Parasitic Crustacea


There are about 1000 species of crustaceans belonging to 6 subclasses that are parasitic on arthropods and vertebrates. They are described below according to their subclasses.


Copepods include large number of parasites that are categorized into 4 orders as described below.

Order Monstrilloida

This order includes parasites like Monstrilla, Salmincola, Nicothoe, Thaumatopsyllus

Monstrilla adult female is bag-like without appendages and remains attached to the polychaete worm with the help of mandibular hooks. There is a pair of eyes and a pair of egg sacs on the body. The female detaches from the host and swims freely releasing eggs in water. Larva has well developed appendages to swim and find a host, into which it penetrates and becomes endoparasite. The larva feeds and grows inside the host and emerges as adult outside the host body.

Salmincola is parasitic on the gills of European salmon and attaches to the host with a bulla which is modified second maxilla.

Nicothoe is a parasite of gills of lobsters. Antennae and mouthparts are modified for sucking blood. Thorax is produced into huge lobes. Egg sacs are attached to abdomen.

Order Cyclopoida

Examples: Ergasilus, Bomolochus

Ergasilus is parasitic on the fills of freshwater fish. It has a large cephalothorax and segmented abdomen with reduced pleopods. Antennule is 5-segmented and antenna is hooked and there is no eye. Maxillipedes are prehensile. Only female is parasitic.

Bomolochus is an ectoparasite of fish. Antennules are small and segmented and antenna is hooked. First thoracic appendages are modified for clinging. There are no abdominal appendages.

Order Notodelphyoida

Examples: Doropygus, Notodelphys

Doropygus is a parasite of tunicates or marine invertebrates. Sometimes it is commensal or temporary parasite.

Order Lerneopoida

Examples are: Lernaea, Clavellisa, Chondrocanthus, Anthosoma

In Lernaea only female is parasitic on the skin and blood vessels of fishes. Maxillae are modified for piercing and sucking. Legs are vestigial. Female is free swimming in the beginning but becomes parasitic later. Cephalothorax is small and abdomen is large and unsegmented, carrying a pair of egg sacs.

Anthosoma is parasitic in the mouth of sharks. It has bag-like body with overlapping lobes. Antenna is chelate and antennule is sensory. Pleopods are reduced and there is a pair of egg sacs attached on the apex of abdomen.

Chondrocanthus is parasitic on the gills and mouth of marine fishes. Body is unsegmented and lobed. Antennae are hook like for attachment. Male is small and remains attached to female.

Order Caligoida

This order includes examples such as, Caligus, Trichiurus, Scianea, Lernaenicus, Stromateas, Lernanthropus, Peniculus

Caligus is ectoparasite on the gill chambers of fish. Antennules are provided with bristles and antenna is hook like for attachment. Oral appendages form piercing and sucking mouthparts. Fifth thoracic appendage is long for swimming. Eyes present.


Examples are Argulus and Dolops

There are 75 species of Argulus that is ectoparasite on the gills of fish. It is a free swimming animal as it has well developed 4 pairs of biramous thoracic legs. Cephalothorax is large and oval. The second maxillipedes is modified for sucking and the first and second maxilla for clinging on to the host. There is a pair of eyes and a sharp spine for puncturing the host skin.


Examples: Basipodella, Microdajus

The parasite is only 0.2 mm long and ectoparasite on deep water crustaceans. Larva is free swimming but loses appendages during metamorphosis. There is a sharp spine on the anterior end for piercing and a mouth tube for sucking. Body is divided into cephalon and trunk, both without any appendages.


There are about 90 species of parasites that infect lungs of invertebrates. Ex. Linguatula, Cephalobena.

They are parasitic in the lungs of reptiles and some mammals in USA, Europe and Australia. They are 2-13 cm long and worm-like, without distinct segmentation. There are 5 appendages on the anterior end; the central one of them carries mouth. There are two pairs of hooks on the ventral side for attachment to the host. Body is covered by cuticle. Intermediate host is a fish.


Order Isopoda

Examples: Epicaridian, Cryptoniscus, Bopyrus, Renocila, Danalia, Portunion, Athelges, Gnathia, Cymothoa

Bopyrus is a parasite of the gill chambers of prawns and shrimps. The larvae are free swimming called Epicaridian and Cryptoniscus which also parasitize copepods, ostracods or Cirripedia. Adult female is oval with a large cephalothorax, which on the ventral side is divided into lobe-like oostegites. Maxillipedes are piercing type and mouth sucking type. Thoracic appendages are 8 pairs and adapted for clinging. Abdomen is small, segmented and without appendages and carries a dwarf male attached to it.

Order Amphipoda

Examples: Cyamus, Trischinostoma

Cyamus is ectoparasitic on whale skin and they are called whale lice. Body is dorso-ventrally flattened and divided into 6 cephalothoracic segments. Abdomen is vestigial. Five pairs of thoracic limbs are supplied with hooks for attachment on the skin of the host. Cephalothorax also carries two pairs of sticky byssus threads for attachment. Antennule is small while antenna is elongated, both being sensory in function.


Order Rhizocephala

Examples: Sacculina, Peltgaster, Peltogasterella, Lerneodiscus

Sacculina is parasitic on crabs. Adult is highly degenerated and is made of root-like processes that invade all parts of body. This is called sacculinainterna, which absorbs nutrition from all over the body. Sacculinaexterna is a bag-like form that appears on the ventral side of abdomen when sexual maturity is reached. It has a genital opening through which nauplius larvae escape into the water. Nauplius spends 3-4 months in water and grows and then molts to become cypris whose body is enclosed into a bivalve shell. Its 3-segmented antennule is hook-like for attachment to the host crab. Cypris attaches to the host crab and transforms into a bag-like kentrogen that discards the shell and appendages. From kentrogen the germ cells migrate through a dart into the haemocoel of the crab. These germ cells get attached to the mid gut and then proliferate to become sacculina interna.

Peltogaster is endoparasite on hermit crab. Its body is bag-like and visceral mass is located inside the mantle cavity. There is not distinct segmentation and appendages are absent in adult. Larva is free swimming with well developed appendages.

Order Apoda

Example: Proteolepas was discovered by Charles Darwin and it is parasitic in the mantle cavity of other barnacles. Body is 11-segmented of which 8 segments are thoracic and 3 abdominal, without appendages. Antenna is modified for clinging on to the host. There is sharp proboscis for piercing and sucking.

Order Acrothoracica

Examples: Alcippe, Trypetasa

They are called boring barnacles as they bore into the shell of snails. In Alcippe the thoracic appendages are less than 6 pairs. Antennae are in the middle of body. Mouth parts are piercing and sucking type of proboscis. Male is small and clings to the female body. Body is enclosed into a bivalve shell which is held in place by an adductor muscle.

Order Ascothoracica

Examples: Ascothorax, Dendrogaster, Laura, Syngogae

Ascothorax is ectoparasitic on sea lilies and serpent stars and also endoparasitic on the corals and sea stars. Body is enclosed in a bivalve carapace. There are 6 pairs of thoracic appendages for swimming. Maxillae are modified for piercing and sucking. First antenna is hook-like for attachment to the host and there is no second antenna. Abdomen is limbless with a caudal fork.