Arthropods

"Arthropods: What Makes Them So Abundant?" and "A Closer Look at Arthropod Features"

What is Panarthropoda?

A group of animals that shed external skeletons and are all segmented, suggesting arthropods are monophyletic.

What is the Phylum Tardigrada?

Tardigrades, or "water bears," are microscopic animals that can survive extreme conditions by entering a cryptobiotic state.

How do tardigrades survive extreme conditions?

They lower metabolism to 0.01% of normal and reduce water content to about 1%.

Why do tardigrades use less water?

To prevent freezing at low temperatures.

What are the three main types of taxonomic groupings?

Monophyletic (common ancestor and all descendants), Paraphyletic (common ancestor but not all descendants), and Polyphyletic (no common ancestor).

How does molecular phylogeny affect classification?

It has shown that many classic groups are actually paraphyletic or polyphyletic.

What are the two major developmental pathways in animals?

Protostomes (develop mouth first) and Deuterostomes (develop anus first).

What are the defining features of arthropods?

Exoskeleton, segmented body, paired jointed appendages, and distinct body units (tagmata).

Why are arthropods so successful?

Versatile body plan, rapid reproduction, ability to adapt to various environments, and strong exoskeleton for protection.

What are the three main body segments (tagmata) in arthropods?

Head (sensory organs), Thorax (locomotion), and Abdomen (digestion and reproduction).

What are the main subphyla of arthropods?

Chelicerata (spiders, scorpions, horseshoe crabs), Hexapoda (insects), Trilobitomorpha (extinct trilobites), Crustacea (crabs, lobsters, shrimp), and Myriapoda (centipedes and millipedes).

What is unique about Chelicerata?

They lack antennae and use specialized claw-like structures for catching prey, which evolved into fangs in spiders.

How do book lungs function in Chelicerata?

They are folded membrane structures that maximize oxygen intake and provide energy for movement.

What is the role of Malpighian tubules in arthropods?

They function as excretory organs, filtering waste and maintaining water balance.

What is unique about horseshoe crabs?

They have a single carapace covering their prosoma, compound eyes, and a tail (telson) for flipping themselves over.

What are the main groups within Chelicerata?

Araneae (spiders) use silk and have venomous fangs, Scorpions have venomous stingers and pectines for sensing pheromones, Acari (mites & ticks) are small, often parasitic, and economically significant.

What makes Myriapoda different from other arthropods?

They have a single pair of antennae, simple eyes, and are more closely related to Pancrustacea than Chelicerata.

How do centipedes differ from millipedes?

Centipedes (Class Chilopoda) are predatory, venomous, and have one pair of legs per segment, while Millipedes (Class Diplopoda) are detritivores, slow-moving, and have two pairs of legs per segment.

Why are millipedes important in evolution?

They were possibly the first animals to move onto land around 428 million years ago.

What is the largest arthropod subphylum?

Hexapoda, which includes insects and is one of the most diverse groups of animals.

How do arthropods grow despite having a rigid exoskeleton?

They undergo molting (ecdysis), where they shed their old exoskeleton and grow a new, larger one.

What is the exoskeleton of arthropods made of?

Chitin, a tough and flexible polysaccharide that provides protection and support.

How do insects breathe?

Through spiracles (small openings on their exoskeleton) connected to a tracheal system for gas exchange.

What is hemolymph?

The circulatory fluid in arthropods, which functions like blood but is not enclosed in vessels.

What is the function of compound eyes in arthropods?

They provide a wide field of vision and detect movement efficiently, making them excellent for avoiding predators.

How do crustaceans differ from other arthropods?

They have two pairs of antennae, specialized appendages, and mostly live in aquatic environments.

What is metamorphosis in insects?

A developmental process where insects change form, either through incomplete metamorphosis (gradual changes) or complete metamorphosis (distinct larval, pupal, and adult stages).

What is the difference between complete and incomplete metamorphosis?

Complete metamorphosis includes four stages (egg, larva, pupa, adult), while incomplete metamorphosis has three stages (egg, nymph, adult) without a pupal stage.

Why are insects ecologically important?

They act as pollinators, decomposers, and a food source for many animals, playing a vital role in ecosystems.

How do some arthropods communicate?

Through pheromones, visual signals, and mechanical vibrations.

What is the function of the antennae in arthropods?

