Biología-Marina-Nivel-Intermedio: October 2023

Tuesday, October 31, 2023

Assignment Mollusks: What determine a snail´s size before reproduction?

Goal: Design an experiment that will provide information about how smails detect the presence of crayfish in their water.

Biologists studying snails found that the size of a particular species of snail reaches before beginning reproduction depends on the environment. If the water in which the snail lives comes from an area in which snails were prayed on by crayfish, the snail grows to be about 10 mm in length before reproducing. If the water comes from an area containing only snails, only crayfish, or only crushed snails, the snail grows to a length of only about 4mm before reproduction.

Analysis:

Biologists know that larger snails are not eaten by crayfish. Growing large quickly before reproducing has survival value for the snail because it then will not be eaten by the crayfish. How might the young snail detect the presence of crayfish in the water?

Thinking Critically: Design an experiment that will provide information about how smails detect the presence of crayfish in their water.

Monday, October 30, 2023

Observation of the reproductive system of sea urchins

The sea urchin is an animal that was related to the starfish. Some people have described the sea urchin as a round thing that looks like a pincushion. The fertilization of sea urchin eggs takes place outside the sea urchin's body. This is how we can collect eggs and sperm from sea urchins and observe in the laboratory how fertilization is carried out. We will also be able to observe how the zygote of the sea urchin divides, as well as the early stages of its development.

Fauna, Mares, Sea Creatures, Under The Sea, Starfish, Ocean, Plants ...

MATERIALS:

Sea urchin eggs and sperm are in separate containers.
Sea urchin zygotes
Compound Microscope
Slides,
Coverslips,
Excavated Slides,
Dropper

METHOD

PART A: Observation of eggs and sperm

1. Place a drop of sea urchin egg suspension on an excavated slide. Look through the microscope at the eggs with the lowest magnification objective. Make a multi-egg outline. When you're done with your drawing, save the preparation for later use.

2. Place a drop of sea urchin sperm suspension on a flat slide. Protect it with a coverslip. Look through the microscope at the highest magnification of the preparation. If you can't clearly see the sperm, adjust the lighting through the diaphragm until it looks more accurate. If the cells you see are moving, you can be sure that you are looking at live sperm.

PART B: Fertilization

1. To the egg preparation you did in part A of point 1, add a drop of sperm suspension. Look through the microscope with the lowest magnification objective of the mixture of the two suspensions. Look carefully at an egg and focus your attention on the sperm around it. How can you tell when the egg has been fertilized?

PART C: Observation of eggs and sperm

1. Prepare excavated slides using fertilized egg suspensions given to you by your master. Examine them under the microscope with the lowest magnification objective and look for various phases of their development. Compare the phases you encounter in your preparation using the drawings in the figure.

2. Look at various egg suspensions and try to find as many phases of sea urchin embryo development as you can. You may need to observe these suspensions on the second day.

Almost all sexually reproducing organisms have sperm and eggs. These two cells join together during fertilization and form a zygote. These are cells and processes that you've observed in the lab. Why is the egg fertilized by a single sperm? In fact, more sperm are produced than eggs. The moment the first sperm penetrates the egg, a membrane is formed around it, called a fertilization membrane, and prevents another sperm from entering the egg. The zygote divides into two cells, which in turn form four, and so on. These divisions are made by mitosis. Based on what you know about mitosis, what must be happening inside the nucleus of each of these cells before they divide? How can you prove that your idea is correct?

From Biología: Modelos y procesos

Harold G. Liebherr

Marine Invertebrate: Ribbon Worms

Also called Nemertean worms, ribbon worms can reach great lengths of at least 160 ft (50 m), although many are small and inconspicuous. While they are commonly slightly flattened, the longest are cylindrical and are often called bootlace worms. The majority of ribbon worms live in the sea under the rocks, among undergrown or in sediment, and some are parasitic. A few species live inside the shells of mollusks and crabs.

Nemertean worms have long, unsegmented bodies with strong muscles in the body wall that can shorten the worm to a fraction of its full length. Unlike flatworms, ribbon worms have blood vessels and a complete gut with mouth and anus. It is often difficult to distinguish between the front and rear end of the worm, but most species have many simple eyes at the front. The most characteristic feature of these worms is a strong, tubular structure called a proboscis that lies in a sheath above the gut. It can be thrust out by hydrostatic pressure, either through the mouth or a separate opening, and is used to capture prey. In some species, the probiotic is armed with a sharp styler.

Most marine ribbon worms have separate sexes and their numerous, sample gonads produce either eggs or sperm. These are usually shed into the sea through pores along the sides of the body. Some species cocoon themselves together in a mucous net where the eggs are duly fertilized. In some types of ribbon worms, the eggs develop directly into juvenile worms, while others initially hatch into juvenile worms, while others initially hatch into various types of larvae. The long, fragile bodies of ribbon worms tend to break easily but they have the useful ability to regenerate any lost parts. Some species even use regeneration as a method of asexual reproduction, where the body breaks up into several pieces and each piece develops a new head and tail.

From Ocean: American Museum of Natural History

Facts: Marine Flatworms

Saturday, October 28, 2023

Marine Worms: Flatworms, Round Worms, Ribbon Worms, and Segmented Worms

MARINE INVERTEBRATE

LESSON 3 MOLLUSKS

MARINE WORMS

Wednesday, October 25, 2023

El primer vídeo de un calamar gigante cazando en las profundidades del o...

North Atlantic giant squid are the largest living invertebrates in the world. They reach a size of up to 18 meters long. They can weigh metric tons. Squids possess a highly developed nervous system and a complex brain. Their eyes work just like the eyes of humans. From the squid's head extend long tentacles resembling the octopus's arms. Octopus and squid are members of the phylum Mollusca of the Animal Kingdom.

Language integration: Spanish

Los calamares gigantes del Atlántico Norte son los invertebrados vivientes más grandes del mundo. Alcanzan un tamaño de hasta 18 metros de largo. Pueden llegar pesar toneladas métricas. Los calamares poseen un sistema nervioso muy desarrollado y un cerebro complejo. Sus ojos funcionan igual que los ojos de los humanos. De la cabeza del calamar se extienden largos tentáculos parecidos a los ¨brazos del pulpo. El pulpo y el calamar son miembros del filum Mollusca del Reino Animal.