Arthropods: Characteristics and Diversity

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Questions and Answers

What is a characteristic of arthropods?

Bilaterally symmetry (correct)

Radial symmetry

Asymmetry

No symmetry

What percentage of known animal species are arthropods?

One out of every four

One out of every five

Two out of every three (correct)

One out of every two

What is a key factor in the diversity and success of arthropods?

Tagmata and jointed appendages

Open circulatory system and chitin

Segmentation and hard exoskeleton (correct)

Radial symmetry and bilateral symmetry

What is the function of the exoskeleton of arthropods?

Protection, flexibility, and desiccation prevention Signup and view all the answers

What is unique about the appendages of arthropods?

They may be modified for sensory functions, food handling, or walking and swimming Signup and view all the answers

What is the process called when arthropods shed their outer covering?

Ecdysis Signup and view all the answers

What is the name of the fluid that circulates in the open circulatory system of arthropods?

Hemolymph Signup and view all the answers

What is the purpose of tagmata in arthropods?

Specialized purposes Signup and view all the answers

What is unique about the way millipedes lay their eggs?

They lay eggs in a nest and guard them. Signup and view all the answers

What is the main difference between the larvae of millipedes and the adults?

Larvae have one pair of legs per segment, adults have two. Signup and view all the answers

What is the primary source of food for most millipedes?

Decayed plant matter Signup and view all the answers

What is the purpose of the repugnatorial gland in millipedes?

To secrete toxic or repellent fluids when disturbed Signup and view all the answers

What is unique about the bodies of symphylans?

They are soft-bodied and have 14 segments Signup and view all the answers

How do male scutigerellans transfer sperm to females?

By placing a spermatophore at the end of a stalk Signup and view all the answers

What is the primary difference between pauropods and millipedes?

Pauropods are soft-bodied, millipedes are hard-bodied Signup and view all the answers

What is a characteristic of the antennae of symphylans?

They are long and unbranched Signup and view all the answers

What is the primary function of Malpighian tubules in spiders and insects?

To serve as excretory structures Signup and view all the answers

How do rectal glands help spiders conserve water?

By reabsorbing potassium and water from the tubules Signup and view all the answers

What is the purpose of a courtship ritual in spiders?

To allow the female to choose a mate Signup and view all the answers

What is the primary function of coxal glands in spiders?

Modified nephridia at the base of legs Signup and view all the answers

What is the venom of the brown recluse spider?

Hemolytic, destroying tissue around the bite Signup and view all the answers

How do scorpions capture their prey?

Using their pedipalps to seize insects and spiders Signup and view all the answers

What is the characteristic feature of harvestmen (order Opiliones)?

A broadly joined abdomen and cephalothorax Signup and view all the answers

What is a unique feature of scorpions' reproductive biology?

They are viviparous or ovoviviparous, brooding young within their reproductive tract Signup and view all the answers

What is a major threat to freshwater crustaceans?

Over-dilution with water Signup and view all the answers

What do gills of freshwater crustaceans need to absorb actively?

Na+ and Cl- Signup and view all the answers

What is unique about the urine of marine crustaceans?

It is isotonic with blood Signup and view all the answers

What is the function of the pair of supra-esophageal ganglia in crustaceans?

To connect to eyes and antennae Signup and view all the answers

What is the role of sensory hairs on the body of crustaceans?

To detect touch Signup and view all the answers

What is the function of the statocyst in crustaceans?

To detect movement and balance Signup and view all the answers

How do most crustaceans reproduce?

By brooding eggs in brood chambers Signup and view all the answers

What is unique about the development of crayfish?

They develop directly without a larval form Signup and view all the answers

What is unique to the nauplius of maxillopods?

A maxillopodan eye Signup and view all the answers

What is the main function of antennules in copepods?

Swimming Signup and view all the answers

Which subclass of maxillopods consists of tiny, copepod-like ectoparasites of deep-sea benthic crustaceans?

Tantulocarida Signup and view all the answers

What is the primary mode of nutrition for free-living copepods?

Filter feeding Signup and view all the answers

Which subclass of maxillopods lacks gills?

Branchiura Signup and view all the answers

What is the typical length range of pentastomids?

1-13 cm Signup and view all the answers

What is the characteristic feature of barnacles?

A hard, chitinous cuticle Signup and view all the answers

What is the typical habitat of tantulocarids?

