Cyclops – Habitat, Morphology, Life Cycle, Control, Importance

What is Cyclops?

Cyclops is a genus of small freshwater crustaceans which belongs to the subclass Copepoda. It is commonly referred to as water flea due to its small size and free swimming nature. It is named after the one-eyed giants of Greek mythology as a single median eye is present at the centre of the head which may be red or black in colour. The body is pear-shaped and divided into two regions, the anterior broad prosome formed by head and thorax and the posterior narrow urosome ending into two caudal appendages. The size generally ranges from 0.5 to 5 mm and five pairs of legs and two pairs of antennae is present which are not easily visible without magnification. Females are easily identified as two egg sacs are attached to the body.

These organisms are found all over the world in freshwater habitats such as ponds, lakes and slow-flowing water bodies especially near vegetation. Movement is jerky in nature and is produced by the action of legs and antennae. Cyclops are omnivorous and raptorial feeders and actively hunt their food. The diet includes algae, plant fragments, rotifers, nematodes and small aquatic animals including fish larvae. During unfavourable conditions such as winter or drought this organism may enter into diapause or may form a protective slime covering.

The life cycle begins with egg which hatches into a nauplius larva. The nauplius is unsegmented and does not resemble the adult form. It undergoes several moults to form copepodid stage and finally develops into a sexually mature adult. Ecologically Cyclops acts as an important food source for small fishes but it also acts as an intermediate host for parasites like Guinea worm and fish tapeworm which creates health problems in humans. Some species are useful as they are used in biological control of mosquito larvae.

Definition of Cyclops

Cyclops are a genus of freshwater copepods characterized by their single large eye, named after the mythical creature from Greek mythology. They are commonly referred to as water fleas and play important roles in freshwater ecosystems, serving as intermediate hosts for various parasites such as the guinea worm and Diphyllobothrium latum.

Characteristic features of Cyclops

The characteristic features of Cyclops are listed below–

• It is a microscopic freshwater crustacean measuring about 0.5 to 5 mm in length.
• The body is pear-shaped and distinctly divided into anterior prosome and posterior urosome.
• The body is usually transparent but may appear green, red, blue or orange depending on species and food.
• The head is fused with first thoracic segment forming cephalothorax and is covered by a carapace.
• The posterior end bears fork-like caudal rami provided with bristles and spines.
• Five pairs of thoracic legs are present of which first four pairs are biramous and used for swimming.
• The fifth pair of legs is reduced and vestigial in nature.
• Two pairs of antennae are present and the first pair is long uniramous and segmented.
• In male the first antennae are geniculate and modified for grasping the female during mating.
• A single median eye is present at the anterior end of head which is red or black in colour.
• Respiratory organs are absent and respiration occurs through general body surface.
• Heart and blood vessels are absent and circulation takes place by movement of body fluids.
• Excretion is carried out by maxillary glands.
• Female carries two egg sacs attached laterally to the abdomen.
• Locomotion is jerky or hopping type produced by movement of legs and antennae.

Habitat of Cyclops

The habitat of Cyclops includes the following points–

• It is commonly found in freshwater bodies such as ponds, lakes, marshes and swamps.
• It mainly inhabits stagnant or slow-moving water like ditches, pools and irrigation canals.
• It is mostly present near plant-covered banks of water bodies where vegetation is abundant.
• It can also be found in temporary or ephemeral water sources such as roadside puddles and vernal pools.
• Some species are reported from subterranean habitats like underground caves, groundwater and sinkholes.
• It may occur in specialised microhabitats such as phytotelmata where water is stored in plants like bromeliads.
• Most species prefer shallow eutrophic water but some forms inhabit cold deep lakes at depths more than 6 meters.
• Although it is mainly a freshwater organism it is occasionally found in brackish water conditions.

