Atrina fragilis

Last updated

Contents

Fan mussel
Atrina-fragilis 01.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Pteriida
Family: Pinnidae
Genus: Atrina
Species:
A. fragilis
Binomial name
Atrina fragilis
(Pennant, 1777)
Synonyms

Pinna fragilis

Atrina fragilis, the fan mussel, is a species of large saltwater clam, a marine bivalve mollusc in the family Pinnidae, the pen shells.

The fan mussel, Atrina fragilis is one of the largest (30 to 48 cm long) and rarest bivalve molluscs occurring in northern European waters and the only member of the family Pinnidae to inhabit UK waters. [1] It is one of the largest (30 to 48 cm long) European bivalve molluscs. It is one of the rarest species of marine mollusc in the United Kingdom - so rare that surveys of nearly 9,000 sites around Britain between 1987 and 1998 found none. [2] The fan mussel has a larval stage that is very difficult to identify due to the rarity of the specimen. [1] Atrina fragilis is greatly affected by the industrialization of the fishing industry and it has impacted the distribution of the rare species. [1]

A short underwater video of Atrina fragilis and habitat; off the Welsh coast

Description

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 also have 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. [3] It has two valves that are equal with prominent gaps between the two shells and a hinge on the dorsal side. [3] The shell has concentric growth and disturbance lines with 8-12 low, wavy ridges radiating out from the umbones. [3] The shell colour is a light golden or yellow-brown to darker brown or chestnut. [3]

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. [3] They have also been recorded from north Scotland down to Mauritania, including the Iberian Peninsula, and into the Mediterranean. [3] Atrina fragilis lives embedded in sublittoral fringe (approximately 400 m), subtidal muds, sandy muds or gravels. [3] 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. [3] Though embedded, between one and two thirds of the shell is buried, therefore leaving the fan mussel vulnerable to fishing trawlers. [3]

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. [2] The species is also vulnerable to industrial activity. [1]

Atrina fragilis prefers to reside on the sublittoral fringe and subtidal muds in order to embed itself or attach its byssal threads to small stones underneath the softer substrate. [1] The biology of the mussel is not well understood, with information on its reproduction and early life-history particularly sparse. [1] Efforts are being made to identify Atrina fragilis larvae to implement effective conservation of the rare species. [1] Because of its brittle shell, the fan mussel is sensitive to the effects of benthic fishing gears and its distribution is believed to have been impacted by fishing over the past half century. [1]

The shells are anchored to the sand by fine gold-coloured silk produced by special glands located in the muscular foot. This silk or byssus are fine threads which historically was used to make special royal fabrics. This was called Pinna silk or sea silk, although the species more frequently used was Pinna nobilis of the Mediterranean.

Lifecycle

The fan mussel is often solitary but populations occur as small groups or patches of individuals forming small beds in rocky areas. [3] Fan mussels typically eat phytoplankton through suspension feeding and have a lifespan of anywhere between 20-100 years. [3] 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. [1]

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. [1] Growth lines have been used to estimate the age of adult bivalves. [1] However, concurrent molecular and morphological analyses indicate that early-stage larvae were present in the water column during late summer and early autumn. [1] This suggest that A. fragilis follows the same pattern of spawning in the summer and winter season that is found in other pinnids at temperate latitudes. [1] The pelagic larval stage is believed to be four months in length before settling in the benthic region as adult bivalves. [1] DNA barcoding has been used to identify the largely undocumented larvae of Atrina fragilis. [1] 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. [1] The fan mussel is a benthic species which is torn from its habitat by trawling nets and industrial fishing gear. [1] The displacement of a mussel from its habitat is detrimental to the animal and scientists are studying the species to help in conservation efforts. [1]

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. [1] Conservation efforts of the fan mussel are hindered due to the very limited knowledge scientists have of the life cycle and breeding season. [1] The fan mussel is a protected species in the United Kingdom, under the Wildlife and Countryside Act 1981 – since 1998 has been a crime to kill, injure, possess or sell fan mussels. [4] The United Kingdom Biodiversity Action Plan designates it a Priority Species for conservation. [5]

Footnotes

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Stirling, David A; Boulcott, Philip; Bidault, Mathias; Gharbi, Karim; Scott, Beth E; Wright, Peter J (2018-08-01). "Identifying the larva of the fan mussel, Atrina fragilis (Pennant, 1777) (Pinnidae)". Journal of Molluscan Studies. 84 (3): 247–258. doi: 10.1093/mollus/eyy015 . hdl: 2164/12291 . ISSN   0260-1230.
  2. 1 2 "Rare giant fan-shells found in Plymouth Sound". Devon Great Outdoors. BBC News. 28 July 2004. Archived from the original on 2005-12-18. Retrieved 2016-01-01.
  3. 1 2 3 4 5 6 7 8 9 10 11 Tyler-Walters, Harvey; Wilding, Catherine (2017). "Fan mussel (Atrina fragilis)". MarLIN: 28. doi:10.17031/marlinsp.1157.2 via Marine Life Information Network: Biology and Sensitivity Key Information Reviews.
  4. Protection for wild animals on Schedule 5 of the Wildlife and Countryside Act, 1981. Website accessed 7 August 2009.
  5. "UK BAP priority marine species". UK BAP priority species. Joint Nature Conservation Committee. 2014-12-19. Archived from the original on 2015-09-12. Retrieved 2016-01-01.

