Gulf and Caribbean Research

Volume 6 Issue 1

January 1977

Larval Cestode Parasites of Edible Mollusks of the Northeastern Gulf of Mexico

Edwin W. Cake Jr. Gulf Coast Research Laboratory

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Recommended Citation Cake, E. W. Jr. 1977. Larval Cestode Parasites of Edible Mollusks of the Northeastern Gulf of Mexico. Gulf Research Reports 6 (1): 1-8. Retrieved from https://aquila.usm.edu/gcr/vol6/iss1/1 DOI: https://doi.org/10.18785/grr.0601.01

This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf and Caribbean Research by an authorized editor of The Aquila Digital Community. For more information, please contact [email protected]. Gulf Kesearch Reports, Val. 6, No. 1, 1-8

LARVAL CESTODE PARASITES OF EDIBLE MOLLUSKS OF THE NORTHEASTERN GULF OF MEXICO

EDWIN W. CAKE, JR. Oyster Biology Sectioti, Gulf Coast RcJseurcli Laboratory, Ocean Springs, Afississippi 39564

.4BSTRAL'T Ten distinct of larval cestodes were obtained from 43 ediHe, or potentially edible, benthic mollusks of the northeastern Gulf of Mexico. Three of the infected mollusks, American oysters, Crassostrea virginica (Gmelin), Atlantic bay scallops, Argopecten irradians concentricus (Say), and sunray venus clums, Manocallisfa nimhosa (Lightfoot), are important commercial species in the eastern Gulf and the remainder are occasionally eaten by epicurean shellfishermen or \vcre consumed by prehistoric, ahoriFina1 Indians of the Gulf coast. The cestodes represent four orders, seven families and iiinc rccogized genera and include tlie trypanorhynclis. E~rtefrarl~~~izcht~ssp. (of Cakc 1975) and Purucliristizncllu sp. (of Cake 1975), the Iecanicephalideans, Pol~~pocephalussp. (of Cake 1975) and Tvkoceplzalun? sp. (of Burton 1963), thc tetraphyllideans, Dioecotuenia currcellatu (Linton 1890), Anthohotlrriurn sp. (of Cake 1975). Rhirzebotliriuin sp. (of Cake 1975). Acurff/ioDot/f,-itin7 sp. (of Regitii 1963), and Acanthohotlrriirm sp. (of Harry 1969), and the diphyllidean, 6ckirioDotliriicni sp. (of Cake 1975). Infected mollusks were widely distributed in coastal estuarine and marine habitats ippi Sound to the Keys. Pelecypods appear to serve as primary intermediate hosts and molluscivorous gastropods appear to serve :IS setonclary intermediate or paralciiic (transport) hosts for tliesc cestodes which in turn utilize demersal el;rsmohranch fish ;IS final hosts. None of these ccstodes are kiio\vri to infect Ii~irriansand the only potential harm is to the qiulity anti qimntity of the edihle molluscan tissuea.

