ZOOLOGY PacketApril 6th-17th, 2020

Summer King

This packet contains:

1. An introduction to Zoology

2. Explanation of Taxonomy

3. A Scientific news article covering a subdiscipline of Zoology (this week we are focusing on Entomology)

4. Instructions for the ongoing semester project

5. Assignment for the weeks of Apr 6-17

6. Information from encyclopedia.com to assist you in researching your topics

7. Anatomy of a Jellyfish

What needs to be turned in for a grade?

2-3 pages of your Animal Phyla project should be turned in every 2 weeks

Optional/Enrichment included:

Scientific articles Some weeks I will include labs, dissections, animal anatomy

** If labs are completed or you do something hands on that correlates with what we are reading about or what you are researching for the Animal Phyla project, please let me know! Send me pictures on remind/email, or tag @TheBurgScience and #Team DCS on Twitter! **

ZOOLOGY

Zoology (also known as animal science) is the branch of biology devoted to the study of animal life. It covers areas ranging from the structure of organisms to the subcellular unit of life. Some zoologists are interested in the biology of particular groups of animals. Others are concerned with the structure and function of animal bodies. Still others study how new animals are formed and how their characteristics are passed on from one generation to another. Zoologists study the interactions of animals with one another and their environments, as well as the significance of the behavior of animals.

Zoology is both descriptive and analytical. It can be approached either as a basic science or as an applied science. A worker in basic zoology is interested in knowledge of animals for its own sake without consideration of the direct application of the information gained. In contrast, workers in applied zoology are interested in information that will directly benefit humans and animals (medicine, for example).

Historically, the study of zoology can be viewed as a series of efforts to analyze and classify animals. The ancient Greek philosopher Aristotle is credited with devising the system of classifying animals that recognized similarities among diverse organisms in the fourth century B.C.E.; he arranged groups of animals according to mode of reproduction and habitat. Zoology began to emerge as a science in the 12th century and long was dominated by studies of anatomy and efforts at classifying animals. The Swedish botanist Carolus Linnaeus developed a system of nomenclature that still is used today — the binomial system of genus and species — and established as a discipline taxonomy, the science of classification according to a predetermined system.

Zoology today is as diverse as the animal kingdom it studies, broadening its range to include such fields as genetics and biochemistry. It now is considered an interdisciplinary field that applies a great variety of techniques to obtain knowledge of the animal kingdom. For instance, the genetic study of DNA from various animals can provide insights into their evolutionary history. Zoologists who concentrate on the morphology (the study of structure, including muscles, bones, cells and cellular components) employ many techniques first developed in the biochemistry lab.

SUBDISCIPLINES OF ZOOLOGYSubdisciplines that concentrate on specific divisions of animal life:

EntomologyInsects

HerpetologyAmphibians and reptiles

IchthyologyFish

Invertebrate ZoologyAnimals without backbones

MalacologyMollusks

MammalogyMammals

OrnithologyBirds

PrimatologyPrimates

OTHER SUBDISCIPLINES

EcologyInteractions between animals and their environment

EmbryologyDevelopment of animals before birth

EthologyAnimal behavior

PaleontologyFossils

SociobiologyBehavior, ecology and evolution of social animals such as bees, ants, schooling fish, flocking birds and humans

Careers:

The types of jobs zoologists perform also are quite diverse. The zoology undergraduate major is chosen by many students who seek a career in one of the several health care professions (veterinary medicine, medicine, dentistry) or careers in the environmental sciences. Jobs are available in the agricultural, biotechnological/pharmaceutical and environmental/ecological fields. There are jobs available working outdoors doing fieldwork as well as working in a lab. Career options include positions in government departments, environmental agencies, education (including universities and colleges) and industry (including consulting firms and biomedical companies). Depending on the way the biological sciences are organized at a particular college or university, the student interested in majoring in zoology actually could receive a degree in biology with a concentration in zoology.

TAXONOMY:In order to keep all the different types of animals and our knowledge of these animals in some type of order, a classification system was born. Scientific information is split into a number of levels known as Taxonomy: Kingdom, Phylum, Class, Order, Family, Genus, Species. (one silly way to remember this is King Phillip, Come Out For Goodness Sake!)

