Question

You and your friends are excited about what you have learned about the phylum Arthropoda. You have three Arthropods in front of you: a spider, grasshopper and a crab. How would you distinguish these three organisms into their specific subphyla?

Answer 1

SPIDER

Phylum : Arthropoda

Subphylum : Chelicerata

Class : Arachnida

Order : Araneae

Brief Description Subphylum Hexapoda

The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders, arachnids (including scorpions, spiders, and potentially horseshoe crabs), and several extinct lineages, such as the eurypterids.

The Chelicerata originated as marine animals in the Middle Cambrian period; the first confirmed chelicerate fossils, belonging to Sanctacaris, date from 508 million years ago.[ The surviving marine species include the four species of xiphosurans (horseshoe crabs), and possibly the 1,300 species of pycnogonids (sea spiders), if the latter are indeed chelicerates. On the other hand, there are over 77,000 well-identified species of air-breathing chelicerates, and there may be about 500,000 unidentified species.

Like all arthropods, chelicerates have segmented bodies with jointed limbs, all covered in a cuticle made of chitin and proteins. The chelicerate bauplan consists of two tagmata, the prosoma and the opisthosoma, except that mites have lost a visible division between these sections. The chelicerae, which give the group its name, are the only appendages that appear before the mouth. In most sub-groups, they are modest pincers used to feed. However, spiders' chelicerae form fangs that most species use to inject venom into prey. The group has the open circulatory system typical of arthropods, in which a tube-like heart pumps blood through the hemocoel, which is the major body cavity. Marine chelicerates have gills, while the air-breathing forms generally have both book lungs and tracheae. In general, the ganglia of living chelicerates' central nervous systems fuse into large masses in the cephalothorax, but there are wide variations and this fusion is very limited in the Mesothelae, which are regarded as the oldest and most primitive group of spiders. Most chelicerates rely on modified bristles for touch and for information about vibrations, air currents, and chemical changes in their environment. The most active hunting spiders also have very acute eyesight.

Chelicerates were originally predators, but the group has diversified to use all the major feeding strategies: predation, parasitism, herbivory, scavenging and eating decaying organic matter. Although harvestmen can digest solid food, the guts of most modern chelicerates are too narrow for this, and they generally liquidize their food by grinding it with their chelicerae and pedipalps and flooding it with digestive enzymes. To conserve water, air-breathing chelicerates excrete waste as solids that are removed from their blood by Malpighian tubules, structures that also evolved independently in insects.

While the marine horseshoe crabs rely on external fertilization, air-breathing chelicerates use internal but usually indirect fertilization. Many species use elaborate courtship rituals to attract mates. Most lay eggs that hatch as what look like miniature adults, but all scorpions and a few species of mites keep the eggs inside their bodies until the young emerge. In most chelicerate species the young have to fend for themselves, but in scorpions and some species of spider the females protect and feed their young.

Spider, (order Araneida or Araneae), any of more than 46,700 species of arachnids that differ from insects in having eight legs rather than six and in having the body divided into two parts rather than three. The use of silk is highly developed among spiders. Spider behaviour and appearance are diverse, and the araneids outside Europe, Japan, and North America have not been thoroughly collected and studied.

All spiders are predators, feeding almost entirely on other arthropods, especially insects. Some spiders are active hunters that chase and overpower their prey. These typically have a well-developed sense of touch or sight. Other spiders instead weave silk snares, or webs, to capture prey. Webs are instinctively constructed and effectively trap flying insects. Many spiders inject venom into their prey to kill it quickly, whereas others first use silk wrappings to immobilize their victims.

Size range >  Spiders range in body length from 0.5 to about 90 mm (0.02–3.5 inches).Female spiders generally are much larger than males, a phenomenon known in animals as sexual size dimorphism.

Many female orb weavers, such as those in the families Tetragnathidae and Araneidae, show extreme size dimorphism, being at least twice the size of males of the same species. The extreme difference in body size appears to have arisen through selection processes favouring fecundity in females and “bridging” locomotion in males. Bridging is a technique used by spiders for orb web construction; the spider produces a silk thread that is carried by the wind and becomes attached to an object, forming a bridge. Small, light males can build and traverse silk bridges more rapidly than larger, heavier males can. Scientists suspect that this gives small males more mating opportunities, thereby favouring selection for their small size.

