The malacologicalsocietymalacological society of Japan

Cytological Relationships of some Pacific Gastropodsi･2

J. B. BuRcH3 (The 406th Medical Laberatory, U.S. Army Medical Command, Japan and The University of Michigan, Ann Arbor, Michigan, U,S.A.)

IJSC V ?'i':- Jdi Hti J(l! ts{ cD fiEM ECtl t):-i ]'4 ts pm tw ma en

J. B. A---.e

(I'ptLIa Text-fig, 1 ; fi Tables 1-17)

Introduction

Information on the chromosomes of snails of the Pacific area is scarce, and it is

only recently that any reliable data have been gathered. Nevertheless, it is of in-

terest and value to compare what cytologica! information is available for Pacific

gastropod mollusks with similar information on snails from other geographical regions, and to discuss the cytotaxonomic value of current data and the prospective usefulness

of cytological studies as anticipated in the future.

The existing reliable information on chromosome numbers and the taxonomic use-

fulness of this information was reviewed by BuRcH (1965a) for the gastropod Euthy- neura and by PA'rrF.RsoN (1967a) for the gastropod Streptoneura. From these

reviews it was observed or concluded that in the 1) haploid chromosome

numbers (including polyploid numbers) range from 5 to 72; 2) although different

chromosome numbers characterize certain taxa within this subclass, the chromosome

numbers of the various comprised by these taxa remain remarkably constant ;

3) therefore, mechanisms responsible for addition or deletion of chromosomes must

operate at a very low frequency or efficiency in these taxa;4) changes in chromo-

some numbers among the higher systematic categories are brought about through

aneuploidy ; 5) polyploidy has been found only in the , but even there it is notcommon and, when present, is evident mainly at the species level, Although polyploidy, where it exists, may produce new species, it does not appear to be of

significance in the formation of higher taxa; 6) in most cases, the more advanced

1) Contribution No. 11, Asian Mollusks Program, Institute of Malacology. This paper was pre-

"Evolution, sented to Symposium No. 4, Distribution and Migration of Plants and in the Pacific Area" at the E'eventh Pacific Science Congress, Tokyo, Japan, 1966. Gratefu] acknowledgement is made te the National Research Council, National Academy of Sciences, Washington, D. C., fer travel funds to attend th{s Congress. 2) This investigation wa$ sponsored by the Commission on Parasitic Diseases of the Armed Forces Epidemiological Board, and was supported (in part) by the U. S. Army Medical Research and Development Comrnand and (in part) by research grants GB-3006 and GB-787 from the National Science Foundation, Washington, D. C, 3) Supported by a Research Career Program Award (Ne. 5-K3-AI-19, 451) from the National Institute of Allergy and Infectious Diseases, U. S. Public Health Service.

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BuRcH: Cytological Relationships of Some Pacific Gastropods 119

groups among the Euthyneura, or those often considered more specialized, also have the greater number of chromosomes (Text-fig. 1). In the Streptoneura, it was observed or concluded that 1) haploid chromosome

numbers range from 7 to 47 ; 2) like the Euthyneura, the Streptoneura exhibit a con-

servativeness in chromosome numbers, with variation in chromosome numbers seldom

more than ± 2 bivalents in the lower taxa; 3) within the Streptoneura, the Archaeo-

and Mesogastropoda have relatively low numbers, whereas the mere

advanced order Neogastropoda has higher numbers ; 4) however, with the fragmentary information available, there appears to be no general clear-cut correlation between

"primitiveness" !ow chromosome numbers and among the various groups. However,

within the Viviparacea, such a correlation may exist ; 5) polyploidy, suspected in the

Hydrobiidae, and reported in the Thiaridae, needs to be confirmed.

Chromosomes have been studied of snail species from the following Pacific areas :

Japan, Taiwan (Forrnosa), New Zea!and, New Ca!edonia, the Solomon Islands, the Marshall Islands. Hawaii and the Galapagos Islands. In order to provide a framework

of reference for chromosome numbers of Pacific snails, I would like to briefly review

eurrent information on chromosome numbers in gastropods.

The Opisthobranchiate Orders

In the Notaspidea only one species has had its chromosome number determined, Pleurobranchaea novae2ealanditze from Japan, with 12 pairs of chromosomes (Table 1).

In the Nudibranchia, chromosomes have been studied in 17 species of 14 genera and

10 families, all from the Pacific area. It is of considerable interest to note that all

of these had the same chromosome number, h =13.

Table 1. Chromoseme Numbers in Notaspidea and Nudibranchia'

Chromosome 1 Family I.ecality No, Genera No. Species Nurnber (n)

Notaspidea Pleurobranchidae 12 Japan i 1 / 1 Nudibranchia Dorididae 13131313131313131313 Japan / 4121111111 52211I1121

Marshall Is, Dendrodorididae i Japan, Triophidae japan Goniodorididae Japan E :ilt1 Fimbriidae 1, Japan Dotonidae i Japan Arminidae l Japan

Cuthonidae , Japan ': Facelinidae Japan i1! Favorinidae Marshall Is. l1i

" From INABA & Hmoi'A, 1954, 1958 ; INABA, 1959b,c, l961a; Bulusu & NATARA,JAN, 1967.

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In the other opisthobranch groups, 17 species have been fpund to have 17 pairs of chromosomes, which again demonstrates the great conservativeness of chromosome

numbers in the lower Euthyneura (Table 2). Only in the Smaragdinellidae of the Cephalaspidea, the Polybranchiidae of the Sacoglossa, and the Soleolifera (Table 3)

have haploid numbers other than 17 been found, and, except for the sacoglossan,

these have not varied from 17 more than ± 1 bivalent

Table 2.ChromesomeNumbers inOpisthobranchs"

Chromosome Family Locality No. Genera No. Species Number (n)1213

Notaspidea JapanJapan, i 115 118

Nudibranchia Marshall Is, . Entomutaemata 17 '' Japan 1 1 Anaspidea /F

Aplysiidae 17 Japan,Marshall Is. 4 4

Cephalaspidea / Acteonidae 1717171718 JapanJapanJapanMar$hall 11112 11122 Philinidae l' Aglajidae 1 1

Atyidae Is.

