''Cyclops bicuspidatus'' -- now considered a member of the genus ''Diacyclops''—is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

copepod Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...

found throughout the world, except

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, but relatively rare in North America; it inhabits small perennial and ephemeral ponds and wetlands. Because of earlier taxonomic changes, in North America ''D. bicuspidatus'' has been confused with the primarily planktonic ''Diacyclops thomasi'' (S.A. Forbes, 1882) and with the primarily benthic ''D. navus'' (Herrick, 1882) which were formerly considered as subspecies of ''D. bicuspidatus'' but are now considered as separate species. ''D. thomasi'' occurs from Alaska to Texas and is characteristic of the Laurentian Great Lakes of

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. In contrast to ''D. bicuspidatus'', ''D. thomasi'' is a winter or cold water species found throughout the year in the Laurentian Great Lakes with peak abundance occurring in May or June. Males grow up to long, while females are larger at . In North America, ''D. bicuspidatus'' has been reported from

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

and the

USA The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 states and a federal capital district, Washington, D.C. The 48 contiguous ...

as far south as

Louisiana Louisiana ( ; ; ) is a state in the Deep South and South Central regions of the United States. It borders Texas to the west, Arkansas to the north, and Mississippi to the east. Of the 50 U.S. states, it ranks 31st in area and 25 ...

whereas ''D. thomasi'' has been reported from

Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...

and

as far south as

Morelos Morelos, officially the Free and Sovereign State of Morelos, is a landlocked state located in south-central Mexico. It is one of the 32 states which comprise the Political divisions of Mexico, Federal Entities of Mexico. It is divided into Mun ...

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

Distribution and classification

''D. bicuspidatus'' has a

cosmopolitan distribution In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

, although several of its

subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...

are more restricted, possibly representing

cryptic species In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

. For example, most specimens from

can be ascribed to ''D. b. thomasi'' (= ''Diacyclops thomasi''), while ''D. b. limnoria'' is restricted to

Lake Constance Lake Constance (, ) refers to three bodies of water on the Rhine at the northern foot of the Alps: Upper Lake Constance (''Obersee''), Lower Lake Constance (''Untersee''), and a connecting stretch of the Rhine, called the Seerhein (). These ...

. Taxonomy within the group is uncertain, and some subspecies may even belong to different genera.

Ecology

In the Great Lakes, ''D. thomasi'' is

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

until the fourth

instar An instar (, from the Latin '' īnstar'' 'form, likeness') is a developmental stage of arthropods, such as insects, which occurs between each moult (''ecdysis'') until sexual maturity is reached. Arthropods must shed the exoskeleton in order to ...

and

omnivorous An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize ...

thereafter. Its prey includes

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

rotifer The rotifers (, from Latin 'wheel' and 'bearing'), sometimes called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic Coelom#Pseudocoelomates, pseudocoelomate animals. They were first describ ...

s, small

cladocerans The Diplostraca or Cladocera, commonly known as water fleas, is a superorder (biology), superorder of small, mostly freshwater crustaceans, most of which feed on microscopic chunks of organic matter, though some forms are predatory. Over 1000 sp ...

, young

s and

fish larvae Ichthyoplankton (from Greek: wikt:ἰχθύς, ἰχθύς, , "fish"; and πλαγκτός, , "drifter") are the Fish eggs, eggs and larvae of fish. They are mostly found in the sunlit zone of the water column, less than 200 metres deep, which ...

. In turn, ''D. thomasi'' is eaten by

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

including the alewife,

bass Bass or Basses may refer to: Fish * Bass (fish), various saltwater and freshwater species Wood * Bass or basswood, the wood of the tilia americana tree Music * Bass (sound), describing low-frequency sound or one of several instruments in th ...

, bloaters,

ciscoes The ciscoes (or ''ciscos'') are salmonid fish that differ from other members of the genus ''Coregonus'' in having upper and lower jaws of approximately equal length and high gill raker counts. These species have been the focus of much study rece ...

, carpsuckers,

perch Perch is a common name for freshwater fish from the genus ''Perca'', which belongs to the family Percidae of the large order Perciformes. The name comes from , meaning the type species of this genus, the European perch (''P. fluviatilis'') ...

sculpin A sculpin is a type of fish that belongs to the superfamily Cottoidea in the order Perciformes.Kane, E. A. and T. E. Higham. (2012)Life in the flow lane: differences in pectoral fin morphology suggest transitions in station-holding demand acros ...

, shiners, whitefish and

walleye The walleye (''Sander vitreus'', Synonym (taxonomy), synonym ''Stizostedion vitreum''), also called the walleyed pike, yellow pike, yellow pikeperch or yellow pickerel, is a freshwater perciform fish native to most of Canada and to the Northern ...

s. In

Lake Ontario Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north, west, and southwest by the Canadian province of Ontario, and on the south and east by the U.S. state of New York (state), New York. The Canada–United Sta ...

, the population of ''D. thomasi'' declined significantly after the invasive cladoceran '' Cercopagis pengoi'' was introduced.

References

{{Taxonbar, from=Q3808950 Cyclopidae Freshwater crustaceans Crustaceans described in 1857