Not to be confused with Modiolus modiolus

Modiolus modiolus

Modiolus modiolus, common name northern horsemussel, is a species of marine bivalve mollusk in the family Mytilidae.-Description:...

also known as the
horse mussel.

The horse mussel, Atrina squamifera, is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of bivalve

Bivalvia

Bivalvia is a taxonomic class of marine and freshwater molluscs. This class includes clams, oysters, mussels, scallops, and many other families of molluscs that have two hinged shells...

 pen shell. It is a marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 mollusc in the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Pinnidae

Pinnidae

Pinnidae is a family of large saltwater clams sometimes known as pen shells. They are marine bivalve molluscs in the order Pterioida.The shells are fragile and have a long and triangular shape, and in life they are anchored in sediment using a byssus...

. It is endemic to South Africa.

Distribution

This species is found from Saldanha Bay to Port Alfred, subtidally to at least 35 m.

Description

This animal has a large fragile shell and can grow up to 390 mm in total length. It has 6-12 ribs running longitudinally down its shell. Each rib bears translucent cup-like projections. The shell does not close at the posterior end and the dark-rimmed white flesh can be seen inside.

Ecology

The horse mussel is a filter feeder. It usually lies buried vertically in mud or sand although it can also be seen on the wooden decks of the trawler wrecks Orotava and Princess Elizabeth in Smitswinkel Bay. The shell is often heavily overgrown with other invertebrates. The mantle cavity often contains small pea crabs

Pinnotheridae

Pinnotheridae is a family of pea crabs. Pea crabs are tiny soft-bodied crabs that live commensally in the mantles of certain bivalve molluscs...

 and shrimp

Shrimp

Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...

s which eat food filtered from the gills.