A new interstitial flatworm (Turbellaria: Promesostomidae)
from the Indian Ocean
G.G. De Clerck
D e Clerck, G . G . A n e w interstitial flatworm (Turbellaria: Promesostomidae) f r o m the Indian O c e a n . In:
J. v a n d e r L a n d (ed.), Results of the O c e a n i c Reefs' E x p e d i t i o n to the Seychelles (1992-1993), v o l u m e 1.
Z o o l . V e r h . L e i d e n 297, 30.xii.1994: 37-41, figs 1-8.— I S S N 0024-1652/ISBN 90-73239-37-0.
G . G . D e C l e r c k , L i m b u r g s Universitair C e n t r u m , Diepenbeek, B e l g i u m . Present address: Vossestraat
29,1745 M a z e n z e l e , B e l g i u m .
K e y w o r d s : T u r b e l l a r i a ; T y p h l o p l a n o i d a ; Promesostomidae; Indian O c e a n ; Seychelles; K e n y a .
Paraproboscifer alacerregis, representing a n e w genus a n d a n e w species of the interstitial t y p l o p l a n o i d
flatworms
is described f r o m the Seychelles a n d K e n y a . It is placed i n the turbellarian f a m i l y P r o m e s o -
stomidae, T h e type locality is o n M a h é Island, Seychelles.
Introduction
Martens & De Clerck (1994) gave a preliminary report on the results of their studies on the interstitial and parasitic Platyhelminthes during the Oceanic Reefs' expedition to the Seychelles i n 1992 and 1993. Several undescribed species were mentioned but none of them was described i n the cruise report. The first description of a
new species, also representing a new genus, is given below. In the preliminary report
it is listed as Promesostomidae n.gen. n.sp.
Description
Turbellaria - Typhloplanoida
Family: Promesostomidae
Paraproboscifer alacerregis gen. et spec. nov.
(figs 1-8)
T y p e l o c a l i t y . — Baie Beau V a l l o n ; N . W . coast of M a h é (Seychelles). Station n o . 641B. Fine sand f r o m
shallow p o o l , i n seagrass m e a d o w . M i d d l e to h i g h eulittoral, 27.xii.1992.
O t h e r localities.— Port L a u n a y N a t i o n a l M a r i n e Park, southern part of bay; M a h é (Seychelles). Station
no. 646A. V e r y fine s a n d f r o m b e y o n d reef front. D e p t h : 2-3 m , 29.xii.1992.
M c K e n z i e p o i n t , M o m b a s a (Kenya), v e r y fine sand i n a shallow intertidal p o o l , m i d d l e to h i g h eulittoral, 01.10.1991.
M a t e r i a l . — Seychelles: live observations of several specimens; w h o l e m o u n t s of two specimens i n lactophenol, one of them designated as holotype. K e n y a : live observations of one specimen; paraffin sections of t w o specimens
stained w i t h H e i d e n h a i n ' s iron h e m a t o x y l i n u s i n g eosin as
counterstain.
M a t e r i a l is deposited i n the collection of the Z o o l o g y Research G r o u p , L i m b u r g s Universitair C e n t r u m , Diepenbeek, B e l g i u m .
D e r i v a t i o n of n a m e . — T h e genus name is a reference to the muscles a r o u n d the r h a b d o i d tracts, the
species n a m e is i n h o n o u r of the author's wife.
General description.— The white slender animals (about 1 m m in whole mounts)
tend to move around like slow Proseriates with a very contractile headpart. Eyes are
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de Clerck. A new interstitial flatworm from the Indian Ocean. Z o o l . V e r h . Leiden. 297 (1994)
lacking. The two rhabdite tracts are strongly developed (up to 170 μιη long) and are
surrounded by circular muscles. The basophilic rhabdites are about 11 μιη long. The
pharynx is situated just i n front of the middle of the body and has a diameter i n the
mounted holotype of 91 urn. The epidermis is cellular with very long cilia. The epi­
dermal basophilic rhabdites (length: 3 μηι-8.4 um) are scarcely dispersed over the
whole body, but highly concentrated i n the tail region.
Male organs.— The paired testes are situated in front of the pharynx. The two
seminal vesicles merge together just before entering the globular copulatory bulb.
The globular part of the cell bodies with the nuclei of the basophilous prostate
glands are concentrated in the proximal part of the bulb, while the tubiform and
secretion-filled cell necks surround the distal part of the ejaculatory duct. N o extraca­
psular glands were observed. The ejaculatory duct ends i n a short spiny cirrus
(length of cirrus: 10-11 urn; length of spines: 9 urn) which is surrounded by a a sclerotised papilla (length: 14-17 urn; width: 15 urn). The wall of the male antrum is slight­
ly sclerotised.
Female organs.— The paired ovovitellaria start just behind the pharynx with the
posteriorly situated ovary part lying next to the copulatory organ. Both ovovitellaria
open laterally into the stalk of the terminal bursa by means of short ovovitelloducts.
Large glands with a fine eosinophilous secretion and small ones with coarse basophi­
lous secretion are associated with these ducts. A first, terminally situated globular
bursa is connected with the genital atrium by means of a long muscular bursa stalk.
