An evaluation of members of the genera Clithon and Neritina

Molluscan Research 25(2): 75–84 

http://www.mapress.com/mr/ 

ISSN 1323-5818 

Magnolia Press 

An evaluation of members of the genera Clithon Montfort, 1810 and Neritina 

Lamarck 1816 (Gastropoda: Neritidae) 

ALISON HAYNES 

Institute of Applied Sciences, University of the South Pacific, P.O. Box 1168, Suva, Fiji. 

Email alisonh@connect.com.fj 

COPYRIGHT © 2005 MALACOLOGICAL SOCIETY OF AUSTRALASIA 

Abstract 

The spermatophores, the male head region and penis and the operculum of 10 species of Clithon and 14 species of Neritina are 

described. The female reproductive systems of species of Clithon and Neritina are compared. The study confirmed that two 

genera can be recognised. Species of Clithon, whether spined (e.g., C. spinosa, C. corona) or not (e.g., C. olivaceus, C. 

oualaniensis), have a curved indentation along the middle of the operculum, spermatophores with a long filament, a penis 

pouch in the head region and a short vaginal duct. Neritina species are more variable but their spermatophores lack a long filament, 

they have no penis pouch and they have a long vaginal duct that leaves the vagina near the spermatophore sac. 

Introduction 

Key words: Neritidae, Clithon, Neritina, operculum, penis, spermatophore, polymorphism 

In the past, authors (Baker 1923; Kay 1979; Komatsu 1986, 

Bandel 2001) have been inconsistent in placing freshwater 

species, belonging to the family Neritidae, in the genera 

Clithon Montfort, 1810, Neritina Lamarck, 1816 or 

Theodoxus Montford, 1810. 

It has long been established that species of Theodoxus 

have no larval stage but develop with the aid of nurse cells 

into small adults (Bondeson 1940; Fretter and Graham 1962; 

Holthuis 1997). In addition, the modern distribution of 

Theodoxus is European, Middle Eastern and North African 

(Andrews 1935; Brown 1980; Holthuis 1997; Bandel 2001). 

The eggs of Clithon and Neritina develop into free 

swimming veligers and usually settle in brackish water (Ford 

1979; Govindan and Natarajan 1972; Nishiwaki and Koike 

1985; Schneider and Frost 1986) with many adults of both 

species spending the rest of their lives and laying their eggs 

in egg cases in fresh water. Others, e.g. Neritina auriculata 

and Clithon diadema, remain all their lives in brackish water 

(Andrews 1935; Benthem Jutting 1956; Starmühlner 1976; 

Haynes 1988b). Both genera are distributed in tropical 

regions of Asia and the Pacific and Indian Ocean islands. 

Neritina species are also found in Central America, the 

Caribbean and along the West African coast (Andrews 1937; 

Brown 1980; Houston 1990; Russell 1941). 

Recently Bandel (2001) suggested that Clithon was not 

a valid genus and that all species previously designated 

Clithon should be classified as Neritina, although this is not 

the generally held opinion (Starmühlner 1976, 1983; Haynes 

1985,1988a, 2001a; Holthius 1997). Bandel (2001) described 

specimens that he thought resulted from the two genera 

interbreeding in the rivers of Bali (Indonesia) and in the 

Matutinao River, Ceba (Philippines). However, many species 

of neritids are polymorphic (Grünberg 1976, 1982; Gardner 

and Mather 1995; Haynes 2001b) and identification using 

shell shape and colour patterns can be confusing and 

misleading. Bandel (2001) based his conclusions on a study 

of protoconchs, shells and some radulae. 

Studies of the reproductive anatomy of neritids show 

general uniformity but there is considerable variation in their 

secondary sexual characteristics. Andrews (1937) studied the 

spermatophores of Neritina gagates Lamarck,1822; Neritina 

virginea (Linné, 1758); N. pulligera (Linné, 1758) and N. 

vespitina Sowerby, 1849, while Starmühlner (1976 1983, 

1993) illustrated reproductive systems and spermatophores 

of many Clithon and Neritina species. 