Morphology of Cyclops

The morphology of Cyclops shows the following features–

• The body is clearly divided into two regions, an anterior broad prosome and a posterior narrow urosome.
• A distinct articulation is present between the prosome and urosome which lies between the fifth and sixth thoracic segments.
• The size of the organism is very small and microscopic ranging between 0.5 to 5 mm in length.
• The head is fused with the first thoracic segment forming cephalosome and it is covered by a shield-like carapace.
• A single median eye is present at the anterior centre of head. This eye is naupliar in nature and appears red or black in colour.
• The first pair of antennae or antennules are long uniramous and segmented. These are used for sensing movement in water and for locomotion.
• In males the antennules are geniculate and are modified for holding the female during copulation.
• Four pairs of well-developed swimming legs are present on the thoracic segments. These legs are biramous and help in jerky swimming movement.
• The fifth pair of legs is reduced and vestigial and is useful in identification of species.
• In females the first two abdominal segments fuse to form a genital segment which bears reproductive openings.
• The posterior abdominal segments are legless and cylindrical in nature.
• The body ends into a telson bearing a pair of caudal rami provided with setae and spines which help in balance.
• Heart and respiratory organs are absent and respiration takes place through general body surface.
• Excretion is carried out by maxillary glands present in the cephalic region.
• Female carries two egg sacs attached laterally to the genital segment which is a characteristic feature of Cyclops.

Cyclops diagram

Reproduction of Cyclops

The reproduction of Cyclops takes place in the following manner–

• Sexes are separate and male and female individuals are present.
• Male actively searches the female with the help of sensory hairs present on antennae which detect chemical signals in water.
• The first pair of antennae in male is geniculate and is used for holding the female during copulation.
• During mating the male transfers spermatophores into the genital opening of female.
• The sperm is stored in a seminal receptacle present in the female body and can be used for fertilizing eggs later.
• Female does not require repeated mating as stored sperm can fertilize many batches of eggs.
• Fertilised eggs are carried in two egg sacs attached laterally to the genital segment of female.
• Each egg sac contains few to several eggs depending on the species.
• Eggs hatch within few days and give rise to free swimming nauplius larva.
• The nauplius larva is unsegmented and undergoes several moults.
• After naupliar stage it transforms into copepodid stage which resembles the adult form.
• The copepodid passes through further moults and finally develops into sexually mature adult.
• During unfavourable conditions the organism may undergo diapause and reproduction resumes when conditions become suitable.

Respiratory process of Cyclops

The respiratory process of Cyclops shows the following features–

• Specialised respiratory organs such as gills are completely absent.
• Heart and blood vessels are not present and a true circulatory system is lacking.
• Respiration takes place through general body surface and this is referred to as cutaneous respiration.
• Dissolved oxygen from surrounding water diffuses directly through the thin body wall.
• Gas exchange mainly occurs through intersegmental membranes which are permeable.
• Oxygen enters the body cavity known as hemocoel which is filled with colourless haemolymph.
• The haemolymph transports oxygen to different tissues and organs.
• Circulation of haemolymph is maintained by rhythmic pulsation of the alimentary canal.
• Movement of gut helps in distributing oxygenated fluid throughout the body.
• This type of respiration enables Cyclops to survive in water with low oxygen concentration.

Role of Cyclops as intermediate host for human parasites

Cyclops serve as intermediate hosts for human parasites in the following ways–

• Humans get infected by drinking unfiltered water containing Cyclops harbouring infective larvae.
• Larvae of Guinea worm enter the body of Cyclops and undergo development inside its digestive tract.
• When infected Cyclops is swallowed by humans the copepod is digested in stomach.
• The released larvae penetrate the intestinal wall and migrate through tissues causing dracunculiasis.
• Cyclops acts as first intermediate host of fish tapeworm Diphyllobothrium latum.
• Procercoid larvae of the tapeworm develop inside the body cavity of Cyclops.
• Infected Cyclops are eaten by small fishes and larvae encyst in fish tissues.
• Humans become infected by consuming raw or undercooked infected fishes.
• Cyclops also act as carriers of nematodes responsible for gnathostomiasis.
• In untreated water Cyclops may carry cholera bacteria on their body surface.
• Presence of Cyclops in drinking water facilitates spread of cholera to humans.

Life cycle of Cyclops

The life cycle of Cyclops is completed through the following stages–

1. Egg stage– The fertilized eggs are produced in female Cyclops and are carried in two egg sacs (ovisacs) which are attached laterally to body. Each egg sac contains few to several eggs and these eggs remains attached to female body. After few days the eggs hatch into larval form.

