THE INVERTEBRATA

PREFACE

This book is intended for the use of students who have completed a year's study of the principles of zoology and of the anatomy and physiology of a series of invertebrate types such as is provided by any of several elementary textbooks in use in this country. The types commonly included in these books-various Protozoa, Hydra, Ascaris, and the Liver Fluke, Earthworm Leech, Crayfish, Cockroach, Pond Mussel, and Starfish-are not here described in detail. We have endeavoured to provide the student with a classification of the Invertebrata which proceeds as far as is usual in an honours course, with a concise statement of the characteristic features of each of the groups mentioned, and with a more detailed statement and discussion of matters of importance or interest concerning them. The choice of examples has been difficult, and we have not always been able to include all those we should have wished, but a fairly full account of certain representative genera has been given. The writing of the book has been shared among us as follows : Chapters I-IV, X, XI (except Onychophora), XII, XVIII and XIX have been written by L. A. Borradaile, Chapters V (except Ctenophora), VII-IX, XIII, XV-XVII, and the Onychophora in Chapter XI by F. A. Potts, Chapter VI and the Ctenophora in Chapter V by J. T. Saunders, and Chapter XIV jointly by F. A. Potts and L. E. S. Eastham, but each of us has read and criticized the work of the others. We desire to express our grateful thanks for valuable advice and criticism to Dr S. J. Hickson, Professor D. Keilin and Dr S. M. Manton ; for much care bestowed upon the illustrations to Messrs A. P. Hayle, J. F. Henderson, and C. F. Pond; and for valuable assistance in the preparation of the index and in other matters to Mr B. Newman. 'For permission to reproduce illustrations acknowledgement is due to Messrs Geo. Allen & Unwin, Ltd. (Textbook of Zoology, Sedgwick); Messrs A. 8z C. Black, Ltd. (Treatise on Zoology, ankester): the Council of the Cambridge Philosophical Society (Biological Reviews); Cambridge University Press (The Determination of Sex, Doncaster, Plant Biology, Godwin, Ciliary Movement, Gray, Zoology, Shipley and MacBride, Primitive Animals, Smith, Palaeontology, Wood) ; Herrn Gustav Fischer, Jena (Ergebnisse u. Fortschritte der Zoologie, Lehrbuch der Pyotozoenkunde) ; Herren Walter de Gruyter & Co. (Handbuch der Zoologie) ; the Council of the Linnean Society of London (Zoological Journal) ; Messrs Macmillan & Co., Ltd. (Cambridge Natural History, Harmer and Shipley, Human Protozoology, Hegner and Taliaferro, Textbook of Comparative Anatomy, Lang, Textbook of Zoology, Parker and Haswell) ; Messrs Methuen & Co., Ltd. (Textbook of Entomology, Imms); Oxford University Press ( The Animal and its Environment and Manual of Zoology, Borradaile). Acknowledgement to the authors of the works from which these illustrations are taken is made in the legends.
THE AUTHORS
CAMBRIDGE
February, I932

TABLE OF CONTENTS

CHAPTER I

Introduction: The Invertebrata

CHAPTER II

Subkingdom Protozoa
[Phylum Protozoa]
Class Mastigophora (Flagellata)
Subclass Phytomastigina
Order Chrysomonadina
Order Cryptomonadina
Order Euglenoidina
Order Chloromonadina
Order Dinoflagellata
Order Volvocina
Subclass Zoomastigina
Order Rhizomastigina
Order Holomastigina
Order Protomonadina
Order Polymastigina
[Suborder Polymastigina s.str.]
[Suborder Diplomonadina]
[Suborder Hypermastigina)
Class Sarcodina (Rhizopoda)
Order Amoebina
Order Foraminifera
Suborder Monothalamia
Suborder Polythalamia
Order Radiolaria
[Suborder Peripylaea (Spumellaria)]
[Suborder Actipylaea (Acantharia)]
[Suborder Monopylaea (Nassellana)]
[Suborder Tripylaea (Phaeodaria)]
Order Heliozoa
Order Mycetozoa
Class Sporozoa
Subclass Telosporidia
Order Coccidiomorpha
Suborder Coccidia
Suborder Haemosporidia

I The names of groups which are mentioned in the test but not formally defined are here placed in square brackets.