Distribution

Spiders are found on all continents (except Antarctica, although spider fragments have been reported there) and at elevations as high as 5,000 metres (16,400 feet) in the Himalayas. Many more species occur in the tropics than in temperate regions. Though most spiders are terrestrial, one Eurasian species is aquatic and lives in slow-moving fresh water. There are a few species that live along shores or on the surface of fresh or salt water.

Importance

• All spiders are predators. Because of their abundance, they are the most important predators of insects. Spiders have been used to control insects in apple orchards in Israel and rice fields in China. Large numbers of spiders have also been observed feeding on insects in South American rice fields and in fields of various North American crops. Modern pest-management strategies emphasize the use of insecticides that do the least damage to natural predators of insect pests.   
• Many spiders produce venom for use in capturing prey, few species are toxic to humans. The venom of the black widow (genus Latrodectus) acts as a painful nerve poison. The bite of the brown recluse and others of the genus Loxosceles may cause localized tissue death. Other venomous spiders include the tarantula-like funnel-web spider (genus Atrax) of southeastern Australia and some African members (baboon spiders) of the family

External features

• The bodies of spiders, like those of other arachnids, are divided into two parts, the cephalothorax (prosoma) and the abdomen (opisthosoma).
• The legs are attached to the cephalothorax, which contains the stomach and brain.
• The top of the cephalothorax is covered by a protective structure, the carapace, while the underside is covered by a structure called the sternum, which has an anterior projection, the labium.
• The abdomen contains the gut, heart, reproductive organs, and silk glands.
• Spiders (except the primitive suborder Mesothelae) differ from other arachnids in lacking external segmentation of the abdomen and in having the abdomen attached to the cephalothorax by a narrow stalk, the pedicel.
• The gut, nerve cord, blood vessels, and sometimes the respiratory tubules (tracheae) pass through the narrow pedicel, which allows the body movements necessary during web construction.
• Among arachnids other than spiders, the tailless whip scorpions (order Amblypygi) have a pedicel but lack spinnerets. Spiders, like other arthropods, have an outer skeleton (exoskeleton). Inside the cephalothorax is the endosternite, to which some jaw and leg muscles are attached.
• Spiders have six pairs of appendages. The first pair, called the chelicerae, constitute the jaws. Each chelicera ends in a fang containing the opening of a poison gland.
• The venom ducts pass through the chelicerae, which sometimes also contain the venom glands. The second pair of appendages, the pedipalps, are modified in the males of all adult spiders to carry sperm (see below Reproduction and life cycle). In females and immature males, the leglike pedipalps are used to handle food and also function as sense organs. The pedipalpal segment (coxa) attached to the cephalothorax usually is modified to form a structure (endite) that is used in feeding.
• The pedipalps are followed by four pairs of walking legs. Each leg consists of eight segments: the coxa, attached to the cephalothorax; a small trochanter; a long, strong femur; a short patella; a long tibia; a metatarsus; a tarsus, which may be subdivided in some species; and a small pretarsus, which bears two claws in spiders that do not build webs and an additional claw between them in web-building ones.
• The young of two-clawed spiders often have three claws. The legs, covered by long hairlike bristles called setae, contain several types of sense organs and may have accessory claws. A few species use the first pair of legs as feelers. Spiders can amputate their own legs (autotomy); new but shorter legs may appear at the next molt.

Diet and Feeding Habits

Spiders prey on many different organisms and employ a wide range of strategies to capture prey. They may trap prey in sticky webs, lasso it with sticky balls, mimick it to avoid detection, or chase and tackle it. Most detect prey mainly by sensing vibrations, but active hunters have acute vision.

Spiders can only consume liquids because they lack chewing mouthparts. They use chelicerae, pointed appendages such as the fangs at the front of their cephalothorax, to grasp prey and inject venom. Digestive juices break the food down into a liquid, which a spider can then ingest.

