Cabrillo Aquarium Exercise: The Invertebrates
Directions to the Cabrillo Marine Aquarium, San Pedro:
From PIERCE take the San Diego Freeway south to the Harbor (110) Freeway - San Pedro.
Continue on the Harbor Freeway south, take the Catalina exit/Harbor Blvd (towards Vincent
Thomas Bridge). Turn right at the end of the offramp and take Harbor Blvd. all the way to 22nd
St. Turn right on 22nd and then left on Pacific Ave (second traffic light). Take Pacific Ave with
Fort Mac Arthur on your left to 36th street. Turn left onto Stephen White Drive and follow curve
to right to Cabrillo Beach. There is limited free parking along the street or pull into the lot at the
Aquarium for hourly parking. Weekdays during the winter parking is (was?) free. The
aquarium is open at 10am to 5 pm Tuesday though Sunday in September. Starting in October the
hours are 12 - 5pm Tuesday through Friday and 10 am - 5 pm weekends. The aquarium is closed
on Mondays. The number is 310/548-7562.
What to do before going.
Read over this exercise and look up each group of organisms in your text. By first reading and
studying the organisms you will better benefit from the aquarium visit and be able to complete
the exercise more quickly.
What to do once you are there:
On arrival obtain a Visitor=s Guide from the information desk. This has a map and a listing of
the major exhibits. In the exercise that follows I reference the exhibit by its name in bold italics
to make it easier for you to locate the information.
For each of the organisms look at the exhibits indicated and list the genus of the organisms
that belong to the group described after Aexamples:@.
Breakfast/Lunch/Dinner. I recommend the Lighthouse Deli on the corner of Pacific Ave. and
39th St. Just 3 blocks toward the water past Stephen White Drive.
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Sponges (Phylum Porifera)
The body is covered with a perforated Askin@ (epidermis) and body penetrated by
numerous small channels forming the body cavity (spongocoel). Channels lined with flagellated
Acollar@ (choanocyte) cells. Feeding is accomplished by creating a current with flagellae
(microscopic Awhips@) of collar cells that draws water in through skin and through channels
where food is trapped by the collar cells. The prey is primarily phytoplankton, bacteria and
detritus. Sponges are found mostly in dark areas: beneath rocks, and in caves due to poor ability
to compete with faster growing alage for space. Exception is in the tropics where the grazing
pressure from fishes on algae allows the less palatable sponges to persist in lighted areas.
Animals That Look Like Plants, Filter Feeders
- examples:
Jelly fish, Aemones, Corals, Sea fans (Phylum Coelenterata/Cnidaria)
All have radial symmetry and possess primitive gut or gastrovascular cavity. Two body
forms possible: medusa: swimming bell with tentacles on edges or margins of bell or polyp:
benthic (attached) column with tentacles surrounding mouth, attaches with a bottom or pedal
disc. Tentacles surround the mouth and are used for prey capture and defense. The stinging cells
on the tentacles are called nematocysts and work even when the tentacles are detached from the
animal (Stinging Tentacles) may form or of both medusae and polyps. Some attached (benthic)
on hard bottoms (anemones, corals, sea fans), some anemones are infaunal (burrow into soft
bottoms), jellyfish and most siphonophores are planktonic. Dispersal is by planktonic planula
larva and medusae, budding for rapid exploitation of resource (space).
Hydroids (Class Hydrozoa)
Hydroids are small and soft bodied with multiple anemone-like polyps on a common
branching structure - some eresmble feathers. They feed on microscopic plankton by passive
suspension feeding. The siphonophores colonies of medusae and polyps together.
At The Mercy of Currents
- examples:
True Jelly Fish (Class Scyphozoa)
The swimming bell or medusae dominant life phase with long feeding tentacles for prey
capture.
Moonjellies, Plankton
- examples:
Sea Anemones, Hard and Soft Corals, Sea Pens, Sea Pansys (Class Anthozoa)
All have are polyps attached to hard surfaces or burrowed into mud/sand. Solitary
(anemones, cup-corals) and colonial forms (stony coral heads, branching corals) are common.
The corals have a skeletal cup (theca) of either CaCO3 (stony corals) (House Builders) or softer
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organic materials (sea fans). Many anemones and corals have microscopic lage, the
zooxanthellae, which provide the animals with sugar for growth in exchange for a place to live
and nutrients (above Plant-like Animals).
A Mudflat Metropolis
Plantlike Animals
To left of Tidepool Animals (in chainlink enclosure) and in Territorial Fish
Stinging Tentacles
- examples:
Clams, Snails, Octopus, Chitons, Tusk Shells (Phylum Mollusca)
The body can be separated into three component parts: (1) the foot: used for
locomotion/attachment, can be extended from shell if present; (2) the visceral mass: contains the
organs, located above (dorsal to) the foot; and (3) the mantle: skin (membrane) surrounding the
visceral mass to form the mantle cavity, possesses glands with which to secrete the shell.
