Savory - Arachnida 1977

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12 I. PROLEGOMENA The following considerations apply to both Acari and Araneae, and probably also to the Opiliones. \Vith the increase in the numbers of interested zoologists and with a consequent increase in the number of collecting expeditions, penetrating into more and more inaccessible regions, the stream of newly discovered species has grown from a trickle to a flood. The time may be not far distant when even full-time specialists will be overwhelmed by the cascade of "new" species. A consequence of this will be a recurrence of the state of affairs that existed in the late nineteenth century: the descriptions become so numerous, the literature so extensive, the languages used so diverse, that the individual systematist is certain to miss records of many species unfamiliar to himself. Names, which will one day be recognized as synonyms, will be given by the hundred before the end of the present century. The history of the nomenclature of spiders gi;-es support to this prophecy. In Bonnet's "Bibliographia Araneorum" there are references to about 250,000 names, and it is evident that on an average each species has received five names. This reduces an estimate of a quarter of a million species to about 50,000. But in his last volume Bonnet informs us that about 15,000 names have been used once only in all the literature before 1939: it is safe to assume that nearly all of these have been described, and are now known, by other names; and this reduces 50,000 to 35,000. The same is true, ifless emphatically, of the names that have been used twice only, so that critical analysis must put the world's spiders known in 1940 at about 30,000. It is axiomatic that the largest orders will have the widest range, but there is more to the subject of geographical distribution of the Arachnida than this. A simple survey, which will be elaborated in a later chapter, shows that the 12 living orders may be described as follows. (i) Four orders which are widely dispersed all over the world, including even the frigid regions of the sub-arctic and sub-antarctic: Araneae, Pseudoscorpiones, Acari and Opiliones. (ii) Four orders which are confined to the tropical or hot subtropical belt, but which are widespread within it: Scorpiones, Amblypygi and Cropygi. Four orders which are sporadically distributed and found only in limited and well-separated areas: Cyphophthalmi, Palpigradi, Ricinulei and Schizomida. A biological feature that follows immediately on the subject of distribution, and is connected with it, is that of size. In general terms, Arachnida are among the small animals of the world, but, by itself "small" is a rather meaningless adjective. The facts may be summarized as follows. 2. THE CI~ASS ARACHNIDA 13 (a) There are four living orders in which the length of the largest species does not exceed 1 cm. These are Pseudoscorpiones, Palpigradi, Schizomida and Cyphophthalmi. There are four orders in which the length of the largest species exceeds 6 cm. These are Araneae, Uropygi, Solifugae and Scorpiones. (c) This leaves four orders of intermediate or average size: Acari, Ricinulei, Opiliones and Amblypygi. It is to be observed that in each group there is an order, named first, which has a wide or very wide distribution, as well as an order, named · second, which has a very limited distribution. From this it follows that no correlation between size and distribution can be detected when a whole order is considered as an indivisible unit. Geographical barriers must affect smaller units, sub-orders or families, and will be considered in the appropriate chapters in Part Ill. Distribution in space leads to a consideration of distribution in time. The Eurypterida were aquatic animals, whose fossilized remains have been found in all the Primary strata from the Cambrian to the Permian, but in no later rocks. Probably most of them were marine, but there is evidence that some lived in streams and lakes. The earliest known scorpion is the Silurian species, Palaeophonus nuncius; Carboniferous scorpions are fairly numerous: they showed most of the features that characterize living forms and it appears that the order really reached its acme during this era. The De,·onian strata have yielded both spiders and mites, and all remaining orders, except Cyphophthalmi and Pseudoscorpiones, are represented in the Carboniferous, many of them, notably Solifugae and Opiliones, in forms which differed in no essentials from the species living today. Five orders which rose to comparative prominence during the Carboniferous have since disappeared. The Anthracomarti survived until the Permian, to this extent outliving Kustarachnae, Haptopoda, Architarbi and Trigonotarbi. All these orders have left no more evidence of their ancestors than of their descendants. These facts are remarkable, and the conclusion to which Berland ( 1933) has come is sufficiently striking. Such evolution as can be perceived, he writes, is not a progressive change, and progress is the essence of evolution, but a mere replacement of one form by another, apparently equivalent or comparable to it. This implies that the study of fossil Arachnida leads to the conclusion that the hypothesis of an evolution taking place by slow successive degrees is simply not in accordance with the facts. The subject of the geological record of Arachnida and its bearing on the course of their evo.lution are considered more fully in Chapter 11.
