Contributions to Zoology, 70 (3) 175-179 (2001)

SPB Academic Publishing bv, The Hague

Short notes and reviews

classification: of the Simplifying hydrozoan inappropriateness group

Hydroidomedusae in a phylogenetic context

Antonio+C. Marques

Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de

São Paulo. Av. Bandeirantes, 3900, 14040-901, Ribeirão Preto, SP, Brazil, e-mail: [email protected]

Keywords:: , Hydroidomedusae, classification, nomenclature,

Abstract ated classifications and models of phylogeny si-

multaneously. In phonetics, classifications reflect

The systematics ofHydrozoa is consideredfrom the viewpoint overall similarity, not necessarily phylogeny (Hull, of logical consistency between phylogeny and classification. 1988: 122; Mayr and Ashlock, 1991: 128). With The validity of the nominal taxon Hydroidomedusae (includ- regard to the higher levels of hydrozoan classifi- all of the is dis- ing groups Hydrozoa except ) cation, no cladistic or phenetic classifications have cussed with regard to its distinctness and inclusive relationships.

In been proposed. All classifications seem general, phylogenetic systematic evidence suggest that the hydrozoan use of the is term Hydroidomedusae inappropriate given our to be based on gradistic or essentialistic principles, current level of It is concluded that understanding. no new, or although the majority of their proponents would names until broader resurrected, are necessary before or a not characterize them as such. phylogenetic revision ofthe Hydrozoa is accomplished. In classification should my view, a represent one

of the possible hypotheses of phylogeny (cf. the

principle of logical consistency by Hull, 1964). In Introduction

other words, “if the cladogram that follows the true

phylogeny (assuming that the true phylogeny could Classification of is organisms a way to “systema- be known) is the same as the cladogram expressed tize” biological information within some kind of by a classification, then the classification is clearly logical framework. Therefore systematics could be ” consistent with phylogeny (Platnick, 1979: 542; the viewed as science of classifying or organizing For my italics). Hydrozoa, Bouillon (1981, 1985) organisms into a hierarchical perspective. By the provides examples of a classification logically term information biological we mean any prop- consistent with proposed hypotheses ofphylogeny, erty intrinsic to the organism, such as ecology, although these phylogenies were constructed with- morphology, molecular constituents, behavior, etc. the out use of rigorous phylogenetic or cladistic Hence, taxa formed only by convenience (e.g., methods. Petersen (1990), Marques (1996), Pena economical assuming importance or by the per- Cantero & Marques (1999), and Marques & Migotto sonal preference of its proponent) ought to be dis- (2001) provide examples of phylogenetic and couraged. cladistic approaches as a basis for the classifica- Darwin (1859) effectively focused the attention tion of The aim of this is to dis- of hydrozoans. note biologists to reflect on issues of descent and cuss in light ofknown aspects of the phylogeny of divergence from common ancestors. Subsequently, the the for a taxon workers Hydrozoa justification “Hydro- like Julian Huxley, Ernst Mayr, and George idomedusae” by Bouillon et al. (1992). G. in Simpson, what came to be called the “Mod- ern Synthesis”, accommodated both grades and clades (cf. Mayr & Ashlock, 1991). Cladistics

excluded and (Hennig, 1950, 1966) grades gener-

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classification The Hydrozoan uniqueness of such groups implies that they

represent monophyletic lineages that are distinct

delineated of A historical review of hydrozoan classifications by a set autapomorphies.