All of the scientific information about a living thing is called it's "Taxonomy"

So, for example, if you're talking about a Trumpeter Swan, it's taxonomy is:

Kingdom: animal (scientific name: Regnum animale)

Phylum: animals with a backbone (scientific name: Chordata)

Class: Bird (scientific name: Aves)

Order: Water fowl (scientific name: Anseriformes)

Family: Anatidae

Genus: Cygnus

Species: buccinator

Entomology in the News:

Heading Off a Locust Invasion Using NASA Satellites TOPICS:Earth ObservatoryEntomologyNASABy NASA EARTH OBSERVATORY APRIL 1, 2020

Swarm of locusts. A small swarm of locusts (40 million) can consume as much food as 35,000 people.A single desert locust (Schistocerca gregaria) can consume its body weight in vegetation in one day. That may not sound like much for one 2.5-gram locust, but when 40 million of them gather—considered a small swarm—they can devour as much food as 35,000 people. In one day, a small swarm can jeopardize a farmer’s livelihood.

Since December 2019, croplands in Kenya have been inundated by the voracious insects. By January 2020, at least 70,000 hectares (173,000 acres) of land were infested—Kenya’s worst locust event in 70 years. In February, the swarms spread to ten countries in eastern Africa, threatening food supplies for millions of people. Ethiopia and Somalia have seen their worst

locust infestations in 25 years. The United Nations (UN) has warned that the upcoming rainy season may make things worse.

NASA-funded scientists are partnering with the UN and relief organizations to better understand where locusts are likely to swarm. Using remote sensing observations of soil moisture and vegetation, researchers are tracking how environmental conditions influence locust life cycles and hoping to stop outbreaks before they spread.

January 14 – 20, 2020. Credit: NASA“The approach that helps prevent large-scale infestations is to catch the locusts very early in their life stages and get rid of their nesting grounds,” said Lee Ellenburg, the food security and agriculture lead for SERVIR at NASA’s Marshall Space Flight Center. The joint program between NASA and the U.S. Agency for International Development (USAID) uses satellite data to improve environmental decision-making in developing nations. The team also partnered with staff at the Desert Locust Information System of the UN Food and Agriculture Organization (FAO) to learn more about locust behavior.

Desert locusts have three main life stages: egg, hopper, and adult. Once they are mature adults, locusts are difficult to find on the ground and eradicate because they can fly 50 to 150 kilometers (30 to 90 miles) per day, especially if winds are strong. However, eggs and hoppers (when they’re still developing wings) have limited mobility and are easier to target.

The maps on this page show two important environmental parameters for locust development: soil moisture and vegetation. Soil moisture is important because females almost always lay their eggs in wet, warm, sandy soil. In general, they do not lay their eggs unless the soil is moist down to 5-10 centimeters (2-4 inches) below the surface. After eggs hatch, the abundance of nearby vegetation becomes the important parameter because it provides sustenance for maturing locusts and guides migration patterns.

The image at the top of the page shows average soil moisture over eastern Africa for January 14-20, 2020, during the early stages of the locust invasion. The preliminary estimates—developed by scientists at the University Corporation for Atmospheric Research and the University of Colorado—use NASA’s Cyclone Global Navigation Satellite System (CYGNSS) micro-satellites and are integrated with NASA’s model-based Land Information System.

“The data we have so far show a strong correlation between the location of sandy, moist soils and locust activity,” said Ashutosh Limaye, NASA’s chief scientist for SERVIR. “Wherever there are moist, sandy locations, there are locusts banding or breeding.” Desert locusts rapidly reproduce, so SERVIR researchers are working with FAO to pinpoint potential breeding locations and suggest targeted areas for pesticide sprays.

“Our goal is to learn from FAO how to find out where the breeding grounds are,” Ellenburg added. “If the prevailing conditions indicate that locusts will hatch and be taking off, the goal is to go early and destroy their nesting grounds.”

