6. THE PHYLA PORIFERA, CNIDARIA AND PLATYHELMINTHES
233
cysts enclosing cercariae may extend beyond June. Uzmann is of the
opinion that this occurs " presumably as a direct result of the lower
prevailing temperature." According to Stunkard and Uzmann (1 969)
the release of cercariae in greatest numbers occurs in the later winter
and spring, thus suggesting that cercarial development is enhanced by
lower temperature.
Uzmann (1953) has also examined the effect of ambient temperatures
on cercariae. Those maintained in filtered sea water at 21°C will only
survive for 24-48 h. Those maintained at 14OC are healthy until the
fourth day but all are moribund or dead by the seventh day. Among
those maintained a t 7°C) twenty-nine of the seventy-five cercariae
tested are still active after 12 days. The obvious endurance of cercariae
at the lowest temperature tested is meaningful when the natural
developmental cycle is considered. Uzmann has stated :
While it has not been established that spontaneous emergence of cercariae
occurs more frequently at any particular temperature, it is important to
note that maturation of cercarial generations occurs during late winter and
spring when the annual temperature is at its lowest (2"-8"C.).
It is known that P. maculatus cercariae will undergo periodic
contraction and elongation after escaping from Mytilus edulis and
" effects a serpentine but random progress upon the substratum "
(Uzmann, 1953). Although it has well-developed suckers, it seldom
utilizes these. Uzmann has also reported that they " do not manifest
any pronounced taxes. . . " but the specific experiments performed were
not reported.
Physiology. Nothing is known about the physiology of P. maculatus
other than their better survival rate at low temperatures.
Pathology. The ability of Mytilus edulis to survive parasitization by
P. maculatus has not been examined under controlled conditions
although Uzmann believes that their longevity is impaired. He has
stated that : " The severe intensity of the parasitism suggested that
C. milfordensis (= P. maculatus) infections are probably lethal under
temporary or sustained periods of ecological conditions unfavorable to
the host. "
The reproductive system of Mytilus edulis consists of a racemose
complex of follicles and ducts which ramify throughout the visceral
mass and mantle lobes. Just prior to spawning, the system is greatly
swollen and occupies the mantle lobes. In parasitized specimens, what
Uzmann refers to as a '( blocking layer ) ) of sporocysts develops in the
vascular system and causes a serious reduction in the efficiency of
circulatory system, including that of the mantle, and thus precludes
233
cysts enclosing cercariae may extend beyond June. Uzmann is of the
opinion that this occurs " presumably as a direct result of the lower
prevailing temperature." According to Stunkard and Uzmann (1 969)
the release of cercariae in greatest numbers occurs in the later winter
and spring, thus suggesting that cercarial development is enhanced by
lower temperature.
Uzmann (1953) has also examined the effect of ambient temperatures
on cercariae. Those maintained in filtered sea water at 21°C will only
survive for 24-48 h. Those maintained at 14OC are healthy until the
fourth day but all are moribund or dead by the seventh day. Among
those maintained a t 7°C) twenty-nine of the seventy-five cercariae
tested are still active after 12 days. The obvious endurance of cercariae
at the lowest temperature tested is meaningful when the natural
developmental cycle is considered. Uzmann has stated :
While it has not been established that spontaneous emergence of cercariae
occurs more frequently at any particular temperature, it is important to
note that maturation of cercarial generations occurs during late winter and
spring when the annual temperature is at its lowest (2"-8"C.).
It is known that P. maculatus cercariae will undergo periodic
contraction and elongation after escaping from Mytilus edulis and
" effects a serpentine but random progress upon the substratum "
(Uzmann, 1953). Although it has well-developed suckers, it seldom
utilizes these. Uzmann has also reported that they " do not manifest
any pronounced taxes. . . " but the specific experiments performed were
not reported.
Physiology. Nothing is known about the physiology of P. maculatus
other than their better survival rate at low temperatures.
Pathology. The ability of Mytilus edulis to survive parasitization by
P. maculatus has not been examined under controlled conditions
although Uzmann believes that their longevity is impaired. He has
stated that : " The severe intensity of the parasitism suggested that
C. milfordensis (= P. maculatus) infections are probably lethal under
temporary or sustained periods of ecological conditions unfavorable to
the host. "
The reproductive system of Mytilus edulis consists of a racemose
complex of follicles and ducts which ramify throughout the visceral
mass and mantle lobes. Just prior to spawning, the system is greatly
swollen and occupies the mantle lobes. In parasitized specimens, what
Uzmann refers to as a '( blocking layer ) ) of sporocysts develops in the
vascular system and causes a serious reduction in the efficiency of
circulatory system, including that of the mantle, and thus precludes