INTRODUCTION Only one case of human infection by a related cestode is This repit was deiived from a three-year stndy of lai-val known. Heinz (1954) reported that a five-year-old Ecua- cestode parasites of shallow-water, benthic mollusks of the dorian boy spontaneously passed a Heputcrxylori sp. larva eastern Gulf of Mexico. During that study 2,470 niollusks, (Trypanorhyncha) while in a bathtub. The author hypothe- representing 36 gastropod species, 55 pelecypod species, and sized that tlie larva came from an impropcrly cooked marine one octopod, were collected fi-om 30 localities between Bay fish or that area which is commonly infected. This should St. Louis, Mississippi, and the Dry Tortugas archipelago of not be considered a true infection since the larva did not Florida and examined for larval cestodes. A list of hosts and establish itself in thc boy's body. parasites and a provisional key to the molluscan cestodes of The cestode nomenclature follows that of Schmidt (1970) the eastern Gulf of Mexico has been published elsewhere with the exception of Anthobotlirium Beneden, which he (Cake 1976). For the sake of brevity, the literature pertain- splits, and Rhinebothriuin Linton, which hc does not recog- ing to molluscan cestodes of the Gulf is presented in synoptic nize. The molluscan nomenclature follows that of Abbott form in Tablc 1. (1 974). The infection data reported and analyzed herein were derived from those mollusks which are harvested by com- MATERIALS AND METHODS mercial and sport shellfishermen. from thosc occasionally Benthic mollusks were collected at 30 Gulf coast localities cunsumed by epicurean sliellfisherrnen, fiom those which between Bay St. Louis, Mississippi, and Dry Tortugas, were consumed by aboriginal Indians of the northern Gulf Florida, from shallow, subtidal, grass, mud and sand flats coast, and from congeners of edible mollusks. These four and and oyster reef habitats via skin and scuba diving, categories are based on present edibility standards, on the wading, hand and shovel digging, etc. Based on preliminary suggestions of the late epicurean, Euell Gibbons (1964), and studies (Cake 1972), large pelecypods (i.c., clams, oysters, a senior Gulf coast zoologist, Gordon Gunter (1971), and pen shclls, scallops) afld molluscivorous gastropods (i.e., on archaeological data rrom Willey (1949) and Percy (1 973). conchs, tulip snails, whelks) were collected and transported Gibbons considered almost any marine or estuarine mollusk dive in 190-liter Styrofoam containers to several coastal edible but his choices in the Gulf wcre restricted to 10 marine laboratories for dissection and examination. The gastropods and 12 pelecypods. Gunter reported that 15 following tissues and organs were examined for cestode gastropods and 21 pelecypods from the Gulf were edible or larvae: in pelecypods-the gills, labial palps, stomach and potentially edible. Willey and Percy reported shell remains stomach walls, intestine and intestine walls, intestinal of 17 gastropods and 14 pelecypods from aboriginal Indian pouches (if present), digestive gland and diverticula, gonads, garbage mounds (or kitchen middens) along the northern and foot musculature; in gastropods-the valve of Leiblein Gulf coast of Florida. (if enlarged), esophagus and esophageal pouches (if present), 2 CAKE

TABLE 1. Synoptic review of larval cestode parasites reported from mollusks of the Gulf of Mexico.

Geographic Larval Cestode Species Molluscan Hosts Tissue Location Locality Reference Remarks

TRYPANORHYNCHA Parachristianella sp. Argopecten irradians Encysted singly along St. Teresa Beach, Cake 1972 Encysted (as P. dimegacantha Kruse) concentricus (Say) walls of intestine of Florida Macro ea Nista nimbo sa all hosts; and in foot (Light foot ) musculature of M. Spisula solidissima nimbosa and S. s. similis (Say) sim ilis N.ybelinia sp. (as “Scolex” Donax variabilis Say Digestive gland Galveston Beach, Wardle 1974 sp. VIII) A trina sem intrda (Lamarc k) Texas LECANICEPHALIDEA Polypocephalus sp. A. i. concentricus Digestive gland St. Teresa Beach, Cake 1972 Encysted singly Florida in small groups in clear-walled sacs Tylocephalum sp. Crassostrea virginica Gills, palps, gut Apalachicola Bay, Burton 1963 Encysted (Gmelin) epithelium Florida Tylocephalum sp. C. virginica Connective and Choctawhatchec Quick 1971 Encysted Leydig tissues and Tampa Bays, Florida Tylocephalum sp. (of A. i. concentricus Digestive tract walls, St. Teresa Beach, Cake 1972 Encysted Burton 1963) M. nimbosa and digestive gland of Florida S. s. similis all hosts; foot of M. nimbosa and S. s. sim ilis TETRAPHYLLIDEA Acanthobothrium sp. Melongena corona Gmelin Mantle cavity Live Oak Island, Regan 1963 Free in cavity (as “Scolex pleuron ec lis” Apalachee Bay, Mueller) Florida Acanthobothrium sp. tulipa Linnl Digestive tract Mullet Key, Fried1 and Free in gut (of Regan 1963) Tampa Bay, Simon 1970 Florida Acanthohothrium sp. F. tulipa Digestive tract Alligator Harbor Hamilton and Free in gut (of Regan 1963) Fasciolaria lilium (Region), Franklin Hyram 1974 hunteria (Perry) County, Florida Pleuroploca gigan tea (Kiener) M. cororw Polinices duplicatus (Say) Acanthobothrium sp P. gigan tea Digestive tract Galveston Beach, Wardle 1974 Free in gut (of Regan 1963) Thais haemastoma (Linng) Texas and off- shore platforms in area Acanthobothrium sp. Raeta (= Anatina) Gutwall cysts or sacs Galveston Bay, Harry 1969 Plerocercoids (as “S~ilexpleuronectis” plicatella Lamarck Texas share cysts or Mceller) sacs Acanthobothrium sp. Tagelus pleheius Stomach and Galveston Bay, Wardle 1974 Free in gut (of Harry 1969) ( Solander) intestines Texas Macoma constricta (Bruguikr e) Dio eco tarnia ca ncella ta Arwdara ovalis Stomach and Galveston Beach, Warc‘le 1974 Free in gut (Lint on) (Bruguibe) intestines Texas Anthobothrium sp. M. nimhosa Visceral mass/mantle St. Teresa Beach, Cake 1972 Claviform sac (as Rhodobothrium sp.) cavity Florida containing worm hangs in mantle cavity Anthobothrium sp. D. variabilis Visceral mass/mantle Galveston Beach, Wardle 1974 Claviform sac (of Cake 1972) cavity Texas containing worm hangs in mantle cavity LARVALCESTODE PARASITES OF EDIBLEMOLLUSKS 3

