Title: Bulletin
Identifier: bulletin7073sout (find matches)
Year: 1971- (1970s)
Authors: Southern California Academy of Sciences
Subjects: Science; Natural history; Natural history
Publisher: Los Angeles, Calif. : The Academy
Contributing Library: New York Botanical Garden, LuEsther T. Mertz Library
Digitizing Sponsor: The LuEsther T Mertz Library, the New York Botanical Garden

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161 BULLETIN SOUTHERN CALIFORNIA ACADEMY OF SCIENCES VOLUME 72
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Figure I. Feeding currents and outgoing respiratory current of Petrolisthes cinctipes. on small material, begins with a stroking motion of the endopodites of the third maxillipeds. The endopodites straighten dorsally, one at a time. Fine, tapered, pinnate setae spread out from the last three segments, forming a net. (Henceforth, this filtering net and its segments will be called the fan.) The fan is held open and then bent down- ward toward the basis of the appendage. As one fan bends downward, the other straightens upward. The entire process usually takes less than a second, with an average rate of 80 strokes per minute. If food is scarce, the fans may be held extended for up to ten seconds at a time. The segments of the fan can swivel, allowing both fans to stroke in the same direction. In this case, the endopodite closest to the source of food straightens, swivels to face the oncoming food, opens the fan, turns back to the original position, and then bends downward. Cur- rents generated by the stroking of the endopodites can pull in nauplii of Artemia salina from a dis- tance of 4 mm from the dactyls of the fans. These currents bring in material ventrally, dorsally and laterally, except where either the respiratory current dominates over them or the action of the maxillipeds interferes with them (Fig. 1). Contrary to the observations of MacGinitie and MacGinitie (1968), the second maxilliped does not fan plankton and detritus from the water. In- stead, the setose end of the endopodite reaches up to the fan of the third maxilliped when the fan bends downward. This end sweeps gathered ma- terial toward the mouth. Incoming particles appear to be sorted by both the first maxillipeds and the first maxillae. The first maxillipeds move rapidly during feeding, but since they are covered by the second maxillipeds, it has been impossible to diagnose their activities. Par- ticles to be ingested pass between the first maxillae. The mandibles remain slightly agape during most of the feeding period (closing only about three or four times per minute) as long as the animal is captur- ing fine particles. Certain particles (notably the eggs of Artemia salina) are sorted for rejection before ingestion. These particles move dorsally along the setae of the first maxillae, instead of passing between them. They are transferred to the terminal portion (the "flagellum" of Nicol, 1932) of the exopodite of either the second or third maxilliped on the side from which the respiratory current is originating. While one flagellum continues to beat with the respiratory current, the other with the particles flicks them into the current, which carries the re- jected material away. If too many rejected particles build up. the crab snaps its abdomen, sending up- ward a blast of water that clears the filtering ap- pendages. Ingested material passes into the short esophagus, which leads into the large, chitinous stomach. Food seems to be sorted by circular bands of setae, each band of a given size, located in the cardiac stomach. After sorting, the food is ground into a relatively homogeneous chyme by the gastric mill. Digestible material goes through the pyloric stomach to the white, branched digestive glands lateral to the pyloric stomach. Undigestible particles (particularly fine sand grains) traverse the long hindgut to be ejected as long, stringy, mucus-covered feces. The minimum size of food taken by Petrolisthes cinctipes is governed by the spacing between the branch hairs on the setae of the fans. Depending on the size of the animal, these hairs are spaced from 3 to 30 microns apart. Hairs on the distal portion of the setae average 21 microns apart, while the spacing of the proximal hairs tapers to an average 9 microns apart. Foods most acceptable to the captive specimens were the diatoms Skeletonema costatum, and Thalas- siosira sp., unidentified ciliated protozoans, and newly-hatched nauplii of Artemia salina. Five ani- mals took filaments of Spirogyra sp. Only one accepted tissue from Mytilus californiantts. The crabs would not eat suspensions of goldfish food, dead cyclopoid copepods, muscle tissue from Cancer sp.. Plocamium sp., Polysiphonia sp., or pieces of finely-chopped fish. Eggs of Artemia salina usually were rejected into the respiratory current. Stomachs of freshly-killed field specimens varied in their contents. In all but two of the nineteen examined, fine sand grains were found. The next most common contents were bits of plant detritus (in eight stomachs), the diatom Coscinodiscus sp. (five stomachs), and two taxa of foraminiferans (five stomachs). In one stomach each were the diatom lsthmia sp., the diatom Chaetoceros sp., pieces of filamentous red algae, a harpactacoid copepod, a hydroid polyp, and a cypris larva. Kurup (1964) called Petrolisthes cinctipes a scavenger as well as an algal feeder. The scarcity of times that it was observed to feed on dead animal tissue, the frequent rejection of algal fila- ments and of chopped fish or invertebrate muscle tissue, and the varied stomach contents, however.

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