Holthius (1997) undertook a more rigorous analysis of 

the characters of the Neritopsina (Neritimorpha) including 

the genera of Clithon and Neritina. She placed Clithon 

species in a separate genus but tentatively placed all Neritina 

and Septaria (limpet) species in the genus Septaria Férrusac, 

1807 (because the genus Septaria predates the genus 

Neritina). However, this decision was based on a study of 

only one species of Septaria, S. janelli (Récluz, 1841) and 

the suggestion that all species of Neritina and Septaria 

should be combined in the genus Septaria cannot be justified 

when all 13 species of Septaria are considered (Haynes 

2001b). 

In the present study the opercula, spermatophores, 

penes and female reproductive systems of many species of 

both Clithon and Neritina were investigated. 

Material and Methods 

Clithon and Neritina species were collected from various 

streams on the islands of Taveuni, Ovalau, Viti Levu (Fiji), 

Éfate, Pentecost (Vanuatu), Guadalcanal, Makira, New 

Georgia (Solomon Islands), Moorea (French Polynesia), 

Mauritius, Hawaii, Costa Rica, Trinidad and Dominica (see 

Table 1) were preserved in 80% ethanol and later dissected in 

the laboratory. The shell, operculum, male head and 

spermatophores were studied and compared. Female 

specimens of each species were dissected and the anatomy 

compared. Spermatophores were removed from the 

spermatophore sac of female specimens of each species. 

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The shells of the species investigated are illustrated in 

Figs 1 and 2 and their taxonomic data, distribution and 

TABLE 1. Species investigated, their synonyms, distribution and taxonomic information. 

HAYNES (2005) MOLLUSCAN RESEARCH, VOL. 25 

voucher numbers at the Australian Museum, Sydney are 

listed in Table 1. 

Species Synonyms Distribution Type AM No. 

Clithon bicolor (Récluz,1843) Nerita bicolor South east Asia Philippines C436883 

Solomon Is. MNHN 

Vanuatu examined 

Clithon corona (Linné, 1758) Nerita corona South east Asia Asia C436884 

Neritina corona Pacific Is. not MHNG 

Neritina brevispina Lamarck, 1816 French Poynesia examined 

Clithon coronata (Leach, 1815) 

Clithon brevispina Riech,1937 

Nerita coronata Indian Ocean Islands Not examined C436885 

Nerita longispina Récluz, 1841 

Clithon diadema (Broderip, 1832) Nerita diadema Récluz,1841 South east Asia Islands of the C436886 

New Guinea, Sol. Is. South Seas. 

Clithon diadema Vanuatu, Samoa, Whereabouts 

Souleyetana Riech; Starmühlner Fiji unknown 

Clithon francoisi (Nabille,1895) Neritina francoisi Sol. Islands, Vanuatu Not examined C436887 

Clithon glabrata) (Sowerby, 1849) Neritina glabrata West Africa Not examined missing 

Clithon olivaceus (Récluz, 1843) Nerita olivacea South east Asia Luzon, C436888 

Neritina olivacea Pacific Is. not French Polynesia Philippines 

Clithon olivacea Riech MNHN examined 

Clithon oualaniensis (Lesson, 1931) Pictoneritina Asia and Pacific Ovalau, Fiji C436889 

oualaniensis MNHN 

Neritina oualaniensis examined 

Clithon pritchardi (Dohrn, 1861) Clithon corona Vanuatu, New Caledonia, Fij Fiji, BMNH C436890 

Starmühlner, 1976 examined 

Clithon spinosus (Sowerby, 1825) Neritina spinosus French Polynesia Tahiti, BMNH C436891 

(ex Budginin) Neritina souleytana examined 

Clithon squarrosus (Récluz, 1843) Nerita squarrosus South east Asia, Negros, C436892 

Neritina squarrosus N. Guinea, Sol. Is. Philippines 

Vanuatu MHNG 

examined 

Neritina auriculata Lamarck, 1816 Neritina taitensis Asia, Indian Ocean Ile Marie C436893 

