POSSIBLE ANSWERS FOR TAKE-HOME ASSIGNMENT # 2
INVERTEBRATE ZOOLOGY FALL 1999
DR. W. CRONE (303 FTZ, 629-7439, cronewil@hvcc.edu)
Topic: SPONGES; CNIDARIANS; FLATWORMS; ROUNDWORMS
From Sir Arthur Conan Doyle, The Adventure of the Lion's Mane:
...His back was covered with dark red lines as though he had been terribly flogged by a thin wire scourge. The instrument with which this punishment had been inflicted was clearly flexible, for the long, angry weals curved round his shoulders and ribs. There was blood dripping down his chin, for he had bitten through his lower lip in the paroxysm of his agony. His drawn and distorted face told how terrible that agony had been...
In this adventure of Sherlock Holmes, a bather meets a gruesome fate after an encounter with Cyanea capillata (Fig. 18-14 indicates why it's often called the lion's mane).
The bather met up with a marine organism that contained stinging structures associated with long, flexible delivery. These stings were potent enough to kill him and cause a great deal of pain in the process. Local reactions to the stings in the form of weals was also mentioned in the selection. An organism consistent with these features would be a large jellyfish with long tentacles, on the order of the lion's mane jellyfish Note: later in the story, Sherlock Holmes finds it at the bottom of a tidal pool; try: http://www.tirkzilla.com/holmes/ [check under the Case Book of Sherlock Holmes] if you're interested in reading it on-line. The stinging structures that are unique to cnidarians, the nematocyts, are designed to evert out microscopic threads containing neurotoxins. In a large jellyfish like C. capillata, these are evidently powerful enough to penetrate human skin and cause local pain and damage.
(sources: week 5 lecture notes and handout; text, Ch. 18, pp. 392, 396, 397, 402, 403, 404)
The flatworms are dorsoventrally flattened, with a solid body filled with parenchyma cells between the epidermis and a multiply-branched gut. In contrast, roundworms are round (surprise!) in cross section, with a thin, complete mouth-to-anus gut bathed in pseudocoelomic fluid and a body wall of epidermis, musculature, excretory canals, and nerve cords not in direct contact with the gut. To minimize the distance for diffusion to all of the parenchyma cells, the free-living flatworm's gut contains multiple diverticuli or branches. The roundworm gut, although thin, allows processing and potential specialization along its length. The fluid in the pseudocoelom, while not actively pumped by a structure like a heart, is stirred enough by the thrashing movements of the nematode to allow it in assisting in distribution of nourishment from the gut to the body wall structures.
(sources: week 6 lecture notes and handout; text, Ch. 19, pp. 417-419; Ch. 20, pp. 434, 438, 439))
Sense organs would be useful to search for food, avoid predators, steer in movements, or sample/vary the diet. Sponges are sessile, multicellular agregates that function at a cellular level, with choanocytes (collar cells) working individually to set up a flagella-driven water current to strain out food in their collars. Spicules and production of bad tastes can make sponges less vulnerable to prey. As a result of this body structure and life style, sponges do not have sense organs (or any other organs, for that matter!).
(sources: week 4 lecture notes and handout; text, Ch. 17, pp. 381-387)
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Please send comments and questions to: cronewil@hvcc.edu
Copyright 1999 by Wilson Crone
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This page updated on October 14, 1999