The presentation describes a very interesting relationship between Green crab and barnacle parasite Sacculina carcini.

1. Sacculina carcini- Green
crab
An Interesting host-
parasite relationship
behind
B. Naveen Rajeshwar
AAH-Pb0-06
AAH 602- Advances in parasitology
Submitted to Dr. Rajendran K. V., Ph.D

2. Rhizocephala
• The Rhizocephala are a bizarre, highly modified group of barnacles
that parasitize mostly decapod crustaceans
• Most rhizocephalans parasitize brachyuran and anomuran crabs. A few are parasites
on caridean shrimp, stomatopods, peracarids and even other barnacles.
• The well-studied Sacculina carcini infects more than 10 crab species from several
genera
• Rhizocephalans- found in deep sea to the pelagic & in high intertidal habitats &
extend into brackish waters

3. Sacculina carcini
 Sacculina carcini, the crab hacker barnacle, is a species of
parasitic barnacle in the family Sacculinidae.
 A parasitic castrator of crabs.
 The parasite most often use green crab (Carcinus maenas) as
host.
 Other host range- Carcinus aesturarii, Liocarcinus depurator
(Harbour crab), Pirimela denticulata, Necora puber (Velvet crab),
and the Liocarcinus holsatus (Flying crab)
 It can be found attached to the crab's abdomen and affect
consumption rates by humans
Scientific classification
Kingdom Animalia
Phylum Arthropoda
Subphylum Crustacea
Class Maxillopoda
Order Kentrogonida
Family Sacculinidae
Genus Sacculina
Species S. carcini

4. Anatomy
The body of the adult parasite can be divided into two parts:
1. The "externa" where the bulbous reproductive organ of the parasite sticks out of
the abdomen of the host.
2. The "interna" which is inside the host's body.
Interna composed of root-like tendrils that wrap themselves around the host's
organs especially around the hepatopancreas of crustaceans.
It gives its group name of Rhizocephala, meaning "root-head".
This area is primarily for absorbing nutrients, which would explain why most
concentrate in that region.

5. Distribution and habitat
 Habitat Regions- saltwater or marine
 Aquatic Biomes- pelagic, Benthic, coastal
 Depth- 0-200m
 During their larval stage (Cypris) they are pelagic, but as they form into adults they live
as ectoparasites on crabs.
 The parasite's range largely coincides with that of this host, which is usually the coasts of
Western Europe and North Africa.
 The green crab, however, has been expanding its range and has become established in
both North and South America, Southern Africa and Australia, that made the parasite to
present outside its natural territory.
 These crabs all live in shallow water over sandy, rocky, or muddy substrates

6. Female cyprid finds and
crawls on suitable carb’s
surface.
Settle base of a seta
Develops into
a kentrogon, which inserts
a stylet into the crab
Vermigon moves inside,
develop tendrils, take over
nervous system, intestine,
stomach of host- Interna
Push out a sac- Externa
Holds eggs inside, fertilised
by male parasite which
enter via a pore
Female with the externa,
can live as long as the
crab host survives &
male as long as female
Hundreds of eggs produced
every day & remain in sac
for six weeks & released as
nauplius (N1-N5) cyprid
When the parasite eggs are ready for release, the crab will climb onto a rock, bob about to
release them and waft them on their way- Manipulation?
Life cycle

8. Larval development and dispersal
Despite the parasitic life style, larval development of Rhizocephala is virtually
identical to that of other Cirripedia.
There are several naupliar instars and a terminal cyprid, the settlement stage
unique to all species.
Larval development is entirely lecithotrophic and normally of short duration,
lasting two to three days in warm waters, about two weeks at 10°C, but up to 30 days
in the arctic.
As a probable adaptation to enhance survival or dispersal, several rhizocephalans
release their larvae as cyprids, including most deep sea species, all freshwater and
semi-terrestrial species.

9. Female parasite strategies
• Female cyprids probably rely on odour trails/chemosensory ability in the water
column to locate the host.
• At settlement, the cyprids recognise the host by means of carbohydrate or
glycoprotein cues in the epicuticle.
• The host’s behavioural defences can be circumvented by three means:
efficient host finding
avoidance of detachment before penetration
avoidance of the host’s immune response coupled with a rapid takeover of
host control.
• Rhizocephalans settle at specific sites on the host, but always in areas with a thin or
soft cuticle to facilitate penetration.