Neripteron auriculata and Pacific MNHN 

Neritina ( Neripteron) auriculata examined 

Neritina canalis Sowerby, 1825 South East Asia, Pacific 

Islands, including French 

Polynesia 

Iles des Mers du Sud 

missing 

C436894 

Neritina gagates Lamarck,1822 Neritina mauritiana Indian Ocean Is. Examined C436895 

Morelet, 1867 East Africa Type MNHN 

Neritina granosa Sowerby, 1825 Neritina (Neritona) granosa Hawaiian Is. Not examined C436896 

Neritina latissima Broderip, 1853 Neritina (Neritona) latissima Pacific coast of Central & 

tropical South America 

Not examined C436897 

Neritina macgillivrayi Reeve, 1855 Neritina (Neritona) macgillivrayi South East Asia, Sol. Is., Port Carteret C436898 

Neritona macgillivrayi N. Caledonia, Fiji, Samoa BMNH examined 

......continued on the next page

GENERA CLITHON AND NERITINA 77 

TABLE 1 (continued) 

Species Synonyms Distribution Type AM No. 

Neritina neglecta Clithon neglectus Hawaiian Islands Not examined C436899 

Pease, 1860 Clithon(Neritoclithon) neglectus 

Neritina owaniana Wood, 1828 Neritina (Neripteron) owaniana West Africa Ivory Coast C436900 

Results 

Two or more unspent spermatophores were found folded 

within the spermatophore sac of most females. They were 

long, cream, shiny tubes and were different in shape in each 

species. Also present within the spermatophore sac was a 

dark granular liquid with fragments of empty 

spermatophores. The open end of one spermatophore was 

often inside the vagina while the rest remained in the 

spermatophore sac. 

The spermatophores of Clithon species , C. bicolor 

(Fig. 3B), C. corona (Fig. 3F), C. diadema (Fig. 3J), C. 

pritchardi (Fig. 3N), C. spinosus (Fig. 4C), C. squarrosus 

(Fig. 4H), C. coronata (Fig. 4M), C. oualaniensis (Fig. 4P), 

C. olivaceus (Fig. 5C), C. francoisi (Fig. 5H) were all similar 

MCZ as Neritina 

tiassalensis Binder 

Neritina pulligera (Linné, 1767) Nerita pulligera Asia, Madagascar 

1954. examined 

India C436901 

E. Africa, Pacific Is paratype Sumatra 

Not Fr. Polynesia MCZ examined 

Neritina punctulata Lamarck, 1816 Neritina (Nereina) punctulata Atlantic coast of Port Antonio C436902 

tropical America, Jamaica 

Caribbean Is. Not examined 

Neritina taitensis Lesson 1831 Neritina dilata French Polynesia, Tahiti C436903 

Neritina (Neripteron) taitensis S. Pacific Is., MNHN 

Philippines examined 

Neritina turrita (Gmelin, 1791) Nerita roissyana Indo-Pacific, Guam Not examined C436904 

Recluz,1841; Taiwan, Fr. Polynesia 

Neritina variegata Lesson, 1831 

Neritina roissyana 

Neritina (Vittina) 

turrita 

Neritina (Vittoida) South East Asia New Ireland C436905 

variegata Sol. Is., Vanuatu 

Fiji, Samoa, Guam, 

Ponape, Truk 

missing 

Neritina vespitina Sowerby 1849 Theodoxus vespitina 

Neritina (Neripteron) 

vespitina 

Hawaiian Islands Not examined C436906 

Neritina virginea (Linné, 1758) Neritina (vitta) Tropical coast N.S. St Dominique, C436907 

virginia & C. America, Caribbean NHMG, examined 

AM Australian Museum; BMNH The Natural History Museum, London; MCZ Museum of Comparative Zoology, Cambridge; MHNG Museum d'Histoire 

Naturelle. Geneva; MNHN Museum National d'Histoire Naturelle, Paris (Cowie, 1998; Cowie et al., 1995; Kabat & Finey, 1992; Pointier & Marquet, 1990; 

Riech, 1937) 

with a long open-ended filament. Similarly all Clithon 

species, had a pouch in the anterior head region where the 

penis is usually tucked away (Figs 3E, I, M, 4A, B, F, 5A, B, 

F.,G). Although not illustrated here, Holthuis (1997) 

mentioned the presence of a penis pouch in C. oualaniensis. 

