Centipedes

Chilopoda. Spanish: Ciempiés, escolopendras (General); alacranes (Puerto Rico). Portuguese: Centopéias, lacraias (Brazil). Nahuatl: Petlazolcoameh, sing, petlazolcoatl (Mexico). Scolopenders.

Centipedes (Kaestner 1968: 356—388, Lewis 1981) are slender, very elongate, and many segmented arthropods, resembling millipedes only in a very general way. They are distinguished by bodies with only one pair of legs per segment. The latter are clearly distinct, not fused into pairs. The number of segments varies from 15 to 181; no species has an even number of pairs of legs and never, therefore, has one hundred legs, as the group's common name suggests. Centipedes possess a single pair of long, very flexible antennae and mandibulate, forward-projecting mouthparts. The ante-riormost legs are modified into four-jointed, sharply pointed fangs (forcipules) connected to internal venom glands.

These ubiquitous arthropods exhibit a large size range. The majority are relatively small (BL 1-5 cm). Some very large chilopods belong to the Scolopendromor-pha (Bucherl 1974). Scolopendra gigantea (fig. 4.9c) of the West Indies is gigantic, attaining a body length of 27 centimeters (Bucherl 1971). Because of their great size, such centipedes are greatly feared. They sometimes bite humans, causing pain and often a local inflammation but usually nothing more serious, notwithstanding horror tales in the literature (Minelli 1978). Scolopenders (Scolopendra spp.) are most often the offending species. It is probably a myth that they leave a wound with each leg if they crawl on bare skin, although the legs are tipped with sharp claws that may cause a prickling sensation. There is no evidence that the legs contain venom glands, although some centipedes produce noxious chemicals from other parts of the body. The chemical composition of centipede venom is still virtually unknown. Bucherl (1946, 1971), experimenting with five of the largest and most common Brazilian species on laboratory animals, concluded that the venom from actual bites, while capable of giving intense pain, was too weak to seriously harm humans. In fact, it most probably can be handled with impunity. Some even have been gathered for use as human food. Von Humboldt and Bonpland (1852: 1:157) saw Chaymas Indian children drag 45-centimeter-long centipedes out of ground burrows and devour them directly.

Centipedes are most at home in warm, humid retreats where they hide by day under stones or logs on the ground, beneath loose bark, in rotting wood, and in caves and similar niches. The house centipede (Scutigera coleoptrata; fig. 4.9d) is com mon in dwellings. Centipedes emerge at night to prey on other small surface-dwelling invertebrates, especially earthworms and insects. Some Scolopendra take small vertebrates (mice, lizards, toads) in captivity, and this may be their chief food in nature also, which may explain the generally large size of the members of this genus. They are quick and easily subdue their prey with a venomous bite from the anterior fangs.

The taxonomy of centipedes is still unsettled. Classifications of higher groups vary greatly, and many species remain un-described. Four orders are usually recognized: the many-legged, wormlike, soil-dwelling Geophilomorpha; the short-bodied Lithobiomorpha, with 15 pairs of legs; the Scutigeromorpha, which has 15 pairs of very long, spiderlike legs; and the large, flattened Scolopendromorpha, with 21 or 23 pairs of legs. The last is the most familiar group, with many members belonging to the genus Scolopendra, The ten Neotropical species range over the northern half of South America and the Caribbean islands of Jamaica and Trinidad. Centipedes are commonly called alacranes in Puerto Rico, a name that should be reserved for Scorpionida (Santiago-Blay 1985).

References

Buchf.rl, W. 1946. A^ao do veneno dos escolo-pendromorfos do Brazil sobre alguns ani-mais de laboratorio. Inst. Butantan Mem. 19: 181-197. Bucherl, W. 1971. Venomous chilopods or centipedes. In W. Bucherl and E. E. Buckley, eds., Venomous animals and their venoms. 3: Venemous invertebrates. Academic, New York. Pp. 169-191. Bucherl, W. 1974. Die Scolopendromorpha der neotropischen region. Zool. Soc. London Symp. 32: 99-133. Kaestner, A. 1968. Invertebrate zoology. Vol.

