The terminology of larval cestodes or metacestodes

8Jarecka and FreemanTwo additional systems of larval cestode terminologywere developed essentially contemporaneously(Jarecka, 1970a,b, 1975; Freeman, 1973) and sharea common feature, derived from Moniez (1880) andVillot (1883), namely that features observable duringdevelopment, particularly the presence or absence ofa cercomer and a primary lacuna are given considerablesignificance. Beyond this commonality, theydiffer in that the system of Freeman (1973) subsequentlyrelied on larval cestode morphology alone,while that of Jarecka (1975) incorporated, as a feature,whether the cestode larva occurred in its first or secondintermediate host (Table 3).In the system proposed by Jarecka (1970a,b,1975), larval cestodes in the first intermediate hostwere termed cercoids, while those in a second intermediatehost were termed metacercoids. Cercoidscould possess a cercomer, but, by definition, metacercoidslacked a cercomer. Cercoids were sub-dividedinto the: (1) procercoid, which is bothriate but lacksa primary lacuna (gymnosomic in the terminologyof Jarecka, 1975); (2) cercoscolex, which is acetabulate,lacks a primary lacuna and has a withdrawnor retracted scolex (= Gryporhynchus of earlier authors);(3) cysticercoid, which has a primary lacuna(cystosomic in the terminology of Jarecka, 1975), isacetabulate and has a withdrawn scolex; and (4) cysticercus,which is acetabulate, invaginated and lacks acercomer. The metacercoid, in the second intermediatehost, lacks a cercomer and may be either a bothriateplerocercoid or an acetabulate plerocercus. Thesystem of terminology proposed by Jarecka (1970a,b,1975) thus retains the traditional terms cysticercus,cysticercoid and plerocercoid. Procercoid was originallyapplied to the caudate (= with cercomer) stagesof pseudophyllideans in the first intermediate hostprior to development of the bothria (Janicki & Rosen,1917). The re-definition of the term by Jarecka (1975)meant that it also included the caudate, bothriate larvalcestodes of caryophyllideans and overcame theanomaly, for pseudophyllideans, of development ineither two intermediate hosts (e.g. Diphyllobothrium,Ligula; see Janicki & Rosen, 1917; Rosen 1920) ora single intermediate host (e.g. Bothriocephalus; seeRobert et al. 1988; Scholz, 1997). Her term ‘cercoscolex’described proteocephalidean metacestodes(Scholz, 1997) as well as those of the family Gryporhynchidae.The term plerocercus, previously appliedto trypanorhynch metacestodes retracted withina bladder-like cysts (Dollfus, 1942), was used forunspecified acetabulate cestodes in the second intermediatehost. Under her system, trypanorhynchanmetacestodes would have been termed plerocercoids.A subsequent modification of this system was proposedby Gulyaev (1997a) to include presumed stagesin the evolution of larval cestodes, in which Spasskii’s(1951) term amphicyst, for linstowiid metacestodes,was added to the range of cercoids, tetrathyridiumwas added to the range of metacercoids and theterm plerocercoid was replaced by blastocyst for trypanorhynchmetacestodes (Table 4). Gulyaev (1997a)introduced two additional terms (Table 4), protolarvafor metacestodes lacking a primary lacuna and larvacystoidsfor metacestodes lacking a cercomer orbladder, but retained the term larvacyst (= larvicyst)of Skrjabin (1937) for cysticercoids, cysticerci and theblastocysts of trypanorhynchs.The system utilised by Freeman (1973) (Table 3)differed in that, while incorporating the absence orpresence of a primary lacuna (termed ‘primitive’and ‘neoteric’, respectively) and the presence or absenceof a cercomer, the number of intermediate hostswas essentially disregarded and the morphology ofthe larval cestode only was considered. In Freeman’ssystem (1973), the traditional terms procercoid, cysticercus,cysticercoid and plerocercus were retained.Several new terms were used by Freeman (1973). Precysticercuswas coined for metacestodes without acercomer, with a primary lacuna and in which thescolex was invaginated (e.g. Linstowiidae). This termis synonymous with amphicyst of Spasskii (1951)and Gulyaev (1997a). The term neoplerocercoid wascoined for trypanorhynch metacestodes lacking a blastocyst(Freeman, 1973, p. 511), currently allocated tothe suborder Homeacanthoidea by Campbell & Beveridge(1994). However, Freeman (1973, p. 521) alsosuggested that the same term, neoplerocercoid (pp.521, 528-9), could be applied to anoplocephalid andhymenolepidid metacestodes based upon the developmentof the scolex from the ‘fore body’ (p. 521) andlacking a cercomer in their fully-developed form. Itmay be that Freeman intended to use the term neoplerocercusfor trypanorhynchs and neoplercercoidfor cyclophyllideans, but that there are typographicalerrors in the published paper. Freeman’s term postplerocercoidwas coined for larval cestodes such as thoseof Ligula, in which evidence of segmentation is apparentin the larval stage. The other term coined by Freeman(1973) was strobilocysticercoid for Lateriporus,in which segmentation is present in the larval cestode.