NotvitatesAMERICAN MUSEUM PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2835, pp. 1-44, figs. 1-40, table 1 November 12, 1985 The West African Pygmy Herrng Sierrathrissa leonensis: General Features, Visceral Anatomy, and Osteology PETER J. P. WHITEHEAD1 AND GUY G. TEUGELS2 C O N T E N T S Abstract ..................... .................................... 2 Introduction .......................................................... 2 Acknowledgments ......................................................... 3 Abbreviations ......................................................... 4 External Features ......................................................... 4 Visceral Anatomy ......................................................... 7 Skeleton .......................................................... 11 Chondrocranium ......................................................... 12 Ethmoid Region ......................................................... 13 Jaws ..................................................................... 14 Circumorbital Series ........................................................ 15 Opercular Series ......................................................... 16 Hyopalatine Arch ......................................................... 16 Hyal Arch and Branchiostegal Rays ................. .......................... 18 Branchial Skeleton ......................................................... 19 Neurocranium .............................................................. 23 Pectoral Girdle and Fins ..................................................... 26 Pelvic Girdle and Fins ...................................................... 29 Dorsal Fin .......................................................... 31 Anal Fin .......................................................... 32 Vertebral Column and Intermuscular Bones ........... ........................ 33 Caudal Skeleton ......................................................... 36 ' Research Associate, Department ofIchthyology, American Museum ofNatural History. Current address: Zoology Department, British Museum (Natural History), London SW7 5BD. 2 Ichtyologie Gen6rale et Appliqu6e, Mus6um National d'Histoire Naturelle, 75231 Paris. Copyright © American Museum of Natural History 1985 ISSN 0003-0082 / Price $4.45 2 AMERICAN MUSEUM NOVITATES NO. 2835 Biology ................ 37 Habitat ................ 38 Feeding ................ 39 Breeding ................ 39 Migrations ................ 40 Distribution ................ 40 Discussion ................ 40 List of Study Materials ................ 42 Literature Cited ................ 43 ABSTRACT The minute freshwater herring Sierrathrissa leo- gonads at only 21-26 mm SL are described and nensis Thys van den Audenaerde, 1969, first re- the distinction from juvenile Pellonula clarified. corded from Sierra Leone, has sometimes been General features of the species are given, as well claimed as nothing more than the ummetamor- as descriptions and illustrations of its visceral or- phosed larva of a species of Pellonula (or perhaps gans and most of the 900 bony or cartilaginous Cynothrissa). Fully mature specimens with ripe elements of its anatomy. INTRODUCTION The largest evolutionary radiation offresh- Odaxothrissa); genera with the characteristic water Clupeidae occurs in the rivers and lakes clupeid scutes greatly reduced (Laeviscutella) of West Africa, where 13 genera comprising or even absent except for the ubiquitous pel- about 23 species have been recorded (Poll, vic scute (Congothrissa); genera with scales 1974; Poll, Teugels, and Whitehead, 1984). almost entirely lacking (Thrattidion); genera This is in striking contrast to the paucity of with the usual six or seven branchiostegal marine Clupeidae and Engraulidae off West rays reduced to three (Congothrissa); and African coasts, where only four genera are genera with the 2nd supramaxilla small (Mi- found (Sardinella, Ethmalosa, Ilisha, and crothrissa, Poecilothrissa), minute (Pota- Engraulis -all but the first monotypic in this mothrissa), or absent (Congothrissa, Thrat- area). By comparison, there are 14 marine tidion ). This general tendency toward clupeoid genera and about 24 species known reduction is also found in overall size and is from the Guianas area on the Western side carried to an extreme in Thrattidion nocti- ofthe Atlantic (Whitehead, 1973, pp. 10-1 1). vagus, which is mature at under 20 mm SL. Although the West African freshwater clu- Thus, when Thys van den Audenaerde peids appear to belong to a single subfamily, (1969) described Sierrathrissa leonensis from the Pellonulinae,3 they show considerable di- Sierra Leone, a species which he believed ma- versity. There are carnivores with large