Journal of Conchology (2011), Vol.40, No.6 583

TAXONOMIC REVISION, HABITATS AND BIOGEOGRAPHY OF THE LAND SNAIL FAMILY DISCIDAE (GASTROPODA: PULMONATA) IN THE CANARY ISLANDS

1 1 2 3 3 David T. Holyoak , Geraldine A. Holyoak , Yurena Yanes , Maria R. Alonso & Miguel Ibáñez

1Quinta da Cachopa, Barcoila, 6100–014 Cabeçudo, Portugal. 2Instituto Andaluz de Ciencias de la Tierra (CSIC-Universidad de Granada), Camino del Jueves s/n, 18100, Armilla, Granada, Spain. 3Departamento de Biologia Animal, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Islas Canarias, Spain.

Abstract The endemic Macaronesian Canaridiscus, provisionally placed in the Discidae genus Atlantica, are closely linked to the peculiar laurel forest habitat of these islands. Knowledge of Atlantica (Canaridiscus) is increased here with the descrip- tion, for the first time, of the genital system of three more of its species. The epiphallus is apparently lacking and the penis is much longer than that known from any of the Discidae of Europe and North America; generally it is too large to be more than partly accommodated in the distal female genital tract. Keraea has been regarded as an endemic Macaronesian genus of Discidae known only from a few shells, but its Madeiran species has been identified as a Trochulus (Hygromiidae) and its type species (from Tenerife) also matches Hygromiidae, not Discidae. The origin and relationships of the Macaronesian Discidae are discussed. The simplest explanatory model is apparently that they represent the last living relicts of a more diverse fauna of Discidae that lived in Europe during the Tertiary; Atlantica (Canaridiscus) was probably isolated early on from the remaining Discidae. Recent literature reports multiple patterns of colonisation of Madeira and the Canaries that have varied between different groups of plants and animals. Hence, it is argued that it is unwarranted to expect to find only the single pattern of colonisation among the land snails of each of these archi- pelagos that was advocated by Waldén (1984). Key words Africa, Atlantica, Canaridiscus, genital anatomy, Laurasia, laurisilva, Macaronesia, Madeira, North America, paleobiogeography, penis length, Tertiary relict

Introduction third species designated as Discus (Canaridiscus) by Rähle & Allgaier (2011). The archipelagos located in the eastern Atlantic Despite the remarkable diversity of Discidae Ocean, known as the Macaronesian region, con- in these islands, representative specimens pre- tain a rich and diverse native malacofauna that served and available in most collections of has undergone extensive speciation and adap- Mollusca are rather rare. Moreover, although tive radiation. However, many snail taxa are still intensive fieldwork has been performed in poorly known, including the family Discidae. Madeira and the Canary Islands over the last few Recent checklists of the non-marine Mollusca decades, Discidae taxa are infrequently encoun- of Macaronesia (Bank, Groh & Ripken, 2002; tered in field surveys. Indeed, four of the species Seddon, 2008; Fauna Europaea database project, were included in the list of European globally 2011), together with the data in Thiele (1931) extinct taxa by Fontaine et al. (2007), namely recognise about 14 endemic species of Discidae Discus engonatus (Shuttleworth 1852), D. retex- from Macaronesia, which were grouped into the tus (Shuttleworth 1852), D. textilis (Shuttleworth genera Discus Fitzinger 1833 and Keraea Gude 1852) and Keraea garachicoensis (Wollaston 1878). 1911. Two species were cited for Madeira, nine In contrast with the anatomical data known for in the Canary Islands and several in the Cape European and some North American Discidae Verde Islands (Thiele, 1931), probably the three (Fig. 1A–C), there has hitherto been no informa- listed by Wollaston (1878) in Patula (Iulus). More tion published on the internal anatomy of the recently, two new species from the Canary Islands Canary Islands and Madeiran species (with the grouped in the subgenus Canaridiscus, provision- exception of the three species recently named ally as Atlantica (Canaridiscus), were added to by Yanes et al., 2011 and Rähle & Allgaier, 2011), these checklists (Yanes et al., 2011) as well as a so they have been known only by their shell characters. Hence their affinities have remained Contact author : [email protected] mysterious. 584 DT Holyoak et al

Figure 1 Genital anatomy of some Europaean (A, B), North American (C) and Canarian (D) Discidae species: A Discus (Discus) ruderatus (Hartmann 1821) (from Riedel & Wiktor, 1974: fig. 117); B D. (Gonyodiscus) rotundatus (O.F. Müller 1774) (from Uminski, 1962: fig. 1); C Anguispira kochi (L. Pfeiffer 1845) (from Pilsbry, 1948: fig. 304); D Atlantica (Canaridiscus) saproxylophaga Alonso, G. Holyoak & Yanes in Yanes et al. 2011 (drawn from Yanes et al., 2011: fig. 3C). Parts: ag albumen gland; bc bursa copulatrix; go genital orifice; hd hermaphroditic duct; p penis; pr penis retractor; vd vas deferens. The scale bar corresponds only to A, B and D (C was drawn originally without a scale bar).

In this paper we revise the systematics of the for the first time, confirming their allocation to Canary Islands species assigned to the Discidae. the subgenus Canaridiscus. The relationships of The genital system of three species is described the Macaronesian Discidae with those of Eurasia Discidae of the Canary Islands 585

Figure 2 Geographical distribution of some Atlantica (Canaridiscus) species (only those species with precise recent data have been included). The arrows show the symbols of the only one-kilometre squares of the UTM grid with records located outside the laurel forest. Note: In the four one-kilometre UTM grid squares with A. (C.) saproxy- lofaga (on La Gomera Island), the species A. (C.) ganoda was also found. and North America are discussed, leading to a R.T. Lowe 1863 (Fig. 4C), a syntype of H. retexta consideration of their likely origins and history. Shuttleworth 1852 (Fig. 4D), a syntype of H. Conservation status of the Macaronesian forms is engonata Shuttleworth 1852 (Fig. 4E), a syntype also reassessed. of H. putrescens R.T. Lowe 1861 (Fig. 4F), a syn- type of H. scutula Shuttleworth 1852 (Neubert Methods & Gosteli, 2003: pl. 14, fig. 2), a syntype of H. textilis Shuttleworth 1852 (Neubert & Gosteli, Snail specimens were drowned by immersion 2003: pl. 14, fig. 3), the shell drawings of the in water, then fixed in 80% ethanol. Maps of holotype of Discus gomerensis Rähle 1994 (Rähle, geographical distribution (Fig. 2) were pro- 1994: figs 1–3), as well as a paratype of Atlantica duced using MapViewer software (Golden (Canaridiscus) saproxylophaga Alonso, G. Holyoak Software Inc.). The photographic methodology & Yanes in Yanes et al. 2011 (Fig. 5A) and the hol- was described by Ibáñez et al. (2006). Drawings otypes of A. (C.) anagaensis Ibáñez & D. Holyoak of shell outlines (Fig. 3) were obtained semi- in Yanes et al. 2011 (Fig. 5B) and D. (C.) rupivagus automatically, adopting the methods used by Rähle & Allgaier, 2011 (Fig. 4H). Yanes et al. (2009b). Standardised measurements of the shells (Table 1, Fig. 3) were made following Institutional and other abbreviations Yanes et al. (2009a), using the software analySIS® (Soft Imaging System GmbH). Abbreviations for BDUNM Biology Department, University of shell characters and measurements are shown in New Mexico, Albuquerque, U.S.A. Fig. 3. The number of shell whorls was counted DBUA Departamento de Biologia, using the methodology described by Kerney et Universidade dos Açores, Portugal al. (1979: 13). “Proximal” and “distal” refer to the CMNH Carnegie Museum of Natural position in relation to the ovotestis. Comparisons History, Pittsburgh, U.S.A. have been made with photographs of a syntype FMNH Field Museum of Natural History, of Patula (Iulus) garachicoensis Wollaston 1878 Chicago, U.S.A. (Fig. 4A), a possible syntype of H. gueriniana GBIF Global Biodiversity Information R.T. Lowe 1852 (Fig. 4B), a shell of H. calathoides Facility, Switzerland 586 DT Holyoak et al

