East African Slugs Of The Family Urocyclidae

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Special Supplement No. 7

APRIL 1961

by B. VERDCOURT, PH.D., P.L.S., B.SC. and R. POLHILL, B.A.

Cover design by Mrs. V. M. Hemming Price Shs. 7/50
4th April, 1961

Eait African Slugs



Simroth in Nova Acta Leop.-Carol. 54, 54 (1889); Pilsbry in Bull. Am. Mus. Nat. Hist. 40, 295 (1919) Rather large to very large slugs with small globular flagellum and a tubular lime gland; dart sac
usually very large with thick muscular walls containing calcareous darts which are often very long (save in the subgenus Atrichotoxon). Genotype, T. heynemanni Simroth


In tropical regions the problems of specific differentiation are often much more difficult than, for example, in Britain; this is not merely due to the great difference in the amount of work which has been carried out in the latter country. Species do appear to grade into each other in some tropical groups and the more material one examines the more confused does the situation become. When a little material is available from a small area one finds that several distinctive forms appear to be recognisable but when an abundance of material is available from a much wider area these distinctions often break down.

At present in this family of slugs, we are describing but sometimes not naming the various varieties which have come to hand, until there is a better understanding of what constitutes true specific characters. Several warnings are necessary to would-be describers of slugs who have not seen populations of these aninials in the field. Colour variation is spectacular in some areas, e.g. in slugs on Mt. Kulal and in the Nyambeni Hills (both in Kenya) there is amazing variation in the colour scheme but there is a certain basic underlying pattern which is only evident to a field worker, e.g. in one area a slug may vary from greenish-yellow to bright salmon and yellow or be greenish with big spots all over it but the head is always greenish-yellow and the fringe reddish-salmon; in other areas another range of colour variation may be found in another variant but the fringe is always purple and one receives the impression that these two populations are clearly distinguishable by certain basic colour
patterns. In other areas, however, species are uniform in colour.

This genetic stability or instability in the matter of colour has been used as a subspecific character even where other morphological characters are obscure. Apart from these intrinsic difficulties there
are some practical ones. Examination of the darts to see if they have the crystals produced (Le. are hairy) should be done under water, in which case the hairs spring out; examined dry or in certain
mounting media the hairs are closely adpressed and appear to present merely a roughening of the dart surface. We have made this error ourselves and it is so easy to do that not too much notice should be taken of old descriptions, although Simroth undoubtedly was aware of this difficulty; The shape of the dart sac, degree of bilobing at the apex and size· of the darts varies as the slug reaches maturity. A previously unknown fact is that there are darts present in the dart sacs of quite juvenile slugs; as the sac grows so do the darts. Another fact which must be borne in mind before too much emphasis is placed on some morphological characters one has discovered, is that there are often
distinct phases, where first the female ducts and then the male ducts are relatively undeveloped, e.g. the fact that one finds an albumen gland in one individual four times as large as that in another may be of no value whatsoever as a character. The relative positions of various twists and loops of the ducts in situ also vary a good deal-it is easy to imagine that these are going to vary and get orientated in slightly different ways as different individuals mature.

The well-marked subgenera may be separated by a key similar to that given by Pilsbry:-

1. Oviduct entering at or near the apex (distal end) of the combined atrium and dart sac


I. Oviduct entering at middle or base (proximal end) of combined atrium and dart sac .


2. Four to six darts in pairs (14 in T. robustum)

subg. Trichotoxon

t 2. No darts


3. Eight or more slender needle-like darts

3. One spiral dart


subg. Atrichotoxon subg, Polytoxon subg. Spirotoxon

The subgenera of Trichotoxon are to my mind considerably more distinct than the group of genera related to Urocyclus but I have hesitated to raise them to full generic rank.
Subgenus Trichotoxon sensu stricto

Subgenus Diplotoxon Simroth in Reise in Ostafrika A. Voeltzkow 1903-5,Wiss. Ergebn. 2, 593

t Continued

from Journ. E. Afr. Said to be two only

Nat. in T.

Hist. Soc. 23, 240 roccatii Pollon.


