THE PARASITIC CRUSTACEANS OF FISHES FROM THE BRAZILIAN AMAZON . 5 . BRASERGASILUS GEN . NOV . ( COPEPODA : CYCLOPIDEA ) , A " THREE-LEGGED " ERGASILID , WITH TWO NEW SPECIES AND THE PROPOSAL OF ABERGASILINAE SUBFAM

Brasergasilus jaraquensis gen. et sp. nov. and B. anodus sp. nov. (Copepoda: Cyclopidea: Ergasilidae), gill parasites of Semaprochiiodus insignis (Schomburgk) and Anodus elongatus Spix, are described from the Amazon River. The new genus has only three pairs of swimming legs and in this respect Is similar only to one species from New Zealand, Abergasilus amplexus Hewitt, 1978. The two genera also have in common a three-segmented prehensile antenna. Abergasilus, however, has the base of the second antennal segment developed into a massive spine which abutts against the claw-like third segment. The new genus completely lacks this fundamental structure. Adltionally, Abergasilus has six free thoracic segments while the new genus only has f ive. Abergasilinae Subfam. nov. is pro­ posed for these two genera and their three species. Ergasilinae nom. nov. Is provisionally defined and proposed to include the other 11 genera of the family. The type species of Brasergasilus gen. nov. is B. jaraquensis sp. nov. and it can be distinguished from B. anodus sp. nov. by the following characteristics: 1) The type species is larger and of a greenish coloration while B. anodus has fewer pigment granules that are of a bluish tint. 2) B. jaraquensis has a more slender second antenna and the most abrupt bend of the claw occurs distally; the second antenna of B. anodus is thicker and the abrupt bend Is found proximally. 3) The uropod of the type species has two setae and two small spines, while that of the olher species has three setae and lacks spines. 4) The first leg of B. jaraquensis is laterally serrate while that of B. anodus is pectinate. The two species parasitize two different genera of host f ish and are probably host specific.


INTRODUCTION
The ergasilid fauna of South America is still but little known and, prior to the present series, only 10 species had been reported from this continent.Amazonian ergasilids are reported in the studies of Cressey (1970, in Cressey & Collette, 1970), Thatcher (1981aThatcher ( & 1981b)), Thatcher & Robertson (1982), and Thatcher & Boeger (in press).At present, 14 species of ergasilids are known to occur on the South American continent, with 6 of these being native to the Amazon River Basin.
Ergasiiids are parasitic copepods in which only the female is found attached to the gills of a fish host.Males, and all immature stages, occur as free-living elements in the zooplankton (Kabata, 1970(Kabata, & 1981)).Since the parasitic females are highly pathogenic, they repre sent a serious economic problem in relation to pisciculture.The present report is part of a conti nuing study which plans to eluci date the morphology, systematics, pathogenicity, ecology, host speci ficity and control of these parasi tes.
Recently, two undescribed species of an unusual new genus of ergasilid have been found para sitizing Amazonian fishes.This new form has a female with only three pairs of swimming legs, instead of the usual five pairs.World-wide, only one "three--legged" ergasilid has been pre viously reported, and that species occurs in New Zealand (Hewitt, 1978).This difference in the number of appendages is so basic as to require the erection of a new Subfamily, which is herein proposed.

MATERIALS AND METHODS
The methods used in this study were explained in Thatcher (1981a) and in Thatcher & Robertson (1982) Antennae (Figs. 2 & 3): first antenna of six segments, bea ring simple setae; setal formula = 0-2-3-2-1-4.Prehensile (second) antenna three-segmented; second segment with simple sensillum on medial margin, distally; terminal segment more curved near distal portion; ratio of segmental lengths = 1:1.8:3.Thorax (including genital seg' ment) of five free segments (Fig. 1); thoracic segments V and VI reduced, and without appendages.Genital segment sub -spherical (Fig. 4).Abdomen of three seg ments; nearly equal in size.Each uropod with one long and one short seta and two spines, late rally (Fig. 4).Mouth parts (Fig. 9): mandible two-segmented, with bristled tip; palp simple, with bristles postero-mediaHy; first maxilla lacking; second maxilla of two segments, terminal segment elongate and bristled on tip.: Leg 1 (Fig. 6); endopod two-segmented; both seg ments serrate laterally; first seg ment with a single, plumose seta medially; second segment with one, plumose seta medially and four terminally; two large, rasp--like spines terminally: exopod three-segmented; first two seg ments serrate laterally; segment one with a single, large spine; second segment with a single, plumose seta medially; terminal segment bearing five, plumose setae and two, rasp-like, large spines.Leg 2 (Fig. 7): both rami three-segmented; all segments of endopod serrate laterally; first segment with a single, plumose seta medially; second segment with two, plumose setae medially; terminal segment with four, plu mose setae and a single, rasp like spine: first exopodal seg ment with a single, rasp-like spine and a few serrations la terally; second segment with a single, plumose seta medially; ter minal segment with six, plumose setae and a single, rasp-like spine.Leg 3 (Fig 8): both rami threesegmented; first endopodal seg ment with a single, plumose seta medially and few thin spinules laterally; second segment with two, plumose setae medially and few long, slender spinules lateral ly; terminal segment with four, plumose setae, one elongate spine and few thin spinules; first exopodal segment with a single, lateral spine; second segment with a sin gle, plumose seta medially; termi nal segment with six, plumose setae and a single, small spine.