Figure 3 Drawings of the shell of Atlantica (Canaridiscus) anagaensis Ibáñez & D. Holyoak in Yanes et al. 2011, showing the placement of the measurements obtained (plane view, in mm or mm2). Measurements: AB aperture breadth; AH aperture height; AP aperture perimeter; AS aperture surface area; BH body whorl height; BP body whorl frontal perimeter; BS body whorl frontal surface area; D1 maximum shell diameter; D2 shell diameter per- pendicular to D1; D3 maximum first whorls diameter; FH first whorls height; FP first whorls frontal perimeter; FS first whorls frontal surface area; SFP shell frontal perimeter; SFS shell frontal surface area; SH shell height; SP shell dorsal perimeter; SS shell dorsal surface area; UD umbilicus diameter.

IZUC Institute for Zoology, University of Review of systematics of discidae Cologne, Germany The generic names Discus and Gonyodiscus were ICZN International Commission on introduced by Fitzinger (1833) for European Zoological Nomenclature Discidae. The widespread (apparently) Holarctic JSGC J. Santana private collection, Las species Helix ruderata Hartmann 1821 became the Palmas de Gran Canaria, Spain type species of Discus by subsequent designa- Kya thousands of years ago tion of Gray (1847), and the central and south- Mya millions of years ago eastern European Helix perspectiva Megerle von NHMUK The Natural History Museum, Mühlfeld 1816 the type species of Gonyodiscus by London, U.K. monotypy. Adams & Adams (1858) united these NHMV Natural History Museum Vienna, genera into Discus. Austria The family Discidae Thiele 1931 of current NMBE Naturhistorisches Museum, Bern, lists comprises species from various parts of the Switzerland Holarctic that were all placed by Thiele (1931) PAS Polish Academy of Sciences, Poland in the family Endodontidae, subfamily Discinae, UMA Universidade da Madeira, Funchal, genus Discus. Adoption of the name Discidae Madeira, Portugal in preference to Patulidae (based on Patulinae UTM Universal Transverse Mercator Tryon 1866) follows Bouchet & Rocroi (2005). cartographic projection system Thiele grouped the Discinae species in several Discidae of the Canary Islands 587 A. (C.) rupivaga 1 11,8 10,8 94,1 35,5 3,1 24,6 25,2 0,5 6,4 2,3 12,8 2,6 22,3 25,1 3,8 2,1 4,5 5,7 10,4 A. (C.) engonata 1 6.7 6.7 34.1 22.1 3.7 15.2 17.3 1.1 4.6 3.1 10.1 2.6 12.1 16.4 3.3 1.9 1.9 2.2 5.7 A. (C.) retexta 1 6.7 6.5 32.5 21.5 3.1 13.7 16.6 0.9 4.4 2.9 9.7 2.1 10.8 15.7 3.1 1.5 2.0 2.1 5.6 A. (C.) gomerensis 1 7.8 7.6 45.5 25.4 3.5 18.2 18.7 1.2 5.7 4.0 12.2 2.4 14.2 18.0 2.1 1.7 2.8 3.1 7.1 A. (C.) putrescens 3 8.9–9.5 8.2–8.7 54.0–61.2 27.3–29.8 4.2–4.5 24.2–27.3 20.9–22.6 0.9 4.9–5.1 2.7–3.0 10.3–10.8 3.3–3.6 21.3–24.6 20.9–22.3 2.5–2.8 2.2–2.4 3.2–3.3 4.5–5.1 8.5–9.0 ): AB aperture AH breadth; aperture height; AP aperture 2 A. (C.) scutula 4 7.1–8.0 6.7–7.6 35.8–45.3 21.8–25.6 2.7–3.0 13.0–16.1 16.3–19.0 0.6–0.8 5.0–5.6 2.2–3.0 10.5–11.9 2.0–2.2 10.8–13.2 15.9–18.4 4.3–5.0 1.5–1.9 1.3–1.8 1.2–2.0 4.3–5.5 A. (C.) kompsa 2 7.8–7.9 7.3–7.4 42.5–43.9 23.7–24.2 4.3–4.6 24.2–25.6 19.6–20.0 0.9–1.0 5.2–5.3 2.9–3.6 11.1–11.5 3.3–3.7 20.6–22.7 18.7–19.5 2.1–2.5 2.4–2.5 2.9–3.2 3.9–4.6 8.3–8.9 A. (C.) ganoda 4 8.4–8.8 7.9–8.3 49.5–54.7 25.6–27.2 4.4–5.6 26.5–33.2 20.7–22.7 0.7–1.1 5.1–5.7 2.4–4.1 10.6–12.5 3.7–4.4 24.0–29.1 20.2–21.8 2.4–2.6 2.6–2.9 3.1–3.4 4.9–6.1 9.1–10.1

textilis A. (C.) 4 7.1–8.0 6.5–7.7 34.5–44.9 21.3–24.9 3.6–4.5 17.7–23.8 17.4–20.1 0.8–1.1 4.6–5.4 2.5–3.9 10.0–11.6 2.6–3.4 14.5–19.9 16.7–19.2 1.9–2.5 1.9–2.4 2.6–3.0 3.2–4.6 7.3–8.8

area; area; UD umbilicus diameter; n number of specimens measured. A. (C.) anagaensis 3 7.1–7.5 6.6–6.8 34.7–37.4 21.6–22.7 3.3–3.6 17.9–19.4 17.4–18.4 0.5–0.7 4.2–4.3 1.5–2.0 8.8–9.1 2.7–2.9 16.3–17.4 17.2–18.0 2.1–2.4 2.2–2.4 2.6–2.8 3.5–3.7 7.9–8.0

