KEY TO THE SHALLOW WATER SPECIES OF Octopus OF THE

DWhatley

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From the 1966 referenced PDF found here: OCTOPUS MAY A, A NEW SPECIES FROM THE BAY OF CAMPECHE, MEXICO
The addition of yet a third species, O. maya, indicates the need for a revised key to the shallow water octo pods of the western Atlantic Ocean. The following key is mainly original but is based upon Pickford's earlier key (Pickford, 1945). Like all keys, it should be used with discretion.

KEY TO THE SHALLOW WATER SPECIES OF Octopus OF THE TROPICAL WESTERN ATLANTIC
1. An ocellus or dark spot or ring on each side of the head between
the eye and the second and third arms __ 2
1. No ocellus or dark spot or ring present ._____ 3

2. Ocellus with a narrow blue ring within the spot; animals small;
gills 6-7; ligula index 4-5; eggs small Octopus hummelincki (Adam)
2. Ocellus without a blue ring; animals large; gills 9-10; ligula index 1.4-1.9; eggs large, to 17 mm ____O. maya, new species

3. Mantle, head, and arms covered with close-set papillae; dark
purplish or brownish band on dorsal side of arms; size small;
gills 8-11; ligula index 4.1-5.5; eggs small _____O. burryi (Voss)
3. Mantle, head, and arms not covered with close-set papillae; no
dark band on dorsal border of arms_____4

4. First arms always largest and usually longest, stoutest or coequally stoutest with second arm; animals medium to large; gills 9-13; ligula index up to 14; eggs small ____O. macropus Risso
4. Second and/or third arms longest, usually conspicuously so____5

5. Second and third arms much larger and stouter than first and fourth arms; animals medium to large; gills 6-8; ligula index 3-4; eggs large, to 10-14 mm ____O. briareus (Robson)
5. Second and third arms not markedly larger and stouter than other arms____6

6. Arms very long and slender, asymmetrical in length; mantle small; animals small to medium; gills 11; ligula index 1.8-2.5; eggs not known ____O. defilippi (Verany)
6. Arms not conspicuously long and slender; arms symmetrical or nearly so in length 7

7. Arms stout, moderately short; animals medium to large; gills 7-11; ligula index under 2.5; eggs small, 3 mm or less O. vulgaris (Cuvier)
7. Arms short; animals small; gills 5-7; ligula index 4-7; eggs moderately
large, 5-10 mm -- 0. joubini (Robson)
 

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