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10.2 Amphipoda
10.2.1 General Aspects
Amphipoda is a group of malacostracan crustaceans, more precisely an ingroup of
Peracarida, a group characterised by the evolution of extensive brood care with
the aid of a brood pouch (marsupium) found among all the different (adult female)
representatives of the group (e.g., Richter and Scholtz 2001). Other examples of
peracaridan crustaceans besides amphipods include mysid shrimps, wood lice,
and hooded shrimps. The more widespread known forms of amphipods are gammarideans (scuds). Most amphipod species are marine, but several also occur in
freshwater, and some species live on the beach (sandhoppers) or are fully terrestrial (landhoppers) (e.g., Bousfield 2007). In two ingroups of Amphipoda lifestyles that have been interpreted as parasitic have evolved, in Cyamida and in
Hyperiida.
Cyamidans, whale lice, exhibit a dorso-ventrally flattened body shape unusual
for amphipodans, and possess prominent grasping appendages (e.g., Leung 1967).
The overall arrangement with these sub-chelate appendages is distantly reminding
of the arrangement in some parasitic isopods (see below). Cyamidans have been
proposed to be ectoparasites; they cling to the skin of whales and feed on the outer
layer of the whale skin (Seger and Rowntree 2018 and references therein). The
diet might also be supplemented with algae growing on the surface of the whale
(Leung 1976). It is unclear if the whale loses a significant amount of energy by the
cyamidan. They might therefore also be categorised as commensalistic organisms.
In contrast to other organisms that attach to a larger animal, cyamidans lack a
mobile phase of life. The transmission from one host to another, also across species, occurs via direct contact of the hosts (e.g., Wardle et al. 2000; Seger and
Rowntree 2018 and references therein), i.e. their entire life cycle is directly bound
to their hosts.
Hyperiidans are pelagic marine amphipodans usually occurring at greater depths.
They are associated with cnidarian medusae, ctenophorans or tunicates, in some
species also with colonial radiolarians (e.g. Laval 1980; Anderson 1983), or more
general, with gelatinous planktic organisms. Females of some hyperiidan species
bite small holes into the gelatinous body of the host and transfer their offspring into
the holes for further development (e.g., Crossley et al. 2009). Others crawl into the
tunice of salps and consume the entire animal besides the tunic, the latter then being
used as a floating aid and shelter for the offspring. Additionally, the adults use the
planktic organisms as floating aid as their swimming abilities are rather poorly
developed (Laval 1980). Hyperiidans in captivity are known to cling to any larger
planktic organism. Both adults and immatures feed on the host or on the host’s prey,
with the different species differing significantly in their feeding mode. Hence, hyperiidans have an ecological role straddling in the range of phoresy, parasitism, parasitoidism and predation.
J. T. Haug et al.
10.2 Amphipoda
10.2.1 General Aspects
Amphipoda is a group of malacostracan crustaceans, more precisely an ingroup of
Peracarida, a group characterised by the evolution of extensive brood care with
the aid of a brood pouch (marsupium) found among all the different (adult female)
representatives of the group (e.g., Richter and Scholtz 2001). Other examples of
peracaridan crustaceans besides amphipods include mysid shrimps, wood lice,
and hooded shrimps. The more widespread known forms of amphipods are gammarideans (scuds). Most amphipod species are marine, but several also occur in
freshwater, and some species live on the beach (sandhoppers) or are fully terrestrial (landhoppers) (e.g., Bousfield 2007). In two ingroups of Amphipoda lifestyles that have been interpreted as parasitic have evolved, in Cyamida and in
Hyperiida.
Cyamidans, whale lice, exhibit a dorso-ventrally flattened body shape unusual
for amphipodans, and possess prominent grasping appendages (e.g., Leung 1967).
The overall arrangement with these sub-chelate appendages is distantly reminding
of the arrangement in some parasitic isopods (see below). Cyamidans have been
proposed to be ectoparasites; they cling to the skin of whales and feed on the outer
layer of the whale skin (Seger and Rowntree 2018 and references therein). The
diet might also be supplemented with algae growing on the surface of the whale
(Leung 1976). It is unclear if the whale loses a significant amount of energy by the
cyamidan. They might therefore also be categorised as commensalistic organisms.
In contrast to other organisms that attach to a larger animal, cyamidans lack a
mobile phase of life. The transmission from one host to another, also across species, occurs via direct contact of the hosts (e.g., Wardle et al. 2000; Seger and
Rowntree 2018 and references therein), i.e. their entire life cycle is directly bound
to their hosts.
Hyperiidans are pelagic marine amphipodans usually occurring at greater depths.
They are associated with cnidarian medusae, ctenophorans or tunicates, in some
species also with colonial radiolarians (e.g. Laval 1980; Anderson 1983), or more
general, with gelatinous planktic organisms. Females of some hyperiidan species
bite small holes into the gelatinous body of the host and transfer their offspring into
the holes for further development (e.g., Crossley et al. 2009). Others crawl into the
tunice of salps and consume the entire animal besides the tunic, the latter then being
used as a floating aid and shelter for the offspring. Additionally, the adults use the
planktic organisms as floating aid as their swimming abilities are rather poorly
developed (Laval 1980). Hyperiidans in captivity are known to cling to any larger
planktic organism. Both adults and immatures feed on the host or on the host’s prey,
with the different species differing significantly in their feeding mode. Hence, hyperiidans have an ecological role straddling in the range of phoresy, parasitism, parasitoidism and predation.
J. T. Haug et al.