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A key to some pentastome, nematode and trematode parasites of the American alligator.

Abstract. -- Seventy-five American alligators (Alligator mississippiensis) were obtained from southeast Texas and southwest Louisiana. Necropsy revealed the presence of one species of pentastome (Sebekia mississippiensis), three species of nematodes (Dujardinascaris waltoni, Brevimulticaecum baylisi, Brevimulticaecum tenuicolle) and eight species of trematodes (Acanthostomum coronarium, Acanthostomum loossi, Acanthostomum pavidum, Archaeodiplostomum acetabulata, Crocodilicola pseudostoma, Dracovermis occidentalis, Polycotyle ornata and Pseudocrocodilicola georgiana). All of these parasites have been previously reported in the literature, but were dispersed among numerous sources. As part of this study, a concise key including all of the endohelminths reported during this study of the American alligator was compiled from existing sources.


In 1992, a four year study was initiated to study the infracommunity structure of 75 alligators from southeastern Texas (Scott et al. 1997). Results of this study, including voucher specimens and statistical analyses, were compared to previously reported parasite findings from South Carolina (Hazen et al. 1978).

Though several other parasitological studies (Byrd & Reiber 1942; Brooks & Overstreet 1977; 1978; Sprent 1977; 1979; Deardorff & Overstreet 1979; Overstreet et al. 1985) have been performed on Alligator mississippiensis, there has been no all-inclusive work published outlining identification of all the endohelminths of alligators. Therefore, the purpose of this report is for use as an identification key for the endohelminths of the alligator and as a source for reported measurements of each parasite and their respective eggs. The keys are for identification purposes only, and do not attempt to show phylogenetic relationship. These keys include descriptions of nematode and trematode families. Keys to the genera of given parasites follow under the specified family heading. Nematode information is compiled from Yorke & Maplestone (1926); Hartwich (1974); Sprent (1977; 1979) and Deardorff & Overstreet (1979). Pentastome information is from Overstreet et al. (1985). Finally, trematode information comes from Byrd & Reiber (1942); Brooks & Overstreet (1977; 1978) and Schell (1985). Permission to use line drawings from Sprent (1977; 1979), Brooks & Overstreet et al. (1985), and Schell (1985) was obtained from the publishers of the respective journals. Standard terminology as applies to morphlogical features follows that of Schmidt & Roberts (1989).


Diagnosis. -- Commonly large, stout worms; usually three lips present, less often two or none; esophagus simple, muscular, lacking specializations, occasionally with posterior ventriculus, with or without appendix; intestine occasionally with one or more appendices at esophagointestinal junction; preanal sucker present in a few species; eggs usually with sculptured uterine layer, unembryonated when laid, juveniles infective to host in second (perhaps third) stage; parasites of all classes of vertebrates. Basal region of lips without collar of fibriae, postlabial region naked or provided with three tongue-like prolongations of lips united by folded membranes with cordon-like cuticular thickenings, or with thickenings consisting of transversely striated ribs. Postlabial region without cuticular peculiarities, or provided with cordon-like or rib-like structures.


1a. Esophagus with oblong to cylindrical posterior ventriculus with one dorsal and one ventral longitudinal suture-like depression, or with small globular ventriculus giving off posteriorly directed appendix with such depressions or rarely two appendices. Excretory system asymmetrical, confined to left lateral chord. Excretory pore situated between base of subventral lips or near nerve ring. Intestinal cecum present or absent. Parasites of mammals, birds, reptiles and fishes .................... Anasakidae

1b. Esophagus without ventriculus or with globular to ellipsoidal ventriculus without longitudinal sutures; from ventriculus two anteriorly and three posteriorly directed appendices may arise. Excretory system symmetrical, the right lateral canal of which may be somewhat reduced. Excretory pore situated near nerve ring. Lips well defined, distinctly offset from anterior end; each lip with single, separate dentigerous ridge on anterior margin of inner surface, or dentigerous ridges absent. Interlabia present or absent. Esophagus with or without ventriculus. Intestinal cecum present or absent. Parasites of mammals, birds, reptiles or amphibians, rarely of fishes .................... Ascarididae


The Family Anisakidae is represented by a single species.