DISCUSSION
The Family Ergasilidae, as pre sently conceived,.contains more than 70 species of Ergasilus and an additional 24 species distribu ted in 10 other genera.Yamaguti (1963) did not divide this group into Subfamilies as he did for the Bomolochidae.The occurence in New Zealand of Abergasilus Hewitt, 1978, and the presence in Amazonia of Brasergasilus gen.nov., both having only three pairs of swimming legs, require a new evaluation of the Ergasilidae.Al though Hewitt (1978) did not discuss the matter, it should be admitted that neither of these ge nera conforms to the definitions of Ergasilidae currently in use (ie.Yamaguti, 1963& Roberts, 1970).These definitions indicate that fe males should have four pairs of swimming legs and a fifth pair of vestigial legs.Hewitt (1978) re ported some ventral spines on the pre-genital segments of Abergasi lus that he thought might repre sent vestigial legs, but this inter pretation seems unlikely.Vestigial legs in ergasilids are typically re presented by setae, not spines, and in any case, the spines are in the wrong position.Careful exa mination of Brasergasilus failed to reveal any vestigial legs, so we are forced to conclude that neither genus has them.In addition to a reduction in number of legs, these genera also show greatly reduced fifth and sixth thoracic segments.These are the segments which normally bear the fourth and fifth pairs of legs in ergasilids.It is therefore necessary to propose the new Subfamily Abergasilinae for the two genera and to tentati vely define Ergasilinae to include the other 11 genera of Ergasilidae.Undoubtedly, it will be found ne cessary to further divide this Fa mily in the future, after other unusual Amazonian forms have been described.A redefinition of the Family and of the Order Cyclopidea will also be attempted at that time.
The fundamental difference between Brasergasilus gen.nov.and Abergasilus Hewitt, 1978, is that the latter has a large, spineshaped projection from the base of the second segment of the prehensile antenna which abutts against the claw-like third joint.The new genus completely lacks this basic structure.Additionally, Abergasilus has six free thoracic segments, and the rami of all legs are three-segmented, whereas in the new genus there are only five free thoracic segments and the first endopod is two-segmented.
Brasergasilus jaraquensis sp nov.and B. anodus sp.nov.can be distinguished by the following characters: 1) the type species is slightly larger and has more pigmentation, with an overall greenish hue, while the latter has scattered, bluish pigment granu les; 2) the prehensile antenna of B. jaraquensis is slender, and the claw has its most abrupt curvature distally, while in B. anodus, the antenna is stouter and the princi pal bend is proximal; 3) the uropod of the type species bears two setae and two small spines, whereas that of the other species has three setae and lacks spines; 4) the first leg of B. jaraquensis is laterally serrate, while that of B. anodus is pectinate.It is also worth noting that these species were found on different genera of host fishes and they are probably host specific.ABSTRACT Brasergasilus jaraquensis gen.et sp.nov.and B. anodus sp.nov.(Copepoda: Cyclopidea: Ergasilidae), gill parasites of Semaprochiiodus insignis (Schomburgk) and Anodus elongatus Spix, are described from the Amazon River.The new genus has only three pairs of swimming legs and in this respect Is similar only to one species from New Zealand, Abergasilus amplexus Hewitt, 1978.The two genera also have in common a three-segmented prehensile antenna.Abergasilus, however, has the base of the second antennal segment developed into a massive spine which abutts against the claw-like third segment.The new genus completely lacks this fundamental structure.Adltionally, Abergasilus has six free thoracic segments while the new genus only has five.Abergasilinae Subfam.nov. is pro posed for these two genera and their three species.Ergasilinae nom.nov.Is provisionally defined and proposed to include the other 11 genera of the family.The type species of Brasergasilus gen.nov. is B. jaraquensis sp.nov.and it can be distinguished from B. anodus sp.nov.by the following characteristics: 1) The type species is larger and of a greenish coloration while B. anodus has fewer pigment granules that are of a bluish tint.2) B. jaraquensis has a more slender second antenna and the most abrupt bend of the claw occurs distally; the second antenna of B. anodus is thicker and the abrupt bend Is found proximally.3) The uropod of the type species has two setae and two small spines, while that of the olher species has three setae and lacks spines.4) The first leg of B. jaraquensis is laterally serrate while that of B. anodus is pectinate.The two species parasitize two different genera of host fish and are probably host specific.(Aceito para publicação em 7/2/83)
and Museu de Zoologia da Universidade de Sâo Paulo, Brazil.Etymology: The generic name of the host is used for the specific name.Species Diagnosis (based on 30 specimens studied and 10 measu red): General measurements are given in Table 4. Céphalothorax bluntly rounded anteriorly; head fused with first two thoracic seg ments (Fig. 10).Eyespot large, hour-glass shaped; smalt blue (Co lor 70).Body with sparse campa nula pigmentation (Color 71) ven tral ly.Ovary and eggs buff-yellow (Color 53).

TABLE 1 . Measurements, in micrometers, of adult females of
B. jaraquensis gen.et sp.n.

TABLE 2 .
Antennal measurements, in micrometers, of adult females of B. jaraquensis gen.et sp.n.

TABLE 3 .
Relationships of Spines to Setae on the Legs of B. jaraquensis gen.et sp.n.

TABLE 4 . Measurements, in micrometers, of adult females of
B. anodus sp.n.

TABLE 5 . Antennal measurements, in micrometers, of adult females of
B. anodus sp.n.

TABLE 6 . Relationships of Spines to Setae on the Legs of
B. anodus sp.n.