The phyletic status of the

(Platyhelminthes, Turbellaria, Tricladida)

by

Ian R. Ball

Department of Biology, University of Waterloo, Ontario, Canada, and Institute of Taxonomie Zoology,

University of Amsterdam, The Netherlands

&

Nicole Gourbault

Laboratoire de Zoologie (Vers), Muséum National d'Histoire Naturelle, Paris,

Abstract the prediction was made that future work would

The distribution of the Planaria is in- amphiatlantic genus demonstrate that the European and the

compatible with our current hypothesis of the historical did share American species most probably not an biogeography of freshwater . New anatomical in than each did studies the that is ancestor common more suggest possibility the genus not strictly recently with other monophyletic; new karyological data are strongly corrob- of Europe and North orative of that conclusion. The karyotypes of the American America, respectively. Thus, the falsification of species of Planaria are almost identical with those of many the that the Planaria is mono- other North American Planariidae and quite distinct from hypothesis genus a

that of the European species. These are inconsistent the findings phyletic group protects larger biogeographical Planaria form with the hypothesis that the species of a hypothesis from its own potential falsifier. Therefore dis- strictly monophyletic group. the amphiatlantic In and the we karyological junction is apparent, not real, and the earlier biogeographical present paper present

hypothesis is protected from one potential falsifier. comparative anatomical data from which we con-

clude, as predicted, that the distribution of the

Planaria does not the earlier INTRODUCTION genus falsify hy- pothesis because the amphiatlantic disjunction is This is earlier Ball paper a sequel to an essay by apparent, not real (Ball, 1975: 418). the of (1975) on formulation biogeographical hy-

In that MATERIALS AND METHODS potheses. essay a hypothesis was erected The used for species this study, and their were to account in historical terms for the known distri- provenances,

as follows: bution of freshwater the planarians throughout Planaria dactyligera dactyligera Kenk, 1935. Twin Springs One of the critical of that world. factors hypothesis near Mountain Lake, Giles County, Virginia, U.SA. Col-

lected by Ian R. Ball and Nicole 2 October concerned certain holarctic and in Gourbault, genera, partic- 1975. ular the Planaria. As at conceived genus present Planaria dactyligera musculosa Kenk, 1969. Ossippee, Ala-

Ball this mance Collected (Kenk, 1969; et al., 1969) genus com- County, North Carolina, U.S.A. by Ian

R. Ball and Nicole Gourbault, 14 September 1975. prises two species in eastern North America and Planaria torva (Müller, 1774). Rivière , Beuvrequen one wide-spread in Europe [a single record of a near Marquise, Pas-de-, France. Collected by Liesbeth endemic northern species to India (Whitehouse, de Vries and Hilde Veenstra, 10 February 1977. All these forms studied both has is were morphologically and 1913) never been substantiated and it karyologically. Sections were stained with Mallory-Heiden- doubtful that the record is valid]. hain; in all other respects the methods of study were those of This distribution amphiatlantic pattern (Ball, our previous work (Ball & Gourbault, 1975).

deemed 1975: fig. 11) was to be incompatible MORPHOLOGICAL CONSIDERATIONS with the historical hypothesis put forward for

that discussed in the reasons are fully earlier paper. Currently the family Planariidae contains almost

In that failed if the Pla- short, hypothesis genus 80 species comprising seven genera (Ball, 1977). naria formed Since Over half the included in the a strictly monophyletic group. species are genus the value the which is explanatory of hypothesis was high defined only by primitive

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characters and cannot be regarded as strictly mono- In his original description of Planaria dactyl-

phyletic (Ball, 1975: note 19). Most of the re- igera, Kenk (1935) described its adenodactyl as

defined The maining genera are monothetically. being of the Planaria torva-type. Superficially they of Planaria differ from those of species Phagocata may appear to be similar, but in detail they are

in one in their of an only respect, viz., possession not. The of P. d. adenodactyl dactyli gera (fig. IB)

of a certain in the adenodactyl type copulatory is never curved and whereas the musculature is

apparatus. The monophyly of the therefore genus principally circular there are numerous longi- the of homol- depends upon correct assessment fibres tudinal scattered throughout the organ and between the of ogous relationships adenodactyls at its boundaries. The is organ entirely posterior the various species. to the male atrium, not lateral to it, and thus it is

