Home › Sea Life › Marine Biology › Invertebrates › Mollusks
[Kingdom: Animalia] [Subkingdom: Eumetazoa] [Superphylum: Lophotrochozoa] [Phylum: Mollusca]
Biological resources suggest 85,000 types of marine molluscs exist in the world today. Nonetheless, the recognised number of living mollusk species excludes another 100,000 fossil species.
This section contains a comprehensive list of mollusk species (the largest marine phylum), with fun and interesting facts about the behavioural patterns of mollusks in the ocean.
Oceanic invertebrates with a soft body and a hard carbonate shell are most likely marine mollusks (British spelling 'molluscs').
This diverse clade of invertebrate species accounts for around 23% of all known organisms living in the seas and oceans worldwide.
In fact, if we exclude the phylum Arthropoda, mollusca (Latin word for 'soft') make up the largest phylum of extant (surviving) animals.
As a consequence of that, the species differs in ecology, habitats, diet, and especially in their body structure.
Simply put, marine mollusks make up an enormous group of gastropod invertebrates that includes various species of sea snail, sea slug (nudibranchia), mussels, nautiloids, oysters, clam, squid, and octopodes.
In reality, the phylum mollusca contains two entirely extinct members (Ammonites and Belemnites). However, the taxonomic classes that make up the major clades of living soft-bodied organisms, include:
The majority of mollusk specimens live in the oceans and have a protective hard shell usually as a single unit and not jointed exoskeletons like crustaceans have. They broadly exhibit an open circulatory system.
Most of the 30,000 bivalve marine mollusc species thrive in saltwater and freshwater environments. The headless bivalvia is a mollusc with a hinged shell.
Nonetheless, some of the typical molluscan organs are absent, including the odontophore and several other radula structures.
Instead, they rely on a muscular, wedge-shaped, ventral foot to carry out most of their bodily functions. The twin shells can also lock closed as a defence mechanism, as in giant clams (Tridacna gigas) for example.
In fact, squids and octopuses don't have an outer shell and they only exist in saltwater biomes. In general, these marine predators are bigger and faster than other species in this mollusks list.
The planispiral shell of the nautilus means they are the only cephalopods that have a robust external casing. The biggest mollusc is the giant squid (up to 13 metres long), Whereas, most ocean snails are good examples of small mollusks (micromollusk).
They feed on other mollusks, crustaceans, and small fishes. More than 800 different Cephalopods display bilateral mollusk symmetry.
Studies suggest there are around 60,000 mollusk snail and slug species living in various seawater and freshwater habitats around the world.
Snails also exist in terrestrial environments. Snail mollusks are characterised by their single spiralling shell (e.g. pelagic sea butterflies). Whereas, the vast majority of snails without shells are slugs.
Fun Fact: Living gastropods (marine snails, cowries, and sea slugs) account for around 80% of all ocean mollusks, believed to be close to 120,000 different specimens.
The common octopus (Octopus vulgaris) is a marine mollusk belonging to the biological order Octopoda. In reality, there are at least three hundred (300) different types still in existence today.
This section contains a collection of fun and interesting facts about octopus, including where they live, what they eat, and how these eight-limbed mollusks reproduce.
You can find this group of slow-moving marine gastropod mollusks living in every ocean. Even so, there are some key differences between the different species of these shelled organisms.
This section contains interesting sea snail facts with extra details explaining how their role in saltwater seas and oceans differs to that of their land-based counterparts.
Here are five cool facts about mollusks to help beginners distinguish these unsegmented, soft-bodied, animals from other species in a comprehensive list of invertebrates.
The anatomical diversity, in both appearance and behaviour, differentiates sea mollusks from other ocean animals and plants.
Most of the phylum mollusca are soft-bodied and nonsegmental, usually with bilateral symmetry. A single, limpet-shaped calcareous shell, a tough exoskeleton made from chitin, covers the head and foot (the main body) in many specimens.