The opercula of all Clithon have a groove on the outer 

surface (Figs 3D, H, L, P, 4E, J, O, R, 5E, J) which appears 

as a ridge on the inner surface (Figs 3C, G, K, O, 4D, I, K, N, 

Q, 5D, I). The thin horn border on the outer edge of each 

operculum was narrow and orange coloured. 

Although the spermatophores and penes of Neritina 

species were more variable, none of the spermatophores had 

a long filament, and no Neritina had a penis pouch. Neritina 

variegata and Neritina turrita (Fig. 5L, M, Q) had 

spermatophores enclosed in an envelope and a penis that was

78 

flat and folded (Fig.5K, P). Baker (1923) placed them in the 

subgenera Vittoida and Vittina respectively (Table 2). N. 

variegata had two different types of spermatophores (Fig. 

5L, M ); both kinds were obtained from specimens living in 

the same stream on Ovalau island, Fiji, suggesting that they 

were from the same species, although the existence of cryptic 

species cannot be discounted. N. variegata is unique among 

Neritina and Clithon in lacking a thin horn border to its 

operculum (Fig. 5N, O). Other Neritina have an amber to 

dark red border on the outer edge. 

FIGURE 1. Ventral view of the shells of the species investigated: 

A. Clithon bicolor, length 24 mm (Melsisi R., Pentecost, Vanuatu); 

B. Clithon corona, length 23 mm (La Marona R., Éfate, Vanuatu); 

C. Clithon coronata, length 18 mm (Bae de Cap, Mauritius); D. 

Clithon diadema, length 15 mm (Naisogo Creek, Ovalau, Fiji); E. 

Clithon francoisi, length 16 mm (La Marona R., Éfate,Vanuatu); F. 

Clithon olivaceus, length 19 mm (Naisogo Creek, Ovalau, Fiji); G. 

Clithon oualaniensis, length 8 mm (Taveuni, Fiji); H. Clithon 

pritchardi, length 23 mm (Naisogo Creek, Ovalau, Fiji); I. Neritina 

neglecta length 10 mm (Kolekole R. Hilo, Hawaii); J. Clithon 

spinosus, length 22 mm (Maatea R., Moorea, French Polynesia); K. 

Clithon squarrosus, length 20 mm (Melsisi, Pentecost, Vanuatu); L. 

Neritina auriculata, length 14 mm (Moorea, French Polynesia); M. 

Neritina canalis, length 21 mm (Naisogo Creek, Ovalau, Fiji). 

FIGURE 2. Ventral view of the shells of the species investigated: 

A. Neritina gagates, length 18 mm (Bae de Cap, Mauritius); B. 

Neritina granosa, length 30 mm (Kolekole R. Hilo, Hawaii); C. 

Neritina latissima, length 23 mm (Rio Tarcolitos, Costa Rica); D. 

Neritina macgillivrayi, length 23 mm (Puha R., New Georgia, 

Solomon Islands); E. Neritina oweniana, length 20 mm (Ivory 

Coast); F. Neritina pulligra, length 31 mm (Nabukavesi Creek, Viti 

Levu, Fiji); G. Neritina punctulata, length 20 mm (Layou R., 

Dominica); H. Neritina taitensis, length 13 mm (Moorea, French 

Polynesia); I. Neritina turrita, length 18 mm (Opunohu R., Moorea, 

French Polynesia); J. Neritina variegata, length 18 mm (Naisogo 

Creek, Ovalau, Fiji); K. Neritina vespitina, length 27 mm (Waiakea 

ponds, Hilo, Hawaii); L. Neritina virginea, length 18 mm (Shark R., 

Trinidad). 


The Indian Ocean N. gagates ( Fig. 6A, B) and the 

Caribbean N. virginea (Fig. 6G, H) and N. punctulata (Fig. 

6K, L) have similar folded spermatophores and folded penes. 