A. (C.) saproxylophaga 4 12.1–15.8 10.9–14.5 96.3–169.0 35.8–49.5 5.4–6.9 43.1–72.2 27.4–36.7 1.2–1.7 7.2–9.9 5.3–11.0 15.1–20.7 4.2–5.3 37.8–61.3 26.8–35.8 3.4–4.5 3.2–4.0 4.7–6.0 9.0–13.0 12.8–15.6 Data on the shell characters measured (minimum – maximum, in mm or mm A. (A.) gueriniana 2 5.5–6.1 5.2–5.8 21.3–26.8 16.9–18.9 2.4 8.9–9.5 12.8–14.0 0.7–0.8 3.6–4.0 1.8–2.0 7.6–8.4 1.5–1.7 6.9–7.6 12.5–13.8 2.4–2.9 1.4 1.6–2.0 1.2–1.4 4.8–5.3 Table 1 Table

perimeter; AS aperture surface area; BH body whorl height; BP body whorl frontal perimeter; BS body whorl frontal surface area; D1 maximum shell diameter; D2 shell diameter perpendicular to D1; D3 maximum first whorls diameter; FH first whorls height; FP first whorls frontal perimeter; FS first whorls frontal surface area; SFP shell frontal perimeter; SFS shell frontal surface area; SH shell height; SP shell dorsal perimeter; SS shell dorsal surface n D1 D2 SS SP SH SFS SFP FH D3 FS FP BH BS BP UD AH AB AS AP 588 DT Holyoak et al

Figure 4 Shells of: A Keraea garachicoensis, a syntype of Patula (Iulus) garachicoensis Wollaston 1878 (NHMUK 1985.2.2 73–75; photo by J. Ablett) from Tenerife; B possible syntype of Helix gueriniana R.T. Lowe 1852 (NHMUK 1875.12.31.219; photo by J. Ablett) from Madeira; C specimen of Helix calathoides R.T. Lowe 1863 (photo by Dinarte Teixeira, UMA), from Deserta Grande Islet, Madeiran Archipelago, currently considered as a subspecies of A. gueriniana (Bank et al., 2002) – the arrows mark the location of two pairs of palatal tooth-shaped lamellae, visible by transparency on the outer wall of the body whorl; D syntype of Helix retexta Shuttleworth 1852 (NMBE 18783; © 2006 GBIF Switzerland/Eike Neubert), from La Palma (firstly published by Neubert & Gosteli, 2003: pl. 14 fig. 4); E syntype of Helix engonata Shuttleworth 1852 (NMBE 18790; © 2006 GBIF Switzerland/Eike Neubert), from Tenerife (firstly published by Neubert & Gosteli, 2003: pl. 14, fig. 1); F syntype of Helix putrescens (NHMUK 1875–12–31–299; photo by J. Ablett), from La Palma; G specimen of Discus gomerensis Rähle 1994, from drift debris of a stream in Las Rosas ravine, La Gomera; H holotype of Discus (Canaridiscus) rupivagus Rähle & Allgaier 2011 (from Rähle & Allgaier, 2011: fig. 1A). Discidae of the Canary Islands 589

Figure 5 Shells of Atlantica (Canaridiscus) species: A paratype of A. (C.) saproxylophaga Alonso, G. Holyoak & Yanes in Yanes et al. 2011 (JSGC), from La Gomera (first published by Yanes et al., 2011: fig. 2A); B holotype of A. (C.) anagaensis Ibáñez & D. Holyoak in Yanes et al. 2011, from Tenerife (first published by Yanes et al., 2011: fig. 2B); C specimen of A. (C.) textilis, from La Palma (first published by Yanes et al., 2011: fig. 2C); D specimen of A. (C.) scutula, from Montaña Grande, Tenerife; E specimen of A. (C.) ganoda, from Mériga, La Gomera; F specimen of A. (C.) kompsa, from Los Corchos, El Hierro. sections mainly on the basis of shell characters. the Madeiran species Helix gueriniana R.T. Lowe His Nearctic sections comprise Anguispira Morse 1852, as D. (A.) semiplicatus (L. Pfeiffer 1852), 1864, Mexicodiscus Pilsbry 1926 and Planogyra which has 2–3 pairs of tooth-shaped lamellae on Morse 1864. The Palearctic sections were Discus the interior of the outer wall of the shell body- s. str., Gonyodiscus, Atlantica Ancey 1887 and whorl (see Fig. 4C). Section Keraea of Thiele Keraea. Section Atlantica of Thiele included only included Patula (Iulus) garachicoensis Wollaston 590 DT Holyoak et al

