A Q O R E A N A , S U P P L E M E N T 1995: 261-278

O N T H E I D E N T I T Y O F A R I U N C U L U S M O R T I L L E T I A N D A R I O N P A S C A L I A N U S I N T H E A Z O R E S , W I T H A C O M M E N T O N T H E M E D I T E R R A N E A N D I S T R I B U T I O N

O F . A R I O N I N T E R M E D I U S ( M O L L U S C A , P U L M O N A T A )

Thierry Backel jau*, Teresa Rodriguez**, Carlos B r i t o * * * , Kurt Jordaens**** & L u c De Bruyn****

* R o y a l Be lg i an Institute of Natural Sciences, Ma laco logy Section, Vautierstraat 29, B - 1 0 4 0 Brussels , B e l g i u m .

**Facultade de B i o l o x i a , Departamento de B i o l o x i a , Univers idade de Santiago de Compostela , E-15706, Espana.

***Universidade dos Acores , Departamento de B i o l o g i a , PT-9502 Ponta Delgada, Sao M i g u e l , Acores , Portugal.

****Univers i ty of Antwerp ( R U C A ) , Department of B i o l o g y , Evolut ionary B i o l o g y Group, Groenenborgerlaan 171, B-2020 Antwerp , B e l g i u m .

ABSTRACT Azorean A r i u n c u l u s m o r t i l l e t i is shown, to be a misidentification of

the endemic carnivorous slug P l u t o n i a a t l a n t i c a . Similarly, Azorean A v i o n p a s c a l i a n u s is in fact A. i n t e r m e d i n s . Hence, only three arionids occur in the Azores: A . l u s i t a n i c u s , A . d i s t i n c t u s and A. i n t e r m e d i u s . The identity of A. p a s c a l i a n u s is discussed more generally and it is con­cluded that Simroth's interpretation of this species refers to A . i n t e r m e ­d i u s . Finally, some considerations on the Mediterranean distribution of this latter species are provided.

RESUMO Demonstra-se que A r i u n c u l u s m o r t i l l e t i dos Acores e uma identifica-

cao errdnea da lesma carnivora endemica P l u t o n i a a t l a n t i c a . Similarmen-te, A v i o n p a s c a l i a n u s dos Acores 6, de facto, A. i n t e r m e d i u s . Deste modo, apenas tres ariomdeos ocorrem nos Acores: A. l u s i t a n i c u s , A . d i s t i n c t u s e A. i n t e r m e d i u s . Discute-se mais geralmente a identidade de A. p a s c a ­l i a n u s e cpnclui-se que a interpretacao de Simroth com relacao a esta especie refere-se a A. i n t e r m e d i u s . Finalmente, acrescentam-se algumas consideracoes sobre a distribuicao desta ultima especie.

I N T R O D U C T I O N

B a c k h u y s (1975) r eco rded four ar ionid species in the Azores : A r i o n h o r t e n s i s Ferussac, 1819, A . i n t e r ­medius Normand , 1852, A . p a s c a l i a ­nus M a b i l l e , 1868 and A . l u s i t a n i c u s

M a b i l l e , 1868. Subsequent authors amended this l ist i n three ways: (1) A z o r e a n A . h o r t e n s i s was shown to be A . d i s t i n c t u s M a b i l l e , 1868 (De Winter , 1984); (2) Azorean A . p a s c a ­l i a n u s appeared gene t i c a l l y i n d i s ­t ingu i shab le f r o m A . i n t e r m e d i u s

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and was therefore assigned to this species (Backe l j au et al„ 1992) and (3) A r i u n c u l u s m o r t i l l e t i L e s s o n a , 1881 was reported as a new species for the archipelago (Seixas, 1981a, b,

1 9 9 2 ) . The present paper aims at cor­

rect ing Seixas ' (1981a, b, 1992) re­cords of A r i u n c u l u s and at supple­menting the work of Mangane l l i &

S I M R O T H (1886) G E R M A I N (1930) a t r i u m bipartite undivided implantation of pedunculus on posterior atrial compartment on anterior part of the atrium size of pedunculus long short

L E S S O N A (1881) G E R M A I N (1930) Length of animal 20-25 mm 45 mm

0 _

— 0

FIG. 1. Reproductive organs of A r i u n c u l u s m o r t i l l e t i as figured by Simroth (1886) (a) and Germain (1930) (b). Note that Germain's (1930) figure is virtually a copy of the original drawing by Lessona (1881). Abbreviations: a, atrium; aa, anterior atrial compartment; e, epiphallus; o, oviduct; p, pedunculus of the spermatheca; pa, posterior atrial compartment.

