CHARACTERS, Fitzinger, 1833
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https://doi.org/10.1046/j.1096-3642.2002.00010.x |
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https://doi.org/10.5281/zenodo.15490865 |
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persistent identifier |
https://treatment.plazi.org/id/03AD87E5-FF82-FF8A-2D1A-FAD2A9B8DA7A |
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treatment provided by |
Carolina |
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scientific name |
CHARACTERS |
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The characters of the genitalia are shown in Figure 2 View Figure 2 . The numbering refers to Table 1 View Table 1 and the cladogram ( Fig. 3 View Figure 3 ).
1 The so-called stimulator, which is apparently an adaptation to reciprocal copulation, is one of the most important characters for the systematics of the Stylommatophora ( Hausdorf 1998a) . The glandula amatoria is considered to be homologous to the stimulator. A stimulator is present in most vitrinids except Vitrina , Calidivitrina and some species of Plutonia , namely P. media (Lowe, 1854) (see Appendix) and P. brevispira (Morelet, 1860) ( Mordan & Martins, 2001) .
2 In the outgroups, Semilimax and Vitrinobrachium , the stimulator inserts at the atrium. The stimulator of Semilimacella cephalonica (Rähle) is basally fused with the vagina ( Rähle, 1980). In Semilimacella carniolica (O. Boettger) the stimulator apparently inserts at the vagina ( Mildner, 1982) and in Semilimacella bonelli (Targioni Tozzetti) it inserts at the atrium ( Forcart, 1960; re-examined). Semilimacella carniolica and Semilimacella bonelli are probably sister species. Both species are characterized by duplicated stimulator papillae. In Semilimacella cephalonica the gland of the stimulator is bilobed, but there is only a single stimulator papilla. It is assumed that the stimulator of Semilimacella cephalonica represents the plesiomorphic state in Semilimacella . The situation in Semilimacella carniolica can easily be derived from that state by a further fusion of the distal sections of vagina and stimulator. If this is true, the atrial insertion of the stimulator of Semilimacella bonelli must be due to a shortening of the fused section and is therefore a secondarily derived state. On the basis of this interpretation, the stimulator of Semilimacella might represent an intermediate state between the atrial stimulator and the glandula amatoria, where the stimulator is completely fused with the vagina. In Vitrina there is a vestige of a stimulator at the atrium of juvenile specimens ( Umiński, 1968). However, it cannot be excluded that this is a rudiment of a stimulator which was basally fused with the vagina, because the vagina is missing in Vitrina . In Eucobresia , Phenacolimax , Plutonia , Oligolimax and Arabivitrina the stimulator is completely fused with the vagina and forms the glandula amatoria.
3 Eucobresia and some Plutonia and Oligolimax species have no external stimulator gland.
4 The external gland of the stimulator is distinctly longer than it is wide in the outgroups and in Semilimax , whereas it is about as long as or shorther than it is wide in the other vitrinids.
5 The external gland of the stimulator forms a uniform sheath around the proximal stimulator section in the outgroups and in Semilimax , Vitrinobrachium , Arabivitrina , and some Plutonia species. In the other vitrinids, it is divided into lobes.
6 In Semilimax and Vitrinobrachium the stimulator is used to fix the copulation partner ( Künkel, 1933), whereas the stimulator contacts the partner only temporarily during copulation in the other Stylommatophora for which the mating behaviour is known. 7 The penis is inserted into the vagina or the bursa copulatrix of the copulation partner in most Stylommatophora : however, it transfers the sperm on external parts of the everted genitalia in Vitrinobrachium , Phenacolimax , Plutonia and, probably, all other genera with a well-developed glandula amatoria.
8 A penial tunica is present in the outgroups and in most genera of the Vitrinidae . It is missing in Plutonia , Oligolimax , Arabivitrina and Calidivitrina . 9 The penial tunica usually covers most of the distal part of the penis, except in Eucobresia and Phenacolimax .
