Description

Daddy-long-legs present all the typical characteristics of arachnids, with the body divided into two regions, cephalothorax and abdomen, although these two regions are not clearly differentiated, giving daddy-long-legs the aspect of "waistless spiders." The cephalothorax generally has a pair of median eyes on top of an ocular tubercle. The eyes are simple, i.e., not compound as in insects and crustaceans. The cyphophthalmids lack eyes entirely or have a pair of lateral eyes. The cephalothorax also bears a pair of chemical-secreting organs, known as repugnatorial glands.

The cephalothorax has one pair of chelicerae for manipulating the food particles, one pair of palps of either tactile or prehensile function, and four pairs of walking legs, enormously long in some Eupnoi and Laniatores species, surpassing 15 cm in some species. The palps of most Laniatores are relatively large and have two rows of spines acting as a grasping organ. The second pair of walking legs is sometimes modified and acquires a tactile function.

Another distinctive characteristic of the Opiliones is that the females have a long ovipositor with sensory organs on the tip that are used to check the soil quality where they will lay the eggs. Except for some mites, similar organs are not known for any other arachnids. The males have a penis or copulatory organ, which may be muscular or alternatively operated by hydraulic pressure. Copulatory organs are also unique among the arachnids, again with the exception of certain mites. Fertilization is thus internal and direct (unlike in spiders, which use the palps for the indirect internal fertilization).

Figure 1 is an example of a typical daddy-long-leg, Odiellus troguloides, from the western Mediterranean.

FIGURE 1 O. troguloides, one of the most typical daddy-long-legs from the western Mediterranean region, with an elongated body reaching almost 1 cm in length. This species has considerable sexual dimorphism, females being much larger and more globose than males. Juveniles of this species hatch in the spring, quickly reach maturity, and die in the fall.

FIGURE 1 O. troguloides, one of the most typical daddy-long-legs from the western Mediterranean region, with an elongated body reaching almost 1 cm in length. This species has considerable sexual dimorphism, females being much larger and more globose than males. Juveniles of this species hatch in the spring, quickly reach maturity, and die in the fall.

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