Nematode Parasitism of Sea Urchins


Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Endoparasitic nematode infection.

Scientific name or taxonomic affiliation

  1. Echinomermella matsi (enoplid Mermithoidea, atypical to most mermithoid nematodes in that the parasitic stage is the adult, not juvenile, and females are ovoviviparous with retention of eggs and larvae in the pseudocoelom; vulva and vagina have not been observed).
  2. Echinomermella grayi (an enoplid Mermithoidea similar to E. matsi).
  3. Echinocephalus pseudouncinatus (superfamily Spiruroidea, family Gnathostomidae, with only larval stages occuring in sea urchins).
  4. Unidentified nematode.

Geographic distribution

  1. Northern Norway.
  2. Around the British Isles.
  3. Southern California and the west central coast of Baja California, Mexico. One specimen reported from the echnoid Arbacia punctulata near woods Hole, Massachusetts, USA.
  4. Near Acapulco, Mexico.

Host species

  1. Strongylocentrotus droebachiensis.
  2. Echinus esculentus.
  3. Arbacia punctulata, Centrostephanus coronatus, and one specimen from Strongylocentrotus purpuratus. Also reported from abalone. These invertebrates serve as intermediate hosts for this nematode which are adults in elasmobranch fish.
  4. Astropyga pulvinata.

Impact on the host

  1. Infected sea urchins have a lower than normal gonad index (gonad size reduced up to 75% in infected sea urchins with a test greater than 35 mm in diameter). In addition, 73.6% of the infected sea urchins were of unknown sex with no evidence of gonad development. Apparently a large propostion of the echnoids were being castrated a juveniles (Hagen 1996). Mathematical analysis supported the hypothesis of increased parasite-related mortality making this parasite one of the few known causes of a macroparasite epizootic among shellfish. Host mortality is presumably induced by the synchronized release of numerous nematode larvae in the perivisceral coelom of the sea urchin from large ovoviviparous females (about 700,000 larvae per female). The life cycle of the nematode external to the sea urchin is unknown but large numbers of worms in individual hosts suggests that the infective stages are locally abundant. The reproductive capacity of the S. droebachiensis population at Godfystraumen, Norway, was reduced by 50% between July 1983 and February 1991 when prevalences of E. matsi in S. droebachiensis increased from 5.5% to 65.4%. The initial hypothesis that this macroparasite may function as a terminator of sea urchin outbreaks (increases in sea urchin populations such that destructive grazing occurs in kelp forests converting the habitat to urchin-dominated barren grounds) was rejected because kelp forest recovery was interrupted at Værøy Island in northern Norway by unexpected recurrence of distructive sea urchin grazing despite prevalences of E. matsi in the sea urchin population comparable to those that corresponded to kelp forest recovery (Hagen 1995a,b).
  2. Relatively rare and appears to be of minor importance in echinoids.
  3. Growing juvenile nematodes progressively invade the gonadal tubules resulting in suppression of gametogenesis, especially towards the oral or distal end of infected tubules. Pearse and Timm (1971) suggested that encysted juveniles block the passage through the tubule of some hormonal substance that regulates echinoid gametogenesis. Prevalences of infected sea urchins were between 40% and 80% in some locations.
  4. Effect unknown.

Diagnostic techniques

Gross Observations:

  1. In heavily infected sea urchins of unknown sex, the gonad is miscoloured and atrophied and the gut appears thin, fragile, and compressed. Adult (males 10 to 40 mm long, unfertilized females 30 to 50 cm long and gravid females about 60 cm long) and juvenile nematodes occur exclusively within the perivisceral coelom coiled around the lantern and often between the gut or gonad and the body wall of the host.
  2. Less than 12 large nematodes (up to 37 cm in length and 2 mm in width, but most (62%) are less than 150 mm in length) lie coiled freely in the perivisceral cavity of its host. In healthy E. esculentus, the nematode colour is glistening white but takes on a green colour (probably derived from the host) in urchins which show pathological changes and tissue necrosis (from causes other than the nematode).
  3. Coiled juvenile nematodes encysted in dense connective tissue produced by host. Occasionally, atrophy occurs in the gonad distal (towards the oral end) to the site of infection when nematodes are encysted within a main tubule (probably the gonoduct).
  4. Nematodes observed in gonad of host.


  1. None reported.
  2. None reported.
  3. The encysted nematode is surrounded by extensive nutritive phagocytic tissue within a fibrous cyst wall. Adjacent uninfected tubules may appear normal.
  4. None reported.

Methods of control

No known methods of prevention or control.


Comely, C.A. and A.D. Ansell. 1988. Invertebrate associates of the sea urchin, Echinus esculentus L., from the Scottish west coast. Ophelia 28: 111-137.

Hagen, N.T. 1987. Sea urchin outbreaks nematode epizootics in Vestfjorden, northern Norway. Sarsia 72: 213-229.

Hagen, N.T. 1992. Macroparasitic epizootic disease: a potential mechanism for the termination of sea urchin outbreaks in northern Norway? Marine Biology 114: 469-478.

Hagen, N.T. 1994. Is the righting response a useful indicator of functional well-being in the green sea urchin, Strongylocentrotus droebachiensis? In: David, B., A. Guille, J.-P. Féral and M. Roux (eds), Echinoderms through Time. Balkema, Rotterdam, pp. 693-698.

Hagen, N.T. 1995a. Sea urchin outbreaks and epizootic disease as regulating mechanisms in coastal ecosystems. In: Elefheriou, A., A.D. Ansell and C.J. Smith (eds), Biology and Ecology of Shallow Coastal Waters. Olsen & Olsen, Fredensborg, pp. 303-308.

Hagen, N.T. 1995b. Recurrent destructive grazing of successionally immature kelp forests by green sea urchins in Vestfjorden, northern Norway. Marine Ecology Progress Series 123: 95-106.

Hagen, N.T. 1996. Parasitic castration of the green echinoid Strongylocentrotus droebachiensis by the nematode endoparasite Echinomermella matsi: reduced reproductive potential and reproductive death. Diseases of Aquatic Organisms 24: 215-226.

Hopkins, S.H. 1935. A larval Echinocephalus in a sea urchin. The Journal of Parasitology 21: 314-315.

Jangoux, M. 1990. Diseases of Echinodermata. In: Kinne, O. (eds), Diseases of Marine Animals. Volume III: Introduction, Cephalopoda, Annelida, Crustacea, Chaetognatha, Echinodermata, Urochordata. Biologische Anstalt Helgoland, Hamburg, Germany, pp. 439-567 (specifically see pgs. 475-482).

Jones, G.M. and N.T. Hagen. 1987. Echinomermella matsi sp.n., an endoparasitic nematode from the sea urchin Strongylocentrotus droebachiensis in northern Norway. Sarsia 72: 203-212.

Millemann, R.E. 1963. Studies on the taxonomy and life history of Echinocephalid worms (Nematoda: Spiruroidea) with a complete description of Echinocephalus pseudouncinatus Millemann, 1951. The Journal of Parasitology 49: 754-764.

Pearse, J.S. and R.W. Timm. 1971. Juvenile nematodes (Echinocephalus pseudouncinatus) in the gonad of sea urchins (Centrostephanus coronatus) and their effect on host gametogenesis. The Biological Bulletin (Woods Hole, Mass.) 104: 95-103.

Citation Information

Bower, S.M. (1997): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Nematode Parasitism of Sea Urchins.

Date last revised: December 1997
Comments to Susan Bower

Date modified: