Contraction of circular muscles decreases thickness and lengthens the body, contraction of longitudinal muscles increases thickness and shortens the body.d.How does an earthworm’s motion differ from that of a snake and nematode?Earthworms’ motion includes more shortening and lengthening, peristaltic waves, while snakes and nematodes are more undulatory.e.What features of Lumbricus indicate that it is an annelid?Segmentation and bristles (setae).Question 6a.How many setae are on each segment of the earthworm? 8. b. Are they paired? Yes. Question 7 a. How many segments of an earthworm have a heart? 5.
b. Does the ventral nerve cord traverse the entire length of the body? Yes. c. Is the inside of the digestive tract the same from the pharynx to the end of the intestine? Explain. No, there is specialization as crop stomach, etc. d. How could absorption in the intestine be increased without increasing the intestine’s length? Increase the surface area, such as a typhlosole. e. How do the layers of musculature in an earthworm differ from those of a nematode? Annelids have circular as well as longitudinal muscles. f. List two or three features of an earthworm cross section that distinguish the dorsal and ventral surfaces. Position of the nerve cord, position of pairs of setae and nephridia. Question 8 a. What is the difference in general body shape of leeches compared to oligochaetes or polychaetes? Leeches are flat; oligochaetes and polychaetes are cylindrical. b. What function other than feeding do suckers serve? Locomotion. c. Are setae visible on a leech? No. d. Is internal segmentation of a leech as distinct as that of an oligochaete? No, internal segmentation of a leech is greatly reduced. e. Consider objective 1 listed at the beginning of this exercise. How could production of a packetlike spermatophore contribute to the evolutionary success of leeches in their environment? The spermatophore would protect the eggs from the environment, therefore ensuring their survival to adulthood and breeding. Question 9 a. Now that you have examined the unifying characteristics of mollusks and annelids, can you list three or four characteristics that they share with flatworms and nematodes as their close ancestors? Reproductive, body cavity surrounded by mesoderm, and digestive system. b. Draw and label three coelomic body plans and list which of the phyla in Exercise 37 and 38 are associated with each plan. Acoelomate: Platyhelminthes, pseudocoelomate: Nematodes, coelomates: Mollusks, and Annelids.
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- Annelid, Dugesia