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Re: Two Headed Spider

I find the posting of Ken's note here about an spider in Baltic amber quite
interesting for a reason other than the specific nature of the post. There
are quite a few people who frequent this list, and collect meteorites who
also collect or study inclusions in amber (myself included). In fact,
several meteorite dealers post amber information or amber specimens for
sale in their pages. Therefore, I feel little guilt addressing
amber-related issues in this forum. However, if amber is too great a
stretch for this List, I will refrain from deliberately diverting from this
group's posted theme.

Now, regarding the two-headed spider; I did look closely at the photograph
posted on Ken's page. First of all, my feeling is that since spiders don't
even have one head, the prospect of two is highly unlikely.

Insects do have a separate body segment called a head. A spider, on the
other hand, has only two body segments, an abdomen and a cephalothorax (a
combination of a thorax and a head). Four pairs of legs are attached to
spider's cephalothorax. Inside the cephalothorax are found the stomach, the
poison glands, and the brain. The top of cephalothorax is covered with a
hard plate called a carapace. The top of the carapace is where the eyes
(usually eight) are found. The mouthparts are located at the anterior end
of the cephalothorax.

In Ken's photograph of the spider in Baltic amber, I believe what appears
to be a pair of "heads" are actually pronounced pedipalps on a mature male
spider. Pedipalps look much like a ninth pair of legs, but they are
shorter, and used for reproduction rather than mobility. Especially in
males, the tip of the pedipalp is enlarged giving them a bulbous head-like
appearance . The attachment point for each palp is on the cephalothorax,
between the front-most leg attachment point, and the mouthparts.

Since Ken's photograph clearly shows one body segment as the attachment
point for the legs, I have to conclude that only one head-region is
present. The "pair of heads" are actually the ends of the folded or
enlarged palps. Since the palps have openings which are used during
reproduction, it is possible air was released as the spider was dying in
its amber tomb. This bubble at the end of the palp not only magnifies the
size of the already enlarged palp, but also provides an expected head-shape
if one is looking for a head on a spider.

Either way, Ken has an excellent intact spider specimen in amber.

Any other thoughts out there about this from fellow amber enthusiasts?


Martin Horejsi