Day 11 Arthropods

Arthropoda

(Jointed Foot)

Arthropods are the largest animal phylum on the planet with more than a million species named and recent studies suggest there might be between 30 and 50 million species on the planet

-3 out of 4 animals on the planet are arthropods

-The largest group of arthropods are the insects

Arthropod Characteristics

-Segmented body/ Metamerism modified by specialization of body regions for specific function (tagmatization)

-Bilaterally symmetrical

-Ventral nervous system

-Coelom reduced to only surrounding the gonads

-Open circulatory system

-Complete digestive tract

-Paired Jointed appendages

-Exoskeleton- made of chitin

-Molt their exoskeleton to grow

-Metamorphosis often present (helps reduce competition between immature and adult stages

Because Arthropoda is so large their are many classes and subphyla

Here are the ones we will study

Subphylum Trilobitomorpha

Trilobites lived during the Paleozoic Era, specifically from the Cambrian period to the Permian period. Their time on Earth spanned about 270 million years, from roughly 521 million years ago (in the Cambrian) to around 252 million years ago (at the end of the Permian). They first appeared in the Early Cambrian and went extinct during the End-Permian mass extinction.

Trilobites were incredibly diverse, with thousands of species, and they thrived in the world's oceans. Their long existence and variety of forms make them one of the most successful and recognizable groups of extinct arthropods.

Subphyla Chelicerata

They all have chelicerae which are fangs that can move

Class Arachnida

-Greek Arachne- Spider

-Have book lungs

-Four pair of walking legs

-Spiders, scorpions, ticks, mites, harvestmen

Class Activity:

Take out a sheet of paper and write your answer to the question in large print then hold up your paper so the teacher can see it.

1. How many limbs does a spider have?

2. How many legs does a spider have?

3) How many arms does a spider have?

Book Lungs

Book lungs are specialized respiratory organs found in most arachnids (such as spiders, scorpions, and harvestmen) that allow them to breathe. These organs are called "book lungs" because of their structure, which resembles the pages of a book. Here's how they work:

Structure: Each book lung consists of a series of thin, flat, leaf-like membranes stacked together. These membranes are highly vascularized, meaning they have lots of blood vessels, which are crucial for gas exchange.
Location: The book lungs are located on the underside of the spider's abdomen, typically in pairs (two book lungs, though some species have more). They are housed in a cavity called the "respiratory chamber."
Function:
- Gas exchange: The main function of the book lungs is to facilitate the exchange of gases (oxygen and carbon dioxide). Air enters the respiratory chamber through small openings called spiracles. These spiracles are located on the abdomen and allow air to flow in.
- Oxygen diffusion: The air passes over the thin, stacked membranes, where oxygen from the air diffuses into the spider’s blood vessels, while carbon dioxide, a waste product, diffuses out into the air to be expelled. The large surface area of the membranes (due to their stacked, book-like structure) makes this gas exchange process efficient.
Ventilation: Unlike vertebrates, spiders don’t have a diaphragm or a complex mechanism to actively inhale or exhale. Instead, they rely on passive air flow. This can be enhanced by movements like expanding and contracting their abdomen or through the use of additional structures like tracheae (in some species) for supplementary oxygen intake.

In short, arachnid book lungs work by using a stack of thin, vascular membranes to allow efficient gas exchange in a passive way, relying on external air flowing through the spiracles into the respiratory chamber.

Order Araneae (Spiders &Tarantulas)

-Latin - spider

-True spiders - over 40,000 species

-Have a cephalothorax and abdomen

-Make many different types of web

-Males use pedipalps to pass a spermatophore or sperm sac to the female

Curly Hair Tarantula

Black Widows

Watch and enjoy this short and interesting video

Jumping Spiders

Watch and enjoy this short and interesting video

Order Scorpiones (Scorpionodea) (Scorpions)

-Over 2,000 species

-Have pincher pedipalps

-Prosoma is what the legs are attached to

-Preabdomen (body)

-Postabdomen (tail)

-Abdomenal sting (Stinger)

-Males lay down a spermatophore and position females over it

Scorpion Vs Mouse

Watch and enjoy this short and interesting video

There are some other orders of arachnids that have an appearance somewhere in between that of a scorpion and that of a spider. Because each of these orders does not have that many species or we do not normal encounter them we do not have to learn them. But they have fascinating behaviors and body structures.

Order Thelyphonida (Uropygid)

-Greek Uropygid - Oura - Tail and puge - rump

-These are Whipscorpions Also called Vinegaroons

Vinegaroons

Watch and enjoy this short and interesting video

Order Amblypygi

-Greek - Blunt Rump

-Tailless whipscorpions or whip spiders ) Commonly called cave spiders or cave scorpions

Order Pseudoscorpionida

-Very small

-Harmless to humans but beneficial since they eat cloths moths, mites, and ants

Order Solifugae

-Latin sol - sun and fugere flee

-1,000 species

-The sun spiders and camel spiders

Order Acarina (Ticks & Mites)

-Greek Akari - mite

-50,000 species

-Mites are an arachnid that usually lives on or around an animal and feeds on its blood. Mites are specific to groups of animals. For example there are bird mites, reptile mites, etc.