Baker (1923) placed N. gagetes and N.virginea in the 

subgenus Vitta but N. punctulata in the subgenus Nereina 

(Table 2). 

The group comprising Neritina vespitina (Fig. 7 E, H), 

N. auriculata (Fig. 7I, L) and N. tatiensis (Fig. 7M, P) all 

have similar spermatophores with a spiral band that appears 

as a white thread attached to the outer membrane. They also 

have similar penes with a papilla and all have winged shells 

(Figs 1L, 2H, K). They have been placed in the subgenus 

Neripteron (Baker 1923; Starmühlner 1976). The Hawaiian 

species N. neglecta (Fig. 8A–D), although without wings, 

has similar spermatophores with a spiral. It appears to be 

related to this group and is not a Clithon as previously 

classified (Baker 1923). Other species apparently in this 

group, that were included in the subgenus Neritina by Baker 

(1923), are the widely distributed species N. pulligera (Fig. 

8E - H) and N. canalis (Fig. 8I–L). N. petitii, N. porcata and 

N. squamipicta (not illustrated) also have spermatophores 

with a spiral thread and belong to this group (pers. observ.). 

Neritina macgillivrayi (Fig. 8M–P) differs from the 

other congeners in having a small, grooved penis, rigid 

swollen spermatophores and a wide horn border to the 

operculum. It has been placed in the subgenus Neritona with 

N. granosa; both have a wide horn border to their operculum 

but their spermatophores and penes are dissimilar from other 

taxa (Figs 8M, N, 7 A, B).


TABLE 2. Subgenera of Neritina species, proposed by Baker, 1923 and later used by Starmühlner and others. 

Subgenus Origin Species 

Baker, 1923 Starmühlner, 1976, 1983, 1988 

Neritina Lamarck, 1816 pulligera pulligera, canalis, petitii, porcata, asperulata 

Neripteron Lesson,1831 latissima 

oweniana 

taitensis 

vespitina 

auriculata 

Neritona Sowerby, 1841 granosa macgillivrayi 

Nereina Cristofori & Jan, 1832 punctulata punctulata 

Vitta Morch,1852 virginea 

glabrata 

virginea 

Vittina Baker, 1923 turrita, turrita 

gagates gagates 

Vittoida Baker, 1923 variegata 

turtoni 

turtoni 

variegata 

FIGURE 3. A–D. Clithon bicolor (Melsisi, Pentecost, Vanuatu), A, 

male head with penis (dorsal view); B, spermatophore; C, D, 

operculum, inner (C) and outer (D) views. E–H. C. corona (La 

Marona, Éfate, Vanuatu), E, dorsal view of penis showing position 

of pouch; F, spermatophore; G, H, operculum, inner (G) and outer 

(H) views. I–L. C. diadema (Naisogo Creek, Ovalau, Fiji), I, dorsal 

view of penis; J, spermatophore; K, L, operculum, inner (K) and 

outer (L) views. M–P C. pritchardi (Naisogo Creek, Ovalau, Fiji), 

M, dorsal view of penis; N, spermatophore; O, P, operculum, inner 

(O) and outer (P) views. Scale bar = 1 mm 

e eye, f filament, hb horn border, p penis, pa papilla, pp penis 

pouch, r ridge, t tentacle, s snout, v vagina. 

FIGURE 4. A–E Clithon spinosus (Maatea R., Moorea, French 

Polynesia), A, penis stored in pouch; B, dorsal view of penis; C, 

spermatophore, D, E, operculum, inner (D) and outer (E) views. 

F–J C. squarrosus (Melsisi, Pentecost, Vanuatu), F, penis stored in 

pouch; G, dorsal view of penis; H, spermatophore; I, J, operculum, 

inner (I) and outer (J) views. K–L C. glabrata (Angola), 

operculum, inner (K) and outer (L) views. M–O C. coronata (Bae 

de Cap, Mauritius), M, spermatophore; N, O, operculum, inner (N) 

and outer (O) views. P–R C. oualaniensis (Taveuni, Fiji), P, 

spermatophore; Q, R, operculum, inner (Q) and outer (R) views. 

