STARFISHES. 



One of the most unique and interest- 

 ing branches of the animal kingdom is 

 that division called by scientists Echino- 

 dermata, comprising animals familiarly 

 known as starfishes, sea urchins, sand 

 dollars and sea cucumbers. So far as 

 is known no member of this group of 

 animals has ever ventured on land or 

 into fresh water. All are inhabitants of 

 the ocean and are found from the tide- 

 washed shore to the abysses of the sea. 



The present article deals with the 

 true starfishes (Asteroidea) and a good 

 idea of the general structure may be 

 gained by a careful examination of a 

 specimen of the common five-finger (As- 

 terias vulgaris) so common on the New 

 England coast. It is made up of a cen- 

 tral disk or body, from which extend 

 five rays or arms, whence the name star- 

 fish. The animal is protected by a hard 

 framework or skeleton, composed of 

 many limestone plates, attached by a 

 tough membrane and covered with a 

 skin. Between these plates there are 

 many small openings through which the 

 water enters the body cavity. The plates 

 are armed with numerous spines, at- 

 tached by a ball and socket joint. Some 

 of these spines bear little pincer-like or- 

 gans called pedicellarise, which are capa- 

 ble of considerable movement. Many of 

 these little organs are arranged in groups 

 about the spines, which swell at the point 

 of attachment to the surface of the star- 

 fish, thus forming a shelf or base, around 

 which these organs arrange themselves 

 in the form of a wreath, the spine pro- 

 jecting high above the center. The ex- 

 act function of these little organs is not 

 known, although they have been seen to 

 catch small animals, such as Crustacea, 

 and this is probably one of their duties. 



The lower or actinal surface of each 

 arm is deeply channeled and perforated 

 by many holes or pores, through which 

 the little ambulacra or water-feet are 

 thrust. These serve as organs of loco- 



motion, of respiration and of perception. 

 These water-feet form a part of the won- 

 derful water-vascular system, which con- 

 sists of a madreporic body, or sieve-like 

 organ, opening on the dorsal or actinal 

 surface and situated between two rays. 

 It opens into a tube called the stone 

 canal, which . enters a circular vessel 

 called the circum oral water tube, sur- 

 rounding the mouth, and a long radial 

 canal, to which the water-feet are at- 

 tached, opens from this tube and extends 

 along the inner surface of each ray. The 

 water enters the madreporic body, circu- 

 lates through the stone canal, the circular 

 and radial tubes, and finds its exit 

 through the ambulacra. The water sys- 

 tem is directed and controlled by a set 

 of nerves, extending from a ring of nerve 

 matter surrounding the mouth. 



The true vascular or blood system con- 

 sists of a heart or haemal canal, which 

 runs parallel with the stone canal from 

 the madreporic body to the oral water 

 tube. A set of circular and radial ves- 

 sels supplies every part of the animal 

 with the vital fluid. 



The digestive system is simple and 

 consists of a mouth, a stomach, which 

 is large and sends a lobe into the base 

 of each arm, and an intestine of greater 

 or lesser length, ending in a small anal 

 opening on the dorsal surface. The 

 coeca or liver consists of two long, tree- 

 like masses, nearly filling each ray and 

 conecting with the stomach by a short 

 duct. 



Starfishes are very destructive to the 

 oyster beds along the Atlantic coast of 

 the United States, thousands of bushels 

 of oysters being destroyed in a few days 

 by them. The little starfishes attack 

 the young oysters and as the former 

 increase in size they move about in vast 

 numbers, resembling in this respect the 

 grasshoppers and locusts of the west 

 and being fully as destructive. In a 

 paper in a Bulletin of the United States 



35 



