Poor Man’s Oyster (mussel; snail; clam)

There have been many seafood claims on the term “poor man’s oyster,” with mussels, snails and clams all claiming the title. (“Poor man’s oyster” is also the name of a plant.) Mussels have been called “poor man’s oysters” since at least 1868 and they’re still called that today.
 
Snails have been called “poor man’s oysters” since 1886, but the nickname is seldom used for snails today. Peter Freuchen, author of Book of the Seven Seas (1957), called clams “the poor man’s oyster,” but almost no other author has given clams this title.
 
 
(Oxford English Dictionary)
poor man, n.
(...)
1891 Tit-Bits 8 Aug. 277/2 There are thousands of costers who earn a livelihood by the sale of..mussels, which are regarded as the poor man’s oyster.
   
Google Books
The Ocean World
By Louis Figuier
New York, NY: D. Appleton & Co.
1868
Pg. 363:
The mussels, like the oysters, are gregarious, and widely diffused over all European seas. They abound on both sides the Channel, their lower price having procured for them the name of “the poor man’s oyster;” but it is infinitely less digestible and savoury than its congener.
 
Google Books
20 April 1876, The Leisure Hour, pg. 288, col. 2: brushwood on the fore-shore, somewhat resembling sheep-hurdles, roughly interlaced together with boughs, to serve as homes or clinging-posts for teh Mussels.
Here, although Grimod de la Reyniere named the mussel l’huitre du paum, this poor man’s oysterhas held its unchallenged rank as only second to oysters in the menus of the bourgeoisie and the cartes of restaurants, figuring in soups and entrees, stews and sauce, scallop and mince.
   
Google Books
The History of the Year 1876
By James Mason
London: Ward, Lock, and Tyler
1877
Pg. 30:
The mussel as an article of food ia well worthy of cultivation, and the title of “poor man’s oyster” is not at all a bad one, as mussels are largely consumed by those to whom the oyster is an unattainable luxury.
 
Google Books
Old Folks at Home
By Clara L. Matéaux
London: Cassell Petter & Galpin
1878
Pg. 177:
The “poor man’s Oyster,” as some have called the humble Mussel, is well looked after in France, where there are bouchois or Mussel farms—that is, long lines of posts and brushwood on the fore-shore, somewhat resembling sheep-burdles, roughly interlaced together with boughs, to serve as homes or clinging-posts to the Mussels.
   
Google Books
Sea Pictures
Drawn with Pen and Pencil
By James Macaulay
The Religious Tract Society
London; Printed by William Cloews and Sons, Limited
1882
Pg. 158:
The common mussel is an article of enormous consumption, and has been well called “the poor man’s oyster.”
 
29 July 1886, Iowa State Reporter (Waterloo, Iowa), pg. 2, col. 4:
THE snail harvest has just begun in France. The “poor man’s oyster” is so appreciated that Paris alone consumes about forty-nine tons daily, the best kind coming from Grenoble or Burgundy.
   
Google Books
June 1887, The Laws of Life: A Family Health Journal, pg. 164:
The snail in France is called the “poor man’s oyster,” and so fond is he of them that forty- nine tons are said to be daily eaten in Paris.
 
Google Books
The Murrey Collection of Cookery Books
By Thomas J. Murrey
New York, NY: Frederick A. Stokes Company
1895
Pg. 44: 
MUSSELS.
The Mussel is called the poor man’s oyster; but why the poor should have a monopoly of this very useful shellfish, the writer is at a loss to comprehend.
   
Google Books
Book of the Seven Seas
By Peter Freuchen
Published by Messner
1957
Pg. 367:
Clams, which have been called the poor man’s oysters, live in sandy or muddy bottoms and make their way through the sediment in search of food.
   
Google Books
Essential Seafood Cookbook
By Murdoch Books Pty Limited
Published by Murdoch Books
2004
Pg. 244:
BLACK MUSSELS
Sometimes referred to as ‘poor man’s oyster’ or “blue mussel”, the mussel is full of flavour.
 
Google Books
Frankie’s Place:
A Love Story
By Jim Sterba
New York, NY: Grove Press
2004
Pg. 14:
Julia Child called them (mussels—ed.) “poor man’s oysters.”
   
Google Books
Pike Place Public Market Seafood Cookbook
By Braiden Rex-Johnson
Edition: 2, illustrated
Published by Ten Speed Press
2005
Pg. 74:
Nicknamed “poor man’s oysters,” mussels taste like a cross between an oyster and a clam.
     
Google Books
The Gourmet Cookbook:
More Than 1000 Recipes
By Ruth Reichl
Boston, MA: Houghton Mifflin Harcourt
2006
Pg. 119:
Mussels were once dismissed as “poor man’s oysters,” but they can hold their own with oysters any day—and they are sweeter and tenderer than clams.