Deep-sea benthic environments Signup and view all the answers

Study Notes

Phylum Arthropoda

Arthropods are multicellular, bilaterally symmetrical, triploblastic, and have a true coelom (protostomes)
They are segmented, with two out of every three known species of animals being arthropods
Members of the phylum Arthropoda are found in nearly all habitats of the biosphere

General Characteristics of Arthropods

Arthropods have achieved great diversity and abundance due to their segmentation, hard exoskeleton (made of chitin), and jointed appendages
Segments have combined into functional groups called tagmata, which have specialized purposes
As arthropods evolved, segments fused, and appendages became more specialized
Arthropods have an open circulatory system with an exoskeleton that is protective and flexible
The exoskeleton prevents desiccation, provides places for muscle attachment, and does not allow for growth, requiring molting (ecdysis)

More Efficient Locomotion

Each segment bears a pair of jointed appendages, which have sensory hairs and may be modified for sensory functions, food handling, or walking & swimming

Class Arachnida - Order Araneae (Spiders)

In spiders and insects, Malpighian tubules serve as excretory structures, conserving water and allowing organisms to live in dry environments
Many spiders have coxal glands, modified nephridia, at the base of legs
Reproduction involves a courtship ritual, with males storing sperm in pedipalps and inserting them into female genital openings
Eggs develop in a cocoon in the web or are carried by the female
Young hatch in about two weeks and may molt before leaving the egg cocoon
Not all spiders are dangerous, with some being allies of humans in the battle with insects
Some species of black widow spiders, brown recluse spiders, and Australian and South American spiders are the most dangerous and aggressive

Class Arachnida - Order Scorpiones (Scorpions)

Scorpions feed on insects and spiders, seizing them with their pedipalps
The last segment contains a bulbous base and a curved barb that injects venom
Scorpions are viviparous or ovoviviparous, with females brooding young within their reproductive tract

Class Arachnida - Order Opiliones (Harvestmen)

Harvestmen differ from spiders in that their abdomen and cephalothorax are broadly joined rather than constricted
Some harvestmen have live young (viviparous)
Young resemble little adults, with no metamorphosis

Class Diplopoda (Millipedes)

Millipedes have two pairs of legs on each segment
The head has one pair each of antennae, mandibles, and maxillae
The body is more cylindrical
Millipedes live in dark, moist places, feeding on decayed plant matter or occasionally living plants
They are slow-moving, coiling up when disturbed
Toxic or repellent fluids are secreted when disturbed from repugnatorial glands
After copulation, females lay eggs in a nest and guard them
Larvae have only one pair of legs per segment

Class Pauropoda

Pauropods live in moist soil, leaf litter, decaying vegetation, or under bark and debris
They are soft-bodied, small (2 mm or less), and have approximately 500 species
The head lacks true eyes, has branched antennae, and a pair of sense organs
There are 12 trunk segments, with 9 pairs of legs but none on the first or last two segments
One tergal plate covers two segments, lacking tracheae, spiracles, and a circulatory system

Class Symphyla

Symphylans live in humus, leaf mold, and debris
They are soft-bodied, with 14 segments, 12 of which bear legs and one bears a pair of spinnerets
Males place a spermatophore at the end of a stalk, which the female stores in special pouches
Eggs are fertilized and attached to moss or lichen
Young hatch with only 6 or 7 pairs of legs
Small (2–10 mm) with centipede-like bodies

Subphylum Crustacea

Crustaceans constantly threatened by over-dilution with water
Freshwater crustaceans have urine that is isosmotic with blood
Marine crustaceans have urine that is isosmotic with seawater
Crustaceans have a pair of supra-esophageal ganglia connected to eyes and two pairs of antennae
The nervous system includes a ventral nerve cord with a pair of ganglia for each somite
Eyes and statocysts are the largest sensory organs
Chemical sensing of taste and smell occurs in hairs on antennae and mouth

Class Maxillopoda

Maxillopods generally have 5 cephalic, 6 thoracic, and 4 abdominal segments plus a telson
The nauplius of maxillopods has a maxillopodan eye – unique to this group

Class Maxillopoda – Subclass Copepoda

Copepods are planktonic crustaceans, lacking a carapace
They retain the simple maxillopodan eye in adults
Antennules are used in swimming
They are very diverse, with some species being parasitic and highly modified
Free-living copepods may be the dominant consumer
Some species are intermediate hosts of human parasitic tapeworms and nematodes

Class Maxillopoda – Subclass Tantulocarida

Subclass Tantulocarida is a recently described group
There are approximately 12 species
They are tiny copepod-like ectoparasites of deep-sea benthic crustaceans

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Description

Learn about the characteristics of arthropods, including their body structure, symmetry, and coelom. Discover why they have achieved great diversity and are found in nearly all habitats.