They detect chemical signals, vibrations, and environmental changes.

How do scorpions capture prey?

They use pincers to grasp prey and a venomous stinger to subdue it.

Why are trilobites significant?

They were one of the earliest known arthropods and provide important fossil evidence of early animal evolution.

How do aquatic arthropods like crabs breathe?

They use gills to extract oxygen from water.

What is the function of silk production in spiders?

It is used for web-building, prey capture, egg protection, and movement.

What adaptation allows some insects to live in dry environments?

A waxy exoskeleton that helps prevent water loss.

What does the term Crustacea mean?

Derived from Latin crusta (shell) + acea (belonging to); means "shell owner."

What is the general habitat of crustaceans?

Mostly aquatic and marine; only one terrestrial group, the woodlouse.

How diverse are crustaceans in size and form?

Extremely diverse, ranging from 0.5 mm to 4 metres in leg span.

How many crustacean species are currently described?

At least 67,000 species.

What roles do crustaceans play in ecosystems?

Key roles in aquatic food chains; some species are commercially important.

What type of development do many crustaceans undergo?

Moulting with partial cuticle shedding and formation of a new one.

What does the moulting process involve?

Filling body with air or water to break off the old cuticle along weak lines.

What does it mean that Crustacea is a paraphyletic group?

It doesn't include all descendants (Hexapods), which are now grouped in Pancrustacea.

What is Pancrustacea?

A monophyletic group combining crustaceans and hexapods, based on genetic and morphological similarities.

What kind of limbs do crustaceans have?

Biramous limbs - two branches, each with different functions.

What are the functions of crustacean antennae and antennules?

Antennae detect environmental changes and pheromones; antennules detect nearby stimuli.

What are maxillipeds?

Modified thoracic limbs used for manipulating food and assisting mouthparts.

What are swimmerets used for?

Primarily reproduction and sometimes respiration.

How are crustacean legs specialised?

Legs are adapted for walking, ventilation, respiration, grasping, and reproduction.

What are the three parts of a typical crustacean limb?

Exopod (outer), Endopod (inner), and Protopod (base connecting the two).

What evolutionary change occurred in arthropod limbs?

From simple biramous forms to highly specialised appendages.

What did fossil trilobites reveal about ancestral limbs?

Biramous legs also served as gills, showing multifunctionality.

What are uniramous legs and how did they evolve?

Single-branched legs thought to have evolved multiple times independently.

Which genes control limb development in arthropods?

Hox genes, shared widely across animals.

What is Evo-Devo and how is it relevant to crustaceans?

Evolutionary developmental biology; studies how development drives morphological evolution.

How is the body of advanced crustaceans different from primitive ones?

Shortened trunks, specialised limbs, and development of a carapace.

What evolutionary trend is seen in the body plan of crustaceans?

Trunk shortening and fusion of segments to form the cephalothorax.

What adaptations help crustaceans live in freshwater or on land?

Water-retentive cuticle, dilute body fluids, ion uptake through gills or body surface, and direct development.

What is the carapace and how does it form?

Formed from the posterior head fold and fused thoracic segments.

What are the main advantages of the carapace?

Hydrodynamics, feeding efficiency, respiratory protection, and brooding chamber for offspring.

How do crustaceans use the carapace for respiration?

Gills are housed in a chamber under the carapace, protected and irrigated.

How is the carapace useful on land?

It retains water and allows for gas exchange in air-filled cavities above the gills.

What reproductive benefit does the carapace provide?

Forms a brooding chamber to protect and retain eggs during development.

Give examples of crustacean groups that use the carapace for brooding.

Branchiopods, clam shrimps, and Daphnia.

What is the function of abdominal appendages in crustaceans?

Found in Remipedia and Malacostraca, used for swimming and reproduction.

What is the cephalothorax?

A fused head and thorax covered by the carapace, seen in decapods.

How have crustacean limbs evolved for food handling?

From basic appendages to specialised maxillipeds that sort and manipulate food.

How are the thoracic limbs modified in decapods?

Into maxillipeds for feeding; gills arise from leg bases (epipodites).

What ventilates the gills in advanced crustaceans?

The scaphognathite, found on the second maxilla.

How does leg specialisation show in advanced crustaceans?

Legs adapted for distinct roles: walking, swimming, reproduction, respiration, and food sorting.