10 There is at least one distinct pilaster in the penis of the vitrinids which is partly formed by the penial gland. In Arabivitrina and Calidivitrina the pilaster is partitioned into a proximal glandular section, a short median section with a distinctly lamellated structure ( Neubert, 1998: figs 97 and 106), and an undifferentiated distal section. The penial pilaster of the two Azorean Plutonia species P. pelagica (Morelet, 1860) and P. laxata (Morelet, 1860) is also partitioned into a proximal glandular section and a median section with a distinctly lamellated structure ( Mordan & Martins, 2001). However, in contrast to the pilaster of Arabivitrina and Calidivitrina , the distal section is divided into two branches. Nevertheless, it should be checked more thoroughly whether the lamellated median section of Arabivitrina and Calidivitrina might be homologous to that of the two Azorean Plutonia species.
11 A more or less well-developed penial gland is present in all vitrinids, but is missing in the outgroups. The secretions of this gland are probably involved in sperm transfer and thus undertake some of the functions of the spermatophore, which is missing in the Vitrinidae .
12 The right ommatophoral retractor muscle passes between the penis and the female genitalia in Cryptozona , Eucobresia , Phenacolimax , Arabivitrina and some Semilimax and Calidivitrina species.
13 The right ommatophoral retractor muscle runs left of or below the penis retractor muscle in Troglaegopis , Semilimacella , Vitrina and Oligolimax , but it runs right of or above the penis retractor muscle in all other vitrinids.
14 The penial retractor inserts at the diaphragma in the outgroups and in most groups of the Vitrinidae . It inserts at the columellar muscle only in Vitrinobrachium .
15 The vas deferens enters the penis terminally in Semilimacella , Vitrina , and Plutonia finitima (Morelet, 1860) , whereas it inserts at the penis subterminally or laterally in all other groups of the Vitrinidae .
16 The bursa copulatrix inserts at the vagina or at the atrium in the outgroups and in all groups of the Vitrinidae except in Vitrinobrachium in which it inserts at the penis.
17 The radular marginals are unicuspid or have at most one ectoconus in the outgroups and in most Vitrinidae . They are multicuspid in Vitrina , Semilimacella and in a few species of Plutonia and Oligolimax .
PHYLOGENY
Two equally and maximally parsimonious trees (length 25 steps, consistency index excluding uninformative characters = 0.636) have been found in a branch-and-bound search with the program PAUP and the character matrix ( Table 1 View Table 1 ). The two trees differ only in the relationships of Semilimax and Vitrinobrachium . A consensus tree of the two trees is shown in Figure 3 View Figure 3 .
The unresolved trichotomy is due to two conflicting characters, the function of the stimulator vs. the length of the stimulator gland. Among the Stylommatophora for which the mating behaviour has been studied, Semilimax and Vitrinobrachium are the only ones which use the stimulator to fix the copulation partner ( Künkel, 1933). In the other Stylommatophora the stimulator contacts the mating partner only temporarily during copulation. Therefore the use of the stimulator to fix the mating partner might be a synapomorphy of Semilimax and Vitrinobrachium . Unfortunately, the mating behaviour of Troglaegopis (Zonitidae) (the stimulator of which resembles that of Semilimax ) as well as the mating behaviour of several other vitrinids, e.g. Semilimacella , is unknown. Therefore, it cannot be excluded that the unusual function of the stimulator is an autapomorphy of the Vitrinidae or originated even earlier.
If this insufficiently known character is excluded from the cladistic analysis only a single mostparsimonious tree is found, in which Semilimax is the sister group of the remaining vitrinids, as in one of the two maximally parsimonious trees based on all characters. The clade including all vitrinids except Semilimax is supported by the shortening of the stimulator gland.
The result of the present cladistic analysis differs fundamentally from the hypothetical scheme proposed by Schileyko (1986). The differences are primarily due to the assumption of Schileyko (1986) that the glandula amatoria is the plesiomorphic character state of the stimulator. This assumption is based on the presupposed homology of the stimulator of the Vitrinidae with the capsular gland of other Limacoidea s. l. . However, Hausdorf (1998a) has shown that the capsular gland is not homologous with the stimulator. An outgroup comparison with the stimulator of the Zonitidae or the Helicarionoidea demonstrates that the atrial stimulator represents the plesiomorphic character state and that the glandula amatoria is apomorphic.
Moreover, Schileyko (1986) ignored the findings of Umiński (1968), who discovered a rudiment of an atrial stimulator in Vitrina . Therefore, Schileyko (1986) derived Vitrina directly from his hypothetical stem form, which has only a capsular gland but no stimulator. Actually, the stem species of the Vitrinidae did not have a capsular gland, because this organ is missing in all vitrinids as well as in their sister group, the Boettgerillidae – Limacidae – Agriolimacidae . Schileyko (1986) overlooked the fact that Vitrina only differs from Semilimacella in that the atrial stimulator is reduced.