1878 from Tenerife and some species from the Canaridiscus. Hence, current understanding of Cape Verde Islands, without providing their the Discidae species from the Canary Islands can names. be summarised in Table 2, which also presents Pilsbry (1948) raised Anguispira to the rank data on distribution for each island and refers to of genus in the Discidae, added a new Nearctic the figures of their shells in this paper. subgenus Discus (Nematodiscus) based on shell The entire genital systems of some of the characters and described the pallial complex in European Discus species were figured by Anguispira and Discus, which have the lung long Uminski (1962) and Riedel & Wiktor (1974) (Fig. and narrow without large or noticeable branches 1A, B), these being similar to those of the North on the pulmonary vein, kidney triangular, a little American Discus and the Anguispira species fig- longer than the pericardium and the secondary ured by Pilsbry (1948) (Fig. 1C). Uminski (1962) ureter closed. Pilsbry also presented drawings of showed differences in the structure of the genital the jaw and radula of Discus patulus (Deshayes organs of Discus ruderatus, D. perspectivus and D. 1830) as well as those of the genital system and rotundatus, justifying their taxonomic arrange- some details of Anguispira alternata (Say 1816) ment in the subgenera Discus s. str. (the first- and A. kochi (Fig. 1C). Uminski (1963) reported named species) and Gonyodiscus (the other two on the taxonomy of D. marmorensis H.B. Baker species). The penis of D. (Discus) (Fig. 1A) is 1932, and Solem (1976) made a detailed ana- an elongated cone with the narrow distal end tomical study of the distal genitalia and radula of communicating with the genital atrium and the three Anguispira species, A. alternata, A. cumber- penial retractor inserted on the wider proximal landiana cumberlandiana (I. Lea 1840) and A. picta end of the penis and arising from the diaphragm. (G.H. Clapp 1920). Contrary to earlier literature, The vas deferens joins the penis laterally, at one Solem found that the vas deferens enters the side of the wide proximal end and the pros- penis directly through a simple pore (without an tate is distinctly elongated. In D. (Gonyodiscus) epiphallus) and the penial retractor muscle arises (Fig. 1B) the penis is cylindrical and elongated, from the diaphragm, not the columellar muscle. the penial retractor is attached to the penis lat- He also noted that the marginal radular teeth erally and the vas deferens connects with the of Anguispira are not multicuspid, maintaining penis terminally. The prostate is triangular or a basically bicuspid condition, the outermost semicircular in shape. Schileyko (2002) described marginals showing splitting of side cusps. On some additional characters of the Discus genital some individual outer marginal teeth there is a system, mainly related to the internal anatomy weak endocone. Schileyko (2002) raised Discus of the penis (without penial papilla) and free (Gonyodiscus) section Antediscus Baker in Pilsbry oviduct (with several pilasters, folds and plicae). 1948 to the rank of a subgenus of Discus and He also showed (Schileyko, 2002: fig. 1384B) the gave detailed drawings of the genital systems presence of a markedly swollen distal zone of the of Anguispira alternata, A. (Zonodiscus) kochi and bursa duct and a small stimulator in the proximal Discus (Discus) ruderatus. end of the penis in Anguispira (Zonodiscus) kochi. Bank et al. (2002) grouped eight Canary Islands Finally, the two Atlantica (Canaridiscus) species species in “Discus (Gonyodiscus?)” and included as well as the new species recently described Patula garachicoensis in Keraea. Their allocation to by Rähle & Allgaier (2011) differ from the other Discus (Gonyodiscus) and Keraea has since been Discidae mainly by their remarkably long penis, adopted by the Fauna Europaea database project ca. eight times the maximum shell diameter in (2011), which also included Helix deflorata R.T. A. (C.) saproxylophaga (Fig. 1D). It is much longer Lowe 1854 from Madeira in Keraea, a species than that known from any of the Discidae of previously classified in Iulus by Wollaston (1878). Europe and North America and too large to be Yanes et al. (2011) raised Atlantica to the rank more than partly accommodated in the distal of a genus of Discidae and described a new female genital tract. subgenus, Canaridiscus, provisionally allocated The absence of the epiphallus was noted by as Atlantica (Canaridiscus), and two new species Uminski (1962) in the subgenera Discus (Discus) from the Canarian Islands. Rähle & Allgaier (2011) and D. (Gonyodiscus) and by Solem (1976) in described a new Canaridiscus species, retaining Anguispira. The connection between the vas defe- the genus Discus with subgenera Atlantica and rens and the penis in A. (C.) saproxylophaga (Yanes Discidae of the Canary Islands 591 4A 4D 4E 4F 4G 4H 5A 5B 5C 5D 5E 5F Figure Figure (this paper) Tenerife Tenerife La Palma La Gomera La Palma Tenerife La Gomera La Palma La Gomera La Gomera Tenerife El Hierro Island ( Canaridiscus ) engonata putrescens gomerensis textilis scutula ganoda rupivaga saproxylophaga anagaensis kompsa Microxeromagna? Xerotricha? garachicoensis Atlantica A . ( C .) A . ( C .) A . ( C .) A . ( C .) A . ( C .) A . ( C .) retexta A . ( C .) A . ( C .) A . ( C .) A . ( C .) Current Current name (this paper) retextus engonatus putrescens gomerensis textilis scutulus ganodus kompsus rupivagus saproxylophaga anagaensis ( Gonyodiscus ) Keraea garachicoensis Discus D . ( G .) D . ( G .) D . ( G .) D . ( C .) A . ( C .) A . ( C .) D . ( G .) D . ( G .) D . ( G .) D . ( G .) Usual name (bibliography) et al . 2011 Current Current understanding of the Discidae species from the Canary Islands. Table 2 Table Alonso, G. Holyoak in & Yanes rupivagus Rähle & Allgaier 2011 R.T. Lowe putrescens R.T. 1861 Wollaston 1878 garachicoensis Wollaston saproxylophaga anagaensis Ibáñez & D. Holyoak in Yanes ) Shuttleworth 1852 Shuttleworth 1852 ( C .) ( C .) et al . 2011 ( Iulus ) ( Lucilla Helix retexta Helix engonata Shuttleworth 1852 Helix Discus gomerensis Rähle 1994 Discus ( Canaridiscus ) Atlantica Yanes Atlantica Helix textilis Helix scutula Shuttleworth 1852 Helix ganoda J. Mabille 1882 Patula Helix kompsa J. Mabille 1883 Original name 592 DT Holyoak et al et al., 2011: fig. 3F) is similar to that described Family Discidae Thiele 1931 (1866) by Solem (1976) in Anguispira, so an epiphal- lus is apparently also absent in the subgenus [syn: Patulidae, see Bouchet & Rocroi, 2005: 11, Canaridiscus. 268; ICZN, 1999: Art. 40.2]. Type genus: Discus Fitzinger 1833. Observations Genus Atlantica Ancey 1887

Family Hygromiidae Tryon 1866 Type species by monotypy: Helix gueriniana R.T. Genus Keraea Gude 1911 Lowe 1852, from Madeira Island.

Type species by original designation: Patula Subgenus Atlantica (Canaridiscus) Alonso & (Iulus) garachicoensis Wollaston 1878 (Gude, 1911: Ibáñez in Yanes et al. 2011 271). [syn: Iulus Wollaston 1878, non Linnaeus 1758]. Type species by original designation: Atlantica We studied photographs of a syntype of (Canaridiscus) saproxylophaga Alonso, G. Holyoak Patula garachicoensis (Fig. 4A), which apparently & Yanes in Yanes et al. 2011, from La Gomera belongs to a species of the Hygromiidae, not to Island. the Discidae. The shell is somewhat immature, In addition to A. (C.) saproxylophaga, A. (C.) with nearly 4½ whorls and maximum diam- anagaensis and A. (C.) rupivaga, we were able to eter of 6.7 mm. It shows irregular ribs above, study the genital systems of three other Discidae apparently with some hair-pits and perhaps faint species from the Canary Islands: A. (C.) ganoda hints of a blotched colour pattern, and looks (Fig. 6A) from La Gomera, A. (C.) kompsa (Fig. like an old shell of a hygromiid of the genera 6B) from El Hierro and A. (C.) scutula (Fig. 6D, Microxeromagna Ortiz de Zárate López 1950 or E) from Tenerife. These last three species have Xerotricha Monterosato 1892. the basic structure and arrangement of the geni- Patula garachicoensis and Helix deflorata share talia similar to those of the three former species, similar shell characters, differing in dimensions. although there are differences mainly in the penis Wollaston (1878) indicated that the shell diam- length. Hence they can be shown to belong in the eter of the only specimen of H. deflorata (a single subgenus Canaridiscus. The remaining Discidae adult shell with a large umbilicus and the basal species from the Canary Islands for which the whorl conspicuously – though not very greatly genital anatomy remains unknown are also likely, – deflexed at the aperture) is about “5½ lines” therefore, to be species of this subgenus. (11.6 mm) and that of P. garachicoensis, with 5–5½ The longest penis is that of A. (C.) saproxylo- whorls, is “3½ lines” (7.4 mm). Seddon (1996a) phaga, followed in turn by A. (C.) ganoda, A. (C.) considered H. deflorata to be a junior synonym rupivaga, A. (C.) anagaensis, A. (C.) kompsa and A. of the European species now known as Trochulus (C.) scutula. The shortness of the penis of A. (C.) striolatus (C. Pfeiffer 1828) following comments scutula is perhaps related to the thinness of the from the late H. W. Waldén, who had seen the soft part body (Fig. 6C, its maximum diameter specimen and commented that it is a shell of being 1.1–1.2 mm), but it is proportionally longer that species (in lit. to Wells & Chatfield, 1992). than those of the genera Discus and Anguispira. Whereas Bank et al. (2002) listed H. deflorata as The “ampulla” of the hermaphroditic duct has a valid taxon, Bank (2009) does not include H. been found only in Atlantica saproxylophaga and deflorata or Trochulus striolatus in a list of recent A. (C.) ganoda. The talons of A. (C.) saproxylo- terrestrial gastropods of the Madeiran archipel- phaga, A. (C.) anagaensis, A. (C.) ganoda and A. ago. (C.) kompsa are similar to, but seemingly less Besides P. garachicoensis and H. deflorata, three developed, than those of Anguispira alternata and species from the Cape Verde Islands were grouped A. kochi drawn by Pilsbry (1948: figs 304D, E), as by Wollaston (1878) in Patula (Iulus): Helix gorgo- well as that of A. cumberlandiana cumberlandiana narum Dohrn 1869; H. bertholdiana (M. Pfeiffer drawn by Solem (1976). 1852); and H. bouvieri (A. Morelet 1873). These are also likely to be species of Hygromiidae rather Affinities of the Discidae genera: Discus, Anguispira than of Discidae. and Atlantica (Canaridiscus) share many shell Discidae of the Canary Islands 593

