We analyzed 556 specimens from the family Magelonidae collected during surveys made along the continental shelf of the Pacific coasts of Mexico (Gulf of California, Gulf of Tehuantepec, and the state of Guerrero). The study area covers latitudes 15°35′N to 31°20′N and longitudes 94°00′W to 114°23′W. Additional material from the northern Gulf of Mexico (USA region) belonging to the USNM collections was also examined. Earlier records of magelonids in the Mexican Pacific include
Magelona pacifica,
M. pitelkai,
M. sacculata, and
M. californica. A new genus (
Meredithia), characterized by the presence of acicular spines in abdominal parapodia, as well as four new magelonid species are described. Affinities to related species in both genera (
Magelona and
Meredithia) are discussed.
Magelona marianae is the only species in the genus with bidentate hooded hooks and notopodial lateral lamellae distally crenulate. In
Magelona tehuanensis, the tip of the prostomium is crenulate with frontal horns, dorsal medial lobes and tridentate abdominal hooks.
Meredithia spinifera is characterized by the presence of large hooded recurved spines in some abdominal anterior setigers (10–17); in
Meredithia uebelackerae large hooded recurved spines are present in notopodia from setiger 36. A key is provided for species found in the Mexican Pacific.
