April 2004 Unknown

THIS MONTH'S WINNERS:

April's contest had a near-record number of entrants. Almost all submissions recognized our unknown as a centric diatom, but only three placed it in the correct genus. Among the genera of similar diatoms submitted were: Stephanodiscus, Cyclotella, Actinoptychus, and Conscinodiscus.- close guesses, but not the accurate identification. The three prize winners for this month are:

Katherine Courtney Moorpark College California

Brian Raygor J.M. Bennett High School Maryland

Gina Stephens Teacher in training University of Maryland

Please note: Prize winners are now drawn each month from the total pool of correct answers for that month.

Thanks to all of those who submitted an entry to this contest.

Good luck this month!

A Wheel of Glass - Arachnoidiscus ehrenbergi

Arachnoidiscus ehrenbergi is a large centric diatom sometimes reaching almost a milimeter in diameter. In both the scanning electron micrograph (left) and in transmitted light micrograph (right), you can clearly see the strong radial ribs which distinguish the genus from other genera such as Coscinodiscus. Diatoms are a type of algae, a general catagory now recognized as containing several distinct taxonomic groupings. Diatoms live as single cells or in chains linked together. One distinguishing feature of the group is the protective covering, or frustule, made of silicon dioxide which the individual cells secrete by collecting silica ions out of the water. Diatoms live in both freshwater and in the oceans. Arachnoidiscus ehrenbergi is fairly common in the Pacific Ocean.

In this scanning electron micrograph, you see both the inside and outside of the frustule. Note the pennate diatom sitting on top of the top frustule half.

Our new video, The Biology of Algae, and DVD -Branches on the Tree of Life - Algae, provide excellent resources for teaching about diatoms and other types of algae, and for teaching about the evolutionary relationships among this diverse collection of organisms.

 

For a concise and revealing teaching video about Arthropods, get our video/DVD: Branches On the Tree of Life: Arthropods. For a rich overview of marine intertidal ecology, see our program: The Biology of Seashores.