OCCASIONAL PAPERS OF THE MUSEUM OF ZOOLOGY UNIVERSITY OF MICHIGAN

CHRORlIOSOMES OF THE SUCCINEID SNAIL CA TIhTELLA RO TUNDATA1

PUBLISHEDreports of haploid chromoso~nenumbers of the "pulmon- ate" land snails (, ) indicate that the numbers range krom n=17 to 34 (Fig. 1). The , to ~vhich Cat in ella rotundala (Gould, 1848) belongs, has the lowest haploid numbers recorded for any pulrnonate species, which, until this report, was 17. This number (n=l'i) was found in three species ol Japanese succineids by Inaba (1945) and Koyama (1955). With the exceptioil of these three species, the break in the ranges 01 chroinoso~nenumbers between the land and the aquatic "pulmonates" seemed so sharp as to draw special note by cytologists studying the groups (Inaba, 1959; Burch and Heard, 1962). The aquatic "pulmonates" (Order Basomma- tophora), except lor the polyploit1 species (see Burch, 1960 a, c, 196-1; Burch, Basch, and Bush, 1960), all have fewer than 20 pairs of chromo- somes. Nearly all ok the land styloill~natophoran"p~~lmonates" seeined to have 20 or more pairs 01 chroillosoines (Burch, 1960 21; Burch and Kim, 1962; Inaba, 1959). In view 01 the much higher numbers so far known to occur in the Succineidae, but especially in the other stylo~nmatophoranfamilies, it was quite unexpected to find a succineid land snail that had only five pairs of chromosomes. It is on this species, Catinella ~otundatn,that the present paper is based. Grateiul acknowledginent is made to Yoshio Kondo for help in collecting tlle specinlens ant1 to Anne Gisinann for critically reading the manuscript.

1 This investigation was supported (in part) by a Public Health Service re- search career program award (number 1-K3-AI-19, 451-01) and by research grants 2 T1 A1 41-MA1 from the National Institute of Allergy and Infectious Diseases, U. S. Public Health Service, and GB 787 from the National Science Foundation, Washington, D. C., U.S.A. The l';~~rlilySucc.ineitl:~e, which com1)rises the ":1111ber snails," has ;I world-witle distril)ntion. Sllclls oS tlie sl)ec:ies oll'er l'cw ch:trac.ters wliich hell) in tlleir c.l;issific;~tioi~;111d ;I<-cortlingly sut.cirieid syste~ll:~tics 1l;ls 1;lggctl I~cl~it~tlthat ol Illany other Ian(l sn;~ilgroi~ps. Kecerlt ails- :o~nit.;~lst~tdies (Quick, 193.3, 1034, 1956, 1939 n, 1); Boettgcr, 19.39; 1'ilsl)l-y, 19.18; Otlhner, 1950) have co~lsidcrablyinipl.ovetl systeinatics witlli~ithe I:~ir~ily,I~ut much c.i-itic.:~lwork l-er~l;tinsto bc tlonc in order to c..;t:~blisl~;I c.oniljlctely s;~tisl:~ctorycl;~ssificatio~~. No. 638 Ch~ornosotncsof Sntrils 3

Quick (1933) tlivitletl the Uatrlily into two main groups which arc distinguished by the presence or absence ol a penial sheath. Odhner (1950) gave these two groups forinal sublainily names: Succineinae lor the group wit11 a penial sheath, Catinellinae for the group without the sheath. He thought that the subfamily Ca tinellinae contained the most prin~itivespecies ol the two, and divided it into three genera: Ctrlinelln Pease, 187 1, the nlost specializetl, Qz~icitinOdhner, 1950, in- termetliate, ;ind I~zdos~rc.c.i~~~euRao, 1924, the illost primitive or the three genera. Otlhner (1950) recognized three subgenera within the genus Cnti- nelln: (:nli?zella s.s., Q~rickella Boettger, 1939, ant1 1I4edinppendi.x Pilsbry, 1948. It is diflicult to ascertain which subgenus shol~ldbe con- sitleretl the lrlore primitive. ISecause of the relative lengths (i.e., nearly equal) ol the spermathecal duct and the penis, Cntinwllt~s.s. might Ije consideretl the more specialized, but its shorter vagina ant1 sinlple penis (~~itlloutan appendix) arc strong indications that it should I)e pl;~cetlin ;I more priinitive position. Cnlinelln s.s. is restricted to the Pacific islands, Medinppendix is lountl in North ilnlcrica, ant1 Q~ricltellnoccurs in western Europe. The species treated in the present study, Calinelln ?.otz~ndntn,belongs to the subgenus Clitinelln s..s.