Scale bar = 1 mm. 

f filament, g groove, pa papilla, pip penis in pouch, r ridge, s 

snout.

80 

FIGURE 5. A–E Clithon olivaceus (Naisogo Creek, Ovalau, Fiji), 

A, penis stored in pouch; B, dorsal view of penis; C, 

spermatophore; D, E, operculum, inner (D) and outer (E) views. 

F–J C. francoisi (Kirikiri R., Makira, Solomon Islands), F, penis 

stored in pouch; G, dorsal view of penis; H, spermatophore; I, J, 

operculum, inner (I) and outer (J) views. K–O Neritina variegata 

(Naisogo Creek, Ovalau, Fiji), K, dorsal view of penis; L, M 

spermatophores; N, O, operculum, inner (N) and outer (O) views. 

P–S Neritina turrita (USP drain, Viti Levu, Fiji), P, dorsal view of 

penis; Q, spermatophore; R, S, operculum, inner (R) and outer (S) 

views. Scale bar = 1 mm. 

em enveloping membrane, f filament, g groove, p penis, pa 

papilla, pip penis in pouch, s snout, se spermatophore. 

The opercula of all Neritina species lack the median 

groove (ridge) found in Clithon species. The lower apophysis 

(peg) on the operculum varied in the species of Neritina, 

from absent in N. neglecta (Fig. 8 C, D) or very small in N. 

granosa (Fig. 7 C, D) and N. oweniana (Fig. 6E, F) to large 

in N. gagates (Fig. 6C, D) and N. latissima (Fig. 6Q, R). 

The female reproductive systems are similar to other 

Neritidae (Starmühlner 1976; Holthuis 1997, Haynes 2001b). 

Those of Clithon and Neritina (Fig. 9A–F) are very similar 

except in one respect. Clithon bicolor (Fig. 9A) and C. 

olivaceus (Fig. 9B) are typical of all Clithon dissected. The 

vaginal duct is short, leaving the vagina not far from the 

vaginal opening, while in all Neritina (Fig. 9C–F) it leaves 

the vagina much closer to the spermatophore sac and often it 

is at first closely applied to the vagina. A shorter vaginal duct 

is apparently possible in Clithon species because the long 

filament of the spermatophores extends along the vagina and 

allows the sperm to enter the vaginal duct more directly. 


FIGURE 6. A–D Neritina gagates (Bae de Cap, Mauritius) A, 

dorsal view of penis; B, spermatophore; C, D, operculum, inner (C) 

and outer (D) views. E–F N. oweniana (Liberia), E, F, operculum, 

inner (E) and outer (F) views. G–J N. virginea (Shark R., Trinidad), 

G, dorsal view of penis; H, spermatophore; I, J, operculum, inner (I) 

and outer (J) views. K–N N. punctulata (Layou R., Dominica), K, 

dorsal view of penis; L, spermatophore; M, N, operculum, inner 

(M) and outer (N) views. O–R N. latissima (Rio Tarcolitos, Costa 

Rica), O, dorsal view of penis; P, spermatophore; Q, R, operculum, 

inner (Q) and outer (R) views. Scale bar = 1 mm. 

e eye, g groove, p penis, s snout, t tentacle 

Discussion 

Many species, attributed to Clithon, when living in brackish 

water, have individuals with spined shells. The presence of 

spines is sometimes given as a diagnostic character of 

Clithon (e.g., Cossmann 1925). It is true that all neritid 

specimens with spines belong to the genus Clithon, but all 

Clithon species do not have spines. Young specimens of 

Clithon diadema, C. corona, C. spinosus, C. bicolor, C. 

squarossus and C. pritchardi usually do have spines. 