B A C K E L J A U E T A h : . A R I U N C U L U S A N D A R I O N I N T H E A Z O R E S 2 6 3

G i u s t i (1988), Backel jau et a l . (1992) and Rah le (1992) wi th respect to A . i n t e r m e d i u s and A . p a s c a l i a n u s .

T H E IDENTITY OF A V U N C U L U S M O R T I L L E T I N T H E AZORES

L e s s o n a (1881) , S i m r o t h (1886) and G e r m a i n (1930) provided contra­d ic to ry m o r p h o l o g i c a l and anatomi­cal data about A r i u n c u l u s m o r t i l l e t i (Table 1; F i g . 1). The geographic d i s t r ibu t ion of this species is there­fore s t i l l poorly known. It seems as i f the species is conf ined to the P iemontese A l p s i n I ta ly (Lessona, 1881; L e s s o n a & P o l l o n e r a , 1882; A l z o n a , 1971; Bishop , 1980) and the "Departement V a r " i n France ( F l o ­rence, 1889; Germain , 1930).

It was thus surprising that Seixas (1981a , b) r eco rded A r i u n c u l u s m o r t i l l e t i and A r i u n c u l u s sp. f rom the A z o r e s . However , Seixas ' (1981b) spec imens were m i s i d e n t i f i e d and a c t u a l l y re fe r to the e n d e m i c A z o r e a n carn ivorous s lug P l u t o n i a a t l a n t i c a (Morelet , 1860). This can be inferred f rom the f o l l o w i n g fea­tures ment ioned by Seixas (1981b): (1) the chestnut co lour ('cor casta-nha'), (2) the pneumostome situated i n the posterior ha l f of the mantle ( F i g . 2), (3) the more central ly l o ­cated mantle (F ig . 2c-d) ( 'Manto qua-se a meio do corpo 1 ), (4) the sharp, posterior dorsal keel (F ig . 2) ( 'Qui -lha dorsa l bem marcada ') , (5) the charac te r i s t i c f o r m of the t a i l i n con t r ac t ed spec imens ( F i g . 2c -d ) , and (6) the topology of the genital apparatus, pa r t i cu la r ly of the A r i ­u n c u l u s sp. of Seixas (1981b) (F ig .

3 a). The fact that there was no sper-matheca ('a ausencia do r e c e p t £ c u l o seminal ' ) i n this spec imen is not surpr i s ing , for i n P . a t l a n t i c a the sma l l spermatheca is imp lan ted on the posterior end of the di la ted part of the oviduct (F ig . 4) and can be over looked easi ly. The structure of the ' t w o - l o b b e d ' penis i n S e i x a s ' (1981b) A r i u n c u l u s sp. (F ig . 3a) is typ ica l of P . a t l a n t i c a (F ig . 4), as w e l l as the structure of the oviduct w i t h i ts d i l a t e d p o r t i o n i n the middle ( 'com uma dilatacao a meio ' ) . The relat ively long and slender geni­tal a tr ium, f ina l ly , is also characte­ristic of P . a t l a n t i c a (compare F i g s . 3a and 4).

The dimensions of Seixas ' (1981b) material also correspond to those of P . a t l a n t i c a . Moreover , the specimen referred to as A r i u n c u l u s sp. was c o l l e c t e d a long the aquaduct near P ico do Carvao, where P . a t l a n t i c a is c o m m o n ( d ' A r r u d a Fu r t ado , 1882; Simroth, 1891; Backhuys , 1975). W e vis i ted this site at several occasions and each time we observed P . a t l a n t i ­c a , but never A r i u n c u l u s sp. F i n a l ­l y , an examina t ion of the a l c o h o l spec imen ( l e g . M . M . P . Seixas) of this supposed A r i u n c u l u s sp. ( C o l ­l ec t ion of the " M u s e u B o c a g e " N ° . 10328, see Seixas , 1992) conf i rmed its identif icat ion as P . a t l a n t i c a .

