126 UNDERWATER GUIDE TO MARINE LIFE 



sperm-bearing arm is actually detached from the male and placed in the mantle 

 cavity of the female. This arm was originally thought to be a separate animal, a 

 worm, and was named Hectocotylus. Most octopuses do not lose their sexual 

 arms during copulation, however. 



Cephalopods can be divided into two groups on the basis of how many arms 

 they have. The squids have ten arms, two of which are much longer than the 

 rest. These are very swift-swimming animals which are common near shore or 

 at sea the world over. They eat fishes and invertebrates. The common squid, 

 Loligo, is a common shore form and reaches a length of Wi feet. Sepiotenthis 

 (^color fhotograph^ is found in the West Indies and is very beautifully colored. 

 Both of these show preference for traveling in schools in precise military 

 formation. Sometimes as many as several dozen may be seen lined up swimming 

 together. 



The octopuses have eight tentacles, usually all of equal length, and are of 

 bottom-living habits, eating other invertebrates such as molluscs and crustaceans 

 mostly. Some are small and pelagic and fairly good swimmers. Others are 

 extremely flattened and sluggish, spending most of their time attached to rocks. 

 But most are shy and nocturnal, though active, bottom animals. Klingel (1944) 

 gives a sympathetic account of the common octopus, Octofiis (Color Plate 10^ 

 He says that the best way to spot the home of one of these shy animals is to take 

 note of the presence of a pile of shells and stones which the octopus accumulates 

 near its home. After feeding, the octopus has the peculiar habit of drawing hard 

 objects to its body. 



Octopuses show fear by means of a livid white color phase, but they also 

 have color phases composed of virtually every shade or pattern imaginable. Ink 

 is used both for a defensive smoke screen and for recognition of one octopus 

 by another at night. The paper argonaut, Argonmita, is an octopus, the female 

 of which forms a beautiful papery shell as an egg case. The argonaut is an animal 

 of rather deep tropical waters, but it appears at the surface when it is breeding. 



BRAGHIOPODS: Phylum Brachiopoda— Figure 41 



This phylum is mentioned chiefly because one species holds the geological 

 longevity record for all animals; Lingiila has been in existence for 400 million 

 years. Brachiopods are not now very varied, but were among the most common of 

 animals many million years ago. They look like bivalve molluscs since they 

 have two shells and filter-feed on plankton, but they are actually quite diff^erent 

 anatomically. The lamp shells are brachiopods that grow attached to rocks by a 

 stalk. Brachiopods are fairly common in deep water offshore, but a few are 

 found in shallow waters. 



ECHINODERMS: Phylum Echinodermata ("spiny-skinned") 



The starfishes and their allies form an important group evolutionarily 

 speaking since they have a larva that looks very much like the larva of some 

 prochordates. Therefore, the chordates (including vertebrates) and the echino- 

 derms are thought to have common ancestry. 



Adult echinoderms are characterized by the tube feet by means of which 