Prey

Spiders may prey on any of the following:

• arthropods (such as insects and other spiders)
• small birds
• frogs
• reptiles
• amphibians
• small mammals
• sometimes: pollen and nectar

Silk

Almost all spiders produce silk. Silk-producing spinnerets are usually located under the tip of a spider's abdomen, which enables them to spin a long strand of silk behind them. Silk production is no simple endeavor for spiders as it requires great time and energy. Because of this, some species have been recorded consuming their own silk when they are finished with it to store for later use.

There are many different types of silk and each type serves a different function for the spider.

Types of Silk and Their Functions

• Attachment: clinging to surfaces
• Cocoon: forming a protective case for eggs
• Dragline: web construction
• Glue-like: capturing prey
• Minor: web construction
• Viscid: capturing prey
• Wrapping: wrapping prey in silk to allow for consumption

Spider silk is highly regarded as a marvel of engineering by scientists for its structural properties. It is fine yet strong, resistant to many solvents, and even possesses thermal conductivity properties. Researchers have been studying spider silk for years in the hopes of understanding it well enough to manufacture a synthetic version for human use.

Species

Common Species

• Orb weaver
  • Known for weaving large, circular webs.
• Cobweb spider
  • This species includes the venomous black widow spider.
• Wolf spider
  • Large nocturnal spiders that hunt at night
• Tarantula
  • These huge, hairy hunting spiders make great pets.
• Jumping spider
  • These are tiny spiders with big eyes and the tendency to leap.

Grasshopper

Phylum : Arthropoda

Subphylum : Hexapoda

Class : Insecta

Order : Orthoptera

Brief Description Subphylum Hexapoda

The name Hexapoda denotes the presence of six legs (three pairs) in these animals as differentiated from the number of pairs present in other arthropods. Hexapods are characterized by the presence of a head, thorax, and abdomen, constituting three tagma. The thorax bears the wings as well as six legs in three pairs. Many of the common insects we encounter on a daily basis—including ants, cockroaches, butterflies, and flies—are examples of Hexapoda.

Amongst the hexapods, the insects (Figure 1) are the largest class in terms of species diversity as well as biomass in terrestrial habitats. Typically, the head bears one pair of sensory antennae, mandibles as mouthparts, a pair of compound eyes, and some ocelli (simple eyes) along with numerous sensory hairs. The thorax bears three pairs of legs (one pair per segment) and two pairs of wings, with one pair each on the second and third thoracic segments. The abdomen usually has eleven segments and bears reproductive apertures. Hexapoda includes insects that are winged (like fruit flies) and wingless (like fleas).

Grasshopper, any of a group of jumping insects (order Orthoptera) that are found in a variety of habitats. Grasshoppers occur in greatest numbers in lowland tropical forests, semiarid regions, and grasslands. They range in colour from green to olive or brown and may have yellow or red markings.

The grasshopper senses touch through organs located in various parts of its body, including antennae and palps on the head, cerci on the abdomen, and receptors on the legs. Organs for taste are located in the mouth, and those for smell are on the antennae. The grasshopper hears by means of a tympanal organ situated either at the base of the abdomen (Acrididae) or at the base of each front tibia (Tettigoniidae). Its sense of vision is in the compound eyes, while change in light intensity is perceived in the simple eyes (or ocelli). Although most grasshoppers are herbivorous, only a few species are important economically as crop pests.

The femur region of the upper hindlegs is greatly enlarged and contains large muscles that make the legs well adapted for leaping. The male can produce a buzzing sound either by rubbing its front wings together (Tettigoniidae) or by rubbing toothlike ridges on the hind femurs against a raised vein on each closed front wing (Acrididae).

Some grasshoppers are adapted to specialized habitats. The South American grasshoppers of Pauliniidae spend most of their lives on floating vegetation and actively swim and lay eggs on underwater aquatic plants. Grasshoppers generally are large, with some exceeding 11 cm (4 inches) in length (e.g., Tropidacris of South America).