Figure 6 A, B, D, E, genital systems; C, body of the animal extracted from the shell. A Atlantica (Canaridiscus) ganoda; B A. (C.) kompsa; C–E A. (C.) scutula. Parts: a atrium; ag albumen gland; au auricle; bc bursa copulatrix; bcd bursa copulatrix duct; e egg; f foot; go genital orifice; hd hermaphroditic duct; o oviduct; p penis; pr penis retractor; t talon; v vagina; vd vas deferens; ve ventricle. and anatomical character-states, as follows: a umbilicus that reveals all the whorls including shell moderately to strongly depressed, radi- the nucleus; lung long and narrow, without large ally ribbed, with the base having a widely open or noticeable branches on the pulmonary vein; 594 DT Holyoak et al kidney triangular, a little longer than the peri- subtropical or warm-temperate areas with high cardium; secondary ureter closed; male genital humidity and relatively stable temperatures. The system lacking flagellum and epiphallus; penis older literature indicates that they were gener- without penial papilla; bursa copulatrix small; ally found on the ground beneath the trunks bursa duct long and very thin, without diver- of decaying trees, pieces of rotten wood, dead ticulum. leaves, or sometimes beneath stones (Mousson, The genera Discus and Anguispira share similar 1872; Wollaston, 1878). Recent finds were mostly characters of the genital system, notably a short in undisturbed, humid laurel forest, closely penis (Fig. 1A–C), whereas Atlantica (Canaridiscus) associated with rotting wood. The two recently clearly differs from both of them because it has a described species, A. (C.) saproxylophaga and A. much longer penis (Fig. 1D). Therefore the rela- (C.) anagaensis, were found inside the humid tionship of Atlantica (Canaridiscus) with Discus trunks of decaying trees, beneath them, or in and Anguispira is apparently more distant than both types of site. that between the last two genera. Exceptional finds in other habitats include the holotype of A. (C.) gomerensis (an empty white shell) and the species A. (C.) rupivaga. A. (C.) Generic classification gomerensis was found in a ravine outside the lau- risilva, near the Macizo de Teselinde (La Gomera Due to the unknown anatomical and genetic Island), but about 2 km to the north-east of the characteristics of Atlantica gueriniana from Epina mountain, which has laurel forest (Fig. 2, Madeira (the type-species of the genus Atlantica), the arrow on La Gomera map). Some specimens the existence of close relationships between the of this species were also collected by J. Santana Madeiran and Canary Islands Discidae can only (JSGC; Fig. 4G) in Las Rosas ravine (UTM: be surmised. Nevertheless, they have generally 28RBS8420, 250 m altitude), about 8 km east of similar shell characters as described above and the type locality; the latter locality is not included both are related to the peculiar laurel forest on the map because the shells were from stream vegetation type (laurisilva) of these archipela- deposits. A. (C.) rupivaga was found hidden in gos in northern Macaronesia (Wollaston, 1878), narrow crevices of shattered, northeast-exposed although the Madeiran species was recently volcanic rocks, as well as between stones at the found outside the laurisilva, in drier but well base of these rocks, at an altitude of 600 m; it is vegetated regions (Cameron & Cook, 1999) and the only A. (Canaridiscus) species known to live in A. gueriniana calathoides occurs in dry habitats of narrow rock crevices. the Desertas (which have their maximum alti- The main vegetation type at the A. (C.) rupivaga tude at 442 m). Thus, we provisionally group locality nowadays is pine forest (Rähle & Allgaier, Canaridiscus in Atlantica, raising the latter to 2011: fig. 1C) but this forest results from re- generic rank in the Discidae, because Canaridiscus afforestation begun between 1960 and 1970 (Del is not closely related to the genera Discus and Arco et al., 1990, 2006) on an area where the ancient Anguispira. Future study of the genital system of vegetation was mainly laurisilva. Although the the Discidae species from Madeira is needed to species has evidently survived this change from either confirm the position of Canaridiscus as a laurisilva to pine forest, its survival was probably subgenus of Atlantica or raise it to generic rank. due to the adaptation to living in rock crevices. However, future studies of the Discidae combin- In addition, some specimens of A. (C.) scu- ing anatomical and molecular techniques may tula from Tenerife (localities outside the Anaga modify our understanding of the systematics of mountains, between 1000 and 1250 m altitude) the whole family. and A. (C.) textilis from La Palma (to 1500 m altitude), were found outside the laurisilva, in pine forest (Fig. 2, see arrows on Tenerife and Habitats La Palma maps). In the case of A. (C.) scutula, it is possible that these few occurrences are from The Canarian Discidae species have a narrow areas where laurel forest occurred formerly but range of habitats. The Canary Islands species regressed mainly as a consequence of human mostly live in the laurisilva, a forest found in impacts much as in the A. (C.) rupivaga locality; Discidae of the Canary Islands 595 there is abundant evidence of historic reduction nates from the Carboniferous coal forests (ca 300 in extent of the laurel forests (Parsons, 1981; de Mya) were regarded as representing the earliest Nascimento et al., 2009; Fernández-Palacios et al., Stylommatophora by Solem & Yochelson (1979), 2011). In the case of A. (C.) textilis, it is more likely but some of these have been reidentified as non- that a natural regression of the higher-altitude stylommatophoran eupulmonates by Bandel laurel forests has occurred due to changes in (1991, 1997) and attribution of Carboniferous fos- the moist trade winds, which are essential for sils to several Recent stylommatophoran families the presence and development of the laurisilva, is now regarded as highly controversial (Mordan since there is currently no laurisilva in the Canary & Wade, 2008). The suggestion has been made Islands above 1200 m altitude (Yanes et al., 2009c: that no land snails survived the mass extinc- Fig. 2). Survival of A. (C.) scutula and A. (C.) tion event at the end of the Permian (250 Mya) textilis could perhaps be related to the pres- with a loss of up to 95% of all species (Wade ence of trunks of decaying trees and pieces of et al., 2006). However, not all animal taxa were rotten wood in the pine forest that has replaced equally affected by this event and terrestrial laurisilva. invertebrates appear to have survived the crisis better than marine animals or terrestrial tetra- Discussion pods (Stworzewicz et al., 2009); for example, only eight of the 27 orders of Paleozoic insects Evolution and biogeographical history of Discidae became extinct, and nearly half of the remaining The occurrence of endemic Discidae in the ones survived to the present day (Labandeira & Canary Islands, which differ widely in anatomy Sepkoski, 1993). from the living European and North American Solem & Yochelson (1979), in their detailed species, is described above. All of the Canary study of North American Upper Paleozoic land- Islands they inhabit have ages of less than 12 snail fossils, placed Protodiscus priscus (Carpenter Mya, so we are confronted with a problem in 1867) within the Discidae based on its shell sculp- explaining the occurrence there of taxa more ture. Subsequent workers have regarded it as distinctive than any of those on the geologi- belonging to an uncertain family but possible the cally much older European and North American Pleurodiscidae (Nordsieck, 1986), or perhaps the continents. This is addressed in the following Valloniidae (Stworzewicz et al., 2009). This species sections of the Discussion, through consideration has also been found in Early Permian (250–260 of: time-scales for evolution of Stylommatophora Mya) sediments of the Upper Silesian-Cracow and of Discidae in particular, based on fossil Upland (Karniowice, S. Poland), indicating it records and “molecular-clock” studies; timing occurred not only in proto-N. America, but also in of separation of the European and American the European part of the Pangea supercontinent continents and the European-African connec- (Stworzewicz et al., 2009). There are additional tion, as deduced from geochronological, geo- records of fossil pulmonates from the Middle magnetic and other geological data; evidence of Jurassic (Planorbidae representing the Hygrophila the volcanic origins and ages of the Canary and from the Doggerian Epoch, 188–163 Mya) and Madeiran archipelagos; origins of the land snails Late Jurassic (Ellobiidae and Siphonariidae from and other biota of Madeira and the Canaries, the Malm Epoch, 163–144 Mya), but no undis- including evidence that Canaries Discidae were puted fossil Stylommatophora from before the mainly restricted to relict laurel forests; the his- Cretaceous (130 Mya: Bandel, 1991, 1997; Zilch, tory of laurisilva in the western Palearctic; and 1959). Fossils of species assigned to the Discidae the most parsimonious model to explain distri- have been recognised from the Upper Cretaceous butional history of Discidae in the Canaries and (65–100 Mya), Eocene, Oligocene and Miocene in other regions. Terminology for divisions of the America (Henderson, 1935; Pilsbry, 1948; Pierce & geological record and the ages assigned to them Constenius, 2001), and there were many Tertiary here follow Gradstein et al. (2005) and Ogg et al. species reported from Europe (Wenz, 1923; Zilch, (2008). 