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East African Slugs

(1910) and in S.B. nll,turf. Ges. Lpz. (1895-6), 149-150 (1897). Subgenotype, T. heynemanni Simroth. Subgenus Dendrotoxon Pollonera in Ann. Mag. Nat. Hist. (8), 8, 332 (1911)
This was proposed for T. kempi Pollon., T. presioni Pollon. and T. keniensis Pollon. and no subgenotype was chosen. I hereby choose T. keniensis since that species does have an anatomy rather different from Trichotoxon sensu stricto and the name will therefore be available if necessary.
Subgenus Trichotoxon is characterised by the strong muscular dart sac combined with the atrium, with the oviduct entering at the distal end. The species are usually very large. Pollonera defines his Dendrotoxon by saying that on the upper extremity of theepiphallus there is a true but very small flagellum instead of a calcareous gland.

Key to the species

l. Penis entering base of dart sac; spermatheca and oviduct entering at apex



1. Penis spermatheca and oviduct all entering at the apex of the dart sac ..

T. robustum

(Simroth does not make the anatomy of T. neumanni and T. athrix clear-from the simple

Latin diagnoses where he says "praecedente (i.e. robustum) similis" one might conclude

that they were both similar to robustum but the number of darts he mentions indicates that

they should be referred to the subgenus Polytoxon)

2. Vagina with globose swelling below the junction of the oviduct and spermathecal duct;

dart sac containing three pairs of darts; body with glaring white spots of secretion.


T. martensi

2. Vagina tubular, absent or adnate to the dart sac; in the last case often swollen but other

characters not as above



3. Mantle with marked longitudinal raised rugae giving a corrugated appearance. Body

white or grey-ochraceous, or greenish-yellowish-white, a few of the grooves of the hind

body black. Dart sac-atrium 2.5-3 cm. long, acutely bifid at apex; base of oviduct swollen,

vagina adnate to sac. (Usambaras and Teita area)

T. heynemanni

(See text for discussion of T. conradti)

3. Mantle reticulate or if rugose other characters not as above



4. Mantle "sulcate and rugose", tops of rugae calcareous white; body brownish covered

with blackish-grey large spots and minute white spots of calcareous secretion. Dart sac-

atrium swollen just above the base and below the apex, bilobed but lobes blunt and not

diverging, about 23 mm. long in total length. (Aberdares) ..

T. kempi

(N.B. The specimen I have identified with this has very hairy darts) 4. If body spotted then without spots of white secretion



5. Vagina or bases of oviduct and spermathecal duct leaving middle of truncate apex of

atrium-dart sac



5. Vagina adnate to one side of the bifid apex of the atrium-dart sac


6. A greenish-brown slug with purple fringe; rain forest of E. Usambaras (3,000 ft.) .

7 T. sp.

6. A greenish-ochre coloured slug covered, when adult, with a mottling of small white irregular

spots; bamboo forests of Kenya highlands (c. 10,000 ft.) ....

T. bambuseti

7. Dart sac-atrium about 3 cm. long, deeply bifid at apex with divergent, sharply pointed

lobes; vagina apparently entering about 1 cm. below the points of the lobes (mantle said

to be rugose)

T. prestoni

7. Dart sac not so sharply bifid at apex nor vagina situated so far below the apex ..


8. Body grey-buff with clusters of obscure bluish spots and a few large white spots; dart sac

large, bulbously enlarged at the base, sharply narrowed above, vagina adnate to apex.

(Zanzibar, Pemba Island) (dart sac appears to be just over 3 cm. long) .

T. voeltzkowi

8. Mainland slugs without above characters combined


9. Dart sac rather swollen below, bluntly bifid at apex; vagina adnate, oviduct swollen at the

base. Darts about 1 cm. long. (Uganda, Sese Islands)


T. maculatum

9. Dart sac more cylindrical, bluntly bifid or quite truncate at the apex, vagina adnate, oviduct scarcely swollen at base. Darts (adult) much longer. Mantle finely reticulate. (Kenya) . 10

10. Dart sac-atrium 2.1-4 cm. long with correspondingly longer darts. Body whitish or yellow-

ish, head greenish, back often deeply suffused with purple· or salmon-red, fringe always

purple or salmon-red. (Kenya, Nyambeni-Meru area) ..