Are the was compiled and discussed by Bouillon et al. Siphonophorae monophyletic vis-a-vis

(1992). From a methodological perspective, all the other hydrozoans? This is not clear in Bouil-

proposed classifications for the Hydrozoa have been lon et al. (1992), and I can see no justification other

than that essentialistic, i.e., focused on grades of evolution. ofhistorical convenience. Students of the

Bouillon al. also observed that do not deal with et (1992) most pre- Hydrozoa generally siphonophores,

derived vious classifications have not been adequate. Al- possibly because of their very morphol-

and life histori- though these classifications based their arguments ogy, ecology, history. Obviously,

of historical cal on the assembling taxa within con- convenience is not enough of a reason to separate

cepts of some proposed names; the idea that a clas- a group. Perhaps the most striking difference in

sification should represent some actual phylogenetic the siphonophore lineage is its “high degree of deter-

1987: knowledge has not been considered. As a substi- minancy of form” (Mackie et ah, 110-113).

tution for those former inadequate classifications, The modular construction of siphonophores is based

Bouillonet al. (1992) resurrected the name Hydro- on definite growth zones along an anterior-poste-

idomedusae (originally proposed by Claus, 1877a, rior axis. Derivatives of both polypoid and medusoid

1877b) stating, “Our proposal is to divide the class stages are found attached to the axial free-floating

Hydrozoa into two subclasses, the Hydroidome- (Kirkpatrick & Pugh, 1984). Observing the

the 1992: dusac and Siphonophorae” (Bouillon et ah, singular morphology of the Siphonophorae, one

282). Thus, within the Class Hydrozoa, the siphono- might conclude that this group is highly modified

and distant from all phores would be juxtaposed against all other hy- so, phonetically other Hydro-

such drozoans. Although Bouillon et al. (1992) did not zoa. Indeed, phenctic classification reflects

justify the existence of such a subclass Hydroido- similarity relationships, which are not necessarily

medusae with defined several the result any clearly features, congruent with, or of, rigorous phylo-

authors have followed al. them, e.g., Pages et (1992), genetic relationships.

Pages & Gili (1992), and Boero et al. (1996). Oth- However, could siphonophores have a common

with ers prefer to use the term Leptolida for this same putative ancestor some other hydrozoan sub-

Cornelius Under such a grouping, e.g., (1995), Vervoort (1995), hypothesis, following an

of the andBrinckmann-Voss & Arai (1998), a name whose event cladogenesis, siphonophore lineage

underwent accelerated use was already denied by Bouillon et al. (1992). an process of anagenesis and/

Still others simply still consider Hydrozoa to sim- or specialization of form, resulting in a long and

include several unnested Schuchert differentiated In this Petersen ply groups, e.g., highly lineage. regard,

(1998) and Collins (2000). (1979: 109 more explicitly; 1990: 105) suggested

Since Darwin hierarchical classifications indi- a possible relationship between Siphonophorae and

cate relationships of subordination within nested the Anthomedusae, Leptomedusae, and Limnome-

sets. Since Hennig, we focus on trying to identify dusae. Schuchert (1996: 13) was even more expli-

natural that reflect cit in his that “affinities monophyly, groups common statements, considering

ancestry. If we presume that the label “Hydrozoa” [of Anthomedusae] with the Siphonophora and

(here considered a monophyletic group) is hypoth- Laingiomedusae are not established. All three taxa

have the manubrium esized to be derived from a single ancestral line- gonads on as a possible synapo-

then all descendants could be in Desmonemes in the age, grouped morphy. occur only Siphono-

subordinate If of these and Anthoathecata and patterns. any subgroups are phora [= Anthomedusae]

indicate A joined together under a taxon name, e.g., the Hydro- may a closer relationships. taxon Hydro-

idomedusae of Bouillon et al. (1992) and posed idomedusae (Bouillon et ah, 1992) which includes

against another, i.e., the Siphonophorae, this would all Hydrozoa except the Siphonophora is there-

” then necessarily imply that members of these sub- fore most probably not a natural taxon (my ital-

groups are related and share a common lineage. ics).

