MARINE GAMMARIDEAN AMPHIPODA 517 



GNATHOPODS 



Judgment of gnathopods 1-2 as: feeble together (fig. 165a), normal (basic gam- 

 maridean with gnathopod 2 powerful), powerful together (fig. 115a). 



GNATHOPOD 1 (excluding coxa 1) 



Present, vestigial, or absent (Bateidae and Paranamixis only). 



Size (or length) relative to gnathopod 2: smaller, equal, larger. 



Sexual dimorphism: similar or different in male and female. 



Articles: 



2: Length in relation to coxa 1 (rarely important except when coxa 1 abnormal). 



3: Length normal; or elongate (like fig. 3a). 



Merochelation: with strong thumb-like extension (rare). 

 Length relative to article 6 ( %). 

 Posterior lobe: present, weak, absent. 



Carpochelation: with strong distoposterior tooth or teeth forming thumb 

 or guarding article 6. 

 6: Breadth: relative to article 5; wider, equally wide, narrower. 



Shape: ovate, pyriform, quadrangular, rectangular, linearly rectangular, 



styliform. 

 Palm: 



Present, absent, undecided. 



Slope: transverse, oblique: slight; moderate; extreme. 

 Chela if present: parachelate (describe if strongly chelate). 

 Definition of proximoposterior corner of palm: spines, protuberance, tooth, 



change in slope only. 

 Ornamentation: special spines, teeth. 

 7: Fit of the dactyl to palm: congruent, overlapping, not fitting. 



Shape and ornaments: claw-like (normal); vestigial; absent (rare); with 

 special setae or spines; hidden in setae or cirri; fiagelliform. 

 Distal articles especially scaly or with small stiff setae (Lysianassidae). 



GNATHOPOD 2 



Articles : 



Length normal; elongate (Jig. 3a). 



Merochelation: with strong thumb-like extension. 



Length relative to article 6 ( %^. 



Posterior lobe: present, weak, absent. 



Carpochelation: with strong distoposterior tooth or teeth forming thumb or 



guarding article 6. 

 Scales or stiff setae (pineapple cushion of Lysianassidae). 

 General shape: cup-like, elongate rectangle, ovate. 

 Breadth relative to article 5: wider, equal, narrower. 



Shape: ovate, pjTiform, rectangular, linearly rectangular, mitten-like (Lysi- 

 anassidae, Talitroidea), quadrangular. 

 Palm: 



Present, absent, undecided. 



Slope: transverse; oblique: slight, moderate, extreme. 



Chela if present: parachelate (describe if strongly chelate). 



Definition of proximoposterior corner of palm: spines, protuberance, tooth, 

 change in slope only. 



Ornamentation: special spines, teeth. 