2. Nauplius stage – After hatching the young one is called nauplius larva. It is free swimming and very small in size. The body is unsegmented and only three pairs of appendages are present. This stage passes through several moults (usually six naupliar stages) and gradual growth takes place.

3. Copepodid stage -The last nauplius stage changes into copepodid stage by moulting. In this stage segmentation of body is clearly visible and it resembles miniature adult form. This stage also undergoes six successive copepodid stages and further development of appendages is seen.

4. Adult stage -After final moulting the copepodid transforms into adult Cyclops. The adult is sexually mature and capable of reproduction. Mating takes place and fertilization is internal. After fertilization female again forms egg sacs and life cycle is repeated.

5. Diapause (resting stage)– Under unfavorable conditions such as low temperature or drying of water body Cyclops enters a resting or dormant stage. This stage helps in survival during adverse conditions and normal life cycle continues when favourable condition returns.

Ecological importance of Cyclops

The ecological importance of Cyclops can be explained as follows–

• It acts as an important link in aquatic food chain by connecting algae and bacteria with higher organisms.
• It functions as both primary and secondary consumer by feeding on algae, microorganisms and small animals.
• It is a raptorial predator and actively preys upon rotifers, nematodes and small crustaceans.
• Larger species may attack newly hatched fish fry and influence fish population structure.
• Some species help in controlling mosquito population by feeding on early larval stages.
• It also acts as scavenger by consuming organic detritus, dead organisms and biofilm.
• It serves as an important food source for larval and juvenile fishes, amphibians and other aquatic animals.
• It provides high nutritional value as it is rich in proteins, fatty acids and vitamins.
• The chitinous exoskeleton helps in digestion of fishes by acting as ballast material.
• It acts as an intermediate host for Guinea worm causing dracunculiasis in humans.
• It also serves as first intermediate host for fish tapeworm and some nematode parasites.
• Presence of Cyclops in drinking water is associated with spread of cholera bacteria.
• It is widely used as live food in aquaculture and aquarium industries.
• In aquarium it helps in cleaning by feeding on algae and organic debris.

Economic importance of Cyclops

The economic importance of Cyclops includes both beneficial and harmful aspects which are listed below–

Beneficial importance

• It serves as an important natural food for larvae of many economically important fishes in aquaculture.
• It is rich in protein and essential fatty acids and supports better growth of fish fry.
• It is widely used in aquarium trade as live or frozen food for ornamental fishes.
• It helps in biological control of mosquitoes by feeding on mosquito larvae and reducing disease transmission.
• It is used as a test organism in ecotoxicological studies to assess pollution in aquatic ecosystems.
• It plays an important role in maintaining aquatic food chain which supports commercial fisheries.

Harmful importance

• It acts as an intermediate host for Guinea worm causing dracunculiasis in humans.
• It also transmits fish tapeworm and other parasites affecting human health.
• It helps in spreading cholera bacteria in untreated drinking water.
• Its presence in water supplies increases cost of water filtration and treatment.
• In fish hatcheries larger species may prey upon newly hatched fish fry.
• It acts as intermediate host for fish parasites which reduces health and market value of fishes.

Methods used to control Cyclops populations

The following methods are used to control Cyclops populations–

1. Physical and engineering methods

• Water is filtered through fine cloth which helps in removing Cyclops from drinking water.
• Boiling of water is effective as Cyclops are killed at about 60°C.
• Providing safe water supply through pipelines and tubewells helps in preventing infestation.
• Abolition of stepwells and stagnant water sources reduces breeding sites.

2. Chemical methods

• Chlorine is applied to water at suitable concentration to destroy Cyclops.
• Excess chlorine affecting taste and smell can be neutralized by sodium thiosulfate.
• Chlorine dioxide is used in water treatment systems to inactivate copepods.
• Copper based chemicals are effective in killing Cyclops in aquariums.
• Pesticides may be used but are generally avoided due to environmental effects.

3. Biological and ecological methods

• Introduction of small fishes like Gambusia and barbel helps in biological control.
• These fishes feed on Cyclops and reduce their population naturally.
• Modification of aquatic habitat to make conditions unfavourable helps in population control.