Makenna Fisher and Tyler Smith Phylum Rotifera Makenna Fisher and Tyler Smith

General Characteristics- Size and Shape Rotifers may resemble squares, circles, and other geometric shapes. While others can have asymmetrical bodies. There is no specific body shape. Rotifers are between 0.004 and 0.02 inches long, they are microscopic organisms. They contain an average of about 1,000 cells for each organism. Scientists have a hard time discovering more about ancient rotifers because their small bodies create poor fossils for study.

General Characteristics- Basic Anatomy The body is divided into four main sections: head, neck, body, and foot. The head supports the cilia, which propel the water into the organism’s mouth. The neck contains a throat-like tube that funnels water into the organs of the rotifer. The foot acts as an oar or spine to give the organism some control over the movement. Rotifers are bound together by thin layers of clear skin, but they also contain a harder shell called a lorica. They are invertebrates, meaning they do not have a spine or a skeletal structure to maintain their form.

General Characteristics- Feeding The jaw of a rotifer is called a trophi. The trophi’s job is to break down edible material in the water. The edible material then funnels through the organism’s body. They survive by eating smaller chunks of organic matter, including plankton and other microscopic organisms. Obviously, rotifers are prey for other animals as well. They are typically consumed by shrimp and other shellfish.

External Features Cuticle: A cuticle covers rotifers external surface. In many species, the cuticle thickens to form the lorica. The cuticle or lorica provides protection, as mentioned earlier. The fluid in the pseudocoelom provides hydrostatic support. But cuticle is the main supportive element. Hydrostatic- The equilibrium of liquids to the pressure exerted by the liquids. Epidermis: The epidermis is syncytial. In this cac plasma membranes are absent between the nuclei. Syncytial- multiple cell fusions of unicellular cells. Head: The head contains the corona, mouth, sensory organs and brain. The corona surrounds buccal field. Buccal field is a large ciliated area. Trunk: The trunk is the largest part of a rotifer. It is elongated and saclike. The anus occurs dorsally on the posterior end of trunk.

Organ Systems Nervous System: Excretory System: Rotifers have a small brain located just above the mastax, which has a bunch of little nerves branching off of it and running through the body The number of nerves throughout the body all depends on the size of the rotifer itself Excretory System: Buccal tube leads to pharynx Salivary glands release digestive enzymes and lubricate food particles Esophagus connects mastax to the stomach Short intestine is connected to the anus by a cloaca Nephridial Duct leads from flame bulb protonephridia The protonephridia is a web of dead-end tubules lacking openings, the ends are called flame cells, it opens up into the bladder. This system exchanges gases and removes nitrogenous wastes through body surfaces.

Habitat Mostly planktonic Found in freshwater environments, although many are also found in water films and droplets within soil. Mainly littoral (meaning they are found near the shore), but have been found at depths of 400 m or greater. About 25 species are colonial. These colonies may be sessile or free-swimming. When observed by scientists, these colony members do not appear to share their resources with each other.

Development and Reproduction After fertilization, eggs develop a multi-layered membranous shell Then attached to substrate or carried by female Some species alternate between parthenogenetic and sexual reproduction Females produce diploid eggs, which develop without fertilization If conditions become less favorable, eggs grow into mictic females which produce haploid ova Ova develop into males Males produce hardy zygotes which hatch into amictic females Parthenogenesis is the most common method of reproduction Male either inserts his copulatory organ into a female cloaca or he attaches to her and injects sperm through her body wall

Behavior Mostly motile and planktonic Move by ciliary movement Also capable of moving by “creeping” along the ocean floor They attach the foot with secretions from pedal glands They then extend their body, attaching their head to the substrate Then they release the foot and use muscle bands to move the body forward Some species are sedentary The pedal glands then release secretions that hold the organism in place.

Ecosystem Roles These organisms play a crucial role in connecting the microbial loop to the food web. The dissolved organic carbon is taken in by the bacteria that the rotifers consume. Meaning a portion of the energy dissolved within the organic matter is returned to the original food web. Essentially, this process gives BACK to the food web, which benefits all organisms within the aquatic system. They may also serve as indicators of water quality. Rotifers are very important basal consumers. In aquatic systems, they consume bacteria, algae, and protists.

References Rotifera. (n.d.). Retrieved March 23, 2017, from http://www.els.net/WileyCDA/ElsArticle/refId-a0001588.html Writer, L. G. (2013, April 18). Characteristics of Rotifera. Retrieved March 23, 2017, from http://animals.mom.me/characteristics-rotifera-4468.html Wright, J. (n.d.). Rotifera (wheel or whirling animals). Retrieved March 23, 2017, from http://animaldiversity.org/accounts/Rotifera/