1959; Harzhauser & Binder, 2004; Harzhauser et al., 2008). Time-scales for evolution of Stylommatophora and On the basis of a “molecular-clock” approach, of Discidae Records of fossil terrestrial pulmo- Tillier et al. (1996) suggested that divergence and 596 DT Holyoak et al rapid early diversification of the Stylommatophora tently by discontinuous filter routes that linked it occurred around 90–60 Mya (Late Cretaceous to mainly to Laurasia until the Early Miocene (ca. 23 Paleocene), which is at least roughly congru- Mya), when a definitive connection with Eurasia ent with the 130 Mya demonstrated by fossils. was established (Gheerbrant & Rage, 2006). This Wade et al. (2001) and Wade et al. (2006) pre- connection was interrupted on its western side sented the fullest molecular studies currently at the start of the Pliocene (ca. 5 Mya), when the available of the Pulmonata. They revealed an Straits of Gibraltar were formed. early separation into an “achatinoid clade” and a “non-achatinoid” lineage, both of which contain Volcanic origins and ages of the Canaries and Madeira families originating in the Mesozoic southern The Canarian and Madeiran archipelagos are supercontinent of Gondwanaland. Some of these comprised exclusively of volcanic islands that had a wide distribution in Gondwanaland before rose above sea-level in the Tertiary, after the its fragmentation in the Late Jurassic (around 150 Atlantic had almost reached its present-day Mya), from which it is reasonably assumed that width. The oldest dated rocks known to still the initial diversification of Stylommatophora exist on land that is subaerially exposed are in took place even earlier. Wade et al. (2001) showed the eastern Canaries (15.5–20.6 Mya), but these that the Discidae are not closely related to islands lack laurel forests and also Discidae. This Punctidae, Charopidae or Otoconchidae as sug- is no doubt because the moist trade winds ascend gested by previous studies. Instead, the Discidae to altitudes higher than those of both islands appears as an early offshoot of a very large clade (with the exception of a small peak on each that later gave rise successively to Cerionidae, of them). Although Fuerteventura now has a Haplotrematidae, Spiraxidae and eventually to maximum altitude of 806 m (La Zarza Peak), it all Helicoidea. In addition, it is clear that the is estimated to have reached about 3000 m high Discidae are not only known exclusively from in the Miocene (Stillman, 1999). The western the Holarctic (living or as fossils), but that they Canaries range from 1.1 Mya (El Hierro) and show no close affinity with any group originating 1.7 Mya (La Palma) to 7.5 Mya (Tenerife) and 12 in Gondwanaland, strengthening the likelihood Mya (La Gomera) (Carracedo et al., 2005). The that they originated in the northern superconti- small island of Porto Santo is the oldest of the nent Laurasia. Madeiran islands (10 Mya) and it lacks Discidae; the larger Madeira island is up to 5 Mya but has Timing of separation of the European and American suffered renewed vulcanism as recently as 2.5 continents and the European-African connection Mya. However, Fernández-Palacios et al. (2011) Prior to the separation of Gondwanaland and have recently argued from geological evidence Laurasia (Triassic, 248–213 Mya) the single large that large and high islands may have been con- land mass (Pangea II) comprised Laurasia in the tinuously available in northern Macaronesia for north (with proto-North America as its south- very much longer than is indicated by the surface ern part, proto-Europe as its northern part) and of the oldest current island of the region, possibly Gondwanaland in the south (with its northern for as long as 60 Mya. part comprised of proto-South America in the west, proto-Africa in the east) (Scotese, 2001). Origins of the land snails and other biota of Madeira During the Jurassic, Gondwanaland and Laurasia and the Canaries Currently, because of the separated and the developing Atlantic Ocean unknown anatomical and genetic characteristics separated Laurasia into proto-North America of Atlantica gueriniana from Madeira, the exist- and proto-Europe. By the Late Jurassic (152 Mya) ence of close relationships between the Madeiran the Atlantic Ocean was still much narrower than and Canarian Discidae can only can be sur- at the present day and seas of approximately mised. Nevertheless, as discussed above, we similar width separated North America from provisionally group all of these taxa in Atlantica South America and Europe from Africa (Smith et based on the similarities in shell shape and main al., 1973). Geological and paleobiogeographical habitats. data show that Africa was isolated from the Mid- Waldén (1984) indicated that “the most con- Cretaceous to Early Miocene, i.e. for ca. 75 Mya, spicuous difference between the land-mollusc but also that this isolation was broken intermit- faunas of Madeira and the Canary Islands is the Discidae of the Canary Islands 597 complete absence of taxa with north-west African trast, the liverwort Radula lindenbergiana Gottsche affinities on Madeira, despite the fact that they ex C. Hartmann may have had a refugium in the hold a similar position relative to the African Macaronesian archipelagos during Quaternary continent”. Indeed, Porto Santo, the oldest island glaciations, from which it subsequently recol- of the Madeiran archipelago, was susceptible to onised the European continent (Laenen et al., colonisation for over 10 Mya without major vol- 2011). Among angiosperms, the four genera of canic activity and colonists are thought to have Lauraceae that characterise the Macaronesian arrived by island-hopping from Europe (i.e. the laurisilva all occur in both the Canaries and south-west Iberian Peninsula) through a former Madeira, with Apollonia and Ocotonia absent from island chain now remaining as seamounts (Cook, both the Azores and neighbouring continental 2008). It has been suggested that the Canary regions, whilst Persea and Laurus also occur in Islands were colonised by land-snails from neigh- the Azores and the latter is present addition- bouring north-west Africa, possibly on floating ally in southern Europe and north-west Africa vegetation rafts (Alonso et al., 2000; Arnedo et al., (Hohenester & Weiss, 1993; Fernández-Palacios 2001; Yanes et al., 2009b). An Afrotropical origin et al., 2011). All of these trees have large fleshy seems likely for the endemic Canary Islands fruits that are likely to be dispersed primarily genus Gibbulinella (Rowson et al., 2011). However, by frugivorous birds, principally pigeons, so it the Canarian Discidae have close ecological ties is surely no coincidence that endemic frugivo- to the laurel forest, as do several other genera rous pigeons occur in the laurisilva of Madeira of land snails present in both the Canaries and (Columba trocaz Heineken 1829) and the Canaries Madeira (Craspedopoma L. Pfeiffer 1847, Lauria (C. bollii Godman 1872, C. junoniae Hartert 1916). J.E. Gray 1840, Leiostyla R.T. Lowe 1852, Columella All three of these birds specialise in Lauraceae Westerlund 1878). Hence greater similarity of fruits and all are thought to have derived from the land-snail faunas of these archipelagos is the European and North African continental spe- evident than was implied by Waldén’s (1984) cies C. palumbus Linnaeus 1758 (Goodwin, 1977; analysis. Cramp et al., 1985; Emmerson, 1985; Oliveira et Different groups of plants show differing pat- al., 2002; Marrero et al., 2004). terns of phytogeographical affinity between the In contrast to the vast Tertiary colonisation archipelagos in northern Macaronesia. There are of northern Macaronesian islands deduced for relatively few endemic genera of angiosperms many of the plants discussed above, a molecu- compared to older island archipelagos or conti- lar study of Erica arborea Linnaeus (Ericaceae) nental fragments: ca 15 of them being found only demonstrates colonisation of both Madeira in the Canaries, 4 only in the Madeiran archipel- and the Canaries during the Pleistocene via the ago (Chamaemeles, Monizia, Musschia, Parafestuca), Mediterranean basin, from refugia in East Africa none only in the Azores, three in both the (Désamoré et al., 2011). Erica arborea has very Canaries and Madeira, one in the Canaries and small dry seeds and it may be surmised that the Azores (Lytanthus), one in Madeira and the these are readily dispersed over long distances. Azores (Melanoselinum) and one in all three archi- Overall, it is probably unsurprising to find mul- pelagos (Aichryson) (Good, 1964; Press & Short, tiple patterns of colonisation of Madeira and 1994). Analyses of floristic data sets for liverworts the Canaries that have varied between different (Hepaticophyta) and Pteridophyta support (or groups of organisms, partly no doubt due to their cannot reject) existence of an Azorean-Madeiran- differing propagules and dispersal agents, partly Canarian clade, whereas a similar analysis of the due to differing climatic or ecological tolerances, mosses (Bryophyta) resolves the Canary Islands but perhaps also sometimes due only to chance. as sister to North Africa (Vanderpoorten et al., Consequently, it is unwarranted to expect to find 2007). Even within the liverworts, Plagiochila only a single pattern of colonisation among the stricta (Dickson) Dumortier from the Canaries land snails of each of these archipelagos. has been demonstrated to have close Neotropical affinities and origin by a wealth of molecular, History of laurisilva in the western Palearctic In phytochemical and morphological data (Rycroft the western Palearctic the laurel forest veg- et al., 2002); its microscopic spores might of course etation type is now restricted to middle lev- have been wind-blown across the Atlantic. In con- els (600–1200 m a.s.l.) in the mountains of the 598 DT Holyoak et al