December 15, 2019 – March 15, 2020, 2020. Credit: NASAThe map above depicts changes in green vegetation across eastern Africa between Dec 15, 2019, and March 15, 2020. Derived from data collected by

the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, the Normalized Difference Vegetation Index (NDVI) is a measure of the health and greenness of vegetation based on how much red and near-infrared light it reflects. Healthy vegetation with lots of chlorophyll reflects more near-infrared light and less visible light.

“Once locusts lay the eggs and hatch, they start looking for vegetation to feed on,” said Catherine Nakalembe, a food security researcher with SERVIR and NASA Harvest. “They start migrating, looking for more to eat, and then keep multiplying.”

Nakalembe says vegetation across the region is much greener than average years—in fact, the greenest vegetation observed by satellite since 2000 for the December to March time period. Between October and December 2019, the Horn of Africa received up to four times more rainfall than average, making it one of the wettest “short rain seasons” in four decades. The extra rain made for robust plant growth and bountiful conditions for locusts.

With the upcoming “long rain season” (March through May) in east Africa, conditions could be ripe for more infestations, Nakalembe notes. The NASA team is refining several satellite datasets to assess the damage already caused and to create forecasts of where and how much longer locust outbreaks might occur.

“We work in close coordination with national ministries through our regional partners, and we hope the outcomes from our ongoing work can ultimately support those who are in the front line of managing the current outbreak,” said Nakalembe.

NASA Earth Observatory images by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview and soil moisture data from Cyclone Global Navigation Satellite System (CYGNSS) micro-satellites integrated with NASA’s model-based Land Information System. Story by Kasha Patel.

The NASA SERVIR and Harvest programs are working closely with Global and Regional FAO offices, USAID, World Food Program (WFP), the SERVIR Hub in East and Southern Africa at the Regional Center of Resources for Mapping Development (RCMRD) in Nairobi, Kenya, the SERVIR Hub in West Africa at the AGRHYMET based in Niamey, Niger, the Greater Horn of Africa IGAD Climate Prediction and Applications Center, NASA Short-term Prediction Research and Transition Center (SpoRT) NASA Earth Science Disasters Program, and several satellite missions to provide information and direction on where resources should be directed to mitigate locust outbreaks.

Assignment for April 6-17:Every semester the Zoology students construct a scrapbook for the phyla and classes of the Kingdom Animalia. There are 18 total categories. We are still going to construct this booklet this semester. Every 2 weeks I will assign you 2-3 categories to complete and by the end of the year you will have completed your Animal Phyla project!

For each of the phyla/class, the following information is required:

- Name of the phyla/class- Vertebrate or Invertebrate- At least one picture of an organism in the group (labeled with the name)- List of at least 5 organisms in the group - Habitat- Mode of reproduction- Body plan (symmetry)- Locomotion (do they move, how do they move?)- Interesting facts

This week I want you to look up the above info for the following categories:

1. Porifera

2. Cnidaria

3. Nematoda

** You can look up the information you need with a simple google search. I have also included summaries of each category from encyclopedia.com. The work can be completed in any format: Word, PowerPoint, written by hand, etc. Only one phyla/class per page. At the end of the semester all of your work should be bound together like a book. My hope is that you learn about living things as you are doing this project. If you ever have any questions, please email me at summer.king@dcsms.org **

PoriferaThe phylum Porifera contains all the species of sponges. Phylogenetically, Porifera is most closely related to Protista, making it the first animal phylum to have evolved to be multicellular. This also makes Porifera the simplest in form and function. Sponges arose 550 million years ago in the pre-Cambrian period, evolving from colonial protists, groups of identical single cell organisms that live together. Evidence for this comes from specialized cells called choanocytes which sponges use in feeding. Although sponges are made up of many cells with specialized functions, their cells are not organized into true tissues. This lack of true tissue layers makes sponges different from all other animals except protozoans, which are not multicellular. Sponges also lack symmetry, true organs, a digestive or respiratory system, a nervous system, muscles, and a true mouth.

Sponges are sessile ; they are attached to one place and do not move around. They range in size from over 1 meter (3 feet) long to 2 millimeters (less than 1/8 of an inch) long. All sponges live in water, from the deepest seas to the shallow coastal waters. Most species are marine and can be found in all the oceans; only 3 percent live in fresh water. All sponges have the ability to completely regenerate an adult from fragments or even single cells. Sponges reproduce sexually, with one sponge producing both sperm and eggs from the choanocytes at different times, giving rise to a larvae that is free living (not sessile). A very few species reproduce asexually by budding . Some of the first naturalists like Aristotle mistakenly thought sponges were plants because they do not move and can regenerate.

