Is it a mite?

t

Common names

spiders

Probability of encounter

high

Quarantine importance

High for some taxa because of medical importance or potential general predator problems. Many large species are used in the pet trade and some may have small, endangered populations.

Similarity to mites

Spider-like build and lack of segmentationsegmentation:
in mites distinct external segments have been lost but remnants of segmentation may be represented by hysterosomal folds or transverse arrays of setae and other cuticular sense organs.  In theory, all chelicerates have a prosoma composed of 6 segments (cheliceral, pedipalpal, and four leg-bearing segments = body segments I-VI).  Ventrally the positions of the prosomal segments can be identified by the insertions of their appendages, but dorsally they are obscured.  The opisthosoma is thought to comprise an additional 12-13 segments (body segments VII-XVIII or XIX), but appears to be somewhat to much reduced in most mites, except possibly Opilioacarida.  In early derivative Acariformes (e.g., many Endeostigmata), hysterosomal folds are thought to represent segmentation and in the Grandjean system are designated (from the sejugal furrow to the anus): C, D, E, F, H, PS AD, AN, PA.  There is disagreement in the literature over the origin of 'segments' C and D.  Adherents of Grandjean consider them to be opisthosomatic (with C probably representing a fusion of the pregenital [body segment VII] and genital [VIII] segments).  Others believe that C and D are the dorsal regions of the last two prosomal segments that bear leggs III and IV (i.e., body segments V & VI).
resemble mites, but mites do not have spider waists.

Morphology

Normal adult length: >5 mm
Bodybody:
the idiosoma of mites.
tagmata: prosomaprosoma:
(= cephalothorax) the anterior body region in arachnids; usually not distinct in mites.
(cephalothoraxprosoma:
(= cephalothorax) the anterior body region in arachnids; usually not distinct in mites.
), opisthosomaopisthosoma:
(= abdomen) the posterior body division in arachnids; usually not distinct in mites because of the fusion of the opisthosoma with part of the prosoma to form the idiosoma.
(abdomen)
Eyes: 4 + 4 ocelliocellus:
(pl. ocelli) a simple eye.  Mites with eyes usually have one or two pairs of lateral ocelli, but some Opilioacarida have three pairs.  Additionally, some acariform mites have one or two median ocelli on the underside of the naso.
maximum
Antennae: absent
Mouthparts: fang-like chelicerae; feeler-like 5-segmented palps with distaldistal:
towards the free end of an appendage.
claws (not present on palps of adult males); terminal segment of palps in males is swollen
Legs: 4 pairs (NB—some have long, leg-like spinnerets)
Distinguishing features: fangs, spinnerets, pedicel

Comments: Spiders all have two clearly defined bodybody:
the idiosoma of mites.
regions separated by a narrow waist (pedicel), fang-like mouthparts and abdominal spinnerets that produce silken threads. Male spiders have swollen palps.

Diversity

>38,000 spp.

References

• Platnick 2003Platnick 2003:
  Platnick NI. 2003 Jan. The World Spider Catalog. Version 3.5. American Museum of Natural History, New York.
• Tree of Life Web Project 2006Tree of Life Web Project 2006:
  Tree of Life Web Project. 2006. Araneae. Spiders. Version 07 December 2006 (temporary). The Tree of Life Web Project, http://tolweb.org/