13. Acanthocephala collected by the Swedish Expedition to the Juan Fernandez Islands (1916-1917).1 By H. J. VAN CLEAVE, Urbana, Illinois. With Plate 5. Through the courtesy of Professor T. ODHNER, I have been granted the opportunity of studying the Acanthocephala taken by the Swedish Pacific Expedition (1916–17), directed by Dr. C. SKOTTSBERG, to the Juan Fernandez Islands off the coast of Chile. This collection, though relatively small, is of considerable importance because of the extremely meagre data available regarding the acanthocephalan fauna of the west coast of South America. Worms of this group occur as parasites in the intestine of all the groups of vertebrates but are frequently overlooked by general collectors. Most of the studies on Acanthocephala from South America have been conducted upon collections from Brazil. The few isolated instances of studies from other localities on the same continent indicate that collections from widely separated localities are fairly sure to contain distinctive species not encountered in other regions. Previous studies have demonstrated that many species af Acanthocephala are sharply limited in the extent of their geographical distribution. No lists are available that would make possible a comparison of the species collected by the Expedition and those that might be encountered on the nearest mainland. In the collections secured by the Expedition but three species of Acanthocephala are represented. Two of these are from the intestine of fishes and the third from the intestine of a gull. The fish parasites include a new species of the genus Rhadinorhynchus and another new species for which it has been necessary to erect a new genus, Tegorhynchus for which T. brevis is designated as type. A single specimen of the genus Arhythmorhynchus from Larus dominicanus belongs to a previously unrecognized species which is here described as Arh. teres. 1 Contributions from the Zoological Laboratory of the University of Illinois, No. 173. Genus Rhadinorhynchus Lühe 1911. The genus Rhadinorhynchus was created by LÜHE (1911) to include the single species Rhad. pristis which occurs in fishes, chiefly of the Mediterranean. The addition of another species, Rhad. horridus from Egypt, and the recognition of the phylogenetic relationship existing between these two species and LINTON'S Echinogaster sagittifer, caused LÜHE (1912) to suggest the possible justification for recognition of a sub-family Rhadinorhynchinae. This sub-family was definitely recognized by the present writer (VAN CLEAVE, 1918) in a paper which placed three additional species from North America within the same subfamily. Rhadinorhynchus selkirki, new species. Described from five females and one male preserved in alcohol. Females 14 to 20 mm. long and from 0,6 to 0,8 mm. in maximum diameter. Single observed male 6 mm. long and 0,46 mm. in diameter. Proboscis long, cylindrical; 2 mm. or more in length and from 0,2 to 0,25 mm. in diameter; armed with 12 (in one instance 14) longitudinal rows of about 24 hooks each. Hooks on ventral surface (Fig. 4) much longer and heavier than corresponding hooks on dorsal surface (Fig. 3). Hooks in adjacent rows alternating except at the extreme base of proboscis where the basal hooks of all rows occur at approxim ately the same level thus forming a single circle of 12 hooks, each about 89 p. long. Comparison of hook lengths on ventral and dorsal surfaces of proboscis of Rhad. selkirki (hooks are numbered from base toward tip of proboscis. Lengths are in u). I 2 3 4 5 6 7 8 Ventral row 89 83 89 94 Dorsal row 89 53 53 53 94 94 94 94 In preserved specimens proboscis protrudes toward ventral side of anterior extremity at almost a right angle. Posterior region of body curved so that dorsal surface lies on concave rather than the more usual position on convex surface of body (Fig. 1). Proboscis receptacle 2,5 to 3,8 mm. long, double walled, with the retractors of the proboscis receptacle emerging from the posterior margin. Anterior region of body-proper provided with spines which are grouped into two fields. The spines at the anterior extremity of the body-proper form an irregular collar, the individual spines of which measure form 41 to 88 p. Immediately posterior to this collar is a region entirely devoid of spines. This in turn is followed by an area bearing conspicuous spines (Fig. 2). In some individuals spines of this region attain a length of 115 p. though they more frequently measure from 45 to 95 p. About 1,5 mm. from the anterior extremity of the body-proper there is a rather marked enlargement in the diameter of the body. In some specimens this was especially conspicuous as a hump upon the ventral surface. A craterlike depression observed on this prominence in two individuals superficially resembled a sucker but closer observation demonstrates that such a depression is probably due to a mutilation of the body surface caused by the accidental extraction of one or more