Order Gregarinidea
Suborder Schizogregarinaria
Suborder Eugregarinaria
Subclass Neosporidia
Order Cnidosporidia
[Suborder Myxosporidia]
[Suborder Microsporidia]
[Suborder Actinomyxidea]
Order Haplosporidia
Order Sarcosporidia
Class Ciliophora
Subclass Ciliata
Order Holotricha (Aspirigera)
Suborder Prociliata
Suborder Astomata
Suborder Gymnostomata
Suborder Vestibulata (Hymenostomata)
Order Heterotricha
Suborder Polytricha
Suborder Oligotricha
[Tribe Tintinnina)
[Tribe Entodiniomorpha]
Order Hypotricha
Order Peritricha
Order Chonotricha
Subclass Suctoria

CHAPTER III

Subkingdom Parazoa
[Phylum Porifera)Class Calcarea
Class Hexactinellida
Class Demospongiae
[Order Tetractinellida)
[Order Monaxonida]
[Order Keratosa]
[Order Myxospongiae)

CHAPTER IV

Subkingdom Metazoa

CHAPTER V

Phylum Coelenterata
Subphylum Cnidaria
Class Hydrozoa
Order Calyptoblastea
Order Gymnoblastea
Order Hydrida
Order Trachylina
Suborder Trachymedusae
Suborder Narcomedusae
Order Hydrocorallinae
Order Siphonophora
Order Graptolitoidea
Class Scyphomedusae (Scyphozoa)
[Order Stauromedusae)
(Order Discomedusae)
Class Actinozoa (Anthozoa)
Order Alcyonaria
Order Zoantharia
Subphylum Ctenophora
(Class Ctenophora)
[Order Tentaculata]
(Order Nuda]

CHAPTER VI

Phylum Platyhelminthes
Class Turbellaria
Order Acoela
Order Rhabdocoelida
Order Tricladida
(Suborder Paludicola)
[Suborder Maricola)
(Suborder Terricola]
Order Polycladida
Class Trematoda
(Order Temnocephalea)
Order Heterocotylea
Order Malacocotylea
Class Cestoda
Order Monozoa
Order Merozoa

CHAPTER VII

Phylum Nemertea
Phylum Rotifera

CHAPTER VIII

Phylum Nematoda

CHAPTER IX

Phylum Annelida
Class Chaetopoda
Order Polychaeta
Order Oligochaeta
Class Archiannelida
Class Hirudinea
Class Gephyrea
Order Echiuroidea
Order Sipunculoidea

CHAPTER X

Phylum Arthropoda

CHAPTER XI

Subphylum Onvchophora
Subphylum Trilobita

CHAPTER XII

Subphylurn Crustacea
Class Branchiopoda
Order Anostraca
(Order Lipostraca)
Order Notostraca
Order Conchostraca
Order Cladocera
Suborder Calyptomera
Suborder Gyznnomera
(Tribe Ctenopoda)
[Tribe Anomopoda)
Class Ostracoda
Class Copepoda
Appendix: Branchiura
Class Cirripedia
Order Thoracica
Order Acrothoracica
Order Apoda
Ordex Rhizocephala
Order Ascothoracica
Class Malacostraca
Subclass Leptostraca
Subclass Hoplocarida (Stomatopoda)
Subclass Syncarida
Subclass Peracarida
Order Mysidacea
Order Cumacea
Order Tanaidacea
Order Isopoda
Order Amphipoda
Subclass Eucarida
Order Euphausiacea
Order Decapoda
(Suborder Penaeidea)
[Suborder Caridea]
[Suborder Palinura)
[Suborder Astacura)
[Suborder Anomura)
[Suborder Brachyura)

CHAPTER XIII

Subphylum Myriapoda
Class Chilopoda
Class Diplopoda
[Class Pauropoda]
(Class Symphyla]

