Sea urchins are echinoderms, Class Echinodea, relatives of seastars 
and the like. The skeleton is calcium carbonate (I'm 99% sure 
carbonate, not apatite). There is no chitin, but there likely is 
protein around the units of CaCO3 ("units" because I'm not sure if 
the building blocks are single crystals). Rather like mortar around 
bricks.
Maybe. I'd guess that's the microstructure, but to be honest I forget 
-- I used to know, but that neuron may have died.
Further, if these are critters from the intertidal or hard 
substrates, they are very likely to have iron crystals, perhaps iron 
oxide or magnetite, in the tips of the teeth. This is most common on 
the sea urchin taxa that gnaw algae, coral, and other encrusting 
critters off of rocks, coral, etc.
I haven't tried to section anything like echinoderm "bone", but the 
last time I was after similar microstructure (clam shells), I broke 
the shells and looked at the edges with a SEM. Depending on the 
actual information sought, this may be a better approach than 
sectioning and LM or TEM.

Phil

>Dear Bob,
>Not being up on the classification of sea urchin (crustacean?), I was
>wondering if they would have some chitin along with minerals to deal with???
>Rose
>----- Original Message -----
>From: 
>To: 
>Sent: Thursday, December 20, 2001 10:04 AM
>Subject: Undecalcified tooth sections
>
>
>>  Fellow histonetters,
>>
>>  I have just been presented a project to section undecalcified sea urchin
>teeth.
>>   Of which, I do not have any experience, but this is the best way to gain
>>  experience.  I have checked the histonet archives and found a debate
>between a
>>  cryoJane Tape transfer system or a durable cryostat fitted with a tungsten
>>  carbide knife.  Could anyone give further information to specific
>literature or
>>  books that could help me get this set up.
>>
>>  Bob Meyer, HTL
>>  Northwestern University
>>
>>
>>

-- 
Philip Oshel
Supervisor, AMFSC and BBPIC microscopy facilities
Department of Animal Sciences
University of Wisconsin
1675 Observatory Drive
Madison,  WI  53706 - 1284
voice: (608) 263-4162
fax: (608) 262-5157 (dept. fax)