Reproduce sexually with either separate sexes or hermaphroditically (have both male and female
sex organs). Dispersed by a free swimming veliger larvae. There are six classes in total, althoug
we will examine only five. Classes: Ampineura, (Monoplacophora), Scaphopoda, Pelecypoda,
Gastropoda, Ceplalopoda
Chitons (Class Amphineura)
The shell consists of 8 articulating (jointed) plates held in place by a fleshy girdle. There
is no distinct head, only a mouth. Locomotion is by a muscular foot. Mostly grazers that feed
with a file-like radula.
Across from Plantlike Animals in the display case beneath Seaweeds
Borers on Rocky Shores
- examples:
Snails, sea slugs, nudibranchs (Class Gastropoda)
The snails have shells and distinct heads with Aeyes@ and tentacles. They may have gills
or "lungs", but in the nudibranchs, which lack a shell, the gills are exposed on their dorsal
surfaces (backs). In the sea slugs the shell is small and internal. All have a file-like toungue
called a radula which used for either grazing algae or boring into shells of prey.
Predators of Plantlike Animals
Predatory Snails Bursa
below Diets of Stars
Seashore Vegetarians
Meals in the Mud
- examples:
 archaeogastropods: (limpets and abalone) simple shell lacks spiral

neogastropods: spiral shells, many predators (welks)
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
sea slugs and nudibranchs: shell internal or lacking, gills in mantle fold or on dorsal
surface, distastful and often with warning coloration, some incoorporate nematocysts
from ingested cnidarians
Tooth or Tusk Shells (Class Scaphozoa) Note: may not be able to find
Tusk -like shells of- live buried in sand/mud.
-examples:
Clams, Oysters, Mussels, etc. (Class Pelecypoda/Bivalvia)
Members of this group lack heads and the foot is adapted for digging into mud/sand in
most. The shell composed of two hinged valves. The mantle may form a siphon or tube to
surface in the infaunal species. Oysters and rock scallops cement one of the valves to a rock.
Mussels attach to the surface of hard surfaces with a byssus or Abeard@. All are active
suspension feeders. Pearls are formed when foreign objects are introduced between the shell and
the mantle tissue.
Buried Alive
Animals That Bore
- examples:
 clams: burrow into substratum - mud to rock

oysters/scallops: one valve attached to substratum - large adductor muscles to hold
valves closed

mussels: byssus to attach - ribbed with inflated shell to live on surface
* pholids: bore into hard substratum with acidic secretions and shell
Squid, Octopus, Cuttlefish, Nautilus (Class Cephalopoda)
The cephalopods are highly motile and voracious predators that use tentacles and a
powerful parrot-like beak to attack their prey. The body is a bag or tube that is inflated with
water to form a hydrostatic skeleton, that is water under pressure like in a baloon. The head is
surrounded by strong sucker covered tentacles. Movement by jetting action as water is shot out
of the body cavity. All are capable of dramatic color change by use of special organs called
chromatophores. Octopus have been shown to be capable of considerable learning.
Octopus, Adaptable Cephalopods (across from Fish Divesrity)
- examples:
* octopus: use beak and/or drilling for prey capture
 squid: swim with finlets and jetting
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* nautaloids: chambered shell used for buoyancy control
Lobsters, Shrimps, Crabs, Barnacles, Sowbugs, Sand Crabs, etc. (Phylum Arthropods, Class
Crustacea)
All crustaceans have a hard external skeleton (exoskeleton) with jointed (articulated) legs,
swimming appendages, and antennae. Mouth contains crushing plates or mandigble. Must shed
skeleton to grow in a molting cycle. In most species the abdomen is straight, liek a shrimp,
hoever in the crabs it is small and folded up underneath the thorax (chest-like area). Reproduce
sexually with separate sexes, females hold eggs (brood) on abdomen until eggs hatch. Dispersal
by several planktonic larval stages.
Copepods (Subclass Copepoda)
Small (1/4 inch) and shrimp-like with long antennae used for swimming. Planktonic
grazers on phytoplankton; very abundant: lowest consumer on food chain of pelagic (water
column). Some are parasitic on fish.
To Left of Hunters of Rocky Shore, The Twilight Zone (across from Plankton)
- examples:
Barnacles (Subclass Cirripedia)
Described as "nothing more than a little shrimp-like animal standing on its head and
kicking food into its mouth"
The small organisms settle from plankton on their heads and cement to the substratum.
They then secrete CaCO3 plates around the body to form familiar Ashell@. Active suspension
feeder uses hair-like cirri on "legs" to filter planktonic food (Filter Feeders - External Filter and
to left of Sandy Beach tank). Gregarious settlement important for survival and reproduction.
They are simultaneous hermaphrodites practicing reciprocal insemination.