TABLE 1 (Continued). Synoptic review of larval cestode parasites reported from mollusks of the Gulf of Mexico.

Geographic Larval Cestode Species Moliuscdn Hosts Tissue Location Locality Reference Remarks

TETRAPHYLLIDEA (Continued) Rhineholhrium sp. A. i. concentricus Stomach and St. Teresa Beach, Cake 1972 Frcc in gut, (as Echeneibothrium sp.) M. nimbosu digestive diverticula Florida confined in S. s. similis diverticula Rhinebothrium sp. A. serriinuda Stomach and Galveston Bcach, Wardlc 1974 Free in gut, (of Cake 1972) Oepidula fornicata intestine Texas confined in (Linni) diverticula C. plana Say Dosiriia discus Reeve Noetiu ponderosa (Say) Periplorna inequale (C. B. Adatns) R . plica t ella stomach and stomach walls, digestive gland and diverticula. Parachristianella sp. (of Cake 1975) All examinations were made with the aid of a stereo- Order: Lecanicephalidea scopic, dissecting microscope. The larvae were removed or Family: Lecanicephalidae excised (if encysted), identified (usually to family or species Genus: Polypocephalus sp. (of Cake 1975) type), counted and either fixed and preserved or placed in Family: Cephalobothriidae petri dishes of filtered seawater (at 30°/00salinity and Genus: Tylocephalum sp. (of Burton 1963) ambient temperature) for further observations. Selected Order: Tetraphyllidea larvae of Acanthobothrium spp., Rhinebothrium sp., and Family: Dioecotaeniidae Polypocephalus sp. were incubated for up to 150 hours in Genus: Dioecotaenia cancellata (Linton 1890) a glucose-enriched, artificial elasmobranch saline medium Family: Phyllob othriid ae (vide: Kcad ct al. 1960; Hamilton and Byram 1974) to Genus: Anthobothrium sp. (of Cake 1975) facilitate identification. During incubation some larval fea- Rhinebothrium sp. (of Cake 1975) tures (e.g., apical suckers and bothridial precursors) were Family: Onchobothriidae lost or modified (e.g., quadriloculate bothridia became Genus: Acanthobothrium sp. (of Regan 1963) triloculate withterminal suckers or pads onAcanthobothrium Acanthobothrium sp. (of Harry 1969) spp. larvae), and some rudimentary adult features developed Order: Diphyllidea (e.g., bothridial hooks on larvae of Acanthobothrium spp.). Family: Echinobothriidae The larvae were killed in an expanded or relaxed condi- Genus: Echinobothrium sp. (of Cake 1975) tion with tepid tap water or hot (ca 50°C) alcohol-formalin- Those ten species and two unidentified tetraphyllidean acetic acid (AFA), fixed in AFA, and preserved in 70% larval forms are illustrated in Figures 1-1 8. The unidentified ethanol with 5% glycerine. Large post-plerocercoids of forms (Figures 15 and 16) are probably early plerocercoids Anthobothrium sp. were killed in an expanded condition of Acanthobothrium sp. (of Regan 1963) (Figure 9) and (bothridia attached to petri dish bottom) with liquid nitro- Rhinebothrium sp. (of Cake 1975) (Figures 11, 12, and 13), gen and fiied and preserved as above. The larvae were respectively. The early plerocercoids of each species con- stained with either Van Cleave’s combination hematoxylin currently infect the same molluscan host as the advanced, or Erlich’s acid hematoxylin and mounted on slides via identifiable plerocercoids and in some instances a complete standard helminthological techniques. developmental sequence of plerocercoids is present in a single host. RESULTS A complete list of molluscan hosts for these cestodes was Ten distinct species of larval cestodes were recovered published previously (Cake 1976, Table 1). The edible mol- from 43 edible or potentially edible, benthic mollusks of luscan hosts of each cestode are listed along with appropriate the eastern Gulf of Mexico. The cestodes represent four bibliographic data on their actual or potential edibility in orders, seven families and nine recognized genera as follows: Table 2. Order: Trypanorhyncha Seven species of edible pelecypods (by present standards) Family: Eutetrarhynchidae were infected by one or more larval cestode species. Three Genus: Eutetrarhynchus sp. (of Cake 1975) of those pelecypods-bay scallops, Argopecten irradians 4