W i t h respect to Se ixas ' (1981b) A r i u n c u l u s m o r t i l l e t i (this mater ia l is lost) some points remain obscure: (1) none of Seixas ' (1981b) spec i ­mens (not even the A r i u n c u l u s sp.) were reported to have a shel l plate under the mantle ('nao tern l imace la

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sob o manto ' ) , (2) the specimens iden t i f i ed as A r i u n c u l u s m o r t i l l e t i have a less slender body than A r i u n ­c u l u s sp. ( F i g . 2a-b) and (3) they have a different geni ta l t opo logy , p a r t i c u l a r l y w i t h respect to the structure o f the geni ta l a t r ium, the oviduct and the 'penis', as w e l l as to the implanta t ion of the spermatheca, w h i c h opens direct ly into the genital atr ium (compare F i g . 3a-b). Because o f these con t rad ic to ry observat ions it is possible that Seixas (1981b) not on ly confused A r i u n c u l u s m o r t i l l e t i wi th P . a t l a n t i c a , but also wi th A v i o n d i s t i n c t u s M a b i l l e , 1868. B r o w n i s h

b

24 mm

specimens of this species are indeed common in Sao M i g u e l .

T H E IDENTITY OF A R I O N P A S C A L I A N U S

A r i o n p a s c a l i a n u s was for the first time recorded f rom the A z o r e s by Backhuys (1975), who ment ioned the fo l l owing features: (1) body co­lour pale-white to grey; (2) foot sole whi t e to y e l l o w i s h ; (3) tuberc les consp icuous ; (4) two very d i s t inc t dark lateral bands; (5) lateral bands forming a lyre-shaped f igure on the mantle; (6) right lateral band enclo­ses the pneumostome; (7) middle of

d

18 mm •

FIG. 2. External morphology of Azorean A r i u n c u l u s m o r t i l l e t i (a-b) and A r i u n c u l u s sp. (c-d) as figured by Seixas (1981b) (reproduced with permission).

B A C K E L J A U E T A L . \ A R I U N C U L U S A N D , A R I O N I N T H E A Z O R E S 2 6 5

the back and mantle wi th a grey area anus for the first time from Made i ra , m o t t l e d w i t h b l a c k spo ts ; (8) H e also remarked that there are no between the spotted area and the s i g n i f i c a n t a n a t o m i c a l d i f f e r e n c e s lateral bands, there are two narrow, between this M a d e i r a n fo rm and A . l igh te r areas; (9) largest spec imen i n t e r m e d i u s . e x t e n d e d i n a l c o h o l : 15 m m . The Azorean specimen P i n F i g . 5 Recent ly , Rahle (1992) re l ied on this cor responds e x a c t l y to B a c k h u y s ' descr ip t ion to record A . cf. p a s c a l i - (1985) descr ipt ion and Rahle ' (1992)

FIG. 3. Reproductive organs of Azorean A r i u n c u l u s sp. (a) and A r i u n c u l u s m o r t i l l e t i (b) as figured by Seixas (1981b) (redrawn with permission). . Abbreviations as in Fig . 1; pe, penis; vd, vas deferens. . • ' •. ' • i.

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i l l u s t r a t i o n of A . p a s c a l i a n u s . It was therefore identif ied as A . p a s c a ­l i a n u s by Backe l j au et a l . (1992) , who, used a l lozyme electrophoresis to compare this type w i t h tWp co lour morphs o f true A . i n t e r m e d i u s ( Y and G i n F i g . 5). This showed that the three; morphotypes (P, G arid Y ) cannot be separated e lec t rophore t i -c a l l y and do not warrant a specif ic status. However , this does not mean that the A z o r e a n slugs referred to as A . p a s c a l \ a n u s by Backhuys (1975) and B a c k e l j a u et a l . (1992), or ma­te r i a l f r o m M a d e i r a i d e n t i f i e d by Rah l e (1992) are indeed the species o r i g ina l l y meant by M a b i l l e (1868).

A c t u a l l y , M a b i l l e (1868) wanted

to remove the homonymy between A . fuscatus Ferussac, 1819 and M o r e -let's (1845) A . f u s c a t u s , for he be­l i e v e d that two di f ferent spec ies were, i n v o l v e d . Heynemann (1873a, b) a l ready r emarked that M a b i l l e often in t roduced new species and genera us ing interpretations of des­cr ipt ions and s ingle f igures, wi thout having seen the material i n question. M a b i l l e ' s (1868) notes on A . p a s c a ­l i a n u s are therefore only a summary of More le t ' s (1845) data. T h i s is evident since M a b i l l e ' s (1868) o w n d e s c r i p t i o n s c o n s i s t o f a L a t i n d i agnos i s and F r e n c h d i s c u s s i o n , whereas notes concerning new names are briefer and not substructured

a

FIG. 4. Reproductive organs of P l u t o n i a a t l a n t i c a as figured by Simroth (1891) (a-b) and d'Arruda Furtado (1882) (c). Abbreviations as in Figs. 1 & 3.

