The taxonomic position of the echurian Ochetostoma capense is reviewed based on examination of type material and on specimens from the type locality. On the basis of the disposition of the inner oblique muscle layer, the species is transferred to the genus Listriolobus and is re-described as L. capensis

Biseswar, R

Moodley, L.G.

English

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s. Afr. J. Zoo\. 1989, 24(4) 337 The proposed transfer of the echiuran Ochetostoma capense to the genus Listriolobus R. Biseswar* and L.G. Moodley Department of Zoology, University of Durban-Westville, Private Bag X54001, Durban, 4000 Republic of South Africa Received 22 August 1988; accepted 5 June 1989 The taxonomic position of the echurian Ochetostoma capense is reviewed based on examination of type material and on specimens from the type locality. On the basis of the disposition of the inner oblique muscle layer, the species is transferred to the genus Listriolobus and is re-described as L capensis. Gebaseer op die ondersoek van die soortmateriaal en van monsters van die soortlokaliteit word die taksonomiese posisie van een van die Echiura, Ochetostoma capense, hersien. Op grand van die rangskikking van die binne-skuinsspierlaag, word die spesie oorgeplaas na die genus Listn"olobus en word hier herbeskryf as L. capensis. 'To whom correspondence should be addressed Introduction Ochetostoma capense was erected by Jones & Stephen (1955) from numerous specimens obtained from the Zwartkops River estuary near Port Elizabeth. The species was also recorded from Durban Bay and Langebaan Lagoon. In a brief report, Wesenberg-Lund (1963) noted its occurrence as far as 3,6 km upstream from the estuary mouth of the Zwartkops River. Mathew (1976) undertook histological studies of the integuments in echiurans and overlooked the nature of the inner oblique muscle layer of this species. In a comprehensive report on the species of Ochetostoma from southern Africa, O. capense was briefly diagnosed by Biseswar (1988). Histological studies of the body wall of type material and of specimens obtained from the type locality, however, have revealed that the placement of this species in the genus Ochetostoma is erroneous. On the basis of the disposition of the inner oblique muscle layer it is proposed that the species be transferred to the genus Listriolobus. A revised description of the species, together with the proposed taxonomic change is given below. Systematic section Family Thalassematidae Bock, 1942 Subfamily Ochetostomatinae Dattagupta, 1976 Genus Listriolobus Spengel, 1912 Diagnosis Longitudinal muscles of body wall grouped into bands which in young specimens are faint or visible only in the posterior region. Inner oblique layer of muscles not separated into transvere fascicles between the longitudi-nal bands. Two to three pairs of gonoducts; gonostomal lips elongate and spirally coiled. Interbasal muscle between the setae is present. Type species: Listriolobus bahamensis Fischer Remarks The generic name Listriolobus was proposed by Spengel (1912) for specimens collected from Indonesia and the Bahamas. Fischer (1926) subsequently provided the specific names billitonensis and bahamensis for the specimens and later Fisher (1946) designated L. bahamensis as the type species of Listriolobus. The genus now contains nine species. There are four genera in the subfamily Ochetostomati-nae, namely, Ochetostoma, Listriolobus, Lissomyema and Ikedosoma, where the longitudinal muscle layer of the body wall is aggregated into discrete bands. In the rest of the echiurans this muscle forms a continuous sheet. In echiurans, the presence or absence of longitudi-nal muscle bands is an important taxonomic character in the classification above the generic level. Internal to the longitudinal muscle is a layer of oblique muscles. It was only after the publication of Spengel's paper in 1912 and Wharton's in 1913 that the taxonomic importance of this muscle layer was realized. The arrangement of the inner oblique muscle is a valid character in distinguishing Ochetostoma from Listriolo-bus. In the former, this muscle is aggregated into fascicles between the longitudinal muscle bands whereas in the latter it fOnTIS a continuous sheet. The taxonomic position of several species assigned to the genus Ochetostoma is doubtful because some of the earlier descriptions contain no information about the oblique muscles. Distribution. This genus has a fairly wide distribution mainly in tropical and subtropical waters of the Indo-Pacific and Atlantic Oceans. Listriolobus capensis (Jones and Stephen, 1955) Ochetostoma capensis Jones and Stephen, 1955: 273-278, Figs 1-3, Table 1; Wesenberg-Lund, 1963: 142. Ochetostoma capense Stephen and Edmonds, 1972: 430-431; Day, 1974: 50; Mathew, 1976: 151-158. Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2010). 338 S.-Afr. Tydskr. Dierk. 1989,24(4) Figure 1 Histological section of the body wall of Listriolobus capensis showing the arrangement of the muscle layers. cm = circular muscle, ct = connective tissue, ep = epithelium, 1m = longitudinal muscle, pap = papillae, om = oblique muscle. Description Proboscis small in preserved specimens, about one-eighth of trunk length and in living specimens one-twelfth to one-third; ventral edges crenate when extended, but thrown into a series of tight ridges when contracted. Colour of proboscis varies from cream, through different shades of cream-yellow, to light orange. Trunk cylindrical or sausage shaped, up to 140 mm in length and typically widest at posterior end. Trunk thickly covered with papillae on anterior ventral surface but fewer at posterior end. Papillae aligned in rows in middle region of trunk. Colour of trunk variable, ranging from dark grey-brown to purple-brown. Longitudinal muscles gathered into seven main bands, most conspicuous at ends of trunk. A few weakly developed bands occur between the main bands. Inner oblique muscle layer, between the longitudinal bands, not arranged in fascicles (Figure 1.) Gonoducts two pairs, postsetal, usually half to three quarters as long as trunk, but sometimes quite short. Gonostomal lips extended into long spiral filaments. Interbasal muscle present, passing through a loop of the neuro-intestinal vessel (Figure 2). Intestinal ring sinus located at end of foregut; neuro-intestinal vessel paired (Figure 2). Anal vesicles long, thin, brown tubes of variable length, from one- to three-quarters trunk length and bearing minute ciliated funnels which are most numerous towards their free ends. Ventral setae one pair, consisting of a long, straight shaft with a flattened, curved terminal blade. Terminal end is set slightly askew from cylinder part of shaft. Material This analysis is based on a study of 13 specimens collected from the type locality and on the examinations of the holotype of O. capense (Reg No: 1958.23.41), the two figured specimens of Jones & Stephen 1955 (Reg No: 1958. 23.43) and four paratypes (Reg. No. 1958.23. 43) obtained from the Royal Scottish Museum. For histological details, strips of the body wall of six specimens, including two paratypes, were sectioned at 8-10 ~m and stained with haematoxylin and eosin. Drawings were made with the aid of a camera lucida. Slim Figure 2 Anterior part of the trunk cavity of Listriolobus capensis showing the blood system. dv = dorsal vessel, ibm = inter basal muscle, int = intestine, irs = intestinal ring sinus, niv = neuro-intestinal vessel, ss = setal sac, vv = ventral vessel. Remarks Jones & Stephen (1955) obviously overlooked the disposition of the oblique muscle when assigning their species to the genus Ochetostoma. Their original description of the species makes no mention of this important feature. In their monograph, Stephen & Edmonds (1972), however, state that the oblique muscles between the longitudinal bands form fascicles. Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2010). S. Afr. J. Zoo!. 1989,24(4) The nature of the oblique muscle layer may not be readily discernible from gross morphological observations. Mathew (1976), also holds the view that the real nature of this muscle can be determined only after examination of histological sections of the body wall. Histological studies by the present authors clearly show that the oblique muscle layer, although of variable thickness, forms a continuous sheet and is not separated into transverse fascicles as in Ochetostoma. On the basis of this character it is proposed that O. capense be moved to the genus Listriolobus. It is rather surprising that this feature was also overlooked by Mathew (1976) who examined histological sections of the body wall of specimens obtained from the Royal Scottish Museum. Another feature that tends to support this taxonomic change is the presence of an interbasal muscle in L. capensis as in all the known species of Listriolobus. Four echiuran genera were previously known from the southern African region, namely, Ochetostoma, Thalas-sema, Anelassorhynchus and Echiurus. The genus Listri-olobus was not recorded previously from this region. Listriolobus capensis appears to be an endemic species. Since its discovery at the three localities mentioned above, it has not been reported from beyond the south-ern African region. Of the species of Listriolobus so far described, two, namely L. bulbocaudatus and L. brevirostris, possess seven longitudinal musclc bands and two pairs of gono-ducts and hence appear to be closely related to L. capensis. Listriolobus bulbocaudatus, described by Edmonds (1963) is based on four specimens from Mud Island, Moreton Bay, Queensland. The latter species, however, differs from L. capensis in possessing a trunk that is expanded at the posterior end into a fleshy, bulbous structure which bears a number of rings of very large, prominent wart-like papillae. Listriolobus brevirostris, described by Chen & Yeh (1958), is known from specimens obtained from Kiao-Chow Bay, Shantung. In this species, the proboscis is short, truncated and nearly open at the base. The trunk is somewhat fusiform, tapering at either end and up to 120 mm in length. According to the authors, the papillae are arranged in transverse rows which are more evident on the ventral and ventro-lateral surfaces of the anterior third of the body. The papillae are small, round, ampulla-like, of variable size and occur either singly or in groups of 2-3. Hence L. brevirostris differs from L. 339 capensis in the shape of the trunk and in the nature and distribution of the dermal papillae. Acknowledgements The loan of type material by the curator of the Royal Scottish Museum is gratefully acknowledged. Thanks are due to Dr Jennifer A. Day of the Department of Zoology, University of Cape Town for the loan of specimens collected from the type locality. We are also indebted to the University of Durban-Westville for providing facilities for this investigation. References BISESWAR, R. 1988. Ochetostoma (Echiura) from southern Africa with a description of a new species. Ann. S. Afr. Mus. 98(2): 29-75. CHEN, Y. & YEH, C.C. 1958. Notes on some Gephyrea of China with descriptions of four new species. Acta. zool. sin. 10: 265-278. EDMONDS, S.J. 1963. Two new echiuroids (Echiuroidea) from Australia. Trans. R. Soc. Aust. 87: 243--247. FISCHER, W. 1926. Sipunculiden und Echiuriden der Hamburger Siidsee-Expedition 1908-1909. Mitt. zool. Staatinst. und Zool. Mus. Ramb. 42: 104-117. FISHER, W.K. 1946. Echiuroid worms of the North Pacific Ocean. Proc. U.S. natn. Mus. 96: 215-292. JONES, C.M. & STEPHEN, A.c. 1955. A new species of echiuroid worm (Ochetostoma capensis) from the Cape Province, South Africa. Trans. R. Soc. S. Afr. 34: 273--278. MATHEW, J. 1976. Integuments in echiurans. Proceedings of the International Symposium on the Biology of the Sipuncula and Echiura, Kotor, June 1970. (Eds) Rice, M.E. and Todorovic, M. 2: 127-133. SPENGEL, J.W. 1912. Uber den Hautmuskelschlauch gewisser Thalassema-Arten und seine Bedeutung fur die Systematik dieser Tiere. Verh. dtsch. zool. Ges. 22: 309-317. STEPHEN, A.c. & EDMONDS, S.J. 1972. The phyla Sipuncula and Echiura. Trustees of the British Museum (Natural History). WESENBERG-LUND, E. 1963. South African sipunculids and echiurids from coastal waters. Vidensk. Meddr. dansk. naturh. Foren. 125: 101-146. WHARTON, L.D. 1913. A description of some Philippine Thalassemae with a revision of the genus. Philipp. 1. Sci. 8: 243--270. Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2010). 

The proposed transfer of the echiuran Ochetostoma capense to the genus Listriolobus

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The proposed transfer of the echiuran Ochetostoma capense to the genus Listriolobus

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