Turbellarian Parasitism of Sea Urchins


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Endoparasitic flatworms or turbellarians in sea urchins.

Scientific name or taxonomic affiliation

All described species belong to the rhabdocoel family Umagillidae.

  1. Syndesmis echinorum
  2. Syndisyrinx (=Syndesmis) antillarum.
  3. Syndisyrinx (=Syndesmis) franciscanus.
  4. Syndisyrinx (=Syndesmis) evelinae.
  5. Syndisyrinxcollongistyla.
  6. Syndisyrinx (=Syndesmis) compacta, Syndisyrinx (=Syndesmis) mammilata, Syndisyrinx (=Syndesmis) philippinensis.
  7. Several unnamed species of umagillid turbellaria.

Geographic distribution

  1. Mediterranean Sea; and a similar species observed in sea urchins from San Juan Island in Washington State, U.S.A.
  2. Dry Tortugas, Florida, U.S.A.
  3. West coast of North America with most investigations conducted on specimens from the coast of California and Washington State, U.S.A.
  4. Coast of St. Barthélemy and Bay of St. Jean, Caribbean Sea.
  5. Caribbean Sea including the coasts of St. Barthélemy and Jamaica, and probably also Puerto Rico and Haiti.
  6. Philippines.
  7. Coast of Europe.

Host species

  1. Strongylocentrotus (=Paracentrotus) lividus, Echinus acutus, Sphaerechinus granularis and a similar species from Strongylocentrotus pallidus and Strongylocentrotus droebachiensis.
  2. Diadema antillarum and Lytechinus variegatus.
  3. Strongylocentrotus franciscanus, Strongylocentrotus purpuratus, Strongylocentrotus pallidus, Strongylocentrotus droebachiensis and Lytechinus anamesus.
  4. Echinometra lucunter.
  5. Echinometra lucunter, Echinometra viridis, Lytechinus variegatus and Lytechinus williamsi, and probably also Tripneustes ventricosus.
  6. Echinometra oblonga.
  7. Echinus esculentus, Echinus acutus, Strongylocentrotus (=Paracentrotus) lividus, Sphaerechinus granularis, Strongylocentrotus droebachiensis, and Psammechinus miliaris.

Impact on the host

High prevalence and intensity (up to 186 with an average of 29 turbellaria per host) of S. franciscanus were observed in the sea urchins near San Juan Islands, Washington. Despite earlier reports of turbellaria inhabiting the coelom of sea urchins, all turbellaria are now believed to be confined to the intestinal tract of the host but are easily displaced into the coelom during dissection (S. franciscanus experimentally introduced into the perivisceral coelom of Strongylocentrotus pallidus and Strongylocentrotus droebachiensis quickly became enclosed in a dense layer of aggregated coelomocytes and were dead within seven days). Some turbellaria ingest intestinal tissue of the host and symbiotic intestinal ciliates or materials that were ingested by the host (e.g., S. franciscanus), while other species (S. echinorum) are believed to subsist entirely on host intestinal tissue. The lack of physical damage to the intestinal wall suggests that the turbellaria only consume naturally sloughed epithelial cells. However, umagillids are believed to compete with their hosts for nutrients. The life cycle of these hermaphroditic flatworms is direct. For example, egg capsules of S. franciscanus, with a conspicuous filament and containing 2-8 oocytes and yolk cells (produced at a rate of 1 per 1.5 days), exit the host with the faeces. At 8 to 10 °C embryogenesis takes about two months and fully formed embryos can survive in the egg capsule for an additional 10 to 11 months. The egg capsules apparently only hatch once they have been consumed by a sea urchin and the turbellaria matures within the intestine of a single host.

Diagnostic techniques

Wet Mounts:

  1. Living turbellaria (up to 5 mm long and 1.2 mm wide) are usually reddish brown in reflected light and pinkish in transmitted light when viewed through a compound microscope.
  2. About 50% smaller in length and width than Syndisyrinxfranciscanus as described below in item c).
  3. Living turbellaria (about 2 to 3 mm long, 1.6 to 2.5 mm wide and 0.5 mm in maximum thickness) are bright red with a dark brown or yellow median longitudinal line which marks the extent of the intestine.
  4. Living turbellaria (1.1-2.8 mm by 0.7-1.5 mm) are bright red.

Methods of control

No known methods of prevention or control.


Hertel, L.A., D.W. Duszynski and J.E. Ubelaker. 1990. Turbellarians (Umagillidae) from Caribbean urchins with a description of Syndisyrinx collongistyla n. sp. Transactions of the American Microscopical Society 10:273-281.

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. 461-474).

Kozloff, E.N. and C.A. Westervelt. 1987. Redescription of Syndesmis echinorum François, 1886 (Turbellaria: Neorhabdocoela: Umagillidae), with comments on distinctions between Syndesmis and Syndisyrinx. The Journal of Parasitology 73:184-193.

Lehman, H.E. 1946. A histological study of Syndisyrinx franciscanus gen. et sp. non., an endoparasitic rhabdocoel of the sea urchin, Strongylocentrotus franciscanus. The Biological Bulletin (Woods Hole, Mass.) 90:295-311.

Mettrick, D.F. and J.B. Jennings. 1969. Nutritional and chemical composition of the rhabdocoel turbellarian Syndesmis franciscana, with notes on the taxonomy of S. antillarum. Journal of the Fisheries Research Board of Canada 26:2669-2679.

Shinn, G.L. 1981. The diet of three species of umagillid neorhabdocoel turbellarians inhabiting the intestine of echinoids. Hydrobiologia 84:155-162.

Shinn, G.L. 1983. The life history of Syndisyrinx franciscanus, a symbiotic turbellarian from the intestine of echnoids, with observations on the mechanism of hatching. Ophelia 22:57-79.

Shinn, G.L. 1993. Formation of egg capsules by flatworms (Phylum Platyhelminthes). Transactions of the American Microscopical Society 112:18-34.

Citation Information

Bower, S.M. (1998): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Turbellarian Parasitism of Sea Urchins.

Date last revised: May 1998
Comments to Susan Bower

Date modified: