Market squid

Phylum: Mollusca

Class: Cephalopoda

Order: Teuthoidea

Family: Loliginidae

Species: Doryteuthis opalescens

We recently received some fertilized market squid eggs! The market squid is a common cephalopod along the central coast of California. In the spring and fall, huge schools of the squid enter Monterey Bay to spawn. They lay large, communal egg masses on the sandy seafloor and then die.

[image from SeaNet]

Each egg mass consists of groups of eggs contained within a jelly capsule membrane. The eggs themselves contain a large ball of yolk surrounded by a transparent shell. The embryo begins formation through epiboly, where cells at the top of the yolk mass migrate around to the opposite pole, encapsulating the yolk with a layer of cells in the process. The market squid, like other cephalopods, exhibits direct development and will hatch out as a miniaturized adult.

[5/9/13] Several days after we received the eggs, the blastoderm began to differentiate into new structures and bilateral symmetry was developed.

The circular, raised cap on the end of the embryo will give rise to the mantle in the adult animal. The two bulges beneath the developing mantle are the rudimentary eye-stalks, and in their center the early stages of the eye can be seen.

Here, bilateral symmetry can be seen as the embryo rotates within the egg shell. The embryo appears to be ciliated and often moves. The space within the egg shell seems to be filled with a cloudy fluid of some sort.

L. opalescens

[5/10/13] The shape of the forming embryo is even more distinct at this point. The rudimentary arms of the squid can be seen as a ridge or little projections around the center of the embryo beneath the eye stalks.

[5/11/13] The mantle now overhangs the body on both sides, and the eye stalks are much larger. The project of the yolk into the mantle and eye-stalks can be seen clearly. The rudimentary arms are even more distinct at this stage. Newly visible are the inner and outer siphon-folds, which will eventually form the siphon in the adult animal. The siphon-folds are seen as paired, symmetrical ridges of tissue in the center of the embryo between the eye stalks. The presence of the siphon indicates that this will be the ventral side of the adult animal.

[5/12/13] The embryo is much more complex. The arms have elongated and the mantle and mantle cavity (where the gills are forming) are even more distinct. Rudimentary fins can be seen on the surface of the mantle.  The rectum is now present as a raised hollow rod and the free edges of the two inner siphon folds have bent towards each other to form the opening of the siphon. The eye stalks are even more complex and the yolk protuberances no longer entirely fill them. See this diagram.

If you look closely, you can see some sort of contraction in the center of the embryo.

                                      

Arnold, John M., William C Summers, Daniel L. Gilbert, Richard S. Manalis, Nigel W. Daw, and Raymond J. Lasek (1974). A Guide to Laboratory Use of the Squid Loligo Pealei. Woods Hole, MA: Marine Biology Laboratory, 74pp. [x]

Brooks, W. K. Anniversary Memoirs of the Boston Society of Natural History ; Pub. in Celebration of the Fiftieth Anniversary of the Society's Foundation. 1830-1880.Boston: Society, 1880. Web. [x]

-Jacqueline Brockhurst