Figure 203

Scorpion morphology, adult, ventral view, with legs be yond coxae and most of metasoma (postabdomen) not shown. (From

Keegan, 1980, with permission of University Press of Mississippi.)

1200 sensory pegs per pectinal tooth have been reported in Leiurus qmnquestriatus.

The metasoma, or "tail," is divided into five segments, plus the telson (Fig. 20.5). The segments are well scle-rotized and may bear longitudinal ridges, or keels, along their dorsal, lateral, and ventral surfaces (Fig. 20.5). The nature and location of these keels can serve as

FIGURE 20.4 Sternum, genital opercula, and pectines of Ct-n-truroidts vinatus (Buthidae), located on venter of scorpion at level of third and fourth pairs oflegs. (From Keegan, 1980, with permission of University Press of Mississippi. )

important taxonomic characters. The telson consists of a bulbous base, called the vesicle or ampulla, and a curved, sharply pointed terminal spine, the aculeus. Just below the aculeus the telson also may bear a small, median subaculear tubercle or accessory spine (fig. 20.5D). The vesicle contains a pair of venom glands and associated musculature. The venom glands may be simple and saclike or more complexly folded, with pouchlike extensions that greatly increase the surface area of the secretory epithelium. The venom is discharged by contraction of die muscles surrounding the glands which compress the glands against the vesicle wall. The venom is forced out through the pair of venom ducts that open near the tip of the aculeus.

The prosomal appendages of scorpions are a pair of chelicerae (Fig. 20.6B), a pair of pi nee r-like pedipalps (Fig. 20.6A), and four pairs of walking legs. Each che-licera consists of three segments. The terminal, third segment serves as a movable finger which opposes the second segment, or hand (manus)y bearing an anterior apophysis called the fixed finger. Both fingers are armed with teeth which facilitate the grasping and tearing of food. The pedipalps are six-segmented, each consisting of a coxa, trochanter, femur, patella (genu), tibia, and tarsus. The distal-most segment (tarsus) forms a movable finger which opposes the fixed finger of the tibia, or hand. The various numbers and arrangements of keels, tubercles, denticles, granules, and trichobothria (sensory hairs) on the

FIGURE 20.6 Centruroides vittatus (Buthidae). (A) Chelate (pincer-lifce) tibia and tarsus of pedipalp, used for seizing prey; (B) Chelicera, showing the movable tarsus and fixed finger of the tibia for crushing and tearing prey. (Adapted from Keegan, 1980, with permission of University Press of Mississippi.)

FIGURE 20.6 Centruroides vittatus (Buthidae). (A) Chelate (pincer-lifce) tibia and tarsus of pedipalp, used for seizing prey; (B) Chelicera, showing the movable tarsus and fixed finger of the tibia for crushing and tearing prey. (Adapted from Keegan, 1980, with permission of University Press of Mississippi.)

hand, patella, and femur of the pedipalp are important taxonomically. The walking legs consist of the same six segments as the pedipalps, plus a seventh terminal segment, the pretarsus, which bears a pair of lateral claws and a single, small median claw. The tarsus is divided into two tarsomeres. The presence of tibial spurs and pedal spurs on the tarsomeres can be helpful in identifying certain groups of scorpions.

Although scorpions are sexually dimorphic, it generally takes a specialist to reliably distinguish males and females. There are no uniform gender-specific, external morphological characteristics for determining the sex that apply to all scorpions. Instead, determinations are based on comparative morphological differences that often require familiarity with gender-related traits within conspecifics. In general, however, compared to females of the same species, males are smaller and less robust. Males tend to be relatively more slender than females, but there are many exceptions. In some genera, the pedipalp chelae of males are longer and more slender, whereas in other genera they are shorter and thicker. The males of some species have special depressions for accepting the female's pedipalp fingers during mating. Usually, the metasoma of males is relatively longer and more slender than that of females; however, it is sometimes shorter and thicker, being different with each species. The pectines are often strikingly different, with the males having larger pectines with more pectinal teeth. In some cases the males can be recognized by the presence of a pair of genital papillae protruding posteriorly from beneath the genital operculum.

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