In certain parts of the world, grasshoppers are eaten as food. They are often dried, jellied, roasted and dipped in honey or ground into a meal. Grasshoppers are controlled in nature by predators such as birds, frogs, and snakes. Humans use insecticides and poison baits to control them when they become crop pests.

Identification

The group that contains the insects familiar to most people as grasshoppers. Also includes the Pygmy Mole 'Crickets' (Tridactylidae), which are not closely related to crickets. Characteristics:

back legs large, modified for jumping

antennae usually shorter than body

antennae have fewer than 30 segments (more than 30 in Ensifera)

ovipositor short (not obvious), structural details--4 valves, as opposed to six in Ensifera (see Tree of Life)

auditory organ (tympanum) if present, is on the abdomen (typically on front tibiae in Ensifera)

stridulation (if performed) typically accomplished by rubbing serration of inner surface of hind femur across veins of front wing--mechanism typically involves just the forewings in Ensifera

Food

Feed almost exclusively on plants, though some will scavenge dead plant and animal material at times.

Characteristics

Grasshoppers have the typical insect body plan of head, thorax and abdomen. The head is held vertically at an angle to the body, with the mouth at the bottom. The head bears a large pair of compound eyes which give all-round vision, three simple eyes which can detect light and dark, and a pair of thread-like antennae that are sensitive to touch and smell. The downward-directed mouthparts are modified for chewing and there are two sensory palps in front of the jaws.

The thorax and abdomen are segmented and have a rigid cuticle made up of overlapping plates composed of chitin. The three fused thoracic segments bear three pairs of legs and two pairs of wings. The forewings, known as tegmina, are narrow and leathery while the hindwings are large and membranous, the veins providing strength. The legs are terminated by claws for gripping. The hind leg is particularly powerful; the femur is robust and has several ridges where different surfaces join and the inner ridges bear stridulatory pegs in some species. The posterior edge of the tibia bears a double row of spines and there are a pair of articulated spurs near its lower end. The interior of the thorax houses the muscles that control the wings and legs.

Crab

Phylum : Arthropoda

Subphylum : Crustacea

Class : Malacostraca

Order : Decapoda

Crabs are members of the crustacean order, along with lobsters (Nephropidae), crayfish (Astacoidea) and all other marine insects. All crustaceans are members of the arthropod phylum. Arthropoda is the most diverse phylum on Earth and accounts for over 75 percent of all living things. Despite this diversity, crabs have a number of features that, when combined, distinguish them from similar creatures. Some creatures share a few of these characteristics, but no creature shares them all.

Decapod

Almost all crabs are decapods, meaning they have 10 legs. Horseshoe crabs (Chelicerata) have eight legs and are more closely related to spiders. In this regard, crabs have a similarity to lobsters and crayfish, but having 10 legs is a crucial distinction that separates crabs from centipedes (Chilopod), spiders (Araneae), millipedes (Diplopoda), ticks (Acarina) and scorpions (Dromopoda). The 10 legs of all decapods are situated in bilateral symmetry, with five on each side.

Hard Exoskeleton

The hard “crust” is a defining characteristic of crabs, lobsters and prawns. This exoskeleton distinguishes crustaceans from other arthropods, such as krill (Euphausiacea), but not terrestrial crustaceans such as woodlice and pill bugs (Armadillidiidae). The exoskeleton is a crucial feature of crustaceans, as it is one of the few means by which they avoid predation. In order for the vast majority of hard-shelled creatures to achieve mobility, they have jointed appendages. This is a common trait of arthropods, but is not shared by millipedes, centipedes and terrestrial insects, who have hard shells but unjointed legs.

Double Antennae

Most crabs have two pairs of antennae. This feature distinguishes them from non-decapod crustaceans, plus more distantly related arthropods, such as mites. Antennae are also a distinguishing feature between different crab species. While the vast majority of crabs have this distinguishing feature, the horseshoe crab does not.

Sideways Walking

The one feature that crabs have that no other related species have is the preference to walk sideways. While it might be easy to assume this trait is a defining ability, it is not, as most decapods crustaceans have the ability to walk sideways, but show no preference for doing so. Only the crab displays such a preference, despite its ability to walk in any direction.

