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Two new species of land snails of the genus Rahula from PeninsularMalaysia (Gastropoda: Euconulidae)

Junn Kitt Foon1* & Mohammad Effendi Marzuki2

Abstract. Two new species of the genus Rahula are described from Peninsular Malaysia. Rahula limbooliati, newspecies, is distinguished from congeners by the presence of five or six distinctly raised spiral ridge striations atprotoconch and widely-spaced (5–8 ribs per mm), slightly prosocline radial ribs that terminate abruptly sub-peripherally at teleoconch as well as a semi-closed umbilicus. Rahula tonywhitteni, new species, is distinguishedfrom congeners by its prominent radial ribs angled towards the apex at protoconch that become slightly prosoclineand densely-arranged (12–15 ribs per mm) at teleoconch as well as its open umbilicus.

Keywords. Mollusca, limestone karsts, range extension, Pahang, Perak

reproductive anatomy is unknown for Rahula. As such,Rahula remains diagnosed by conchology only.

Without reproductive anatomy and molecular data, the fa-milial and subgeneric classifications for Rahula remain con-tentious (Gittenberger et al., 2017a). Based on conchology,Rahula has been placed in families HelicarionidaeBourguignat, 1877 (Zilch, 1959; Gittenberger et al., 2017a,2017b), Ariophantidae Godwin-Austen, 1888 (Thiele, 1931;Schileyko, 2003) and Euconulidae Baker, 1928 (Vermeulenet al., 2015). In view of this, we followed the taxonomicdecision of Vermeulen et al. (2015) for convenience andconsidered the familial assignment tentative pending fur-ther evidence.

Rahula has two subgenera: Sinaenigma Pilsbry, 1934 andRahula sensu stricto (Pilsbry, 1934; Schileyko, 2003).Sinaenigma was erected to accommodate one western Chinaspecies R. (S.) chengweiensis Pilsbry, 1934, which shareswith Rahula sensu stricto strong radial rib sculpture butdiffers by being low conoidal and without peripheral keel.Pilsbry (1934) considered the subgeneric placement ofSinaenigma in Rahula as provisional pending anatomicalanalysis.

Rahula sensu stricto has a Tropical East Asian distributionencompassing a wide area from north-eastern India andBhutan in the west to northern Vietnam in the east as well asSumatra and Borneo in the south, although most of its speciesappear to be very range-restricted (Godwin-Austen, 1907,1918; Schileyko, 2003; Vermeulen et al., 2015; Gittenbergeret al., 2017a, 2017b). Only 19 species and one subspeciesof Rahula are known across tropical East Asia so far, withno species reported in between these known localities,especially in central Sundaland encompassing PeninsularMalaysia (Ray & Rajagopalaiengar, 1953; Gittenberger etal., 2017a, 2017b).

INTRODUCTION

The genus Rahula Godwin-Austen, 1907 was first erectedto accommodate Helix macropleuris Benson, 1859 onaccount of its conically trochiform shell with regularly raisedribs on its spire, which differs from other small shelledpulmonates such as Kaliella Blanford, 1863, MicrocystinaMörch, 1872 and Thysanota Albers in Albers & von Martens,1860 (Godwin-Austen, 1907). The genus Rahula includesspecies of land snails characterised by small shells (2 to5 mm) that are globular conical to conically trochiform withmore or less distinct peripheral keel, simple peristome aswell as the diagnostic regular-spaced and raised radial ribs(Godwin-Austen, 1907; Godwin-Austen, 1918; Schileyko,2003; Vermeulen et al., 2015; Gittenberger et al., 2017a,2017b). Rahula species vary in umbilicus sizes from almostclosed to wide (up to one fifth of shell width) and protoconchwith radial and spiral sculpture variations (Gittenberger etal., 2017a, 2017b).

