Lab Activity 9.2
Biota 3: Molluscs Found on Beachrock Surfaces

  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 molluscs of beachrock surfaces.

Top  Instruction

Use the information below to fill out the checklist of the biota of beachrock 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 molluscs found on top of beachrock at Playa Estacion, Puerto Penasco, Sonora, Mexico.

It should be used to complete lab activity 9.2.

 

Arca pacifica
"Ark shell"
Phylum  Mollusca
Class  Pelecypoda
Order   Arcoida
Family   Arcidae
Morphology Commonly 3 - 4 inches, dull white, with a toothed hinge extending the length of the shell. Irregular ribbing with V-shaped brown bands. The live shell is often covered with a brown, fibrous frowth and is found anchored to a rock by its byssus threads.
Feeding Filter feeders
Defense Can close its shell to conserve moisture. May also tightly close shell if disturbed.
Reproduction Separate sexes and spawning
Habitat Intertidally to deep water. Specifically: pavement surface
Distribution Scammon's Lagoon, Baja California, and throughout the Gulf, south to Peru.
Other  

 

Chama mexicana

"Mexican jewel box"
Phylum  Mollusca
Class  Pelecypoda
Order   Veneroidea
Family   Chamidae

Morphology Light brown to red shell with two rows of large spines and many smaller ones that break off with age. The shell is variable in shape and has a pinkish interior. The lower valve is cemented to the rock surface. Up to 3.5 inches long.
Feeding Filter feeding
Defense Difficult to dislodge or pry open
Reproduction Separate sexes and spawning
Habitat On intertidal rocks
Distribution Gulf of California
Other Shells serve as a habitat for various species of boring orgainisms.

 

Modiolus capax

"Horse mussel"
Phylum  Mollusca
Class  Pelecypoda
Order   Mytiloidea
Family   Mytilidae

Morphology A swollen orange-brown shell covered with a "beard" of serrated brown hairs distinguishes this mussel from any other. The shell lacks any strong sculpture.
Feeding Filter feeders.
Defense The serrated hairs provide camoflouge for the mussel as well as a place for other animals to grow. Can close its shell to conseve moisture - may also tightly close shell if disturbed.
Reproduction Separate sexes and synchronous spawning
Habitat Intertidally on rocky substrate.Particularly in crevices and cavities in rocks and reefs, where it can avoid the full impact of the surf.
Distribution Northern California to Peru and throughout the Gulf of California.
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  

 

Muricanthus nigritis

"Black murex"
Phylum  Mollusca
Class  Gastropoda
Order   Neogastropoda
Family   Muricidae

Morphology off white shell with dark brown to black spines and a siphonal canal that extends from the anterior of the aperature. Up to six inches long.
Feeding Carnivorous on bivalves and other molluscs
Defense Thick shell
Reproduction  
Habitat On rocks and mud flats in the lower intertidal and shallow subtidal.
Distribution Gulf of California
Other  



Lab Activity 9.2 Biota 2