Diagnosis. -- Cuticular rings with posterior spines. Lips flattened and expanded outwards. Interlabia absent. Esophagus stout, claviform, with small ventriculus giving off a long, single or double appendix. Parasites of teleost fishes and, rarely, reptiles.


Diagnosis. -- Esophagus with globular to ellipsoidal posterior ventriculus, from which may arise two anteriorly and three posteriorly directed appendices. Parasites of crocodilians and, rarely, of fishes. Specific measurements for members of the Family Ascarididae are given in Table 2.


1a. Esophagus with several posterior ventricular appendices; intestinal cecum present or absent .................... 2

1b. Esophagus without posterior ventriculus, small muscular esophageal bulb; intestinal cecum present .................... Dujardinascaris waltoni (Fig. 1a)

2a. Ventricular appendices club-shaped .................... Brevimulticaecum baylisi (Fig. 1b)

2b. Ventricular appendices lobulated, teat-shaped .................... Brevimulticaecum tenuicolle (Fig. 1c)




The Phylum Pentastomida is represented by a single species.


Male. -- Body 5.6 mm long; width 0.5 mm at cephalothorax, 0.9mm at abdomen; cephalothorax triangular in some individuals. Annuli numbering 69-70, with spinelike cuticular projections prominent in some individuals. Two pairs of sensory papillae, with each group forward of anterior hook and parallel to annuli; cephalic lobe paired, at anterior of body forward of sensory papillae. Hooks claw-shaped, having a broad base; talon relatively short; outer convex surface forming hump with minute spines. Fulcrum 0.13mm long (straight line between ends); outer surface rugose, without spinules; anterior outer portion projecting against base of hook as relatively small spinose shield; shield not touching hook when hook bent forward. Oral cadre oblong, 0.17 mm long by 0.07 mm wide, with opening an oblong ring; distal portion of mouth ring lightly sclerotized dorsally and open ventrally. Intestine sinuous especially in posterior half, with hemosiderin usually abundant in gastrodermis. Rectum length about equal to midbody diameter. Anus terminal.

Female. -- Body 10 mm long maximum, with width of cephalothorax 0.6 mm; cephalothorax roughly triangular, not demarcated sharply from abdomen; abdomen 1.6 mm at widest level. Annuli numbering approximately 70, difficult to distinguish in midregion. Anus terminal. Uterovaginal pore anterior to, but not contiguous with, anus on same annulus. Tegument relatively thin, delicate. Hooks, fulcrum and oral cadre similar to those of male.


Diagnosis. -- Mouth at anterior end of body, usually surrounded by oral sucker. Not in blood vessels of host; pharynx usually present; testes one or two, rarely multiple. Always hermaphroditic; usually parasitic in some internal organs of host. Oral and ventral suckers present. Ventral sucker near midbody or anterior to middle of body. Bulbous or foliaceous tribocytic organ posterior to ventral sucker, sometimes overlapping it; body usually divided into distinct fore- and hindbody; copulatory bursa and genital pore at posterior end of body; organs of reproduction confined to hindbody.


