Arguably the most sophisticated protostome feeders are those that obtain food by hunting, which requires the animal to locate, pursue, and handle prey. Most invertebrates locate prey by chemoreception; others use vision, tactile, or vibration, or some combination thereof. Predators can be classified as stalkers, lurkers, sessile opportunists, or grazers.
Planarians (Platyhelminthes) are an excellent example of animals that obtain food through hunting. The vast majority of planarians are carnivorous. They are active and efficient hunters because of their mobility and sensory systems. They feed on many different invertebrates, including rotifers, nematodes, and other planarians, and have several different methods of capture. One of the most common methods is to wrap their body around a prey item and secure it with mucus. An interesting example of this behavior can be found in terrestrial planarians. The terrestrial planarian Microplana termitophaga feeds on termites by living near termite mound ventilation shafts. The planarian stretches itself into the shaft and waves its head until a termite comes in contact, at which time the termite becomes stuck on the mucus produced by the worm. An interesting note is that it is not generally agreed upon that Platyhelminthes are protostomes.
Another interesting method that protostomes use to stalk prey can be found in members of the phylum Onychophora. These are wormlike animals that some scholars believe bridge the gap between annelids and arthropods. The velvet worm Macroperipatus torquatus forages nocturnally on crickets and other selected invertebrates and approaches its prey undetected by utilizing slow movements. When the potential prey is recognized as an item to be consumed, the worm attacks it by enmeshing the organism in a glue-like substance squirted from the oral cavity.
Perhaps the most well-known examples of hunting proto-stomes are the spiders in the phylum Arachnida. Members of the family Lycosidae, colloquially known as wolf spiders, can hunt by day, although some species hunt at night. Some wolf spiders pounce on prey from their burrow, while others actively leave the burrow on hunting trips. The jumping spiders of the family Salticidae and some lynx spiders of the family Oxyopidae also hunt for prey. Once found, the spiders can leap upon it from distances as much as 40 times their body length. Other examples of hunting behavior can be found in the metallic hunting wasp Chlorion lobatum, which specializes in capturing crickets, and in the army ant Eciton burchelli, which forms large colonies and searches for prey on the forest floor.
Protostomes must defend themselves against an impressive array of predators. To survive against an attack, various strategies have evolved. These strategies include active mimicry, flash and startle displays, and chemical/physical defense.
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