The only published anatomical description for the genusRahula is that in the original description of R. koboensis byGodwin-Austen (1918). He described R. koboensis as aspotted white animal with banded black visceral sac, broadperipodial margin, distinct mucous pore at extremity of shortfoot, tricuspid radula and a somewhat straight front jaw withslight central projection. The taxonomically informative

RAFFLES BULLETIN OF ZOOLOGY Supplement No. 35: 137–142Date of publication: 31 March 2020http://zoobank.org/urn:lsid:zoobank.org:pub:22882CC5-194E-4A2C-840E-ADBA8050E59C

1Institute for Tropical Biology and Conservation, Universiti Malaysia Sabah, JalanUMS, 88400 Kota Kinabalu, Sabah, Malaysia; and Rimba, 22-3A, Casa Kiara 2,Jalan Kiara 5, 50480 Kuala Lumpur, Malaysia. Email: junnkitt@rimbaresearch.org(* corresponding author)

2Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, JalanDatuk Mohammad Musa, 94300 Kota Samarahan, Sarawak, Malaysia.

© National University of SingaporeISSN 2345-7600 (electronic) | ISSN 021-2445 (print)

138

In recent years, intensified malacofaunal surveys acrossPeninsular Malaysia have led to discoveries of many newspecies including two new Rahula species, which aredescribed herein. The discovery of these two new speciesmarks a new genus record for Peninsular Malaysia and fillsa major geographical gap for Rahula.

MATERIAL AND METHODS

Materials examined were extracted from leaf litter duringsurveys of limestone hill malacofauna in Peninsular Malaysiaby Clements et al. (2008) and Foon et al. (2017). Theseexamined materials are deposited at the BORNEENSIScollection (BOR/MOL), Institute for Tropical Biology andConservation, Universiti Malaysia Sabah and the collectionfor the second author (Abbreviation: ME). The latter willeventually be deposited in the Sarawak Museum, Kuching,Malaysia. Locations of limestone hills follow the codes inthe Peninsular Malaysia limestone karst database (Liew etal., 2016).

The two new Rahula species are described and comparedwith type illustrations and descriptions of congeners listedin the Rahula review by Gittenberger et al. (2017a) andreferences therein. Our taxonomic study is based onconchological characters only. As all species of the genusRahula lack a distinct lip, which could be used as a

taxonomic reference point, the largest intact specimen amongmaterials examined was chosen for measurements of shellheight (SH), shell width (SW), aperture height (AH),aperture width (AW) and number of ribs per mm (Vermeulenet al., 2015). The diameters of the first four whorls (DA,DB, DC, DD) were also measured (Vermeulen & Whitten,1998; Vermeulen et al., 2015). The calculation of number ofwhorls (NW) follows Vermeulen & Whitten (1998). Inaddition, some larger paratype shells were also measured.

TAXONOMY

Family Euconulidae Baker, 1928

Rahula Godwin-Austen, 1907

Type species. Helix macropleuris Benson, 1859

Rahula limbooliati, new species(Fig. 1A–G)

Type specimens. Holotype: (BOR/MOL 14214), PHG 02Gunung Senyum, Pahang, Peninsular Malaysia (3.7038°N102.4356°E), coll. G. R. Clements, 2006. Paratypes: 26 ex.(7 shells measured) (BOR/MOL 14215), same data asholotype; 1 ex. (ME 861), PHG 03 Bukit Jebak Puyuh,Pahang, Peninsular Malaysia (3.6945°N 102.4482°E), coll.

Foon & Marzuki: Two new Rahula from Peninsular Malaysia

Fig. 1. Rahula limbooliati, new species. A, holotype, from PHG 02 Gunung Senyum, Pahang, Peninsular Malaysia (BOR/MOL 14214);B, paratype, from PHG 03 Bukit Jebak Puyuh, Pahang, Peninsular Malaysia (ME 861); C, paratype, from PHG 01 Kota Gelanggi, Pahang,Peninsular Malaysia (ME 2134); D, close-up of the apical whorls of BOR/MOL 14214; E, close-up of the apical whorls of ME 861;F, close-up of the apical whorls of ME 2134; G, close-up of the umbilical side of BOR/MOL 14214 shell showing fine sculpture.

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139

loca

lity

shel

l hei

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fdi

amet

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(AH

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W; m

m)

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; mm

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m)

(DC

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)(D

D; m

m)

R. l

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ype

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546

0.65

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OR

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2)Ph

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452.