Sponges depend on the water currents flowing through them for food and gas exchange. Sponges have specialized cells for gathering small particles of

food from the water and distributing the food around the organism. Water comes in through pores along the body wall into the spongocoel , the main cavity of a sponge, and flows out a large opening in the top called an osculum. Choanocytes, also called collar cells, are specialized feeding cells which line the spongocoel. Choanocytes have a flagellum that extends out of the cell and sweeps food particles into a sticky, collarlike opening. They are similar in shape and function to certain colonial protists, such as the choanoflagellates. Amoebocytes, which digest food and transport it around the sponge, are specialized cells that move around the sponge's body under the epidermis , the outer layer of cells, through a jellylike middle cell layer. Amoebocytes move in a way that is similar to how amoebae move. Amoebocytes secrete hard structural fibers called spicules, which are made of calcium carbonate or silica. In some sponges, amoebocytes secrete other materials that make up the skeleton called spongin which are flexible fibers made of collagen. Only sponges have spicules. This structural feature is part of what divides sponges into different classes.

There are over nine thousand identified species of sponges, and more are identified all the time. These species are classified into three classes: Demospongiae, Calcarea, and Hexactinellida.

Most species of sponges are in the class Demospongiae. Sponges in this class are mostly marine, but the class also contains the few species that do live in fresh water. Because the materials that make up the skeleton and spicules of these sponges are so varied; the overall sizes and shapes of the sponges are also varied. The amoebocytes of the sponges in Demospongiae contain pigment, giving these sponges many different bright colors.

Sponges within the class Calcarea are characterized by spicules made of calcium carbonate. All species in Calcarea have spicules of a similar size and shape. Most species are not colored. Calcarea sponges are usually less than 15 centimeters (6 inches) tall, and live in the shallow ocean waters along coasts.

Glass sponges make up the class Hexactinellida. They are unique because their spicules have six points and a hexagon shape. The spicules fuse together to form elaborate lattice skeletons which make the sponges look as if they are made of glass. Most Hexactinellida live in the Antarctic Ocean and are found in deep waters, from 200 meters (650 feet) down.

see also Phylogenetic Relationships of Major Groups.

Laura A. Higgins

Bibliography

Anderson, D. T., ed. Invertebrate Zoology. Oxford: Oxford University Press, 1998.

Barnes, Robert D. Invertebrate Zoology, 5th ed. New York: Saunders College Publishing, 1987.

Campbell, Neil A., Jane B. Reece, and Lawrence G. Mitchell. Biology, 5th ed. Menlo Park, CA: Addison Wesley Longman, Inc., 1999.

Purves, William K., Gordon H. Orians, H. Craig Heller, and David Sadava. Life: The Science of Biology, 5th ed. Sunderland, MA: Sinauer Associates Inc. Publishers, 1998.

CnidariaCnidaria is one of the more primitive animal phyla. It includes aquatic organisms such as jellyfish, sea anemones, corals, and hydras. Most cnidarians are marine, although a few, such as the well-known hydra, are freshwater species.

Characteristics of CnidariansAll cnidarians are characterized by radially symmetric body plans, rather than the bilaterally symmetric body plans that are found in most other animal phyla. Although cnidarians are more advanced than sponges (phylum Porifera) in that they possess distinct tissue layers, they lack many of the features of more advanced animal

