Blg 316 - Arthropods

What is the most abundant group of animals on Earth?

Arthropods

In what environments have arthropods adapted to live?

They have adapted to all land environments and climate

How do arthropods affect human populations?

- provide important products

- cause diseases

- contribute to economic losses

What are the key reasons for arthropods diversity and abundance?

- Versatile exoskeleton (provides protection and mobility)

- Segmentation and appendages (for efficient locomotion)

- Efficient respiratory system (air distributed directly to cells)

- Highly developed sensory organs

- Complex behavior patterns

- Trophic breadth through metamorphosis (reduces competition)

What are the 2 major groups of bilaterians?

Protostomia and deuterostomia

What are the major groups under protostomia, and how do they differ?

• Lophotrochozoa (spiral cleavage)

• Ecdysozoa (cuticle molted)

What defines the subphylum Chelicerata?

Having chelicerae (mouthparts) instead of mandibles.

What are the key characteristics of Chelicerata?

- No mandibles or antennae

- Two tagmata

- Six pairs of cephalothoracic appendages:

• 1 pair of chelicerae

• 1 pair of pedipalps

• 4 pairs of walking legs

What are the two subclasses of Merostomata?

• Eurypterida (Giant water scorpions, extinct, largest arthropods)

• Xiphosurida (Horseshoe crabs, ancient marine group)

What are the key features of horseshoe crabs (Xiphosurida)?

• Carapace

• Abdomen

• Telson

What are the key characteristics of sea spiders?

• Four pairs of walking legs

• Suctorial proboscis

• Reduced abdomen

• Males use ovigers to carry eggs

What are the key characteristics of spiders?

• All predaceous

• Chelicerae function as fangs

• Cephalothorax and abdomen joined by a thin pedicel

• Web spinning for prey capture

• Some are cryptic or stalk prey

What are the body regions of scorpions?

• Short cephalothorax

• Abdomen (preabdomen and postabdomen)

• Stinging apparatus

How do scorpions care for their young?

Well-developed young stay with their mother until their first molt.

What are the key characteristics of camel spiders?

• Large chelicerae for shredding prey

• Nonvenomous

• Usually less than 1 cm long, but some reach 15 cm

How do harvestmen differ from spiders?

• No constricting pedicel

• Easily shed legs if grasped

• Pincer-like chelicerae

• Feed mainly as scavengers

What are the key features of ticks and mites?

• Cephalothorax and abdomen completely fused

• Mouthparts located on a capitulum

• Some are free-living; others are parasites

• Can transmit diseases and cause economic harm

What disease is caused by ticks of the genus Ixodes?

Lyme disease

Why do chigger bites itch?

• Chiggers inject enzymes that liquefy skin cells.

• The skin forms a hardened tube, which the larva uses to feed.

• Scratching removes the chigger but leaves the tube, causing irritation.

What is Lyme disease, and how is it transmitted?

Caused by Borrelia burgdorferi bacteria

• Carried by Ixodes ticks

What are the symptoms of Lyme disease?

Arthritis-like symptoms; can develop into a chronic, disabling disease if untreated.

What are the two tagmata of Myriapoda?

head and trunk

What are the key characteristics of myriapodas body structure?

One pair of antennae

Mandible and two pairs of maxillae

Legs are uniramous

What is the feeding behavior of centipedes?

They are predators

How many pairs of legs do centipedes have on each segment?

Each segment contains one pair of legs, except for the segment behind the head and the last two.

What is a distinctive feature of centipedes' body?

Centipedes are dorsoventrally flattened.

What modification do the maxillipeds on the first segment of centipedes have?

They are modified into venom claws.

How are centipedes' eyes structured?

They have a pair of eyes made up of a group of ocelli.

What is a key characteristic of millipedes' appendages?

Most segments have two pairs of appendages, except for the first four thoracic segments, which have only one pair.

How many pairs of walking legs do sea spiders have?

Four pairs of walking legs

What do sea spiders use their proboscis for?

They use a suctorial proboscis for feeding.

What is a distinctive feature of sea spiders' bodies?

Sea spiders have a much reduced abdomen.

How do male sea spiders care for their eggs?

Males use ovigers (a pair of legs) to carry egg masses.

What organisms are included in the class Arachnida?

Spiders, scorpions, whip scorpions, pseudoscorpions, ticks, mites, harvestmen, etc.

What are the two main body parts of arachnids?

cephalothorax and abdomen

Which animals are included in the Myriapods group?

Centipedes, millipedes, pauropods, and symphylans, but not insects.

How do scorpions capture and consume prey?

Pedipalps: Capture prey

Chelicerae: Rip prey apart

What are the two main groups within Subphylum Crustacea?

- Vericrustacea contains most of the well-known crustaceans.

- Oligostraca contains ostracods, branchiurans, and pentastomids.

How is the body of an ostracod enclosed?

The body is enclosed in a bivalve carapace.

How many segments does an ostracod have?

Five cephalic, six thoracic, and four abdominal segments plus a telson.

What is a distinctive feature of ostracods' trunk segments?

There is fusion of trunk segments.

How many thoracic appendages do ostracods have?

Thoracic appendages are reduced to two or one.

What is the primary habitat of most ostracods?

Most ostracods crawl or burrow in marine and freshwater sediment.

