THE STEINHART AQUARIUM - Gulf of Guinea Science ...

76 A Docent Field Guide to the Species of the Steinhart Aquarium
black compound eyes set on short eyestalks.
Legs and claws have red and orange bands
with white spots; the dark brown claws
have short spines on the dorsal surface. Max
carapace length: 4 cm.
Diet: Hermit crabs generally feed on detritus
but may scavenge on dead animal and plant
material.
Reproduction and Development: In October,
the females carry their brood of eggs under
the abdominal telson flap. The first brood
hatches in February and March. Adult
females can carry up to three broods with the
last brood hatching in September. The larval
and advanced developmental stages of these
hermit crabs lasts a total of 73 days depending
on temperature.
Remarks: When hermit crabs outgrow their
shells they are vulnerable to predation until they
locate and move into a larger shell.
A point of interest: the holotype of Pagurus
armatus was lost in the Great Chicago Fire of 1871.
Hairy Hermit Crab
Pagurus hirsutiusculus (Paguridae)
Distribution: Alaska to southern California;
Siberia, Japan; common in San Francisco Bay.
Habitat: Intertidal tidepools, gravelly beaches,
and under rocks and algae; more abundant in
protected water. Tolerant of brackish water.
Appearance: Length to 3 cm, but generally
smaller. Antennae grayish brown with white
bands and spots. Walking legs white, often
with blue bands. Body remarkably hairy.
Diet: Generally a scavenger feeing on detritus
and dead animal matter, though also feeds on
seed weed and occasionally takes live prey.
Reproduction and Development: LIke other
crabs, female attaches eggs to her pleopods
(swimming legs), carrying up to 5 broods
through spring and summer. Larvae are
planktonic, metamorphosing through various
stages before settling to the bottom.
Mortality/Longevity: Preyed upon by fish,
primarily sculpins.
Remarks: Unlike most hermit crabs, this species
usually chooses a shell so small that the snail cannot
withdraw its body completely for protection.
When a predator is encountered, the hairy hermit
crab may abandon its shell completely, depending
instead on speed for defense.
Vampire Crab
Geosesarma sp.’vampire” (Sesarmidae)
Distribution: Southeast Asia.
Habitat: Inhabits forests or near running fresh
water. On land, usually make burrows for
hiding and resting.
Appearance: Carapace length: c. 2.5 cm. Small
pincers, similar in size. Pincers and other
appendages tend to be purplish, carapace
variable in color from reddish to blue. Eyes
may be a bright neon orange or red.
Diet: Active during the day; feeds mostly on
insects, alive or dead. May also take other small
invertebrates.
Reproduction and Development: This crab
genus is quite unusual, the only group known
to reproduce in a freshwater environment.
Other crabs, even the few terrestrial species,
must return to salt or at least brackish water
to reproduce; the eggs ultimately hatch
into planktonic larvae that “go to sea” to
metamorphose through a variety of stages
before developing into the adult form. The
mostly terrestrial vampire crab, on the other
hand, has large eggs. The young go through
their larval stages within the egg, and hatch
out as fully developed small crabs. Are being
bred successfully in captivity. Like all crabs,
the female has a wide abdomen where eggs
are cemented and protected until they hatch.
Mortality/Longevity: Life span: 2–3 years.
Remarks: Genus Geosesarma consists of about
40 members, all small terrestrial crabs. The
“vampire crab” was described fairly recently.
The common name seems a reference to the
glowing eyes, reminiscent of the vampires in
old movies.
Another species of Geosesarma from Malaysia
seems to live symbiotically with several species
of pitcher plants. The crab uses the plant as a
safe harbor from predators, and in return drops
its own insect prey and feces that nourish the
plant.
CLASS CIRRIPEDI.A
(BARNACLES AND THEIR KIN)
Acorn Barnacle
Balanus glandula (Balanidae)
Distribution: Aleutian Islands, Alaska to Baja
California.