Lab Activity 9.4
Biota 1: Organisms Found on the Tops of Boulders

  Directions

Study the instructional material below. Be sure to click on each of the photographs for an enlarged view in a separate window. The larger version is necessary to complete the assignment. It opens in a separate window which can be resized by grabbing the bottom right corner and dragging it. It can also be moved by grabbing the top heading bar and dragging it. Be sure to close the extra window by using the X in IBM, or the close box in MAC when you are finished using them.

  Introduction


In this lab activity you will study the organisms on the tops of boulders.

Top  Instruction

Use the information below to fill out the checklist of the biota of boulder microhabitats.

Be sure to write about what you are learning in the lab section of your notebook. You will be expected to answer questions about the lab activity during the lab self test and lab quiz. It helps to have your text and coloring books open beside you for support.

 
Supporting Information
Refer to the Assigned Readings Below:
Marine Biology Textbook none
Marine Biology Coloring Book none
 

This picture gallery summarizes the biota found on top of boulders at Playa Estacion, Puerto Penasco, Sonora, Mexico.

It should be used to complete lab activity 9.4.

 

Ulva rigida

"Sea lettuce"
Division  Chlorophyta
Class  Chlorophyceae
Order   Ulotrichales
Family   Ulvaceae

Morphology Thin, green, membranous blades. Usually lobed and ruffled. Up to four inches in length.
Habitat On rocks in the upper intertidal
Distribution Alaska to Chile and throughout the Gulf of California
Other Competes for space with the barnacle Chthamalus anisopoma

 

Clibanarius digueti
"Red-fingered hermit crab"
Phylum  Arthropoda
Class  Crustacea
Order   Decapoda
Family   Diogenidae
Morphology Red in appearance, has an unexplained olive color phase. Light speckling (blue) over the chelipeds and walking legs, antennaes are bright red to orange, carapace is tan to gray.
Feeding Filter feeders and scavengers
Defense Occupies the shell of a dead snail
Reproduction Separate sexes. Females brood eggs on pleopods until they hatch. April - September, the male gives a chase over a 12 hour period where the female is rotated, jiggled, tickled, and finally, seduced.
Habitat In the mid and upper intertidal zones, sandy short habitats with rock outcrops or shell debris, mangrove swamps, under boulders and rock surfaces.
Distribution Lower Pacific Baja and throughout the Gulf of California
Other Most common hermit crab of the Gulf of California. Gregarious at low tide forming clusters of up to 700 individuals. Disperse when the tide is changing.

 

Chthamalus anisopoma

"Small acorn barnacle"
Phylum  Arthropoda
Class  Crustacea
Order   Thoracica
Family   Chthamalidae

Morphology Volcano shaped shell whitish to gray and composed of 6 overlapping plates with ribbed margins.
Feeding Filter feeding with long feathery legs passed through the water as a basket.
Defense Surrounded by hard shelly plates
Reproduction Simultaneous, cross-copulating hermaphrodites. Hatchlings are nauplius larvae that develop in the plankton.
Habitat Attached to rocks in the upper intertidal
Distribution Central California to and throughout the Gulf of California
Other Most common Gulf barnacle and prey for Acanthina angelica and Heliaster kubiniji

 

Ostrea palmula

"Palm oyster"
Phylum  Mollusca
Class  Pelecypoda
Order   Pterioida
Family   Ostreidae

Morphology White to light blue shell. Highly variable shape. Lower valve with fan shaped edge is cemented to rock surface. Upper valve flat to concave. Two to three inches in diameter.
Feeding Filter feeding
Defense Thick shell that can be held tightly shut is very difficult to prey loose from rock. Palm-shaped lower valve protects the vulnerable edge where the two valves meet making it very difficult to prey the valves apart.
Reproduction Separate sexes and spawning
Habitat On rocks and mangrove roots in the upper intertidal
Distribution Lower Pacific Baja, throughout the Gulf of California, south to Ecuador
Other  

 

Acanthina angelica

"Unicorn shell"
Phylum  Mollusca
Class  Gastropoda
Order   Neogastropoda
Family   Thaididae

Morphology Dull gray, high spire with large nodes below the suture; large spine on outer aperture, purplish-brown to glossy white interior.
Feeding Often occur in large clumps while feeding on barnacles. Apertural spine possibly used to pry open the opercular plates of acorn barnacles
Defense Thick shell
Reproduction Fertilization is internal - females deposit egg capsules under rocks.
Habitat On rocks in mid to high intertidal zone on or near barnacles.
Distribution Gulf of California, Puerto Penasco, Sonora, Mexico.
Other  

 

Serpulorbis margaritaceus

"Large worm snail"
Phylum  Mollusca
Class  Gastropoda
Order   Mesogastropoda
Family   Vermetidae

Morphology Pale brownish tubes wound into a flat spiral. Has no trapdoor (operculum). Diameter 3 inches.
Feeding Fashions a net of mucus strings which traps debris and tiny animals. They may float free in water or be stretched across a crack between 2 rocks, anchored to the snail by only a string. When full, the snail pulls in and eats net and all.
Defense Thick shell with small opening
Reproduction Spawners
Habitat Intertidally on rocks or shells.
Distribution Gulf of California to Southern Mexico.
Other One of a small group of snails that lives cemented to one spot.