Stars 



OF THE SEA 



Bx Rachel Wharton 



Astropecten 

 articulata, 

 margined 

 sea star 



In the constant beach battle for 

 the prettiest shell or sand dollar, one 

 thing trumps all: the starfish. As the 

 most recognizable member of the 

 marine community, it's literally the 

 star of the sea. With almost perfect 

 symmetry, the creature seems to hold 

 a celestial power. 



Starfish are strictly marine, and 

 most North Carolina species live 

 around the subtidal zone or on the 

 sandy seafloor of the continental shelf. 

 Of more than 2,000 species known 

 worldwide, only 30 to 40 can be found 

 in Tar Heel waters, with the greatest 

 variety south of Cape Hatteras. But 

 except for shrimpers, divers or re- 

 searchers, most people never see these 

 warm water species. Only a few types 

 of starfish commonly wash on the 

 shore. One of the best times to search is 

 after winter storms and cold fronts, 

 which often strand marine organisms 

 on the beaches. 



One of these species is the 

 margined sea star, Astropecten 

 articulata, so named because of the 

 whitish line around its upper body. 

 Another is the grey sea star, or Luidia 

 clathrata. Both of these starfish are 

 usually foggy gray and reach about 3 to 

 5 inches in diameter. 



The most familiar of the southeast- 

 ern starfish is the common sea star, or 



Asterias forbesi — often seen as a 

 chubby, wine-colored starfish with 

 orange-yellow knobs, measuring about 

 6 inches across. Bill Kirby-Smith, 

 zoologist at the Duke University 

 Marine Lab, calls it the "freshman 

 zoology starfish" because it is 

 dissected in class. 



Starfish are members of the 

 phylum Echinodermata, a word that 

 stems from the Greek words echino, 

 meaning hedgehog, and derma, 

 meaning skin. In any survey of the 

 animal kingdom, says Kirby-Smith, 

 the echinoderms are important. They 

 are an evolutionary step away from 

 the chordates, the phylum to which 

 humans belong. 



In the constant beach battle for 

 the prettiest shell or sand dollar, 

 one thing trumps all: the starfish. 

 As the most recognizable member 

 of the marine community, 

 it's the star of the sea. 

 With almost perfect symmetry, 

 the creature seems to hold 

 a celestial power. 



Of course, another reason to study 

 the organism is its symmetry. This 

 symmetry — unique to echinoderms 

 such as starfish and sea urchins — is 

 emphasized throughout the animal's 

 body. Although humans have bilateral 

 symmetry (two arms, two legs, two 

 eyes), starfish have radial symmetry 

 — five symmetrical sections. 



Most starfish have five arms, but 



many have as many as 25 or 50, 

 always in multiples of five. The 

 common seastar's arms are very 

 long, and the central body is small. 

 In others, such as the Pacific sea bat 

 (named for the flesh between its 

 arms), the body looks more like a 

 pentagon. 



The starfish's mouth is located 

 in the center of its body on its 

 underside. Around the mouth is a 

 nerve ring, which connects to radial 

 nerves in each arm. The starfish has 

 no brain, just this simple nervous 

 system. It relays impulses from arm 

 to arm. At the tip of each arm are 

 delicate sensors that can detect food 

 or chemicals, and a sensitive eyespot 

 that can perceive shadows and light. 

 Along the underside of each arm runs 

 a groove from which thousands of 

 flexible tube feet extrude. 



Tube feet are the movers and 

 shakers in the starfish's water 

 vascular system, another trait unique 

 to echinoderms. On the top of the 

 starfish, a small circular sieve plate 

 rests between the intersection of 

 two arms. 



Water is brought in through the 

 sieve plate and carried to the arms 

 and feet. Through hydraulic power, 

 the feet blow up and deflate, blow up 

 and deflate, moving the animal 

 forward. Most starfish have a sucker 

 at the end of each tube foot that 

 enables it to cling and climb. The 

 margined sea star and the grey sea 

 star have pointed tube feet to move 

 themselves across soft sand. 



In general, starfish reproduce 



14 MARCH/APRIL 1996 



