Chapter 34: The Invertebrates (Part 3, Week 7) Flashcards
[Start 34.5 Ecdysozoa: The Nematodes and Arthropods]
What is the sister group to Lophotrochozoa, a monophyletic group of animals that includes flatworms, rotifers, bryozoans, brachiopods, mollusks, and annelids?
Ecdysozoa (ek-duh-suhs-o-zoah)
Although the separation is supported by molecular evidence, the Ecdysozoa are named for a process called WHAT which is the process by which an animal molts, or breaks out of its old exoskeleton, and secretes a newer, larger one?
Ecdysis (ek-duh-suhs)
What do all ecdysozoans possess which is a anonliving covering that both supports and protects the animal?
Cuticle
A waxy surface coating that helps to reduce water loss from plant surfaces. Also, a nonliving covering that serves to both support and protect an animal.
Once formed, however, the cuticle typically cannot increase in size, which restricts the growth of the animal inside.
The solution for growth is the formation of a new, softer cuticle under the old one. The old one then splits open and is sloughed off, allowing the new, soft cuticle to expand to a bigger size before it hardens.
What was the critical innovation that led to other changes in ecdysoans?
Why? What does it impede and what do they have instead that is used?
The evolution of a cuticle.
A thick cuticle, as in arthropods, impedes the diffusion of oxygen across the skin.
Such species acquire oxygen by lungs, gills, or a set of branching, air-filled tubes called tracheae.
How did the ability to shed the cuticle also open up developmental options for the ecdysozoans?
For example, many species undergo complete metamorphosis, changing from a wormlike larva into a winged adult.
Why can’t animals with internal skeletons undergo metamorphosis?
Because growth occurs only by adding more minerals to the existing skeleton.
What was another significant adaptation of ecdysozoans which permitted the species to live in dry environments?
Internal fertilization.
A variety of appendages specialized for locomotion evolved in many species, including legs for walking or swimming and wings for flying.
T/F Because of these innovations, ecdysozoans are an incredibly successful group.
True
Review: Of the 8 ecdysozoan phyla, what are the two most common groups?
Nematodes and arthropods.
A relatively new concept supported by molecular data, and it implies that the process of molting arose only once in animal evolution. In support of this, certain hormones that stimulate molting have been discovered to exist only in both nematodes and arthropods.
What does the name for nematodes come from in Greek and what is their physical characteristic and size?
From the Greek nematos, meaning thread.
AKA roundworms.
They are small, thin worms that range in size from less than 1mm to about 5 cm, although some parasitic species measuring 1 m or more have been found in the placenta of sperm whales.
Where are nematodes found?
Everywhere! as parasites.
A shovelful of soil may contain a million nematodes. Over 25,000 species are known, but there are probably at least four times as many undiscovered species.
Both nematodes and annelids are wormlike in appearance. How are they different?
An annelid is segmented and possesses a true coelom, whereas a nematode is unsegmented and has a pseudocoelom. In addition, nematodes molt, but annelids do not.
What is the cuticle secreted by in nematodes and what is it primarily made of?
The cuticle is secreted by the epidermis and is made primarily of collagen, a structural protein also present in vertebrates. The cuticle is shed periodically as the nematode grows.
Why do nematodes result in thrashing of the body for muscle contraction movement rather than smoother wormlike movement?
Because beneath the epidermis are longitudinal muscles but no circular muscles.
What functions asboth a fluid-filled skeleton and a circulatory system?
Since the anthropods have the stronger cuticle, how do nematodes move gas?
The pseudocoelom.
Through diffusion of the cuticle.
Nematodes have a complete digestive tract composed of a mouth, pharynx, intestine, and anus. The mouth often contains sharp, piercing organs called stylets, and the muscular pharynx functions to suck in food.
Excretion of metabolic waste occurs via two simple tubules that have no cilia or flame cells.
Facts of Reproduction in Nematodes
- Nematode reproduction is usually sexual, with separate males and females, and fertilization takes place internally. Females can up to 100,000 eggs a day!
- In some species, they produce hermaphrodites and males. Can cross fertlize with males or self fertilize.
- C. elegans is a model organism for the process of development since it is trasnparent and composed of relatively few cells, and the generation time is short.
- Consists of about 1000 somatic (cells other than sperm and egg cells; called germ cells).
Flip for different facts about different kinds of parasitic nematodes!
- The large roundworm Ascaris lumbricoides
is a parasite of the small intestine that can reach up to 30 cm in length. Over a billion people worldwide carry this parasite. - Hookworms (Necator americanus), so named because their anterior end curves dorsally like a hook, are also parasites of the human intestine.
