Atrina fragilis

The shell of the fan mussel tapers to a point at the umbos, and is very brittle. It is yellowish to dark brown with blackish patches. The two valves are equal and triangular in outline, with prominent gapes. The shell surface has a sculpture of concentric lines and 8 to 12 ribs, which may have fluted spines. Shells can reach up to 48 cm in length, and the largest individuals may be 10 to 12 years old. Atrina fragilis have also been found in the Mediterranean Sea. ==Taxonomy and Identification==

Atrina fragilis has a large (30-48 cm in length by 15-24 cm wide), triangular, thin and fragile shell that tapers to a point. It has two valves that are equal with prominent gaps between the two shells and a hinge on the dorsal side. The shell has concentric growth and disturbance lines with 8-12 low, wavy ridges radiating out from the umbones. The shell colour is a light golden or yellow-brown to darker brown or chestnut. ==Habitat and Distribution==

The most recent records of the rare bivalve Atrina fragilis are from Scotland in deep waters around the Shetland Isles and Orkney, and the west coast of Scotland, with scattered records from north-east Scotland, the south coast of England, the Channel Isles, Pembrokeshire in south Wales and Northern Ireland. They have also been recorded from north Scotland down to Mauritania, including the Iberian Peninsula, and into the Mediterranean. Atrina fragilis lives embedded in sublittoral fringe (approximately 400 m), subtidal muds, sandy muds or gravels. The fan mussel, like many other mussels, attaches to small stones by the secretion of strong byssal threads through their byssus gland to avoid being swept away in the ocean. Though embedded, between one and two thirds of the shell is buried, therefore leaving the fan mussel vulnerable to fishing trawlers. ==Biology==

This species lives with the narrow half of its shell anchored in the sediment, but the large part of the fragile shell protrudes from the sea floor. Thus, unfortunately, it is vulnerable to damage by fishing trawlers. Fan mussels typically eat phytoplankton through suspension feeding and have a lifespan of anywhere between 20–100 years. The fan mussel grows approximately 6 μm each day and the size can reach up to 770 μm before attaching to the substrate as adult bivalves. Reproduction The biology of A. fragilis is not well understood, its reproduction and early life-history is particularly sparse and no descriptions of A. fragilis larvae exist in the literature. Growth lines have been used to estimate the age of adult bivalves. However, concurrent molecular and morphological analyses indicate that early-stage larvae were present in the water column during late summer and early autumn. This suggests that A. fragilis follows the same pattern of spawning in the summer and winter season that is found in other pinnids at temperate latitudes. The pelagic larval stage is believed to be four months in length before settling in the benthic region as adult bivalves. DNA barcoding has been used to identify the largely undocumented larvae of Atrina fragilis. This technique will allow scientists to identify fan mussel habitats and oceanic larval distribution so that in the future proper conservation efforts may be implemented in those areas. ==Threats==

Atrina fragilis is sensitive to the effects of benthic fishing gears and its distribution is believed to have been impacted heavily by the industrialization of fishing over the past half century. The fan mussel is a benthic species which is torn from its habitat by trawling nets and industrial fishing gear. The displacement of a mussel from its habitat is detrimental to the animal and scientists are studying the species to help in conservation efforts. ==Conservation==

Currently, there are two marine protected areas (MPAs) in the OSPAR network that include A. fragilis as a feature identified for protection; the South-West Deeps (England) and the Small Isles (Scotland) MPAs. The United Kingdom Biodiversity Action Plan designates it a Priority Species for conservation. ==Footnotes==