Its lumen, containing sperm, is surrounded by large, distinctly delimitated cells and
touches both ovovitellaria laterally, but without a direct connection. A second, trian­
gular shaped bursa opens dorsally in the common genital atrium and is surrounded
by longitudinal muscles. This bursa is suspended in the body cavity by three muscle
bundles, which may give it its triangular shape.
Discussion
With its single connection between the ovaria and the outside world Paraprobosci­
fer alacerregis should be placed in the Promesostomidae Den Hartog, 1964. Due to the
presence of a strongly developed atrial bursa, the genus is placed in the 'Coronhelmisgroup' within the Brinkmanniellinae Karling et al., 1972 (see also Ehlers, 1974; Ehlers
& Ehlers, 1981). The overall organisation, the presence of a cirrus and the long epi­
dermal cilia clearly suggest a relationship with Cilionema Karling et a l , 1972. The
most striking differences are the possession of circular muscles around the rhabdoid
tracts i n Paraproboscifer and the so called 'cup cells' in Cilionema. The presence of
muscles around the rhabdoid tracts is a clear autapomorphy for the newly erected
taxon.
We agree with Karling et al.(1972) and Ehlers & Ehlers (1981) that the monophyletic character of this 'Coronhelmis-group' is highly questionable. The Brinkmannielli­
nae is defined on plesiomorphic characters only (Karling et al., 1972) as is the family
Promesostomidae. We have started to work on a revision of the whole family and
untill we get more clearness about the relationships between the different genera the
genus w i l l be placed i n the above mentioned taxa: family Promesostomidae, subfa­
mily Brinkmanniellinae.
de Clerck. A new interstitial f latworm f rom the Indian Ocean. Z o o l . V e r h . Leiden. 297 (1994)
39
Acknowledgements
The authors wishes to thank Dr. J. van der Land, chief-scientist, for allowing his
participation i n the expedition and the Netherlands Marine Research Foundation
(SOZ) for the financial support. I am also grateful to the Seychelles Fishing Authority
for the use of their laboratories and technical support, and the National Parks and
Conservation Devision in Victoria, Mahé, for transport facilities.
References
A x , P., 1977. P r o b l e m s of speciation i n the Interstitial F a u n a of the Galapagos. In: W . Sterrer & P. A x
(eds), T h e M e i o f a u n a Species i n T i m e a n d Space. W o r k s h o p S y m p o s i u m , B e r m u d a Biological Sta­
tion, 1975.— M i k r o f. Meeresb. 61: 29­43.
Ehlers, U . , 1974. Interstitielle T y p h l o p l a n o i d a (Turbellaria) aus d e m L i t o r a l d e r N o r d s e e i n s e l S y l t . —
M i k r o f . Meeresb. 49:1­102.
Ehlers, U . & B. Ehlers, 1981. Interstitielle F a u n a v o n Galapagos. X X V I I . Byrsophlebidae, Promesosto­
m i d a e , Brinkmanniellinae, K y t o r h y n c h i d a e (Turbellaria, T y p h l o p l a n o i d a ) . — M i k r o f . Meeresb. 83:
83­115.
G e r l a c h , S. Α . , 1977. M e a n s of M e i o fa u n a l Dispersal. In: W . Sterrer & P. A x (eds), T h e M e i o f a u n a Spe­
cies i n T i m e a n d Space. W o r k s h o p S y m p o s i u m , B e r m u d a Biological Station, 1975.— M i k r o f. M e e r ­
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K a r l i n g , T . G . , V . M a c k ­ F i r a & J. D ö r j e s ,
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M a r t e n s , E . E . & G . G . D e Clerck, 1994. Interstitial a n d parasitic Platyhelminthes f r o m the coasts of the
Seychelles. In: J. v a n d e r L a n d (ed.), Oceanic Ree f s of the Seychelles. Netherlands Indian O c e a n
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de Clerck. A new interstitial flatworm from the Indian Ocean. Z o o l . V e r h . Leiden. 297 (1994)
Figs 1-3. Paraproboscifer alacerregis gen. et spec. nov. 1, free h a n d d r a w i n g of slightly squeezed specim e n ; 2, h o r i z o n t a l reconstruction of the genital organs v i e w e d f r o m the left; 3, dorsal v i e w .
A b b r e v i a t i o n s : B: bursa; BS: b u r s a l stalk; C B , C O B : copulatory b u l b ; C G A : c o m m o n genital a t r i u m ;
C G P : c o m m o n genital pore; C I : cirrus; G B : globular b u r s a ; O W : o v o v i t e l l a r i u m ; P H : p h a r y n x ; R:
rhabdites; SP: sclerotised p a p i l l a ; S V : seminal vesicle; T : testis; T B : triangular bursa.
de Clerck. A new interstitial flatworm from the Indian Ocean. Z o o l . V e r h . Leiden. 297 (1994)
41
Figs 4-6. Paraproboscifer alacerregis gen. et spec. nov. 4, slightly squeezed
live specimen; 5, head region s h o w i n g rhabdite tracts (phase contrast);
6, horizontal section of the muscles a r o u n d the rhabdite tracts.
Figs 7-8. Paraproboscifer alacerregis gen. et spec. nov.7, male copulatory
organ, specimen f r o m Seychelles; 8, male copulatory organ, specimen
from Kenya.