Introduction
Invertebrates are classified in relation to their lack of backbone or spinal column. A few distinguishing characteristics of invertebrates include distinctive respiratory organs, segmentation, radial and bilateral symmetries, and body organization.
This experiment required us to dissect and examine an earthworm and a squid. The squid’s taxonomic classification derives from the Family Loligindae, Order Teuthoidea, Class Cephaopoda, Phylum Mollusca, and Kingdom Animalia. The earthworm’s taxonomic classification derives from the Species Terrestris, Genus Lumbricus, Family Lambricicdae, Order Haplotaxida, Class Clitellata, Phylum Annelida, and Kingdom Animalia.
The objective of this lab is to dissect and examine the squid and earthworm. During the dissection, we were to detect and recognize any and all major external and internal features and structures of the two species. Also during this lab we were to comprehend and practice fundamental methods of dissection procedures and terminology.
Dissection Methods
Squid
Earthworm
Dissection Results
Photograph 1 – Squid: External Anatomy
Photograph 2a – Squid: Internal Anatomy
Photograph 2b – Squid: Internal Anatomy (Detailed)
Photograph 3 – Earthworm: External/Internal Anatomy
Anatomy and Physiology Discussion
Squid
Squids are soft-bodied cephalopods that are located throughout all the oceans (Project Oceanography, 2001). The mantle of the squid is used to protect the squid’s internal organs and regulate the water flow throughout the body (Project Oceanography, 2001). Contractions of the mantle direct the oxygen-rich waters across the gills in order for the squid to breathe (Project Oceanography, 2001). Harder contractions are utilized to produce thrust and propel the squid throughout its environment (Project Oceanography, 2001). The funnel of the squid is located behind and below the head of the squid and is flexible enough to propel the squid in many directions. The squid also utilizes its fins in order to provide additional lift to finely adjust the position of movement (Hotchkiss, Wilkes, & Ridenour, 2004).
Cephalopods also have the largest brains of all invertebrates and the brain is dominated by the optic lobe (Project Oceanography, 2001). The optic lobe is required to obtain information of its surroundings from the eyes (Project Oceanography, 2001). Similar to the eyes of mammals, the squid also has a lens, retina, iris, and cornea (Project Oceanography, 2001). Located below the head are the mouth, beak, and radula of the squid. The radula is a tongue-like structure with a belt of teeth. Along the radula, mouth, and beak, are the eight arms and two tentacles. The tentacles are used in order to quickly catch their prey and then the arms are used to bring the prey towards the squid and maneuvered into the mouth. Food is then grasped in the beak of the squid and then transported into the throat by the radula. Digestion of food in squids begins in the stomach, with the caecum also preforming some digestions (Project Oceanography, 2001). The stomach then dumps the contents into the intestines and finally the contents are then moved into the rectum and through the anus (Hotchkiss, Wilkes, & Ridenour, 2004).
Squids have three hearts, one at the base of each gill. The gill hearts receive blood that is rich in oxygen from the blood vessels and then pump the blood back into the systemic heart which serves the internal organs and the mantle (Hotchkiss, Wilkes, & Ridenour, 2004).
The skin of the squid is lined with chromatophores which consist of sacks of pigment that can be used to hide or show a given color. These chromatophores are generally used to create patterns that form communication among other squid (Project Oceanography, 2001). For defense, squids tend to squirt ink out of their ink sacs when panicked. This ink also contains a chemical that acts as a warning sign for other squids in the area (Project Oceanography, 2001).
In male squids, sperm is produced in the wall of the testis and are expelled out of the spermatophore into the female mantle cavity or at the base of the buccal cavity (Arkhipkin, 1992). Females produce eggs in the ovary, kept in the proximal end of the oviduct (Arkhipkin, 1992). Eggs usually pass out of the oviduct in clusters and are coated in proteinaceous secretions to aid in fertilization (Arkhipkin, 1992).
Earthworm
Earthworms are invertebrates that belong to the phylum Annelida, class Oligochaeta (Martin, Black, & Hawthorne, 1999). One of the basic requirements of earthworms is that they are required to stay moist in soil to remain active (Martin, Black, & Hawthorne, 1999). Advantages of moist soil include the ability to exchange gasses through a water film on the integument and to allow easier burrowing and movement (Martin, Black, & Hawthorne, 1999). Earthworm use bristle like organs that help them cling on to the slippery surfaces of soils located on the segments of the body (Martin, Black, & Hawthorne, 1999). Each of the segments located on the earthworm serve different functions. Alongside the anterior end of the earthworm are located the mouth and the prostomium. The prostomium is a lobe which acts as a covering for the mouth and is also used to wedge cracks open in the soil to allow the earthworm to crawl (Martin, Black, & Hawthorne, 1999). In addition to the bristle like organs alongside the earthworm, a mucus is secreted via various skin glands to aid in movement throughout the soil (Martin, Black, & Hawthorne, 1999).
The digestive tract of the earthworm is optimized for burrowing and feeding activities (Martin, Black, & Hawthorne, 1999). The earthworm swallows the soil and muscles mix the swallowed materials and pass it into the digestive tract. Enzymes in the digestive tract are then mixed with the materials and release amino acids, fluids, sugars, and other smaller organic molecules (Martin, Black, & Hawthorne, 1999).
Earthworms are hermaphroditic, but they do not self-mate (Martin, Black, & Hawthorne, 1999). A mutual exchange of sperm by two earthworms is required in order to mate. The sperm and egg cells are mixed with nutritive fluid and then deposited in cocoons produced by the clitellum (Martin, Black, & Hawthorne, 1999).
Conclusion
After dissecting and thoroughly inspecting both organisms, the group gained the ability to learn from first hand experiences about the major external and internal features and organs. We also gained the ability to understand and complete basic dissection techniques and terms.
References
Arkhipkin, A. I. (1992). Reproductive System Structure, Development and. Atlanta: J. Northway.
Hotchkiss, N., Wilkes, D., & Ridenour, S. (2004). Squid Lab. Baltimore.
Martin, J. P., Black, J. H., & Hawthorne, R. M. (1999). Earthworm Biology and Production. Gainsville: University of Florida.
Project Oceanography. (2001, Spring). Retrieved from www.marine.usf.edu: http://www.marine.usf.edu/pjocean/packets/sp01/sp01u7p2.pdf
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