Smaragdinellidae Marshall Is. Saceglossa i1i11

Elysiidae 17 Japan, Italy 1411 2511

Stiligeridae 17 Japan, Italy Juliidae 17 JapanItalyMarshall 11,' Polybranchiidae 716-18

Soleolifera Is,, Japan, !I India, U. S, A. 4 5 1 1BvRcH,

* From 1959c, MANeiNo &SOIMI, 1964i NATARAJAN, 1959, 1960; 1965a;

BuRcHINABA.,& NATARAJAN,1961a; 1967.

Table 3. Chromosome Numbers in Soleolifera'

Species Chromosome LocaHty /1/I Number (n)i1 Veronicellidae

Veronicelta floridana , 1617 U, S, A. i Laevicaulis alte l India Onchidiidae Onchidella kurodai i 1718 JapanMarshall / 1 Onchidella evelinae Is. Onchidium

/ verracutatum 18 India

* From 1959, 1960; INABA, 1961a; BuRcH, 1965a;

BvzRcHNATARAJAN,& NAaTARAJA)i, 1967.

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Buku]it :CytologicalRelationships of SomePacificGastropods 121

The Basommatophora

In the primitive marine Basommatophora, the haploid chromosome number of the 4 species of SiPhonaria studied is 16 (Table 4). Additionally, I recently studied (un- published) another Japanese species, S. sirius, which also had 16 pairs of chromosomes.

The haploid chromosome number of Salinator taleii of the operculated Amphibolidae is

18, the number found in most of the other Basommatophora studied. In the EIIobiidae,

haploid chromosome numbers range from 17 to 19, but most species have 18 pairs of

chromosomes (MEyER, 1955; NATARA.TA/N, 1958a; BuRcii, 1960al NATARAJAN & BuRcH, 1966).

In the primitive freshwater Basommatophora, the 3 species studied all had 18 pairs of chromosomes (Table 5). Acroloxus lacustris is cytologically quite distinct from all other Euthyneura, and quite different from the New Zealand Latiafluviatilis,

where some think its atfinities lie Csee HuBENDIcK, 1962). In the higher limnic Basommatophora, 7 species of the Physidae have been studied, all with the haploid number 18 (LE CALvEz & CERTAiN, 1950; BuRcH, 1960a; BuRcH

& BusH, 1960; INABA, 1965). In the Lymnaeidae, 34 species have been studied, 23 of

which had 18 pairs of chromosomes (Table 6). But the 9 species of the Radix

Table 4. Chromosome Numbers in Marine Basommatophora* - ... tt tttt .ttttttttttmttt.t.. .. tt-- tttt tt .==.. CNhurmO ii･ species I8rSO(Mt)e Locaiity

Siphonariidae Siphenaria l'aPonica 16 Japan SiPhonaria g"aneensis, 16 Marshalt ls. / laciniosa l･ 16 New Caledonia SiPhonaria ' , 1 SiPhonaria Pectinata / 16 / Florida, U. S. A. Amphibolidae ! Salinator takii 18 Japan ,. . ! -

* From INABA, 1953 ; NA'rARAJAN & BuRcH, 1966.

Table 5. Chromosome Nurnbers of Primitive Aquatic Basommatophora*

Chromosome Spec.ies Locality Number (n)

Latiidae

Latia neritoides 18 Zealand / New Chilinidae / Chilina nttviatitis 18 Uruguay Acroloxidae

Acroloxus lacustris 18 Eng]and

* From BuRcJt, BuRcH & PAT7･EKsON,1963; NATARAJAN &

BvRcH, 1966,1962;

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Table6. Chromosome Numbers in Lymnaeidae* tt tt ' 1 Chromosome I Genera No, Species Numbers Cn) , ' '' / Bakerilymnaea-- l' 16 1'

Radix 17 9 i L,ymnaea 18 1

Stagnicola 18 11

Acella 18 ･ 1 / Pseudosuccinea 18 1

Butimnea 18 1 Fossaria 18-19 'i 4 Lanx 18 3

Fishereta 18 2 ' * From PERRoT, J.-L., lg3o, lg34; PERRoT & pl]Rl[oT,'lggs; LE CAnvEz & CERTAiN, 1950; BuRcH, 1960a, 1963a, 1965a, and unpublished,observatiens; NATARAJAN, 1960; BvRcE, Wfnii[AMs, HTs}IENvMA & NATARA,mN, 1964; BuRaH & NATARAJAN, 1965.

from Japan, Taiwan, India, Africa, Madagascar, Turkey, Italy and France had the haploid chromosome number 17. This has given rise.to the speculation (BuRcH, 1965 a) that the original pro-lymnaeid stock had less than 18 pairs of chromosomes, and that this stock gave rise to Radix which gained wide geographical distribution retaining 17 pairs of chromosomes, but one or more times certain populations gained a bivalent. From an early pro-Radix stock (or perhaps from Radix itself) on one or more occa- sions there was a genetic separation of populations which gained an extra bivalent

during or after the separation, resulting in one or more divisions of the family being

characterized by 18 pairs of chromosomes. Regarding Bakerilymnaea, Dr. Yoshio KoNDo (personal communication) has suggest- ed that perhaps B. ollztla (=;) viridis) is an archaic form that entered the Pacific with the Orthurethra during the Late Paleozoic to Early Mesozoic, and gave rise to such species as lvnenaea votutata of Hawaii, L. brevisPira of Sumatra, L. buruane of Indonesia, L. cumingr'ana of the Philippines, and L. Iessoni of Australia, New Guinea and New Zealand.

