BIOTIC Species Information for Musculus discors
|Researched by||Lizzie Tyler||Data supplied by||University of Sheffield|
|Refereed by||This information is not refereed.|
|Scientific name||Musculus discors||Common name||Discordant mussel|
|MCS Code||W1721||Recent Synonyms||Modiolaria discors|
|Additional Information||The nest completely encloses the adult so that Musculus discors is only visible when its valves are open and it is feeding. Smooth specimens, lacking ribs, were reported from Oban and Staffa, in the Hebrides (Jeffreys, 1863).|
|Taxonomy References||Howson & Picton, 1999, Tebble, 1976, Fish & Fish, 1996, Morton, 1992, Phorson, 1996, Ockelmann, 1958, Forbes & Hanley, 1853, Jeffreys, 1863, MacGinitie, 1955,|
||Feeding method||Passive suspension feeder
Active suspension feeder
|Typical food types||Phytoplankton, bacteria, organic particulates and dissolved organic matter (DOM).||Habit||Attached|
|Bioturbator||Not relevant||Flexibility||None (< 10 degrees)|
|Height||Insufficient information||Growth Rate||See additional information|
|Adult dispersal potential||<10m||Dependency||Independent|
|General Biology Additional Information||
The nest may incorporate a variety of pieces of seaweeds or detritus or may be fouled by epifauna, the exact composition depending on the location and habitat, which provide camouflage. For example, the nest may incorporate; the stolons of hydroids, bryozoans, small bivalves and annelids (MacGinitie, 1955; Merrill & Turner, 1963); fragments of Flustra foliacea (Forbes & Hanley, 1853), or fragments or blades of fucoids and laminarians (Thorson, 1935).
MacGinitie (1955) noted that specimens from East Greenland >20mm were nearly always covered by a byssal nest. However, in British Columbia Merrill & Turner (1963) noted that the smallest specimens with nests were 8.1mm in length and most specimens over 15mm had nests, although some specimens up to 18mm in length were without a nest.
|Biology References||Fish & Fish, 1996, Baldock et al., 1998, Könnecker & Keegan, 1983, Ockelmann, 1958, Thorson, 1946, Merrill & Turner, 1963, Forbes & Hanley, 1853, Jeffreys, 1863, MacGinitie, 1955, Cartlidge & Hiscock, 1980, Lauckner, 1983,|
|Distribution and Habitat|
|Distribution in Britain & Ireland||Common around most of the British Isles from Shetland to the Channel Isles.|
|Global distribution||A panartic bivalve, found from the Arctic Circle south through the Bering Sea to Japan or to the Puget Sound in the Pacific or south to New York or Madeira in the Atlantic, including the western Baltic and Mediterranean.|
|Biogeographic range||Not researched||Depth range|
|Migratory||Non-migratory / Resident|
|Distribution Additional Information||
Musculus discors forms gregarious clumps on the holdfasts of seaweeds, especially Corallina officinalis, Fucus spp. Laminaria spp. and Desmarestia sp. On laminarians, Musculus discors may cover the holdfast and bottom part of the stipe (Jeffreys, 1863; Ockelmann, 1958; Tebble, 1976). Small specimens (<20mm) were reported nestled in interstices between barnacles and the old holdfasts of tunicates (MacGinitie, 1955). Merrill & Turner (1963) found Musculus discors fouling the upper surface of the sea scallop Placopecten magellanicus.
Most records reported Musculus discors in the shallow subtidal to depths of up to 50m in the British Isles. However, it has been reported to be abundant above 30-40m in east Greenland, to form a well developed community at 60-100m in the Fosse de la Hague in the English Channel (Cabioch, 1968), to occur from 0 -374m in the Barents Sea (Ockelmann, 1958), and to be common in most trawls from 130-741 ft (ca 39-225m) at Point Barrow, Alaska (MacGinitie, 1955).
Musculus discors occasionally forms dense aggregations, especially in strong tidal streams, covering rock surfaces, forming the biotope MCR.Mus.
Large to very large boulders
Gravel / shingle
|Physiographic preferences||Open coast
Strait / sound
Ria / Voe
Enclosed coast / Embayment
|Biological zone||Lower Eulittoral
|Tidal stream strength/Water flow||Strong (3-6 kn)
Moderately Strong (1-3 kn)
Weak (<1 kn)
|Salinity||Variable (18-40 psu)
Full (30-40 psu)
|Habitat Preferences Additional Information|
|Distribution References||Thorson, 1935, Tebble, 1976, Fish & Fish, 1996, Baldock et al., 1998, Könnecker & Keegan, 1983, Ockelmann, 1958, Thorson, 1946, MacGinitie, 1955, Murray, E. et al., 1999, Thorpe, 1998, Könnecker, 1977, Cartlidge & Hiscock, 1980, Bruce et al., 1963, Seaward, 1990, Brazier et al., 1999,|
|Reproductive type||Protandrous hermaphrodite
||Developmental mechanism||Direct Development
|Reproductive Season||Insufficient information||Reproductive Location||As adult|
|Reproductive frequency||Annual episodic||Regeneration potential||No|
|Life span||3-5 years||Age at reproductive maturity|
|Generation time||3-5 years||Fecundity|
|Egg/propagule size||300 µm diameter||Fertilization type||Insufficient information|
|Reproduction Preferences Additional Information||
Musculus discors is a protandrous hermaphrodite, male when small then becoming female when larger and older. One year olds are functionally male. In the following year eggs begin to develop and individuals pass through a hermaphroditic phase (2-3years olds) becoming functional females by the third year of life (Thorson, 1935; Ockelmann, 1958). Some third year individuals were found to be functionally male, suggesting that reversion may occur (Thorson, 1935).
Large eggs (300 by 220 µm) are laid in 3-4 rows in mucus strings within the adult nest. Embryos of 400µm in length are found in the mucus strings. Development is direct, there is no pelagic phase, the juveniles leave the egg string as free living crawl-aways (Thorson, 1935; Ockelmann, 1958).
Eggs are laid throughout summer, with a peak in August in east Greenland (Thorson, 1935; Ockelmann, 1958). Egg strings were found in May in the Holbaek fjord in the Øresund Sound, Denmark (Thorson, 1946). Martel & Chia (1991) reported a peak of juveniles in British Columbia during summer. However, no information on reproduction in the UK was found.
Brooding of offspring is a common trait in boreal and arctic marine benthic invertebrates (Ockelmann, 1958; 1965). Small juvenile Musculus discors often remain within the nest, near the edge of the adult shell, feeding in the currents produced by the adult, and larger juveniles may be found in the outer fringes of the nest (Merrill & Turner, 1963). Brooding and low levels of vagility may explain the dense aggregation and gregarious clumps of individuals found in this species but suggests that dispersal is poor. However, Martel & Chia (1991) reported that juvenile Musculus discors (<1 mm) were caught in off-bottom intertidal collectors and one specimen in offshore collectors. Therefore, juvenile Musculus discors are probably capable of drifting on fine byssal threads (bysso-pelagic transport) and may be carried considerable distances, albeit in small numbers.
|Reproduction References||Thorson, 1935, Ockelmann, 1958, Thorson, 1946, Martel & Chia, 1991b, Merrill & Turner, 1963,|