Spisula solidissima
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Spisula solidissima |
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| ( Dillwyn , 1817) |
Spisula solidissima is a type of mussel from the family of trough mussels (Mactridae). The range of the species stretches from the Canadian east coast, along the US American east coast to the Gulf of Mexico near the border with Mexico. The animals can reach an age of up to 34 years.
features
The even-folded, strongly inflated, very large housing is up to 22 cm long. It is almost equilateral, with the forward-sloping vertebrae just in front of the midline. The housing outline is rounded-triangular, the length / height ratio is about 1.4. The anterior and posterior dorsal edges are slightly convex and each slope moderately steep. Front and rear ends are well rounded. The closed case gapes at the rear end. The ventral margin is broadly rounded.
There is an external and an internal ligament . The external ligament is a very small, dark brown band that lies behind the vertebra. The internal ligament sits in a large, triangular shape ( chondrophor ). A lunula is not developed. The area is indistinct and not delimited.
The left flap shows two cardinal teeth forming an inverted V-shaped structure just in front of the ligament fossa. The posterior lateral tooth is only half as long as the anterior lateral tooth. Close to the edge of the case and running parallel to it, there are small, lamellar posterior teeth in front and behind. In the right valve there is only a single, hook-shaped cardinal tooth, and two weakly developed, lamellar, anterior and posterior lateral teeth. The top and bottom of the lateral teeth of the left valve and the insides of the two lateral teeth of the right valve are notched. The mantle is only slightly indented, the apex of the bay only extends a little beyond the posterior sphincter impression. There are two sphincters.
The whitish to whitish-yellowish shell is thick-walled and very firm (name! Latin. Solidissima = very firm). The ornamentation consists of fine concentric lines and pits. The respective growth sections are clearly marked. There are radial pale brown rays on the (cream) white shell. The periostracum is a thin yellow-brown glossy layer that is easily rubbed off. The inner edge of the case is smooth.
Geographical distribution, habitat and way of life
The distribution area extends over the Arctic and the northern North Atlantic (North America and Europe). In North America the nominate subspecies occurs southwards to Cape Hatteras . The distribution area of the subspecies Spisula solidissima similis (Say, 1822) even extends to Florida and the Gulf of Mexico . Surprisingly, it turned out that a population in Long Island Sound ( Connecticut ), with only a small distribution area of the nominate subspecies, also belongs to the southern subspecies.
Spisula solidissima is found from the low water line to a depth of 173 meters, but more often in water depths of 8 to 66 meters. The highest population densities, however, were found in water depths between 18 and 38 meters. They prefer well-sorted, medium-sized sand, this is where the highest density occurs, but also in fine sand or silty fine sand. In nature they only occur when the water has a salt content of more than 28 ‰, although under laboratory conditions they can withstand salt contents of only 12.5 ‰ for two days without damage.
The animals are of separate sex. Sexual maturity begins in this species, albeit very differently from region to region, already three months after the larvae transition to soil life and metamorphosis. The animals are only 5 millimeters tall at this point. This is very astonishing in that this species can reach a case size of up to 22.6 centimeters and an age of 37 years. In other populations, however, the animals only become sexually mature at the age of four and a shell length of 8 to 9.5 centimeters. The sex products are released into the open water in summer and early autumn. When released into the open water, the eggs have a diameter of 56 µm and contain no significant amount of yolk. A female produces up to 13 million eggs during one spawning period. After 9 hours and 21.7 ° water temperature, the eggs first develop into a planktonic trochophora larva. The speed of development is very dependent on temperature, because at a water temperature of 14 ° the trochophoric stage is only reached after 40 hours. The planktotrophic Veliger larva is already formed after 28 hours at a water temperature of 22 ° ; at a water temperature of 14 ° this is only the case after 72 hours. After 18 days at 22 ° the pediveliger stage is reached. The Pediveliger go over to metamorphosis and soil life after 19 to 35 days and with a housing size of 230 to 250 µm . At a water temperature of 22 ° C the larvae develop optimally, higher or lower temperatures slow down their development. Temperatures higher than 30 ° are fatal for the larvae.