14 I. PROLEGOMENA The most striking features to be mentioned here are the imperfection of the record, with its large gap in the Secondary Era, and the difficulty of arranging the 16 orders in a satisfactory sequence. From what has been written above it should be clear that external features simplify the placing of any species in its correct order. An elaborate key is therefore a conventional addition, rather than a practical necessity, yet, since it is often expected, a simple form follows. There are several different ways in which such keys may be printed; the method used here, and elsewhere in this book, gives to every descriptive clause a number of its own, and never an asterisk or a number shared with another clause. A number in parentheses is the alternative to the number that precedes it. 11. DE ARACHNIDIS I (2) 2 (3) 3 (4) 4 (3) 5 (6) 6 (5) 7 (8) 8 (7) 9 (10) 10 (9) 11 (12) 12 (I!) 13 (14) 14 (13) 15 (16) 16 (15) 17 (18) 18 ( 17) 19 (20) 20 (19) 21 (22) 22 (21) Prosoma and opisthosomajoined across whole breadth Prosoma and opisthosoma separated by a pedicel Body divided into proterosoma and hysterosoma between legs 2 and 3 Body divided into prosoma and opisthosoma behind legs 4 Pedipalpi enlarged, chelate Pedipalpi normal, leg-like Post-abdomen narrow, with terminal sting Post-abdomen normally elliptical Chelicerae large, malleoli on legs Chelicerae normal Odoriferous glands opening on carapace surface Odoriferous glands opening near tips of tubercles \Vith terminal abdominal spinnerets No abdominal spinnerets Cucullus at front of carapace No such cucullus Telson long, as flagellum Telson short or absent Pedipalpi large and spinous Pedipalpi leg-like Flagellum short, four joints Flagellum absent ACARI 3 13 5 7 9 SCORPIONES PSEUDOSCORPIONES SOLIFUGAE !I OPILIONES CYPHOPHTHALMI ARANEAE 15 RICINULEI 17 19 21 UROPYGI PALPIGRADI SCHIZOMIDA AMBLYPYGI A dichotomic table, written in much greater detail and with extra alternatives, and including also the fossil (extinct) orders, is given by Max Vachon in "Encyclopedie de la Pleiade" (1963), Zoologie, Tome II, pp. 101-5.
Page 1 and 2: Arachnida THEODORE SAVORY 2nd editi
Page 3 and 4: Contents Preface Acknowledgements .
Page 5 and 6: MAIAE CARISSIMAE UXORI SECUNDAE LIB
Page 7 and 8: 1 The Phylum Arthropoda The phylum
Page 9 and 10: 6 I PROLEGOMENA The comparison impl
Page 11: 10 I. PROLEGOME);A one time so rare
Page 15 and 16: 18 U. DE ARACHNIDIS it, move to a f
Page 17 and 18: 3. MORPHOLOGY: EXTERNAL APPEARANCE
Page 19 and 20: 26 II. DE ARACHNIDIS 3. MORPHOLOGY;
Page 21 and 22: 30 II. DE ARACHNIDIS yet arachnolog
Page 23 and 24: 34 II. DE ARACHNlDIS curved. It oft
Page 25 and 26: 38 II. DE ARACHNIDIS 4. PHYSIOLOGY:
Page 27 and 28: 42 II. DE ARACHNIDIS fibres run upw
Page 29 and 30: 46 II. DE ARACH~IDIS As a rule the
Page 31 and 32: 50 11. DE ARACHNIDIS (iii) Inversio
Page 33 and 34: 54 II. DE ARACHNIDIS FIG. 21. Newly
Page 35 and 36: 58 II. DE ARACHNIDIS Pseudoscorpion
Page 37 and 38: 62 11. DE ARACHNIDIS of the exoskel
Page 39 and 40: 66 II. DE ARACHNIDIS Sometimes the
Page 41 and 42: 70 II. DE ARACHNIDIS using a scanni
Page 43 and 44: 74 II. DE ARACHNIDIS constitutes th
Page 45 and 46: 78 II. DE ARACHNIDIS think of Arach
Page 47 and 48: 82 II. DE ARACH::-.;IDIS declined t
Page 49 and 50: 86 II. DE ARACHNIDIS .Man is the on
Page 51 and 52: 90 11. DE ARACHNIDIS Autecology con