phyla, such as internal organs and central nervous systems. Most cnidarians possess tentacles, and many also have nematocysts (specialized stinging cells). Both are involved in feeding.Cnidarians are characterized by the presence of three tissue layers, an outer protective epidermis, a middle layer called the mesoglea, and an inner layer called the gastrodermis, whose function is primarily digestive. The mesoglea of cnidarians is not as highly developed as the mesoderm of other animal groups, being primarily gelatinous with only a few fibrous or amoeba-like cells.Cnidarians possess only one digestive opening, which serves as both the mouth and the anus. This opening is surrounded by tentacles and leads to an internal digestive cavity called the gastrovascular cavity .Cnidarians feed using tentacles that are embedded with stinging nematocysts. The nematocysts are springing barbs with small hairlike triggers that are activated by contact with prey. Most nematocysts require stimulation in more than one sensory mode before they will fire. For example, a nematocyst may respond only if there is mechanical stimulation from physical contact with the prey as well as chemical stimulation signaling the presence of suitable prey. As nematocysts fire, barbs unfold and become embedded in the tissue of the prey. At the same time, the nematocysts inject the prey with an immobilizing toxin through a long hollow thread within the barb. Once the prey item has been captured and subdued, tentacles are used by the cnidarians to bring the prey item into the gastrovascular cavity. Within the gastrovascular cavity, the food item is broken into small particles by digestive enzymes secreted by gastrodermal cells lining the cavity. The minute particles are then taken in by the gastrodermal cells, and digestion is completed in digestive vacuoles (small cavities) within these cells. The indigestible remnants of the prey are expelled from the mouth of the gastrovascular cavity.One hypothesis about the origin of nematocysts suggests that they were prokaryotic endosymbionts which lived within eukaryotic cells as mutualists (mutualisms are symbiotic relationships between individuals of two different species, in which members of both species derive benefits from the relationship), the same way

organelles (specialized parts of cells) such as mitochondria and chloroplasts are believed to originate.Unlike more advanced animal phyla, cnidarians lack a central nervous system. Instead, their nerves are organized in nerve nets that cover the entire body. Impulses spread slowly out from the point of stimulation along the nerve net. Some cnidarians, such as jellyfish, have more complicated arrangements of nerves that allow for more complex responses to stimuli as well as more effective patterns of movement.Cnidarians also lack certain tissue types found in other animal phyla, such as true muscle cells. However, they do have fibers that can contract and therefore can be used in capturing prey and in moving about.

Major Groups of CnidariansCnidarians are divided into three major classes. These are the Hydrozoa (hydras and other colony-forming species), the Scyphozoa (jellyfish), and the Anthozoa (sea anemones and corals).

Hydrozoa.The best-known member of the Hydrozoa is the hydra, a freshwater species. However, the hydra is not a typical hydrozoan. For example, the hydra has only a polyp stage, for example, whereas most hydrozoans have a biphasic (two-stage) life cycle that alternates between a sedentary polyp stage and a mobile, bell-shaped medusa stage. The hydra is not strictly sedentary; it moves in a very unusual way, by turning somersaults. In addition, most hydrozoans are colonial, with each colony arising from the asexual budding of a single individual. Members of a hydrozoan colony have interconnected gastrovascular cavities, and the fluid in this cavity is circulated by cells with long, beating flagella . There is typically some degree of division of labor within the colony. Usually, there are feeding polyps, which possess tentacles and nematocysts (stinging cells), and reproductive polyps, which continually bud off tiny mobile medusas. The medusas swim by tightening and relaxing cells within the bell, and are also scattered by prevailing water currents. Medusas release sperm and eggs directly into the water, where fertilization occurs. The zygote (fertilized egg) develops into what is

called a planula larva—the larvae of cnidarians. The larva ultimately settles to the substrate (rocky bottom of the ocean), finds something to anchor to, develops a mouth and tentacles, and becomes a polyp that subsequently buds to form a new colony.

Scyphozoa.The Scyphozoa includes the well-known jellyfish. In this group, the polyp stage is far less significant than among the Hydrozoa, since the medusa stage is dominant. Scyphozoan medusas grow to sizes considerably larger than those found among the Hydrozoa. They range in size from a few centimeters to over 2 meters across. The nervous systems of jellyfish are also more developed than those of other cnidarians. Instead of a simple nerve net, they have a nerve ring around the edge of the bell portion of the medusa. Neurons throughout the rest of the body connect to this ring. This organization allows for faster conduction of impulses from one side of the body to the other, which in turn allows the jellyfish to swim with coordinated contractions of the entire bell.

