The Great Barrier Reef
284
tissues). Examples of sponge-grazing molluscs common on the GBR are spikey chitons (Acanthochitonidae), keyhole- and slit-limpets (Fissurellidae), top
snails (Trochidae), cerithiopsids (Cerithiopsidae), triphoras (Triphoridae) (Fig. 24.1), the majority of cowries
(Cypraeidae) (Fig. 24.5F), side-gilled sea slugs (Pleurobranchidae), and many nudibranchs (Hexabranchidae,
Aegiridae, Dorididae, Discodorididae, Chromodorididae, Actinocyclidae, etc.) (Fig. 24.5G). But there are lots
of other groups of invertebrates that constitute the food
for grazing gastropods apart from sponges. Examples
of hydroid-grazers are top snails (Trochidae) and aeolid
nudibranchs (Flabellinidae, Aeolidiidae, Tergipedidae,
Facelinidae). Examples of hard coral-grazers are coral
snails (Coralliophilidae), wentletraps (Epitoniidae) and
nudibranchs (Tergipedidae). Examples of soft coralgrazers are egg cowries (Ovulidae) and nudibranchs
(Tritoniidae). Examples of bryozoan-grazers are nudibranchs (Polyceridae, Goniodorididae). Examples of
kamptozoan-grazers are nudibranchs (Goniodorididae). Examples of ascidian-grazers are lamellarias
(Velutinidae), bean cowries (Triviidae) and nudibranchs
(Polyceridae, Goniodorididae).
The most remarkable of all these ‘meat’-grazing gastropods are the aeolid nudibranchs (Fig. 24.5H), all of
which feed on cnidarians. After ingestion, the tissue of
their cnidarian prey is separated mechanically by cilia
into digestible material and indigestible stinging cells
(nematocysts), the latter being prevented from firing
through copious volumes of mucus. These stinging cells
are moved (carefully!) along fine branches of the digestive gland by other types of cilia to specialised sacs (cnidosacs; indicated by an arrow in Fig. 24.5H) way out at
the ends of finger-like outgrowths from the dorsal surface of the body (cerata) that otherwise serve for respiration. When a predatory fish takes a bite out of an aeolid,
the nematocyst-loaded cerata are quickly pointed in the
direction of the attacker and the nematocysts are fired
off all at once. So the predator gets a face full of stinging
cells instead of a meal! Aeolids provide the best example
of animals using the defensive structures made by other
organisms for their own defense (kleptoplasty).
The natural progression from grazing other animals
is to feeding upon one’s own kind, and indeed there
are two families of nudibranchs (Polyceridae and
Gymnodorididae) and one family of bubble snails
(Agjajidae) that have members specialising for eating
other sea slugs. This usually involves ingesting the
slug’s body whole.
Instead of grazing ‘meat’ unselectively, some gastropods have become specialised as parasites on specific tissues (like the blood) of their hosts. The best
known ‘blood-suckers’ are pyramidellids (Pyramidellidae) that feed on a range of invertebrate hosts, eulimids (Eulimidae) (Fig. 24.5I) that parasitise echinoderms
(either as ectoparasites or as endoparasites living
entirely in ‘galls’ inside the host) and margin snails
(Marginellidae) that suck the blood of sleeping fishes.
On the GBR, an enormous number of gastropods
actively hunt down mobile prey. Those that prey specifically on polychaetes are cone snails (Conidae, Terebridae), drupes (Muricidae), vase snails (Turbinellidae),
bubble snails (Acteonidae, Aplustridae) and nudibranchs (Vayssiereidae). Mitre snails (Mitridae, Costellariidae) prey only on peanut worms (sipunculans).
Those that prey only on crustaceans are harp snails
(Harpidae), rock snails (Muricidae) and nudibranchs
(Tethydidae). Those that prey only on echinoderms are
helmet snails (Cassidae, Tonnidae) and trumpet snails
(Ranellidae) (Fig. 24.3). Those that only prey on other
gastropods are frog snails (Bursidae), balers (Volutidae)
and cone snails (Conidae). Those that only prey on
bivalves are moon snails (Naticidae) and rock snails
(Muricidae). Those that only prey on fishes are basket
snails (Cancellariidae) and cone snails (Conidae)
(Figs 24.4, 24.5J).
Most species of dove snails (Columbellidae) are carnivorous, eating crustaceans and polychaetes. However,
a few species are scavengers, and, remarkably, two species (one of which, Euplica scripta, occurs on the GBR)
are facultative herbivores, that is, they occasionally eat
algae in addition to their normal diet of crustaceans.
Balers (Volutidae) live on soft substrata, occasionally foraging on hard substrata. They hunt down other
gastropods (like top snails and turban snails, and even
poisonous cone snails) and smother them with their
large foot. Having entrapped the prey, balers often then
‘larder’ them in a special pouch under the foot. This
pouch may contain several gastropods, still alive, that
have been hunted down during a night’s foraging.