2. Wiley lnterscience, New York. Lewis, J. G. E. 1981. The biology of centipedes.

Cambridge Univ. Press, Cambridge. Minelli, A. 1978. Secretions of centipedes. In

S. Bettini, ed., Arthropod venoms. Springer, Berlin. Pp. 73-85.

Santiago-Blay, J. 1985. Aclaraciones en torno a los significantes zoológicos de la voz "alacran" en Puerto Rico. Ciencia 12(2): 43-45.

von Humboldt, A., and A. Bonpland. 1852 [1814-1825]. Personal narrative of travels to the equinoctial regions of America, during the year 1799-1804. 3 vols. Henry Bohn, London. Translated by Thomasina Ross.

hexapods

Possession of three pairs of legs, hence the name Hexapoda, is a constant feature of the Insecta but also of three additional primitive orders, among them the Collem-bola. Because of peculiarities in the anatomy of this assemblage they are separated from the true insects as the subclass Parainsecta. Larval mites and ticks also have six legs but are members of the very distinct subphylum Chelicerata. (See Evolution and Classification, chap. 1.)

springtails

Collembola. Spanish and Portuguese: Colembolos (General).

These minute to small (BL 0.3—10 mm, average 2 mm), soft-bodied insect relatives take their common name in English from a forked appendage located on the underside of the abdomen which is used as a springlike device to propel the animal upward. This form of locomotion is used when the insect is disturbed and can send it many times the length of its body into the air or to the side. Collembola also possess a tubular structure (colJophore) on the midventral part of the first abdominal segment. This is tipped with a bilobed, eversible sac thought to have a function in osmoregulation. Six normal walking legs are present. The head bears four-jointed antennae and poorly formed eyes.

Springtails are often in parallel with insects because of their six legs and general form, but they differ in several fundamental ways, including the presence of muscles in all antennal segments (basal only in true insects), water-repellent substances in the cuticle (not found in insects), and complete cleavage in the embryo (polar in insects). The elongate chewing or sucking mouth-parts are also uniquely withdrawn into a deep pouch in the head.

Although seldom seen and rarely appreciated, these are extremely numerous inhabitants of many different ecological regimes (Christiansen 1964). They prefer damp microhabitats where they are protected from wetting by a hydrophobic cuticle (Ghiradella and Radigan 1974) and are highly characteristic soil and litter animals. The collembolan fauna and population densities of the midlatitude tropical habitats, however, are much less diverse than that of temperate regions, probably because of the comparatively poor litter layer.

They are found often among decomposing plant matter, on which they feed directly, or on associated fungi and algae. A few occur along the seashore, even within the intertidal zone, and are really marine organisms. Others live on the surface of fresh water and even on snow. A few are symbiotic in ant and termite nests. Some eke out a bare existence on Antarctic shores (Rapoport 1971). A considerable cave fauna also exists (Palacios 1983). There are also economically important forms that attack mushrooms, onions, tomatoes, sugarcane, and alfalfa.

Studies on the taxonomy and biology of the Latin American collembolan fauna are only beginning. It is estimated that the approximately 800 known species (Mari Mutt and Bellinger 1989) may represent only 25 percent of the total number actually living in the region. The Latin American fauna has representatives of all the world's twelve common families (Palacios 1990), plus a rare new family (Coenaletidae) that has re

Figure 4.10 SPRINGTAILS AND THYSANURANS. (a) Springtail (Temeritas surinamensis, Sminthuridae). (b) Springtail (Ctenocyrtinus prodigus, Entomobryidae). (c) Silverfish (Ctenolepisma longicaudata, Lepismatidae). (d) Rock hopper (Neomachillelus scandens, Meinertellidae).

cently been found on the island of Guadeloupe (Bellinger 1985). Representative species of the large Latin American fauna are Temeritas surinamensis (Sminthuridae; fig. 4.10a) and Ctenocyrtinus prodigus (Entomobryidae; fig. 4.10b).

References

Bellinger, P. F. 1985. A new family of Collem-bola (Arthropoda, Tracheata). Carib. J. Sci. 21:117-123. Christiansen, K. 1964. Bionomics of Collem-

bola. Ann. Rev. Entomol. 9: 147-178. Ghiradella, H., and W. Radigan. 1974. Col-lembolan cuticle: Wax layer and antiwetting properties. J. Ins. Physiol. 20: 310-306. Mari Mutt, J. A., and P. F. Bellinger. 1989. Catalog of Neotropical Collembola. Flora and Fauna, Gainesville. Palacios, J. G. 1983. Collemboles cavernicoles du Mexique. Pedobiologia 25: 349-355. Palacios, J. G. 1990. Diagnosis y clave para determinar las familias de los Collembola de la region Neotropical. Man. Guias Est. Mi-croartr. (UNAM, Mexico) 1: 1-15. Rapoport, E. H. 1971. The geographical distribution of Neotropical and Antarctic Collembola. Pacific Ins. Monogr. 25: 99-1 18.

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