Ghent University, Evolutionary Morphology of Vertebrates, K.L. Ledeganckstraat 35, B-9000 Ghent (Belgium)

Corresponding author : Stijn Devaere, e-mail : Stijn.Dev1aere@UGent.be, Tel : + (32) 9 /264 52 20, Fax : + (32) 9 /264 53 44

ABSTRACT. A survey of anguilliform African clariids from the Lower Guinea indicated the existence of four species, of which two are new to science. Thirty morphometric features as well as several meristic and descriptive characters have been studied on 174 specimens. Channallabes ogooensis n. sp. is recognized by the combination of distinct serrations on the posterior edge of the pectoral spine, 84–97 vertebrae, 100–113 and 85–102 dorsal and anal fin rays, a pale spot on the skull roof between the anterior and posterior fontanel, absence of an epiotic, skull moderately reduced in size, sphenotic and pterotic showing plate-like outgrowths and the posterior border of mesethmoid indented, making the anterior part of the anterior fontanel situated within the mesethmoid. Channallabes teugelsi n. sp. is recognized by the combination of serrations only on the anterior edge of the pectoral spine, 70–82 vertebrae, 99–109 and 90–100 dorsal and anal fin rays and a clear, pale spot on the skull roof between the anterior and posterior fontanel. The three anguilliform genera Channallabes, Gymnallabes and Clariallabes are diagnosed and two anguilliform species are reassigned. A revised key to all African clariid genera is provided.

KEY WORDS : Clariidae, systematics, Channallabes alvarezi, C. longicaudatus, C. ogooensis, C. teugelsi, new species

INTRODUCTION

A clear taxonomy/systematics and a relatively simple key to identify animals correctly, based on externally visible morphological characters is crucial for field sampling, museums, etc… and thus indispensable for all further biological research.

The anguilliform species of the catfish family Clariidae are of great biological interest, e.g. discovery of terrestrial feeding and its importance for understanding evolutionary transitions in the history of vertebrates (VAN WASSENBERGH et al., 2006) and have recently been subject of several studies (DE SCHEPPER et al., 2004; DEVAERE et al., 2005; 2006).

However, anguilliform clariid taxonomy is not well supported. The only key incorporating the anguilliform clariids is that of POLL (1977), who relied on the limited number of specimens used in the original descriptions of the species. However, we find this key fails to account for intraspecific variation; overlap among species in the ranges of characters used in this key, such as presence of paired fins and number of ribs and vertebrae, limits its utility.

We examined the anguilliform clariid material, including type-specimens, museum specimens and newly collected specimens from the region of interest. Anguilliform clariids of the Lower Guinea are poorly represented in museums worldwide. Only Gymnallabes typus, G. alvarezi and Channallabes apus are frequently found in museums. Most of this material, however, appears to be incorrectly identified. Because correct identifications of the species are difficult, we conducted a systematic survey and morphological analysis.

MATERIALS AND METHODS

We examined 174 anguilliform clariids from the Lower Guinea. Institutional abbreviations are listed in LEVITON et al. (1985), except for Instituto de Biologia Aplicada, Barcelona, Spain (IBAB). For this study, we used museum material, but most specimens were collected from two sampling campaigns in Gabon (1999, 2000). Three large regions have been sampled : northern Gabon in the Woleu River system, close to the border with Equatorial Guinea and Cameroon; the Ivindo River system around Makokou; the Ogowe River system in the vicinity of Franceville. All sampling sites were characterized by shallow, muddy, still water. Most specimens were caught using fyke nets and fish hooks by local fishermen.

For all specimens, 36 point-to-point measurements were taken using digital callipers to 0.1mm (digital ruler, Mauser), following DEVAERE et al. (2004) : total length (TL); standard length (SL); preanal length (PaL); prepelvic length (PPvL); prepectoral length (PPcL); predorsal length (PdL); distance between the occipital process and the dorsal fin (SPDFL); pelvic fin length (PvFL), pectoral fin length (PcFL); pectoral spine length (PcSL); caudal peduncle depth (CPD); body depth at anus (ABD); maxillary barbel length (MxB); external mandibular barbel length (EmnB); internal mandibular barbel length (ImnB); nasal barbel length (NB); interpelvic distance (IpvD); interpectoral distance (IpcD); head length (HL); preorbital length (PoL); skull width (SkW); supraoccipital process length (SpL); supraoccipital process width (SpW); interorbital distance (IoD); anterior nostril interdistance (ANID); posterior nostril interdistance (PNID); rostral skull width (RSkW); orbital skull width (OSkW); skull height (SkH); eye diameter (ED); snout height (SnH); prehyoid length (PhL); internal mandibular interdistance

RESULTS

.