Azores, Madeira and the western Canary Islands. deciduous woodlands, not stenophiles requir- A varied evergreen forest vegetation of similar ing floristically-rich, broadleaved, evergreen for- subtropical affinities, but richer in plant gen- ests. Colonisation of the Canaries by Discidae era, was widespread in Europe (northwards to was apparently restricted to laurisilva habitats the London basin: Reid & Chandler, 1933) dur- so that it almost certainly followed the arrival of ing the Early and Middle Tertiary, 65–24.6 Mya. this vegetation type, while persistence of their Thereafter, the forest became progressively less Discidae to the present day was doubtless related diverse and apparently retreated southwards by to continuing presence of the laurisilva through- the Miocene (24.6–5.1 Mya) and especially the out the Late Tertiary and Pleistocene. Pliocene (5.1–2.0 Mya) (e.g. Krutzsch, 1967; West, 1968; Flenley, 1979; Nilsson, 1983; Fernández- A model of distributional history of the Discidae Palacios et al., 2011). Much of the information that would allow a By the Early Pleistocene, the subtropical ever- detailed understanding of the evolution and green forest had disappeared from the mainland biogeographical history of Discidae is lacking. of Europe and north-west Africa. However, some The fossil record of the family is probably very of its characteristic plants persisted as relicts char- incomplete, the known fossils (shells) cannot acterising the laurisilva on the Azores, Madeira provide the data on genital anatomy that would and Canaries (Fernández-Palacios et al., 2011). allow better assessment of their generic affinities, Four Late Pleistocene marine pollen records from and there has been no molecular study of the offshore of Portugal and Morocco representing phylogeny of the extant taxa. Attempts at recon- the period 250–5 Kya demonstrate that in the structing the history of the family must there- presumed mild (interglacial) stages (respectively fore be generalised and somewhat speculative, 240–190, 125–70, 10–5 Kya) a Mediterranean oak accompanied by recognition that the simplest forest was widespread in the continental areas to explanation may not be the correct one. the east, whereas during colder (glacial) stages The earliest radiation of taxa in the Discidae a steppe-like vegetation (Artemisia rich, partly was probably no older than Upper Cretaceous wooded with Pinus) formed a transition zone (ca. 100–65 Mya), as established by fossils from between the Sahara to the south and the tree-less America (Henderson, 1935; Pilsbry, 1948; Pierce tundras of western Europe (Hooghiemstra et al., & Constenius, 2001), but it could be much older 1992). Roucoux et al. (2001) have subsequently than this. Numerous fossil taxa (Wenz, 1923) demonstrated that the changes in the marine pol- also confirm that the range extended to Europe len record offshore of continental Portugal from through much of the Tertiary (65–5 Mya). By 65–9 Kya closely tracked temperature changes the Late Cretaceous the widening north Atlantic deduced from marine oxygen-isotope data, with Ocean was still much narrower than at the Mediterranean oak forest occurring only during present day, with relatively narrow sea gaps the warm stages. Neither study showed paly- separating the British Isles from Newfoundland, nological evidence for anything resembling lau- Labrador and southern Greenland (e.g. Smith et risilva on the European and north-west African al., 1973). By the Eocene (54.9–38 Mya) the sea mainland during the past 240 Kya and it seems gaps involved were wider, but considerably nar- highly unlikely that most of its characteristic rower than they are today. Throughout the Late plants could have survived there during the Cretaceous and Early Tertiary the vegetation at cold stages (a few exceptions probably included the palaeo-latitude of 30o-40o N was essentially Laurus nobilis Linnaeus and Prunus lusitanica subtropical broad-leaved forest. The Eocene flora Linnaeus, both of which still grow in the Iberian of the London Clay (Reid & Chandler, 1933) Peninsula). gives detailed evidence of this, and Pearson Iberia and the Maghreb are of course rich (1964) provided data suggesting this flora had in endemic biota and the region has repeat- clear tropical affinities. However, Steenis (1962) edly been demonstrated as a likely “Atlantic- has argued that much of this flora may con- Mediterranean refugial area” allowing survival sist of material drifted across the Tethys; Muller of species through the Late Pleistocene cold (1970) found that European Eocene pollen and stages (e.g. Schmitt, 2007), but these are animals spore micro-floras are very different to the few and plants of varied open or aquatic habitats or known Indo-Malayan ones; likewise, Krutzsch Discidae of the Canary Islands 599

