THE BIOLOOY OF ASCIDLANS
51
copepods on their host, but the presence of large numbers can scarcely
be without some effect ; Illg (1958) took about 300 specimens of a species
of Doropygus from the branchial sacs of 20 specimens of an ascidian in
addition to 28 amphipods, five polychaetes and two pinnothcrid crabs
from the branchial or atrial cavities. And, according to Gotto (1067),
several individuals of Notodelphys allmuni often inhabit even small
specimens of Ascidiella aspersa. Moreover some of the copepods are
quite large in relation to the cavity they inhabit, and a single specimen
may occupy fully half of the branchial sac (Gotto, 1961). Nevertheless,
the host generally shows no sign of ill effects, and Corella parallelogramma infected with Ascidicola rosea Thorell appeared to survive, feed
and spawn as well aa uninfected specimens (Gotto, 1957). This suggests
B long-established evolution of the commensal species in association
with the host species. Adaptation is evident in the life cycle of this
copepod, for the female bearing fertilized eggs movcs from the ascidian’s
oesophagus to the stomach, where the eggs are deposited and hatch,
but the nauplii retain the inner egg membranes while passing through
the ascidian’s intestine and rectum, being freed from the membranes
only after leaving the anus (Gotto, 1957). An opposite migration by the
ripe females, from the stomach to the branchial sac, occurs in another
ascidicolous copepod, Enteropsis sphinx (Aurivillius), whose nauplii are
presumably released through the oral siphon (Gotto, 1961).
Another adaptation by a commensal is the timing of breeding in
Ascidicola rosea Thorell, which produces its larvae when a newly settled
generation of the host Ascidiella aspersa is established and can be infected at an early stage (Gage, 1966).
Although many copepods live as commensals in ascidians, others
have adopted a more or less parasitic existence, some in cysts within the
tissues or blood vessels, but the life histories are almost entirely unknown (Illg, 1958). One of the most remarkable is Gonophysema gullmarensis Bresciani and Lutzen (Fig. 20), a species living in the body
wall of Ascidiella aspersa, surrounded by a blood space from which the
parasite, lacking both mouth and gut, presumably obtains its nourishment (Bresciani and Lutzen, 1960). Since the average number of
parasites in a host appears to be about three, however, and the size
only from 1-8 mm, little damage may result. The parasite is surrounded
by a thin membrane of host tissue, indicating some reaction on the part
of the ascidian. But the colonial Distaplia unigerrnis Ivanova-Kazas
has no detectable reaction to the presence of parasitic copepods
(Ivanova-Kazas, 1966).
In addition to the Notodelphyidae, the copepod families specially
associated with ascidians either as commensals or parasites are the
A.M.B.--B
3
51
copepods on their host, but the presence of large numbers can scarcely
be without some effect ; Illg (1958) took about 300 specimens of a species
of Doropygus from the branchial sacs of 20 specimens of an ascidian in
addition to 28 amphipods, five polychaetes and two pinnothcrid crabs
from the branchial or atrial cavities. And, according to Gotto (1067),
several individuals of Notodelphys allmuni often inhabit even small
specimens of Ascidiella aspersa. Moreover some of the copepods are
quite large in relation to the cavity they inhabit, and a single specimen
may occupy fully half of the branchial sac (Gotto, 1961). Nevertheless,
the host generally shows no sign of ill effects, and Corella parallelogramma infected with Ascidicola rosea Thorell appeared to survive, feed
and spawn as well aa uninfected specimens (Gotto, 1957). This suggests
B long-established evolution of the commensal species in association
with the host species. Adaptation is evident in the life cycle of this
copepod, for the female bearing fertilized eggs movcs from the ascidian’s
oesophagus to the stomach, where the eggs are deposited and hatch,
but the nauplii retain the inner egg membranes while passing through
the ascidian’s intestine and rectum, being freed from the membranes
only after leaving the anus (Gotto, 1957). An opposite migration by the
ripe females, from the stomach to the branchial sac, occurs in another
ascidicolous copepod, Enteropsis sphinx (Aurivillius), whose nauplii are
presumably released through the oral siphon (Gotto, 1961).
Another adaptation by a commensal is the timing of breeding in
Ascidicola rosea Thorell, which produces its larvae when a newly settled
generation of the host Ascidiella aspersa is established and can be infected at an early stage (Gage, 1966).
Although many copepods live as commensals in ascidians, others
have adopted a more or less parasitic existence, some in cysts within the
tissues or blood vessels, but the life histories are almost entirely unknown (Illg, 1958). One of the most remarkable is Gonophysema gullmarensis Bresciani and Lutzen (Fig. 20), a species living in the body
wall of Ascidiella aspersa, surrounded by a blood space from which the
parasite, lacking both mouth and gut, presumably obtains its nourishment (Bresciani and Lutzen, 1960). Since the average number of
parasites in a host appears to be about three, however, and the size
only from 1-8 mm, little damage may result. The parasite is surrounded
by a thin membrane of host tissue, indicating some reaction on the part
of the ascidian. But the colonial Distaplia unigerrnis Ivanova-Kazas
has no detectable reaction to the presence of parasitic copepods
(Ivanova-Kazas, 1966).
In addition to the Notodelphyidae, the copepod families specially
associated with ascidians either as commensals or parasites are the
A.M.B.--B
3