THE EASTERN MUD WHELK

 

 

Defining Physical characteristics:

Visceral mass: Consists of all internal organs, twisted 180 and protected by a coiled,univalved shell.

Shell: Ovate, thick, with spire about half shell length; brown, usually eroded.

Foot: muscular organ sitting ventrally below the visceral mass and used for locomotion.the foot. When the foot is withdrawn into the shell, the operculum seals the shell aperture, protecting the snail from both dehydration and predators

Head: contains a pair of retractable tentacles, a proboscis with a mouth at the tip from which the radula protrude when feeding.

Radula¨: a feeding structure which consists of a firm ribbon consisting of “teeth” made of chitin which act as a rasp, scraping food particles such dead animal matter and algae from the substrate.

Siphon: a cylindrical extension of the mantle tissue through which water is drawn into the mantle cavity and across the gill sheets by the movement of gill cilia. The snail moves the muscular siphon back and forth, thus sampling the water from different directions, picking up chemical clues to its surrounding and delivering them to the osphradium. When the whelk is burrowing it will extend its siphon through the substrate to the water above. As a
carnivore and detritivore, Ilynasa uses its siphon can hunt their prey by chemical sensing.Osphradium: a chemical and tactile receptor organ within the mantle cavity to which thesiphon directs water.

Ctenidium (ten-i-de-yum): the prosobranch gill lying within the mantle cavity next to the
osphradium.

Reproduction: Hermaphroditic, each whelk possessing male and female gonads. Two whelks pass sperm to each other, internal fertilization takes place.

Larvae: The young emerge as free-swimming larvae

Habitat: on mud flats, especially near low-tide line.

Niche: Herbivore, feeding on algae and phytoplankton. Also detritivore, feeding on carrion.

Personal Observations: As the Hudson is an estuary and a tidal river, there are two low tides each day. During dead low-tide, when the river bottom is visible, from late May through early October, one can see hundreds and hundreds of Ilynassa on top of the river bottom. Sometimes they are moving along and sometimes they are completely withdrawn into their shells, one supposes, waiting for the return of the water. I have several Ilynassa in my river tanks on my houseboat and in my classroom. They live for years in captivity, feeding on the algae on the side of the tank and carrion particles on the substrate.