Limulus polyphemus

Variations in the development of limulus polyphemus
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Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: some future theories of development, find their proper place and partial explanation. It seemed inadvisable to add further to this paper by detailed reference to the voluminous literature bearing only indirectly on the facts here set forth. So little is known about variations in arthropod embryos, and especially arachnids, and the facts we present are so different in character from those already known, that no injustice will be done previous workers along similar lines by not referring in detail to their publications. The only reference to an abnormality in Limulus that I have been able to find is in an article on " Diploteratology, An Essay on Compound Human Monsters," by Geo. J. Fisher, Albany, 1868. A good figure is there given of an adult (?) animal with a double caudal spine and a symmetrically forked abdomen. DESCRIPTION OF THE DIFFERENT CLASSES OF VARIATION. I. Invagination Of Appendages. This remarkable modification is of comparatively common occurrence in forms which are in other respects more or less abnormaI. It is confined, so far as I have observed, to the thoracic appendages, and most commonly affects the middle ones of the series. It may begin after the appendage is fully formed as a minute, slit-like depression at its distal end, Figs. 10, u, th.ap., th. ap. The slit is always transverse to the long axis of the body, and appears in the stained specimens as a fine line in the middle of a clear band devoid of nuclei. When the invagi- nation is complete, the whole appendage is carried inward, so that in its place is an opening leading into a deep tube with a flattened, conical lumen. The third or fourth appendages on either or both sides may be invaginated, Figs. 10, n, or, as in one case ? the only one observed ? all the thoracic appendages, with...

Endogenous rhythms and entrainment cues of larval activity in the horseshoe crab Limulus polyphemus [An article from: Journal of Experimental Marine Biology and Ecology]
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This digital document is a journal article from Journal of Experimental Marine Biology and Ecology, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
The American horseshoe crab, Limulus polyphemus (Linnaeus), typically inhabits estuaries and coastal areas with pronounced semi-diurnal and diurnal tides that are used to synchronize the timing of spawning, larval hatching, and emergence. Horseshoe crabs spawn in the intertidal zone of sandy beaches and larval emergence occurs when the larvae exit the sediments and enter the plankton. However, L. polyphemus populations also occur in areas that lack significant tidal changes and associated synchronization cues. Endogenous activity rhythms that match predictable environmental cycles may enable larval horseshoe crabs to time swimming activity to prevent stranding on the beach. To determine if L. polyphemus larvae possess a circatidal rhythm in vertical swimming, larvae collected from beach nests and the plankton were placed under constant conditions and their activity monitored for 72 h. Time-series analyses of the activity records revealed a circatidal rhythm with a free-running period of ~12.5 h. Maximum swimming activity consistently occurred during the time of expected falling tides, which may serve to reduce the chance of larvae being stranded on the beach and aid in seaward transport by ebb currents (i.e., ebb-tide transport). To determine if agitation serves as the entrainment cue, larvae were shaken on a 12.4 h cycle to simulate conditions during high tide in areas with semi-diurnal tides. When placed under constant conditions, larval swimming increased near the expected times of agitation. Thus, endogenous rhythms of swimming activity of L. polyphemus larvae in both tidal and nontidal systems may help synchronize swimming activity with periods of high water and inundation.

A Barnacle and Algae Encrusted Horseshoe Crab, Limulus Polyphemus Framed Art Poster Print by Darlyne A. Murawski, 31x25
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A Barnacle and Algae Encrusted Horseshoe Crab, Limulus Polyphemus Photographic Poster Print, 24x18
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