With the help of the gills, Spisula solidissima filters the respiratory water flowing in through the inlet siphon for diatoms and ciliate animals . The animals can still filter particles 4 μm in diameter from the water.
The southern subspecies Spisula solidissima similis remains smaller (up to 122 mm) and is only up to five and a half years old.
Predators and parasites
Spisula solidissima has many predators. In New York Bay, crabs are the main enemies, responsible for 48.3 to 100% of mortality among Spisula solidissima . Moon snails , on the other hand, were only 2.1% involved. Among the moon snails, Euspira heros and Neverita duplicata are particularly worthy of mention. Next was observed starfish Asterias forbesi , the crab Ovalipes ocellatus and Cancer borealis , the horseshoe crab Limulus polyphemus and among fish of haddock Melanogrammus aeglefinus and cod ( Gadus morhua ). The shrimp Crangon septemspinosa primarily hunts young clams, which have only recently come to life on the ground.
The animals are also attack of parasites, so from the thigmotrichen dosinae Sphenophyra , the cyclopoid copepod Myocheres major , a tapeworm -Art from the kind Echeneribothrium , a nematode , previously tentatively called Paranisakiopsis pectinis was identified hyperparasite and haplosporide unicellular Urosporidium spisuli and an anisakine roundworm from the genus Sulcascaris .
Commercial importance
The mussel species is fished on the east coast of the USA and Canada with hydraulic clam dredges. In 1999 a total of 142,370 t was fished.
Taxonomy
The species was first validly described in 1817 by Lewis Weston Dillwyn under the original binomial Mactra solidissima . It is now generally accepted as belonging to the genus Spisula Gray, 1837. Mactra solidissima Dillwyn, 1817 is also the type species of the genus Hemimactra Swainson, 1840, a taxon of the genus group, which is regarded by some authors as a subgenus of Spisula , or is rated as a synonym of Spisula . Mactra gigantea Lamarck, 1818, Mactra procera Dillwyn, 1817 and Mactra similis Say, 1822 are more recent synonyms of Mactra solidissima Dillwy, 1817.
supporting documents
literature
- Fritz Nordsieck : The European sea shells (Bivalvia). From the Arctic Ocean to Cape Verde, the Mediterranean Sea and the Black Sea. 256 p., Gustav Fischer Verlag, Stuttgart 1969 (p. 142 as Hemimactra gigantea )
- Guido Poppe. Yoshihiro Goto: European Seashells Volume 2 (Scaphopoda, Bivalvia, Cephalopoda) . 221 pp., Verlag Christa Hemmen, Wiesbaden 1993 (2000 unc. Reprint), ISBN 3925919104 (pp. 101/2)
- Rainer Willmann: Mussels of the North and Baltic Seas. 310 p., Neumann-Neudamm, Melsungen 1989 ISBN 3-7888-0555-2 (p. 148)
On-line
Individual evidence
- ^ A b c Food and Agriculture Organization of the United Nations Fisheries an Aquaculture Department
- ↑ a b c d Luca M. Cargnelli, Sara J. Griesbach, David B. Packer, Eric Weissberger: Essential Fish Habitat Source Document: Atlantic Surfclam, Spisula solidissima, Life History and Habitat Characteristics. NOAA Technical Memorandum NMFS-NE-142, 22 S., US Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Northeast Region, Northeast Fisheries Science Center, Woods Hole, Massachusetts, 1999 PDF
- ↑ Lewis Weston Dillwyn: A descriptive catalog of recent shells, arranged according to the Linnæan method; with particular attention to the synonymy. Vol. I. pp. 1–580, London, Arch, 1817. Online at www.biodiversitylibrary.org (p. 140)
- ↑ a b MolluscaBase: Spisula solidissima (Dillwyn, 1817)