- Pinworms (Enterobius vermicularis), although a nuisance, have relatively benign effects on their hosts. The rate of infection in the U.S., however, is staggering: 30% of children and 16% of adults are believed to be hosts. Adult pinworms live in the large intestine andmigrate to the anal region at night to lay their eggs, which causes intense itching.
- In the tropics, some 250 million people are infected with Wuchereria bancrofti, a fairly large (100 mm) worm that lives in the lymphatic system, blocking the flow of lymph, and, in extreme cases, causing elephantiasis, an extreme swelling of the legs and other body parts.
Females release tiny, live young called microfilariae, which are transmitted to new hosts via mosquitoes.
What, from the Greek arthron, meaning joint, and podos, meaning foot, constitutes perhaps the most diverse phylum on Earth, and includes including familiar organisms such as spiders, insects, and crustaceans?
Arthropods.
About three-quarters of all described living species present on Earth are arthropods, and scientists have estimated they are also numerically common, with an estimated a billion billion individual organisms.
The huge success of the arthropods, in terms of their sheer numbers and diversity, is related to features that permit these animals to live in all the major areas on Earth, from the poles to the tropics and from marine and freshwater habitats to dry land. These features include an exoskeleton, segmentation, and jointed appendages.
What is the body of a typical arthopod covered by which is made up of layers of chitin and protein?
This can be extremely tough in some parts, as in the shells of crabs, lobsters, and even beetles, yet be so soft and flexible in other parts, between body segments or appendages, to allow for movement?
The exoskeleton.
An external skeleton made primarily of chitin that surrounds and protects most of the body surface of animals such as insects.
In the class of arthropods called crustaceans, the exoskeleton is reinforced with calcium carbonate to make it extra hard.
The exoskeleton provides protection and also a point of attachment for muscles, all of which are internal.
It is also relatively impermeable to water, a feature that may have enabled many arthropods to conserve water and colonize land, in much the same way as a tough seed coat allowed plants to colonize land.
From this point of view, the development of a hard cuticle was a critical innovation. It also reminds us that the ability to adapt to diverse environmental conditions can itself lead to increased diversity of organisms.
What permits arthropods complex movements andfunctions such as walking, swimming, sensing, breathing, food handling, and reproduction.
Jointed appendages.
These appendages are operated by muscles within each segment. In many orders, the body segments have become fused into functional units, or tagmata, such as the head, thorax, and abdomen of an insect.
Facts about Arthropods!
- Cephalization resulted in well defined head, a brain consisting of two or three cerebral ganglia connected to smaller ventral nerve ganglia.
- Have all sensory organs to include balance.
- Compound eyes composed of many independent visual units called ommatidia (many images at once)
- Open circulatory system in which hemolymph is pumped from a tubelike heart into the aorta or short arteries and then into the open sinuses that coalesce to form a cavity called the hemocoel. From the hemocoel, gases and nutrients from the hemolymph diffuse into tissues.The hemolymph flows back into the heart via pores, called ostia, that are equipped with valves.
Repiratory System Facts!
Because the cuticle impedes the diffusion of gases through the bodysurface, arthropods require special organs that permit gas exchange.
- In aquatic arthropods, these consist of feathery gills that have an extensive surface area in contact with the surrounding water.
- Terrestrial species have a highly developed tracheal system - The respiratory system of insects, consisting of a series of finely branched air tubes called tracheae; air enters and exits the tracheae through spiracles, which are pores on the body surface. No gas exchange.
Disgestive system Facts!
- The digestive system of arthropods is complex and often includes amouth, crop (temporarily stores food; an enlarged part of the esophagus), stomach, intestine, and rectum.
- The digestive system of arthropods is complex and often includes amouth, crop, stomach, intestine, and rectum.
- Thestomach has glands called digestive cecae that secrete digestive enzymes.
Excretion is accomplished by specialized metanephridia or, in insects and some other taxa, by Malpighian tubules, extensive tubes that extend from the digestive tract into body cavity, where they are surrounded by hemolymph.
- Nitrogenous wastes are absorbed by the tubules and emptied into the gut, where the intestine and rectum re absorb water and salts and the waste is excreted through the anus. This excretory system, allowing the retention of water, was another critical innovation that permitted the colonization of land by arthropods.
What are the main subphyla and characteristics of Arthropods? (4)
Sort by species count!