The basic haploid chromosome number of the is, undoubtedly, 18. This is the number of 35 of the 44 species so far investigated (Table 7). Five of the

other 9 species are polyploids with a multiple of this number. All Pacific area species

studied, belonging to the genera Caniptoceras, Amerianna, Hk'licorbis, (lyraulus, Segmen- tina, and HiLt\bet{tis, have 18 pairs of chromosomes. Haploid chromosome numbers range from 15 to 60 in the ancylid freshwater (Table 8). Rhodacmea cahazvbensis in the southeastern United States bas 15 pairs of chromosomes, while a species of Anq}tlus from Ethiopia has 30 pairs (BuRcH, unpublished), and the common Anayltts fa{viatilis of Europe has 60 pairs of chromo- somes. Since these species are all morphologically related, they form a polyploid

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BuRcH: Cytological Relationships of Some Pacific Gastropods 123

Table 7. Chromosome Numbers in Planorbidae* '" chromogome Genera No. Species Numbers (n)

CamPtoceras 18 1

// Amerianna 18 1

BiomPhataria 18 5

Hblisoma 18 3

Planorbari"s 18 1

Promenetus 18 1

Planorbula 19 2

AnisusArmiger 18 2

18 1

Hblicorbis 18 1

(lyraulus 18, 36 6 iLl Segnzentina 18 1

MpPeutis 18 1

Bulinus 18, 19, 36, 54, 72 17

IndoPlanerbis 18 1 tttt t. *

From LH CAnvm & CERTAiN, 1950; BoNHAM, 1955; BuReH, 1960 a, 1961, 1964c, 1965u, 1967, and unpublished observations ; NA,rARA,rAN, 1960; BuRcH, WTLmAMs, HTgHmuMA & NATARAJAN, 1964 ; NATARAJAN, BvRcH & GIsMANN, 1964 BuRcH & NATARA,JAN, ;' 1965.

Table 8. Chromosome Numbers in Ancylidae* ttttt tt ttttttttttttt - ---- t ttt ･=- - -･･=t- -- l ' Chromosome Number (n) Locality ."."-.m..SpecieS- ' i Ancylinae I ' Rhodacmea cahawbensis 15 U. S. A, Anaylus sp, 30 i Ethiopia / Ancylus fluviatilis 60 England Ferrissinae

Pettancylus niPPonica 17 JapanJapanTanzania Pettanaylus juPonica 18

Pettancylus sp. 18 Gundlachia foPonica 18 JapanU.

Ferrissia tarda 30 S. A.

Ferrissia parallela 30 U. S. A. Laevapecinae

LaevaPex f'zascus 17 U. S. A.

sp. 17 S. Africa -.-BzarnuPia , ' From BvRc}I, 1960a, 1962, 1965a, b, and unpublished observa- tions; BuRcH, BAscH & BusH, 1960.

serles. Interestingly enough, 2 species of Ferrissia from the United States have 30

of chromosomes, although pairs they are rather dissimilar morphologically from

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Rhodacmea and Anaylus. LaevaPex fletscus has 17 pairs of chromosomes, the same number which occurs in at least one species of its African relative, BurnuPia. In Japan, Pettanaylus 7'aPonica has 18 pairs of chromosomes, the same as does Gundlachia joPonica (perhaps the same species) and a Pettanaylus species of Tanzania (BuRcH, unpublished), closely related morphologically to P. 1'aPonica.'

The

Except for some of the , the basic haploid chromosome numbers of the Stylommatophora are higher than those of the Basommatophora, ubually considerably rangefrom higher(Text-fig. 1).In theOrthurethra, haploid chromosome numbers

Hapleid chrornosorne number$

k.. ts X es Mg V. st, ty, 8 P. ?.

Notaspidea .. Nudibranchia

Cephalaspidea .'.

Sacoglossa

Anuspidea Soieolifera

Archeopu]monata

Branchiopulmonata

Heterurethra -

Orthurethra

Mesurethra

Sigrnurethra

Text-fig. 1. Haploid chromosome numbers of various euthyneuran orders. Polyploid chromosome numbers are not shown (from BuHcH, known 1965a), More recent investigations have extended the ranges of euthyneuran chromosome numbers (BvRcH, 1964a,b; MANCINO & SORDI, 1964 ; BuRcE & NATARA,rAN, 1966).

Table 9. Ranges of Chromosome Nurnbers in Orthurethra & Mesurethra*

f.e) [GeNnOera Famiiy fiEiLgbX,ee,Sgot( spNe2ies Orthurethra 1 Achatinellidae 20-21 1 3

Enidae 24 ' 2 , 3 i Valleniidae i 28 1 2 Mesurethra : ; Clausiliidae 24-28 9 11

Ceriidae 27 1 1 -t ttt *Frem INABA, 1959a; NATARAJAN, 1960; BvRcE & HEARD, 1962; BuRoH & Kbr, 1962; BuRcH, 1965a and unpublished observations.

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BuRell; Cytological Relationships of Some Pacific Gastropods !25

20-28 (Table 9). In the primitive Achatinellidae, the chromosome numbers are re-

latively low, but in the Enidae and Valloniidae they are higher. In the Mesurethra, 11 species of the Clausiliidae have been studied, 9 species from Europe and Japan with 24 pairs of chromosomes and 2 species from Taiwan with 28

pairs of chromosomes. The haploid nurnber of 28 in the latter 2 species raises some

doubt about current classification in this family (BuRcH, 1965a). Magalophaedusa martensii (n::;24) and flemiphaedusa similaris (n==28) are placed in the tribe Megalo- phaeduseae, and Phaedusa subaculus (n=24) and Emphaedusa Pseudosheridani (n--28) are placed in another tribe, the Phaeduseae. The data are fragmentary because of

the very few species examined, but in the face of the conservativeness in chromo-

Table 10. Ranges of Chromosome Numbers in Holopodopes*

i Ranges of No.Genera No.Species Family Chromosome Numbers (n) Achatinacea !

Subulinidae 25-31 21 21

Achatinidae 30 i Rhytidacea Haplotrematidae 29-30 1 2 Bulimulacea

Bulimulidae 29-30 2 2

*From NATARAJAN, 1960; FoRD, 1962; BvRcH, 1965e, and un-

pubiished observations.

Table 11. Ranges of Chromosome Numbers in Aulacopoda*

Ranges of ･ Family No.Genera No. Chromosorne Species Numbers (n) / Endodontacea ili Philomycidae 2425-29 112 262 Arionidae I/iili' Endodontidae 31 Ariophantacea Ariephantidae 25-30 41 61 lf1rt' Helicarionidae 28 Testacellacea

Testacellidae 32 1 1 Zonitacea lt! Vitrinidae 28 1331 1843 Limacidae 24-31 28-31 Zonitidae i Milacidae 33-34

* From Htis･i･ED& BvRoH, 1946; INABA, 1959a; NATARAJAN, 1958b,

1960; BEEsoN, 1960i BuReH, 1965a, and unpublished observations,

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Table 12. Ranges of Chromoseme Numbers in Holopoda*

Ranges of No.Genera No.Species Chromosome Family :/:1! Numbers (n)

Helicacea

Helicellidae 21-262Z-3028-29 46611 5181811

Helicidae : /1 Bradybaenidae iae Helminthoglyptid 29 Camaenidae 29 I Polygyracea ! ! 26-31 6 20 Polygyridae !t

* From BAurmR, 1913 ; PERROT, M,, 1938 a, b ; HusTlcD & BvRcrt,BuRcH, 1946, 1953; KAwABu 1947; INABA, 1959 a; FoRD, 1962;

1965a and unpublis hed observations.