10. • Female cyprids settle in the narrow confines between the gill filaments in the branchial
chamber to avoid being groomed away by the crab.
• Crab uses 5th pair of thoracopods to groom away most of the settled cyprids before
formation of the infective kentrogon.
• As a parasite countermeasure, form protected kentrogon rapidly (<1 hour after
settlement), thus minimising the period when the larvae are critically exposed as cyprids.
• Then the parasite immediately begins to take over control of the host by damaging the
nervous system.

11. Male parasite strategies
 Female cyprid have a hostile environment after settlement. But male cyprid must locate and
inseminate the virgin externa of the female via implantation.
 Male also faces several hurdles mainly due to competition with other males.
 Furthermore, no more than two males can normally be implanted in any parasite, and once a
single male is acquired, the female externa immediately begins to mature sexually.
 Many male cyprids can land on a female yet only the fastest and strongest ones will successfully
inseminate the female.
 When a virgin is found, the male cyprid can penetrate the narrow entrance to the brood chamber,
which contains the paired receptacles that will eventually host the one or two successful males.
 Male settled closest to orifice inject a trichogon stage into brood chamber which reach an empty
receptacle.

12.  Then the trichogon sheds its spiny cuticle, thereby blocking access to any subsequently arriving
competitors.
 Male cyprids have more chemosensory organs than females (highly efficient- locating the externa
 entering a receptacle within few minutes)
 Once established, the male undergoes spermatogenesis and is nourished by the female parasite for
the duration of its lifetime.
 The presence of two receptacles (i.e. two possible males) may therefore benefit the female either by
increasing genetic variability or by insuring continued reproduction when one male accidentally
perish.

13. Reproductive strategies
o Typically, a female S. carcini has two males which live off of it and constantly fertilizes it.
o The female then produces hundreds of eggs a day.
o Eggs are incubated in the abdomen of the host & develop into free-living larvae.
o While a female S. carcini provides no parental care, the hosts provide an efficient means
of distribution for larvae.
o The behaviour of both male and female infected crabs is modified so that they treat the
externa from S. carcini like their own eggs.
o Infected crabs climb to high places with fast currents and disperse larval parasites like they
would their own eggs.
o At this point, the free-swimming S. carcini larvae are entirely independent.

14. Effects on hosts
• Rhizocephalans change the morphology, physiology and behaviour of their hosts so that
hosts become nothing but automatons serving only the purpose of the parasite.
• Almost all Rhizocephala sterilise their host through hormonal or biochemical alteration of
the gonads.
• It destructs the androgenic gland causing feminisation of castrated males.
• Castrated hosts remain altered for life, becoming sterile competitors in the host
population.
• Male crabs will even attempt to mate with sterile, infected females and feminised males!
• Parasitic castration also channels metabolic energy used in host reproduction to the benefit
of parasite.
• The sterile, infected host reacts to its parasite by cleaning and caring of eggs.

15. • This effect also extends to male hosts which are feminised behaviourally as above, but
also morphologically, often acquiring secondary sexual characters of females such as a
broader abdomen used for ‘brood protection’ in female crabs and the development of
female pleopods.
• This elaborate ‘brood mimicry’ is possible because the externa of the parasite generally
protrudes from within the brood chamber of the host.
• Some host species will even assist the parasite by exposing the abdomen when the virgin
parasite must acquire males.
• Additionally, the parasite can arrest the moult cycle of the host (i.e. cause anecdysis)
• The effect on the moult cycle results in large numbers of stunted crabs.
• If the parasite is experimentally removed from the host, female crabs will usually
regenerate their ovaries, but in males, sex change takes place and they develop ovarian
tissue.