T. nyainbenense

(with subsp. violaceum)

10. Dart sac-atrium smaller, even in large adults only 2.2 em. long, often only 1 cm. long.

Body ochraceous, occasionally with a purple fringe



1l.SpeI1lllltheca more globose with shorter duct; dart sac more swollen abo'Ve the base,

-truncate- to vaguelybilobed at apex, penis thicker. {Kenya, Nairobi,- Thika, Katamayu

areas) ............•

- ...

: .,

T. thikense

11. Spermatheca more ovoid with longer: duct, dart sac cylindrical,: not swollen, truncate at

East African Slugs


Fie. 8b

Fig. !I

apex; penis slender. (Kenya, Mt. Kenya, 9-10,000 ft.) (Not identified with any recent

collections-perhaps not adult and juvenile of some other species; the dart sac appears to

be about 14 rom. long and the darts about 9 mm. long)

T. keniense

T. heynemanni Simroth in Nova Acta Leop.-Carol. 54, 54, t.3, f.6, 8 and 10-13 (1889) and in Abh. Senck. naturf. Ges. 18,303, t.l, f.5 and 6 (1894) and in Sitzb. Nat. Ges. Lpz. (1895-6), 149 (1897) and in Die Nacktschnecken Ost-Afrikas 6 (1897). Heynemann mentioned this species without name in Nachrbl. d. deutsch malak. Ges. 1882, 183
A dark olive-green or brownish slug 6.4---6.7em. long (orig. descr.). Simroth in the 1894 reference gives a long description and a coloured figure of a specimen from the East Usambaras; this shows a brownish-ochraceous or whitish-brown slug with a very corrugated mantle and some black marks in the grooves on the sides of the hind body. Dart sac broad just above the base, rather abruptly narrowing above, pointed at the apex; base of the oviduct swollen just above the point where it joins the spermathecal duct; vagina tubular, very distinct. There are two pairs of darts which are described as hairy.
KENYA. Witu, leg. Fischer; Teita, leg. Hildebrandt (chosen as type locality).
TANGANYIKA. Magila, leg. Kretzschmer; Derema in East Usambaras. In the last reference mentioned above Simroth also gives the locality "between Hemkole and Msassa", but see next species.
I have not seen any material from the type locality but the very abundant whitish slug found at Amani and elsewhere in the East Usambaras is this species. The coloured figure given by Simroth (1894) is closely matched by this slug which I have studied in some detail. A description is given below, from life.
Slug up to 15 em. long or even longer, with a strong keel all the way along the back; mantle longitudinally rugose, very sinuate behind, fringe and mantle pale yellowish, body greyish-greenishwhite, sometimes without any markings but usually with blackish reticulated blotches on the body and mantle. These markings are very variable. Head and tentacles pale brownish. Sole pale yellowish with grey central area. Mantle 3.7-4.3 em. long when animal is outstretched, pulmonary orifice large, about 5 rom. in diameter, just behind the middle of the mantle.
A preserved specimen naturally looks different and the specimen from which the dissection