Table13. ChromosomeNumbers intheSuccineidae* 1 Chromosome Species '1 Locality Numbers

CatineUa rotundata 566612151717171719191718181821181819222222Hawaii, U. S. A.

Catinella gabbi U. S. A,

Catinetla texana :lU. S, A,

Catinetla vermeta U. S. A.

Succinella oblonga Holland

Oxyloma ]'aPonica JapanJapanJapanHolland Oayloma hirasei i Oayloma h. ktvansae

Oxyloma etegans

Oayloma sarsi Holland

Oayloma retusa U. S. A.

Oazyloma satleana U, S, A,

Succinea (N.) horticola JapanU. Succinea (N,) concordiaiis S. A. U. A. Succinea CN.) greeri 1/ S. Succinea (N,) urbana U. S. A. Succinea CN,) ovalis U. S. A, Succinea (C.) camPestris U. S, A,

S"ccinea (C,) luteola U. S. A. / Succinea (C, .P) grosvenori U. S. A, i1 S"ccinea (S.) Putris EuropeJapanJapan

Succinea (S.) lauta

Succinea (S,) l. sPhaerica

* From PERRoT, M., 1938a; INABA, 1945; HusTED & BvRcH, 1946 ;1964;1966; KoyAMA, 1955; BvRcH, 1964a, b, 1965a; Bvptyr & KiAuTA, PAFm･ERsoN & BvRcu, 1966 ; BURcE, PATTIil

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BvRcH: Cytolegical Relationships of Some Pacific Gastropods 127

some numbers in the Euthyneura, it is diMcult to explain how only the two identical

numbers, n==24 and n=28, should occur in both tribes. In the advanced suborder , chromosome numbers range from 21 to 34 (Tables 10, 11, 12). Haploid numbers are usually higher than 22 and show greater

`opisthobranchs'. variability than is characteristic of the Basommatophora and A detailed discussion of these chromosome numbers will not be presented here Cfor more information see BuRcH, 1965a), but I would like to point out that identical chromosome numbers in the Iower systematic categories correspond rather well with generic and subgeneric groupings based on gross morphology. The chromosome numbers recently found in the Heterurethran Succineidae (BuRcH, 1964a, b) place this family among the mest cy･tologically interesting groups within the Euthyneura (Table 13). But because of the few species investigated and the scarcity of good anatomical and systematic work on the genera, only a limited dis- cussion of their cytotaxonomy is possible.

The most primitive succineid genus yet studied cytologically, Catinella, has the

lowest chromosome numbers reliably reported to occur among mollusks. A striking conservativeness in regard to chromosome number change is also evident in this genus. The three species investigated of the subgenus MediopPendix all have six pairs of chromosomes, with very similar (if not identical) karyotypes, although their geographic distribution represents a wide continental physiographic range, and in regard to the western U.S.A. species, C. (M.) gnbbi, and the 2 eastern species, C. (M.) vermeta and C. (M.) texana, occur in molluscan physiographic provinces that obviously have been separated for an extremely long time. C. rotundata of Hawaii has one pair of chromosomes less than the 3 mainland species, and on morphQlogical grounds it is

placed in a different subgenus (Catinella s.s,). It will be interesting to see if other

members of Catinella s.s. conform to the expected conservativeness and have only 5

pairs of chromosomes. The haploid chromosome numbers found in the genus Oxyloma range from 15-19. Because of the lack of morphological information on this genus, little can be said about the relationships of the species. However, the similarities in chromosome

numbers of the Japanese and Holland species with 17 pairs of chromosomes suggest that a close phylogenetic relationship may exist between them. On the other hand,

the 2 American species with 19 pairs of chremosomes may well belong to a separate

and distinct systematic division within the genus, resulting from or augmented by their long geographic isolation from the Eurasian stock. The relationship of O. 1-mpo- nica (n=15) to O. hirasei (n=17> is not clear. The haploid chromosome numbers found in the genus Succinea range from 17-22. Thus, this genus is cytologically distinct from Catinella and Succinella, but not from

Oayloma. When the chromosome numbers of the various species of the3 subgenera

of Succinea are compared they do not seem to fall precisely into groups that correspond with the current taxonomic divisions. However, it should be pointed out that sub-

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generic assignments in Succinea are at present very tenuous, awaiting a thorough morphological study of the various species. After such a study is complete, the vari-

ous species of the genus might well fall into distinct groups on anatomical grounds that also correspond to groups ranked by their chromosome numbers. Succt'nea Putris (type species of Succinea s.s.) of Europe and S. Iauta of Japan have the highest number of chromosomes (n='22) reported for the family. These 2 species, in addition to having the same chromosome numbers, are also morphologically similar. The chromosome number

Table 14. Chromosome Numbers of Solomon Island Euthyneuran Snails' ' ' '=" '' - . =''=..="='-'rr.'r.mh.-.='=.tt.=. .. .-..--=-' --="t'･t' 1 i Chromosome Numbers Chromosome SpeCieS of ether Species Numbers (n) in Family"

Basornmatophera ''-'' i Ellobiidae / 1 Rythia scarabaens 18 [1,7(1)i, 17(1), 18(4), 19(1) Stylomrnatophora Subulinidae

La"tellaxis mauritianus 25

Subulin'a octona 31 Bulimulidae

Placostylus mittocheilus 30 29(1) Helicarionidae l r Hblicarion sp. 28

i Vitrinidae 1 1 VitrinoPsis sp. 28 Zonitidae

TrochomorPha sp. 28 29(1),31(1) TroEhomorpha sp, 30 . * From unpublished observations, Chromosome numbers of other species in these families are ]isted in the right column. Num- bers in parentheses refer to total numbers of species with the respective chromosome numbers. The chromosome number in brackets refers to the other chromosorne number reported for the genus Jlythia, ** From HusTED & BuR(]q 1946 ; MEyER, 1955; NATARAJAN, 1958a; BvRau, 1960a and unpublished observations; NATARAJAN &

BuReH, 1966.

