MARIN® GAMMARIDEAiN AMPHIPODA 11 



epistome and upper lip are produced together and occasionally they 

 are fully amalgamated. 



Lower lip: A bilaterally symmetrical complex forming a partition 

 behind the mouth. It is composed of at least a pair of lateral lobes, 

 having their lateral extremities produced, often acutely and often 

 bearing apicomedially a tiny cusp enclosing the meatus of a saHvary 

 duct. About half of the known gammarideans has a pair of medial 

 lobes on the lower hp. 



Mandibles: A pair of appendages attached lateral to the mouth; 

 with the upper and lower lips they form a box around the mouth, 

 permitting buccal closure. The mandibles are powerful and difficult 

 to remove because of their large muscles. Mandibles generally have 

 their anterodistal ends (incisors) cut into a series of teeth for biting; 

 just proximal to the distal teeth may be an articulated process, also 

 toothed, the lacinia mobUis (accessory plate) which may occur on 

 only one of the mandibles. A molar with a grinding surface often 

 occurs on the medioventral surface of the mandible. It may be ridged 

 and toothed (triturative), or smooth, or be completely absent, es- 

 pecially in inquilinous amphipods having the mandibles elongated 

 for piercing and sucking. Most Gammaridea have a 3-articulate 

 palp attached to the dorsolateral surface of the mandible, the palp 

 being used to clean the bases of the antennae. Its absence is mod- 

 erately frequent and often of familial importance, but its reduction 

 to two or one articles is uncommon. 



First maxillae: These are situated posterior to the lower lip. 

 This pair of appendages is small, each bearing a medial free lobe, 

 an outer lobe with heavy spines, and attached to the outer lobe a 

 palp composed of one or two segments, occasionally reduced in 

 size or absent. 



Second maxillae: These are two pairs of lobes behind the first 

 maxiUae, each composed of simple medial and lateral plates, occa- 

 sionally reduced to one plate or absent, rarely with the outer lobe 

 attached to the inner by a basal geniculation or extension. Basal 

 articles of maxillae and maxillipeds are present but rarely are of 

 taxonomic importance. 



Maxillipeds: One pair of appendages posterior to the maxillae, 

 each maxilliped is formed of an inner (proximal) lobe, an outer 

 (distal) lobe and a palp of two to four articles, rarely absent in 

 Gammaridea, but always absent in the pelagic and often inquilinous 

 Hyperiidea and in cyamid Caprellidea. The Ochlesidae, lacking 

 such palps, are assigned to the Gammaridea on the basis of their 

 resemblance to Gammaridea in other morphological features and 

 their supposed benthic habits. In peracaridan phylogeny the max- 

 illipeds were originally the first pair of thoracic legs, but they have 