Related Research Articles

<span class="mw-page-title-main">Mussel</span> Type of bivalve mollusc

Mussel is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval.

<span class="mw-page-title-main">Bivalvia</span> Class of molluscs

Bivalvia, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bivalves have no head and they lack some usual molluscan organs, like the radula and the odontophore. The class includes the clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater, as well as a number of families that live in freshwater. The majority are filter feeders. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment, where they are relatively safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some bivalves, such as the scallops and file shells, can swim. Shipworms bore into wood, clay, or stone and live inside these substances.

<span class="mw-page-title-main">Byssus</span> Fibre secreted by some molluscs

A byssus is a bundle of filaments secreted by many species of bivalve mollusc that function to attach the mollusc to a solid surface. Species from several families of clams have a byssus, including pen shells (Pinnidae), true mussels (Mytilidae), and Dreissenidae.

<i>Dreissena</i> Genus of bivalves

Dreissena is a genus of small freshwater mussels in the family Dreissenidae in the class Bivalvia. They are found attached to firm substrates by threads from underneath the shells and are the only freshwater bivalves to attach to hard substrates in high densities while having a planktonic larval stage. They are considered the most aggressive freshwater invader in the world because of their ability to invade environments in every one of their life cycle.

<span class="mw-page-title-main">Pinnidae</span> Family of bivalves

The Pinnidae are a taxonomic family of large saltwater clams sometimes known as pen shells. They are marine bivalve molluscs in the order Pteriida.

Freshwater bivalves are one kind of freshwater mollusc, along with freshwater snails. They are bivalves that live in fresh water as opposed to salt water, which is the main habitat type for bivalves.

<i>Perna perna</i> Species of bivalve

Perna perna, the brown mussel, is an economically important mussel, a bivalve mollusc belonging to the family Mytilidae. It is harvested as a food source but is also known to harbor toxins and cause damage to marine structures. It is native to the waters of Africa, Europe, and South America and was introduced in the waters of North America.

<i>Pinna</i> (bivalve) Genus of bivalves

Pinna is a genus of bivalve molluscs belonging to the family Pinnidae.

<i>Atrina</i> Genus of bivalves

Atrina is a cosmopolitan genus of bivalve molluscs belonging to the family Pinnidae.

<i>Atrina rigida</i> Species of bivalve

Atrina rigida, commonly called the rigid pen shell, is a species of bivalve mollusc in the family Pinnidae.

<i>Pinna nobilis</i> Species of bivalve

Pinna nobilis, whose common name is the noble pen shell or fan mussel, is a large species of Mediterranean clam, a marine bivalve mollusc in the family Pinnidae, the pen shells.

<i>Modiolus modiolus</i> Species of bivalve

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

<i>Atrina squamifera</i> Species of bivalve

Atrina squamifera, one of several species known as the horse mussel, is a species of bivalve pen shell. It is a marine mollusc in the family Pinnidae. It is endemic to South Africa.

<i>Pinna carnea</i> Species of bivalve

Pinna carnea, commonly called the amber pen shell, is a species of bivalve mollusc in the family Pinnidae.

<i>Atrina seminuda</i> Species of bivalve

Atrina seminuda, the half-naked pen shell, is a species of bivalve mollusc in the family Pinnidae.

<i>Atrina zelandica</i> Species of bivalve

Atrina zelandica, one of several species known as the horse mussel, is a large species of saltwater clam in the family Pinnidae, the pen shells. This species is found around New Zealand.

<i>Pinna rudis</i> Species of bivalve

Pinna rudis, the rough pen shell or spiny fan-mussel, is a species of bivalve mollusc in the family Pinnidae. It is the type species of the genus Pinna. Knowledge about this is sparse, with an absence of specific studies and literature.

<i>Pinna bicolor</i> Species of bivalve

Pinna bicolor, also known as razorfish, razor clam, or pen shell, is a species of large saltwater clam in the family Pinnidae. It is commonly found in shallow waters up to 50 m (160 ft) deep. It can be found embedded in firm muddy intertidal sediments, seagrass beds, and reef flats along continental and island shores.

South-West Deeps (West) MPA, along with the South West Deeps (East) MPA is an offshore Marine Conservation Zone (MCZ), approximately 230 km (140 mi) off Land's End, Cornwall, England, in the Western Channel and Celtic Sea. It was one of twenty-seven MCZs designated on 21 November 2013 by the Marine and Coastal Access Act 2009 and is a predominantly sandy area of the continental shelf, supporting molluscs and crustaceans living in and on the mixed and coarse sediments.

References