The terminology of larval cestodes or metacestodes

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12of novel names.Cysticerci and their modificationsA variety of terms have been utilised to describemono- and polycephalic cysticerci (Table 2), andthese have recently been reviewed by Hoberg et al.(2000). They recognised, apart from the cysticercus,the coenurus in which new scoleces develop by invaginationinto a central bladder (Taenia multiceps, T.serialis), the fimbriocercus, an elongate unsegmentedlarva (T. brachyacantha, T. martis, T. polyacantha)(includes armatetrathyridium) and strobilocercus, witha strobilate collum (including hemistrobilocercus andcoenurostrobilocercus) (T rileyi, T. parva, T. taeniaeformis).They identified a further group of species(T. endothoracicus, T. selousi, T. twitchelli) in whichscoleces are borne on long stalks that arise by exogenousbudding from a central bladder which laterregresses, but for which no name was provided. Inaddition, the terms echinococcus and alveococcusremain for specialised larval cestodes of the genusEchinococcus which are also modified cysticerci.Cysticercoids and their modificationsA number of new terms have been introduced for cysticercoidssuch that the literature on this topic is confusing.Not only have numerous terms been coined,often without acknowledgment of a pre-existing term,but existing terms have been applied incorrectly andthe identity of cestodes described based on larvalforms has often been disputed, thus jeopardising theapplication of the terminology. Consequently, theprincipal terms used to describe cysticercoids arebriefly reviewed.(a) Monocephalic cysticercoids1. Cercocyst (Figure 3A)The cercocyst, originally described by Villot(1883), was based on a larval cestode with a prominent,broad cercomer found in the beetle Tenebriomolitor. It was presumed to be Hymenolepis microstoma,the development of which was describedin greater detail by Caley (1974). Cysticercoidswith cercomers longer than the soma, but withoutlateral outgrowths were considered to be cercocystsby Skrjabin & Mathevossian (1942). Considerablevariation occurs within this group as thecercomer may be long and slender or may be extremelybroad. Numerous hymenolepidid generahave cysticercoids of this type, including Cladogynia(=Flamingolepis) (see Gabrion, 1981), Dicranotaenia(see Neradová-Valkounová, 1971),Diorchis (see Czaplinski & Szelenbaum-Cielecka,1986), Drepanidotaenia (see Ruszkowski, 1932),Fimbriaria (see Neradová-Valkounová, 1971 (describedas a monocercus); Krashnoshchekov &Pluzhnikov, 1984), Fimbriarioides (see Maksimova,1976), Gastrotaenia (see Wisniewski,1971), Hymenolepis diminuta (see Voge, 1960;Gabrion, 1981), H. (s.l.) haldemani (see Bondarenkoet al., 1987), H. citelli (see Voge, 1956),Microsomacanthus (Hymenolepis (s.l.) hopkinsi)(see McLaughlin & Burt, 1970), (H.(s.l.) stylosa)(see Gabrion, 1981, 1977), Nematoparataenia(see Wisniewski, 1971), Parabisaccanthes (seeJarecka, 1960, cited as Drepanidotaenia; Kotecki,1967; Maksimova, 1972), Pseudhymenolepis (seeGabrion, 1981; Jiang et al., 1990), Retinometra(see Jarecka, 1960; Maksimova, 1972; Szelenbaum,1972), Rodentolepis (see Prokopič,1971; Ebermann, 1976), Triodontolepis (seeMatsaberidze et al., 1986), Staphylocystis (seeGabrion, 1981), Wardoides (see Kotecki, 1967);and some species of Wardium (e.g. W. aequabile,W. arctowskii, W. fusa, W. paraporale) (seeGabrion, 1981; Jarecka, 1960, 1984; Maksimova,1986). Cercocysts are thus widespread in the Hymenolepididaeand the majority known are fromcestodes occurring as the adult stage in aquaticbirds. No differentiation has been made betweenspecies which undergo scolex development priorto retraction (‘protocephalic’ scolex developmentof Greaves et al., 1989) (e.g. H. diminuta, seeVoge, 1960) and those in which scolex developmentoccurs following retraction (‘epicephalic’scolex development) (R. microstoma, see Goodchild& Stulken, 1970). Greaves et al. (1989) andJarecka (1975) considered the former mode of developmentprimitive or plesiomorphic. Cercocystsalso occur in the life-cycle of the progynotaeniidgenus Gynandrotaenia (see Gvozdev & Maksimova,1979).2. Microcercus (Figure 3B)Microcercus was a term used initially by Skrjabin& Mathevossian (1942) to designate cysticercoids‘whose caudal annex is greatly reduced, being considerablyshorter than the soma’ (p. 85). Theyselected Rodentolepis fraterna as the exemplarfor this type of cysticercoid. R. fraterna has ashort, broad cercomer in mammalian hosts, but a
