200
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
1. Stylochus ellipticus (Girard, 1850)
(Order Polycladida; suborder Acotylea; family Stylochidae)
This turbellarian, one of the so-called oyster " leeches )', was
originally described by Girard (1850) as Planocera elliptica but it has
since been transferred to the genus Stylochus as S. ellipticus by Hyman
(1939). According t o Hyman (1940b), its synonyms include Planocera
nebulosa Girard, 1853, Stylochopsis littoralis Verrill, 1873, Stylochus
littoralis Lang, 1884, Eustylochus ellipticus Verrill, 1892, and E .
meridionalis Pearse, 1938.
S . ellipticus is a littoral species, living among barnacles, oysters and
shells, on pilings and under rocks. It feeds on oysters, barnacles, and
perhaps other invertebrates, especially pelecypods. It apparently has
no difficulty in entering oysters, especially spat, through slightly
opened valves. According to Loosanoff (1956), this turbellarian was
responsible for the destruction of large numbers of young oysters on
the flats a t Milford, Connecticut. Its geographic range extends from
Texas to Prince Edward Island, Canada, being very common south of
Massachusetts. A good description of this species has been given by
Hyman (1940b).
2. Stylochus frontalis Verrill, 1892
(Order Polycladida; suborder Acotylea; family Stylochidae)
This gray or yellowish gray turbellarian, also known as an oyster
" leech ", was originally described by Verrill (1892a). It has been
referred to as Stylochus inimicus by Palombi (1931b), Pearse (1938)
and Pearse and Wharton (1938), and as S . tenax by Palombi (193613).
This is also a littoral species, being found among living oysters and
oyster shells. Pearse and Wharton (1938), who investigated the cause
of the oyster mortalities in Apalachicola Bay, Florida, could not
definitely state that the destruction was due to S . frontalis, but have
suggested that the oysters are first weakened by some unknown cause
after which this polyclad readily invades those unable to close their
valves. According to Hyman (1940b), S . frontalis feeds primarily on
oysters. It is distributed on oyster beds from Florida t o Texas and
northward to the Carolinas. Its biology has been studied by Pearse
and Wharton (1938) and a good description is given by Hyman (1940b).
3. Stylochus oculiferus Girard, 1853
(Order Polycladida; suborder Acotylea; family Stylochidae)
although it is not known whether it feeds on oysters.
This comparatively rare polyclad is primarily found on oyster beds
Originally
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
1. Stylochus ellipticus (Girard, 1850)
(Order Polycladida; suborder Acotylea; family Stylochidae)
This turbellarian, one of the so-called oyster " leeches )', was
originally described by Girard (1850) as Planocera elliptica but it has
since been transferred to the genus Stylochus as S. ellipticus by Hyman
(1939). According t o Hyman (1940b), its synonyms include Planocera
nebulosa Girard, 1853, Stylochopsis littoralis Verrill, 1873, Stylochus
littoralis Lang, 1884, Eustylochus ellipticus Verrill, 1892, and E .
meridionalis Pearse, 1938.
S . ellipticus is a littoral species, living among barnacles, oysters and
shells, on pilings and under rocks. It feeds on oysters, barnacles, and
perhaps other invertebrates, especially pelecypods. It apparently has
no difficulty in entering oysters, especially spat, through slightly
opened valves. According to Loosanoff (1956), this turbellarian was
responsible for the destruction of large numbers of young oysters on
the flats a t Milford, Connecticut. Its geographic range extends from
Texas to Prince Edward Island, Canada, being very common south of
Massachusetts. A good description of this species has been given by
Hyman (1940b).
2. Stylochus frontalis Verrill, 1892
(Order Polycladida; suborder Acotylea; family Stylochidae)
This gray or yellowish gray turbellarian, also known as an oyster
" leech ", was originally described by Verrill (1892a). It has been
referred to as Stylochus inimicus by Palombi (1931b), Pearse (1938)
and Pearse and Wharton (1938), and as S . tenax by Palombi (193613).
This is also a littoral species, being found among living oysters and
oyster shells. Pearse and Wharton (1938), who investigated the cause
of the oyster mortalities in Apalachicola Bay, Florida, could not
definitely state that the destruction was due to S . frontalis, but have
suggested that the oysters are first weakened by some unknown cause
after which this polyclad readily invades those unable to close their
valves. According to Hyman (1940b), S . frontalis feeds primarily on
oysters. It is distributed on oyster beds from Florida t o Texas and
northward to the Carolinas. Its biology has been studied by Pearse
and Wharton (1938) and a good description is given by Hyman (1940b).
3. Stylochus oculiferus Girard, 1853
(Order Polycladida; suborder Acotylea; family Stylochidae)
although it is not known whether it feeds on oysters.
This comparatively rare polyclad is primarily found on oyster beds
Originally