New Three-Spotted Cichlid Species with Hypertrophied Lips (Teleostei: Cichlidae) from the Deep Waters of Lake Malaŵi/Nyasa, Africa
To date, about 330 currently recognized species have been described from the haplochromine cichlid species flock endemic to Lake Malaŵi, Africa. Several hundred additional species await taxonomic treatment. A new species from this flock belonging to the genus Otopharynx is described from the deep waters of Lake Malaŵi. This species (known from only two demersal trawls made at different localities in water 78–135 m deep) is characterized by the presence of three distinct spots that do not extend to the dorsum and by moderately stout, bicuspid oral jaw teeth in outer series, placing it in the genus Otopharynx. It is a relatively deep-bodied member of this genus that differs from all other three-spotted cichlids by its fleshy, lobed lips. The greatly hypertrophied lips in this species may serve a sensory function by acting as an enlarged substrate for the expression of numerous taste buds in a peri-oral field. Additional characters are presented that distinguish this new species from its congeners. The genus Otopharynx is not defined on the basis of synapomorphies and is likely an artificial group. Nevertheless, it is a recognizable taxon that, for the time being, serves a useful purpose in organizing members of an exceedingly complex species flock, the systematics of which is far from complete.Abstract
Map of Lake Malaŵi (Africa) showing the only two localities at which Otopharynx pachycheilus specimens have been collected. Depths of collection were 125–135 m near Ngara and 78–79 m at Domira Bay
Anatomy of the lips of Otopharynx pachycheilus. Head and lips of (A) paratype (MRAC99-88-P-1, T136; scale bar = 20 mm) and (B) paratype (CU80378, T139; scale bar = 20 mm), showing specimens before sections were removed from the middle and right side of the lips. (C) Sagittal section through the medial portion of the upper lip of specimen T136 (scale bar = 0.25 mm). Orientation of section rotated 45 degrees counterclockwise relative to position of fish in panel A. Shown are the inner, loose connective tissue layer (LCT), containing arteries and veins (BV, blood vessel), and the dermis (De), which is composed of a tight meshwork of collagen fibers but also contains nerve fibers and capillaries. The outer, epithelial layer (Ep) contains numerous taste buds supported by dermal papillae (DP). The arrow indicates a single taste bud, magnified in panel D. (D) Enlarged view of taste bud from panel C (scale bar = 20 μm; taste pore not visible). (E) Enlarged view of a second dermal papilla (DP) and taste bud from specimen T136, showing taste pore (TP) (scale bar = 25 μm). (F) Section tangential to the surface of the epithelium showing dermal papillae in cross-section (specimen T136, rostral portion of upper lip; scale bar = 100 μm). The spacing and distribution of taste buds, which sit atop the papillae, can be seen in this section. (G) Taste bud doublet in cross section, at the level of the basal cells (specimen T139; scale bar = 20 μm)
Four other cichlid species endemic to Lake Malaŵi that have independently evolved enlarged, lobed lips. (A) Cheilochromis euchilus (Gome, on Malaŵi-Mozambique border); (B) Placidochromis milomo (Likoma Island); (C) Melanochromis labrosus (Katale Island); (D) Eclectochromis ornatus (Gome). Photos courtesy of A. Konings
(A) Otopharynx pachycheilus holotype (MRAC99-88-P-4, adult male, 143.3 mm SL; scale bar = 40 mm) and lower pharyngeal element (CU80378, T132) shown in lateral (B) and occlusal (C) views (scale bar = 5 mm)