invertebrate zoology

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Transcript of invertebrate zoology


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    INTRODUCTION No picture of organisms which ignores their physical and organic

    environment can be even approximately complete. Studies of dead animals or their parts or even of living animals in the laboratory, valuable and indispensable as they are, give but partial pictures. In the studies here contemplated we seek a firsthand knowledge of living invertebrate animals in their natural setting, their behavior and interrelations, their distribution within the habitat, the influence of physical condi- tions on this distribution and the correlation between their structures and their behavior patterns on the one hand and the places they occupy in the environment on the other.

    Field trips are naturally of prime importance in such studies. The more time spent in actual study of animals in the field the better. Under most circumstances these periods must each be confined to a part of a day. Experience has amply proved, however, that continuous studies over a period of days increases the values received out of all propor- tion to the time spent. Appendix A gives specific information with re- gard to field trips and the schedules of such trips during the spring and summer courses at Berkeley.

    Such a field study might be thought to require previous courses designed to give the student a knowledge of the animals which make up the faunas to be studied. Certainly the animals must be recognized and known by name if their behavior and ecologic distribution is to be studied. In practice it is usually necessary and perhaps more advanta- geous to combine this type of study with the field study.

    This portion of the work involves the laboratory. It falls natu- rally into four phases (1) the study of those external characters of the various animal types which are used for their classification and identification, (2) preliminary practice in the use of keys for the identification of some member of each group, (3) a study of demonstra- tion sets previous to field trips to give a preliminary knowledge of the important animals to be expected in the particular fauna, and (4) the identification of animals collected on the field trips.

    THE IDENTIFICATION OF INVERTEBRATE ANIMALS A necessary preliminary to the study of any animal is the deter-

    mination of its scientific name or authentic common name. This is necessary if only to make possible the satisfactory designation of the animal in conversation or in class exercises. A correct determination is especially important, of course, if the animal is to be made the subject of a scientific investigation, since in no other way can the facts be made available to others.

    Few students of zoology realize the difficulties involved in identifying with certainty most species of animals, particularly the species of many of the numerous groups known collectively as inverte- brates. A relatively few species are readily recognized because of distinctive color, pattern, or structure. Such an animal, for example, is the striped shore crab, Pachygrapsus crass ipes, which is abundant in rocky crevices above low-tide mark along the Pacific Coast. In many



    other cases, however, identification can only be approximated by the beginner, and in still others even the specialist will find difficulty in making identification. These difficulties are aggravated on the Pacific Coast by the fact that the study of many groups of inverte- brates has been greatly neglected. During the period when systematic work was the vogue in zoology, there were very few zoologists on this coast. With the change in emphasis in zoology these have largely aban- doned this field and few others have entered it. For a few groups such as the Amphipoda, and the littoral copepods, the fauna of the Pacific Coast is largely unknown. In other groups a considerable amount of work has been done, but much remains to be done.

    Some groups, such as the decapod Crustacea, the marine Mollusca and the echinoderms, are fairly well known to systematists. Even here there remains much need for complete and careful systematic revision and mono- graphing. But when all this has been done there will be necessary still another step if this information is to be available to students of zool- ogy or biology not specialists in the particular groups, and also to the intelligent laymen. This is the production of manuals of faunas, con- taining brief diagnostic descriptions and keys to the species, illus- trated, if possible, and accompanied by careful definitions of terms.

    Familiar works of this type are the floras of various regions and in the various mammals for the identification of birds. A Manual of the Common Invertebrate Animals, by H. S. Pratt (Blakiston), is an attempt at such a manual for the identification of the invertebrate animals of the United States. Because of the imperfect knowledge of the local fauna, the first edition was of very little value for identification of the invertebrates of the Pacific Coast. The new edition (Blakiston) is better, but still reflects the difficulties arising from the scope of such an attempt and the lack of available information with regard to the invertebrates of the Pacific Coast.

    Freshwater Bioloa, by Ward and Whipple, represents a more satis- factory attempt in this direction for the animals of the United States which inhabit fresh water. Since many of these tend to be widely dis- tributed, the Pacific Coast species are better covered. In addition, this work includes valuable discussions of the biology of the different groups, as well as directions for their collection and study. Here again, however, there is great need for revisions of the various groups and a new edition is to be hoped for. Every student or teacher of zool- ogy should own this book when the new edition is available.

    Seashore Animals of the Pacific Coast, by Johnson and Snook, repre- sents the only attempt at a comprehensive treatment of our local marine invertebrates. It is a valuable eontribution and it also should he in the library of every student or teacher of zoology or biology located on the Pacific Coast. Its excellent illustrations make possible the definite identification of certain common, forms, but the absence of keys or any comprehensive treatment of the various groups makes it im- possible to use it as a manual. Indeed, the lack of completeness of our knowledge makes it impossible to produce such a general manual at the present time, and if the knowledge were available it could not be com- pressed within the limits of a single volume.

    Between Pacific Tides, by Ricketts and Calvin, published by the Stanford University Press, will be of great value to students of the


    invertebrates of the Pacific Coast and its reading is required of all I students in this course. While it will not serve as a manual for the identification of animals it will give a valuable picture of faunas characteristic of the major environments of the seashore in this area, and its excellent illustrations in conjunction with references to clas- sification lists will make possible the identification of many common animals.

    Fortunately we have a slowly increasing number of well-illustrated, authentic monographs on separate groups of California invertebrates. Such are: Schmitt, University of Cali Fauna of the Pacific Coasts of North. Central. and Northern South Amer- ica (1940, University of Southern California Press) ; Fraser, Hydroids -

    of the.Pacific Coast (1937, The University of Toronto Press), and others. Some of these are in need of revision and others are too technical to be available to the student involved in such a study as this.

    As mentioned in the preface, the Illustrated Key to Nest American Pelecy~od Genera, by Keen and Frizzell (1939, Stanford University Press ), is an excellent example of what can and should be done in this field. Students are encouraged to obtain and use this valuable work. Unfortu- nately it stands practically alone, and even it leaves the species un- determined.

    It will be seen, therefore, that if the invertebrate fauna of a given area of the Pacific Coast is to be used for field studies, it be- comes necessary, as a temporary measure, at least, to develop keys to aid in the identification of the species concerned. Such is the purpose of the keys here given, which are tentative, in many cases requiring to be corrected and amplified as our knowledge increases. It will be noted that in numerous instances the determinations are only to genus, and in some cases even only to the family. This may be because there is only one species concerned in the area, and the burden of scientific names to be learned may be thus reduced, or because either the knowledge is lacking to carry the identifications further, or the identifications are too difficult for any except the specialist.

    It cannot be too strongly emphasized that keys are short-cuts and often very misleading; that their function is merely to clear the way to an approximation, and that identifications made by them, if to be of scientific value, must be reinforced by comparisons with descrip- tions and illustrations in monographs, if such exist, or by comparisons with authentic named specimens, or by submission to a specialist.

    The first two methods are available in a course such as the one for which these keys are designed. Comparison with named specimens should be considered as a last resort, however, since such named col- lections are rarely available and the gaining of experience in the use of keys and works of reference is one of the important opportunities offered by the course.

    A list of the publications and manuscripts most available for verification or identifications of species