The lour specitnens used in this stutly were obtainetl lrotn about 2000 leet elevation on the Paonloho Trail, Koolau Range, Oahu, I-Iawaii. The tissues were killed, fixed, ant1 preservetl in Newcoirrer's (1953) Iluid ant1 stainecl by he acetic-orcein squash technique (La Cour, 19/11). Observations were itlade with Nikon (Nippon Kogaku) nlicroscopes using 100 X (n.a. 1.25) oil iintnersion objectives anti 10 X and 30 X oculars. The chromosoines were tlrawn with the ;rid ol a camera Iucida and reprotlucetl at a table top magnification ol 5700 X. Photogral>hs were taken using a 10 X ocular, oil irntnei-sion objective, a Kotlak Wrattan 5711 (green) filter, ant1 Kodak High Contrast <:opy filirr. OBSERVATIONS The diploid number for Catin~llnlot~rndntn is 10. The five pairs of chromosomes can be tliscerned quite readily in the sperin;~togonial cells (Figs. 2, 8, '3). All of the lliitoti~~hro~nosoirles are lnedianly ton- stricted, or very nearly so, and are rather large in conlparison with those ol other stylominatophoran snails. The largest sperrnatogoni;~l F~c;s.2-7. (:h~.o~iiosomcsof Ctr~irrc./l(r~-otrr~rrl~rt(r: 2, sl,crtn:l~ogoni;rl Jlcraphasc; 3 :111(l4. (li:~ki~icsis:3, \fct:~pli:tsc I: 6, I~IIC l'ropli:~$c~11: 7, (I\-;i(ls :I[ OIIC polc of cell ;II 'I'c~lol,l~;~st~I. .\I1 lig111.c~;IIT of st;~gcsof sl,cr~ii:~~ogc~lc$is:111d ;111 arc magni- iit-cl X 1930. Figs. 2, 1, ;i11(1 fi :II.~-11lio10g1~apl1s 1:1ke11 (I.OII~ a I~I~~I~~I-:II~\~sli(1c-. Figs. 3, 5, :111(l 7 arc pl~otog~~:~l~l~stakcii fr(1111 ;I ~CYIII:~I~CIIIsIi(1c.

cll~-o~~io\o~~~eIIIC:I~III-~C~ IV;I\ 6.0 111it r;~lollg, t11c \111;111~5t ( II~OII~O\OIII~of the \;lnlc tell IV;I\ 3.2 111icr;t long. In all 111;1jol-\t;lge.; 01 110th tli\,i\ion\ ol l~~cio\i\,i.e., prol)h;i\e, ~neta- ~)li;l\e.;I 11 I t10i fi1.e 1x1in of rll~.o~rlo\onlesor five cIlro~no\olnc.\ ~;IIIeasil~, he ol,\ervetl. I)t1ri1ig the di;~kinesi\ of Pro-

1)11:1\e 1 tl~ctl~ro~ilo\o~~ie\ ;11)l)e:11- as [ Iowtl or o11e1i t ircle\ of varying six\ 01- ;15 c l.o\\e\ (Fig\. 3. l, 10). Pl-csurn;ll)l\ cnch 01 the tlo\etl ring- sll;~l)c(l\)i~,;tlell I, II;IS t 11-o cIli;1\111;1tn, :111tl e:1c11 01 the ope11 rings or No. 6.38 Chromosom,es of Snnils 5