13broad and elongate cercomer in coleopteran hosts(Voge & Heyneman, 1957; Schiller, 1959; Voge,1961; Joyeux & Baer, 1961). In addition, bothH. citelli and Microsomacanthus ductilis have cercomersjust slightly shorter than the soma (Voge,1961; Burt & Jarecka, 1984), indicating that therelative size of the cercomer may be difficult toevaluate in certain cases. The intention of thedefinition proposed by Skrjabin & Mathevossian(1942) to distinguish cysticercoids with a greatlyreduced cercomer is readily applicable to those ofthe davaineid genera Raillietina (seeWetzel, 1934;Voge, 1960; Bartel, 1965) and Davainea (see Wetzel,1932; Abdou, 1958). The criterion does notapply to all davaineids as Ophryocotyle has anelongate cercomer (Burt, 1962). Therefore, the definitionof a microcercus is potentially useful, buthas been misapplied in the literature.3. Diplocyst (Figure 3C)The diplocyst was defined initially by Skrjabin& Mathevossian (1942) as a cysticercoid with nocercomer or ‘caudal annex’ in which there aretwo separate retractions into the soma. The descriptionwas based on a cysticercoid describedby Mrázek (1906) from earthworms. Skrjabin& Mathevossian (1942) nominated Aploparaksiscrassirostris as a representative of this type ofcysticercoid.Most species exhibiting the development of adiplocyst belong to Aploparaksis, a hymenolepididgenus parasitic mainly in charadriiform birdsand the diplocyst is found in oligochaets. Bondarenko& Kontrimavichus (1976a,b) consideredthat five species of Aploparaksis (A. bulbocirrus,A. groenlandica, A. furcigera, A. polystictae andA. taimyrensis) exhibited this type of development(see also Demshin, 1976; Gulyaev, 1977)to which can be added A. australis (see Bondarenko,1989), A. clangulae (see Bondarenko &Kondratyeva, 1985), A. filum (see Demshin, 1981;Bondarenko, 1990), A. kulachkovae (see Bondarenko,1987), A. pseudofilum (see Bondarenko,1990) and A. sanjuanensis (see Demshin, 1985).Bondarenko & Kontrimavichus (1976) describedfour variants of the typical diplocyst. A ‘caudatediplocyst’ was considered to be present inA. brachyphallos and A. crassirostris (see Bondarenko& Kontrimavichus, 1976a; Demshin,1984), while a variant, the floricyst, in which thecysticercoid was partially embedded in the cercomer,resembling a closed flower, was present inA. birulai (see Bondarenko & Krasnoschchekov,1978). The ramicercus (Figure 3D), in which thecercomer has 6-10 digitate appendages, was firstnamed by Skrjabin & Mathevossian (1942), basedon a cysticercoid described from Lumbriculus byMrázek (1907). Bondarenko & Kontrimavichus(1976b) identified a ramicercus in A. orientalis andA. secessivus as well as in Wardium chaunense,while Demshin (1971) identified a similar caudatelarva in A. dujardini. Finally, a larval form wasfound in A. xemae in which multiple cysticercoidsbud from the cercomer, becoming detached at anearly stage of development (Bondarenko & Kontrimavichus,1976b); this larval stage was termedan autotomicrocercus and was compared with thestaphylocyst and urocyst (vide infra). A comparablelarval form was also described in Wardiumfreyei by Bondarenko (1977).Gulyaev (1989) coined the term ascocercus forthe larval stage of amabiliids. However, the larvaappears to be identical with a diplocyst exceptthat the scolex may only be partly retracted, orthere may be some indication of segmentation. Theterm ascocercus alludes to the elongate stalked cystwithin which the larva develops. However, ascocercusis simply a minor variant of the diplocyst.4. Monocercus (Figure 3E)The term ‘monocercus’ was originally erected byVillot (1882) for Cysticercus arionis found ina mollusc by von Siebold (1850), characterisedby numerous globular structures around the cysticercoid.Mrázek (1907) indicated that during itsdevelopment the cercomer fragmented into globuleswhich persisted within the larval cestode.Gabrion et al. (1976), Gabrion (1981) and Gabrion& MacDonald (1980) studied the development ofsimilar larval cestodes of Anomotaenia constricta,A. brevis, Paricterotaenia porosa and Eurycestusavocati, all of which exhibited a similar form ofdevelopment and defined a monocercus as being amonocephalic cysticercoid in which a primary lacunais present, the scolex develops externally andretracts, following which the cercomer detachesand fragments. They considered that this type oflarval development was restricted to the Dilepididaeand, in a review of the literature, showedthat a similar mode of larval development occurredadditionally in the genera Amoebotaenia(see Joyeux & Baer, 1936), Trichocephaloides (see
Page 1 and 2: Systematic Parasitology 52: 1-33, 2
Page 3 and 4: 3inum (= Taenia cucumerina). Both L
Page 5 and 6: 5Table 1. Names of larval cestodes
Page 7 and 8: Figure 2. Schematic representation
Page 9 and 10: 9Table 3. Comparison of the systems
Page 11: 11Table 5. Nomenclature employed by
Page 15 and 16: 15from which cysticercoids bud off.
Page 17 and 18: 17ing species are Choanotaenia infu
Page 19 and 20: 19characters upon which a system of
Page 21 and 22: 21Figure 4. Schematic representatio
Page 23 and 24: 23Table 6. Suggested terms for larv
Page 25 and 26: 25new difficulties for this system
Page 27 and 28: 27fimbriocercus (including armatetr
Page 29 and 30: 29Burt, M.D.B. (1962) A contributio
Page 31 and 32: 31host Branchinecta gaini Daday (Br
Page 33: 33Stunkard, H.W. (1937) The life cy

The terminology of larval cestodes or metacestodes

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