*: P < 0.000001

Fig. 3. – Discriminant Function Analysis (DFA) of four groups along (A) root 1 vs. root 2 and (B) root 1 vs. root 3. Group I : all specimens of the Woleu River system, including the type material of Gymnallabes alvarezi (N = 85), Group IIa : specimens of the Ivindo River system, including type material of Clariallabes longicaudatus (N = 67), Group IIb : specimens of the Middle Ogowe River system (N = 6) and Group III : specimens from the following locations; uppermost Ogowe, near Magogo, Lésala and Ndengué, Republic of Congo and Ivindo, Makokou, Gabon, with low number of vertebrae (N = 17).

Fig. 4. – Illustrations of pectoral spine serrations (right pectoral fin). (A) both edges of the spine show strong serrations, pattern found in C. longicaudatus; (B) only the posterior edge of the spine shows strong serrations, anterior edge may show few, reduced serrations, pattern found in C. ogooensis; (C) only the anterior edge of the spine shows strong serrations, pattern found in C. teugelsi; (D) no serration found, pattern found in C. alvarezi.

TABLE 2

FACTOR LOADINGS FOR THE DISCRIMINATION FUNCTION ANALYSIS. The most important loadings of each root are in bold. Abbreviations are defined in the text.

Channallabes alvarezi (Roman, 1970)

Fig. 6. – Illustration of the extent of the supraorbital process of infraorbital IV (right lateral view). (A) supraorbital process reaching the rostral border of the eye, pattern found in C. longicaudatus, C. ogooensis, C. teugelsi and

C. alvarezi; (B) supraorbital process not reaching the rostral border of the eye, pattern found in C. apus (scale = 1mm).

Colour : Alcohol preserved specimens gradually fade from dark brown on dorsal side to whitish brown on ventral side. Both sides separated by white dotted line of lateral line. Skin on jaw muscles has paler brownish colour than surrounding skin of head. Barbels have darkish-brown coloration. Channallabes alvarezi shows no distinct pale region on skull roof.

Distribution : Currently known from the Woleu River system in the region of Oyem, Gabon, type locality is Equatorial Guinea (Fig. 2).

Channallabes longicaudatus (Pappenheim, 1911)

Clariallabes longicaudatus Pappenheim, 1911 : 519, Fig. 3 (type locality : in der Mabelle, Süd–Kamerun)

Holotype : ZMB 18401, Zoologisches Museum, Humboldt Universitat (ZMHU), Berlin, 220mm SL; in der Mabelle, South Cameroon, Pappenheim, 1911.

Nontype material : MRAC A4-31-P-99-105, A4-31P-137-151, A4-31-P-152-157, A4-31-P-159-162, A4-31P-163-164, 34, Gabon, Makokou, River Ivindo, 0° 33’N12° 51’E, S. Devaere, D. Adriaens, A. Herrel, September 2000. MRAC A4-31-P-106-131, A4-31-P132-136, 31, Gabon, Etakaniabe, River Liboumba, 0° 31’N-12° 59’E,

S. Devaere, D. Adriaens, A. Herrel, September 2000. MRAC A4-31-P-158, 1, Gabon, Iyoko, Makokou, 0°32’N-12° 54’E, S. Devaere, D. Adriaens, A. Herrel, September 2000.

Diagnosis : Channallabes longicaudatus differs from

C. alvarezi, C. ogooensis and C. teugelsi in having clear serrations on both sides of the pectoral spine (Fig. 4). Channallabes longicaudatus can be distinguished from C. alvarezi in the low number of dorsal and anal fin rays (98–116 vs. 110–160 and 75–105 vs. 101–155 respectively) and the presence of a pale spot on the skull roof. Further, it differs from C. apus in the presence of an interdigitation between entopterygoid and quadrate and in a large, well-pronounced supraorbital process on the fourth infraorbital, reaching the rostral border of the eye (Fig. 6A). Additionally, C. longicaudatus can be differentiated from C. ogooensis by the presence of an epiotic and a straight posterior edge of the mesethmoid, leaving the anterior fontanel completely enclosed by the frontal bones.

