Redescription of Echetus typicus Kroyer, a Caligid Copepod Parasitic on the Red Drum, Sciaenops ocellatus (Linnaeus)

Abstract

Echetus typicus Kr0yer is a copepod hitherto known only as parasitic on the red drum, Sciaenops ocellatus (L.). A redescription of both sexes is given, based on 14 females and 2 males taken from S. ocellatus in Apalachee Bay, Florida. A comparison with specimens in the U. S. National Museum collections shows them to be identical. The Echetinae Yamaguti, 1963, and the Mappatinae Yamaguti, 1963, two of the five subfamilies of Caligidae, are discussed in regard to their definition and range. It is suggested that, should the Echetinae be accepted on the basis of this subfamily being a group where the adult females show a highly modified fourth thoracic segment, genital segment, and abdomen, then Caligodes Heller, Parechetus Pillai, and Pseudopetalus Pillai should also be included, and the erection of the Mappatinae ought to be reconsidered, for it was based on a single and questionable genus Mappates Rangnekar. Caligulus Heegaard should be included in the Caligidae, and grouped together with Mappates, if the latter has only the fourth thoracic segment free. In 1864, Kroyer published a new species of parasitic copepod which he had obtained from the red drum (or red fish, or channel bass), Sciaenops ocellatus (Linnaeus), at New Orleans. The original description was made from some female specimens which had no head. The rest of the copepod's body, however, seemed to him so different from any of the copepods then known that he established for them a new genus, Echetus, and a new species, typicus. Kr0yer considered that the portion which he obtained (consisting of neck, genital segment, and abdomen) indicated considerable degeneration, and he placed the species in a group which comprises the most degenerate forms, namely, Lernaeocerina (now known as Lemaeoceriformes). Forty-one years later Wilson (1905), by the discovery of some intact specimens in the U. S. National Museum collections, made a correct change of the systematic position and relationship of E. typicus from what he considered to be the most degenerate forms (Lemaeoceriformes) to the least degenerate forms (Caligiformes). He found that the head portion (= carapace), general arrangement of the various body regions, and the details of the appendages show that it belongs to the Caligidae. The identity of the specimens in the USNM collections with those obtained by Kr0yer has been thoroughly discussed by Wilson (1905: 614-615). A rather detailed but inaccurate redescripReceived for publication 17 December 1965. tion of the female was made by Wilson (1905, p. 611-614, pl. XVII, figs. 196-205). The male of E. typicus was, however, not known until 1936, when Bere made a study on parasitic copepods of fishes from the Gulf of Mexico. Since only a single male was represented in her collection, the description based on that partially dissected copepod is inadequate. Although E. typiculs was subsequently reported by Pearse (1952) and Causey (1953, 1955) from the Gulf of Mexico, only the female was obtained and no further consideration of the morphology was made. In the summer of 1965, while the author was making a general collection of parasitic copepods in Apalachee Bay, Florida, he collected 14 females and 2 males of E. typictus. Through a careful study on their external anatomy and comparison with the specimens reported by Wilson (1905) and Bere (1936), a redescription of both male and female is felt to be necessary. The following redescription is based on the material collected by the author. All figures were drawn with the aid of a camera lucida. The letter in the parentheses after the explanation of each figure refers to the scale at which the figure was drawn. Measurements are in millimeters unless otherwise indicated. Redescription of Echetus typicus Kr0yer, 1864