Adenodactyls, or musculo-gland organs, are directed posterio-dorsally and not antero-dorsally. in the common accessory organs copulatory ap- There is no distinct papilla and the unusually of Turbellaria. Within the many aquatic paratus lumen cuboidal nucleate spacious possesses a in the marine planarians they are rare forms but epithelium that is clearly continuous with that of the they are of wide occurrence in the Paludicola, the atrial wall. As in P. torva the musculature is inhabitants of fresh waters. It has long been surrounded by a zone of nuclei and is pierced with known, however, that there are several different fills the numerous gland cells whose secretion types of adenodactyl and that these have been lumen. the musculature is However, very uneven, in acquired independently different genera and medial muscular dia- there being a sphincter or species groups. phragm that divides the adenodactyl into a broad In his long-standing revision of the freshwater ental region and a narrower ectal region. The ectal planarians, Kenk (1930) distinguished between and there is part is the most glandular here a broad three highly differentiated types of adenodactyls, zone of glandular tissue, whose structure is ob- and several minor, or lesser known ones. Of the scured by the copious secretions, interpolated be- three major types the solid adenodactyls of the tween the lumen epithelium and the musculature. tenuis-type, and the characteristically total is of The impression that of a diverticulum muscularized hollow adenodactyls of the Dendro- the atrium that has become heavily muscularized coelum lacteum-type need not concern us further and glandularized (fig. IB). This is especially here. Of more immediate relevance is the adeno- clear in a not fully mature specimen of P. d. dactyl of the Planaria torva-type (fig. lA). This musculosa in which the musculature of the diver- is with type usually strongly curved, a distinct ticulum is not so pronounced (fig. lC), and also is and has lumen, always present singly, a large in P. occulta from 1969: that into Virginia (Kenk, fig- fingerlike papilla projects an outgrowth 12). Kenk has acknowledged in his description of of the genital atrium. The musculature is powerful, this latter species that its adenodactyl differs in consisting primarily of circularly orientated fibres; some details from that of the European species of the dactylose papilla also has circular and lon- the with those genus. gitudinal fibres that are continuous of The function of these is but the atrial wall. The lumen of the is organs unknown, organ narrow, and the of lined and is structurally positionally adenodactyls with a low nucleate epithelium, often

Planaria torva and P. are dissimilar. which also dactyligera filled with an eosinophil secretion can

We do not them as as be seen within the musculature and the surround- regard homologous, having

The diver- a common origin. specialized atrial ing mesenchyme. Presumably the related glands

ticulum of P. is to the pierce the adenodactyl. The nuclei of the adeno- dactyligera comparable

muscles the The hollow glandular of some and dactyl form a layer around organ. organs

is that (Weiss, 1910; Kenk, 1930). As total appearance of a discrete, strongly

Kenk these are not muscular organ embedded in the mesenchyme rightly implies adenodactyls

and laterally to the penis and projecting into the genital may well have been independently acquired by

the and atrium. different species species groups.

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1. within the Planaria. A, frontal section Fig. Adenodactyls genus through the adenodactyl of P. torva. B, sagittal section the of through adenodactyl P. dactyligera dactyli C, section the of immature gera. sagittal through adenodactyl an P. dactyli gera

musculosa. All scale lines 100 at = cm = represent μm. atrium; circular muscle; gl = glandular secretions; lu = lumen of

adenodactyl; nu = nucleus. Drawings by Tran Thi Vinh Hao.

KARYOLOGICAL CONSIDERATIONS centric three submetacentric (c.i. > 37 ), pairs are

and number is the The diploid complement of Planaria torva consists (37>c.i.>25) one pair, 4, on of The borderline between submeta- and subtelocentric. 18 elements. mean relative lengths and

These results in with centromeric indices (c.i.) are given in table I; the are agreement the findings of karyotype is represented by the idiogram of fig. Benazzi & Puccinelli (1961, 1963) for Italian

2A. A conspicuous feature is the large size of populations and with those of Melander (1963)

for material from Sweden. chromosome 1, which is a little over 1.3 times the Gametogenesis was not

for size of the next element. Thereafter the elements studied the French populations, but Benazzi &

decrease gradually in size. With respect to centro- Puccinelli (1963) found meiosis to be normal in mere position, five of the elements, including the both the male and female lines, with 9 bivalents

largest and the three smallest pairs, are meta- showing numerous chiasmata.

3

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TABLE I The data for Planaria in dactyligera are sharp

Relative length and centromeric index of the 9 chromosome contrast to those just described for the European pairs of Planaria torva from France. Means and standard species. Both subspecies were identical karyologic- deviations from five mitotic metaphase plates. ally (cf. figs. 3 & 4) and so data are given only for Chromo- Relative Centromeric Nomenclature P. musculosa which the dactyligera gave most some length Index and clearest results. In this North numerous,

1 22.14 ± 1.29 46.37 ± 2.73 metacentric American endemic the diploid complement com- 2 16.81 ± 0.67 25.62 ± 2.15 submetacentric prises 38 elements. Mean relative lengths and 3 14.53 ± 0.35 31.09 ± 5.14 submetacentric centromeric indices for in 4 11.79 ± 1.04 25.77 ± 0.74 submetacentric the 19 pairs are given

5 9.74 ± 0.71 47.46 ± 2.34 metacentric and table II, an idiogram is given in fig. 2B. Again 6 8.04 ± 0.44 30.06 ± 5.17 submetacentric of the first pair chromosomes is something over 7 6.52 ± 0.87 43.94 ± 5.35 metacentric

± ± 1.3 times the of the second and the 8 5.49 0.31 39.58 1.96 metacentric length pair,

9 5.08 ± 0.42 40.13 ± 2.04 metacentric last 17 pairs decrease in length gradually, more so

than in P. torva. With respect to centromere posi-

tion most of the elements are metacentric. Chro-

mosomes 6 and 16 are on the borderline of sub-

metacentric and those numbered 4, 9, 13 and 18

approach this condition.