Description : Measurements and meristics for holotype and additional specimens given in Table 3. Channallabes longicaudatus has an elongated body (ABD 4.0– 9.8% SL), preanal length 27.3–43.0% SL (Fig. 8). Very short skull length to SL ratio (8.7–15.9%). Skull width 64.4–79.6% of skull length. Skull roof always exposed, width 13.3–42.0% skull length. Eyes always visible. Whitish tube-like anterior nostrils strikingly visible. Lower lip clearly shorter than upper lip.

Unpaired fins continuous. Pectorals always present, length 5.0–9.7% SL, with a firm pectoral spine, length 2.9–6.8% SL. Both edges of pectoral spine serrated. Nine branched pectoral fin rays. Pelvic fins mostly present except in one specimen (intraspecific variation at this level already described by ADRIAENS et al. (2002)). Vertebrae 84–91 (mode = 88). Ribs 12–14 (mode = 13). Branchiostegal rays 8–9. Dorsal fin rays 98–116. Anal fin rays 75–105.

Channallabes ogooensis, new species

Channallabes teugelsi, new species

Diagnosis : Channallabes teugelsi differs from C. longicaudatus and C. ogooensis by serrations on the anterior edge of the pectoral spine only (Fig. 4). Channallabes teugelsi can be distinguished from C. alvarezi in the low number of dorsal and anal fin rays (99–109 vs. 110–160 and 90–100 vs. 101–155 respectively) and the presence of a pale spot on the skull roof. Further, it differs from C. apus in the presence of an interdigitation between entopterygoid and quadrate and in a large, well-pronounced supraorbital process on the fourth infraorbital, reaching the rostral border of the eye (Fig. 6A). Channallabes teugelsi can be diagnosed by the combination of following characters : a number of vertebrae that ranges between 70–82 and a lower lip that reaches almost equally far as the upper lip.

Description : Measurements and meristics for holotype and additional specimens given in Table 3. Body elongate, but not as extreme as other three described species, ABD 6.0–11.6% SL. Preanal length 29.8–40.6% SL (Fig. 10), indicating smaller tail section than C. alvarezi, C. longicaudatus and C. ogooensis. Skull length 12.2– 27.0% SL. Skull width 45.4–71.5% of skull length. Narrow skull roof, width 14.9–57.8% of skull length, clearly visible. Eyes small, remain visible. Whitish tube-like anterior nostrils clearly present. Lower lip almost reaches upper lip.

Unpaired fins continuous. Pectoral fin length 4.5 – 11.3% SL, small pectoral spine, length 2.9–4.6% SL, sometimes present. Pelvic fin length 3.8–7.0% SL. No evidence of pelvic fins in four specimens (MRAC 8-22-P1047-050). Only anterior edge of pectoral spine serrated. Nine branched pectoral fin rays. Vertebrae 70–82 (mode = 72). Ribs 10–12. Branchiostegal rays 8. Dorsal fin rays 99–109. Anal fin rays 90–100.

Lateral plate on frontal wider than orbitosphenoid (Fig. 7B). Distinct plate-like outgrowth on posttemporo-supracleithrum present. Epiotic always present. Two suprapreopercular bones always present, proximal one with platelike process. Two posterior processes present on prevomer. Entopterygoid contacting metapterygoid on rostro-dorsal side and partially on ventral side of latter. Two extended processes present on hyomandibula, for interdigitating with pterotic. Teeth present on dentary, premaxilla and prevomer.

Colour : Alcohol preserved specimens equally light brown along the whole body. Clear whitish spot on the skull roof, between the anterior and posterior fontanel, due to lighter thinning of the neurocranium in that area.

Distribution : Currently known from the Ivindo River system in the region of Makokou, Gabon and the Ogowe River system in the region of Zanaga, Ndengué and Magogo, Rep. Congo (Fig. 2).

Etymology : Named after the late Guy Teugels, as a tribute to his career and his efforts on African catfish taxonomy, especially Clariidae.

Key to the species of Channallabes

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. apus

DISCUSSION

The four species recognized in this study are all assigned to the genus Channallabes, as well as the ones formerly assigned to Gymnallabes (G. alvarezi) and Clariallabes (C. longicaudatus). This generic transfer relies especially on osteological similarities between the species of Channallabes on the one hand and differences with other Gymnallabes and Clariallabes species on the other hand. Those diagnostic characters are discussed below and listed in Table 4.

