14 February 2010

Punctum and Cassis

The news of a YouTube video of a live Punctum minutissimum, one of the smallest land snails in the world—but not the smallest—have been circulating lately in e-mails as well as various facebook and blog posts. Here is a shell of of Punctum minutissimum. This particular specimen was 1.3 mm in diameter.


I took this picture last November when I was visiting the Carnegie Museum of Natural History in Pittsburgh for the 3rd annual meeting of the Ohio (River) Valley Unified Malacologists. When I was getting ready to photograph this tiny shell I needed something to place it on. So I used this huge shell of the marine gastropod Cassis madagascariensis. Let my hand be the scale.


Yes, the Punctum shell was sitting at the apex of the Cassis shell.


The contrast between the sizes of these 2 distant relatives is striking, isn't it? Cassis started out from a protonch, an embryonic shell, that was perhaps only slightly larger than the adult Punctum, but grew to be about 200 times larger than the latter. There are snail species that are even larger than Cassis madagascariensis and others that are even slightly smaller than Punctum minutissimum.

Are equally drastic size differences observed between the largest and smallest members of other animal groups? I will write about that in another post.

Here is a post comparing Punctum minutissimum to Neohelix albolabris, the largest native land snail in eastern North America.


fred schueler said...

Least Shrew & Blue Whale?


Yes, they may hold the size difference record.

John said...

There is a pretty big spread between a bee hummingbird and an ostrich, though I doubt it's as big as between a least shrew and blue whale.

DPC said...

But where to put the limits on what an 'animal group' can include? Hydra viridis and Cyanea capillata are both coelenterates, if you get my drift.


Go by classes.

DPC said...

Fair enough, though relationships within members of classes from different phyla are far from equivalent to each other.

Anyway, for the sake of argument - for molluscs, cephalopods (giant squid vs. Sepiola) must show the greatest size difference.

Denise said...

We in the South have two more snails larger than the Neohelix albolabris. Don't forget Mesodon normalis of the Blue Ridge Mountains (the largest) and Neohelix major (usually larger than N. albolabris), found in North Carolina and South Carolina.

Anonymous said...

If P. minutissimum is not the smallest in the world, which species is?


Punctum smithi is smaller than minutissimum. Carychium minimum, on the other hand, is slightly longer than P. smithi is wide, but because it is also narrow, the former may be the smallest land snail in terms of its volume. However, some marine gastropods may even be smaller.