Meet the Invertebrates: Anemones, Octopuses, Spiders, Ants, and Others

By Katharine Rogers

It is easy for humans to relate to dogs or other mammals, difficult to see any kinship with flower-like anemones, supple octopuses, or many-legged spiders. Yet we are all animals that have to deal with the basic problems of living. Bodies need to be supported and muscles to pull against firm structures. Instead of skeletons, invertebrates use structures such as exoskeletons and cavities filled with fluid. All animals must catch their food, even if they are fixed in one place, digest their food, and get rid of wastes. All must reproduce their kind by finding mates and giving their offspring the necessary start in life. When crayfish moved from the sea to fresh water, they evolved special excretory organs to retain essential salts in their bodies, developed the ability to lie dormant during periods of drought or climatic extremes, and nurtured their young until they were mature enough to deal with 0the stress of living in fresh water. When spiders and insects moved onto the land, their permeable respiratory surfaces had to be enclosed within their bodies, and they evolved internal book lungs and tracheal systems that exchanged oxygen for carbon dioxide through small holes in their exoskeletons. Meet the Invertebrates introduces readers to representatives of the major invertebrate groups, with their wide range of life styles and the adaptations they have evolved to fit them -- the bath sponge, the giant green anemone, the beef tapeworm, the roundworm Ascaris, the common earthworm, the common sea star, the hard shell clam, the giant Pacific octopus, the red swamp crayfish, the garden spider, the German cockroach, the spicebush swallowtail butterfly, and the little black ant.
Meet the Invertebrates explains how these animals “work” physiologically and, in the case of higher invertebrates, psychologically. It describes the animals from a subjective as well as an objective point of view – how they look and behave, live their everyday lives, and perceive the world. An octopus sees the world with eyes much like our own; a spider senses it through legs that detect the minutest vibrations on her web; an ant uses her antennas to smell and feel her nestmates, other animals, and her environment. The book progresses from a sponge, as simple as an animal can be, to the highly developed octopus and ant. When a sponge is subjected to a poke or a chemical stimulus, the particular cells affected react individually. Cnidarians such as anemones evolved nerve cells specialized to receive information and convey it relatively fast, but these are simply connected on a loose network. Flatworms evolved a tiny brain to direct their activities. Octopuses have a large brain with over 30 specialized lobes. They show curiosi-ty and can solve complicated problems; one taught herself to open a child-proof pill bottle in 5 minutes.
The scientific classification given at the end of each chapter shows how the subject fits into the animal kingdom. This is followed by a sampling of human reactions to these animals, from Victor Hugo’s horror of the octopus to Maurice Maeterlinck’s glowing praise of the ant’s courage, generosity and altruism.

• Language: English
• Publisher: Katharine Rogers
• Release date: Jun 16, 2014
• ISBN: 9781311443557

Katharine Rogers

Katharine M. Rogers, a Professor of English Emerita at the City University of New York, moved to Maryland after her retirement and pursued her life-long interest in natural history. When she volunteered at the National Zoo, she was assigned to the Invertebrate Exhibit. There it first occurred to her that invertebrates might be displayed and studied for themselves, rather than taken for granted as pests (cockroaches) or food sources (lobsters). After spending many hours observing the creatures in the Invertebrate Exhibit, she began to see them more from their own point of view, as animals that exist for themselves, perceiving the world in their various ways and dealing with the problems of living as all animals must. She learned that the flower-like anemones were purposefully wafting their tentacles in order to find and secure prey, that the lobster’s nineteen pairs of appendages were diverse tools that it manages with great skill, that the octopus’s jointless arms, covered with suckers that feel and taste, give it capacities for sensation and manipulation that we can only imagine. Then she began to wonder how these alien animals “worked,” both physiologically and, in the case of higher invertebrates, psychologically. This led her to serious research and, ultimately, to an ebook – "Meet the Invertebrates." This introduces readers to thirteen invertebrates, from a sponge, which is as simple as an animal can be, to an active, efficient ant.During her teaching career and first years of retirement, Rogers wrote on literature, especially on issues relating to women. She started research on her first book, "The Troublesome Helpmate: A History of Misogyny in Literature," when she was forced onto unpaid leave after becoming pregnant. This was followed by:"William Wycherley" (author of the Restoration comedy "The Country Wife"),"Feminism in Eighteenth-Century England,""Frances Burney: The World of 'Female Difficulties,'""The Cat and the Human Imagination,""L. Frank Baum: Creator of Oz,""First Friend: A History of Dogs and Humans,""Cat,"and "Pork: A Global History."She lives in Gaithersburg, Maryland, with her husband, our dog, and our cat.

