Paradeontacylix megalaspium, Lakshmi, Triveni, 2007

Lakshmi, Triveni, 2007, Paradeontacylix megalaspium n. sp. (Digenea: Sanguinicolidae) from the carangid fish, Megalaspis cordyla of Bay of Bengal, Zootaxa 1512, pp. 65-68 : 65-67

Paradeontacylix megalaspium n. sp. (Figs 1-4)

Type-host: Megalaspis cordyla (Linnaeus) (Carangidae) , torpedo scad.

Type-locality: Visakhapatnam coast, Bay of Bengal (17°44′N, 83°23′E).

Site: Gill blood vessels.

Prevalence of infection: A total of 110 M. cordyla ranging in fork length from 118-280 mm were examined during March, 2006-January, 2007. Infection with the blood fluke was rare and confined to the months March-May. Only 8 fish ranging in fork length from 192-280 mm showed the infection, each infected fish carried 1-4 flukes. Altogether 18 flukes were collected. The prevalence of infection was 1.6% and the intensity was 2.2.

Material deposited: Holotype- Zoological Survey of India, Calcutta, India No W 8878 Paratype- NHM, London No. 2007.5.16.1

Etymology: The species is named after the generic name of the host, Megalaspis .

Description: Based on 10 specimens. Body long, slender, worm-like, with parallel sides, pointed anterior and posterior ends, protruding anteriorly as a knob, 1,920–3,520 long 96–192 wide, approximately 20 times longer than wide (Fig.1). Tegument thin, transparent, armed with spines arranged in regular rows along ventrolateral margins, number of rows on each side ranges from 400–450, each row with 4–6 spines in anterior and posterior regions; 8–10 spines in rest of body; spines needle-like (Fig. 2). Spines near posterior region of body not enlarged, similar in size and shape to rest of body spines (Fig. 3). Mouth subterminal, esophagus long, sinuous, 302–576 long, narrow anteriorly, somewhat distended posteriorly, surrounded by gland cells, dividing into ceca at approximately one sixth of body length from anterior end. Ceca H-shaped, anterior branches of ceca short, posterior ones long, narrow, extending to level of ovary. Cecal lumen often contains red blood cells and some yellowish pigment material. Nerve commissure conspicuous, at a distance of 80-184 from anterior end.

Testis follicular, follicles small, approximately 70–86 in number, arranged in two irregular rows in intercecal region between cecal bifurcation and ovarian zone. Follicles disrupted in some specimens and testis appears as single irregular mass. Testicular field 995–1552 long, 72–80 wide, occupies ~50 percent of total body length. Vas deferens originates from testis, crosses ovary, proceeds posteriorly towards left as a sinuous tube, continues as seminal vesicle enclosed in cirrus sac (Fig. 4). Prostatic cells absent. Cirrus short, thick-walled. Male genital pore submedian on dorsal side, at a distance of 312–384 from posterior end of body. Ovary post-testicular, appears as large irregular mass composed of 2 lobes contiguous with one another, 140–240 long, 112–160 wide, postovarian space 528–680, approximately one fifth of body length. Oviduct originates from posterior border of ovary as narrow duct, joins vitelline duct to form ootype, surrounded by small, diffuse, inconspicuous Mehlis’ gland. Seminal receptacle, Laurer’s canal absent. Uterus originates from ootype, first descends, turns back, proceeds anteriorly, describes few coils posterior to ovary, then finally opens out through submedian female genital pore, a little anterior to male genital pore. Eggs small, oval, 20–24 long, 12 wide, eggshell thin, membranous, transparent. Vitelline follicles small, numerous, occupy most of area between nerve commissure and ovary, form two thick lateral zones, intrude into testicular zone. Vitelline duct narrow, runs parallel to oviduct. Excretory vesicle not observed.

Discussion. The characters of the genus, including the H-shaped ceca, follicular testis, presence of separate male and female genital pores and postovarian distribution of uterus, fit into the generic diagnosis of Paradeontacylix McIntosh, 1934 as given by Smith (2002). Six species are known in the genus: P. sanguinicoloides McIntosh, 1934 from Seriola lalandi ; P. odhneri ( Layman, 1930) from the puffer Takifugu porphyreus (= Spheroides borealis ); P. sinensis Liu, 1997 from T. oblongus (= Fugu oblongus ); P. godfreyi Hutson & Whittington, 2006 from Seriola lalandi ; P. grandispinus Ogawa and Egusa, 1986 , and P. kampachi Ogawa and Egusa, 1986 both from farmed Seriola purpurascens . Hutson & Whittington (2006) compared the morphological characters of the four species of the genus recorded from Seriola spp. Two species, P. odhneri and P. s i n e n s i s, were recorded from puffer fishes, but do not show any specialized features attributed to occurrence in different taxa of hosts. The present species, also from a carangid fish, can be distinguished from all these six species by possessing the following combination of characters: long slender worm-like body with 400–450 rows of marginal tegumental spines, each with 8–10 spines along major part of body; the absence of enlarged posterior tegumental spines; and presence of 70 to 86 testis follicles, occupying 50% of body area. Two other species P. k a m p a c h i from Japan ( Ogawa & Egusa 1986) and Spain ( Montero et al. 2003) and P. s i n e n s i s from China ( Liu 1997) also do not possess enlarged spines at posterior region. Paradeontacylix megalaspium n. sp. closely resembles P. k a m p a c h i but differs from it in the long slender body, more anteriorly placed and irregularly shaped ovary, in the lesser number of rows of spines (510–590 in P. kampachi ) and in the extent of testis (50% of body area in P. megalaspium n. sp. as against 29– 32% in P. kampachi ). Paradeontacylix sinensis has fewer testis follicles (29–32) that occupy a greater proportion of body length (~69%).

Paradeontacylix godfreyi , P. sanguinicoloides and P. grandispinus possess enlarged integumental spines at posterior end. Paradeontacylix godfreyi further differs in having more transverse rows of marginal tegumental spines (690–890), more number of testis follicles (99) but occupying a lesser percent of body area (18–25%). P. sanguinicoloides has 60 testis follicles occupying 41% of body and 580–654 rows of spines ( McIntosh 1934). Paradeontacylix grandispinus is very different in that it has a spatulate body and a lesser number of testis follicles (19–32), occupying only 27–38 % proportion of body ( Ogawa & Egusa 1986). Further, it possesses a receptaculum seminis formed by the dilatation of oviduct which is lacking in P. megalaspium n. sp. Paradeontacylix odhneri is only briefly described but is distinct from P. meg alaspium n. sp. in the more posteriorly placed ovary which lies at one ninth of body length from posterior end ( Layman 1930). The description of this species does not provide details of the arrangement of tegumental spines and the number of testis follicles. Hence a detailed comparison with this species can not be made.

Paradeontacylix megalaspium n. sp. exhibited narrow specificity to Megalaspis cordyla . None of the species of carangids occurring at Visakhapatnam coast examined by us (e.g. Carangoides malabaricus , C. ferdau , Selar crumenopthalmus, Chorinemus tol) along with the samples of M. cordyla , showed infection with the fluke.

Acknowledgment. The financial assistance provided by Ministry of Environment and Forests, Government of India, under the AICOPTAX program is gratefully acknowledged.

FIGURES: Paradeontacylix megalaspium n. sp. from Megalaspis cordyla . 1. Holotype, entire specimen, ventral view; 2. Rows of body spines; 3. Posterior region of body, enlarged view to show arrangement of body spines; 4. Enlarged view of posterior part, showing terminal genitalia