B A C K E L J A U E T A L . : A R I U N C U L U S A N D A R I O N I N T H E A Z O R E S 2 6 7

F I G . 5. C o l o u r morphs of A z o r e a n Arion intermedius studied by B a c k e l j a u et al.

(1992) . G , grey type; P, Arion pascalianus type; y, yel low type.

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(e.g. A . d i s t i n c t u s ) . In any case, M a b i l l e (1870) con­

f i rmed his bel ieve that A . fuscatus Ferussac, 1819 and More le t ' s (1845) A . fuscatus are different. H e even added the f o l l o w i n g footnote on A .

fuscatus Fe russac , 1819 ( M a b i l l e 1870): "(1) N o n A r i o n f u s c a t u s , More le t , M o l l . Portugal , 1845 qui est V A r i o n B a e t i c u s , J. M a b i l l e . - Nec A r i o n fuscatus More le t , l ies Acores , p. 137, 1860, espece differente."

So three quest ions have to be so lved: (1) why d id M a b i l l e (1870) int roduce the name A . b a e t i c u s for M o r e l e t ' s (1845) Portuguese A . fus­c a t u s , even though two years earlier he already renamed this species as A . p a s c a l i a n u s , (2) why did he sepa­rate M o r e l e t ' s (1845, 1860) Po r tu ­guese and A z o r e a n A . f u s c a t u s , and (3) why d id he believe that A . f u s c a ­tus Fe russac , 1819 and M o r e l e t ' s (1845) Portuguese A . fuscatus were different species? Unfortunately, as M o r e l e t ( 1 8 7 7 ) a n d P o l l p n e r a ( 1 8 9 0 a ) a l r e a d y n o t e d , M a b i l l e (1868, 1870) d i d not e x p l a i n his points o f view.

W e su rveyed the l i terature for M a b i l l e ' s (1870) A . b a e t i c u s , b u t found no th ing about this species . A l s o the Z o o l o g i c a l R e c o r d d id not provide any clue. So, for the time be ing we consider A . b a e t i c u s as nomen n u d u m .

P r o b a b l y M a b i l l e (1870) separa-: ted M o r e l e t ' s Portuguese and A z o ­rean A . f u s c a t u s , because M o r e l e t (1845, 1860) was not very conse­quent i n his descriptions. The Por ­tuguese a variety of A . fuscatus was

indeed described as " n i g e r , l a t e r i -bus c i n e r e i s " ( M o r e l e t , 1 8 4 5 ) , whereas the same var ie ty f rom the A z o r e s was character ized as " c i n e -r e o - f u s c u s " (Morelet , 1860). A se­cond Azorean variety was referred to as "f$ r u f o - f u s c u s , f a s c i i s evanescen-t i b u s " (Morele t , 1860). S ince M a ­b i l l e often re l ied on co lour features alone to erect new species (e.g. G e o -m a l a c u s a n d r e w s i M a b i l l e , 1867; see H e y n e m a n n , 1873a, b) , i t i s not surpr is ing that he spl i t ted More le t ' s Portuguese, and Azorean A . f u s c a t u s .

Current ly we think that much of the confusion about A . p a s c a l i a n u s also stems f rom s ize and c o l o u r considerat ions. M o r e l e t (1845) re­ferred to Portuguese A . fuscatus as "un petit mollusque ... dans les pro­por t ions du F u s c a t u s " [ s i c ] and " V A r i o n portugais est no i r , tandis que ce lu i de Ferussac est brun fon-ce". Since Ferussac's (1819) A . fus­catus measured 52 m m ( infe r red f rom his figure), M a b i l l e (1868) may have interpreted this size as contra­dic tory w i t h More le t ' s (1845) state­ment " sma l l " . T h i s , together w i t h the c o l o u r d i f ference , m i g h t have s t imula ted M a b i l l e (1868) to g ive More le t ' s (1845) A . fuscatus the sta­tus of separate species. However , 52 m m may have been smal l for More le t (1845) who , for example , a f f i rmed about L i m a x s q u a m m a t i n u s "cette l i -mace est la plus petite que je con-naisse" (25 m m inferred f rom his PI. I l l f i g . 2). Furthermore, he stated that L i m a x v a r i e g a t u s "atteint a peine 5-6 centimetres", w h i c h sug­gests that i n More le t ' s (1845) o p i -

B A C K E L J A U E T A L . : A R I U N C U L U S A N D A R I O N I N T H E A Z O R E S 2 6 9

n i o n such size was not par t icu lar ly large ( logical i f i n the same work he dealt w i th species of up to 160 mm).