TABLE II

Relative length and centrometric index of the 19 chromosome

of Planaria musculosa from pairs dactyligera North Carolina.

Means and standard deviations from eight mitotic metaphase plates.

Chromo- Relative Centromeric Nomenclature

some length Index

1 9.15 ± 0.44 44.98 ± 0.82 metacentric

2 6.72 ± 0.16 47.79 ± 1.67 metacentric

3 6.28 ± 0.21 43.12 ± 1.37 metacentric

4 5.96 ± 0.23 38.54 ± 0.76 metacentric

5 5.81 ± 0.21 46.07 ± 1.65' metacentric

6 5.66 ± 0.21 36.78 ± 1.95 meta/sub-

metacentric

± 7 5.45 0.10 47.15 ± 1.77 metacentric

8 5.23 ± 0.17 46.26 ± 1.25 metacentric

9 5.21 ± 0.14 39.86 ± 2.30 metacentric

10 5.04 ±0.15 42.01 ± 1.76 metacentric

11 4.96 ± 0.07 44.11 ± 1.40 metacentric

4.81 ± 12 0.07 44.47 ± 3.83 metacentric

13 4.64 ±0.15 39.83 ± 1.55 metacentric

14 4.55 ± 0.07 42.88 ± 1.98 metacentric

15 4.44 ±0.13 45.13 ± 2.62 metacentric

16 4.25 ± 0.17 39.19 ± 2.36 meta/sub-

metacentric

17 4.12 ± 0.16 45.09 ± 2.20 metacentric

18 3.92 ± 0.29 38.14 ± 0.59 metacentric

19 3.62 ± 0.29 45.89 ± 0.60 metacentric

Gametogenesis in both the male and female

lines is normal. For spermatogenesis many figures of diakinesis were observed but sometimes they 2. of Fig. Idiogram analyses A, Planaria torva, from the data were difficult to because of of table and analyse overlapping in I B, Planaria dactyligera musculosa, from the data in table II. the bivalents. in I Diagrams by Tran Thi Vinh Hao. However, 10 spermatocytes an

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Planaria 3. Planaria musculosa, chromosomes at Fig. 4. dactyligera dactyligera chromosomes at Fig. dactyligera , mitotic metaphase. mitotic metaphase.

the of with P. undoubted number of 19 bivalents was observed, ally affinities P. dactyligera rest not and most of them because of the but with of North American are ring-shaped torva a group pla-

chiasma terminalization. In all have complete squashed nariids of which, no doubt, a common ovaries we found oocytes in the pachytene stage. origin in, and are endemic to, North America. On

also had but later the of is These 19 bivalents no stages present knowledge karyotype P. torva

and estimates of its derivation were seen. unique must await

The karyotypes of Planaria torva and P. dac- further studies of European forms.

tyligera musculosa obviously bear little resem- DISCUSSION AND CONCLUSIONS blance to one another, neither in chromosome

number and in the behaviour of morphology, nor The monophyly of the genus Planaria as currently

there the bivalents during spermatogenesis. In fact recognized rests solely on the presumed homol-

is that relates the the the three only one real similarity and to ogies between adenodactyls of species

high relative length of the first pair of chromo- (Kenk, 1969: 556). We have attempted to dem-

this feature onstrate on anatomical that somes, being a even more pronounced comparative grounds

in and Amer- this is the it is that a large number of European North not case. Moreover, noteworthy

all the American that extend ican Planariidae (Benazzi & Gourbault, 1974; species possess testes

Gourbault In the feature in & Ball, in preparation). fact the only to mouth region, a common

Planaria is almost identical nearctic whereas in P. karyotype of dactyligera Phagocata species, torva

from the with that of Phagocata fawcetti California they are throughout body-length. Thus we

(cf. fig. 2B with Ball & Gourbault, 1975: fig. 3) assume that the American and European species and from from of a number of other Planariidae eastern have been derived independently spatially

America in and The North (Gourbault & Ball, prepara- temporally segregated ancestors. new

data with this view- tion). karyological are consistent

The of The karyological data are unequivocal. point. The American species Planaria are merely

of Planaria is unlike that of of of the karyotype dactyligera specialized species Phagocata group

characterized = P. torva, bears little resemblance to that of other by a particular karyotype {In 38)

and is almost identical with that is found neither in Planaria European Planariidae, torva nor any that of several North American Planariidae. That other European freshwater hitherto in- these the Benazzi Benazzi- latter belong mostly to genus Phagocata, vestigated karyologically (cf. &

characterized an ill-defined genus only by primitive Lentati, 1976).