Starmühlner (1976) suggested that spines were present when 

species of Clithon lived in brackish water but were absent 

when they lived in fresh water. This was not confirmed when 

Haynes (1988b) collected Clithon pritchardi along the length 

of streams in Fiji. When C. pritchardi were measured and the 

presence or absence of spines noted, 80% of those with 

spines were between 5–20 mm long while 85 % between 15–


30 mm long were without spines. This suggested that age 

was more important in determining the presence or absence 

of spines. It is likely that the spines get broken off through 

wear. However, the Pacific species Clithon castanea, C. 

oualaniensis, and C. chlorostoma have never been found 

with spines and C. francoisi and C. olivaceus rarely have 

spines (Haynes 1988a, 1993, 2000). Many Clithon species 

live in brackish or tidal water, but C. castanea and C. 

olivaceus live well beyond the reach of the tide in steep, fast 

flowing streams in Fiji (Haynes 1988a). 

FIGURE 7. A–D N. granosa (Kolekole R.,Hilo, Hawaii) A, dorsal 

view of penis; B, spermatophore; C, D, operculum, inner (C) and 

outer (D) views. E–H N. vespitina (Waiakea ponds, Hilo, Hawaii), 

E, dorsal view of penis; F, spermatophore; G, H, operculum, inner 

(G) and outer (H) views. I –L N. auriculata (Moorea, French 

Polynesia), I, dorsal view of penis; J, spermatophore; K, L, 

operculum, inner (K) and outer (L) views. M–P N. taitensis 

(Moorea, French Polynesia), M, dorsal view of penis; N, 

spermatophore; O, P., operculum, inner (O) and outer (P) views. 

Scale bar = 1 mm. 

e eye, p penis, pa papilla, s snout, sb spiral band, t tentacle. 

Shells of the small-sized Clithon oualaniensis have 

many colour and pattern forms (Grüneberg 1976, 1982; 

Gardener and Mather 1995) while the shells of many Clithon 

and Neritina species in a particular stream can resemble one 

another in colour and markings (Resh et al. 1990; Haynes 

1993, 2000). This does not indicate that interbreeding has 

taken place but more likely that shell markings are induced 

by selection or environmental factors. Gardner and Mather 

(1995) found that populations of C. oualaniensis in 

Queensland, Australia were highly polymorphic but 

nevertheless belonged to the same gene pool. The differences 

in shell form frequencies were related to microhabitats and 

were due to a combination of frequency dependent selection 

and selection for crypsis. 

FIGURE 8. A–D Neritina neglecta (Kolekole R., Hilo, Hawaii), A, 

dorsal view of penis; B, spermatophore; C, inner surface of 

operculum; D, outer surface of operculum. E–H N. pulligera 

(Nabukavesi Creek, Viti Levu, Fiji), E, dorsal view of penis; F, 

spermatophore; G, H, operculum, inner (G) and outer (H) views. 

I–L N. canalis (Opunohu R., Moorea, French Polynesia), I, dorsal 

view of penis; J, spermatophore; K, L. operculum, inner (K) and 

outer (L) views. M–P N. macgillivrayi (Puha R., New Georgia, 

Solomon Islands), M, dorsal view of penis; N, spermatophore; O, P, 

operculum, inner (O) and outer (P) views. Scale bar = 1 mm. 

g groove, p penis, pa papilla, s snout, sb spiral band, t tentacle, v 

- vagina 

Polymorphism in the genera Clithon, Neritina and 

Septaria has led to erroneous identification of specimens by 

Starmühlner (1976, 1983) and Haynes (1985, 1988a) who 

placed female Septaria suffreni in S. porcellana). Bandel 

(2001) made several wrong identifications, e.g. his 

specimens from Bali with a horn border in his figures 126-

82 

129 are identified as Neritina variegata but are probably N. 

turrita or N. zigzag. They are not N. variegata, as it is the one 

Neritina species that lacks a horn border on its operculum. 

Bandels Septaria porcellana, collected from Umzamba 

Interbreeding was suggested between Clithon and 

Neritina species by Bandel (2001), but it is highly unlikely 

considering the differences in the male and female 

reproductive anatomy of each genus (e.g. shape of the 

spermatophores and penes and the length of the vaginal 

duct). Such differences would lead to incompatibility during 

spermatophore transfer and egg fertilization 

Baker (1923) divided the genus Neritina into five 

subgenera (Table 2); Neritona, Neripteron, Vittina, Vitta and 

Neritina and these further into eight more divisions. These 

divisions were based mainly on radular differences. 

