BULLETIN OF MARINE SCIENCE VOLUME 16 1966 NUMBER 2 LARVAL STAGES OF CARDIODECTES SP. (CALIGOIDA: LERNAEOCERIFORMES), A COPEPOD PARASITIC ON FISHESl JU-SHEY HO Boston University, Boston, Massachusetts ABSTRACT Five postembryonic stages of a fish copepod belonging to the genus Cardiodectes Wilson were recovered from pelagic snails, Janthina globosa Swainson, in the West Indies. They are probably identical with those found in Creseis sp., with those reported in Janthina exigua Lamarck in the Med- iterranean Sea, and with those recently collected from Janthina janthina (L.) in Madagascar. A comparison with adult metamorphosed females of Cardiodectes medusae US (Wilson) and Peroderma cylindricum Heller reveals that these larvae belong to Cardiodectes, a genus characterized by having only three pairs of functional swimming legs and two labial flaps encircling the mouth tube. The five stages of development are: free-swimming copepodid, chalimus I, chalimus II, chalimus III, and free- swimming adult form. Each stage is separated by one molt. Sexual dimor- phism is not observable until chalimus II. INTRODUCTION The copepods of the group Lernaeoceriformes are some of the most eccentric and bizarre ectoparasites of marine fishes and cetaceans. They were discovered as early as the time of Aristotle but most species of the group are known only from females; nothing is known of the males. This is because of their peculiar mode of life history, in which, after copulation, only the female is capable of penetrating into the tissue of the final host (if the first host is not the final one) to carryon her parasitic life. The male dies without even attaching to the final host. Among the approxi- mately 20 known genera in the Lernaeoceriformes, a relatively complete life history is known in only one species of three different genera: Lernaeocera branchialis (L.) (Sproston, 1941), Sarcotretes scopeli Jungersen (Jungersen, 1911), and Pennella varians Steenstrup & Lutken (Rose & Hamon, 1953). Because of such incomplete knowledge of the life history and lack of knowledge about the male, the classification of this group of copepods has been rather confused by various investigators' different con- 'This study was submilted originally in partial fulfillment of the requirements for the degree of Master of Arts at Boston University. 160 Bulletin of Marine Science [16(2) TABLE 1 NUMBERS OF DEVELOPMENTAL STAGES OF COPEPODS FROM PELAGIC SNAILS (Janthina sPP.) ------- Locality Barbados, Barbados, 12°07' S 11°25' S W. Indies W. Indies 44°20' E 44°25' E --~ ---- - Call. date 9/8-9/11 7/24-8/1 8/10 10/31 1963 1964 1964 1964 Total No. of examined 41 46 35 3 125 snails infested 40 36 35 3 ] 15 Copepodid 230(62) 37(2) 8](4) 65(] ) 413(69) Chalimus I 889 74 101 89 ]153 Chalimus II 21 54 43 38 156 Chalimus III (1) 118 184 ]19 13 434 Chalimus III '? 218 256 268 7 749 Adult (1) 935(74) 625(48) 1409(181 ) 147(42) 3] 16(345) Adult '? 11 5 18 - 34 Pair 441 166 57 90 754 Total 3304 1577 2153 539 7573(414) ---- Note: The figures in parentheses indicate the number of copepods discovered in the washings (preservative). jectures and interpretations. For instance, the genus Lernaea lacks chalimus stages in its development but has been included in this group of copepods by many copepodologists on the basis of the superficial resemblance of the metamorphosed adult female to Lernaeoceriformes. This resemblance, however, is probably only the result of convergent evolution. In 1952, Rose & Hamon reported the discovery of a series of develop- mental stages of a lernaeoceriform copepod in Algerian pelagic snails, Creseis sp., but they were not able to identify the larvae. Furthermore, each developmental stage was unsatisfactorily described by them. Monod & Dollfus (1934) also discovered lernaeoceriform larvae in Janthina exigua Lamarck from Monaco, but, like Rose & Hamon (1952), they did not propose any known genus or species for them, and only a brief statement was made. Having the opportunity of obtaining pelagic snails, Janthina globosa Swainson, from the West Indies, the author was able to collect a large number of copepod larvae. This made possible a detailed morphological study of each stage. These stages were compared with those found in Janthina janthina (L.) from Madagascar. Extensive survey of the structure of the appendages of certain metamorphosed females of lernaeoceriform copepods has shown that these larvae, from the West Indies, Madagascar (Table 1), and the Mediterranean Sea, belong to the genus Cardiodectes Wilson. ] 966] No: Larval Cardiodectes 161 This work was made possible by a grant from the National Science Foundation (GB-1809) to Dr. Arthur G. Humes, to whom the author's sincere acknowledgment is extended for his most valuable advice and for providing the material from Madagascar. He also wishes to thank Dr. Richard