SPIDERS, the common English name of Arachnida of the order Araneae, resembling the Pedipalpi in many structural points, but differing from them as well as from all other Arachnida in retaining short abdominal appendages known from their silk-manipulating function as spinnerets or spinning mamillae, with which are associated silk glands.
Hansen (10) has recognized that the " praegenital somite " persists in a rudimentary condition, forming a " waist " to the series of somites in the Pedipalpi and Araneae.
Other side - tending downwards from the scorpion towards the Acari - are the Pedipalpi, the spiders, the book-scorpions, the harvest-men and the water-mites.
The breathing-organs of the opisthosoma, when present, represented by two pairs of stigmata, opening either upon the 1st and 2nd (Pedipalpi) or the 2nd and 3rd somites (Solifugae, Pseudo-scorpiones), or by a single pair upon the 3rd (?
A prae-genital somite is often present either in a reduced condition forming a waist (Pedipalpi, Araneae, Palpigradi) or as a full-sized tergal plate (Pseudoscorpiones); in some it is entirely atrophied (Solifugae, Holosomata, and Rhynchostomi).
It is probable that the Pedipalpi, Araneae, and Podogona have been separately evolved as distinct lines of descent from the ancient aquatic Arachnida.
- The Pedipalpi are confined to the tropics and warmer temperate regions of both hemispheres.
The Pedipalpi have no poison glands.
Appendages of 1st pair have two segments, as in Pedipalpi, but are furnished with poison gland, and are retroverts.
Opisthosoma when segmented showing the same number of somites as in the Pedipalpi; usually unsegmented, the prae-genital somite constricted to form the waist; the appendages of its 3rd and 4th somites retained as spinning mammillae.
Opisthosoma consisting of only ten somites, which have no tergal and sternal elements, the prae-genital somite contracted to form a " waist," as in the Pedipalpi; the last three narrowed to form a A B prae-1 2345 6789 io I I111I IV V VI gen Opisttaosoma Prosoma FIG.
Kraepelin, Das Thierreich (Scorpiones et Pedipalpi) (Berlin, 1899); Peters, " Eine neue Eintheilung der Skorpione," Mon.
(4) x., 1872, p. 413; Cook, " Hubbardia, a New Genus of Pedipalpi," Proc. Entom.
Orders: Pedipalpi, A raneae, Palpigradi, Solifugae, Pseudoscorpiones, Podogona, Opiliones, Rhynchostomi (Acari).
PEDIPALPI, Arachnida (q.v) related to the spiders, and serving in a measure to bridge over the structural interval between the latter and the scorpions.
It is from this structural feature that the term "pedipalpi" has been derived.
In the tailless division of the Pedipalpi, undo Mexican tailed Pedipalp (Mastigoproetus giganteus).
Apart from the Tartarides, the Pedipalpi are large or medium-sized Arachnida, nocturnal in habits and spending the day under stones, logs of wood or loosened bark.
The Pedipalpi feed upon insects, and like spiders, are oviparous.
Pedipalpi date back to the Carboniferous Period, occurring in deposits of that age both in Europe and North America.
Moreover, the two main divisions of the order, which were as sharply differentiated then as they are now, have existed practically unchanged from that remote epoch., ' ' In spite of the untold ages they have been in existence, the Pedipalpi are more restricted in range than the scorpions.
Finally the name Tarantula, in a scientific and systematic sense, was first given by Fabricius to a Ceylonese species of amblypygous Pedipalpi, still sometimes quoted as Phrynus lunatus.
Lateral eyes also are often present which are monostichous with aggregated lenses (Limulus)or with isolated lenses(Scorpio), or are diplostichous with simple lens (Pedipalpi, Araneae, &c.).