Gymnallabes : we diagnose Gymnallabes by the combination of the following characters. Lateral skull bones are extremely reduced. The infraorbital series consists of small, tubular bones, lacking any plate-like processes. Consequently, infraorbital IV lacks a supraorbital process. The suprapreopercular bones similarly lack any plate-like outgrowth. Plate-like extensions of the frontal, sphenotic and pterotic bones are absent thus exposing the dorsal side of the adductor mandibulae complex completely (Fig. 11A–C).

Clariallabes : the complex genus Clariallabes is characterized by an elongated body, that is somewhat intermediate between that of most species of Clarias and the extremely anguilliform genera (postanal length in Clariallabes between 50–65% SL). Clariallabes can be diagnosed by the combination of the following characters. The lateral skull bones (infraorbitals and suprapreoperculars) are quite large in Clariallabes, all bearing a clear plate-like outgrowth (Fig. 11A, B). A small gap is present between the fourth infraorbital and suprapreopercular bone. The lateral plates of the frontals (Fig. 11C), sphenotics and pterotics are large, covering the adductor mandibulae complex partially. The first dorsal fin pterygiophore is situated anterior to the sixth post-Weberian vertebrae. The dorsal and anal fins are not or only partially confluent with the caudal fin, with the different fins clearly distinguishable (TEUGELS et al., unpubl.). It has to be noted that little is known about the osteology of Clariallabes species, or of interspecific variation within the genus. The diagnosis given above is based on the current knowledge of species like C. melas, C. longicauda and C. mutsindoensis.

Channallabes : the following combination of characters helps to discriminate Channallabes; the infraorbitals are reduced but the third and fourth infraorbitals still bear a small plate-like outgrowth (Fig. 11A). On the fourth infraorbital a supraorbital process is present, partially or completely bordering the eye dorsally (Fig. 6). The suprapreopercular bones are reduced but a small plate-like extension is present on the proximal one (Fig. 11B). The lateral plates of the frontals are reduced, reaching only slightly more lateral than the orbitosphenoid (Fig. 7, 11C). Finally, the first dorsal fin pterygiophore is situated posterior to the sixth post-Weberian vertebrae.

TABLE 4 COMPARISON AMONG Channallabes, Gymnallabes AND Clariallabes

Differences between C. apus of the Congo basin and the Lower Guinea species are apparent both genetically (JANSEN et al., 2006) and osteologically. For example, C. apus differs in having an articulation process on the second infraorbital that never contacts with the lateral ethmoid (an obvious contact is found in the Lower Guinea taxa). Also, C. apus is distinct in bearing an interdigitating joint between the entopterygoid and the quadrate (DEVAERE et al., 2001) and in the absence of a fenestra between the scapulo-coracoid and the cleithrum.

The distinction between C. alvarezi and the other new species is clear and based on several characteristics, as noted by DE SCHEPPER et al. (2004). It is the only Lower Guinea species lacking a pale spot on the head and is characterized by a high number of dorsal and anal fin rays.

Channallabes teugelsi can be distinguished from the other Lower Guinea species mainly based on meristic characters, especially the low number of vertebrae, with a maximum of 82 (Fig. 1). Even though these specimens are small, size-related allometry could not explain the low vertebral count. Moreover, an independence of the total number of vertebrae from the length of the fish has been reported for fishes in general as well (LANDRUM & DARK, 1968).

Channallabes longicaudatus and C. ogooensis show the greatest overall similarity, and as a group can easily be distinguished from the rest (Fig. 1). Several qualitative, osteological features are useful in their discrimination, such as serrations on both edges of the pectoral spine in

C. longicaudatus (instead of only on the posterior edge) and the presence of the epiotic in C. longicaudatus (absent in C. ogooensis). In addition, the indented mesethmoid distinguishes C. ogooensis from C. longicaudatus.

The geographic distribution shows that the four species mainly occur in the following large river systems : C. alvarezi occurs in the Woleu and the other species originate mainly from the Ivindo/Ogowe. While C. teugelsi can be found both in the Ogowe and Ivindo, C. longicaudatus is situated mainly in the Ivindo River (the exact type locality is unclear), and C. ogooensis only in the Ogowe River (more specifically upstream from the confluence of the two large rivers). According to THIEME et al. (2004), these locations are located in two separate freshwater ecoregions : the central west coastal equatorial and the southern west coastal equatorial, respectively. The northern tributaries of the Ogowe River (Abanga, Okano and Ivindo) are included in the central west coastal equatorial freshwater ecoregion because of faunal affinities with the other rivers of that ecoregion, and show less affinity with the mainstem Ogowe (THIEME et al., 2004).