284
tissues). Examples of sponge-grazing molluscs common on the GBR are spikey chitons (Acanthochitonidae), keyhole- and slit-limpets (Fissurellidae), top
snails (Trochidae), cerithiopsids (Cerithiopsidae), triphoras (Triphoridae) (Fig. 24.1), the majority of cowries
(Cypraeidae) (Fig. 24.5F), side-gilled sea slugs (Pleurobranchidae), and many nudibranchs (Hexabranchidae,
Aegiridae, Dorididae, Discodorididae, Chromodorididae, Actinocyclidae, etc.) (Fig. 24.5G). But there are lots
of other groups of invertebrates that constitute the food
for grazing gastropods apart from sponges. Examples
of hydroid-grazers are top snails (Trochidae) and aeolid
nudibranchs (Flabellinidae, Aeolidiidae, Tergipedidae,
Facelinidae). Examples of hard coral-grazers are coral
snails (Coralliophilidae), wentletraps (Epitoniidae) and
nudibranchs (Tergipedidae). Examples of soft coralgrazers are egg cowries (Ovulidae) and nudibranchs
(Tritoniidae). Examples of bryozoan-grazers are nudibranchs (Polyceridae, Goniodorididae). Examples of
kamptozoan-grazers are nudibranchs (Goniodorididae). Examples of ascidian-grazers are lamellarias
(Velutinidae), bean cowries (Triviidae) and nudibranchs
(Polyceridae, Goniodorididae).
The most remarkable of all these ‘meat’-grazing gastropods are the aeolid nudibranchs (Fig. 24.5H), all of
which feed on cnidarians. After ingestion, the tissue of
their cnidarian prey is separated mechanically by cilia
into digestible material and indigestible stinging cells
(nematocysts), the latter being prevented from firing
through copious volumes of mucus. These stinging cells
are moved (carefully!) along fine branches of the digestive gland by other types of cilia to specialised sacs (cnidosacs; indicated by an arrow in Fig. 24.5H) way out at
the ends of finger-like outgrowths from the dorsal surface of the body (cerata) that otherwise serve for respiration. When a predatory fish takes a bite out of an aeolid,
the nematocyst-loaded cerata are quickly pointed in the
direction of the attacker and the nematocysts are fired
off all at once. So the predator gets a face full of stinging
cells instead of a meal! Aeolids provide the best example
of animals using the defensive structures made by other
organisms for their own defense (kleptoplasty).
The natural progression from grazing other animals
is to feeding upon one’s own kind, and indeed there
are two families of nudibranchs (Polyceridae and
Gymnodorididae) and one family of bubble snails
(Agjajidae) that have members specialising for eating
other sea slugs. This usually involves ingesting the
slug’s body whole.
Instead of grazing ‘meat’ unselectively, some gastropods have become specialised as parasites on specific tissues (like the blood) of their hosts. The best
known ‘blood-suckers’ are pyramidellids (Pyramidellidae) that feed on a range of invertebrate hosts, eulimids (Eulimidae) (Fig. 24.5I) that parasitise echinoderms
(either as ectoparasites or as endoparasites living
entirely in ‘galls’ inside the host) and margin snails
(Marginellidae) that suck the blood of sleeping fishes.
On the GBR, an enormous number of gastropods
actively hunt down mobile prey. Those that prey specifically on polychaetes are cone snails (Conidae, Terebridae), drupes (Muricidae), vase snails (Turbinellidae),
bubble snails (Acteonidae, Aplustridae) and nudibranchs (Vayssiereidae). Mitre snails (Mitridae, Costellariidae) prey only on peanut worms (sipunculans).
Those that prey only on crustaceans are harp snails
(Harpidae), rock snails (Muricidae) and nudibranchs
(Tethydidae). Those that prey only on echinoderms are
helmet snails (Cassidae, Tonnidae) and trumpet snails
(Ranellidae) (Fig. 24.3). Those that only prey on other
gastropods are frog snails (Bursidae), balers (Volutidae)
and cone snails (Conidae). Those that only prey on
bivalves are moon snails (Naticidae) and rock snails
(Muricidae). Those that only prey on fishes are basket
snails (Cancellariidae) and cone snails (Conidae)
(Figs 24.4, 24.5J).
Most species of dove snails (Columbellidae) are carnivorous, eating crustaceans and polychaetes. However,
a few species are scavengers, and, remarkably, two species (one of which, Euplica scripta, occurs on the GBR)
are facultative herbivores, that is, they occasionally eat
algae in addition to their normal diet of crustaceans.
Balers (Volutidae) live on soft substrata, occasionally foraging on hard substrata. They hunt down other
gastropods (like top snails and turban snails, and even
poisonous cone snails) and smother them with their
large foot. Having entrapped the prey, balers often then
‘larder’ them in a special pouch under the foot. This
pouch may contain several gastropods, still alive, that
have been hunted down during a night’s foraging.