Page 53 and 54: 11. PHYLOGENY: EVOLUTION 95 11 Phyl
Page 55 and 56: 98 II. DE ARACHNIDIS An obvious ass
Page 57 and 58: 102 II. DE ARACHNIDIS start preserv
Page 59 and 60: 106 II. DE ARACHNIDIS Here are thre
Page 61 and 62: 110 11. DE ARACHNIDIS Araneae, and
Page 63 and 64:
13 The Order Scorpiones [Scorpionid
Page 65 and 66:
118 Ill. PROLES ARACHNES 13. THE OR
Page 67 and 68:
122 III. PROLES ARACHNES CLASSIFICA
Page 69 and 70:
126 III. PROLES ARACHNES 14. THE OR
Page 71 and 72:
130 Ill. PROLES ARACHXES The lowly
Page 73 and 74:
134 Ill. PROLES ARACHNES to be seen
Page 75 and 76:
16. THE ORDER SCHIZOMIDA 139 16 The
Page 77 and 78:
142 Ill. PROLES ARACHKES power, an
Page 79 and 80:
146 III. PROLES ARACHNES DISTRIBUTI
Page 81 and 82:
150 III. PROLES ARACHNES chelicerae
Page 83 and 84:
154 Ill. PROLES ARACHNES FIG. 53. S
Page 85 and 86:
158 Ill. PROLES ARACHNES (vi) Lobed
Page 87 and 88:
162 III. PROLES ARACHNES is found i
Page 89 and 90:
166 III. PROLES ARACHNES 4 (3) Chel
Page 91 and 92:
20. THE ORDER TRIGONOTARBI 171 20 T
Page 93 and 94:
174 Ill. PROLES ARACHNES 22 The Ord
Page 95 and 96:
178 III. PROLES ARACHNES The family
Page 97 and 98:
182 III. PROLES ARACHNES are above
Page 99 and 100:
186 Ill. PROLES ARACHNES opisthosom
Page 101 and 102:
190 Ill. PROLES ARACHNES Sub-order
Page 103 and 104:
194 III. PROLES ARACIINES 25. THE O
Page 105 and 106:
26 The Order Acari 26. THE ORDER AC
Page 107 and 108:
202 III. PROLES ARACHNES Tetrastigm
Page 109 and 110:
206 Ill. PROLES ARACHNES 26. THE'.
Page 111 and 112:
210 Ill. PROLES ARACHNES ( 1) Notos
Page 113 and 114:
214 Ill. PROLES ARACHNES The sevent
Page 115 and 116:
218 Ill. PROLES ARACHNES family, Ho
Page 117 and 118:
222 Ill. PROLES ARACHNES posterior
Page 119 and 120:
226 III. PROLES ARACHNES 28. THE OR
Page 121 and 122:
230 Ill. PROLES ARACHNES From the f
Page 123 and 124:
234 Ill. PROLES ARACHNES 29. THE OR
Page 125 and 126:
238 Ill. PROLES ARACHNES The chelic
Page 127 and 128:
242 IlL PROLES ARACHNES 29. THE ORD
Page 129 and 130:
30 Economic Arachnology The Arachni
Page 131 and 132:
250 IV. DE ARACHNOLOGIA Although th
Page 133 and 134:
··~~- -..... 254 IV. DE ARACHNOLO
Page 135 and 136:
31 Historical Arachnology The histo
Page 137 and 138:
262 IV. DE ARACHNOLOGIA spiders qui
Page 139 and 140:
266 IV. DE ARACHNOLOGIA little was
Page 141 and 142:
32 Practical Arachnology The practi
Page 143 and 144:
274 IV. DE ARACHNOLOGIA hard. In th
Page 145 and 146:
278 IV. DE ARACHNOLOGIA EXCURSUS A
Page 147 and 148:
33 Chemical Arachnology In the stud
Page 149 and 150:
286 IV. DE ARACHNOLOGIA not very pl
Page 151 and 152:
290 IV. DE ARACHNOLOGIA seventeenth
Page 153 and 154:
294 IV. DE ARACHNOLOGIA A new aspec
Page 155 and 156:
298 IV. DE ARACHNOLOGIA For more th
Page 157 and 158:
36 The Spider's Web The webs that s
Page 159 and 160:
306 V. HETEROGRAPHIA a number ofver
Page 161 and 162:
310 V. HETEROGRAPHIA dramatically p
Page 163 and 164:
314 ( i) ( ii) ( iii) (iv) (v) V. H
Page 165 and 166:
318 V. HETEROGRAPHIA this may be ad
Page 167 and 168:
322 V. HETEROGRAPHlA .1\Jenge in 18
Page 169 and 170:
326 VI. EPILEGO:VIENA Vellard, J.,
Page 171 and 172:
i 330 Vl. EPILEGO~iENA Lamoral, B.
Page 173 and 174:
334 VI. EPILEGOMENA Ill. Bibliograp
Page 175 and 176:
INDEX ANIMALIUM 339 Index Animalium
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Savory - Arachnida 1977

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