CHAPTER XIV

Subphylum Insecta (Hexapoda)
Class Apterygota (Ametabola)
Order Thysanura
Order Collembola
Order Protura
Class Pterygota (Metabola)
Subclass Exopterygota (Heterometabola)
Order Orthoptera
[Suborder Cursoria]
[Suborder Saltatoria)
Order Dermaptera
Order Isoptera
Order Plecoptera
Order Embioptera
Order Psocoptera
Order Odonata
(Suborder Zygoptera]
[Suborder Anisoptera]
Order Hemiptera (Rhynchota)
(Suborder Heteroptera)
[Suborder Homoptera)
Order Ephemeroptera
Order Mallophaga
Order Anoplura Order Thysanoptera
Subclass Endopterygota (Holometabola)
Order Neuroptera
Order Mecoptera
Order Trichoptera
Order Lepidoptera
Order Coleoptera
Order Hymenoptera
Order Diptera
Order Aphaniptera
Order Strepsiptera

CHAPTER XV

Subphylum Arachnida
Class Scorpionidea
Class Eurypterida
Class Xiphosura
Class Araneida
Class Acarina
[Order Notostigmata)
[Order Cryptostigmata]
[Order Prostigmata)
(Order Stomatostigxnata)
(Order Heterostigmata)
[Order Parastigmata]
(Order Mesostigmata)
[Order Metastigmata)
Class Phalangida
[Class Palpigradi)
[Class Pedipalpi)
(Class Pseudoscorpionidea]
(Class Solifugae)
Class Pantopoda (Pycnogonida)
Class Tardigrada
Class Pentastomida

CHAPTER XVI

Phylum Mollusca
Class Amphineura
Order Polyplacophora
Order Aplacophora
Class Gasteropoda
Order Streptoneura (Prosobranchiata)
SuborderDiotocardia(Aspidobranchiata)
Tribe Rhipidoglossa
Tribe Docoglossa
Suborder Monotocardia (Pectinibranchiata)
Tribe Rachiglossa
Tribe Taenioglossa
[Subtribe Platypoda]
[Subtribe Heteropoda]
Tribe Toxiglossa
Order Opisthobranchiata
Suborder Tectibranchiata
Suborder Nudibranchiata
Order Pulmonata
Suborder Basommatophora
Suborder Stylommatophora
Class Scaphopoda
Class Lamellibranchiata
Order Protobranchiata
Order Filibranchiata
Order Eulamellibranchiata
Order Septibranchiata
Class Cephalopoda (Siphonopoda)
Order Dibranchiata
Suborder Decapoda
Tribe Belemnoidea
Tribe Myopsida
Tribe Oegopsida
Suborder Octopoda
Order Tetrabranchiata
Suborder Nautiloidea
Suborder Ammonoidea

CHAPTER XVII

Phylum Polyzoa
Class Endoprocta
Class Ectoprocta
Order Phylactolaemata
Order Gymnolaemata
Suborder Cyclostomata
Suborder Cheilostomata
Suborder Ctenostomata
1 References in brackets are to the pages on which examples are described.
Phylum Brachiopoda
Class Ecardmes
Class Testicardines
Phylum Chaetognatha
Phylum Phoronidea

CHAPTER XVIII

Phylum Echinodermata
[Subphylum Eleutherozoa)
Class Asteroidea
Class Ophiuroidea
Class Echinoidea
Order Endocyclica
Order Clypeastroida
Order Spatangoida
Class Holothuroidea
Order Aspidochirotae
Order Pelagothurida
Order Elasipoda
Order Dendrochirotae
Order Molpadida
Order Synaptida (Paractinopoda)
[Subphylum Pelmatozoa]
Class Crinoidea
Class Amphoridea
Class Carpoidea
Class Thecoidea (Edrioasteroidea)
Class Cystoidea
[Order Diploporida]
[Order Rhombifera]
Class Blastoidea

CHAPTER XIX

Phylum Chordata
Subphylum Enteropneusta (Hemichorda)
[Class Balanoglossida)
[Class Pterobranchia]
Subphylum Tunicata (Urochorda)
Class Larvacea
Class Ascidiacea
Class Thaliacea
Order Pyrosomatida (Luciae)
Order Salpida (Hemimyaria)
Order Doliolida (Cyclomyana)
[Subphylum Cephalochorda]
[Subphylum Vertebrata]

