each species has a fixed number of cells at maturity

What is unique about the muscle structure in nematodes?

Nematodes have only longitudinal muscles, lacking circular muscles

How are nematode muscles innervated?

Muscles send out processes to the nerve cords

What type of circulatory system is characteristic of arthropods?

Open circulatory system

Arthropods' coelom is primarily used for which function?

Surrounding the gonads and excretory organs

Arthropods' excretory system primarily consists of

Malpighian tubules

The molting process in arthropods is also referred to as

Ecdysis

The arthropod exoskeleton is unique from other phyla in that this structure contains what unique material

Chitin

The main function of arthropods' hemolymph is

Nutrient distribution and waste removal

What type of circulatory system do annelids typically have?

Closed

What structure is used by annelids for excretion?

Metanephridia

What is the primary function of the annelid's coelom?

Hydrostatic skeleton

How do annelids primarily respire?

Through the skin or parapodia

What is the main role of setae in annelids?

To aid in locomotion and defense

Which statement is true about annelid reproduction?

Some are hermaphroditic, and others are dioecious.