BIOTIC Species Information for Musculus discors
Researched byLizzie Tyler Data supplied byUniversity of Sheffield
Refereed byThis information is not refereed.
Reproduction/Life History
Reproductive typeProtandrous hermaphrodite
Developmental mechanismDirect Development
Reproductive SeasonInsufficient information Reproductive LocationAs adult
Reproductive frequencyAnnual episodic Regeneration potential No
Life span3-5 years Age at reproductive maturity
Generation time3-5 years Fecundity
Egg/propagule size300 µm diameter Fertilization typeInsufficient information
Larval/Juvenile dispersal potentialVery limited (<1m) Larval settlement periodNot relevant
Duration of larval stage   
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,
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