Anthozoa.The Anthozoa includes the sea anemones and the corals. These species lack the medusa stage altogether, and exist exclusively in the polyp form. Anthozoans tend to have more highly developed contractile cells (cells capable of contracting) than other cnidarians, as well as a more highly developed, thicker mesoglea, which often forms a fibrous connective tissue. Corals secrete a hard, limy skeleton and can form huge reefs, such as the Great Barrier Reef off the coast of Australia. Coral reefs are an impressive ecosystem, one of the most diverse and productive on Earth.see also Phylogenetic Relationships of Major Groups.Jennifer Yeh

BibliographyAnderson, Donald Thomas. Atlas of Invertebrate Anatomy. Sydney, Australia: UNSW Press, 1996.

Barrington, Ernest James William. Invertebrate Structure and Function. New York: Wiley, 1979.

NematodaThe Phylum Nematoda consists of the species commonly known as roundworms. There are approximately 12,000 described species, but the actual number could be many times higher. Nematode worms are extremely abundant; often, several hundred species, and as many as a million individuals, inhabit a square yard of soil. Nematodes are also extremely varied ecologically. They are found in almost every imaginable habitat , including terrestrial (land-based), freshwater, and saltwater ecosystems , as well as within other organisms as parasites. Nematodes can be herbivorous, carnivorous, or parasitic, and include both generalists (who make use of a wide variety of resources) and specialists (who make use of only particular resources). They play a particularly critical role in decomposition and nutrient cycling, where they are often the intermediate decomposers that partly break down organic materials so that they can then be dealt with by bacterial decomposers.

Characteristics of NematodesRoundworms are small, slender, unsegmented worms which are tapered at both ends. They have a circular cross section. Different species of nematodes are often difficult to distinguish because of their fairly uniform external morphology, or outer appearance.

Nematodes are characterized by an external (outer) layer of cuticle that is secreted by the hypodermis underneath it. The cuticle is somewhat rigid. However, it is flexible enough to permit bending and stretching, and can be penetrated by gases and water. The cuticle is molted , or shed, several times during the worm's growth. The hypodermis underlying the cuticle is a syncitium—that is, it consists of large cells with more than one nucleus. A layer of muscle cells is found beneath the hypodermis. All nematode muscle fibers run lengthwise along the animal's body. This single, unvaried orientation limits nematodes to their characteristic, and somewhat awkward, pattern of movement, a flailing whiplike motion that is produced by alternate contractions (shortenings and thickenings) of muscle cells on either side of the animal's body. The rigidity of the cuticle layer also limits the motion of nematodes.

Nematodes lack a true coelom (body cavity) since their internal cavity is not lined by cells originating from the embryonic mesoderm. Instead, they possess a fluid-filled pseudocoel (incomplete coelum) that contains the intestine and reproductive organs.

The nematode nervous system is characterized by an rear nerve ring around the area of the pharynx (area deep inside the mouth cavity) and two pairs of lengthwise nerve cords that run down the body. There are also dorsal (back) and ventral (belly) nerve cords as well as a set of lateral nerve cords across the body. These nerve cords transmit sensory information and coordinate movement. Nematodes have a variety of sensory receptors, including tactile (touch) receptors at the front and back ends of the body, and chemosensory (chemical-sensitive) cells at the front end. They also have light-sensitive organs organized either in ocelli (simple eyes) or distributed along the surface of the body.

Nematodes have a complete gut with a mouth and an anus. Teeth, which are used to pierce animal or plant matter, aid in obtaining food. The pharynx is muscular and pumps food through the gut, and nutrients are absorbed in the intestine. There is no internal system of circulation, so the transport of nutrients and wastes is achieved by diffusion (scattering). Specialized cells for excretion, which are known as rennette cells and are unique to the phylum, remove nitrogen-laden wastes. These are expelled from the nematode directly through the body wall, in the form of ammonia.

Nematodes breathe across their entire body surface. This gas exchange strategy is adequate because of the small size of the worms, which means they have a high ratio of surface area to volume.