1 2 3 5 6

7 11 12

18

Figures 1 - 18. Larval cestodes of Gulf of Mexico (after Cake 1976). 1. Longicaudate, invaginated acanthorostellobothridio- cysticercoid of Echinobothrium sp. (of Cake) from Nussurius vibex. (Cut-away view showing invaginated scolex.) 2. Scolex of Echinobo- thrium sp. (of Cake) from N. vibex. 3. Metabasal armature of internal tentacle surface of Eutetrurhynchus sp. (of Cake) tentaculo- neoplerocercoid from Plewoplocugiguntea. 4. Tentaculo-neoplerocercoidof Eutetrurhynchus sp. (of Cake) from P. gigun tea. 5. Side view of metabasal armature of tentacle of Puruchrisrianellu sp. (of Cake) tentaculo-neoplerocercoid from Macrocullistu nimbosu. 6. Tentaculo- neoplerocercoid of Paruchristianella sp. (of Cake) from M. nimbosu. 7. Bothridio-postplerocercoid of Anrhobothrium sp. (of Cake) from Anuduru trunsversu. 8. Claviform capsule containing bothridio-postplerocercoid of Anthobothrium sp. (of Cake) from A. trunsversu.(Cut- away view showing coiled postplerocercoid.) 9. Bothridio-plerocercoid of Auznthobothrium sp. (of Regan) from OIiw suyam. 10. Both- ridio-plerocercoid of Acanthobothrium sp. (of Harry) from Ensis minor. 11. Botluidio-plerocercoid of Rhinebothrium sp. (of Cake) from Argopecten irrudians concentricus. 12. Bothridio-plerocercoid of Rhinebothrium sp. (of Cake) from Busycon spirutum pyruloides. 13. Contracted scolex (bothridia) of Rhinebothrium sp. from E. s. pyruloides. 14. Bothridio-plerocercoid of Dioecotueniu cancellato (Linton 1 890) from Chione cancellato. 15. Uniacetabulo-plerocercoid of Acunthobothrium sp. (of Regan) from Fusciohria tuliw. 16. Uniacetabulo-plerocercoid of Hhinebothrium sp. (of Cake) from C. cuncellutu. 17. Encysted, acaudate glando-procercoid of Tylocephu- lum sp. (of Burton) from Argopecten irrudiuns concentricus. 18. Tentaculo-plerocercoid of Polypocephulus sp. (of Cake) from A. i. concentn'cus. LARVALCESTODE PARASITES OF EDIBLEMOLLUSKS 5

TABLE 2. Summary of larval cestode parasites of edible or potentially edible benthic mollusks of the eastern Gulf of Mexico.