ca- tured at about 20 mm SL, it seemed that this nine teeth and the dorsal gill arch elements was merely another example of pellonuline separated in the midline (Cynothrissa, dwarfism and reduction (ofscutes, pelvic fin- rays, branchiostegal rays, etc.). However, 3 As yet inadequately defined, but uniting species that Roberts (1972, pp. 19-20) denied rather cat- lack an anterior supramaxilla (and occasionally the pos- egorically that these were adults and he terior also), have i7 pelvic finrays (occasionally i6), and claimed that Sierrathrissa was nothing more retain the posterior frontal fontanelles in adults. Con- than the unmetamorphosed form of a well- gothrissa gossei, originally placed in a separate family of Pellonula by Poll (1964), was later relegated to a tribe of the Pel- known species (or perhaps Cy- lonulinae (Poll, 1974); Taverne (1977) disagreed but, nothrissa). He equated thejuvenile Pellonula being the most recent statement, his acceptance of the described from the Gambia river by Svens- family Congothrissidae had to be followed by Poll and son (1933, pp. 47-48, fig. 16) with "Sierra- Teugels (1984). thrissa" and noted that Svensson, and later 1985 WHITEHEAD AND TEUGELS: PYGMY HERRING 3 5mm FIG. 1. Sierrathrissa leonensis, 25.4 mm SL, ex Sandje River at Tonde, Wouri system, Cameroon (MRAC 73-29-P-2059-2107). Johnels (1954, pp. 16-17), who named the Prof. AlfJohnels very kindly donated 14 syn- adults as Pellonula afzeliusi, both comment- types of P. afzeliusi to the British Museum ed on the larval features of specimens less (Natural History), of which four were that than about 30 SL. Similarly, Daget (1954, p. species (25.0-30.2 mm SL), but 10 were Sier- 68) supposed that his Microthrissa miri (i.e., rathrissa (13.2-28.4 mm SL, the largest being P. afzeliusi) underwent metamorphosis. As a ripening female). There could be no doubt Roberts pointed out (in litt. and during a visit that Sierrathrissa leonensis is a distinct species to London in 1976), the most distinctive fea- ofdwarfherring in West Afiican fresh waters. tures of Sierrathrissa (only three branchios- The additional specimens and the dissec- tegal rays, rudimentary scutes, few gillrakers, tions prompted further investigation of Sier- and one less pelvic finray than usual) are pre- rathrissa, so that the original description can cisely those one would expect in a larval stage. now be enlarged to include more morpho- Moreover, it was unlikely that a small di- metric and meristic data, as well as a descrip- vergent species would occur in rivers as far tion ofthe visceral anatomy and osteology of apart as the Gambia and the Niger, and in this minute species. Presumably its nearest any case he knew of no fully mature speci- modern relative is among the other 20 or so mens of Sierrathrissa and conversely, no de- freshwater clupeids of West Africa, perhaps scriptions of very small Pellonula that did a species of Pellonula, but until the juveniles not include the diagnostic features of Sier- ofthese have been studied in comparable de- rathrissa. tail, it is unwise to speculate on what may be The problem was in part resolved by Otobo advanced characters in Sierrathrissa or broach (1978), who reported sexually mature Sier- the philosophical question ofwhether its lar- rathrissa of both sexes in Lake Kainji, Ni- val features are primitive or derived. geria, and also by Teugels and Thys van den Audernaerde (1979), who compared small P. afzeliusi with similar sized Sierrathrissa and ACKNOWLEDGMENTS showed that, in addition to the differences We owe special thanks to Mr. J. Chambers already noted, Sierrathrissa lacks postclei- of the British Museum (Natural History) for thra, has a quite different growth pattern of making the alizarin and alcian blue prepa- the frontals, and has the dorsal fin much fur- rations and to Dr. W. IvantsoffofMacquarie ther back on the body (behind the pelvic in- University for providing the scanning elec- sertion). One of us (PJPW) received a Nige- tron microscope (SEM) photographs. The rian sample in fairly fresh condition, which whole fish drawing was made by Mr. A. Rey- included sexually mature and fully ripe in- gel of the Musee Royale de l'Afrique Cen- dividuals ofboth sexes, thus confirming Oto- trale. We are also indebted to Drs. P. H. bo's observations, and not long afterwards Greenwood and C. Patterson for reading this 4 AMERICAN MUSEUM NOVITATES NO. 2835 13-2 ~ i 1575 X~~~~~~~~ ,17~3 FIG. 2. Sierrathrissa leonensis, 13.2-20.9 mm SL, ex Gambia River, part of syntypical series of Pellonula afzeliusi (BMNH 1977.11.29.5-9). paper and for offering many helpful criticisms EXTERNAL FEATURES (figs. 1-5) and suggestions. Acknowledgment is made to the British An adult 6 of25.4 mm SL is shown in