INTRODUCTION

The Invertebrata have long since ceased to constitute one of the primary divisions in the scientific classification of the Animal Kingdom. Their name is now no more than a convenience for designating a group of phyla with which it is often necessary to deal as a whole. The primary lines of real cleavage in the Animal Kingdom divide it, not into Vertebrate and Invertebrata, but into three unequal sections, the Protozoa, Parazoa and Metazoa, which are ranked in the following chapters as subkingdoms. Between the Protozoa, which are without cellular differentiation and contain a large group of photosynthetic members, and the Metazoa, in which such differentiation is always strongly marked and photosynthesis is absent, there is a gulf which is in fact far deeper than that which sunders the Protozoa from the lower plants. The view, indeed, has been put forward that these two components of the Animal Kingdom are not, as is usually held, directly related to one another, but arose, with the Plants, as entirely distinct branches of an ancestral stock of living beings. The Parazoa or sponges-unique among many-celled organisms in possessing collared flagellate cells are probably derived from the Protozoa by an origin distinct from that by which the latter group gave rise (if they did so indeed) to the Metazoa. Within the Metazoa, the most significant difference is that which exists between the Coelenterate or Diploblastica and the triploblastic phyla which constitute the rest of the subkingdom. The Coelenterate, which typically start life as a simple, two-layered, ciliate larva, the planula, either retain throughout life the two-layered condition, or depart from it only by the immigration, late in development, of cells from the two primary layers (ectoderm and endoderm, p. 120) into the space (blastocoele) between those layers. The triploblastic animals always possess a true third layer (mesoderm) which is early developed and forms important organs. They are the great majority of animals, and compose a number of phyla. The brigading of these phyla is a difficult task-one, indeed, which it is at present impossible to effect completely. Two main stocks, however, stand out fairly clearly. The Annelida, Arthropoda and Mollusca-by the plan of their central nervous system, the mode and position of origin of their mesoderm, the types of cleavage of the ovum and of larva (the trochosphere) which the Annelida and Mollusca share, and the cuticle and segmentation which the Annelida and Arthropoda have in common-constitute one of these stocks. The other comprises the Echinodermata and Chordata. Its members exhibit a common mode of origin of the mesoderm, primitively as hollow pouches, from the gut wall; they possess, or give indications of, three primary mesodermal segments; the cleavage of their ova is entirely different from that which is characteristic of the Annelida and Mollusca; and between the larvae of the lowest chordates (the Enteropneusta) and those of certain echinoderms there is a remarkable and detailed resemblance. The remaining phyla, smaller and less important, are difficult to relate either to the foregoing groups or to one another. By the type of cleavage of their ova and the possession of flame cells (p. 107), the Platyhelminthes or flatworms seem to be related to the annelid stock. Their lack of coelom is a difficulty in this respect. The structure of the adults of the Rotifera and of the larva of the Polyzoa, which has the character of a trochosphere, might link these groups to the same stock. Some other small phyla (Brachiopoda, Chaetognatha) have possibly distant relationship to the echinoderm-chordate grouping. Others, notably the Nematoda, are extremely isolated and enigmatical. In the great assemblage of triploblastic phyla, the backboned animals, or Vertebrata properly so-called, stand as a branch of one phylurn, the Chordata. Yet their considerable numbers, the size, high organization, and intelligent activity of their members, and the fact that Man is one of them, give them an importance so great that they have always been the subject of a distinct department of zoological study, and were at one time regarded as a primary branch of the Animal Kingdom. That standing they have lost; but it is still necessary for many purposes to treat them apart. The term " Invertebrata" is retained to cover all the non-chordate phyla and the chordates other than the Vertebrata. In that sense it is used in this book. Only the Cephalochorda (Amphioxus), which, though they are not vertebrates, have much in common with those animals, are left aside as best studied with them. The limits of the several phyla are, with one or two exceptions, agreed among zoologists. As much cannot be said for the lower grades of the classification. Different views upon phylogeny, and considerations of convenience, lead to many divergences as to the extent and rank of the various divisions in the systems preferred by different authorities; and even when there is agreement as to the limits of a group different names may be applied to it. In no two works will quite the same arrangement be found. This fact should be borne in mind by the student in using the table of classiflcation which will be found as the Table of Contents at the beginning of this book.

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