In the of data that features (Ball & Gourbault, 1975: 11-13; Ball, light these we deny Planaria

is and that the 1975: note 19) is not without interest. Karyologic- a monophyletic genus amphiatlantic

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exhibited the has supported by the National Research Council of Canada disjunction by "genus" any its cultural and via through exchange programme operating meaning in terms of the earlier biogeographical grant A0016. For all this help we are grateful. hypothesis (Ball, 1975). The retention of the

in is The REFERENCES genus its present sense misleading.

is the formulation of number of species involved so small that BALL, I. R., 1975. Nature and biogeographical

hypotheses. Syst. Zool., 24: 407-430. claim of convenience will not suffice for its justi- 1977. On the classification of , phylogenetic aquatic fication, and it is less than convenient if it conveys planarians. In: T. G. KARLING & M. MEINANDER eds.,

erroneous biological information. So far as known The Alex Luther Centennial Symposium on Turbellaria. Acta zool. fenn., 154: 21-35. there are no true amphiatlantic relationships exhib- BALL, I. R. & N. GOURBAULT, 1975. The morphology, ited by freshwater planarians. karyology, and of a new freshwater planarian It follows that the American species cannot be of the genus Phagocata from California (Platyhelmin- thes: Turbellaria). Life Sei. Contr., R. Ont. Mus., 105: the retained in genus and our formal taxonomie 1-19.

are as follows: proposals BALL, I. R., T. B. REYNOLDSON & T. WARWICK, 1969. The

taxonomy, habitat and distribution of the freshwater

triclad Planaria torva (Platyhelminthes: Turbellaria) in Genus Planaria Müller, 1776. Britain. J. Zool., Lond., 157: 99-123.

BENAZZI, M. & G. BENAZZI-LENTATI, 1976. cyto- Type species: Fasciola torva Müller, 1774, desig- genetics, 1. Platyhelminthes: 1-182 (Gebr. Borntraeger, nated Kenk, 1930. Berlin/Stuttgart).

& Étude de Diagnosis: as given by Kenk, 1930: 293. BENAZZI, M. N. GOURBAULT, 1974. caryologique quelques populations hypogées de la planaire Phagocata

(Fonticola) vitta (Dugès, 1830). Caryologia, 27: 467-

484. Genus Paraplanaria gen. nov.

BENAZZI, M. & I. PUCCINELLI, 1961. Il corredo cromosomico

Type species: Planaria dactyligera Kenk, 1935, di Planaria torva (O. F. Müller). Atti Ass. Genet, ital.,

7: 234-235. here designated. & 1963. di Planaria torva (O. F. , Cariologia like Planariidae with a Diagnosis: Phagocata- Müller). Caryologia, 16: 653-661.

musculo-glandular posterior diverticulum of the GOURBAULT, N. & I. R. BALL, in preparation. The com- of North American freshwater atrium. parative karyology pla- narians. Other species: Planaria occulta Kenk, 1969: 549- KENK, R., 1930. Beiträge zum System der Probursalier

The new name is intended to the (Tricladida Zool. 59: 259- convey concept paludicola). Anz., 145-162;

302. of similarity, not relationship. 1935. Studies on triclads. J. Elisha Mitchell , Virginian scient. Soc., 51: 79-133.

1969. Freshwater triclads (Turbellaria) of North ACKNOWLEDGEMENTS ,

America. I. The genus Planaria. Proc. biol. Soc. Wash.,

Liesbeth de Vries and Hilde Veenstra (Institute of Taxonomie 82: 539-558. of collected material Zoology, University Amsterdam) our MELANDER, Y., 1963. Cytogenetic aspects of embryogenes-is

from northern and in North Carolina France our fieldwork of Paludicola, Tricladida. Hereditas, 49: 119-166.

and was facilitated Dr. Reinhardt (Chapel A., Virginia by Rieger WEISS, 1910. Beiträge zur Kenntniss der australischen carried Hill, North Carolina). Further laboratory studies were Turbellarien. I. Tricladen. Z. wiss. Zool., 94: 541-604.

out at the Department of Invertebrate Zoology, Royal Ontario WHITEHOUSE, R. H., 1913. Zoological results of the Abor

Museum. Our work on the karyotaxonomy of North American Expedition, 1911-12, xxii: Freshwater Planaria. Ree.

of which this forms small has been Indian 8: planarians, paper a part, Mus., 317-321.

Received: 16 May 1978

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