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BuRs]H: Cyto!ogicalRelationships ofSome PacificGastropods 129

Solomon Islands Euthyneura

Very recently, I have had the opportunity to deterrnine the chromosome numbers

of a few snails from the Solomon Islands in the south Pacifia This study is still

quite incomplete, but nevertheless, these chromosome numbers are shown in Tables 14 and 15. As can be observed from Table 14, the chromosome numbers of the

euthyneuran E!lobiidae, Bulimulidae and Zonitidae correspond well with those already

reported for other species of these families from other geographical areas. Other

than the Solomon Island specimens, no other species of the Subulinidae, Helicarionidae

and Vitrinidae have been studied.

Table 15. Chremoseme Numbers of Solomon Islands Streptoneuran Snails' iNC.hlhObM.?.sO(rn.slCh'.Ofil:OtShFO,.rn,.eslpN species y..",.Mi.RerS r [ Streptoneura l Archaeogastropoda l 1 Helicinidae 1 i i Palaeohelicina sp. 1 18 1 pleuropoma $p, ls l - i PlezaroPoma sp. 18 / Mesogastropoda ! L

Pupinidae i - PuPina sp. 13 l Assimineidae t [ Assiminea sp, 15 12(2),15C2) i AdelomorPha sp. 17 1 Thiaridae i 1 Y.e,i.a.n.o,i.dgi,s･.p',,.I g: I[lgli,)･,3,s,?zz･,4"si4,7,(,L)]

' From unpublished observations. Chromosome numbers of other species in these families are listed in the right column. Num- bers in parentheses refer to total numbers of species with the respective chromosome numbers, The chromosome numbers in brackets refer te ether chromesome numbers reported for the genus MeSanoides, " Frorn PA'm'ERsoN, 1967b; JAcoB, 1958, 1959,

Streptoneura

Available information on the chromosomes of streptoneuran snails have recently been reviewed by NisHiKAwA (1962) and PATTERsQN (1967a). Therefore, a summary will not be presented here. However, I would like to review our recent studies on

cytotaxonomy of some Japanese Hydrobiidae and Pleuroceridae.

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The hydrobiid genus Onconzelania was divided into 3 genera and 19 species by BARTscH <1936, 1939, 1946). ABBoTT (1948) and Kuo & MAo (1957) considered the group to contain only 1 genus with 4 species: OncomeJania forinosana (Taiwan), O.

hmpensis (China mainland), O. nosoPhora (Japan), and O. quadrasi (PhiLippines). In our cytological studies, we found that the latter 4 species had 17 pairs of chromo- somes (Table 16), and that the pairing behavior of their chrornosomes at meiosis

Table 16. Chromosome Numbers of Pomatiopsinae*

Chromosome Nos. i 'l'-Male'"l (2n)l SpecieS Locality i/ F-em-a16 11 Oncomelania O. h"Pensis nosoPhora 34 34 JapanChina O, huPensis huPensis 34 34 mainland

O. huPensis 34 34 TaiwanPhilippines formosana1''1'[1l!1 O. huPensis quadrasi 34 34 PomatioPsis

P, catlprnica 3434(XX) 1 3433

sex determining mechanism for the Pomatiopsis specles are givell in parentheses.

in Fi hybrids was normal. Only normal bivalents with 1, 2 or 3 chiasmata were

observed, and no univalents, trivalents, er quadrivalents were found. In addition, all

segments of each chromosome seemed to pair completely. When this cytological information is coupled with the great morphologica] sirnilarity found between the 4

species, the ease of their hybridization, and the non-reduced viability of the hybrids,

"species" then the 4 so-called of Onconeelania should be interpreted as no more than

geographicalpopulations or races of the same species. On shell shape, O. nosoPhora,

O. formosana and O. quadrasi form a north to south step-cline, the Japanese species

being relatively long and slender, the Philippine species being relatively shorter and

broader, and the Taiwan species falling between the two extremes.

The chromosomes of the 4 species of the closely related North American genus

Pomatiopsis are noticeably larger than those of Oncomelania, but also, except for P.

californica, their chromosome numbers differ.

In studying the pleurocerid species of SemisulcosPira of the Lake Biwa area,

(BuRcr{ & DAvTs, unpublished), it was only when distinct chromosomal differenees were

found that the species could be clearly separated and the limits of variability estab-

lished. In addition, once the specles were clearly separated, other specific features

became evident.

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BvRnH: Cytolegical Relationships of Some Pacific Gastropods 131

The haploid chromosome numbers of the Semisulcospira species that we were able

to investigate range from 7 to 20 (Table 17), which, in the conservative Gastropoda, is quite a wide range in variation. There seems to be no indication that polyploidy has been involved here. In those species with less than 18 pairs of chromosomes,

one or more extra or supernurnerary chromosomes were often feund. For example, in S. niPonica, S. decipiens, and S. reticulata, specimens were found with 13 pairs of chromosomes. However, the caryotypes of these 3 species and S. nakasekoae are rather distinct.

Chr'omosome numbers of Solomon Islands streptoneuran snails are shown in Table 15. In the Assimineidae, although the haploid number･15 had already been feund in

2species of Japanese Assiminea (PATTERsoN, 1967b), the relatively high haploid num- ber 17 has not yet been reported in the family.

It is interesting to note the high (polyploid?) chromosome number of the thiarid Balanocochlis, and to compare it to the high numbers reported by JAcoB (1959) for

several Indian thiarid species.

Other than the Solomon Island specimens, no other species of the Helicinidae or

Pupinidae have been studied.