Larval Cestode Species

References to Edible Mollusks - 1. Gibbons 1964 2. Gunter 1971 3. Percy 1973 Edible Mollusks Found to be Infected 4. Willey 1949 During the Present Study 5. Present Study

GASTROPODS: Busycon contrarium (Conrad) (as B. preversum-2) X X Busycon spiratum pyruloides (Say) X xx xx X Cantharus cancellarius (Conrad) X xxX X X Crepidula spp. xx xx X Fasciolaria lilium hunter,ia (Perry) (as F. distans-3) X xx xx X Fasciolaria tulipa (Linne) (as Fasciolaria sp.-3) X xx xx X Melongena corona Gmelin X xxx X X fulvescens Sowerby X Murex sp. [probably M. pomum (Gmelin)] X X Oliva sayana Ravenel X X X Pleuroploca gigantea (Kiener) (as Fasciolaria g-3) X X X X Polinices duplicatus (Say) xx X X X Thais haemastoma canaliculata (Gray) (as Thais sp.-1) X X PELECYPODS: Arca sp. X Argopecten irradians concentricus (Say) (as Pecten sp.-3, 4) xx xx xxxx Atrina rigida (Lightfoot) X xx X Atrina seininuda (Lamarck) xx X Chama macerophylla (Gmelin) X Chione (spp.-1) cancellata (Linn;) xxx X X Crassostrea virginica (Gme!in) (as Ostrea v.-3,4) X Crytopleura costata (Linne) X X Dinocardium robustum (Lightfoot) (as Cardium sp.-3) X Donax variabilis (Say) X X X Dosinia discus (Reeve) xx X X Dosinia elegans Conrad X X Ensis spp. X xx X X Laevicardiuni sp. X Macro ca llista macula ta (Linn;) X X Macrocallista nimbosa (Light foot) X X X Mercenaria campechiensis (Gmelin) (as Venus sp.-3) X Mercenaria m. texana (Dall) (as Venus m.-3,4) X Modiolus m. squamosus Beauperthuy X X Noetia ponderosa (Say) X xx X X Periglypta listeri (Gray) X Pinctada imbricata Rading X Pinna carnea Gmelin X Pseudochama radians (Lamarck) X Pseudomiltha floridana (Conrad) (as Lucina f.) X Pteria colymbus (Roding) X Spisula solidissima similis (Say) X X X X Spondylus americanus Hermann X Tagelus plebeius (Solander) X X Tagelus spp. X X Dachycardium egmontianum (Shuttleworth) X X *Uniacetabulo-plerocercoids of Acanthobothrium sp. (Regan) and/or Rhinebothrium sp. (Cake) 6 CAKE concentricus (Say); American oysters, Crassostrea virginica (Say); the shells, Thais spp.; the pen shells, Atrina spp. (Gmelin); and sunray Venus clams, Macrocallista nimbosa and Pinna carnea Gmelin; the Venus clams, Chione spp.; angel (Lightfoot)-are harvested commercially in the northeastern wing clams, Crytopleura costata (Link); the cockles Dino- Gulf. Four additional species-the southern and Texas qua- cardium robustum (Lightfoot), Dachycardium egmontia- hog clams, Mercenaria campechiensis (Gmelin) and M. num (Shuttleworth), and Laevicardium spp.; the jackknife mercetzaria texana (Dall); the surf clam, Spisula solidissima clams, Ensis spp.; the mussels, Modiolus spp.; and the similis (Say); and the coquina or beach clam, Donax variabi- tagelus clams, Tagelus spp. Gunter (1971) listed eight ad- lis (Say)-are frequently collected and consumed by sport ditional (infected) edible or potentially edible Gulf mollusks shellfishermen, skin and scuba divers and beachcombers. including the cancellate cantharus, Cantharus cancellarius Large quantities of oysters are consumed raw (alive on the (Conrad); the banded tulip snail, Fasciolaria lilium hunteria half shell), while the remaining species are baked, broiled, (Perry) (as F. hunteria); the giant eastern murex, Murex chowdered, fried, steamed, etc., prior to consumption. Oc- fulvesceizs Sowerby; the lettered olive, Oliva sayana Ravenel; casionally coquina clams are eaten raw by epicurean beach- the halt-naked pen shell, Atrina seminuda (Lamarck); the combers. disk clam, Dosinia discus (Reeve); the Florida lucine, Eight species of cestodes were recovered trom these seven Pseudonziltlia floridaiza (Conrad) (as Lucina 5);the pon- edible pelecypods and their infection data are summari~ed derous ark, Nuelia ponderosa (Say); and the stout tagelus in Table 3. One should note that the larvae of Tylocephalum clam, Tagelus plebeius (Lightfoot). The larval cestode para- sp. and Parachristianella sp. were the most prevalent in that sites of these edible mollusks are presented in Table 2. group. Tylocephalum larvae occurred in all seven pelecypods. Seven additional potentially edible (and inrected) pelecy- Bay scallops were infected by the largest number of species, pods are included in Table 2 because of their abundance and seven, while oysters contained only one species. fleshy appearance or because they are congeners of edible The seven pelecypods cited above do not constitute the only edible mollusks that harbor larval cestodes. According to species. Notable among this group are the princess Venus Euell Gibbons (1964), mollusks of 14 additional (infected) clam, Periglypta listeri (Gray), the calico clam, Macrocallista genera and/or species that occur in the Gulf are edible. These maculate (Linn;), and the Atlantic thorny oyster, Spondylus include the fulgur whelks, Busycon contrarium (Conrad) and americanus Hermann. R. spiratuirz [subpsecies pyruloides (Say)] ; the slipper shells, Prchistoric aboriginal inhabitants of the eastern Gulf Crepidula ~pp.,the Atlantic moon snail, Polinices duplicatus coast harvested and consumed numerous species ofmolluscan