Because of biased sampling, i.e. swamps generally being less sampled than rivers, the occupation of that swampy niche by the anguilliform clariids could explain the possible non-continuous distribution of C. teugelsi in the Ogowe and Ivindo. Additional targeted sampling would be required to verify this.

As a consequence of the reassignment of several species in different genera, as well as the description of new species with a more elaborate analysis of intraspecific and interspecific biometric ranges presented in this paper, an updated key based on that of POLL (1977) to the genera of the African Clariidae is presented here.

1a Adipose fin absent or very short (less than 25% SL); more than 50 dorsal fin rays. . . . . . . . . . . . . . . . . . . .2

1b Adipose fin large (24–33% SL); less than 50 dorsal fin rays . . . . . . . . . . . . . . . . . . . . . . . .Heterobranchus

2a Unpaired fins separate from or only partially fused with caudal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2b Unpaired and caudal fins form continuous fin fold .10

3a Eyes present, sometimes small; skull roof exposed between jaw muscles . . . . . . . . . . . . . . . . . . . . . . . . .4

3b Eyes absent; skull roof invisible . . . . . . . Uegitglanis

4a Eyes lateral, adjoining lateral border of skull; dorsal and caudal fins clearly separate (gap 10% SL); lateral dermal skull bones large and separate . . . . . . . . . . . .5

4b Eyes laterodorsal or dorsal, not adjoining lateral border of skull; dorsal and caudal fins fused or slightly separated (gap max 5% SL); lateral dermal skull bones continuous, closely adjoining or are reduced in size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

5a Dorsal fin rays 54 or less; elongated neural spines 9– 12; suprapreopercular and posttemporo-supracleithrum in contact; no serrations on pectoral spin

5b Dorsal fin rays 59 or more; elongated neural spines 5– 8; suprapreopercular and posttemporo-supracleithrum with distinct gap; pectoral spine serrated anteriorly

6a Suprabranchial organ with developed arborescent structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

6b Suprabranchial organ absent or vestigial and incomplete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

7a Head short (11–26% SL); lateral head bones separate; distance between anus and caudal fin base 50–65% SL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Clariallabes

7b Head long (20–34% SL); lateral head bones in contact (often fused in larger specimens); distance between anus and caudal fin base 50% SL or less. . . . .Clarias

8a Skull length 14–19% SL; skull roof width 15–36.5% of skull width; infraorbital IV and suprapreopercular reduced and distinctly separate; vertebrae 59–71 . . .9

8b Skull length 20–21% SL; skull roof width more than 50% skull width; large infraorbital IV and suprapreopercular in close proximity; vertebrae 51–52

9a Extremely dorsoventrally flattened skull (skull height 22.9–37.1% of skull length); abdominal depth 4.1– 6.5% SL; skull roof width 26.0–36.5% of skull width; vertebrae 65–71; ribs 9–11. . . . . . Platyclarias

COMPARATIVE MATERIAL EXAMINED

Gymnallabes typus : BMNH 1866.12.4.1–2, 2, 139– 150mm, Nigeria, probably Old Calabar, West Africa (Syntypes).

Channallabes apus : BMNH 1873.7.28 : 16, 1, 135mm, Angola, interior of Ambriz, 7° 50’Z-13° 06’E (Holotype).

ACKNOWLEDGMENTS

The authors thank F. Verschooten (University of Ghent) for the assistance in preparing the radiographs. We thank J. Friel, J. Snoeks, E. Vreven and J. Sullivan for their critical comments. The Museum für Naturkunde der Humboldt-Universitaet, Berlin and the Instituto de Biologia aplicada, Barcelona for taking photographes of the type specimens. Special thanks to M. Stiassny,

C. Hopkins, J. Okouyi (M’Passa, Makokou) and the I.R.A.F. (Gabon) for assistance during collecting efforts. We are grateful to M. Parrent (MRAC) for his help with the collections. Research was funded by the BOF of the Ghent University (project 01104299 and 01103401) and the FWO (project G.0388.00).

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Received: June 8, 2006 Accepted: January, 11, 2007