522 U.S. ISPATIONAL MUSEUM BULLETIN 271 



mesosome. The pereon or thorax. [Term rarely used.] 



metasome. Pleonites 1-3. [Term rarely used.] 



molar. A process of the mandible, located on the midmedial margin; when 

 completely developed it is a large, massive, subcylindrical body with a surface 

 of ridges and teeth used for grinding (triturative) (fig. 2/). 



ommatidium (singular), ommatidia (plural), ommatidial (adjective). Terms 

 applying to the parts of the subintegumentary compound eye, not to be confused 

 with the corneal lenses of the integument of Ampeliscidae. 



palm. A posterior surface or margin of article 6 of a gnathopod or pereopod on 

 which article 7 (dactyl) closes for the purpose of prehension; usually recog- 

 nizable because of expansion of article 6 or by occurrence of special spines or 

 ornamentation and usually with a proximal defining limit marked by a change 

 in marginal slope or occurrence of special spines (fig. 2e). 



palp. Terminal articles of a buccal appendage, in Amphipoda occurring only 

 on mandibles, first maxillae, and maxillipeds as the stenopodous terminal 

 articles distal to the expanded outer plates or main body. 



parachelate. A rarely used term in Amphipoda applied to propodochelate 

 gnathopods and pereopods in which the immovable finger is distinct, but 

 article 6 is otherwise unexpanded or nonpalmate and the dactyl strongly 

 overlaps the apex of the immovable finger; gnathopods of various Eophliantidae 

 are good examples but the term may also be applied to numerous other cases, 

 such as those linear, chelate gnathopods of Sebidae, Didymocheila, and various 

 second gnathopods of Lysianassidae. 



peduncle. The basal articles of a fundamentally biramous appendage; in 

 Amphipoda applied to antennae, pleopods, and uropods; antenna 1 with three 

 peduncular articles, antenna 2 with five peduncular articles (but appendage 

 not biramous) ; pleopods with one definitive f eduncular article but remnants 

 of others occurring proximally; uropods each with one peduncular article 

 (fig. 1). 



pereon. The complex of seven free thoracic segments bearing gnathopods and 

 pereopods, not including the maxillipeds (fig. 1). 



pereonite. A segment of the pereon. 



pereopod. A walking, grasping, standing, or feeding appendage attached to a 

 pereonite; normally composed of seven articles, including coxa; in Amphipoda 

 the first two pairs are often termed gnathopods and only the last five pairs of 

 thoracic legs are called pereopods (fig. 1). 



plate. A flattened lobe on an article of a maxilla or maxilliped. 



pleopod. A biramous swimming appendage on pleonites 1-3, one pair for each 

 pleonite (fig. 1). 



pleon. The abdomen (of six free segments in Gammaridea, rarely with some 

 segments coalesced). See metasome and urosome. 



pleonite. A segment of the pleon. 



prebuccal complex. The labrum and epistome together. 



prehensile. Adapted for seizing or grasping; applicable to but rarely used for 

 gammaridean gnathopods; especially useful in denoting pereopods of cyphocarids 

 Isaea, Pleonexes, etc., which either are subchelate or chelate, or have distinct, 

 spinose palms or nonskid surfaces indicating their use in grasping. 



propodochelate. Synonymous with chelate. 



propodus. The sixth article of a thoracic appendage (especially used to denote 

 the palmar article of a gnathopod). 



scale, scale-like. Terms applied to the accessory flagellum when forming a 

 small lamella immovably fused to article 3 of antenna 1 ; and to the inner ramus 

 of uropod 3 when strongly reduced and plate-like. 



