Chelicerate Arthropods Subphylum Chelicerata

Usually 6 pairs of appendages: 1st pair (chelicerae) jawlike or fanglike; 2nd pair (pedipalps) somewhat feelerlike (sometimes clawlike, rarely leglike); remaining pairs leglike. Antennae absent. Usually 2 body regions, cephalothorax (bearing the appendages) and abdomen. Legs often with an extra segment (patella) between femur and tibia.

SEA SPIDERS Class Pycnogonida Not illus.

Identification: Long-legged, spiderlike marine animals, with a small cephalothorax (head and thorax) and a very small abdomen. Usually 5 pairs of legs.

Sea spiders have a leg spread of 1 to several cm., and generally occur beneath low tidemark. They have a sucking proboscis and feed on other small animals.

HORSESHOE CRABS Class Xiphosura

Identification: Body with a broadly oval shell and a long slender tail. Abdomen with leaflike gills on ventral side. Large animals, up to lj^ ft.

Horseshoe crabs are marine animals with a very distinctive appearance. They are fairly common along the seashore.

WATER BEARS Class Tardigrada Not illus.

Identification: Minute animals, 1 mm. or less, with 4 pairs of unsegmented legs, each leg with several claws.

TONGUEWORMS AND ARACHNIDS 53

Water bears occur in fresh- and saltwater, mud, sand, and various other damp places. They are not often encountered.

TONGUEWORMS Class Linguatulida Not illus.

Identification: Immature stages with 4-6 pairs of legs. Adults wormlike and legless, living as parasites in the mouth or respiratory track of various vertebrates.

This is an aberrant group, and may or may not be correctly placed in the Chelicerata. Tongueworms are not common, and are unlikely to be encountered by users of this book.

ARACHNIDS Class Arachnida

Identification: Adults nearly always with 4 pairs of segmented legs (rarely the pedipalps are leglike). Usually not wormlike.

This is the largest and most often encountered chelicerate class. Its members are very widely distributed. Several types within the class merit separate consideration.

Scorpions, Order Scorpionida. Relatively large arachnids (to 4 or 5 in.). Pedipalps large and clawlike. Abdomen distinctly segmented and ending in a sting usually curved upward. Scorpions occur in the South and West and are largely nocturnal. They feed chiefly on insects and spiders. The sting of a scorpion can be quite painful, and in some cases (2 species occurring in Arizona) may be fatal.

Whip-scorpions, Orders Microthelyphonida, Pedipalpida, Schizopeltida, and Amblypygi. Scorpionlike, but abdomen oval, segmented, and lacking a sting. Pedipalps not clawlike. 1st pair of legs longer than others. Some species have a long whiplike tail. Principally tropical; our species occur only in the southern states. They vary from a few mm. to 4 or 5 in. and are predaceous. A few of the larger species give off a vinegarlike odor when disturbed.

Wind-scorpions, Order Solpugida (not illus.). Spiderlike, but with body only slightly constricted behind cephalothorax, chelicerae very large, abdomen segmented. Solpugids occur in the desert areas of the Southwest; they are nocturnal, spending the day in burrows or under stones, cow chips, and other objects and foraging at night. They are fast-running animals about an inch long or less and are predaceous.

Pseudoscorpions, Order Chelonethida. Small (generally 5 mm. or less), flattened, oval-bodied arachnids with large clawlike pedipalps. Normally occur under bark or in debris. They are moderately common.

Daddy-long-legs or Harvestmen, Order Phalangida. Body oval and compact. Legs extremely long and slender. Abdomen segmented. These common and well-known animals are found in wooded areas or in fairly dense vegetation. Most feed on dead insects or on plants. The few long-legged spiders and mites that might be confused with daddy-long-legs have the abdomen unsegmented, and spiders have a strong constriction between the cephalothorax and abdomen.

Mites and Ticks, Order Acarina. Abdomen unsegmented and broadly joined to cephalothorax. Body more or less oval, usually minute (some ticks may be several mm.). This is the largest order in the class, and its members occur almost everywhere, often in considerable numbers. Many are free-living and many are parasites of other animals. The free-living mites are probably most abundant in the soil and in debris, where their populations may number several million per acre. Some parasitic forms are important pests of man and domestic animals (chiggers or harvest mites, scab and mange mites, ticks): chiggers are annoying pests of man, and a few act as disease vectors; scab and mange mites are pests of both man and animals; some of the ticks are also important disease vectors. Spider mites are serious pests of various cultivated plants, especially orchard trees and greenhouse plants. Water mites, many of which are reddish or orange, are common inhabitants of ponds. A few mites are gall makers, usually forming small pouchlike galls on leaves.

Spiders, Order Araneida. Abdomen strongly constricted at base, nearly always unsegmented, with a group of fingerlike spinnerets at posterior end. Spiders are common and well-known animals occurring in many habitats. They feed on insects and other small animals, paralyzing their prey with venom from glands opening on the chelicerae. Spiders are venomous

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