Book preview

MEET THE

INVERTEBRATES

By Katharine M. Rogers

Smashwords Edition

Copyright © 2014 Katharine M. Rogers

License Notes

This ebook is licensed for your personal enjoyment only. This ebook may not be re-sold or given away to other people. If you would like to share this book with another person, please purchase an additional copy for each recipient. If you're reading this book and did not purchase it, or it was not purchased for your use only, then please return to your favorite ebook retailer and purchase your own copy. Thank you for respecting the hard work of this author.

Ebook formatting by www.ebooklaunch.com

ACKNOWLEDGMENTS

I would like to thank the following scientists for reading my chapters and correcting my mistakes: Dr. Sean Brady of the Department of Entomology and Drs. Stephen Cairns, Jerry Harasewych, Christopher Mah, Rafael Lemaitre, and Klaus Ruetzler of the Department of Invertebrate Zoology, all at the National Museum of Natural History; Dr. Eric P. Hoberg of the Biosystematic Unit of the Parasite Biology, Epidemiology and Systematics Laboratory, United States Department of Agriculture; and Dr. Mike Vecchione of the National Marine Fisheries Service, NOAA. I am very grateful for their generosity in sharing their time and knowledge with me.

TABLE OF CONTENTS

Preface

1. The Animal Kingdom

2. The Bath Sponge, Spongia officinalis

3. The Giant Green Anemone, Anthopleura xanthogrammica

4. The Beef Tapeworm, Taenia saginata

5. Ascaris lumbricoides, a Roundworm

6. The Common Earthworm, Lumbricus terrestris

7. The Common Sea Star, Asterias forbesi

8. The Hard Shell Clam, Mercenaria mercenaria

9. The Giant Pacific Octopus, Enteroctopus dofleini

10. The Red Swamp Crayfish, Procambarus clarkii

11. The Garden Spider, Araneus diadematus

12. The German Cockroach, Blattella germanica

13. The Spicebush Swallowtail Butterfly, Papilio troilus

14. The Little Black Ant, Monomorium minimum

Where to Meet Invertebrates

Select Bibliography

About the Author

PREFACE

HOW I MET THE INVERTEBRATES

I grew up reacting to invertebrates as most people do — shrimps are tasty in garlic sauce, sponges are convenient for sopping up water, roaches swarm disgustingly over kitchen surfaces, earthworms on a rain-washed sidewalk are unoffending but nevertheless slimy and disgusting. I devoured horror stories that made the most of huge featureless worms that ooze inexorably along the ground, big-eyed ants or spiders running along on too many legs, alarmingly flexible octopus tentacles whipping out from murky ocean depths to affix people with their suckers. Invertebrates seem alien and therefore wrong: they don't have the right number of limbs and don't move the way we do; they are soft all through, lacking firm parts to give them shape, or else they are covered with hard shells that make them seem like impervious machines.

