Wikipedia:Reference desk/Archives/Science/2021 April 30

= April 30 =

Selenocosmia crassipes
Am I seeing this right? Does it really have nine legs? (In the photo, it seems to have nine legs.) — Preceding unsigned comment added by 32.209.109.127 (talk • contribs)
 * Could be a random mutation, or maybe, if it's a species capable of limb regeneration, it lost one of its legs previously and the regrowth went somewhat awry. PaleCloudedWhite (talk) 00:49, 30 April 2021 (UTC)
 * The seeming extra leg at the head end is not a leg, but one of the spider's two pedipalps, which are relatively larger in this species than is the case in many others.
 * Spiders, formally the Order Araneae, are part of the Class Arachnida, in turn part of the Subphylum Chelicerata: as you will see from the diagrams in that last-linked article, different members of the subphylum have different numbers of paired appendages, which include legs, pedipalps and chelicerae, which in spiders are their fangs. These might be thought of as variations on a similar theme, much less distinct in origin than the fins, barbels and jaws of a bony fish, for example, let alone a fish descendant such as ourselves. {The poster formerly known as 87.81.230.195} 90.200.135.95 (talk) 01:09, 30 April 2021 (UTC)
 * So, my question then is does this spider have an injury meaning it lost a pedipalp, or is this a species where one pedipalp grows much larger than the other? Such asymmetry is not unknown in various animals, narwhals and fiddler crabs come to mind.  -- Jayron 32 18:05, 30 April 2021 (UTC)
 * I'm pretty sure the other pedipalp is just momentarily folded under the head and thus hidden: web-searching for pictures of the species (and for other comparable spiders) finds a good proportion showing one or both pedipalps thus hidden/positioned. Pedipalps are more flexible and mobile than the legs since they're used to feel out the immediate terrain and to convey food to the mouth: videos (several are similarly findable) will probably show them in action. {The poster formerly known as 87.81.230.195} 90.200.135.95 (talk) 22:20, 30 April 2021 (UTC)