16. Host strategies
• Ecologically, the effect of castration is the loss of the reproductive fitness of an infected host.
• A successful infection immediately begins to take over control of the hormones and
behaviour of the host.
• Host defences may operate at three levels:
1. Behaviourally, by evasion of the female cyprids
2. Physically and behaviourally, by preventing the larvae from attaching and
penetrating through the carapace
3. Immunologically, by fighting the internal parasite before it becomes established

17. • Female cyprids rely on odour trails to locate the recently moulted odoriferous crabs (exude a
different odour than intermoult crabs)
• There is no evidence for behavioural evasion by crabs, but host grooming is important in
preventing infections.
• Susceptible individuals are those that for several reasons (damage, disease or moulting) are
deficient in their grooming effectiveness.
• Immunologically, the host defences must attack and kill the parasite before it takes over
hormonal control.
• In abnormal hosts there is evidence of cellular reactions to the parasite.
• Melanised internae can be observed in few hosts that survives the loss leading death of the
parasitic externa (hence, death of the parasite).
• Susceptible hosts often show little indication of a defensive response, so the parasite somehow
avoids recognition by the host’s defences.

18. Human impacts
 Sacculina carcini found attached to the crab's abdomen.
 Hence causes economic damage to humans by decreasing the viability of crabs
harvested for human consumption.
 Crabs infected with S. carcini cease moulting, and so do not grow to a suitable size
for eating.
 Carcinus maenas in particular is considered to be of gastronomic importance, and is
frequently eaten in many European countries.
 The Sacculina carcini make many of the host infertile.
 Without reproduction, the population cannot expand and can cause a shortage for
human consumption.

19. Biocontrol agent??
 S. carcini has been considered as a means of controlling invasive crab species, but due to host
specificity it also seems to damage non-invasive crab populations.
 Green crab- Invasive- Threatens native spp.- Alter the spp. & diversity balance in ecosystem
 Goddard et al. (2005) conducted an experiment with 4 species of non-target, native California crabs
(Hemigrapsus oregonensis, H. nudus, Pachygrapsus crassipes and Cancer magister) and invasive
green crab.
 Settlement by S. carcini on the four native species ranged from 33 to 53%, compared to 79% for
green crabs.
 Most native and green crabs settled on by S. carcini became infected.
 Infected green crabs died at more than twice the rate of uninfected green crabs.
 In contrast to green crabs, all infected native crabs died without producing an externa.
 These results indicated that use of S. carcini as a biological control agent could result in the death of
native crabs.
Potential benefits of biological control should be assessed in relation to these
potential non-target effects also.

20. References
• Audet, D., Miron, G. & Moriyasu, M. 2008. Biological characteristics of a newly established green crab (Carcinus maenas)
population in the southern Gulf of St. Lawrence, Canada. Journal of Shellfish Research, 27: 427–441.
• Boschma, H. 1933. New species of Sacculinidae in the collection of the United States National Museum. Tijdschrift der
Nederlandsche Dierkundige Vereeniging, 3: 219–241.
• Boyko, Christopher B. (2015). "Sacculina carcini Thompson, 1836“. WoRMS. World Register of Marine Species.
Retrieved 13 January 2018.
• Hosie, A.M. (2008). "Crab hacker barnacle (Sacculina carcini)". MarLIN. Archived from the original on 15 January 2018.
Retrieved 14 January 2018.
• Jeng, Winnie (2011). "Sacculina carcini". Animal Diversity Web. Archived from the original on 10 May 2017. Retrieved 14
January 2018.
• Melissa (7 October 2013). "The Parasitic Sacculina That Bends Its Host to Its Own Will". Today I found out. Archived from
the original on 14 September 2017. Retrieved 13 January 2018.
• Leung, Tommy (13 May 2014). "The crab-castrating parasite that zombifies its prey". The Conversation. Archived from the
original on 14 January 2018. Retrieved 13 January 2018.
• Cheng, Thomas C. (2012). General Parasitology. Elsevier Science. pp. 756–757. ISBN 978-0-323-14010-2. Archived from
the original on 2018-02-08.
• Kristensen, Tommy; Nielsen, Anders Isberg; Jørgensen, Anders Isak; Mouritsen, Kim N.; Glenner, Henrik; Christensen,
Jens T.; Lützen, Jørgen; Høeg, Jens T. (2012-09-01). "The selective advantage of host feminization: a case study of the
green crab Carcinus maenas and the parasitic barnacle Sacculina carcini“ (PDF). Marine Biology. 159 (9): 2015–2023.

21. Queries..?
Thank you..!