What is the feeding behavior of ostracods?

They scavenge food, feed on detritus, or collect suspended particles from the water.

What is a key characteristic of branchiurans regarding their gills?

They lack gills.

What is the feeding behavior of branchiurans?

Most are fish parasites.

What is the body structure of branchiurans?

They have a broad, shield-like carapace, compound eyes, four biramous thoracic swimming appendages, and a short unsegmented abdomen.

How are the second maxillae of branchiurans modified?

The second maxillae are modified as suction cups.

What type of organisms are pentastomids?

Pentastomids are parasitic tongue worms.

What is the primary host of pentastomids?

They parasitize vertebrate respiratory systems, mostly infecting reptile lungs.

What type of cuticle do pentastomids have?

They have a nonchitinous cuticle that is regularly molted during larval stages.

What are the three tagmata in Crustacea?

head, thorax, abdomen

how many pairs of uniramous legs do crustaceans have?

three pairs of uniramous legs

what are the 2 classes in subphylum crustacea?

entognatha and insecta

What distinguishes Class Entognatha?

The bases of the mouthparts are located in the head capsule (entognathous).

What orders are included in Class Entognatha?

Protura, Collembola, and Diplura.

: What distinguishes Class Insecta?

The bases of the mouthparts are visible (ectognathous).

What are the two main subgroups in Class Insecta?

Subclass Paleoptera and Subclass Neoptera.

What order is included in Class Insecta but is not part of either subclass?

Order Thysanura.

What two orders are included in Subclass Paleoptera?

Odonata and Ephemeroptera.

What three orders are included in Subclass Neoptera?

Orthopterodea, Hemipterodea, and Holometabola.

Which animals fall under the heading Entognatha?

Diplura, Protura, and Collembola.

What are the characteristics of Thysanura in Insecta?

Reduced compound eyes, no ocelli, and two to three caudal filaments.

What is unique about Odonata's larval stage?

They have prehensile labium and massive mandibles.

What distinguishes Ephemeroptera in Insecta?

Vestigial mouthparts in adults.

What feature is characteristic of the Holometabola in Insecta?

Holometabolous development.

What features are associated with Orthopterodea in Insecta?

Biting or chewing mouthparts.

What features are associated with Hemipterodea in Insecta?

Reduced wing venation, four or fewer Malpighian tubules, and piercing or sucking mouthparts.

What is the largest portion of the remaining one-third of animal groups divided into? Which animal groups occupy equal portions in the remaining one-third? What occupies the smallest portion of the remaining one-third?

- Other invertebrates.

- chordates and arthropods

- unicellular eukaryotes

What are some examples of animals in Subphylum Crustacea?

Lobsters, crayfishes, shrimp, crabs, water fleas, copepods, and barnacles.

How many pairs of antennae do crustaceans have?

Two pairs of antennae.

What mouthparts do crustaceans possess?

One pair of mandibles and two pairs of maxillae.

How many appendages does each segment of a crustacean have?

One pair of appendages per segment.

What is the structure of crustacean appendages?

All appendages, except perhaps the first antennae, are biramous.

What are the three main parts of a crustacean's biramous appendage?

A basal protopod, an outer branch called an exopod, and an inner branch called an endopod.

How many segments can primitive crustaceans have?

Up to 60 segments.

How do the number of segments in derived crustaceans compare to primitive crustaceans?

Derived crustaceans have fewer segments.

What are the typical tagmata in crustaceans?

Head, thorax, and abdomen.

What is the cephalothorax in crustaceans?

A fused structure where one or more thoracic segments are joined with the head.

What is the dorsal covering of a crustacean called?

The carapace.

What does the carapace cover in crustaceans?

It may cover most of the body or just the cephalothorax.

What are the anterior-most structures in a crustacean?

antennae

How do the first and second antennae differ in crustaceans?

The first antenna is short with a branched end, while the second antenna is much longer.

What structure covers the stalked eye in crustaceans?

The rostrum.

Where are the mandibles located in crustaceans?

Under the second antennae.

What are maxillipeds?

Three pairs of long appendages posterior to the maxillae, used for handling food.

What is the function of the cheliped in crustaceans?

It is the first walking leg and ends in a claw (chela) used for defense and capturing prey.

How many walking legs do crustaceans typically have?

Five pairs, with the first pair being chelipeds.

What is the function of swimmerets in crustaceans?

Used for swimming and, in some species, carrying eggs.

What structure is found at the end of a crustacean's abdomen?

The telson, with rounded uropods attached.

What is unique about crustacean appendages?

They have jointed appendages that are typically biramous (two-branched).

What is a uniramous appendage?

A single-branched appendage, found in some crustaceans that have lost one branch.

What are the first three pairs of thoracic appendages in crayfish called?

macillipeds

how many pairs of walking legs do crayfish have?

five pairs

what is the function of the first pair of walking legs (chelipeds) in crayfish?

They have strong claws (chelae) used for defense.

What are gonopods in male crayfish?

The first pair of swimmerets, modified for copulation.

What are uropods in crayfish used for?

Backward movement and protection of eggs or young on swimmerets.

What structure divides the thorax and head in crustaceans?

The cervical groove.

What is the combined structure of the thorax and head called?

The carapace or cephalothorax.

What are the curved edges in the center of the thorax called?

The aureola.