Thus M a b i l l e ' s (1868) A . p a s c a ­l i a n u s refers to a slug of at least 52 m m (Pol lonera , 1890a, b). S imroth (1889, 1891), on the contrary, may have interpreted M o r e l e t (1845) and M a b i l l e (1868) l i t e ra l ly for he sta­ted about A . p a s c a l i a n u s that "Das T h i e r s o l i k l e i n se in" (10 m m i n a lcoho l , 15 m m as inferred f rom his f igures) . S imro th (1891) neverthe­less had some doubts on whether the Portuguese ar ionid was the same as M o r e l e t ' s (1845) A . f u s c a t u s . I n ­deed, the sma l l e s t s l u g M o r e l e t (1845) knew was 25 m m , w h i c h is subs tant ia l ly larger than A . p a s c a ­l i a n u s as interpreted by S i m r o t h ( 1 8 9 1 ) .

Tha t M a b i l l e ' s (1868) and S i m -roth's (1891) A . p a s c a l i a n u s are dif­ferent species also fo l lows f rom the fact that S imro th (1891) ment ioned the presence of a thin shell plate i n A . p a s c a l i a n u s , w h i c h related the species to A . m i n i m u s S imroth , 1885 ( = A . i n t e r m e d i u s ) . M a b i l l e (1868), however , assigned A . p a s c a l i a n u s to the genus A r i o n (charac ter ized • by the presence of loose cha lk granu­les), whereas he placed A . i n t e r m e ­d i u s i n G e o m a l a c u s ( cha rac te r i zed by the presence of a consistent shell plate) ( M a b i l l e , 1867, 1870).

P o l l o n e r a (1889, 1890a, b), who descr ibed another Portuguese ar ion­i d , v i z . A . m o l l e r i i Po l lone ra , 1889, observed this too. Because A , m o l l e ­r i i has a shel l plate and measures at most 28 mm, Pol lonera (1889, 1890a,

b) was convinced that i t w o u l d be d i s t inc t f r om M a b i l l e ' s (1868) A . p a s c a l i a n u s . S imroth ' (1889), how­ever, first assigned A . m o l l e r i i to A . p a s c a l i a n u s , but transferred i t later to A . m i n i m u s , retaining A . p a s c a ­l i a n u s as separate species. Subse­quent opinions about A . p a s c a l i a n u s , A . m o l l e r i i and A . i n t e r m e d i u s have been divided: some authors f o l l o w e d Pol lonera (1889, 1890a, b) and con­sidered them as three different spe­cies (e.g. 'Co l l i nge , 1897), whereas others preferred to keep A . m o l l e r i i as ' synonym of either A . i n t e r m e d i u s (e.g. Taylor , 1907) or A . p a s c a l i a n u s (e.g. Hesse, 1926). The only one who discussed this issue i n some depth was Torres M m g u e z (1926), who con­cluded that A . m o l l e r i i and A . pas­c a l i a n u s are different species, wh i l e this latter would be merely a variety of Morelet 's (1845) A . f u s c a t u s .

A s it is u n l i k e l y that any type material of A . p a s c a l i a n u s w i l l turn up (Wiktor & Parejo, 1989), we cur­rent ly agree w i t h Tor res M m g u e z (1926) , s ince f r o m the p r e c e d i n g rev iew it fo l lows that (1) M a b i l l e ' s (1868) and Simroth's (1891) A . pas­c a l i a n u s are different species, (2) A . m o l l e r i i i s different f rom M a b i l l e ' s (1868) A . p a s c a l i a n u s and (3) this la t te r is i d e n t i c a l to M o r e l e t ' s (1845) A , f u s c a t u s . Because A z o r e a n A . p a s c a l i a n u s was ident i f ied us ing S imroth ' s (1891) in terpre ta t ion , we conclude that this is not the species meant by M a b i l l e (1868) or M o r e l e t (1845) (under the name A . f u s c a t u s ) . Cons ider ing the results of Backe l j au et a l : (1992) this also means that i n