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East African Slugs

figured in Fig. 8b was made may be described as follows. Animal 9 em. long and 2 em. wide; 2.3 em. high just behind the mantle. Mantle 3.5 em. long and 3 em. wide, pulmonary orifice 2 em. from posterior margin which is distinctly sinuate. The prominent keel on the back and long ridges on the mantle are as distinctive as they are in life.
The preserved animal is grey-brown or putty-coloured with a few dark lines in the grooves on the sides just behind and below the mantle. The anatomy is similar to Simroth's description, save that the oviduct is not so distinctly swollen as he figures, nor is the vagina separate but adnate. The dart sac is about 2.5-3 em. long, bifid at the apex with two acute points. The darts are huge in two sacs, each containing two; they are 2.8 em. long and 0.7 mm. in diameter, the end is sharply pointed, they are granulated when examined microscopically and under high powers (x 40) are distinctly hairy. The spermatheca is ovoid, 11 mm. long and 7 rom. wide, the duct about 2 em. long; the sac contained two spermatophores with traces of a third; these are massive coils about 7.5-8 em. long when outstretched. The hermaphrodite gland is oval, 12.5 x 6.5 rom. and the hermaphrodite duct is over 5 em. long. The albumen gland is 16 x 7-9.5 mm. The uterus is about three times as long as the albumen gland, much convoluted. (Fig. 8b.)
Another specimen collected at Amani in December 1956 (B. Verdcourt) was dissected. This was about 9 em. long, the mantle 3.1 em. long and 2 em. wide in life (3.5 em. when spread out flat). The posterior margin of the mantle is strongly sinuate with a central rounded portion projecting backwards; the mantle is covered with strong vertical rugulae and there are also cross-ridges. The pallial slit is almost imperceptible; the pulmonary orifice is situated 1.6 em. from the anterior mantle margin. The animal is uniformly ochraceous save for a very few black marks in the grooves between the rugae on the sides of the hind body. The keel is strong throughout its length. The sole areas are 6.5, 5.25 and 6.5 mm. wide respectively. The dart sac was 2.7 em. long and 6.1 mm. wide, cylindrical, not very swollen at the base, bifid at the apex, the lobes being rather pointed. These lobes obviously become more pointed as the dart sac develops. (Fig. 9.) The radula examined was 8.5 rom. long and 4.5 rom .•wide. There are about 106 teeth in each row on either side of the central tooth; the laterals number about 40 followed by some ten transitional teeth. The outermost 15 marginals are irregular in shape; the next 23-32 have a small cusplet on the outer edge of the main cusp; farther towards the middle the marginals have a faint cusp let on the inside of the main cusp. The average width of the long narrow cusp of the marginal teeth is 7.5-9 !to The jaw was bent in the specimen examined, 4.3 rom. wide and 2.8 rom. long.
A ·similar specimen was also dissected. In this the dart sac was 2.4 em. long and only bluntly bifid at the apex, the contained darts being about 2.5 em. long. The pointed ends may only show when the darts are at their maximum development. The spermatheca was 7 rom. long and 6 mm. wide, the duct about 2.3 em. long.
A pale greenish-yellow juvenile slug with yellow fringe, lighter longitudinal wrinkles on the mantle and similar black markings to adult T. heynemanni was collected as follows. I am certain it is a juvenile of the same form that occurs at Amani. Dr. Urban has confirmed that it belongs to Trichotoxon sensu stricto.
TANGANYIKA. Pangani District, Tongwe Mountain, 1950, leg. B. Verdcourt (serial letter CH).
T. conradti Simroth in Abh. Senck. naturf. Ges.18, 305 (1894) and in Die Nacktschnecken Ost-Afrikas 6 footnote (1897) and in Reise in Ostafrika 1903-5, A. Voeltzkow, Wiss. Ergebn. 2, 605, t.26, f.5 (1910)
This species has been very poorly defined and is perhaps no more than a form of the last s~cies. In the original reference it is defined as 'Trixotoxon' conradti and Simroth says that he would be inclined to separate it from T. heynemanni on account of the shape of the darts and because of the bands on the mantle. In the 1897 reference Simroth states that the darts lack hairs, also that the type specimen was not fully developed and the differences in the darts might be juvenile characters. The figure given in the 1910 reference is exceedingly similar to the figure Simroth gave of T. heynemanni. It shows a slug 6.1 em. long and 2 em. high, white (pale flesh or leather-coloured according to the text), with a few of the oblique bands between the rugosities of the back black; there are some marks on the mantle also. As I mentioned the common white slug in the Usambaras is variable in this character.
The. type locality is given as "between Hemkole and Msassa" and it was originally found by L. Conradt. Heynemann (1906) gives the locality as "Burg bei Magila bei Pangani" and Kobelt also gives Magila as a locality. Magila is in the foothills of the East Usambaras and nowhere near Pangani which is on the coast. Pilsbry (1919) states that Hemkole is in the Western Province of Tanganyika but I have elicited the information from various Washambaa that there was a village of Hemkole near Bulwa and another called Msassa near Derema in the East Usambaras; moreover, Conradt, so far as I.know, did not collect in any other part of Tanganyika.
T. voeltzkowi Simroth in Reise in Ostafrika A. Voeltzkow 1903-5, Wiss. Ergebn. 2, 593, t.26, f.3 and 4, t.f.4 (1910)
. Young animal buff with small brown spots and a white dorsal keel. Adult with body grey-buff,