Finally, Schileyko (1986) did not realize the homology of the vaginal papilla of Eucobresia with the papilla of the glandula amatoria. This homology is corroborated by the fact that there is a well-developed muscular section of the stimulator in Eucobresia glacialis (Forbes) , which has to be included into Eucobresia (see Appendix). Moreover, the relationship of Eucobresia to Phenacolimax and the other groups with a glandula amatoria is corroborated by the development of the penial tunica, which surrounds only the proximal section of the penis in Eucobresia and Phenacolimax , whereas it also surrounds parts of the distal section in all groups with an atrial stimulator.
The subdivision of the Vitrinidae proposed by Schileyko (1986) cannot be maintained. The Vitrininae Fitzinger, 1833 sensu Schileyko include the groups in which the stimulator has been lost, namely Vitrina and Calidivitrina , and are polyphyletic. The Semilimacinae Schileyko, 1986 include the groups with an atrial stimulator, Semilimacella , Semilimax and Vitrinobrachium , as well as Eucobresia and are paraphyletic. Only the Phenacolimacinae Schileyko, 1986 ; which are characterized by the glandula amatoria are monophyletic. However, Plutoniinae Cockerell, 1893 is an older name for this group. Because of the low number of genera, a formal division of the Vitrinidae into subfamilies is not necessary.
BIOGEOGRAPHY
The distribution of the genera of the Vitrinidae is summarized in Table 2 View Table 2 and Figure 4 View Figure 4 . The range of the Vitrinidae largely overlaps with the range of its sister group, the limacoid slugs Boettgerillidae – Limacidae – Agriolimacidae . If one assumes that the ancestors of the two sister groups originated by allopatric speciation, their original ranges were smaller than those of the two sister groups are today. For the estimation of the ancestral area of the Vitrinidae and of the limacoid slugs a weighted ancestral area analysis ( Hausdorf, 1998b) has been applied.
The PI values of the Vitrinidae ( Table 2 View Table 2 ), which indicate the relative probability that an individual area was part of the ancestral area, are maximal for the Alps followed by West and Central Europe. The PI value of the Vitrinidae for the Near East (including the Caucasus region) is distinctly lower.
The PI values of the limacoid slugs Boettgerillidae – Limacidae – Agriolimacidae ( Table 3 View Table 3 ) are maximal for the Near East, because the positionally plesiomorphic lineages, namely the Boettgerillidae , Eumilacinae and Mesolimacinae are restricted to that area. Therefore, this region is probably the ancestral area of the Boettgerillidae – Limacidae – Agriolimacidae . Consequently, the Vitrinidae and the Boettgerillidae – Limacidae – Agriolimacidae might have originated by a vicariance event between Central Europe and the Near East.
Some lineages of the Vitrinidae spread from the European mainland. Vitrina dispersed into Asia and North America (and one species even reached Hawaii), Oligolimax also dispersed into Asia and North Africa, Plutonia colonized the Macaronesian Islands (Azores, Madeira, Canary Islands and Cap Verde) and Arabivitrina and Calidivitrina colonized Arabia and East Africa.
Concerning species number, the most important radiation of the Vitrinidae occurred on the Macaronesian Islands. There are more species on the Macaronesian Islands than on the European mainland. The apomorphic position of Plutonia in the cladogram of the Vitrinidae ( Fig. 3 View Figure 3 ) and the uniform bauplan of the genitalia of the Macaronesian species indicate that this radiation is younger than the radiation on the European mainland. On the other hand, the Macaronesian radiation resulted in some of the most extreme forms concerning the body bauplan, namely the only vitrinid slug, Plutonia (Plutonia) atlantica (Morelet 1860) , and Plutonia (Guerrina) , which can entirely withdraw into their ribbed and keeled shells. The ecology of the Macaronesian vitrinids differs from that of the European vitrinids. Whereas the highest diversity of European vitrinids can be found above 1000 m altitude, the highest diversity of vitrinids is below 500 m altitude on the Canary Islands. These biogeographical and ecological patterns are very unusual. The reasons for these patterns have been discussed elsewhere ( Hausdorf, 2001).
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