THE STEINHART AQUARIUM - Gulf of Guinea Science ...

58 A Docent Field Guide to the Species of the Steinhart Aquarium
one exception; however, these anemones
regurgitate if they consume the digestive
gland. Sea hares live one year or less.
Remarks: When alarmed, sea hares exude a
dark purple fluid which gets its color from a
pigment in the red algae in the slug’s diet.
Due to its large nerve cell bodies (in the peripheries
of the 9 major ganglia linked by
nerve fiber tracts), the sea hare has become a
darling of researchers relating overt behavior
of animals to the structure and function of cells
and the cellular network.
CLASS BIVALVIA AKA
PELECYPODA
California Mussel
Mytilus californianus (Mytiloidae)
Distribution: Aleutian Islands, Alaska to
Southern Baja California.
Habitat: Abundant clusters attached to substrate
and each other with byssal fibers in
massive beds. Low intertidal to 40 m deep.
Common in surf-swept rocky areas.
Appearance: Shell length typically to 13 cm (25
cm in some subtidal areas). Blue-black exterior,
sculpted with ribs and irregular growth lines.
Diet: When submerged, filter-feed nearly continuously
on detritus particles and plankton
(esp. dinoflagellates).
Reproduction and Development: Separate
sexes; broadcast sperm or eggs into the sea
where fertilization occurs. Spawn November–
May. Larvae are free-swimming ~ 4 weeks.
After settling and attachment, grows to full
size in about 3 years.
Mortality/Longevity: Preyed on by sea stars,
in our area, esp. the ochre sea star (Pisaster
ochraceus), snails, crabs, birds, and humans.
They create mussel beds—coastal areas densely
covered with mussels—which provide habitat
for many small worms and crustaceans.
Sea otters have devastated formerly extensive
mussel beds in Monterey Bay.
Crocea Giant Clam
Tridacna crocea (Tridacnidae)
Distribution: Malay Peninsula to Australia,
New Guinea, Indonesia, Philippines, Okinawa,
Fiji and Guam.
Habitat: Lives within small cracks on shallow
reef flat corals. This species is a “small” giant
clam; maximum length is 10 cm. Valves have
very short fluted concentric sculpture on the
tests.
Diet: Filter feeds but majority (perhaps approaching
90%) of nutrition is a result of the
activities of endosymbiont zooxanthellae.
Reproduction and Development: Uses valves
of shell to bore into substrate.
Conservation status: Not yet on the IUCN Red
List. Exploited by humans as a food source.
Remarks: The colorful pigments in the mantle
tissue probably reduce light intensity to
protect zooxanthellae.
Giant Clam
Tridacna derasa (Tridacnidae)
Distribution: Cocos Keeling atoll to Australia;
Fiji, Solomon Islands, New Guinea, Palau,
Indonesia and Philippines.
Habitat: Quiet waters, often associated with
sandy or silty habitats in shallow reef flats.
Some occur deeper, to 30 m in clear water.
Appearance: Unmistakable, the common
name says it all. Tridacna derasa is second largest
species in genera, length to 50 cm. T. gigas
is the largest (to 1.37 m) bivalve in the world.
T. derasa weigh to more than 500 kg. Mantles
are typically mottled deep blue, green or turquoise
due to pigments that probably reduce
light intensity.
Diet: Intercellular symbiotic zooxanthellae
photosynthesize and produce food for their
host clam. The gape of all tridacnids is directed
upwards, allowing maximum exposure
to sunlight for their algal symbionts. Like
most bivalves, a giant clam pumps water and
planktonic items into its mantle cavity with its
incurrent siphon. This allows for filter feeding
with its elaborate gill structures, as well as gas
exchange. Expels with its excurrent siphon.
Reproduction: Broadcast spawners; release
sperm and eggs into open waters. Fertilized
eggs develop into planktonic larvae that settle
and attach with byssal threads to the substrate.
Mortality/Longevity: Humans have harvested
this tasty bivalve for years. The giant clam
Tridacna gigas is reputed to live to 200 years.
Conservation Status: Rare in many areas
due to overharvesting as a food for humans.