F1c.4. 8-14. C:arncla 111ricla drawings of chromosomeq of Cntirwlla rot~tndatn:8 ant1 9. sl>e~rnatogoni;~lMetaphase (Fig. 8 is a camera lucida d~atvingof the photo- graphecl tl~~omow,rnrsin Fig. 2); 10, drawing of chromosomes shown in Fig. 3; 11, hfctaphasc-.Inapl~ase I (side view); 12, drawing of hivalente shown in Fig. 5; 1.3, tl~a~ti~igof djads shown in Fig. 7; 14, Ifetaphase TI. All figures are of stage9 of ~1xrnii1togcne~isant1 all are magnified X 19.70. Figs. 8, 9, 11, and 14 were drawn fro111 a temporary slitlc; Fip. 10, 12, and 13 were drawn from a permanent slide.

crosses has only one. The most comtnon configuration of bivalents fount1 (luring (Iiakinesis was four circles and a cross (Figs. 3, 10); less frequent lverc five circles or three circles and two crosses. 'The chroma tin of the filletaphase 1 bivalents is more condensed, giving the 1)ivalents a smoother appearance (Figs. 5, 12). A side view of fiTet;~l~I~ase-~\na~~I~ase1 hivalents is shown in Figure I I. The length of the largest bivalent here is 5.8 micra. The Telophase I and Jleta- G ,J. B. Rnrch Orr. P(I/)PI phase I1 dyads are rloticeably smaller than the Riletaphasc 1 bivalents ol adjacent or ncarby cclls (compare Fig. 11 with Fig. 14, and Fig. 12 with Fig. 13; Figs. 11 ant1 14 tan not be conlparetl with Figs. 12 and 13 because the two slitles were treated differently at the time the illustrations were prepared, i.e., one was temporary and the otl~cr pemianent).

DISCUSSION

The chrolnosomc numbers of Catinella 7.otundatn (n=5, 2n=10) of Hawaii are the lowest yet reported Sor ;I ~uollusk.The previously lowest nu~rlberreportetl for a land snail was n= 17 lor three Japanese succineids. However, I have lou~ldthat C. (~Medicrppendix)vewnetcr of Michigan, U.S.A., has six pairs oP chromosomes, and thereby has only one more bivalent than C. I-ot~~ndaln.The lact that the two members ol' the genus have nearly the same chro~nosolrie number, although widely separatetl geographically and belonging to two difierent sub- genera, points to a cytological conservatisru in gastropods that has been tlenlonstrated in numerous other groups (see Rurch, 19G1). An additional point in connection with the low chroinoso~ile~lum- bers ol C. 1-otun~datnant1 C. 11ern7etc~is that morphologists (see Otlhner, 1950; Pilsbry, 1948) consider Cntinella to be the most primitive ol the succineitl genera. They certainly have the lowest chromosome nuni- bers ol any succincid for which chromosome data are available. This is in accord with previous observations on chromosonie number changes in euthyneuran snails (see Burch, 19G1), is., that increased speciali- zation in snails has been accomp;~nietlby ;I tcndency for increase in chromosome number and decreases in chromosonie nu~nbel-sappe;~r to be rare. 111 lower syste~uaticcategories in the Stylo~n~iiatoljhora, higher chrorr~osomenumbers go with the more highly specialized spe- cics, lower nr~~r~berswith the less specializetl species. Husted and Burcl~(1'346, 1953) were the first to suggest that such a relationship between chrolnosome numbers and nlorphological characters might occur in "pulinonate" gastropods. If the directional increase in chronlosoine numbers ~nentioned above holds true in all cases, one would expect that the subgenus Catinella S.S. (with n15 lor C. rotzrndrrta) is more primitive than the subgenus AIediappendix (with n=G for C. vermela). Because of its short vagina and simple penis, both considered primitive characters, Cntinelln s.s. is indeed considered the inore primitive of the two subgenera. It will be interesting to study the chromosomes ol C. a~e91n~iaof the European subgenus Qz~icitellnwhich, on account ol its No. 638 Chromosomes of Snails 'i less specialized penis, would seein to be less advanced than Mediap- pendix (but more advanced than Catinella s.s.). But of especial in- terest would be a study of the two other catinelline genera, Quickia and Indosz~ccinea,which Odhner (1950) considers even more primitive than Catinella. LITERATURE CITED

Boli.rrc;~r~<,C. R. 1939 Bemerkungen iiber die in Deutschland vorkom~nendenBernsteinschnec- ken (Fam. Succineidae). Zool. Anz., 127:49-64.

