Ilyanassa obsoleta 
System : Marine
Kingdom
Phylum
Class
Order
Family
Animalia
Mollusca
Gastropoda
Neogastropoda
Nassariidae
- General
- Distribution
- Impact
- Management
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Common name
Synonym
Nassarius obsoletus , (Say, 1822)
Nassa obsoleta , (Say,1822)
Nassa obsoleta , (Say,1822)
Similar species
Summary
The eastern mudsnail, Ilyanassa obsoleta (= Nassarius obsoletus), was originally only present on the Atlantic Coast of North America. It is now extremely abundant in North American Pacific Coast locations. In the San Francisco Bay it is reported to have overtaken the native California horn snail (Cerithidea californica), and reduced its population by means of competition and larval predation, leaving only small populations in secluded marsh pans, which are too salty for it to establish.
Species Description
The eastern mudsnail (Ilyanassa obsoleta) is a benthic prosobranch gastropod with a black or dark brown conical shell about 1.5-3cm in length containing 5-6 whorls (Cohen, 2005).
Lifecycle Stages
Eastern mudsnail (Ilyanassa obsoleta) egg capsules hatch into larvae after about ten days. The larvae are free swimming but rely primarily on currents for transport. Larvae feed on phytoplankton 20-30 days before settling and metamorphosing (Cohen, 2005), although this may be delayed until they find desirable substata (Scheltema, 1961). They remain dormant during the winter and almost all of their growth takes place during the summer months. N. obsoletus has a life span of approximately 5 years (Scheltema, 1964).
Uses
The eastern mudsnail (Ilyanassa obsoleta) is popularly kept to clean aquariums.
Habitat Description
Eastern mudsnails (Ilyanassa obsoleta) may be found in the benthic zone of intertidal flats and estuaries. They prefer brackish waters and cling to nutritious substrata (Cohen, 2005). N. obsoletus are temperature sensitive and have been known to develop thinner than normal shells and are known to breed up to three months early if water temperatures are disturbed (Barnett, 1972)
Reproduction
The eastern mudsnail (Ilyanassa obsoleta) reproduces sexually and breeds on incoming tides during the fall and spring seasons. Mudsnails use chemo-reception to aggregate and copulate around oysters and sometimes mussels, on which they deposit capsules containing several eggs. Their deposition on living substrates is believed to decrease the likelihood of the embryo being smothered by sediment, however, they also deposit capsules among eelgrass (Rittschoff, 2002).
Nutrition
The eastern mudsnail (Ilyanassa obsoleta) is a facultative scavenger and deposit feeder which consumes diatoms, minute worms, algae, fish and crustacean remains, and other organic matter, including faeces (Frankenberg 1967) found on underwater surfaces. The mudsnail ingests sediment wholly and its digestive tract breaks down organic matter leaving almost completely inorganic waste (Scheltema 1964).
Pathway
Eastern mudsnails are believed to be transported to the Pacific along with Atlantic oysters on which it lays its eggs (Cohen, 2005).
Principal source: Carlton, J.T.1992. Introduced Marine and Estuarine Mollusks of North America: An end-of-the-20th Century Perspective. Journal of Shellfish Research, Vol. 11 No.2, 489-505.
\r\nCohen, A. N. 2005 Guide to the Exotic Species of San Francisco Bay. San Francisco Estuary Institute, Oakland, CA. www.exoticsguide.org.
\r\nScheltema, R.S. 1964. Feeding habits and growth in the mud-snail Nassarius obsoletus. Chesapeake Science. Vol.5, No. 4, 161-166.
Compiler: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Review: Dr. James (Jeb) Byers, Assistant Professor, Dept. of Zoology, Department of Zoology University of New Hampshire. USA
Publication date: 2008-03-27
Recommended citation: Global Invasive Species Database (2024) Species profile: Ilyanassa obsoleta. Downloaded from http://www.iucngisd.org/gisd/species.php?sc=1321 on 19-04-2024.
General Impacts
The eastern mudsnails (Ilyanassa obsoleta) introduction to the Pacific Coast of North America has caused a change in the native fauna. In the San Francisco Bay the once dominant California horn snail (Cerithidea californica) has been reduced to small populations where habitats overlap. Where the salinity is higher the populations of the California horn snail is able to survive (Race, 1982).
The invasive N. obsoletus preys on the eggs and larvae of the endemic C. californica and as a result, C. californica is restricted to small habitats unsuitable to N. obsoletus. Seasonal migration of these two species has demonstrated that their competition is a recurring problem and not an isolated incident. The invading eastern mudsnail has been found in other Pacific locations but its ecological effects have yet to be evaluated. It is believed to be transported along with Atlantic oysters, the eastern mudsnail poses a threat to new habitats and should be monitored (Race, 1982).
I. obsoleta is also host to several trematode species including one that causes swimmers itch.
