2. CONTENTS
1. Introduction
2. Characteristics of Crustaceans
3. Classification of Crustaceans
4. Parasitism shown by Crustaceans
5. Host of Crustacean parasites
6. Adaptation shown by Crustacean parasites
7. Effect on host
8. Examples of Crustacean parasites
9. Conclusion
3. What is Crustacea?
• It is a class under phylum Arthropod.
• The word “Crustacea” is derived from the Greek word crusta which
means a hard shell.
• Study of crustacea is called Carcinology and the scientists who works in
this field are called Carcinologist.
• There exists around 67,000 species of crustaceans.
What is a parasite?
The word “Parasite” is derived from the Greek word “parasitus”, which
means one who eats at the table of another.
Parasites are organisms that lives on or in another organism called host,
getting their nutrients from the host.
4. CHARACTERISTICS OF CRUSTACEANS
Aquatic organisms
Most are free-living and few are parasitic.
Segmented body. Body is divided into head, thorax & abdomen.
Usually head fused with thorax to form cephalothorax.
Body is protected by a hard exoskeleton.
Cephalothorax is covered by carapace.
Each somite can bear a pair of appendages.
Appendages are biramous.
Head bears a pair of compound eyes, 2 pairs of sensory antennae, one pair of
mandibles (for chewing food) & 2 pairs of maxillae (for positioning the food).
Thoracic segments bear appendages which may be specialised as periopods
(walking legs), maxillipeds (feeding legs).
6. Characteristics
Respiration either by gills or by general body surface.
Reduced coelom.
Excretory organs are either maxillary glands or antennary glands (Green
glands).
Open circulatory system.
Primitive ventral nerve cord and brain.
Most crustaceans are motile and can be herbivores, carnivores or
detrivores. Some are parasites.
Digestive system comprised of a straight tube for grinding food and a
pair of digestive glands.
Sexes are usually separate. Sexual dimorphism is common except
Barnacles are hermaphrodite.
Development is indirect. It includes several larval stages.
8. Parasitism Shown by Crustaceans
Class Crustacea includes diverse group of parasites as follows:
Ectoparasites:- Ex- Branchiura (Argulus) and some isopods.
Endoparasites:-.Ex- Some Copepods and Rhizocephala.
Obligate parasites. Ex-Rhizocephala of Cirripedia which are endoparasites on
decapods.
Facultative parasites.
Some crustacean parasites find a host during the larval stages and
metamorphose once attached to that host and stay with it rest of their lives. Ex-
Tantulo carids
Some other move from one host to another throughout their lives. Ex-
Branchiura.
In some crustaceans female are parasitic while males are freeliving. Ex-
Ergasilidae parasite on gill of fish.
9. Hosts of Crustacean Parasites
In biology, a host is an organism that harbours a parasite, typically
providing nourishment and shelter.
Parasitic Crustaceans use representative from many metazoan phyla.
Ex- Fish, Jellyfish, Ascidians, Corals etc.
Crustaceans itself also serves as host to other parasitic crustaceans. Ex-
Crab, Shrimps etc.
10. Adaptations of Crustacean Parasites
The parasites undergo certain characteristic changes in order to adapt or adjust the parasitic
mode of life. This phenomenon is called as parasitic adaptation.
The crustacean parasites show the following type of modifications to suit their parasitic mode
of life.
1. Degenerate organs
Loss of locomotory organs or appendages.
Reduction of sense organs.
Reduction of gut
2. Attachment organs
• Hooks & suckers
3. Food absorption
• Through suctorial mouth & body surface
11. Effect On Host
The Parasitic Crustacean can affect their host in following ways:-
I. Change the sex of their host.
II. Prevent their host from reproducing.
III.Due to the tight attachment of the parasite some host cannot perform the
process of molting.
IV.Cause several disease in crabs, fishes etc.
V.The growth of the host is also affected.
VI.In extreme cases the host may die.
VII.Parasitic Crustacean serve as both hosts and vectors of viruses as well as of
other microbial pathogenic agent and harm their host.
12. Examples of some crustacean parasites
(A)Sub-class Copepoda
1.Ergasilus (Gill Lice)
It is a parasite on fish.
It may be found on skin, fins.
Only female are parasitic in nature.
Single median eye on the head, terminal
part of second antennae is
modified into hooks and female bears 2 egg pouches.
Fig: Ergasilus attached on fish gill
Fig:Magnified Ergasilus
13. Joining the female there may be several dozen of tiny arrow shaped male
inside the anal bag. The male remain squished between the gall wall and their
massive mate, competing with each other to fertilize the egg of the female.
14. It is also called as “egg eating louse”. It attack the eggs of spiny lobster,
spider coral, smooth fan lobster (Ibacus novemdentatus) etc.
The C.inflatus perfectly mimics the shape and size of the real eggs.
A circular sucker allows it to grip tightly to the host’s egg and its
puncturing mouthparts allow it to feed on their contents.
Fig: C.inflatus attached to the eggs of smooth fan lobster
15. 4.Lernaea spp (Anchor worm)
Lernaea is parasitic among freshwater fish especially in the gill region. Its
parasitic form is long cylindrical with 2 pairs of hook like appendages at one
end.
The larvae are free-swimming and resemble other free-living copepods.
Sexual dimorphism is well marked. Female is vermiform.