Land and Water Breathing

Crabs share the most anatomical similarities with prawns and lobsters, but only crabs, as a species, are able to survive on land and in water. They achieve this through having gills and lungs. Not all crabs can survive on land, such as marine hermit crabs (Clibanarius), but many crab varieties, including the iconic blue land crab (Cardisoma guanhumi), can survive in both marine and terrestrial environments.

Crustaceans belong to the phylum Arthropoda, along with insects, arachnids, millipedes, centipedes, and fossil trilobites. However, crustaceans occupy their own subphylum, Crustacea. The term crustacean derives from the Latin crusta, meaning crust or hard shell. In some references, the crustaceans are classified at the class level, but I choose to follow the classification outlined in Borror and DeLong’s Introduction to the Study of Insects, 7th edition.

The subphylum Crustacea is subdivided into 10 classes:

• Class Cephalocarida – horseshow shrimps
• Class Branchiopoda – tadpole, fairy, and brine shrimps
• Class Ostracoda – ostracods, seed shrimp
• Class Copepoda – copepods, fish lice
• Class Mystacocarida
• Class Remipedia – cave-dwelling blind shrimps
• Class Tantulocarida
• Class Branchiura
• Class Cirripedia - barnacles
• Class Malacostraca – lobsters, crayfish, crabs, shrimps, amphipods, isopods (including pillbugs and sowbugs), ad mantis shrimps

Description

Most of the 44,000 species of crustaceans live in saltwater or freshwater. A small number of crustaceans live on land. Whether marine or terrestrial, crustaceans share certain traits that determine their inclusion in the subphylum Crustacea. As with any large group of organisms, exceptions to these rules will occasionally apply.

Typically, crustaceans have functional mouthparts and two pairs of antennae, although one pair may be greatly reduced and difficult to discern. The body may be divided into three regions (head, thorax, and abdomen), but is often limited to two (cephalothorax and abdomen). In either case, the abdomen will be clearly segmented, usually with a non-segmented area or extension at the hind end (called a terminal telson). In some crustaceans, a shield-like carapace protects the cephalothorax. Crustaceans have biramous appendages, meaning they divide into two branches. All crustaceans breathe via gills.

Diet

We usually think of crustaceans as food, rather than as feeders. The smaller crustaceans – tiny shrimp and amphipods, for example – play an important role as food for larger marine organisms. Most crustaceans are themselves either scavengers or parasites. Terrestrial crustaceans often live on the ground, hidden under rocks or debris in moist, humid environments, where they can feed on decaying vegetation.

Life Cycle

Because the subphylum Crustacea is such a large and diverse group, their development and natural history varies greatly. Like other arthropods, crustaceans must molt and shed their hardened cuticles (exoskeletons) in order to grow. The crustacean life cycle begins with the egg, from which the immature crustacean emerges. Crustaceans may undergo either anamorphic or epimorphic development, depending on the taxon. In epimorphic development, the individual that hatches from the egg is essentially a tiny version of an adult, with all the same appendages and segments. In these crustaceans, there is no larval stage.

In anamorphic development, the individual crustacean emerges without all the segments and appendages of the mature adult. As it molts and grows, the immature larva gains segments and acquires additional appendages, until it reaches adulthood.

In very general terms, anamorphic crustaceans will develop through three larval stages:

• naupli - In the naupli stage, the larva is basically a floating head, with a single eye, and three pairs of appendages which it uses for swimming. Some anamorphic crustaceans skip this larval stage and emerge from the egg at a more advanced level of development.
• zoae - In the zoae stage, the larva has both a cephalon (head) and thorax. By the end of this stage, it will add abdominal segments as well. Zoae swim using biramous, thoracic appendages, and may also have a pair of compound eyes.
• megalopae – By the megalopae stage, the crustacean has added the segments of all three body regions (cephalon, thorax, and abdomen), as well as its appendages, including at least one pair of swimmerets. It looks like a smaller version of an adult​ but is sexually immature.