It was only when I volunteered at the Invertebrate Exhibit in the National Zoo that I began to look at invertebrates as animals that exist for themselves, as living creatures dealing with life's challenges as fish, birds, and mammals must. I also noticed the egocentricity of dividing the animal kingdom into vertebrates - the relatively uniform group that includes, and (we typically assume) culminates in, ourselves - and invertebrates -the many diverse groups that include everybody else. We define these others solely by their lack of a backbone, instead of looking at their many inventive ways of supporting their bodies and anchoring their muscles, as well as solving all the other problems of living. Invertebrate animals range from sponges, sessile creatures that respond vaguely to their surroundings and have barely distinguished cells, to active, highly coordinated octopuses, which have eyes like our own and can learn to open bottles, or ants, which have a more efficient society than ours with a sophisticated system of communication. Actually, 98% of all the animal species on earth are invertebrates.

When I first visited the Invertebrate Exhibit, I admired the flower-like anemones and gazed with fascination and distaste at the many-limbed, jerkily moving lobsters, the large spiders sitting in their orb webs, and the octopus shooting its sinuous tentacles out from the corner where it lurked. It never occurred to me to reflect that the anemones were purposefully wafting their tentacles in order to find and secure prey, that the lobster's nineteen pairs of appendages were diverse tools that it manages with great skill, that the orb web is a marvelous invention for catching flying insects, that the octopus's jointless limbs, covered with suckers that feel and taste, give it capacities for sensation and manipulation that we can only imagine. Before long, I could happily spend half an hour watching an octopus seize a glass rod from her keeper and carefully explore it with the suckers on her tentacles. I was quite put out when I overheard a visitor exclaim as she viewed the handsomely striped slipper lobsters, Oh, how ugly! Although I never could warm up to the hissing cockroaches, I enjoyed holding a tarantula in my hand and admiring its construction. I once had been an arachnophobe myself, but now I could no longer sympathize with visitors who cringed as they passed the handsome orb weavers on their webs. The absurdity of their fear becomes obvious if we make the effort to look at the situation from the spider's point of view: she can run freely along her web and its threads keep her informed of what is going on around her; the last thing she wants to do is leap off it into the face of a huge alien mammal.

Many of us have tried to imagine the world from the point of view of our cat or dog, an animal very close to us. It is considerably more of a challenge to imagine what it would be like to know the world almost entirely through touch or smell, to be encased in armor like an arthropod or utterly flexible like an octopus, or to have six or more limbs to serve our purposes. Meeting the invertebrates made me think about such things, and I invite you to join me.

CHAPTER 1

THE ANIMAL KINGDOM

Animals are just one of several kingdoms of living things. All living things are, as the characters of Star Trek put it, carbon-based life forms - meaning that they are made of complex carbon compounds. Carbohydrates and fats are composed of carbon, oxygen, and hydrogen in definite proportions and arrangements, and proteins contain in addition nitrogen and often phosphorus and sulfur. All living things depend on water: active protoplasm contains 65-96% water: the fluid within cells and the tissue fluids that constantly bathe the cells of multicellular organisms are water solutions. Water is needed to keep their metabolic processes running and to transport essentials around their bodies.

The simplest living things, bacteria, are distinguished from non-living matter by their organization into cells and their ability to reproduce themselves systematically by passing on their heredity through genes. Within each cell is a constant fluid environment where it carries on the processes of converting food to energy to keep itself alive, of synthesizing materials for growth and replacement of worn out or damaged parts, and of reproducing itself. This area must be surrounded by a membranous wall to protect it from the vagaries of the environment outside. Both the volume and the concentration of fluids within a cell must be maintained within rather narrow limits for an organism to function. Therefore the cell membrane is selectively permeable: it admits and retains nutrients and expels wastes; it holds some chemicals in, passes some through, and bars some from entering; it regulates the amount and proportions of water and elements such as sodium and potassium within the cell. Many, though not all, bacteria require oxygen to live; for they need it to release energy from their food.