1a. Cirrus sac absent; fore- and hindbody distinct. Forebody flat or spoon shaped; tribocytic organ bulbous; intestinal parasites of reptiles, birds and mammals. Hindbody contains thick-walled paraprostate organ surrounded by gland cells; parasitic in reptiles (alligators) .......... Family Proterodiplostomidae

1b. Tribocytic organ absent; body not subdivided as described above; copulatory bursa absent .......... 3

2a. Genital pore and cirrus sac in posterior third of body or at posterior tip of body, some distance from ventral sucker, ventral to gonads or ventral to ceca. Testes tandem and some distance from posterior end of body; ovary between testes; body elongate, fusiform or spatulate. Seminal vesicle bipartite, enclosed in cirrus sac; genital pore ventral to left of cecum; vitelline follicles confluent anterior to gonads; parasitic in intestine of reptiles (alligators) .......... Family Harmotrematidae

2b. Genital pore in anterior half or middle third of body, usually anterior to ventral sucker, sometimes immediately posterior to ventral sucker. Genital pore median or submedian. Ovary anterior to testes or between testes. Ventrogenital or genital sac absent. Intestinal ceca without diverticula. Eggs not triangular; cirrus sac usually present. Oral sucker without muscular papillae. Two ceca and two testes; cirrus sac usually present. Spiny proboscides absent. No spiny collar, but one or two circles of large spines around oral sucker; intestinal parasites of fishes and reptiles. Seminal vesicle free in parenchyma, sometimes coiled; oral sucker large, terminal; gonotyl present in some genera; pre- and post-acetabular pits usually present .......... Family Acanthostomidae


Diagnosis. -- Body divided into flat forebody, containing the suckers and bulbous tribocytic organ, and a cylindrical hindbody which contains the organs of reproduction; testes tandem, in middle of hindbody; cirrus sac absent; seminal vesicle free in parenchyma; thick-walled paraprostate organ posterior to testes; genital atrium present; genital pore dorsal, near posterior end of body; hermaphroditic canal present; vitelline follicles in both fore- and hindbody or confined to forebody; parasitic in intestine of reptiles, especially alligators.



1a. Body linguiform, division between fore- and hindbody indistinct; vitelline follicles confined to area between ovary and ventral sucker .......... Crocodilicola pseudostoma (Fig. 3a)

1b. Division between fore- and hindbody distinct .......... 2

2a. Vitelline follicles extend into fore- and hindbody .......... Archaeodiplostomum acetabulata (Fig. 3b)

2b. Vitelline follicles confined to forebody .......... 3

3a. Hindbody with a linear series of accessory suckers on dorsal surface; atrial sucker also present in genital atrium; ejaculatory duct fused with terminus of uterus; hermaphroditic canal thin-walled .......... Polycotyle ornata (Fig. 3d)

3b. Hindbody without accessory and atrial suckers; ejaculatory duct united with side of paraprostate organ; hermaphroditic canal has thick muscular wall .......... Pseudocrocodilicola georgiana (Fig. 3c)


This family is represented in North America by the genus Dracovermis Brooks & Overstreet (1978). Dracovermis occcidentalis (Fig. 4a) has been reported as a parasite of American alligator, Alligator mississippiensis. Specific measurements for D. occidentalis and other trematodes known to infect A. mississippiensis are given in Table 3.


Diagnosis. -- Body flat, spatulate, nonspinous; oral sucker subterminal; ventral sucker in anterior half of body; pharynx present; esophagus short; ceca long; testes tandem, in posterior third of body; ovary intertesticular; cirrus sac in hindbody, anterior to gonads; cirrus spiny; seminal vesicle bipartite, internal; genital pore in hindbody, ventral to left cecum; vitelline follicles around ceca in fore- and hindbody; uterus confined to hindbody; metraterm present. Parasitic in intestine of reptiles.

The genus Dracovermis was formerly assigned to the Family Liolopidae.


Body elongate, spinous; oral sucker terminal, funnel-shaped, surrounded by a row of circumoral spines; ventral sucker smaller than oral sucker, in anterior half of body; pharynx, prepharynx and esophagus present; ceca long, ending blindly, open through separate ani or fuse with excretory vesicle to form a cloaca; one cecum might be vestigial or absent in some species; testes near posterior end of body, tandem; ovary pretesticular; cirrus sac absent; seminal vesicle free in parenchyma; gonotyl and hermaphroditic duct present is some species; genital pore anterior to ventral sucker; preacetabular and postacetabular pits present in some genera; ventrogenital sac absent; vitelline follicles lateral, along ceca in hindbody; uterus pretesticular; eggs embryonated, operculate; excretory vesicle Y- or V-shaped; parasitic in intestine of fishes and reptiles.



