Z250 (1999) - Lec24 Outline- Arthropoda II

Zoology 250 Lecture 24 ARTHROPODA (II):
General features (cont.); Subphyla

1) Most arthropods have paired, compound eyes composed of multiple ommatidia (units with separate cuticular lenses, light-sensitive cells & nerves); the image is a composite of many spots of light
2) Respiratory adaptations depend upon the type of environment:
- 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
3) Arthropod coelom is greatly reduced (limited mainly to the gonads); arises embryologically via schizocoely; most of the primary coelom fuses with the epineural sinus yielding an extensive hemocoel
4) Arthropods are divided into four subphyla based on tagmatization, limb morphology, and location of the mouth in the embryo & adult

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 (*= mouth lies just anterior to this segment):
Acron	none	none	none	none
Segment #1	* chelicerae	antennae	antennae	antennae
Segment #2	* pedipalps/legs	* legs	antennae	(lost)
Segment #3	legs	legs	* mandible	* 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 (*= location of mouth; A= acron; 1,2, etc.= segment number):
in embryo	A*1	1*2	1*2	1*2
in adult:	A1 or 12	1*2	2*3	1*3

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