a) aquatic: book gills occur in primitive aquatic chelicerates (horseshoe crabs); gills in crustaceans are typically exopodites or epipodites, and may be thoracic (most common) or abdominal; gills depend on some method for pumping water
b) terrestrial: 1 or 2 pair of abdominal book 'lungs' occur in many terrestrial arachnids; most uniramians, some arachnids and a few crustacea have spiracle/trachea systems; 'lungs' & trachea depend upon diffusion that may be augmented by inspiration/exhalation
Trait | Chelicerata | Trilobitomorpha | Crustacea | Uniramia | # of TAGMATA | 2: cephalothorax (=prosoma), abdomen (=opisthosoma) | 3: head, thorax, abdomen (=pygidium) | 2: head, trunk (primitive)
3: head, thorax, abdomen (derived) |
2: head, trunk (Myriapoda)
3: head, thorax, abdomen (Insecta) |
ANTERIOR LIMBS
(X= mouth lies just anterior to this segment): |
Acron | none | none | none | none | Segment #1 | X chelicerae | antennae | antennae | antennae | Segment #2 | X pedipalps/legs | X legs | antennae | (lost) | Segment #3 | legs | legs | X mandible | X mandible | Segment #4 | legs | legs | maxilla | maxilla | Segment #5 | legs | legs | maxilla | labium/maxilla | Segment #6 | abdomen limbs (if present) | thorax legs | thorax legs | thorax legs | MOUTH LOCATION
(A= acron; 1,2, etc.= segment number): |
in embryo | A<>1 | 1<>2 | 1<>2 | 1<>2 | in adult: | A<>1 or 1<>2 | 1<>2 | 2<>3 | 1<>3 |
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Copyright © 1998 by A. Richard Palmer. All rights reserved.(revised April 3, 1998)