East African Slugs


mottled with clusters of obscure bluish spots and a very few large black spots; mantle buff, mottled with brown with a few dark spots on the obscure lateral bands. Fringe and keel darkish. Length of adult animal 6.6 em. Dart sac bulbously enlarged at the base, sharply narrowed above; two pairs of hairy darts. Vagina adnate to the top of the dart sac; base of the oviduct a little swollen.

ZANZIBAR. Pemba Island, leg. Voeltzkow.
T. maculatum Simroth in Die Nacktschnecken Ost-Afrikas 6, t.f.1 (1897) and in Rev. Suisse Zoo\. 20, 37, t.3, fA A-E (1912); Pilsbry in Bull. Am. Mus. Nat. Hist. 40, 297, pI. 8, f.9 (1919) This is the "T. heynemanni Simroth oder eine nahe verwandt art" mentioned by Simroth in Sitz. Ber. Naturf. Ges. Lpz. 19-21 (1892-94), 53 (1895)
Slug about 6 em. long, pale buff or grey-brown with or without scattered large blackish spots. Dart sac bifid at the apex, ends bluntish, darts about I em. long. Vagina apparently nil, the ducts entering at the extreme apex of the dart sac. Oviduct swelling small.

UGANDA. Sese Islands, leg. Stuhlmann (type locality); Busu, leg. Carl.

Pilsbry stated that the genitalia of this species had not been described or figured but this is a slip since he mentions the very reference containing both a description and figure a few lines above this statement. Pilsbry described a race perforatum from Rutshuru which has a pore penetrating the mantle to the shell; the typical race is said to lack it ..
T. prestoni Pollonera in Ann. Mag. Nat. Hist. (8), 8, 332, pI. 8, f.8-11 (1911) Body unicolorous, leather-coloured. Mantle longitudinally rugose, pallial aperture very
narrow, pulmonary aperture scarcely antemedian. Back rugose, strongly carinate throughout its length, with profound lateral sulcae. Sole unicolorous, median zone granular, lateral zones transversely sulcate. Dorsum 304 em., mantle 2.6 cm. and sole 7.2 cm. long. Dart sac cylindrical, slightly swollen below, bifid apically with pointed divergent lobes. Vagina apparently nil (but it might have been adnate) entering well below the apex of the dart sac; oviduct tubular not swollen. Pollonera stated that he observed five darts.

KENYA. Between the Igembi Hills and Nyeri, leg. R. Kemp.

T. kempi Pollonera in Ann. Mag. Nat. Hist. (8), 8, 332, pI. 8, f.5-7 (1911) Mantle profoundly sulcate and rugose, brownish-fuscous with the tops of the rugae off-white,
pulmonary aperture distinctly antemedian, pallial aperture narrow but distinct. Back obtusely but strongly carinate, granulose, sides obliquely sulcate; earth-coloured, covered with blackish-grey evanescent large round spots and minute white spots. Fringe transversely sulcate and minutely white punctate. Sole smooth unicolorous, outer areas slightly transversely sulcate. The white spots on the mantle and the small white spots on the body are made up of a calcareous secretion such as is found in some species of Dendro/imax. Dorsum 3.5 cm., mantle 2.2 cm. and sole 6.2 em. long. Dart sac cylindrical with a rounded bulge just above the base, and another below the apex; apex narrowed and bifid, lobes blunt and not diverging; vagina apparently nil (but might possibly be adnate and unseparated by Pollonera in his dissection); oviduct cylindrical. Pollonera states that there are four extraordinarily long darts.

KENYA. Between the Igembi Hills and Nyeri, leg. R. Kemp.

