THE PARASITIC CRUSTACEANS OF FISHES FROM THE BRAZILIAN AMAZON

The female of Acusicola lycengraulidis n. sp. (Copepoda: Cyclopidea) is des­ cribed from the gills of an Amazonian fish, Lycengraulis grossidens Cuvier. The new species differs from the other three known for the genus in having an inflated céphalothorax which incorporates the first leg bearing segment. The new species therefore has only five free thoracic seg­ ments instead of six. Also, A. lycengraulidis n. sp. has a more slender second seg­ ment on the first endopod and a curved and pointed terminal segment on the fourth endopod. The genus Acusicola (Ergasilidae) was proposed by Cressey (1970, in Cressey & Collette, 1970) to include Ergasilus tenax Roberts, 1965, from a Texas crappie, as type, and A. cunula Cressey, 1970, from an Amazonian needlefish. Although Johnson and Rogers (1972) and Kabata (1979) rejected the genus and left both these species in Ergasilus, Thatcher (1984) recognized and emended Acusico­ la and included a third species, A. tucunarense Thatcher, 1984. The latter author also proposed the subfamily Acusicolinae which he defined as those ergasilids ha­ ving a 5—segmented antennule and a 4—segmented latching antenna having a grooved third segment for reception of the opposite claw. Present studies indi­ cate that Acusicola will prove to be an important Neotropical genus. An addi­ tional new species of this genus is herein described and it represents the third known from the Brazilian Amazon. MATERIALS AND METHODS Living ergasilids were collected by severing the gill filaments to which they were attached. They were killed by imersion in 70% alcohol and afterwards removed from the filaments by dissec­ tion. The methods used in their prepara­ tion and study were those explained in Thatcher (1981) and Thatcher & Rober­ tson (1982). Color determinations were made with reference to Smithe (1974). Drawings were made with the aid of a camera lucida and measurements with an ocular micrometer. All measurements are given in microns. SYSTEMATIC SECTION ERGASILIDAE NORDMANN, 1832 ACUSICOLINAE THATCHER, 1984 ACUSICOLA CRESSEY, 1970 Acusicola lycengraulidis n. sp. (Figs. 1-11) Host. Lycengraulis grossidens Cuvier. Site: Gill Filaments. Locality: Tocantins River, Pará, Brazil. Instituto Nacional de Pesquisas da Amazônia, Manaus ACTA AMAZÓNICA 13(5-6) : 943-951. 1983. — 943

The genus Acusicola (Ergasilidae) was proposed by Cressey (1970, in Cressey & Collette, 1970) to include Ergasilus tenax Roberts, 1965, from a Texas crappie, as type, and A. cunula Cressey, 1970, from an Amazonian needlefish.Although Johnson and Rogers (1972) and Kabata (1979) rejected the genus and left both these species in Ergasilus, Thatcher (1984) recognized and emended Acusico la and included a third species, A. tucunarense Thatcher, 1984.The latter author also proposed the subfamily Acusicolinae which he defined as those ergasilids ha ving a 5-segmented antennule and a 4-segmented latching antenna having a grooved third segment for reception of the opposite claw.Present studies indi cate that Acusicola will prove to be an important Neotropical genus.An addi tional new species of this genus is herein described and it represents the third known from the Brazilian Amazon.

MATERIALS AND METHODS
Living ergasilids were collected by severing the gill filaments to which they were attached.They were killed by imersion in 70% alcohol and afterwards removed from the filaments by dissec tion.The methods used in their prepara tion and study were those explained in Thatcher (1981) and Thatcher & Rober tson (1982).Color determinations were made with reference to Smithe (1974) Thorax (Fig. 1) of five free segments; legs 2-5 on free segments.Genital segment subrectangular (Fig. 3).Abdomen (Fig. 3) of three segments.Uropod longer than wide, with long, medium and short setae.Egg sac (Fig. 6) elongate; contains 50-1 50 small eggs.Mouthparts (Fig. 11): mandible bifid, with bristles on posterior margin; palp bristled anteriorly.First maxilla reduced; bearing two small setae.Second maxilla conical; bearing fine bristles.First antenna (Fig. 5) 5-segmented; first segment larger than others.Setal formula = 10-2-3-2-6; setal total = 23.Second antena (Fig. 2) 4-segmented; second segment slightly longer than segments 3 & 4 combined.Third segment with prominent groove about midway on its length which serves to receive the fourth segment (claw) of opposite antenna when these are latched.Claw small, with medial indentation.

DISCUSSION
Acusicola lycengraulidis n. sp. is the fourth species known from the genus and it differs from the other three in having an inflated céphalothorax into which the first leg bearing segment is fused.As a result, the new species has only five free thoracic segments while the other known species have six.Additionally, the new species is the only one of the four which has the second segment of the first endopod more slender than the first and a curved, pointed terminal segment on the fourth endopod.

TABLE II Antennal
Measurements (urn) of 10 Adult Females of Acusicola lycengraulidis n. sp.

TABLE III Relationships
of Spines to Setae on the Legs of Acusicola lycengraulidis n. sp.