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general Simroth 's (1891) A . p a s c a l i ­anus may be referred to A . i n t e r m e ­d i u s (Rodr iguez , 1989; Cas t i l le jo & Rodr iguez , 1991). Hence, only three a r ion ids can cur ren t ly be assigned to the A z o r e a n fauna: A . l u s i t a n i ­cus, A . d i s t i n c t u s and A i n t e r m e ­d i u s . The first of these three, how­ever, s t i l l needs further c o n f i r m a ­t ion. R e l y i n g on Rahle's (1992) data and on our own observations on the M a d e i r a n ar ionids in the co l l ec t ion of the N a t i o n a l M u s e u m of Wales (Cardiff) , we think that A . p a s c a l i a ­nus shou ld be r emoved f rom the faunal l i s t of Made i ra .

T H E MEDITERRANEAN DISTRIBUTION OF A R I O N I N T E R M E D I U S

The occurrence A . i n t e r m e d i u s in the A z o r e s and M a d e i r a (e.g. B a c k -huys, 1975; Walden , 1983; Rahle , 1992) is o f interest to interpret the d i s t r i b u t i o n of this species e lse­where. In Italy and adjacent islands, for example , A . i n t e r m e d i u s has a dis junct geographic range since the species occurs i n L i g u r i a , Tuscany , Cor s i ca , S i c i l y and Calabr ia , but not i n S a r d i n i a and the Cen t ra l A p e n ­nines (F ig . 6).

M a n g a n e l l i & G i u s t i (1988) pro­posed three hypotheses to e x p l a i n th is d i s t r i b u t i o n a l pat tern. F i r s t they i n v o k e d pass ive transport, be­cause "se l f ing species such as A . i n t e r m e d i u s have been shown to be more successfu l i n c o l o n i z i n g new areas". A . i n t e r m e d i u s was indeed in t roduced i n N o r t h A m e r i c a ( C h i ­chester & Getz 1969, 1973), South A f r i c a (S imro th , 1907; C o n n o l l y ,

1912, 1939; V a n Regteren A l t e n a , 1966), N e w Zea land (Barker , 1979) and Aus t r a l i a (Smi th , 1981). M o r e ­over, the western Medi ter ranean has a lways been a r e g i o n o f intense h u m a n a c t i v i t i e s c r e a t i n g m a n y poss ib i l i t i es for passive transport o f o r g a n i s m s .

Nevertheless, M a n g a n e l l i & G i u s t i (1988) cons ide red this e x p l a n a t i o n as the most s impl is t ic . So, they for­mulated a second hypothesis , c l a i m ­ing that A . i n t e r m e d i u s spread f rom the Iberian Peninsula and the E u r o ­pean main land as a consequence of m i c r o p l a t e m o v e m e n t s . I n d e e d , dur ing the lower M i o c e n e , tectonic drift separated Cor s i ca , Sa rd in ia and the C a l a b r o - P e l o r i t a n m i c r o p l a t e f rom the rest of the European main­land . Af te rwards , p robab ly du r ing the Tor ton ian (upper M i o c e n e ) , the C a l a b r o - P e l o r i t a n m i c r o p l a t e de­tached f rom the Sa rdo -Cor s i can m i ­croplate and opened i n this way the Tyr rhen ian B a s i n ( G i u s t i & M a n g a ­n e l l i , 1984).

These geologica l events cou ld ex­p la in the presence of A . i n t e r m e d i u s i n Ca labr ia , S i c i l y and C o r s i c a , but they do not account for the species' absence i n Sard in ia and the Cent ra l Apennines . Fo r Sard in ia M a n g a n e l l i & G i u s t i (1988) suggested that A . i n t e r m e d i u s was e rad ica t ed by "occasional or other factors", such as competi t ion w i t h other slugs l i ke the endemic A r i u n c u l u s i s s e l i i L e s s o n a & Pol lonera , 1882. W i t h respect to the s i tuat ion i n the C e n t r a l A p e n ­nines no explanation was prov ided .

The plate tectonics hypothesis

B A C K E L J A U E T A L : . A R I U N C U L U S A N D A R I O N I N T H E A Z O R E S 2 7 1

FIG. 6. Distribution of A r i o n i n t e r m e d i u s in Italy and adjacent islands (modified after Manganelli & Giusti, 1988).

