Lab Activity 11.1
Planktonic Diatoms and Dinoflagellates


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.


Phytoplankton are planktonic algae such as diatoms and dinoflagellates. These algae are well adapted for living in the open waters of the pelagic environment. They have unique characteristics that allow them to survive in the absence of solid ground. In this lab activity you will examine the characteristics of particular species of phytoplankton that allow them to survive in the open sea.

Top  Instruction

Study the information and the photographs of the various phytoplankton species listed below. Pay particular attention to each species' shape and identifying characteristics. Learn to match each example with its phylum. Write in your notebook about how to tell the difference between diatoms and dinoflagellates and single cells and chains.

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 Chapter 15, pages 325 to 328
Marine Biology Coloring Book Plate 19

Phylum Bacillariophyta (Diatoms)

Diatoms, are the most important phytoplankton in the ocean. Diatoms are usually single celled but often occur in chains of cells. The cell shape of diatoms varies. There are two basic forms. Centric diatoms are radially symmetrical while Pennate types are bilaterally symmetrical. Both types of diatoms have an external cell wall, or theca, composed of silicon dioxide. The theca is usually in two parts, with a slightly larger epltheca fitting snugly over the hypotheca. The cell contents are contained completely within the test. Most diatoms exhibit fine lines on the test surface. These lines are actually rows of very small pores. Exchange across the cell wall occurs through these pores.

Species: Coscinodiscus

Shape: Single, large, checker-shaped cell.

Identifying Characteristics: No spines, tiny pore barely visible on surface.
Species: Ditylum
Shape: Single, large, can-shaped cell.
Identifying Characteristics: Two long spines. Each spine extending from opposite indented end of cell.
Species: Rhizosolenia
Shape: Single, highly elongate cell.
Identifying Characteristics: No spines. Pointed ends.
Species: Nitzschia
Shape: Single, small, spindle-shaped cell.
Identifying Characteristics: Two long spines. Each spine extending from opposite tapered end of cell.
Species: Thalassionema
Shape: Single, highly elongate cell.
Identifying Characteristics: No spines or pointed ends.
Species: Lauderia
Shape: Chain of block-shaped cells.
Identifying Characteristics: No spines. Adjacent cells in contact with one another.
Species: Biddulphia
Shape: Chain of block-shaped cells.
Identifying Characteristics: No spines. Gap between cells. Distinctive strand runs runs across gap between centers of cells.
Species: Stephanopyxis
Shape: Chain of barrel-shaped cells.
Identifying Characteristics: No spines. Gap between cells. Sheath of material runs between cells.



Phylum Pyrrhophyta (Dinoflagellates)

The dinoflagellates are almost entirely marine.They are second only to the diatoms in importance as marine phytoplankton. They have a cell wall composed of cellulose which has a groove around its equator in most species. The equatorial groove contains a flagellum wrapped around it. Another groove perpendicular to the equatorial groove contains another flagellum. The long flagella permits the cells a limited degree of mobility.

Many species of dinoflagellates are bioluminescent and are quite noticeable when disturbed. They glow in the moist sand when disturbed by footsteps. Their glow may also be seen in the wake of a boat and in the crashing waves.

Some species of this division produce strong neurotoxins (poisons that affect the nervous system). When certain environmental conditions are right, a bloom of these algae will occur forming what is commonly called a red tlde. The water is discolored by the dinoflagellates' storage products of oil that are often bright red. Filter-feeding organisms, such as mussels, concentrate these dinofiagellates in their bodies in such great numbers during periods of red tide that they become poisonous. Individuals eating shellfish during the periods of red tide may suffer paralytic shellfish poisoning, which can cause death. The poisons secreted into the waters by these dinoflagellates can also cause death among fish and some fish-eating birds and mammals.

Species: Ceratium

Shape: Single, large, top-shaped cell.

Identifying Characteristics: Three short spines. Distinct groove around middle.
Species: Ceratium
Shape: Single, large, anchor-shaped cell.

Identifying Characteristics: Three long spines. Two of them curving inward. Indistinct groove around middle.

Species: Peridinium
Shape: Single, large, heart-shaped cell.
Identifying Characteristics: Three points. Distinct groove around middle.
Species: Dinophysis
Shape: Single, large, vase-shaped cell.
Identifying Characteristics: Thin fin along one edge of cell. Two stout, extensions near base.

Lab Activity 11.2 Phytoplankton Productivity