Table 17. Chromosome Numbers of Pleuroceridae' tt-t . ... ' -=-"'-"==.'.'..'.L. .. Chromosome Species Locality Numbers (n) semlJsutcogl ira

s.s.s.s,s.s,s,s.s.s.s.habeih, 77121212131418181820 Uji River, Japan yamaguchi Lake Biwa, Japan

niPonica Lake Biwa, , Japan : decipiens Lake Biwa, Japan reticulata i1 Lake Biwa, Japan nakasekoae Uji River, Japan multigranosa Lake Biwa, Japan libertina ll1/1 Shimoda, Japan ornatatracheareznzana Hakone, Japan Hakone, Japan Uji River, Japan Goniobasis

G.G laqueata 1820 U. S. A. livescens U. S: A.

" Frorn BvRcE & DAvis (unpublished);

Summary and Conclusions

1) Cytological studies of Pacific snails have hardly begun. However, cytological

vestigations are currently underway on Pacific area snails, and the usefulness･in-of such studies will increase as more information is compiled.

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・ 132 VENUS ： 25 （3 4）1967

numbers of snails almost 2） Where information is avaiiable ， chro エnosome Pacific ， without exception ， fall within the ranges already determined for chromosome numbers of related snails elsewhere in the world ． used to 3） Accordingly ， chromosome numbers are another character which can be show relationships of species and groups of species ． − At the species subgeneric and levels， chromosome nunlbers may be help 4） ， generic expected ful in some cases for taxon discrimination； in other cases ， they can be

to give Iittle aid ． 5） Complete caryotype analyses and associated cytogelletic studies are very rare for most of the few studies available have been done on any mollusk ． However ， Paci丘c area snails ． Such investigations can be expected to be of great help for − future systematic interpretations involving species discriminati【）n and species rela tionships ，

要 約 ー ー ．丶 の に つ い た か で ニ ュ ジ ラ ソ ド， 太 ト洋 地 区 産 巻 貝 類 の 細 胞 学 的 研 究 は そ 緒 ば り あ る が ， 口 本 ，台 湾 ， ． 二 一 ニ 卩 モ ソ ハ ワ ガ ラ パ ゴ ス の で の が 進 み つ つ あ り， 知 見 の 増 。 ． カ レ ド ア ， ソ 群 島 ， イ 及 び 諸 島 諸 地 域 研 究

大 と 共 に 分 類 学 に 於 け る 有 用 性 も増 す と 悪 わ れ る tt

現 在 知 れ る 限 り に 於 い て は 太 平 洋 地 区 巻 貝 類 の 染 色 体 数 は 世 界 の 他 地 区 で 決定 さ れ た 近 縁 の も の の 変 異 の

は び の を 示 の 1 つ と し て 用 い 得 る も の で あ っ 範 囲 内 に お さ ま っ て い る 。 そ こ で 染 色 体 数 種 及 種 群 類 縁 す 形 質

ベ ル つ で い こ と も に は の レ に の で る が ， 有 効 な て ， 或 る 場 合 ，種 ，亜 属 ，及 び 属 に 於 け る 判 別 役 立 も あ 余 り あ る 。 ’ タ ク 直 神 経 類 （Eu しhyneura ） で は 巨数 染 色 体 は 5 か ら 72 ま で を 示 し て い て ，異 っ た 染 色 体 数 が 或 る 決 っ た 一 サ 吩 類 学 的 単 働 を 特 徴 付 け て い る が ，そ れ ら の タ ク サ 内 で ｝a そ れ に 含 ま れ る 諸 種 の 染 色 体 数 ｝よ著 し く

の に る は こ の タ タ サ の で は に し か か な い に 違 い な い 。 定 で あ る 。従 っ て 染 色 体数 増 減 関す 機 構 れ ら 内 部 稀 働 Polyploidy は 高 次 の 分 ．類 学 的 範疇 に 於 け る 染 色 体 数 の 変 化 は 異 数 1生 （Aneuploidy ） lc よ る 。倍 数 性 （ ） 基 限

ベ ル 一 類 に の み 見 ら れ る に 過 ぎず ， し か も 晋 通 に 見 ら れ る も の で も な く ， ま た 主 に 種 の レ で 起 る 。 般 に 進 化

の ． い Streptoneura で は 染 色 し た 類 或 い は 特 殊 化 し た も の と 思 わ れ る で は ，染 色 体 数 が 多 。 捩 神 経 類 （ ） 半 数

で は し い 始 足 類 と 中 足 類 で は 体 数 は 7 か ら 47 ま で で ，直神 経 類 と 同 様 に 低 次 の 分類学 的 単 位 変 化 難 。 原 腹 腹

ル ー い い 染 色 体 数 が 比 較 的 少 な い が ，新 腹 足 類 で は 多 い 。 し か し 或 る グ プ の 染 色 体 数 が 小 さ か ら と っ て も幾

ー ー ニ bll で つ か の グ ル プ の 中 で 必 ず し も そ の グ ル プ が 原 始 的 と は い え な い よ う に 瓜 わ れ る が ， タ シ 科 の は そ

ワ ニナ で ’ の 様 な 関 係 が 存 在 す る か も 知 れ な い 。借 数 1生 は ヌ マ ツ ボ 承÷に 予 想 さ れ ， ま た ト ウ ガ タ カ 科 診艮告 さ れ

て い る が ，更 に 確 か め られ る 必 要 が あ る 。

つ い の で る 完 全 な 核型分 析 の 研究 は 少 な い が ， そ の 大 部 分 は 太 平 洋地 区 産 の 巻 只 類 に て 行 な わ れ た も あ 。 の で る こ の 様 な研 究 は 将 来 種 の 判 別 と 類 縁 な ど の 分 類 学 的 な 解 釈 上 極 め て 有 用 と な る と 期 待 さ れ 得 る も あ 。

Refere皿 ces

ABBoTT ， R ． T ．，1948 ： Handbook of medically important mo1 】usks of the Orient and the western − − Bu 〃 ． Mus ． comP ． Zool．100 3 ： 245 328， ．1 5． Paclfic． ， （） pls ’ Helix hortensis 7 ． austriaca und der B 舳 TzER ，F ．，1913 ： 亡ber die Chromosomen der Tachea （ ） ， ， ’ − Zel 〜 orsch ． 11 ： 151 169 ． sogenannten einseitigen Bastarde T ． hortensis x T ． aorstria （：a ． Arch ． プ ， a oni − BAms （冫H ， P ．，1936 ： Molluscan intermediate hosts of the Asiatic blood 恥 ke， Schistosoma 丿 ♪ − − confused with them ． ∫廨 〃lsonian 1匝 ∫ ご ， Co 〃 95 5 ： 1 60， ，1 7 ． ‘um ， and species り （） pls