272 ACOREANA S U P P L E M E N T 1995: 261-278

imp l i e s that A . i n t e r m e d i u s already existed before the Miocene , i.e. more than 25 M Y ago. There is however no f o s s i l evidence support ing this pre­mise. O n the contrary, Wenz (1911), Ojkland (1922) and S o l e m (1979) situate the or ig in of the Ar ion idae i n the Miocene , and thus A . i n t e r m e ­d i u s would have been one of the first ar ionids on earth. Th i s is d i f f icu l t to r econc i l e w i t h the current ideas on a r i o n i d phy logeny , w h i c h regard the A r i o n i n a e as the youngest clade i n the fami ly .

O f ' course the f o s s i l record o f A r i o n i d a e is extremely poor and un­r e l i a b l e . The cha lk granules de­scr ibed by W e n z (1911), for exam­ple, were most probably not der ived f rom foss i l ar ionids, but f rom earth­worms (Meijer, 1985). S imi l a r ly , the she l l plates attributed to L e t o u r -n e u x i a p l i o c e n i c a (Sacco, 1885) from the upper P l iocene of Fossana (Pie-mont) (see C o c k e r e l l , 1892; Tay lo r , 1907) might as w e l l be long to a l i m a c i d , m i l a c i d or agr io l imac id slug (S imro th , 1891).

Despite< the l a ck o f f o s s i l data, S i r g e l (1986) suggested a Gondwana o r i g i n for the • A r i o n i d a e , i m p l y i n g that this f a m i l y already exis ted i n the Cretaceous. Ye t , even i f this is correct, i t s t i l l does not warrant a p r e - M i o c e n e o r i g i n for A . i n t e r m e ­d i u s , for terrestr ial pulmonate spe­cies su rv iv ing for such a long t ime (>25 M Y ) are except ional . Indeed, the longev i ty o f species is usua l ly estimated to be of the order of some m i l l i o n s o f years ( W a l d e n , 1983; L e v i n t o n , 1988) and Futuyma (1986)

remarked that "Paleontologis ts have documented numerous cases i n w h i c h organisms that are m o r p h o l o g i c a l l y ind i s t ingu i shab le f rom modern spe­cies extend back into the f o s s i l re­cord for f ive to ten m i l l i o n years or more , a l though i n such ins tances there is no evidence on the evolut ion of characters that might affect re­product ive i so la t ion" (see for exam­ple Stanley & Y a n g , 1987). Cases in point are k n o w n among certain ma­rine mol luscs l i k e N u c u l a nucleus (L innaeus , 1758), H i a t e l l a a r c t i c a ( L i n n a e u s , 1767), C o r b u l a g i b b a ( O l i v i , 1792), C a l y p t r a e a c h i n e n s i s (Linnaeus, 1758), V o l v u l a a c u m i n a t a (Brugiere, 1792), etc. These species have been recorded up to the M i o c e n e and/or Ol igocene (e.g. Gl ibe r t , 1945, 1952) . H o w e v e r , many of them b e l o n g to t a x o n o m i c a l l y confused groups so that their c o n s p e c i f i c i t y w i t h recent taxa is i n doubt. In contrast to these o ld marine " l i v i n g foss i l s" , there are on ly few extant terrestr ia l pulmonate species whose f o s s i l r ecord extends further than the M i o - P l i o c e n e . Hence a p r e - M i o ­cene age for A . i n t e r m e d i u s seems q u e s t i o n a b l e .

M a n g a n e l l i & G i u s t i ' s (1988) "p la te t e c t o n i c s h y p o t h e s i s " ' i s further weakened since it is hard to see how A . i n t e r m e d i u s d i sappeared i n Sardinia , given the successful co­lonizer it is and the variety of habi ­tats i t may occupy. A t t r i bu t ing the assumed e x t i n c t i o n to c o m p e t i t i o n w i t h the endemic A r i u n c u l u s i s s e l i i seems u n l i k e l y , for this latter spe­cies is too rare to be expected to

B A C K E L J A U , E T A L . : A R I U N C U L U S A N D A R I O N I N T H E A Z O R E S 2 7 3

compete eff ic ient ly wi th a cosmopo-l i t i c and eury topic species as A . i n t e r m e d i u s . Moreover , as far as we k n o w , i n no other region where A . i n t e r m e d i u s was introduced the spe­cies disappeared again due to compe­t i t ion wi th loca l fauna elements.

