Part 2.— LIFE HISTORY OF THE SPINY LOBSTER. 



DESCRIPTION. 



EXTERNAL CHARACTERISTICS. 



The spiny lobster, Panulirus argus Latreille (Figs. 265 and 266), is compared fre- 

 quently with the northern lobster, Homarus americanus, but even a cursory examina- 

 tion shows that there are many differences between the two crustaceans. The carapace 

 of the spiny lobster, as the name implies, is studded with many sharp, forward-pointing 

 spines which are arranged in more or less regular longitudinal series. The largest spine 

 projects forward and curves above the eyes. The base of each spine is continuous 

 with a low, flattened ridge which passes forward and downward below the eye. 

 The base of the first segment of the antenna is modified into a padlike structure which 

 engages this ridge and produces a strident sound when the antenna is moved. 



The spiny lobster does not possess chelate appendages or large claws, like those of 

 the northern lobster, the legs all ending in sharp dactyls which bear tufts of setae. The 

 three basal segments of the antennas are very heavy and spinous, and the flagellar are 

 somewhat longer than the body in perfect specimens. The flagellar are heavy and stiff, 

 although they taper out to fine ends, and they are encircled with small spines at irregular 

 intervals for almost the entire length. The inner edges of the flagellar are fringed with 

 short setae which are probably sensory receptors. The antennules, or inner antenna?, 

 are long and biramose, and the inner branch of each is fringed with cilia. 



The pleon, or tail, is smooth and without spines or setae, and each segment is crossed 

 by a furrow which is more or less continuous, being broken in many small individuals. 

 The furrow across the sixth segment of many adults is broken, but it is continuous in 

 many others. The lower angle of each segment is produced into a strong tooth which 

 is directed backward and deeply notched on the posterior margin. 



The first segment of the tail does not bear appendages, but on the next four segments 

 there are paddlelike swimmerets, or pleopods. The inner limb, or endopodite, of these 

 appendages is not developed in the male, but in the female both exopodite and endopodite 

 are developed, and the last three endopodites are developed into biramose structures 

 for carrying the eggs. The tail fan is composed of five parts, the middle one being the 

 telson, or seventh segment of the pleon, and the outer parts, which are the appendages 

 of the sixth segment, known as the uropods, each being composed of exopodite and 

 endopodite. The telson is covered by longitudinal series of small spines directed back- 

 ward, and the distal parts of the tail fan are roughened by minute spines scattered over 



the surface. 



COLORATION. 



The sexes can not be distinguished by their color, although there is well-defined 

 sexual dimorphism, as will be shown presently (p. 293) . The coloration varies from very 

 light shades to very dark shades, but the light and dark areas cover the same regions 



291 