All organisms, including bacteria, have a set of instructions or program, resident in their genes, that directs their development and reproduction. Genes are located on chromosomes and composed of DNA (deoxyribonucleic acid), which is arranged in intertwined strands within the nucleus of a cell and consists of long sequences of four different chemical compounds - adenine, guanine, cytosine, and thymine. A copy of a gene is transcribed onto a messenger molecule when needed; this mRNA directs synthesis of specific proteins on ribosomes outside the nucleus, which may be used to build a structure or to facilitate and regulate chemical reactions. When paired strands of DNA are separated, each can replicate itself to form a new partner and program a new individual. In all living things from bacteria to humans, DNA is formed of the same chemicals in various combinations and is transcribed by essentially the same process. Reproduction involves not only generation of a new organism, but an orderly sequence of changes as it develops into an adult.

Although bacteria are organized into cells, their cells lack definite nuclei. They have only a large chromosome that bears their genes, which direct protein synthesis on ribosomes. Bacteria are placed in their own kingdom, Monera. All the higher kingdoms - Protista, Fungi, Plants, and Animals - are composed of cells that have a nucleus to direct their activities (eukaryotic cells). The nucleus directs metabolism, leads in the process by which a single cell divides and forms two new cells, and determines, in conjunction with the cell's environment, what form a new cell will exhibit at maturity. Although Protista have nuclei, they must, like bacteria, carry out all their vital activities within a single cell. They may have characteristics of plants, animals, and fungi; the more animal-like ones are called Protozoa. The remaining kingdoms are multicellular, although cell divisions are not clearly distinct in fungi. Like animals, fungi must take nourishment from outside themselves. They feed by absorbing nutrients from dead organic matter or from other organisms on or in which they live. Plants are distinguished by their ability to manufacture their own food. They convert carbon dioxide and water into glucose, simple sugar, using their chlorophyll and energy produced by the sun to drive the chemical reactions; through further chemical reactions, glucose can be converted into the complex organic substances of which all living things are made. Because most bacteria and protists, as well as fungi and animals, cannot synthesize glucose, they are ultimately dependent on plants for food. Higher plants are composed of tissues (roots, stems, leaves, and reproductive organs) just as higher animals are.

Animals - from primates down to sponges — must take in food from outside themselves; that means they have to find and capture it, even if this process is as passive as drawing water containing food particles through their body, as sponges do with flagellated cells and clams with ciliated gills. Even if they remain fixed in one spot, they must have at least a few moving parts such as flagella and cilia. These are similar structures, hairlike projections from the cell body, bounded by the same membrane that encloses the cell; flagella are few and relatively long and beat back and forth or in a rotary pattern, while cilia occur in large groups and beat collectively in a power stroke-recovery stroke rhythm. They wave back and forth to move air or liquid along the surface of a cell, and they have the same basic structure in all animals: eleven groups of microtubules, nine fused pairs arranged around the periphery and two isolated microtubules in the center. Cilia or flagella may move food particles into a clam's mouth, or sweep dust particles from a mammal's windpipe, or propel a very small organism through water. In most animals, they move the male reproductive cells. For vigorous movement, higher animals rely on muscle cells, specialized for a particularly high capacity for contraction; that is, shortening and thickening to move body parts by pulling on them. In all but the smallest and simplest animals, a muscle can exert the necessary force only when anchored to some firm structure; it contracts by pulling against a rigid element to which it is attached, and it is extended - that is, returned to its resting length, for muscles cannot extend themselves - by another force, typically an antagonistic muscle pulling on the same rigid element. A human arm bends by contracting the biceps muscle, which extends the triceps; when the triceps contracts, the arm extends by stretching the biceps; both muscles pull against the arm bones.

Skeletons are also needed to support an animal's body and protect its vital organs. Terrestrial animals need them to keep soft tissues from collapsing under their own weight, and even aquatic ones need them to keep from being deformed by external forces such as flowing water. We think of skeletons as rigid structures - the endoskeleton of vertebrates and echinoderms or the exoskeleton of arthropods. But animals such as anemones and worms have hydrostatic skeletons, consisting of fluid-filled cavities bounded by firm body walls with muscles suitably arranged around them.