Mr. R. Polhill has recently discovered a slug which agrees in many ways with Pollonera's description and may well be conspecific. His description and figure are appended.

Body sordid white to biscuit-coloured, speckled dark brown and livid white. Mantle same colour,

but extensive white of many


above. Head and neck Sole opaque, white-grey,

white-flecked. white-flecked.

Upper Body 5

tentacles em. long

brown. in spirit,

Fringe mantle

1.8 em. long, bluntly pointed anteriorly, very slightly trilobed posteriorly; pallial orifice I Mm. from

posterior end. Scarcely any solid caudal region; and 2 Mm. caudal gland starts 4 Mm. from posterior

tip. Body slightly keeled. Shell 7 x 5.5 mm., very thin, raised part of nucleus small and not very

elevated, but opaque area extends 2.5 Mm. from posterior end; concentrically striate. Jaw characteris-

tic of group, crescent-shaped with a median lobe on inner side, but this is not very strongly developed.

Genitalia: atrium-dart sac 20 Mm. long, cylindrical, a little swollen proximally and distally, the dart

sacs forming two conspicuous lobes. Two pairs of darts, 20 Mm. long, slightly curved, blade triangular,

the point formed by two sides only, the third not angled. Blade c. I Mm. long, haft rounded, hairy,

with a few small callouses. Spermatheca, 7 x 6 mm., ovate, pomted distally, duct 11 Mm. long. Penis

10 Mm. long, L-shaped, joining atrium 4 Mm. from aperture, on right-hand side, whence it passes

across to left-hand side and back parallel to atrium. Epiphallus c. II Mm. long in convoluted state,

running forward parallel to right-hand side of penis; lime gland c. 20 Mm. long. Vas deferens passes

forward on left-hand side of penis then twists underneath dart sac; a small flagellum is formed at this