Filter Feeders
- examples:
Isopods, Pillbugs (Order Isopoda)
Represented on land by Asow bugs, or pill bugs@. Most are small and scavange on dead
organisms. A few are parasitic on fish and will readily clean the bones.
To Left of Hunters of Rocky Shore
- examples:
Amphipods (Order Amphipoda)
Small (1/4 inch) shrimp-like creatures found in very large numbers in algae on the
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bottom. Rise up in the water column at night to form the demersal zooplankton which are an
important food of corals. They are also a large part of the diet of bottom Apicker@ fish. They
also act something like like piranas in that they will clean the bones of a dead fish clean
overnight.
Life in Death
To Left of Hunters of Rocky Shore
- examples:
Euphausids, Krill (Order Euphausidacea)
Shrimp-like creatures that are very abundant in areas of hogh productivity, especially in
Antarctica. An important part of the diet of many baleen (suspension feeding ) whales.
The Twiligth Zone (across from Plankton)
- examples:
Shrimps (Suborder Natantia)
A familiar form to all. These demersal creatures feed for the most part on bottom
particulate detritus (pieces of decaying matter) which they pick up with their numerous clawed
legs. The large abdomen coupled with the fan-like tail (telson) is used in a Atail flick) escape
response from predators.
In Octopus tank
Cleaners of the Rocky Shore - Sensible Solutions
Crustaceans
- examples:
Suborder Reptantia
The 1st pair of legs powerful chelipeds (claws)
Lobster, Crayfish (Section Macrura)
These elongate animals have very large abdomens for a strong escape response. They
possess large claws (chelae) which along with the mandilbles are used to crush clams and snails.
The spiny lobster lacks claws.
Crustaceans
- examples:
True Crabs (Section Bracyura)
The body is wider than long and the abdomen is folded beneath. Large chelae (claws) are
used to crush clams and snails, and in the swimming (blue) crabs, to cathc fish.
To left of Hunters of the Rocky Shore
- examples:
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Sand Crabs, Hermit Crabs, Ghost Shrimp (Section Anomura)
These egg-shaped relative of crabs have the abdomen flexed sometimes but not reduced
in size. The sand crabs burrow into the sand and suspension feed (to left of Sandy Beach Wave
tank)with their antennae while the hermit crabs occupy the shell of a snail (Sensible Solutions)
and scavange on algae and detritus. Ghost shrimps form large burrows in muddy bottoms and
deposit feed (Burrowers and Tubewellers).
To left of Hunters of the Rocky Shore
- example:
Sea Urchins, Sea Stars, Sea Cucumbers, Sea Lilies, Sand Dollars, Brittle Stars (Phylum
Echinodermata)
All of the echinoderm groups have a pentamerous (5-part) radial symmetry and all except
the sea cucumbers have hard internal calcareous skeleton. The surface may have bumps or
spines. Movement and prey capture for most is with the water-vascular system: a series of
internally connected tubes that connect to sucker-like tube. Fertilization is by simultaneous
release of sperm and eggs into the water, dispersal is by a planktonic pluteus larva.
Sea Stars (Class Asteroidea)
The body consists of a central disc with radiating arms or rays in multiples of 5. Tube
feet project for movement and prey capture. One of two stomachs may be everted from the
mouth to digest prey outside of the sea stars body (to left of Tidepool Animals). Sea stars locate
prey by specialized tube feet at ends of rays to "smell" (chemoreception) slow moving and sessile
prey (limpets, barnacles. Sea stars also have amazing regenerative abilities (Powers of
Regeneration, next to Diets of Stars).
Predatory Seastars
- examples:
Brittle Stars (Class Ophiuroidea)
The brittle stars have a central disc with thin arms that autotomize (break off) easily.
They move away from light to the protection of crevices and undersides of rocks by negative
phototaxis. Arms with fine spines are typical of suspension feeders; smooth arms typical of
deposit feeders.
Diets of Stars
Nonpredatory Echinoderms
- examples:
Sea Urchins, Heart Urchins, Sand Dollars) (Class Echinoidea)
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The plates are fused to form a spherical to pancake-like shell or test; spines articulate and
may be large. Movement is by either tube feet or by spines. These animals have well developed
chemosensory ability and a specialized five-beak jaw called an Aristotle's lantern.
Nonpredatory Echinoderms
In Bed With Sand Dollars
- examples:
Sea Cucumbers (Class Holothuroidea)
This group has a leathery skin with very small skeletal plates. They lie on their sides or
occupy holes in the substrate. The mouth is surrounded by feeding tentacles fow either scouping
up sediment or suspenskion feeding. Many are have with toxic skin for defense. If disturbed will
change shape and may eviscerate (spew guts out their mouth).
Nonpredatory Echinoderms
- examples:
Sea Lilies (Class Crinoidea) Note: No examples
This is the oldest and most primitive class of echinoderms. They have a stalk and they
move and attach with numerous claw-like cirri. Several feathery appendages are directed
upwards to suspension feed on plankton.
- examples:
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