U. Gooding for providing the material from the West Indies, and Dr. Ruth D. Turner, Museum of Comparative Zoology, Harvard Univer- sity, for the identification of the host snails. MATERIALS AND METHODS The larvae were found either free inside the mantle cavity (free- swimming copepodid and free-swimming adult) or fixed to the gill lamellae (chalimus stages) of the snail. Therefore, in searching for the copepods, only the mantle was removed for examination. The free-swimming forms were frequently recovered from the washings (preservative). Before dissec- tion and study, the copepods were stained with chlorazol black E in lactic acid for three to five hours depending on the concentration of the stain. The wooden slide procedure (Humes & Gooding, 1964) was used to study the appendages of each developmental stage. THE FREE-SWIMMING COPEPODID Figs. 1-] 2 The body (Fig. 1) is of the general free-swimming copepodid form found in the lernaeocerids, with the cephalothorax longer than the meta- some plus the urosome; its surface is covered with irregular dark blotches. (In all figures, the letter in parentheses indicates the scale at which the figures were drawn.) The length varies from 0.42-0.48 mm; the mean width is 145ft. The cephalothorax is oblong, of about equal width through- out its length, rounded anteriorly and nearly truncated posteriorly; it is covered with a weakly developed carapace which shows a clear ventral infolding along the latera] margins (Fig. 13). A scIerotized line showing the demarcation between the head and the rest of the cephalothorax is seen only on the dorsal surface. The two contiguous eyes are well devel- oped, and are in the center of the head beneath the cuticle. Each has a spherical lens embedded in the anterior corner of a densely pigmented blotch. The posterior part of the cephalothorax carries the first pair of legs. Behind the cephalothorax, there are four free segments, of which the last two are rather firmly united and appear as a unit. The first free segment carries the second pair of legs. The second segment is of characteristic trapezoidal shape and bears two stout spines on its posterolateral corners. The third free segment is the shortest one, representing the fourth thoracic segment and bearing no appendages at the present stage. The last free segment is subquadrate in shape, representing a combination of the genital and the abdominal segments and carrying two relatively wide caudal rami. 162 Bulletin of Marine Science [16(2) 6 E E E N E '" on '"ci « w ...J « w'" u ...J l/) « 7 u l/) E E u ...JW « u l/) ~ 1966] Ho: Larval Cardiodectes 163 The first antenna (Fig. 2), usually bent ventrally and pointed postero~ laterally, is indistinctly 4-segmented. Each of the first three segments bears one seta on the anterior side close to the distal end, while the terminal segment is relatively heavily armed, with a stout aesthete projecting from the antero-subterminal portion, and 11 setae distributed around the terminal and the subterminal portions. Of these setae, the two terminal longer ones are bifurcate. Rose & Hamon (1952) described a 5-segmented first antenna, and the distribution of setae was: 0, 1, 1, 2, and 8 plus an aesthete. The different number of segments in the two cases is difficult to explain, since the segmentation of the first pair of antennae at this stage is so poorly developed that it is very difficult to tell the exact number of segments. However, the difference in the nature of the setae is noteworthy, no bifurcate seta being described by them (perhaps not observed?). The second antenna (Fig. 3) is stout and powerful, consisting of two very large first and second segments and a terminal dactylus which forms a subchelate apparatus with the distal end of the second segment and bears a seta on the base of its inner side. The mouth tube is located in a position nearly opposite to the eyes, with the opening facing downward and forward (Fig. 13). The buccal cone is formed by two parts (Fig. 4): a semicircular labium, with its gap facing anteriorly, and a pear-shaped labrum, which fits against this gap. Thus, they form a tubular apparatus and leave two openings on the basal part of the sutures for the insertion of the mandibles into the oral tube. In the distal wall of the labium, there are three sclerotic rings, which, together with the marginal membrane, form the so-called buccal tube. The distal two rings are of about the same width and complete posteriorly, but the proximal one is incomplete posteriorly, with the ends tapering off (Fig. 5). Distal to the rings, there is a thin, sclerotic band, which, at the present stage, appears as a ring made of numerous sclerotic rods. The marginal membrane is distal to this sclerotic band. Another circular mem- brane (Figs. 4, 5) is seen hanging over the sclerotic band and the most distal ring.