670.

921.

447

0.64

0.97

1.47

1.97

5¾Pa

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pe (B

OR

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L 14

215/

3)Ph

g 02

Gun

ung

Seny

um2.

472.

510.

861.

38

0.69

1.07

1.47

1.97

5¾Pa

raty

pe (B

OR

/MO

L 14

215/

4)Ph

g 02

Gun

ung

Seny

um2.

92.

691.

031.

458

0.84

1.26

1.67

2.11

5¾Pa

raty

pe (B

OR

/MO

L 14

215/

5)Ph

g 02

Gun

ung

Seny

um2.

562.

81.

031.

486

0.64

1.07

1.47

2.04

5¾Pa

raty

pe (B

OR

/MO

L 14

215/

6)Ph

g 02

Gun

ung

Seny

um2.

772.

841

1.51

70.

781.

221.

642.

155¾

Para

type

(BO

R/M

OL

1421

5/7)

Phg

02 G

unun

g Se

nyum

2.77

2.76

1.06

1.48

60.

81.

161.

592.

155¾

Para

type

(ME

861)

Phg

03 B

ukit

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k Pu

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3.88

3.73

1.36

2.05

51.

121.

732.

373.

076½

Para

type

(ME

2134

)Ph

g 01

Kot

a G

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4.39

4.62

1.77

2.52

61.

161.

772.

523.

496½

Ran

ge;

2.45

–4.3

9;2.

51–4

.62;

0.86

–1.7

7;1.

30–2

.52;

5–8;

0.64

–1.1

6;0.

97–1

.77;

1.47

–2.5

2;1.

96–3

.49

5¾–6

½m

ean

and

SD3.

01 ±

0.6

33.

04 ±

0.6

41.

11 ±

0.2

71.

64 ±

0.3

7N

A0.

81 ±

0.1

91.

25 ±

0.2

81.

74 ±

0.3

92.

32 ±

0.5

3N

A(n

o. o

f spe

cim

ens)

(n =

10)

(n =

10)

(n =

10)

(n =

10)

(n =

10)

(n =

10)

(n =

10)

(n =

10)

(n =

10)

(n =

10)

R to

nyw

hitte

niH

olot

ype

(BO

R/M

OL

1142

2)Pr

k 01

Gun

ung

Tem

puru

ng2.

142.

341.

091.

2415

0.64

1.04

1.46

2.03

4½Pa

raty

pe (B

OR

/MO

L 11

207)

Prk

01 G

unun

g Te

mpu

rung

1.44

1.78

0.87

0.93

120.

731.

231.

79N

A3

Para

type

(BO

R/M

OL

1253

6)Pr

k 01

Gun

ung

Tem

puru

ng1.

441.

790.

870.

9715

0.51

0.98

1.49

NA

3R

ange

,1.

44–2

.14;

1.78

–2.3

4;0.

87–1

.09;

0.93

–1.2

4;12

–15;

0.51

–0.7

3;0.

98–1

.23;

1.46

–1.7

9;2.

03;

3–4½

;m

ean

and

SD1.

67 ±

0.4

01.

97 ±

0.3

20.

94 ±

0.1

31.

05 ±

0.1

7N

A0.

63 ±

0.1

11.

08 ±

0.1

31.

58 ±

0.1

8N

AN

A(n

o. o

f spe

cim

ens)

(n =

3)

(n =

3)

(n =

3)

(n =

3)

(n =

3)

(n =

3)

(n =

3)

(n =

3)

(n =

3)

(n =

3)

Tabl

e 1.

She

ll m

easu

rem

ents

for R

ahul

a lim

bool

iati,

(new

spe

cies

) and

R. t

onyw

hitte

ni, n

ew s

peci

es. A

bbre

viat

ions

: SD

, sta

ndar

d de

viat

ion;

mm

, mill

imet

res;

NA

, not

app

licab

le. N

ote

that

mea

n an

d st

anda

rd d

evia

tions

are

not

pro

vide

d fo

r num

ber o

f rib

s per

mm

and

num

ber o

f who

rls a

s the

y ar

e no

t mea

ning

ful.