TABLE 3. Larval cestode infection data from seven edible Pelecypods of the eastern Gulf of Mexico.

Larval Cestode Species: (No. Infected Mollusks/No. LarvaeINo. Stations) *

Total Number of Mollusks/ Infected Mollusk Species Stations

Argopecten irradians concentricus (Say) 1/1/1 1/1/1 67/1,460/8 11311 21311 42122213 42/111/4 6815,63918 78/11 Oassostrea virginica (Gmelin) 60195 O/ 13 138120 Donax variabilis Say 2313512 1/1/1 12013 Macrocallista nimbosa (Lightfoot) 11111 60/1,674/1 39146217 6919 Mercemria campechien siu (Gmelin) 611 01/5 26/10 Mercenaria mercenaria texana (Dall) 3147712 412 Spisula xilidissima similis (Say) 11111 23/17/2 30/520/2 814211 3513

*Probably uniacetabulo-plerocercoids of Rhinebothriitm sp. LARVALCESTODE PARASITES OF EDIBLEMOLLUSKS I shellfish that are now known to harbor larval cestodes. ranges, and occurred in smaller numbers of infected hosts. Archaeological data from kitchen middens or garbage The remaining cestode species exhibited more host-speci- mounds at 32 coastal sites west of the Aucilla River in the ficity, but were restricted to fewer habitats and smaller Florida panhandle indicate that coastal Indians consumed geographical ranges. The larvae of Polypocephalus sp. (Cake and/or utilized the shells of at least 18 species of marine 1975) occurred only in bay scallops, A. i. concentricus, and gastropods and 15 species of marine pelecypods (Willey only in shallow bays adjacent to the Apalachicola River in 1949; Percy 1973). In some middens 95% of the faunal northwest Florida. remains consisted of mollusk shells. Larval cestodes pres- ently infect nine of those gastropods and eleven of those DISCUSSION pelecypods (Table 2). The most important consequence of larval cestode infec- Only five potentially edible mollusks listed by Gibbons tions in edible mollusks is the effect that those infections, (1964) and Gunter (1971) appear to be devoid of larval especially heavy infections, have on the health of the host. cestodes. This may be misleading because of the small Heavy infections certainly cause physiological stress which sample size (ten or fewer specimens were examined). These may affect growth, reproduction, and edibility. Heavy in- include the Atlantic ribbed mussel, Geukensia demissa fections of Parachristianellu sp. in sunray Venus clams, M. granosissima (Sowerby) (syn. Modiolus demissus granosissi- nimbosa, severely restrict the passage of food material mus);the hooked mussel, Ischadium recurvum (Rafinesque) through the host’s intestine. Sparks (1963) suggested that (syn. Brachidontes recurvus); the tulip mussel, Modiolus heavy Tylocephalum infections in oysters, C. virginica, at americanus (Leach); and the frons oyster, Lopha frons West Loch, Pearl Harbor, Hawaii, were responsible for the (Linni) (syn. Ostrea frons). low condition index, a measure of fatness or marketability, All of the cestodes found in edible or potentially edible that he observed. [Condition Index = Dry meat weight mollusks of the eastern Gulf utilize elasmobranch fish (gm) X 100/Shell volume (ml).] Wolfe (1976) noted the (sharks, skates or rays) as final hosts and probably will not presence of heavy Tylocephalum infections in Sidney rock develop in humans that consume viable larvae. The majority oysters, Saccostrea (syn. Crassostrea) commercialis Iredale of the cestodes were confined to the mollusk’s visceral and Roughley, from northern Australia. He suggested that region and those tissues are usually separated from the the physiological stress caused by the infections produced edible portion, during processing, and discarded. Those the “poor, transparent, and watery” conditions noted in all cestodes that remain in the edible portion, or in mollusks infected oysters. that are prepared whole, are destroyed by the cooking Pelecypods appear to serve as primary intermediate hosts process. The