An animal's moving parts must be directed and controlled by some integrating system. In all animals, vertebrates and invertebrates above the level of sponges, muscle cells act in response to nerve cells, cells that are specialized for responding to stimuli and rapidly transmitting impulses. They receive information from specialized sensory cells that detect significant changes in an animal's environment and then transmit this information to appropriate muscles or glands so that they will make an appropriate response. Nerve cells are organized into a connected system, so as to integrate sensory information from the environment and coordinate movement in response.

Sensitivity or irritability, the power of responding when external or internal conditions change, is a general characteristic of living cells. Simple reactions, such as turning to or from light and avoiding noxious chemicals, can be found in members of all the kingdoms. Even bacteria can derive information from chemical reactions between their cell membrane and substances in the environment and respond to that information. A plant stem grows toward the light. But such reactions are far more highly developed in animals. All animals respond to chemical stimuli, reacting positively to food and negatively to toxic substances. All respond to touch, from the sponge that closes an external opening when it is poked to the spider that instantly detects the nature and location of anything that strikes its web. Almost all respond to light, positively or negatively, whether they use the eyespots of sea stars or the elaborate image-forming eyes of octopuses. Most animals have georeceptors sensitive to the pull of gravity, to inform them of their orientation up or down; these are especially important to those that swim or float in open water or spend their days buried in mud.

Once they have obtained their food, which usually comes in the form of large complex molecules, animals must break it down into simple compounds that can pass through cell membranes into the cells where it is processed. In sponges this is done by special cells that engulf particles of food, but higher animals have a digestive system to convert starches and complex sugars into glucose and proteins into amino acids. Within cells, glucose is broken down by chemical reactions that release the energy that keeps all vital processes going. This process requires oxygen if it is to take place efficiently and it produces carbon dioxide as a by-product, so animals must constantly take in oxygen and get rid of carbon dioxide. Both oxygen and nutrients must be circulated throughout the body to the cells where they will be used, and wastes must be removed from the cells and then from the body as a whole

However, survival is not enough: to be successful, an animal must reproduce itself; it must pass on the genetic heritage carried in its DNA. Bacteria and, in general, protists do this simply by growing and then dividing their one cell into two (by mitosis); since the chromosomes divide as the cell does, each daughter cell carries the same number of chromosomes as the parent. Sponges, anemones, and flatworms may also bud off some of their cells to become a new, genetically identical organism. However, in most animals (as well as the higher plants), reproduction involves a combination of the genetic material from two individuals of separate sexes. Each parent contributes a gamete, a sperm or egg cell that has divided (by meiosis) so that it has only half the usual number of chromosomes; when the two cells unite at fertilization, each contributes the same number of chromosomes to the zygote that will grow into a new organism, which will consequently be different from either parent. Our initial understanding of this process came from Edouard van Beneden's nineteenth-century research on a lowly roundworm. He described how the worm's chromosomes are halved in meiosis and the full number is restored when the gametes join at fertilization.

Sexual reproduction has the advantage of affording more possibility for change and perhaps improvement in a species' ability to adapt to an environment that is likely to change - in climate, resources, competition, predators, or parasites. On the other hand, it is wasteful. Two individuals each reproducing on their own can produce twice as many offspring as two individuals that must combine their efforts, and the numbers double with each generation. The bacterium Escherichia coli can reproduce every twenty minutes if enough food is available, thus producing sixty-four copies of itself in two hours. Moreover, an organism that reproduces itself is passing on a genetic combination that has proved itself good enough to ensure survival at least to reproductive age. In sexual reproduction that combination is broken up and half is assigned arbitrarily to each gamete; the resulting recombination might well not be as good as either of the parent combinations. In another way, however, sexual reproduction may better serve to preserve the continuity of a species that has proven its success over many generations of natural selection. Mutations, random changes in the structure of genes, are more often deleterious than not; and if an offspring has genes from two parents, a normal gene from one will probably displace a mutated gene from the other.