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East African Slugs

Fig. 10



Fill. 12


East Afri~an Slugs


point. Oviduct leaves from a ventral cleft between dart sacs, about 3 mm. from their tips. Short duct (4 mm. long) suddenly narrows for 2 mm. before junction with vas deferens. Middle region, c. 30 mm. long, is in the form of a hairpin, looping back and then forward on left-hand side of body, then curves sharply back to form a short, much convoluted distal region. Albumen gland elongate, shieldshaped, 14 x 8 mm. Hermaphrodite gland, 6 x 4 mm., ovate-oblong, duct short (10 mm. long, in convoluted shape). (Fig. 10.)
KENYA. Kiambu District, Katamayu Forest, riverine forest, 8,000 ft., 22 May, 1960, leg. R. Polhill 70.
T. keniense Pollonera in Ann. Mag. Nat. Hist. (8), 8, 333, pI. 8, f.3-4 (1911)
Body golden-ochraceous, unspotted, paler ochraceous anteriorly. Mantle granular, not furrowed, pale orange-ochre, pulmonary aperture distinctly postmedian, pallial aperture narrow. Dorsal surface orange-ochre, paler behind, obtusely carinate and ruguloso-granulose, the oblique lateral sulcae only a little impressed. Sole with middle area pale, lateral areas pale brown, transversely sulcate. Dorsum 1.7 em., mantle 1.3 em. and sole 5 em. long. Dart sac cylindrical, truncate at the apex, containing four slightly clavate darts; oviduct and vagina tubular; spermatheca ovoid.
KENYA. Mt. Kenya, 9-10,000 ft., leg. R. Kemp.
T. thikense Verdcourt in Rev. Zooi. Bot. Afric. 45, 57, t.f.I-3 (1951)
Back and mantle pale grey-buff, grey-brown or brownish-orange. Back strongly keeled, keel becoming obscure just behind the mantle. Pulmonary aperture just over one third of the length of the mantle from its posterior margin, pallial pore barely visible. Tentacles and upper part of the head translucent brown; fringe white or dull purple. Sole white, tinged grey, the middle area pale grey. The sides of the body are reticulated and sulcate but the grooves are not marked with any colour. Body 6.5-9.5 em. long (alive and outstretched) and 1.3 em. wide; mantle 3.5-4.5 em. long. Dart sac cylindrical, 2.2 em. long and 0.45 em. wide, swollen above the base to 0.6 em. wide, truncate at the apex; darts 2.5 em. long (in this genus the darts protrude into the lower atrium and are therefore longer than the sac). Spermatheca globular with rather a short thick duct.
KENYA. Thika, Chania Falls Gorge, on walls of the gorge and also on the leaves of shrubs (e.g. Trichocladus ellipticus) near the water, leg. B. Verdcourt (holotype in Congo Museum, Tervuren), other material in the Coryndon Museum, Nairobi, and the Zoological Museum, Berlin.
The figure of the anatomy given in Fig. 11 was drawn by R. Polhill from topotypic material collected by W. Wilkinson (18 March, 1960). His description of the actual specimen used follows: Body 10 em. long, smooth, only faintly lined, keeled. The dart sac is very long (2.5 em.) and markedly cylindrical; darts curved. The penis curves right over and enters low down on right-hand side. The oviduct leaves the sac distally, curling dorsally between dart sacs and then anti-clockwise, forming middle oviduct on right-hand side, this region being much longer relatively than in the following varieties, proceeding a short way (1 em.) posteriorly, then taking a hairpin bend forward for 2 em., crossing over atrium-dart sac and then backwards, forming distal oviduct in 6 mm. This last region is very convoluted, 1 em. long in the natural state. The arrangement illustrated by Verdcourt loc.
dt. p. 58, Fig. 1.A, is rather different, explicable by a slight variation in the growth direction of the
various organs, but the length of the middle oviduct is still characteristic. The spermatheca is a very thin-walled sac, C. 12 x 7 mm., containing spermatophores; the duct 1 em. long.
I have not seen any authentic material of T. keniense but this present species must be very close to it. T. thikense comes from a much lower altitude, the spermatheca is more globose with a shorter duct, the dart sac is much more swollen above the base and then suddenly contracted; the penis also appears to be much thicker. More material from Mt. Kenya is needed for comparison. These differences may not be so great as they sound.
Some observations have been made on the development of T. thikense and these are very important since they show that no reliance can be placed on the lengths of the darts. Relatively undeveloped slugs from the type locality found associated with typical adults have small dart sacs which actually contain small darts. As the dart sac grows larger so do the darts increase in size. I have no doubt about this, having dissected a range of individuals of various sizes all from the same colony at Thika. Mr. R. Polhill has also confirmed my findings by further dissections. A small specimen, 5.3 em. long, had undeveloped genitalia and yet small darts were present; the sac was 7.5 mm. long and the darts were 6.3 mm. long with the apical half dilated, somewhat triangular in section, with a sharp cutting edge. A rather larger slug but by no means fully grown had a dart sac 13 mm. long and much more like the adult shape. Some figures of these juvenile dart sacs are given in Fig. 12.
Several other slugs from the vicinity of Nairobi have been examined which are undoubtedly closely allied to the last two species. They are believed to be varieties or growth forms of T. thikense