IYBOn Chromosomes of Gyi.az~lus circz~instrintus, a freshwater snail. Nature, 1893497-98. 19ROh C;hro~uosonlestudies of aquatic pullnonate snails. Nucleus, 3:l77-208. 196Oc Chrotnosotne numbers of schistosome vector snails. Zeit. Tropenmed. l'arasit., 11:449-52. 19(il The chromosomes of Plnnorbari~cs c0rneu.s Linnaeus, with a discus- sion on the value of chro~nosomenumbers in snail systematics. Basteria, 2.5:45-52. 1964 Cytological studies of l'lanorbidae (: Basommatopliora). I. The African subgenus Bulinus s.s., Malacologia, 1:387-400.

BUIXH,J. B., 1'. F. BAFCH,ASD L. L. BUSH 1960 Chromosome numbers in ancylid snails. Rev. Portuguesa Zool. Biol. Ger., 2: 199-204.

Bu~

BURCH,J. B., AND D. C. KIM 1962 Chro~nosomesof Cerion incnnunz (Binney) (Mollusca: Gastropoda: Sty- lommatophora). Bull. Nat. Inst. Health (Seoul), 5:181-86. GOULD,A. A. 1848 Descriptions of shells collected by the U. S. Exploring Expedition. Proc. Boston Soc. Nat. Hist., 2:182-84.

HUSIXD,L., AND 1'. R. BURCH 1946 The chromosomes of polygyrid snails. Amer. Natur., 80:410-29. 1953 The chromosolnes of the polyvrid snail Allogona profunda. Virginia Jour. Sci., 4:62-64. INABA,A. 1949 Chromosome numbers in some land snails. Venus, Jap. Jour. Malacol., 14:97-102. 1959 Cytological studies in molluscs. 11. A chromosome survey in the stylom- nlatophoric . Jour. Sci., Hiroshima Univ., Ser. B, Div. 1, 18:71-93. KOYAMA,T. 1955 Studies on the chromosome numbers of two species of Succinea ill Japan. Vcnr~s,Jap. Jour. Malacol., 18:259-65. LACOUR,L. 1941. Acetic-orcein: A new stain-fixative for chromosomes. Stain Tcclln., 16: 169-74.

NEWCOMEI<,E. H. 1953 A new cytological and histological fixing fluid. Science, 118:lGl. ODANFK,N. H. 1950 Succincid studies: genera and species of subfamily Catinellillac 710U. l'roc. Malacol. Soc. London, 28:200-10.

Pr,\se, W. H. 1871 Observations sur les espcces de Coquilles tei-restres qui habitenl I'ile de Kauni (iles Hnror~ii),accompagn6cs dc descriptions d'espdcies nozruelles. Jour. Conchyl., 18:87-97. PEHROT,M. 1937 Recherches sur les chromosomcs des puhriones stylom~natophores(Notc prClimitlaire). C. R. Soc. Phys. Hist. nat. Genkve, 54:119-21. 1938 Etude de cytologie cornpark chez les gastC1-opodes pulmonCs. Re\.. suisse Zool., 45:487-566. PILSUKY,13. A. 1948 Land Mollusca of North America (North of Mexico). Acad. Nat. Sci. Philadelphia, Monogr. 3, 2:l-520. QUICK,H. E. 1933 The anatomy of British Succineae. Proc. Malacol. Soc. London, 20:295- 318, Pls. 23-25. 1934 The development of radula and jaw, and the specific diKelcnces in young Sziccinen pfeiffe~iRossm. and Succirzea f)utri.~(L). Ibid., 21:96-103. 1936 The anatomy of some African Succineae, and of Succinea hlingarica Hazay and S. n~istralis Ferussac for cotnparison. Ann. Natal Mus., 8:1'+45, Pls. 1-4. 1939n Some particulars oC four Indopacific Succinea. Proc. Malacol. Soc. Lon- don, 23:298-302. 19391) On Szrccinea clndecola Crawford. Ibid., 23:333-35.

RAO, H. S. 1924. Asiatic Succineidae in the Indian Museum. Rec. Indian Mus., 26:367-408. Accepted for publication May I, 1964