1a. Ovary some distance anterior to testes; some uterine folds posterior to ovary; Seminal receptacle anterior to ovary .................... Acanthostomum loossi (Fig. 4b)

1b. Ovary immediately anterior to testes; uterus entirely preovarian; seminal receptacle posterior to ovary .................... 2

2a. Gonotyle present, anterior to ventral sucker; esophagus shorter than prepharynx; body spines very small .................... Acanthostomum coronarium (Fig. 4c)

2b. Gonotyle absent; esophagus longer than prepharynx; body spines large .................... Acanthostomum pavidum (Fig. 4d)
Table 1. Specific measurements in mm for Goezia lacerticola (from
Deardorff & Overstreet 1979).

 Male Female

Length 3.9 - 8.2 4.3 - 8.8
Width (max.) 0.40 - 0.78 0.43 - 0.85
Lips 0.02 - 0.03 0.02 - 0.07
Nerve ring (from ant. end) 0.13 - 0.23 0.13 - 0.16
Esophagus (length) 0.50 - 0.73 0.63 - 0.95
Cecum 0.33 - 0.47 0.33 - 0.76
Vulva (from ant. end) n/a 1.4 - 2.0
Tail 0.07 - 0.12 0.07 - 0.25
Gubernaculum absent n/a
Spicules 0.34 - 0.87 n/a
Eggs n/a 0.02 - 0.04(dia.)

Table 2. Specific measurements in mm for some of the nematodes known to
infect Alligator mississippiensis (from Sprent 1977; 1979).

 Brevimulticaecum Brevimulticaecum
 baylisi tenuicolle

Length 9.4 - 19.1 9.2 - 15.1
Width (max.) 1.0 0.18 - 0.50
Width (E/I junction) 0.28 - 0.60 0.15 - 0.34
Lips 0.06 - 0.09 0.06 - 0.08
Interlabia 0.02 - 0.03 0.03
Nerve ring to ant. end 0.40 - 0.54 0.35 - 0.52
Excretory pore to ant. end 0.34 - 0.43 0.35 - 0.45
Esophagus (length) 2.0 - 2.7 1.6 - 3.1
Cecum 1.4 - 1.8 1.2 - 2.0
Vulva (from ant. end) 6.8 4.7 - 8.8
Tail 0.09 - 0.30 0.08 - 0.17
Gubernaculum 0.14 0.17 - 0.18
Spicules 5.8 1.23 - 1.34
Ejaculatory duct 1.4 1.12 - 1.30
Eggs 0.06-0.08 X 0.04-0.07 0.05-0.08 X 0.04-0.07


Length 11.8 - 14.0
Width (max.) 0.43 - 0.48
Width (E/I junction) 0.32 - 0.40
Lips 0.08 - 0.09
Interlabia 0.04 - 0.05
Nerve ring to ant. end 0.51
Excretory pore to ant. end 0.60 - 0.66
Esophagus (length) 3.0 - 3.1
Cecum 1.8 - 1.9
Vulva (from ant. end) 6.3
Tail 0.20 - 0.27
Gubernaculum 0.15
Spicules 6.7
Ejaculatory duct 2.2
Eggs 0.04-0.06 X 0.03-0.05

Table 3. Specific measurements in [micro]m (unless specified) of
trematodes known to infect Alligator mississippiensis (from Byrd &
Reiber 1942; Brooks & Overstreet 1977, 1978) (t = total; a = anterior; p
= posterior; d = diameter; l = length; w = width).