However, subsequent researchers (Starmühlner 1976; 


estuary (South Africa), is S. tessellata judging by his figures. 

It is doubtful if S. porcellana is found in East Africa (Haynes 

2001b). 

FIGURE 9. View of female reproductive organs from right side: A, Clithon bicolor (Melsisi R., Pentecost, Vanuatu). B, C. olivaceus 

(Naisogo Creek, Ovalau, Fiji). C, Neritina canalis (Naisogo Creek, Ovalau, Fiji). D, N. macgillivrayi (Puha R., New Georgia, Solomon 

Islands). E, N. granosa (Kolekole R., Hilo, Hawaii). F, N. vespitina (Waiakea ponds, Hilo, Hawaii). Scale bar = 5 mm. 

ag albumen gland, cg capsule gland, de ductus enigmaticus, fo female opening, o ovary, rs receptaculum seminis, s spermatophore sac, 

v vagina, vd vaginal duct, vo vaginal opening 

Holthuis 1997; Haynes 2001b) found radulae unhelpful as 

they vary as much within species as between them. Using 

radulae, Baker(1923) and Komatsu (1986) placed Neritina 

with relatively tall spires (e.g., N. viginea, N. turrita and N. 

variegata) in the subgenera Vitta, Vittina or Vittoida and 

those with flat shells,(e.g., N. auriculata and N. taitensis) in 

the subgenus Neripteron. This division into two subgenera 

on the basis of shell shape flat and high, separated from 

Neritina s. s. (with medium-spired shells) is sometimes 

useful, but the differences in penes, spermatophores and the 

changes in shell shape with age within these proposed 

subgenera make the divisions more of a convenience than a


reflection of actual relationships. As justification for these 

groupings was not confirmed by this study, it is 

recommended that these subgeneric names not be used. 

Generic diagnoses 

Neritina Lamarck, 1816 

Type species: Nerita pulligera Linné, 1766. 

Shells smooth, brown sometimes with patterns of lighter 

stripes, flecks or spots. The first enlarged whorl totally or 

nearly obscures the other whorls. The ventral side has a 

lighter columellar area that is often brightly coloured. The 

columellar edge is smooth or finely serrated. The large 

aperture can be closed by an operculum, which has a smooth 

outer surface and a thin red-brown, horn border (in all but N. 

variegata). The spermatophores are variable in length, with 

or without an enclosing envelope or an internal radial thread, 

but never with an external filament. The vaginal duct is long 

and leaves the vagina near the spermatophore sac. Penes are 

variable and there is never a penis pouch in the male head 

region. 

Clithon Montfort, 1810 

Type species: Nerita corona Linné, 1758, 

Shells similar to those of Neritina except they are more 

likely to be ridged or wrinkled and have spines, especially 

when young. Spines are easily broken off or eroded. Many 

small Clithon, e.g. C. oualaniensis and C. chlorostoma, have 

smooth shells and never have spines (often placed in a 

separate subgenus Pictoneritina). Other larger Clithon 

species e.g. C. olivaceus and C. castanea also lack spines but 

otherwise resemble spined Clithon taxa. The operculum is 

always present. It has a narrow outer orange horn border and 

a curved indentation along the middle from the columella 

edge to the nucleus. There is a large tooth on the serrated 

edge of the columella where the indentation of the 

operculum fits. The spermatophores have a long filament and 

the short vaginal duct leaves the vagina near the vaginal 

opening. The penis fits into a pouch on the right side of the 

head. 

Theodoxus Montford, 1810 

Type species: Nerita fluviatilis Linné, 1758. 

Shells similar to those of Neritina, smooth with lighter 

markings. They differ from Neritina and Clithon in that the 

operculum has both an outer and inner horn border and they 

have no spermatophores or larval stage . 

Acknowledgements 

I thank the University of the South Pacific and the Linnean 

Society of London (Percy Slade Memorial Fund) for funds 

that made this work possible. 

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An evaluation of members of the genera Clithon and Neritina

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