Some species exploit the advantages of both asexual and sexual reproduction. Aphids, for example, can shift between the two systems depending on circumstances. When an aphid finds a suitable new plant shoot, she will reproduce asexually, creating a clone of wingless daughters equally well adapted to this local habitat. But if conditions deteriorate, if the shoot becomes overcrowded or a drought occurs, she will produce winged reproductive offspring that leave the shoot and mate with other aphids so as to bring in new genetic combinations, which will settle on other plants.

However most animals, including all of those in this book, use a sexual system that involves, in all but two cases, the union of female and male gametes and the participation of two individuals. The bath sponge produces both eggs and sperms and releases the sperms into the surrounding water, to be ingested by another sponge and fertilize its eggs. The giant green anemone, the hard-shelled clam, and the common sea star belong to one sex or the other and expel their gametes into the water to be fertilized by gametes from other animals. Tapeworms and earthworms are hermaphrodites; earthworms exchange sperm, but tapeworms have to fertilize themselves because they usually have no companion in a vertebrate's intestine. Roundworms, octopuses, crayfish, spiders, cockroaches, and butterflies come in two sexes and mate as vertebrates do. Ants are a special case: while queens mate with males to produce females, males hatch from unfertilized eggs.

All animals must solve certain problems if they are to survive as individuals and species. Although the solutions sometimes show striking similarities among all animals and even spread into other kingdoms, sponges, anemones, tapeworms, roundworms, earthworms, sea stars, clams, octopuses, crayfish, spiders, and insects have found very different ways to solve the problems we all share.

CHAPTER 2

THE BATH SPONGE, SPONGIA OFFICINALIS

The sponge most of us know is a shapeless lump of matter, tough but light and flexible, and chiefly distinguished by the holes that irregularly penetrate it all over. This is, of course, the bleached fibrous skeleton of an aquatic animal with its flesh scraped off. Sponges were more familiar in the past, before there were artificial substitutes, when their capacity to absorb liquids made them indispensable as cleaning tools. In classical times the fine sponges from the Mediterranean were used not only to wash people's bodies and houses, but to hold water for drinking. Roman soldiers carried them on the march, and Jesus on the cross was offered a sponge soaked with vinegar as a restorative. Even today, natural sponges are often preferred to artificial ones because they are more durable, soft, resilient, and retentive of water.

A living sponge displays little more evidence of animal life than its skeleton does, for its moving parts are all inside. It is essentially an animated filter: it lives by drawing a current of water constantly through its body with the collectively beating flagella of special cells, choanocytes or collar cells, that line its interior, and straining out minute bits of food from this water. The same current brings in oxygen and takes away waste products. A sponge circulates a large volume of water through its body every day; according to one estimate, a wool sponge (related to the bath sponge) passes through 1.9 liters (two quarts) per minute and many hundred liters (several hundred gallons) in twenty-four hours. Because its life depends on the constant water current, it cannot tolerate being exposed to air. If it is, air becomes trapped in its channels and blocks the water flow that should be bringing in food and oxygen; and the choanocytes cannot get rid of the air to start the current up again. (This makes it very difficult to maintain sponges in captivity; most aquariums do not attempt to keep them.) When a live sponge is cut in two, it looks like a piece of light gray liver; the only obvious details are the excurrent (or exhalant) channels leading to the holes from which water is expelled. Bath sponges are usually 3 liters (183 cubic inches) in size, but they may grow to eight (488 cubic inches). They live in warm shallow seas, attached to the bottom like plants. They are most abundant in the Mediterranean and Caribbean Seas and the Gulf of Mexico.

The simplest type of sponge is shaped like a vase, covered on its outer side with epithelial cells (which cover inner and outer body surfaces in all animals) interspersed with numerous microscopic pores and lined on its inner side with choanocytes. The choanocyte flagella draw a current of water in through the pores, past the choanocyte collars, into the main internal cavity, and finally out a large excurrent vent at the top (the osculum). This arrangement, drawing water in through many small pores scattered over the body surface and expelling it through one large opening, helps to keep it flowing in a single direction, so the same water is filtered only once and the used water is driven well away from the sponge. This is essential in a sessile animal that cannot get up