 Length Width

Archaeodiplostomum actabulata 4.80-5.96mm(t)
 2.44-2.96mm(a) 0.83-1.22mm(a)
 2.24-3.07mm(p) 320-770(p)
Acanthostomum coronarium 3.10-7.10mm 0.45-0.90mm
Acanthostomum loossi 1.18-2.92mm 0.23-0.44mm
Acanthostomum pavidum 1.6-10.6mm 0.4-1.1mm
Crocodilicola pseudostoma 1.60-1.88mm(t) 43(d)
 1.00-1.20mm(a) 560-620(a)
 710-740(p) 400-460(p)
Dracovermis accidentalis 1.00-1.75mm 0.38-0.59mm
Polycotyle ornata 1.81-3.12mm(t)
 0.87-1.48mm(a) 430-650(a)
Pseudocrocodilicola georgiana 1.44-1.77mm(t)
 0.96-1.22mm(a) 280-310(a)
 460-810(p) 160-170(p)

 Oral Sucker Acetabulum Ovary

Archaeodiplostomum actabulata 130-160(d) 370-450(d) 87-168(l)
Acanthostomum coronarium 425-690(l) 218-345(l) 161-310(l)
 241-391(w) 138-345(w) 149-345(a/w)
Acanthostomum loossi 92-270(l) 103-172(d) 46-240(l)
 115-240(w) 138-241(a/w)
Acanthostomum pavidum 195-575(l) 138-310(l) 115-379(l)
 72-322(w) 149-425(w) 161-568(a/w)
Crocodilicola pseudostoma 60-70(l) 70(l) 130-160(a/l)
 113-130(w) 140-160(w) 360-370(a/w)
Dracovermis accidentalis 35-72(l) 87-125(l) 58-125(l)
 38-72(w) 93-160(w) 87-174(w)
Polycotyle ornata 35(d) 52-87(l) 87-130(l)
 87-130(w) 100-150(w)
Pseudocrocodilicola georgiana 35-43(d) 61(d) 61-80(d)

 Testes Eggs

Archaeodiplostomum actabulata 170-330(a/l) 87-97(l)
 240-500(a/w) 44-61(w)
Acanthostomum coronarium 138-230(a/l) 29-32(l)
Acanthostomum loossi 92-264(a/l) 23-25(l)
Acanthostomum pavidum 149-460(a/l) 32-35(l)
Crocodilicola pseudostoma 96-104(l)
Dracovermis accidentalis 73-174(a/l) 93-116(l)
 145-290(a/w) 55-64(w)
Polycotyle ornata 113-240(a/l) 87-96(l)
Pseudocrocodilicola georgiana 113-140(a/l) 70-96(l)


We thank Sidney Dupuy for access to the alligators being processed in his slaughter house, and James Dixon for his assistance. We also thank Amos Cooper, Jim Sutherlin, other members of the J.D. Murphree Wildlife Management Area, and the State of Texas for cooperation in the collection of wild alligators and the scientific collecting permit (SPR-0992-562). Our gratitude to Beverly Tomlinson for technical assistance. Three anonymous reviewers from this journal provided suggestions and sound advice for improvement of this manuscript.


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Byrd, E. E. & R. J. Reiber. 1942. Strigeid trematodes of the alligator, with remarks on the prostate and terminal portions of the genital ducts. J. Parasitol., 28:51-73.

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Yorke, W. & P. A. Maplestone. 1926. The Nematode Parasites of Vertebrates. Hafner Publishing Co., New York, 536 pp.

Timothy P. Scott, Steve R. Simcik and Thomas M. Craig

Department of Biology, Texas A & M University, College Station, Texas 77843-3258

Department of Wildlife and Fisheries Sciences

Texas A & M University, College Station, Texas 77843 and

Department of Pathobiology, Veterinary Medicine

Texas A & M University, College Station, Texas 77843

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Author:Scott, Timothy P.; Simcik, Steve R.; Craig, Thomas M.
Publication:The Texas Journal of Science
Geographic Code:1U7LA
Date:May 1, 1999
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