140

Foon & Marzuki: Two new Rahula from Peninsular Malaysia

no spiral ridge. Ventral whorls radial growth lines very fine,dense. Dorsal whorl interstices striations very fine, dense,inconspicuous. Ventral whorls spiral striations very fine,dense, inconspicuous. Umbilicus semi-closed, partiallyobstructed by expanded peristome columellar section.

Distribution. Rahula limbooliati is known from threelimestone hills in central Pahang, Peninsular Malaysia: PHG01 Kota Gelanggi, PHG 02 Gunung Senyum and PHG 03Bukit Jebak Puyuh (Fig. 2).

Remarks. Rahula limbooliati varies in shell size withlocality, whereby shells from PHG 02 Gunung Senyum aresmaller than those from PHG 03 Gunung Jebak Puyuh andPHG 01 Kota Gelanggi (Table 1). Rahula limbooliati issomewhat similar to R. raricostulata Smith, 1893, fromSarawak in having widely-spaced radial ribs but differs inits white shell, less pronounced radial ribs, tall conical spireand absence of a prominent sub-peripheral spiral ridge(Smith, 1893). Rahula limbooliati also resembles R. jucundaBavay & Dautzenberg, 1912, from northern Vietnam, in shellshape but differs in the lack of a prominent sub-peripheralspiral ridge and the presence of prominent radial ribs at theprotoconch (Bavay & Dautzenberg, 1912).

M. E. Marzuki, 2009; 1 ex. (ME 2134), PHG 01 KotaGelanggi, Pahang, Peninsular Malaysia (3.8922°N102.4736°E), coll. M. E. Marzuki, 2010.

Etymology. Rahula limbooliati is named in honour ofDr. Lim Boo Liat, a Malaysian zoologist whose work hasbeen an inspiration for many scientists in Malaysia andSoutheast Asia including the authors.

Diagnosis. Rahula limbooliati differs from all knowncongeners by its conical shell with rounded periphery andsharp sub-peripheral keel without a prominent spiral ridge,5 or 6 distinctly raised spiral ridge striations at protoconch,widely-spaced (5 to 8 ribs per mm), slightly prosocline radialribs which terminate abruptly slightly below the peripheryat teleoconch and semi-closed umbilicus.

Description. Shell small (SH up to 4.39 mm; SW up to4.62 mm; DA 0.64–1.16 mm, DB 0.97–1.77 mm, DC 1.47–2.52 mm, DD 1.96–3.49 mm; NW up to 6½; AH up to 1.77mm; AW up to 2.52 mm; Table 1), solid, opaque, off-white,conical, periphery rounded, sub-peripheral keel sharp. Apexrounded. Surface slightly shiny to dull. Whorls convex,rounded, suture slightly impressed. Protoconch whorlsconvex, radial striation absent, five or six distinctly raisedspiral ridge striations from apex to first prominent radialrib at around 2¼ whorls. Teleoconch whorls convex. Dorsalwhorls radial ribs regular, wide-spaced (5 to 8 ribs per mm),slightly prosocline, prominent, thin but solid. Ribs terminateabruptly slightly below periphery, sub-peripheral keel sharp,

Fig. 2. Map of Peninsular Malaysia (insert) with a close-up of central Peninsular Malaysia showing the limestone hill localities of Rahulaspp. mentioned in this paper. Rahula limbooliati localities: (1) PHG 01 Kota Gelanggi, Pahang; (2) PHG 03 Bukit Jebak Puyuh, Pahang;(3) PHG 02 Gunung Senyum, Pahang. Rahula tonywhitteni locality: (4) PRK 01 Gunung Tempurung, Perak. Red areas are limestone hills,derived from Liew et al. (2016).

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Rahula tonywhitteni, new species(Fig. 3A–F)

Rahula ‘tempurung 1’ – Foon et al., 2017: 71, fig. 27C.