Fig: Leanae female hanging from their host’s gill
16. Fig: Lernaea female and its developmental stages
The male and female mate during the last free-swimming (copepodid) stage of
development.
After mating the male dies and the female burrows into the flesh of a fish and transforms
into an unsegmented wormlike form usually with a portion hanging from the fish’s body.
17. 5. Ommatokoita elongata
Fig: Ommatokoita elongata attached to the eye of a Shark
This species embeds itself only in the eyeballs of the huge Greenland shark, feeding on its
vitreous jelly.
These parasites are so called as ‘Eyeball sucking sea louse.’
Over 85% of these sharks are blinded in one or both eyes by these creatures, but can
fortunately survive by utilizing the rest of their senses.
18. 6.Liriopsis pygmaea (Crab cancer’s cancer)
Fig: Liriopsis pygmaea attached to an another parasite
These are highly degenerate isopods that attach to the externa of a
Rhizocephalan, in turn the Rhizocephalan is attached to its host, Crab.
And just as the crab is castrated by its parasite, the parasite is rendered sterile
by these hyper parasites.
19. (B)Sub-class Branchiura
Argulus (Fish lice)
It is a very common fish parasite.
The body is oval with rounded carapace. Eyes are compound. A set of antenna is modified
into huge barbed suckers.
The mouthparts are adapted for sucking and piercing. Sucking mouthparts with a piercing
stylet and 2 suction cups.
The abdomen end in a bifurcated tail.
Fig:Argulus
20. Fig: Argulus attached to the head and caudal fin of a fish
Some Argulus feed on the host’s mucus coating leaving the underlying scales vulnerable to
bacterial or fungal infections.
Some other use the scraping mouthparts to dig through the flesh of the host and inject a
digestive enzyme breaking down tissue into drinkable sludge.
These vampires cling tightly to the scales of its host with the help of its sucker.
21. (C)Subclass Cirripedia
1. Trypetesa
It selects the gastropod as its host.
It makes a burrow into molluscan shells.
Fig:Trypetesa inside a gastropod shell
Fig:Trypetesa
22. 2. Ascothoracida
Fig: Ascothoracida attached to the body of an echinoderm
These are found growing in or on the bodies of Echinoderms and jellyfishes.
Their bodies are reduced to almost clam-like limbless blobs.
23. 3. Sacculina
It is commonly called as root-headed barnacle or crab cancer.
Shows extreme case of degeneration or specialisation due to parasitism.
Fig: Sacculina attached to the abdomen of a crab
It parasitizes crabs. Adult loses all arthropodan characters and appear like a fleshy tumour
attached to the abdomen of crab on ventral side.
Appendages, segmentation, mouth, anus, alimentation etc. are absent.
24. Fig: Development of Sacculina
It sends root like processes like mycelium of fungus in each appendages of crab and in the
body of crab to derive nutrition.
The lifecycle of Saculina include the naupilus larva which passes through cyprid stage and
then kentrogon stage. In kentrogon form, Saculina injects its soft body into the crab after
its shell fall off
25. It prevent the crab from molting, growing, regenerating and reproducing.
The affected crab directs all of its energy to nourish the Sacculina and caring for
the parasite’s offspring.
Sacculina brings about changes in the secondary sexual character of the host.
Sacculina
26. (D) Sub-class Malacostraca
1. Gnathia
These are similar in behaviour to ticks.
It is an ectoparasite on fishes.
Mouth parts are adapted for piercing and sucking.
After gorging on blood for several days,
the fish chigger molts into a non-parasitic stage until ready to feed again,
alternating in this manner several times in its life.
Female Gnathia are difficult to identify but males are identified easily. The male
looks like an unrelated terrestrial stag beetle, with a few or more limbs.
The male possesses massive horns which are used to grasp females during
copulation.
Fig:Gnathia male & female
27. 2. Cymothoa exigua (The tongue biter)
Fig: C.exigua attaching the fish body Fig: C.exigua attaching the tongue of its host
It is one of the most infamous parasite in the sea. The complete life story of a
tongue-biter has yet to be unravelled.
28. C.exigua initially enter their hosts through the gills, beginning as males but change sex as they
grow older. At her first opportunity, the newly female exigua climbs into the host’s mouth &
attaches itself to the tongue of the host, draining blood through her front claws until the
tongue gradually atrophies and disappears.
Hooking her spiny tail into the remaining stump, the vampiric isopod can now be manipulated
by her host as a fully functional new tongue.
C.exigua is considered as the first confirmed
example of a parasite effectively replacing a
host body part.
Fig: C.exigua replacing the host’s tongue
29. Conclusion
The biology of Crustacean is as diverse as their morphological and
phylogenetic diversity.
They illustrate several unusual phenomenon like egg mimicry, host
feminization, epigametic sex determination, venomous secretion, bizarre
adaptations etc.
Several studies and researches are going on to understand these creatures and
many interesting facts have been known about these organisms. Further
investigation is required to know further about these parasites.
30. References:-
1. R.L.Kotpal ,Invertebrate Zoology
2. E.L.Jordan & Dr. P.S.Verma ,Invertebrate Zoology ,14th edition
3. Carl Zimmer, Parasite Rex, 3rd edition
4. Jonathan Wojcik, Summery of parasitic crustaceans (2011)
