Sea Slugs

Description

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Context: A citizen science project documents unique sea slugs from Visakhapatnam coast.

Details:

What are slugs?

Sea slugs belong to Phylum Mollusca and Class Gastropoda.
They look like naked snails, i.e., without shells.
Sea slugs are of course those found in the sea. There are also slugs that live on land.

Types:

Sea slugs may be generally differentiated into two main groups.
Members of one group breathe with lungs. These include pulmonate sea slugs such as the Onch slugs of the Family Onchidiidae.
Members of another group breathe with gills. These include the Opisthobranchs or just plain sea slugs.

Where seen?

Onch slugs can be found among the rocks near the high water mark, while other slugs are found further down where it is almost always covered in water.
Some are burrowing and many are found on or near their food.
Some sea slugs are stunningly beautiful, among them, nudibranchs.

Features:

Sea slugs range from large sea hares of 10cm to tiny nudibranchs 1cm or less.
Sea slugs generally lack large external shells.
Some many have external shells but cannot fully retract their bodies into these shells like other 'regular' snails do. Other sea slugs may have internal shells.
Most sea slugs don't have any shells at all.
Although they lack shells, slugs are not helpless. Some taste bad, others release toxic or irritating substances.
Yet others incorporate stingers of sea anemones, hydroids and other cnidarians that they feed on and use these to protect themselves.

What do they eat?

Threats:

Some slugs may release highly toxic substances when stressed.
Like other creatures of the intertidal zone, they are affected by human activities such as reclamation and pollution.
Trampling by careless visitors and over-collection can also have an impact on local populations.

PRACTICE QUESTION

Q) Which of the following statements is/are correct with reference to Sea Slug?

a. They lack an external shell.

b. They are found in sea only.