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BuRcH: Cytological Relationships of Sorne Pacific Gastropods 133

BARTscii, P., 1939: A new intermediate hest of the asiatic blood fluke, Schistosoma ]'aPenicum Katsurata. J. }Vask. Acad. Sci,, 29:173-174. '' -, 1946: Schistosomophora in China, with descriptions ef two new $pecies and a note on their Philippine relative. Smithsonian Misc, Coll. 104(20): 1-7. BEEsoN, G. E,, 1960: Chromosome numbers of sLugs. Nature, 186: 257-258. BoNHAM, K., 1955: Sensitivity to X-rays ol the early cleavage stages of the snail Helisoma sub- crenatesm, Groevth, 19(1): 9-18. BuRcH, J. B., 1960a: Chromosome studies of aquatic pulmonate snail$. IVucleus, 3: 177-208.

, 1960b: Chromosumes of PomatiQPsis and Oncomelania. Amer. malacol. Union ann. Raps,, 1959, 26: 15. 1961 : The chromosomes of Planerbarius , cornei{s (LiNNAigiJs), with a discussion on the value of chrornosome numbers in snail systematics. Basteria, 25(4,'5): 45-52, --, 1962: Cytotaxonomic studies ei freshwater limpets (Gastropoda: Basommatophora). I. The European Lake , Acrotoxus lactfstris. uailacJologia, 1<1): 55-72. hi: TAvboR, D. ,1963: W,, WAiiTER, H, J. & BuRcm, J. B., The subgenus Hinkiq)'ia (Lymnaeidae: Stagnicola) in the western United States. Malacolog'ia, IC2): 237- 281. "' --, 1964a: The chromosomes ef Catinella vermeta (, Euthyneura, Succineidae). Acta biel. Acad. Sci. Hhan.v'., 15(1); 87-94. L-' , 1964b: Chromosomes of the succineid snail Catinella retundata. Occ. I'aPs. Mus. Zool., Univ. Miehigan, Ne. 638: 1-8. -, 1964c: Cytelogicai. studies of Planorbidae (Gastropoda: Basommatophora). I. The ` African subgenus Bulimts s.$, A4alacologia, 1(3)/: 387-400. ' 1964d: , Cytotaxonorlly of the genus Oncomelania, intermediate hosts of Scizistosoma juPonica. Amer. matacot. Union ann. Rops,, 1964, 31: 28-29. t'- , 1965a: Chromosomenumbers andsysternatics in euthylleuran snails. Proc. First EuroP. .Mtslacol. Congr,, 215-241. 'T studies ef freshwater limpets ,1965b: Cytotaxonomic (Gastropoda: Basommatophora). III, Japanese Ferrissia and G"ndlachia. Malacologia, 2(2): 253-258. ' ,1967: Chromosomes of intermediate hosts of hurnan bilharziasis. Malacetogia, 5(2): 127-135. P, & , BAscH, B, Bus- L. L., 1960: Chromosome numbers in ancylid snails, Rev, portug, Zoot. Biol. Ger., 2: 199-204. '--' & BvsH, L. I.., 1960: Chromosornes of Physa gyrina Say (Mollusca: ), f. Conchygiol., 100 : 49-54. '''' & HEAHD, W. II,, 1962: Chromosome numbers of two species of Vallonia (Mol]usca, Stylommatophora, Orthurethra). Acta biol. Acad. Sci, Hitng., 12Cl): 305-312, - & Kn!, D, C,, 1962: Chromosomes of Cerion incanz{m (Binney) (Mollusca:Gastropoda: Stylommatephora). Buli. nat. bzst. UeaZth, Korea, 5(1): 181-186. - & NATARA,JAN, R., 1965: Cytological studies of Taiwan freshwater pulmonate snails. Bttll. Inst. Zool., Acad. Sinica, 4(1): 11-17. ---- & , 1967: Chromosomes of some opisthobranchiate mollusks from Eniwetok Ato]1, western Pacific, Pactiic Sci., 21(2): 252-259. ･ -& PATTERsoN, C. M., 1963: Cytotaxonomic studies ef freshwater limpets (Gastropoda; Basommatophora). II. The New Zealand river limpet, neritoides. Malacelogia, 1(2): 313-319.

,- & NATARAJAN, R., 1966: Chromosemes of four species of North American Succineidae. Venus, JZtP, J Mlrtlacoi., 24(4): 342-353. WrnrnAMs, E,, HisuTNvbTA, Y. & NATARA,mN, , J, R., 1964: Chromosomes of some Japanese freshwater snails (Basommatophora : Branchiopulmonata). Malacologia, 1(3): 403-415. BvTeT, L. J. M. & KmvTA, B., 1964 : Voorlopig rapport over de chromosornen van vier Nederlandse succineiden, CorresP. Ned. Mtilacol. Ver., 111: 1163-1164. FoRD, J. M., 1962 : The chromosornes of northwest pulmonate snai]s. Ph. D, thesis, Oregon State Univ., 48 p. HuBENDicK, B., 1962: Studies on Acroloxus (Moll, Basomm.), GbVeborgs Vetensfesamh. Htindl. 9(2): 1-68,

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HvsTED, L. & BuRcH, P. R., 1946: The chromosomes of polygyrid snails. Amer. Nat., 80: 41o-

