MadSci Network: Zoology

Re: Are the cockroach and the shrimp related.

Date: Thu Jan 13 09:31:12 2005
Posted By: Tom Clarke, Post-doc/Fellow, Molecular Biology, Sars International Centre for Marine Molecular Biology
Area of science: Zoology
ID: 1101886017.Zo

Hi Steve,

	Cockroaches and shrimp are distantly related to each other, but it 
is doubtful that is the reason for the common names ‘land shrimp’ and ‘sea 
roach’.  Cockroaches and shrimp are both members of the phylum Arthropoda 
and share some common characteristics, including segmented bodies and 
legs, and a hard outer skeleton.  However cockroaches and shrimp belong to 
two different lineages: the Hexapoda (which includes the insects) and the 
Crustacea (shimp and crabs, but also barnacles and water fleas) 
respectively.  While it is not known for certain when the Hexapoda 
diverged from the Crustacea, the emergence of land dwelling hexapods is 
thought to have occurred during the Silurian period (between 416 and 444 
million years ago).

	It is often hard to tell how common names originated, but they 
usually refer to physical and behavioral resemblances rather than to 
whether or not organisms are evolutionarily related.  The animals usually 
known as ‘sea roaches’ are the isopods in the genus Ligia.  These 
crustaceans have a flattened body with long antenna that looks vaguely 
roach-like and share with roaches the habit of congregating in large 
numbers (usually under beach debris) and fleeing quickly when their 
shelter is exposed.  It is probably from these traits that the common 
name ‘sea roach’ is derived.  I’m less familiar with the term ‘land 
shrimp’ referring to cockroaches… in the part of the world I come 
from, ‘land shrimp’ refers to terrestrial amphipods… small laterally 
flattened crustaceans that, while not true shrimp, are somewhat related to 
isopods.  In this case, physical resemblance between amphipods and true 
shrimp explain the common name. The one time I have heard the name ‘land 
shrimp’ referring to a cockroach is to the use of some large tropical 
cockroaches in food, where they are cooked in much the same way (and used 
in many of the same dishes) as shrimp.  I personally cannot attest to 
whether these roaches actually do taste like shrimp, but if you are 
curious there are several cook books available.

	Hope that helps, 

		Dr. T. Clarke

References and other readings:

1. Tree of Life webpage on arthropod relationships:
-	a good general description of how different arthropod groups are 
related to each other.

2. Regier, J.C. and Shultz, J.W. 1997  Molecular phylogeny of the major 
arthropod groups indicates polyphyly of crustaceans and a new hypothesis 
for the origin of hexapods. Molecular Biology and Evolution 14: 902 – 913

-	Very technical, but presents evidence from comparison of genes 
that show the relationship between the Hexapoda and the Crustacea relative 
to other arthropods.

3. Engel, M.S. and Grimaldi, D.A. 2004. New light shed on the oldest 
insect. Nature 427: 627 – 630
	- Description of the oldest insect, discussing their possible 
origins in the Silurian period.

4. A short descriptive web page on the Ligia exotica, the sea roach:

5.  Entertaining with Insects  by Taylor, R.L. and Carter, J.B. 1976. 
(although I believe it has been recently reprinted)
	- There are several other books available on cooking insects, but 
this is the only work from which I have personally tried a few recipes, 
and it’s the book that ‘started it all’ as far as bug cuisine.

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