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East A,frican Slugs

IIic. 17


Fig. 14

Fia. 15

East African Slugs

Page 9

but abundant adult material is needed. It is possible that keniense, thikense and the slugs mentioned below are conspecific, or perhaps altitudinal races of one species.
T. tbikense Verdcourt var.* A creamy-white slug with a rich purple fringe (in life). Mantle rather smooth, pallial pore minute,
pulmonary aperture situated about the middle of the mantle, 1.5 cm. from the posterior edge. Hind body keeled particularly at the rear. The animal is 6.8 cm. long and the mantle is 3.2 cm. long. The genitalia appear to be adult. The dart sac is cylindrical, bifid at the apex with parallel lobes which are blunt. The vagina is adnate and the oviduct is not swollen at the base. Part of the genitalia are shown in Fig. 13.
KENYA. Uplands, Katamayu Forest, leg. J. G. Williams.
A further specimen collected in the same locality by Mr. R. Polhill is clearly conspecific but although larger the genitalia are less developed. Mr. Polhill's description follows and his figures are reproduced in Fig. 14.
Body 7 cm. long in spirit, mantle 3 em. long, body finely grooved except in caudal region, distinctly keeled. Body very pale yellowish-green, with pink-buff keel and mantle. Head and tentacles dark sepia. Fringe and most of sole purple, but with a whitish band, c. 1/3 of total width, down centre. Shell 7.5 x 6 mm., nucleus raised, rest very thin, membranous, asymmetrical, the apex lying to the left of a line bisecting the nucleus, and the curve of the margin more gradual on the right-hand side; concentrically striate. Atrium-dart sac 12 mm. long, proximal 2.5 mm. narrow, rest sub-cylindrical, broadening slightly to base of the dart sacs, where 3.5 mm. in diameter. Two pairs of darts; darts 7.5 mm.long, straight; blade approximately triangular, 1.8 mm. long; haft slightly angled in proximal part. Spermatheca 2 x 1 mm., oblong, the duct 6 mm. long. The penis enters the atrium-dart sac on the left-hand side anteriorly, just before the sac narrows, it is 11 mm. long; vas deferens running parallel to penis; epiphallus coiled, above 6 mm. long unravelled; lime gland 6 mm. long, angled. Proximal oviduct to junction of vas deferens 3.5 mm., middle region in coiled state 22 mm. long, distal region 4 mm. long. Hermaphrodite gland 8.5 x 6 mm., sub-kidney-shaped, truncate posteriorly; duct 17 mm. long.
KENYA. Kiambu District, Katamayu riverine forest, 8,000 ft., 22 May, 1960, leg. R. Polhill 71.
T. thikense Verdcourt var. A cream-coloured slug with a very strongly keeled back, mantle rather smooth. Pulmonary
aperture 9 mm. from the posterior margin, pallial aperture very small. Total length 5.5 em., mantle 2.8 em. long. The genitalia of this are undeveloped. The dart sac is clavate; the oviduct and spermatheca leave the sac in the middle of the apex. The spermathecal duct and the sac form a narrow tube. (See Fig. 15.)
KENYA. Isolated patch of forest on 01 Donyo Sabuk near Thika, 8,000 ft., leg. J. G. Williams.
Some further material, also from the same locality, has been collected by W. Wilkinson. This has been investigated by R. Polhill but is also immature. (See Fig. 16.)
Body 6 em. long in spirit, mantle 2.8 em. long. Body finely grooved; caudal region behind visceral cavity, I em. long, smooth, unlined, distinctly notched into caudal pore, slightly keeled, but not attenuate. Shell 6.5 x 5.5 mm., whitish with strongly raised nucleus, concentrically striate and, also, two broader, yellowish bands, mid-way, and near periphery. Vestibule 3.5 mm. long, narrow; atriumdart sac 10 mm. long, 2.5 mm. wide at its widest point, flask-shaped. Two pairs of darts, in a distinct pair of lateral lobes near end of sac. so that latter appears trifid. Darts 2.25 mm. long with triangular points c. 1.5 mm. long, haft c. 0.75 mm. long, rounded and narrowing slightly towards middle. Spermatheca scarcely swollen, together with duct 6-7 mm. long. The penis enters proximal region of atrium-dart sac on right-hand side and is 4 mm. long; epiphallus only once coiled, c. 9 mm. long; lime gland 3 mm. long. In natural coiled state, proximal region of oviduct is 2~2.5 mm. long, median part is 11 mm. long and distal part is 3.5 mm. long. Hermaphrodite gland 5.5 x 2.5 mm. with duct 17 mm.long.
KENYA. 01 Donyo Sabuk, 11 March, 1960, leg. W. Wilkinson.
T. thikense Verdcourt var. Mr. R. Polhill found a species of slug to be very abundant in the Karura forest, Nairobi. Although
large specimens were collected, none proved to be completely sexually mature; they undoubtedly belong to the above species but are not quite the same colour as the typical form. See Fig. 17.
Body 8 em. long in life, 6 em. long in spirit. Colour of whole gathering noted as opaque white,
* Further material shows that this might be more properly referred to T. nyambenense subsp. violaceum.

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East African Slugs Of The Family Urocyclidae