429, -- - -- Thechromosomesof thepolygyrid snail Allogona Virginia & ,1953: Profunda, f. Sci., 4: 62-64. INABA, A., 1945: Chromosome numbers in some land snails. Venus, JaP, 1. Malacot., 14: 97-102. - -, 1950a: Studies on species of Pulmonate mollusks based on chromosome number. La -299, Kromosomo, 7: 295 ----- review studies in Mo!lusca. Proc. Biol, Sci, Hiroshima , 1950b: A on the chromosomal Univ., 2: 35-40. - - mollusks. I. Chromosomes in basornmatophoric Pulmonata. , 1953: Cytologicalstudies in J. Sci. Hiroshima Univ,, 14(15): 221-228. ceniea Molluscal La Kromo- , 1958: ChromesomesofAmalthea Schmacher (Gastropoda, somo, 34/36 : 1217-1219. --, 1959a: Cytological studies in molluscs, II. A chromosome survey in the styrommato- phoric Pulmonata, J Sci. Mroshima Univ,, 18; 71-93, - ---, 1959b: On the chromosomes ofa gastropod Dendrodoris (Dendrodoris) nigra ' (Stimpson). J. Sci. Hiroshima Uhaiv., 18:95-98. Cytological studies in rnolluscs. III. A chromosome survey in the opistho- ,1959c: branchiate Gastropoda, Annot. 2oot, JkeP., 32: 81-88. --- ･- of some opisthobranchs. Dobutsugaku Zasshi, ,1961a: Chromosomes (In Japanese>. 70(lf2): 24. --, Malacol., 24(4): 1961b: Cytotaxonomy of the euthyneuran gastropods, Venus, ldP. J. 402-413. ---･--, Maiacot,, 1965: Cytotaxonomic studies of freshwater gastropods (I). Venus, ldP. J. 23(4): 223-228, pls. 15-17. - - & HmoTA, R., 1954: On the chromosomes ef Glossodoris Paltescens, (In Japanese), Po-

butsugaku Zasshi, 63 : 437. -- - 1958: A chromesome survey in ten species of nudibranchs (Gastropoda, &･-- ' Mol]usca). JaP. J. ZooX., 12:157-162, '-' -- & TANAKA, H., 1953 ; Studies on the chromosome numbers of some freshwater gastropods. J. Sci, Hiroshima Univ., 14(15): 213-220, reference te JAcoB, J,, l958: Cytolegical studies of Melaniidae (Mollusca) with special partheno- genesis and polyploidy. II. A study of meiosis in the rare males of the polyploid race of Melanoides tuberculatus and M. Iineatus. Trans. Ray. Soc. Edin., 63:433. ---. 1959 : The chromosernes of six melaniid snails CGastropoda : Prosobranchia). Cytologia, 24(4): 487-497. KAwABE. M., 1947: Notes en the chrornosemes of Bradybaena CEzohelix) gainesi (InJapanese). La Kromosomo, 314 : 133-134, KoyAMA, T,, 1955: Studies on the chromosome numbers of two species of Succinea in Japan. Venus, joP. f. Malacol,, 18:259-265. Kuo, Y,-H. & MAo, S.-P., 1957: On the of Oncomelania-snail host of Schistosoma areas in China. 1'aPonicum. Morphelogical studies of Oncomelania snails from different endemic Chinese Med. J, 75 : 824--831, LE CAT;vHz, J. & CERTAiN, P,, 1950: Donn6es caryologiques sur quelques pulmone$ basommato- phores. C. R. Acad. Sci., Paris, 231:794-795. Sacoglossi del MANciNo, G. & SoRDi, M., 1964: Il corredo cromosomico di alcuni Opisthobranchi mar Tirreno. Atti Soc, Toscana Sci. Nat., Ser. B, 71: 12 p. MEyrm, K, O,, 1955: Naturgeschichte der Strandschnecke Ovatella myosotis (Draparnaud). Arch. Moltuskenk., 84(113): 1-43. NATARAJAN, R,, 1958a: Chromosomes of some e$tuarine basommatophorous snails (Mollusca: Pulmonata) from Portonovo. J, fiool. Soc. india, 10(2): le3-107, ･, 1958b: Chromosomes of three species of South Indian pulmonate snails of the genus CryPtozona MOrch. Curr, Sci., 27:311-312. Oncidium verracutatum Cuv, Gastropeda: , 1959: Chromosome$ of the slug (Mollusca: Pulmonata), J. zool, Soc. india, 11:30-33.

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NAmRAJAN, R., 1960: Further cyto!ogical studies in Pulmonata (Mollusca: Gastropeda). 1. zool. Soc. Jndia, 12(1): 69-79. "' & BvRcn, J. B,, 1966: Chromosomes of some archaeopulmonata (Mollusca: Basommato- phora). Cytotogia, 31(2): 109-116. L'r studies ef Basom- , & G]s}tANN,A.. 1965: Cytological Planorbidae (Gastropeda: matophora) II. Some African Planorbinae, Planorbininae and Bulininae. Malacologia, 2(2): 239-252.

L-'" of species of Succineidae , HvBRTcET, L. & BvRcu, J. B., 1966: Chromosomes eight (Gastropoda, Stylommatophora) from the southern United States. Acta biol. Acad. Sci, Hung,, 17(1): 105-120. NrsHiKAwA, S., 1962 : A cQmparative study of the chromosomes in marine gastropods, with some rernarks on cytetaxonomy and phylogeny. 1. Shimeoitoseki Cotlege Fish., 11(3): 149-186, pls. 1-12. PATTERsoN, C. M., 1963: Cytological studies of pomatiopsid snails, Amer. malaeol. Union ann. RePs., 1963, 29: 13-14. -- in streptoneuran snails. ,1967a: Chremosome numbers and systematics MaZacologia, 5(2): 111-125, - -fi, 1967b: Chromosome numbers of some Japanese freshwater snails, Venus, juP. f, Matacot,, 25: 69-72. -- -' & Buincn, J, B., 1966: The chromosome cycle in the Catineila vermeta (Stylommatophora ; Succineidae). Malacologia, 3(3): 309-325. PERRoT, J.-L,, 1930: Chromosomes et hEt6rechromosomes chez les gast6ropedes pulmon6s. Rev. suisse Zool., 37 (20): 397-434. L' dans les deux lign6es du , 1934: A propos du nombre des chromosomes germinales . gastEropode hermaphredite Limnea stagnalis (vari6te rhodani). Rev. suisse Zool,, 41: 693-697. ''' & PERRoT, M., 1938: Note sur les chromo$omes de cinq especes de limnees. C. R. Soc, Phys. Hist. nat, Geneve (Suppl, Arch, Sci. phys. nat.>, 53: 92-93, PHmtor, M., 1938a: Etude de Cytelogie compar6e chez Ies gast6ropodes pulmones, Rev, suisse Zool., 45(20): 487-566. ' -, 1938b: Note sur les chrornosomes de Archelix et d'Alabastrina arabastrites. C, R. Stic. ･ Phys. Hist, nat. Genave, 45:90-92.

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