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I. the Anthomedusae and after Fig. Relationship among Leptomedusae, Siphonophorae, Marques (1997).

in the manubrium reversal Indeed, Marques (1997), a phylogenetic study gonads on (a from gonads of the (Fig. I), concluded there is a relation- on the radial canals in the more inclusive subgroups, ship among Leptomedusae, Anthomedusae, and and another homoplasy with Laingiomedusae). Fig. 1

The Siphonophorae. Limnomedusae, with no auta- also shows the autapomorphies of Leptomedusae, pomorphy, are a group of uncertain monophyly. Anthomedusae and Siphonophorae. It is interest-

form a clade with the other to note that the Anthomedusae They might possibly ing are weakly sup- hydrozoan subgroups (Trachymedusae, Laingio- ported as a subgroup, since one of the putative medusae, Actinulidae and Narcomcdusae). How- autapomorphies (perradial mesenteries in the

that is A is ever, issue not relevant here. single group medusa [Petersen, 1990]) not accepted by some composed of the Leptomedusae, Anthomedusae, authors (e.g., it is not cited in Schuchert, 1996), and Siphonophorae is supported by the following and the other (arrangement of the polypoid tenta- synapomorphies: 1) polypoid polymorphism; 2) cles in more than one whorl) is reversed in several

of basitrichous isorhizas with of Anthomedusae. The presence (homoplastic groups uncertainty associ-

Anthozoa, considered him atri- ated with these characters leaves by equivalent to two open the

and the chous isorhiza), 3) loss of endodermal question whether or not the siphonophores are a

statocyts on medusae(a reversal, homoplastic with group belonging within the Anthomedusae(raised

that would be Laingiomedusae, a group eventu- by Schuchert, 1996 and also P. Schuchert, pers. ally included in the Anthomedusae see Schuchert, comm.). This possibility could be verified in a more

1996). The sister-group relationship of the Siphono- detailed analysis in which the subgroups ofAntho- phorae and Anthomedusae would be supported by medusae would be included, thus probing for the of presence desmonemes, stenoteles (a doubt- anthomedusan paraphyly. Nevertheless, all of the ful character since the nematocyst is lacking in above hypotheses (Petersen, 1979, 1990; Schuchert,

filiferan with Anthomedusae; also homoplastic 1996; Marques, 1997) cast serious doubt on the

Cubozoa, Actinulidae, and Trachymedusae), and validity of the taxon Hydroidomedusae as a phylo-

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genetically-based clade. Furthermore, if we take Acknowledgements

into account a completely different database, such

as molecular I wish to the of 18S rDNA sequences, phylogenetic acknowledge help Dr. A.E. Migotto, Dr. F.L.

da Silveira de Sao Sao analysis (using both parsimony and maximum like- (Universidade Paulo, Paulo), Dr. H. Ferrarezzi (Institute Butantan, Sao Paulo), Dr. P.F.S. Cornelius lihood) still corroborates the association of Lepto- (The Natural History Museum, London), Dr. Alan Kohn, Dr. medusae, Anthomedusae and Siphonophorae (cf. Claudia Mills (University of Washington), and Dr. Phil Pugh Collins, 2000). (Southampton Oceanography Centre, Southampton) for their

critique of previous versions of the text. Also, the discussions

during the Fourth Workshop of the Hydrozoan Society in Bo-

dega Bay, California were important in the development Conclusion very ofthis contribution,especially the inspired talks by Dr. A. Collins,

Dr. D. Bridge, and Dr. P. Schuchert (the latter not at the Bo- The state of the art as regards hydrozoan phylog- dega meeting). Mr. F. Boero and Dr. J. Bouillon made criticisms

casts doubt to the eny on any use of a taxon Hydroido- manuscript, although they vehemently disagree with most ofwhat is offered here. medusae. This study was supported by FAPESP Systematists are surely far from an ac- (Fundacao de Amparo a Pesquisa do Estado dc Sao Paulo), ceptable and comprehensive phylogenetic hypothe- numbers and process 93/3578-8, 96/10544-0, 97/04572-4. sis the and such concerning Hydrozoa, to propose

is not the purpose of this contribution. However,

it seems likely that present knowledge can offer References clear and testablealternatives to the proposed clades

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