Type specimens. Holotype: (BOR/MOL 11422), PRK 01Gunung Tempurung, Perak, Peninsular Malaysia (4.4182°N101.1921°E), coll. J. K. Foon, 2016. Paratypes: 1 ex. (BOR/MOL 12536), same data as holotype; 2 ex. (1 shell measured,1 broken shell not measured) (BOR/MOL 11207), same dataas holotype; 2 ex. (juveniles, not measured) (BOR/MOL11222), same data as holotype; 4 ex. (broken shells, notmeasured) (BOR/MOL 11392), same data as holotype.

Etymology. Rahula tonywhitteni is named in honour of thelate Dr. Tony Whitten (1953–2017), a colleague and one ofthe world’s key advocate for limestone biodiversityconservation. He is fondly remembered for his deepappreciation of less charismatic limestone karst dwellingspecies especially land snails.

Diagnosis. Rahula tonywhitteni differs from all known con-geners by its conical shell, rounded periphery, somewhatsharp sub-peripheral keel, prominent radial ribs angled to-wards the apex at protoconch, slightly prosocline and nar-rowly-spaced radial ribs (12 to 15 ribs per mm) at teleo-conch and open umbilicus.

Description. Shell small (SH up to 2.14 mm; SW up to 2.34mm; DA 0.51–0.73 mm, DB 0.98–1.23 mm, DC 1.46–1.79mm, DD up to 2.03 mm; NW 3 to 4½; AH up to 1.09 mm;AW up to 1.24 mm; Table 1), thin, semi-translucent, off-

white, conical, sub-peripheral keel somewhat sharp. Apexrounded. Surface slightly shiny. Whorls convex, rounded,suture distinctly impressed upon spiral ridge slightly belowperiphery of previous whorl. Protoconch whorls convex,radial ribs prominent, thin. Apical whorl radial ribs angledtowards apex. Later whorls slightly prosocline. Spiralstriations very fine, dense, somewhat conspicuous.Teleoconch whorls convex. Dorsal whorls radial ribs regular,narrow spaced (12 to 15 ribs per mm), slightly prosocline,prominent, thin. Ribs terminate abruptly slightly belowperiphery, merged into prominent sub-peripheral spiral ridge.Ventral whorls radial growth lines very fine, irregular. Dorsalwhorl interstices striations very fine, dense, regularly spaced,somewhat conspicuous. Ventral whorls spiral striations veryfine, dense, regularly spaced, somewhat conspicuous.Umbilicus open, small.

Distribution. Rahula tonywhitteni is known only from thetype locality, PRK 01 Gunung Tempurung (Fig. 2).

Remarks. Rahula tonywhitteni shares with R. jucunda fromnorthern Vietnam and R. munipurensis Godwin-Austen,1907, from north-eastern India several shell characters:prominent sub-peripheral radial ridge, convex whorls andglobose shell (Godwin-Austen, 1907; Bavay & Dautzenberg,1912). However, the aperture of R. tonywhitteni is moreelongated than in the other two species, which possess morerounded apertures. Rahula tonywhitteni differs from thegeographically close R. limbooliati, new species, in havinga small but open umbilicus, somewhat sharp sub-peripheralkeel and protoconch with prominent radial ribs angledtowards the apex.

Fig. 3. Rahula tonywhitteni, new species. A, holotype (BOR/MOL 11422); B, paratype (BOR/MOL 12536); C, paratype (BOR/MOL11207); D, close-up of the apical whorls of BOR/MOL 11207; E, close-up of the apical whorls of BOR/MOL 12536; F, close-up of theumbilical side of BOR/MOL 11422. All specimens from PRK 01 Gunung Tempurung, Perak, Peninsular Malaysia.

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Foon & Marzuki: Two new Rahula from Peninsular Malaysia

ACKNOWLEDGEMENTS

We thank two anonymous reviewers for their comments.Materials examined were obtained during research workspermitted by the Department of Wildlife and ParksPeninsular Malaysia (JPHL&TN(IP):100 34/1.24Jld 6(14)),the Forestry Department of Peninsular Malaysia (JH/100 Jld.14(9); PPN.PK 600/03/01Jld 9(62); AM-PM-202-16) andthe Economic Planning Unit (Permit number 1773).

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