Diplostomulum elongatus n. sp. (Trematoda), from a Freshwater Fish, Trichogaster fasciatus, from India

Abstract

Seventy specimens of a fresh-water fish, Trichogaster fasciatus, were examined in Lucknow, India, and 2 of these were found to harbor larval cysts of a digenetic trematode. It was determined that the forms were of the genus Diplostomulum, and inasmuch as they could not be identified as to species from existing material, they are described herein as new, and so named to designate the elongate, slender form and the comparative size. The transparent cysts were found attached loosely to the mesentery inside the body cavity. The 2 specimens recovered differ greatly in size, but apparently they are 2 stages of the same species. While alive the larvae showed active movement, both inside and outside the cyst. The specimens were fixed in corrosive sublimate and mounted in balsam. All measurements given below are in millimeters, and were taken from the larger specimen. not well-marked) into flattened forebody slightly concave ventrally, 0.972 long by 0.558 wide, and small hindbody, 0.2 long. Comparatively small oral sucker somewhat ventral, muscular, 0.045 in diameter. Mouth opening sub-ventral. Lateral suckers appear as slightly muscular papillae, postero-lateral to oral sucker. Oral sucker leads directly into muscular pharynx, 0.03 in diameter; prepharynx absent. Short esophagus bifurcates into 2 intestinal ceca, running posteriorly well into hindbody. Muscular acetabulum, 0.07x0.04, rounded in living condition and transversely elongated when fixed, present in anterior to middle of body, 0.5 from anterior end. Hold-fast organ, much posterior to acetabulum near posterior end of forebody, longitud- inally elongated in living state and rounded when fixed, 0.136 in diameter. Compact, elongated hold-fast gland, 0.132x0.03, seen with difficulty in living larva, stains deeply with carmine. Genital anlagen, consisting of irregular mass of undifferentiated cells, present between ceca in hindbody, somewhat posterior to hold-fast gland. Primary excretory system and flame cells obscured by reserve excretory system and not seen. Reserve excretory system divisible into ventral ducts, forming major part of system, and comparatively few dorsal ducts. Excretory pore, present posteriorly, leads into small vesicle that divides into 2 main lateral excretory ducts running anteriorly. Lateral ducts with smaller ducts form excretory system ventrally. Two outer lateral ducts joined by transverse connection just posterior to oral sucker. Main excretory ducts joined in hindbody by 2 posterior transverse excretory ducts. Latter, dorsally, has apparently blind median process directed anteriorly, and connected to 2 lateral excretory ducts at same point. Two lateral excretory ducts joined in hindbody by 2 or 3 short ducts. In forebody, 2 medial lateral excretory ducts connected first by anterior transverse duct, and, proceeding anteriorly, several ducts join 2 lateral excretory ducts up to region of acetabulum. Several ducts loop and rejoin medial ducts on medial side. Anterior to acetabulum, 3 to 4 excretory ducts connect lateral ducts. From posterior side of transverse connection of outer lateral excretory ducts near oral sucker, small duct running posteriorly joins median excretory vesicle just posterior to intestinal bifurcation. Slightly posterior to opening, 2 inner lateral excretory ducts also join median excretory vesicle, latter running behind intestinal bifurcation to hold-fast organ. Posterior end of elongated, spindle-shaped median excretory vesicle passes ventral to transverse con- nection. Vesicle opening into transverse connection anterior to hold-fast organ not seen. Dorsal excretory ducts arise from 2 main lateral ducts in posterior region and branch, in hindbody, to form fine network, of which finer ducts regroup and form duct leading anteriorly into forebody, there branching dorsally to hold-fast organ to form fine network. Fine ducts