Lutraria lutraria
Encyclopedia
Lutraria lutraria is a species
of large marine bivalve
mollusc in the family
Mactridae
. Its common names include the otter shell and the common otter shell. It occurs in coastal regions of the north east Atlantic Ocean where it lives buried in the sand.
of the genus
Lutraria
, the name Mya lutraria being the basionym
used by Carl Linnaeus when he described the species in 1758. It was later determined that there were sufficient differences between it and other Mya
species for the otter shell to be placed in its own genus. The similarity between Mya
and Lutraria
is due to convergence
due to exploitation of the same habitat rather than a close phylogenetic relationship
.
is olive brown. This layer gets worn away over time and is often completely missing in shells found on the beach. There are concentric sculptured lines showing periods of growth and a few faint radial lines near the hinge. The left valve has two cardinal teeth with a third small one behind. The right valve has two small cardinal teeth and a small lateral one.
The flesh of the animal is white. The foot is thick and protrudes through the pedal gape at the posterior end. The mantle
edges are fringed with white and are fused together. The massive siphons can be extended to two or three times the length of the shell and are joined together for their entire length. They are streaked with brown and purple and are housed in a transparent, gelatinous sheath composed of protein and chitin. The siphons are outgrowths of the mantle while the sheath is a continuation of the periostracum. There are two rings of tiny tentacles round the orifice of the inhalant siphon and a single ring and a membrane round the exhalant one. The mantle has a fourth pallial opening near the base of the siphon.
. It draws in water through one siphon and expels it through the other. Respiration takes place as the water current passes over the gills. Waste is periodically expelled through the fourth pallial opening which can also be used for expulsion of water from the mantle cavity.
Trawling may damage or remove the tips of the siphons and bottom feeding fish may nip them off but the animal can regenerate the inner layers over the course of a few days.
Hydraulic blade dredge fishing takes place for razor clams, Ensis
spp., in Scotland and the process was studied to examine its impact. Bottom trawling of the seabed is often preceded by a sand fluidation process designed to loosen the sediment. Dredging damages a considerable portion of the benthic megafauna
including L. lutraria, however this species tends to live at greater depths than is reached by the process. Nevertheless, between 20% and 100% are damaged in a single dredge haul. Some individuals are undamaged but left lying on the surface and it has been found that their ability to rebury themselves is limited. Unlike razor clams, they normally spend their lives in one spot and the foot is relatively small and mainly used for anchorage rather than digging. Any animal unable to rebury itself rapidly is likely to fall prey to the scavengers that move in after a trawl has passed. Such studies are of importance in assessing the ecological consequence and sustainability of fisheries.
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 large marine 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...
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...
Mactridae
Mactridae
Mactridae, also known as trough shells or duck clams, is a family of marine bivalve clams of the order Veneroida.-Characteristics:...
. Its common names include the otter shell and the common otter shell. It occurs in coastal regions of the north east Atlantic Ocean where it lives buried in the sand.
Taxonomy
Lutraria lutraria is the type speciesType species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Lutraria
Lutraria
Lutraria is a genus of medium-sized marine bivalve mollusks or clams, commonly known as otter shells. They live buried in sand to a depth of about , usually below low water mark, with their siphons extended to the sea bed...
, the name Mya lutraria being the basionym
Basionym
Basionym is a term used in botany, regulated by the International Code of Botanical Nomenclature...
used by Carl Linnaeus when he described the species in 1758. It was later determined that there were sufficient differences between it and other Mya
Mya (genus)
Mya is a genus of bivalve molluscs, including seven species:*Mya arenaria Linnaeus, 1758*Mya baxteri Coan & Scott, 1997*Mya eideri Hopner Petersen, 1999*Mya neoovata Hopner Petersen, 1999*Mya neouddevallensis Hopner Petersen, 1999...