Hexpoda (insects such as beetles, butterflies, flies, fleas, grasshoppers, ants, bees, wasps, termites, and springtails) > 1 million species
- Body with head, thorax, and abdomen; mouthparts modified for biting, chewing, sucking, or lapping; usually with two pairs of wings and three pairs of legs; mostly terrestrial, some freshwater; herbivorous, parasitic, or predatory
Chelicerata (spiders, scorpions, mites, ticks, horseshoe crabs, and sea spiders) 74,000 species
- Body usually with cephalothorax and abdomen only; six pairs of appendages, including four pairs of legs, one pair of fangs, and one pair of pedipalps; terrestrial; predatory or parasitic
Crustacea (Crabs, lobsters, shrimp) 45,000 species
- Body of two to three parts; three or more pairs of legs; chewing mouth parts; usually marine
Myriapoda (millipedes and centipedes) 13,000 species
- Body with head and highly segmented trunk. In millipedes, each segment with two pairs of walking legs; terrestrial; herbivorous. In centipedes, each segment with one pair of walking legs; terrestrial; predatory, poison jaws
What do the toxin of the black widow and the oxin of the brown recluse do?
The toxin of the black widow is a neurotoxin, which interferes with the functioning of the nervous system, whereas that of the brown recluse is hemolytic, meaning it destroys red blood cells around the bite.
After the spider has subdued its prey, it pumps digestivefluid into the tissues via the fangs and sucks out the partially digested meal.
What is one of the main characteristics distinguishing arachnids from insects?
All arachnids have a body consisting of two tagmata: a cephalothorax and an abdomen. Insects have three tagmata: head, thorax, and abdomen.
What is a fun fact about spider silk?
Spiders have abdominal silk glands, called spinnerets, and many spin webs to catch prey.
The silk is a protein that stiffens after extrusion from the body because the mechanical shearing causes a change in the organization of the protein’s structure.
Silk is stronger than steel of the same diameter and is more elastic than Kevlar, the material used in bulletproof vests.
Each spider family constructs a characteristic size and style of web and can do it perfectly on its first attempt, indicating that web spinning is an innate (instinctual) behavior.
Scorpion Facts!
- Their pedipalps are modified into large claws, and the abdomen tapers into a stinger, which is used to inject venom.
- Unlike spiders, which lay eggs, scorpions bear live young thatthe mother then carries around on her back until they have their first molt.
Mites and Ticks Facts!
- In mites and ticks (order Acari), the two main body segments (cephalothorax and abdomen) are fused and appear as one large segment.
- Can feed on dead plant or animal material or plants, and even humans (chigger mites) and spread diseases such as typhus.
- Demodex brevis is a hair-follicle mite that is common in animals and humans. The mite is estimated to be present on over 90% of adult humans. Although the mite causes no irritation in most humans,
Demodex canis causes the skin disease known as mange in domestic animals, particularly dogs. - Ticks are larger than mites, and all are ectoparasitic, feeding on the body surface of vertebrates. Their life cycle includes attachment to a host, sucking blood until they are replete, and dropping off the host to molt.
- Ticks can carry a variety of viral and bacterial diseases, including Lyme disease, a bacterial disease so named because it was first observed in the town of Lyme, Connecticut, in the 1970s.
N/A
What have one pair of antennae on the head, and three pairs of appendages that are modified mouthparts, including mandibles that act like jaws?
They are among the earliest terrestial animal phyla known.
Subphylum Myriapoda - Millipedes and Centipedes.
Millipedes (class Diplopoda) have two pairs of legs per segment, as theirclass name denotes (from the Latin diplo, meaning two, and podos, meaning feet), not 1,000 legs, as their common name suggests.
They are slow-moving herbivores that eat decaying leaves and other plant material. When threatened, the millipede’s response is to roll up into a protective coil.
Many millipede species also have glands on their underside that can eject a variety of toxic, repellent secretions. Some millipedes are brightly colored, warning potential predators that they can protect themselves.
Class Chilopoda (from the Latin chilo, meaning lip, and podos, meaning feet), or centipedes, are fast-moving carnivores that have one pair of walking legs per segment.
The venom of some larger species, such as Scolopendra heros, is powerful enough to cause pain in humans. Most species do not have a waxy waterproofing layer on their cuticle and so are restricted to moist environments under leaf litter or in decaying logs, usually coming out at night to actively hunt their prey.
What is the scientific study of insects?
Entomology
They are studied in large part because of their significance as pests of the world’s agricultural crops and carriers of some of the world’s most deadly diseases.
Because approximately one-quarter of the world’s crops are lost annually to insects, researchers are constantly trying to
find ways to reduce pest densities.
We depend on insects such as honeybees, butterflies, and moths to pollinate our crops. Bees also produce honey, and silkworms are the source of silk fiber.
Despite the revulsion they provokein us, fly larvae (maggots) are important in the decomposition process of both dead plants and animals. In addition, we use insects in the biological control of other insects.
