HABITAT SELECTION BY AQUATIC INVERTEBRATES
301
Patiria miniata (Brandt) in southern California. Podarke from Puget
Sound responded similarly to a number of non-host animals, i.e. the
response was not specific, while Podarke from southern California showed
a specific response to their normal host there, Patiria miniata. Hickok
and Davenport (1957) also undertook some preliminary experiments
with another commensal polychaete, Arctonoe fragilis (Baird), which is
recorded from a number of host species of asteroid in the same geographical area. Here, when commensals from three separate host species
were tested, each preferred its own host. The problem is obviously
complex and needs further investigation.
Commensals that have a number of hosts are not common. However, their host relationships pose interesting questions since once
they have met their host, individuals might remain there for the rest
of their life or from time to time move to new hosts of the same (Simon,
1968a), or of a different, species. It is also possible that if they do this
they may spend some time as free-living individuals (Caullery,
1952, p. 10; Gage, 1966a). Hickok and Davenport (1957) have
compared the host preferences of Podarke pugettensis that are
commensal with the starfish Luidia foliolata with those of free-living
members of the species where both types of animal came from the same
geographical area. The commensal individuals easily found their host
in a large container of sea water while the free-living ones did not.
Investigation of problems similar to this will undoubtedly lead to a
fuller appreciation of how commensal relationships arise.
If a commensal can live with more than one species of host (Hickok
and Davenport, 1957; Gage, 1966a;) one should consider whether its
relationships are equally successful with each host species. Unfortunately, nothing is known of this problem in commensal
relationships, but Carton (1964, 1967) has considered the same
problem in his investigation of parasitic copepods. Stellicola clausi
(Rosoll) is an external parasite of the starfishes, Marthasterias glacialis
(L.) and Asterina gibbosa (Pennant). Its morphology is slightly
different when on each host, but not enough to justify species status.
Carton (1964) removed females from their respective hosts and then
replaced them either on to their own or the other host species.
Females from both host species lived longer on their natural host. I n
a later paper Carton (1967) transplanted the parasitic copepod,
Sabelliphilus sarsi Claparkde from its normal host Spirographis
spallanmni Viviani to two other sabellids on which it never occurs,
Sabella pavonina Savigny and Spirographis spallanzani var. brevispinu
Quatrefages. The parasite is eventually rejected after a series of tissue
reactions that culminates in the formation of tt scab around it. Kearn
301
Patiria miniata (Brandt) in southern California. Podarke from Puget
Sound responded similarly to a number of non-host animals, i.e. the
response was not specific, while Podarke from southern California showed
a specific response to their normal host there, Patiria miniata. Hickok
and Davenport (1957) also undertook some preliminary experiments
with another commensal polychaete, Arctonoe fragilis (Baird), which is
recorded from a number of host species of asteroid in the same geographical area. Here, when commensals from three separate host species
were tested, each preferred its own host. The problem is obviously
complex and needs further investigation.
Commensals that have a number of hosts are not common. However, their host relationships pose interesting questions since once
they have met their host, individuals might remain there for the rest
of their life or from time to time move to new hosts of the same (Simon,
1968a), or of a different, species. It is also possible that if they do this
they may spend some time as free-living individuals (Caullery,
1952, p. 10; Gage, 1966a). Hickok and Davenport (1957) have
compared the host preferences of Podarke pugettensis that are
commensal with the starfish Luidia foliolata with those of free-living
members of the species where both types of animal came from the same
geographical area. The commensal individuals easily found their host
in a large container of sea water while the free-living ones did not.
Investigation of problems similar to this will undoubtedly lead to a
fuller appreciation of how commensal relationships arise.
If a commensal can live with more than one species of host (Hickok
and Davenport, 1957; Gage, 1966a;) one should consider whether its
relationships are equally successful with each host species. Unfortunately, nothing is known of this problem in commensal
relationships, but Carton (1964, 1967) has considered the same
problem in his investigation of parasitic copepods. Stellicola clausi
(Rosoll) is an external parasite of the starfishes, Marthasterias glacialis
(L.) and Asterina gibbosa (Pennant). Its morphology is slightly
different when on each host, but not enough to justify species status.
Carton (1964) removed females from their respective hosts and then
replaced them either on to their own or the other host species.
Females from both host species lived longer on their natural host. I n
a later paper Carton (1967) transplanted the parasitic copepod,
Sabelliphilus sarsi Claparkde from its normal host Spirographis
spallanmni Viviani to two other sabellids on which it never occurs,
Sabella pavonina Savigny and Spirographis spallanzani var. brevispinu
Quatrefages. The parasite is eventually rejected after a series of tissue
reactions that culminates in the formation of tt scab around it. Kearn