The terminology of larval cestodes or metacestodes

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