The majority of nematodes are dioecious ; that is, the sexes are separate. Some species, however, are hermaphroditic, having both male and female reproductive organs. In dioecious species, males have a specialized spine for sexual reproduction that is used to open the female's reproductive tract and to inject sperm. Nematode sperm is unusual in that the sperm cells do not have flagella, and move using an amoeboid motion (crawling). While some species are live-bearing, most lay eggs. Eggs escape through a midbody hole called the gonopore in the female. There is no distinct larval stage. Eggs develop directly into juveniles that generally resemble the adults except that they lack mature reproductive organs. Nematodes are also characterized by an unusual feature called "eutely," in which every individual of a given species has exactly the same number of cells. This cell number is achieved by the end of the developmental period, so that subsequent growth of the animal involves increases in cell size rather than in cell number.

Nematodes of Particular InterestSome well-known nematode parasites include hookworms, pinworms, and heartworms. Also included are Trichinella spiralis, which is responsible for trichinosis and uses both pigs and humans as hosts, and filarial worms, which are the primarily tropical parasites responsible for the diseases elephantiasis and river blindness.

The nematode Caenorhabditis elegans is one of the most well-studied living species and has served as a biological model organism for genetic and developmental studies. It was the first multicellular organism for which a complete DNA sequence was obtained.

Jennifer Yeh

Bibliography

Brusca, Richard C., and Gary J. Brusca. Invertebrates. Sunderland, MA: Sinauer Associates, 1990.

Gould, James L., and William T. Keeton. Biological Science, 6th ed. New York: W. W. Norton and Co., 1996.

Hickman, Cleveland P., Larry S. Roberts, and Allan Larson. Animal Diversity.

Since we are not in the lab doing dissections, I figured I could at least share the anatomy of one of the categories you are researching this week. Jellyfish fall in the Cnidaria Phylum.

Jellyfish AnatomyJellyfish come in a huge range of forms, however, their body construction is reasonably similar.

The body of an adult jellyfish consists of a bell shaped hood enclosing its internal structure and from which tentacles are suspended.

Each tentacle is covered with cells called ‘cnidocytes’ (a type of venomous cell unique to the phylum ‘Cnidaria’), that can sting or kill other animals.

Most jellyfish use these cells to secure prey or for defense. Others, such as Jellyfish in the Order ‘Rhizostomae’ have neither tentacles nor other structures at the bell’s edges. Instead, they have eight highly branched oral arms.

Jellyfish lack basic sensory organs and a brain, however, their nervous systems and rhopalia (small sensory structures) allow them to perceive stimuli, such as light and odor and enable them to respond quickly.

Jellyfish feed on small fish and zooplankton that become caught in their tentacles. Most jellyfish are passive drifters and slow swimmers, as their shape is not hydrodynamic. Instead, they move so as to create a current forcing the prey within reach of their tentacles. They do this by rhythmically opening and closing their bell-like body.

Most jellyfish have tendrils or oral arms coated with thousands of microscopic nematocysts (a type of venomous cell). Each nematocyst has a ‘trigger’ paired with a capsule containing a coiled stinging filament armed with exterior barbs. Upon contact, the filament rapidly unwinds, launches into the target and injects toxins. The animal can then pull its prey into its mouth.

Although most jellyfish are not dangerous to humans, a few are highly toxic, such as the Lion’s mane jellyfish (Cyanea capillata) also known as the Deep Spiderfish.

Contrary to popular belief, the menacingly infamous Portuguese Man o’ War (Physalia) is not a jellyfish but a colony of hydrozoans (organisms that are related to jellyfish and corals and belong to the phylum ‘Cnidaria’).

Similarly, the box jellies, notorious along the coast of Australia, are cubozoans, not true scyphozoan jellyfish. Irrespective of the stings toxicity, many people stung by them find them very painful and some people may suffer anaphylaxis (allergic reaction in humans and other mammals) or other severe allergic reactions, similar to allergies to bee stings.

JELLYFISH DIGESTIVE SYSTEM

Jellyfish have an incomplete digestive system whereby they have no intestines, liver or pancreas which are important in the digestion of food in most animals. The absence of these organs means that the same orifice is used for both food intake and waste depositing.

Jellyfish dispose of their waste matter very quickly. Jellyfish cannot afford to carry too much bulk around with them otherwise they would find it difficult to stay afloat.