(1967) found that there is evidence of only a few probably accounts for some of the characters of Indo-Malayan taxa penetrating Europe in warm each of the Madeiran and Canaries species, all of phases. Thus, Daley (1972) was led to suggest which are distinctive single-island endemics. that the London Clay climate of the Eocene was seasonal but frostless, with higher rainfall than Conservation of Macaronesian Discidae The today (for the palaeo-latitude that was then 40º morphological and taxonomic uniqueness of N.), warmer than now, but not as warm as in the Discidae of the Canary Islands, their relict tropical rainforest regions. Occurrence of Eocene nature and restriction predominantly to the lau- coral reefs in the London basin nevertheless risilva habitats, emphasise the importance of their strengthens the evidence for at least a moderately conservation. warm climate. The early Discidae could therefore Fontaine et al. (2007) showed that most of the have had ample opportunity to cross the narrow recent extinctions in Europe have affected taxa north Atlantic Ocean of the Late Cretaceous and with small geographical ranges, along with others Early Tertiary and find suitable habitats on both having strict ecological requirements. Similarly, sides. The much later overseas colonisation of the most European species listed as threatened in Canaries and Madeira demonstrates that repre- the IUCN Red List have small ranges. Most sentatives of the family have the ability to cross Canarian Discidae have small ranges and D. substantial sea gaps. engonatus, D. retextus, D. textilis and Keraea gara- It might seem simpler to imagine early Discidae chicoensis were included in the list of European occurring in the Triassic (248–213 Mya) or Early globally extinct taxa by Fontaine et al. (2007), Jurassic, when proto-Europe and proto-North as was Janulus pompylius (Shuttleworth 1852) of America were a single land mass. However, this the Gastrodontidae, but without details being is much earlier than any fossils assignable to given of the reasons for them being regarded as Discidae. An additional objection to the hypoth- extinct. esis of such ancient existence and spread of Fortunately, among the Discidae species listed Discidae is that their broad-leaved forest habitat by Fontaine et al. (2007) as globally extinct, at did not exist until much later, when a diverse flora least Atlantica (Canaridiscus) textilis is known of angiosperms evolved during the Cretaceous to still survive since we collected several fresh and gradually replaced vegetation dominated shells at two localities on La Palma Island (e.g. by cycads, conifers and ferns (e.g. Axelrod, 1959, Fig. 5C). Similarly, the Madeiran A. gueriniana 1963; Muller, 1970; Wolfe et al., 1975; Hughes, was originally listed as possibly extinct (Wells 1976). & Chatfield, 1992; Groombridge, 1994; Seddon, The following hypothetical outline of bioge- 1996b), then reassessed as extinct (E) in the ographical history of Discidae in Europe and 1996 Red List (Baillie & Groombridge, 1996) northern Macaronesia since the Early Tertiary because it had not been recorded since the 1860s can therefore be suggested as the simplest sce- despite intensive searching since 1983. However, nario accounting for the evidence available. (1) Cameron & Cook (1999) rediscovered it at the The numerous species of the family present in western end of Madeira island at two close, but the Tertiary of Europe (Wenz, 1923; Zilch, 1959), separate locations. It was found there outside included lineages allied to those still extant in the laurisilva, in drier but well vegetated regions, North America. (2) The emergent Madeiran on highly disturbed precipitous hillsides facing islands and Canaries were colonised in the the ocean, differing from the habitats described Tertiary from Europe, North Africa, or both, by in Wollaston (1878). Apparently only shells have Discidae of a lineage no longer present in these been recorded recently, but these are sufficiently continental areas. (3) On the European continent fresh to assume the species is living at these Discidae were reduced to three surviving spe- sites (Seddon, 2000). A. gueriniana calathoides cies (one of them also in NW. Africa) by the Late might possibly also survive in the Desertas and Pleistocene (250–0 Kya), none of which is closely it remains possible that several of the other spe- related to the relict taxa present in the Canaries cies currently listed as extinct will be refound and, probably, also in Madeira. These extinctions living because all of them were from locations resulted from climatic and vegetational changes which have remained undisturbed, or relatively (cf. discussion above). (4) Subsequent evolution undisturbed. 600 DT Holyoak et al

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