MALACOLOGIA, 1976, 15(2): 299-367
THE SYSTEMATICS AND DISTRIBUTION OF LOLIGO
(CEPHALOPODA, MYOPSIDA) IN THE WESTERN
NORTH ATLANTIC, WITH DESCRIPTIONS
OF TWO NEWSPECIES1
Anne C. Cohen
Department of Invertebrate Zoology, National Museum of Natural History,
Smithsonian Institution, Washington, D.C. 20560, U.S.A.
The common squid Loligo pealei Lesueur, 1821, lives on the continental shelf and slope of
the North and South American continents from Nova Scotia to the Gulf of Venezuela.
Statistical analyses show that 1) females have a wider gladius and fewer gill filaments than
males; there also is slight but statistically significant sexual dimorphism in 3 other characters; 2)
populations vary but there are no dines in 50 anatomical measurements. However, southern L.
pealei (Caribbean Sea-Gulf of Mexico) differ in the following ways from northern L. pealei
(eastern United States Atlantic coast); 1) gill length increases faster in relation to mantle length
in the southern squid; 2) there is more variation in the hectocotylus and number of buccal
lappets in the southern squid.
Variation in Loligo pealei appears greater in areas of sympatry with L. plei (= Doryteuthis
plei); much of this variation takes the form of greater resemblance to L. plei. These 2 species
overlap in almost all characters. The ratio of the greatest width of the gladius vane to the
greatest width of the free rachis can be used to distinguish the 2 species. The geographiclrange
of each species is redefined.
Two new species of Loligo are described: Loligo ocula, a large-eyed species caught at
256-362 m in the Caribbean Sea and between Cuba and the Bahamas, and Loligo roperi, a small
species from the Caribbean.
The 4 species are compared. In many characters they show the following relationships:
Loligo ocula is most similar to L. pealei; L. pealei is also similar to L. plei; L. plei is most similar
to L. pealei , but is also similar to L. roperi; L. roperi is the most distinctive of the 4 species.
Loligo roperi matures at a small size and then apparently ceases growing or does not survive
spawning; it may be a somewhat neotenic relative of L. plei. The larger eyes in L. ocula (and
correspondingly larger head and mantle width) may be an adaptation to living at depths greater
than are typical for the Loliginidae.
In the western North Atlantic, the greatest species diversity for both Loligo and the
Loliginidae occurs in the Caribbean Sea. A key to these 4 species of Loligo of the western
North Atlantic Ocean is given.
Interest in Loligo pealei Lesueur, 1821, as
a fisheries resource for bait and food, and as
a source of large axons for neurological
research, has stimulated many studies
chiefly of populations that occur between
Cape Hatteras and Nova Scotia.
The purpose of this study is to clarify the
systematic status of a taxonomically con-
fused group of commercially important
cephalopods. Considerable variation has
been noted in Loligo pealei; some specimens
of L. pealei are so similar to some specimens
of L. plei Blainville, 1823, that misidenti-
fications often occur in spite of existing keys
(Voss, 1956:91). Verrill (1880, 1881),
Arnold (1962), LaRoe (1967), and Voss
(personal communication) have suggested
that variation in L. pealei is geographic. This
study examines variation in L. pealei and
describes and compares the 3 other species
of Loligo which are partially sympatric with
Loligo pealei is the most widely distri-
buted of the neritic squid in the western
Atlantic (LaRoe, 1967), where it has been
reported to extend from Nova Scotia
(Mercer, 1970a) to Colombia (LaRoe,
1967). This is a latitudinal distance of more
than 35 degrees and includes the Caribbean
Sea, the Gulf of Mexico, and the Atlantic
coast of North America (Fig. 1 ).
Vart of this investigation was done in partial fulfillment of the requirements for the degree of Master of
Science, University of Maryland.