Slocephalum larvae that are ingested by while molluscivorous gastropods appear to serve as secondary humans who consume raw (living) oysters, coquina clams intermediate or paratenic (transport) hosts for these larval or other infected pelecypods, are not known to be infec- cestodes. Most of the molluscan hosts are confirmed prey of tive. Experimental evidence obtained during this study sug- demersal elasmobranchs of the Gulf of Mexico. Pelecypods gests that those larvae are destroyed by human digestive and filterfeeding, herbivorous and omnivorous gastropods acids and enzymes. While attempting to remove individual (e.g., Crepidula spp.) become infected by ingesting reproduc- Tylocephalum larvae from small pieces of oyster tissue via tive products (e.g., eggs and gravid proglottids released by digestion (in vitro), I found that a 1% solution of hydro- the definitive hosts) or free-swimming coracidia. Mollusci- chloric acid and pepsin in seawater would kill all encysted vorous gastropods become infected by ingesting infected larvae in a short period of time. pelecypods or gastropods. The first infection mode is based Larvae of Tylocephalum sp. (Burton 1963) were the on circumstantial feeding and infection information (Cheng most abundant, widely distributed, and least host-specific 1966), and the second mode was demonstrated during this of all cestodes that infected edible mollusks. They occurred investigation. Cheng found coracidia of Tylocephalum sp. in in all but three of the 43 infected mollusks covered in this the digestive tract and intimately associated with the gills of report. They were found in mollusks from every type of Tylocephalum-infected oysters, C. virginica. Banded tulips, estuarine and marine habitat sampled and were distributed F. 1. hunteria, infrequent hosts of Rhinebothrium sp. (Cake from the Mississippi Sound to the Florida Keys. Plerocercoids 197.9, exhibited statistically significant increases in total of Rhinebothrium sp. (Cake 1975) were the next most numbers of larvae when fed Rhinebothrium-infected pon- abundant larval forms; they occurred in 24 of 43 infected derous arks, N. ponderosa (unreported data). mollusks from evcry type of marine habitat between the Only one larval cestode,Dioecotaenia cancellata (Linton), Mississippi Sound and the Florida Keys. Three other cestodes, could be identified to species, while the remainder were Parachristianella sp. (Cake 1975) (1 5 of 43), Eutetrarhynchus identified only to a generic level because they lacked defini- sp. (Cake 1975)(11 of43),andAcanthobothriumsp. (Regan tive, adult characteristics. Four larval species, Acanthoboth- 1963) (1 0 of 43) were common parasites of edible mollusks, rium sp. (of Regan), Acanthobothrium sp. (of Harry) but were restricted to fewer habitats, smaller geographic Rhinebothrium sp. (of Cake), and Polypocephalus sp. (of 8 CAKE

Cake), were identified as a result of incubation experiments State University, Department of Oceanography, Tallahassee, using an artificial elasmobranch saline solution (Read et al. Fla.) and Dr. J. E. Byram (Peter Bent Brigham Hospital, 1960; Hamilton arid Byram 1974). Considerable research, Department of Pathology, Boston, Mass.) for financial, lo- including improved infection and incubation experiments, gistical, and technical assistance during the investigation needs to be conducted before these larval forms can be from which this report was derived, and Dr. J. E. Byram for identified completely or described as new species. critically reviewing this manuscript. The author is indebted to the Editor of the Proceedings of the Helminthological ACKNOWLEDGEMENTS Society of Washington for granting permission to use the The author wishes to thank Dr. R. W. MenLel (Florida cestode illustrations fiom Cake 1976

LITERATURE CITED

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