of the cuticular spines. None of the females collected by the Expedition contained fully formed embryos, consequently data for the comparison of these structures with those of closely related species are entirely wanting. Infestation by this parasite does not seem to be excessive for in ten specimens of the host examined but six of the parasites were encountered. Habitat: Intestine of Caranx georgianus C. V. taken at Masatierra by Mr. K. BÄCKSTRÖM in December 1916 and April 1917. Cotypes deposited in the Riksmuseum i Stockholm and in the collection of the writer in Urbana, Illinois, U. S. A. Until recently all Acanthocephala possessing body spines and occuring as adults in the intestine of fishes have been considered as belonging to the single genus Rhadinorhynchus. Such a purely external character has but little value in the determination of phylogenetic relationships. Recently the writer (VAN CLEAVE 1920) has erected a new genus, Quadrigyrus, for which it has been shown that internal structure and finer morphology rendered it impossible to include this genus even in the same family with Rhadinorhynchus despite the fact that both these genera are characterized by the presence of spines on the body wall. There are frequent references in the literature on fish parasites to Acanthocephala bearing body spines but in most of these instances facts concerning the internal organization of the body are entirely wanting. Many such species were described in the epoch during which the genus Echinorhynchus was the only one recognized by most workers for the entire group of the Acanthocephala. As a result, many of the species descriptions of older workers such as DIESING and some of the relatively recent descriptions such as that of Ech. orestiae by NEVEU-LEMAIRE (1905) are completely lacking in details of morphology that are essential for any determination of their generic relationships. It is entirely possible that some of these insufficiently known species may properly belong in genera previously recognized or may necessitate the erection of new genera after their morphology is more completely understood. At present, on the basis of purely external characters it is safer to allow them to remain unplaced until actual determinations of relationships are possible. Specimens from the intestine of Malacopterus reticulatus C. V. taken on Masatierra display unique characters with reference to the structure of the proboscis (Figs. 6 and 7) and the location of the brain. It has been found. necessary to erect a new genus to accomodate these peculiar forms. Later study may show that some of the imperfectly known species bearing body spines may come within the scope of this same genus. Tegorhynchus, new genus. Acanthocephala parasitic as adults in the alimentary canal of fishes. Anterior portion of body-proper clothed with closely set cuticular spines which extend backward from the anterior extremity as an uninterrupted mantle. Proboscis covered by a thick hyaline membrane beyond which the proboscis hooks protrude but a short distance. Posterior extremity of body unarmed, in female terminating in two short, blunt papillae (Fig. 5) between which the genital aperture is located. Wall of proboscis receptacle composed of two muscular layers. Brain located inside the receptacle at its anterior extremity. Lemnisci long, extending about one half the length of the body cavity. Testes contiguous, followed immediately by a cluster of elongated cement glands. Type species: Tegorhynchus brevis, new species. Tegorhynchus brevis, new species. With the characters of the genus. Body short; females 4 to 8,5 mm. long by about 1,4 mm. in maximum diameter, males 3 to 6,5 mm. long by about 0,8 mm. in diameter. Proboscis when fully extended usually over 1 mm. in length and about 0,2 mm. in diameter; armed with 14 longitudinal rows of 17 to 19 hooks each. Hook lengths in " for a single row of hooks from ventral surface of proboscis of ♂ Tegorhynchus brevis. Position in row basal 2 3 4 S 6 7 8 9 10 II 12 13 14 15 16 17 18 Length 53 47 41 35 30 30 30 30 35 41 47.53 60 65 70 70 70 65 Body spines 30 to 35 long (Figs. 8 and 9). Embryos within body cavity of gravid female usually about 60 by 18 μ. Habitat: Numerous individuals were taken from the intestine of Malacopterus reticulatus C. V. in Masatierra by Mr. K. BÄCKSTRÖM, Dec. 16, 1916. Cotypes are deposited in the Riksmuseum in Stockholm and in the collection of the writer in Urbana, Illinois. Appendix. Species from adjacent mainland. Genus Arhythmorhynchus Lühe 1911. A single specimen representing an undescribed species of the genus Arhythmorhynchus was obtained from the intestine of Larus dominicanus at Talcahuano, Chile. This individual is so unquestionably distinct from any previously described representative of the genus that a diagnosis is given here even though a knowledge of the male and data concerning some features of the female, such as the nature of the embryos, are wanting. |