species for the otter shell to be placed in its own genus. The similarity between Mya
Mya (genus)
Mya is a genus of bivalve molluscs, including seven species:*Mya arenaria Linnaeus, 1758*Mya baxteri Coan & Scott, 1997*Mya eideri Hopner Petersen, 1999*Mya neoovata Hopner Petersen, 1999*Mya neouddevallensis Hopner Petersen, 1999...
and Lutraria
Lutraria
Lutraria is a genus of medium-sized marine bivalve mollusks or clams, commonly known as otter shells. They live buried in sand to a depth of about , usually below low water mark, with their siphons extended to the sea bed...
is due to convergence
Convergence
-Mathematics:* Convergence , refers to the notion that some functions and sequences approach a limit under certain conditions* Convergence , the notion that a sequence of transformations come to the same conclusion, no matter what order they are performed in.-Natural sciences:*Convergence ,...
due to exploitation of the same habitat rather than a close phylogenetic relationship
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
.
Description
L. lutraria has a pair of large, elongated oval valves up to 15 cm (6 in) long. They are smooth, glossy and fairly thin. They are a creamy colour and the periostracumPeriostracum
The periostracum is a thin organic coating or "skin" which is the outermost layer of the shell of many shelled animals, including mollusks and brachiopods. Among mollusks it is primarily seen in snails and clams, i.e. in bivalves and gastropods, but it is also found in cephalopods such as the...
is olive brown. This layer gets worn away over time and is often completely missing in shells found on the beach. There are concentric sculptured lines showing periods of growth and a few faint radial lines near the hinge. The left valve has two cardinal teeth with a third small one behind. The right valve has two small cardinal teeth and a small lateral one.
The flesh of the animal is white. The foot is thick and protrudes through the pedal gape at the posterior end. The mantle
Mantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
edges are fringed with white and are fused together. The massive siphons can be extended to two or three times the length of the shell and are joined together for their entire length. They are streaked with brown and purple and are housed in a transparent, gelatinous sheath composed of protein and chitin. The siphons are outgrowths of the mantle while the sheath is a continuation of the periostracum. There are two rings of tiny tentacles round the orifice of the inhalant siphon and a single ring and a membrane round the exhalant one. The mantle has a fourth pallial opening near the base of the siphon.
Distribution
L. lutraria is found off the coasts of north west Europe from Norway south to the Mediterranean Sea and also in West Africa. It is found in soft substrates from the low tide mark down to about one hundred metres. The largest individuals with the longest siphons bury themselves at the greatest depths.Biology
L. lutraria is a filter feederFilter feeder
Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...
. It draws in water through one siphon and expels it through the other. Respiration takes place as the water current passes over the gills. Waste is periodically expelled through the fourth pallial opening which can also be used for expulsion of water from the mantle cavity.
Trawling may damage or remove the tips of the siphons and bottom feeding fish may nip them off but the animal can regenerate the inner layers over the course of a few days.
Hydraulic blade dredge fishing takes place for razor clams, Ensis
Ensis
Ensis is a genus of medium-sized edible saltwater clams, littoral bivalve mollusks in the family Pharidae.In the United States, other common names for species in this genus are razor clams or jackknife clams. This is because the long, narrow, and parallel-sided shape of their shells is unusual in...
spp., in Scotland and the process was studied to examine its impact. Bottom trawling of the seabed is often preceded by a sand fluidation process designed to loosen the sediment. Dredging damages a considerable portion of the benthic megafauna
Megafauna
In terrestrial zoology, megafauna are "giant", "very large" or "large" animals. The most common thresholds used are or...
including L. lutraria, however this species tends to live at greater depths than is reached by the process. Nevertheless, between 20% and 100% are damaged in a single dredge haul. Some individuals are undamaged but left lying on the surface and it has been found that their ability to rebury themselves is limited. Unlike razor clams, they normally spend their lives in one spot and the foot is relatively small and mainly used for anchorage rather than digging. Any animal unable to rebury itself rapidly is likely to fall prey to the scavengers that move in after a trawl has passed. Such studies are of importance in assessing the ecological consequence and sustainability of fisheries.