The th i rd hypothesis o f M a n g a ­n e l l i & G i u s t i (1988) suggests that A . i n t e r m e d i u s arrived i n Cors ica by p a s s i v e t ransport , whereas d u r i n g the Quaternary g lac ia t ions it i n v a ­ded Italy up to Calabr ia . F rom there the species reached S i c i l y v i a a land b r i d g e (yet, pa s s ive t ransport i s nei ther exc luded) . Subsequent c l i ­mat ic changes ( in te rg lac ia l ; warming up) then provoked the disappearance of A . i n t e r m e d i u s i n the Cen t ra l Apenn ines , so that it only survived i n a few, mounta inous areas w i t h more favourable c l i m a t i c condi t ions and where only few compet ing spe­cies ex is ted .

A c c o r d i n g to M a n g a n e l l i & G i u s t i (1988) this exp l ana t i on w o u l d be plausible i f A . i n t e r m e d i u s is a win ­ter or northern species as suggested by Davies (1977). Ye t , this assump­t ion is not reflected by the currently ava i lab le data. In Scandinavia , for e x a m p l e , A . i n t e r m e d i u s r emains restr icted to the north-western coast of N o r w a y up to 65° N . L . , the south­ern part of Sweden and the southern tip of Iceland, whi le it seems to lack i n F i n l a n d ( O k l a n d , ,. 1922, 1925; V a l o v i r t a , 1967; K e r n e y et a l . , 1983). M o s t other A r i o n species i n Scandinavia are not only more wide ly d i s t r i bu t ed throughout this r e g i o n , but also occur at appreciably higher

g e o g r a p h i c a l l a t i t u d e s ( O k l a n d ; 1922, 1925; Backel jau et a l , 1983; Kerney et a l , 1983).

M a n g a n e l l i & Gius t i (1988) point­ed out that their "c l imat ic hypothe­sis" does not expla in the su rv iva l o f A . i n t e r m e d i u s in Cors ica , where the c l imate is par t icu lar ly dry and hot. Therefore they assumed that the C o r -s ican populat ions consist o f strains wh ich are better adapted to the Me-? di terranean c l imate . . H o w e v e r , a l ­though A . i n t e r m e d i u s is indeed a complex of genetic strains ( M c C r a c ^ ken & Selander, 1980; F o l t z et a l , 1982; Selander & O c h m a n , 1983; Backel jau & D e B r u y n , 1991; B a c ­keljau et a l , 1992), there are no data concern ing their e c o l o g i c a l s i g n i f i ­cance . •'

In conclus ion , we think that cur­rently there are no reasons to ex­p l a i n . the distr ibut ion of A . i n t e r m e ­d i u s i n southern Italy and. adjacent i s lands by other phenomena than passive introductions. Note that the occurrence of A . i n t e r m e d i u s i n S i ­c i l y is based on a single sample of seven ind iv idua l s , w h i l e i n : C a l a b r i a the species appears to be known from on ly : one recent and one l i terature r e c o r d ( F i g . 6) ( B a c k e l j a u , 1985; M a n g a n e l l i & G i u s t i , 1988). T h i s seems a further, argument i n favour of the "passive in t roduc t ion hypo­thesis". It cou ld also indicate :that the enigmatic d is t r ibu t ion . . of, A . i n ­t e r m e d i u s 1 in[ Italy is an artifact due to insuff ic ient sampl ing .

A C K N O W L E D G E M E N T S

W e are grateful to Prof. D r . A . M .

274 AgOREANA S U P P L E M E N T 1995: 261-278

Frias Mar t ins (Ponta Delgada) for his support. Dr . M . M . P. Seixas (Lisbon) k i n d l y p rov ided us w i t h the sample of A r i u n c u l u s sp, w h i l e D r . M . Seddon (Cardiff) a l lowed us to study the M a d e i r a n ar ionids i n the c o l ­l ec t ion of the N a t i o n a l M u s e u m of Wales . W e are indebted to Dr . J. V a n Goethem ( R . B . I . N . S c . ) for commenting on the manuscript and to M r . H . V a n Paesschen ( R . B . I . N . S c ) for preparing the i l l u s t r a t i ons . L D B is Sen io r Resea rch Ass i s t an t at the N a t i o n a l F u n d f o r S c i e n t i f i c R e s e a r c h (Belgium) and. K J holds an I . W . O . N . L . fe l lowship^ Th i s work was f inan­c i a l l y suppor ted by F . J . B . R . grant 2 . 0 0 0 4 . 9 1 .

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