Trematocranus pachychilus, Dierickx, Katrien, Hanssens, Mark, Rusuwa, Bosco & Snoeks, Jos, 2018

Dierickx, Katrien, Hanssens, Mark, Rusuwa, Bosco & Snoeks, Jos, 2018, Trematocranuspachychilus, a new endemic cichlid from Lake Malawi (Teleostei, Cichlidae), ZooKeys 743, pp. 153-166 : 156-158

Trematocranus pachychilus sp. n.

Type material.

Holotype: MRAC 99-041-P-4781, 154.6 mm SL, Jafua Bay, Lake Malawi, Mozambique, 12°07.13'S, 34°45.89'E, Coll. Snoeks & Hanssens (4 April 1998). Paratypes: MRAC 99-041-P-4782, 151.9 mm SL, same data as holotype; MRAC 99-041-P-5037-5041 (5), 117.7 - 154.5 mm SL, same data as holotype.

Differential diagnosis.

Trematocranus pachychilus is clearly distinct from all other known species of the genus by its thick lips. It can further be distinguished from T. labifer by its molariform pharyngeal dentition while the latter has slender teeth on the lower pharyngeal jaw ( Eccles and Trewavas 1989).

In T. placodon (Fig. 5C, D) lips are usually very small. While T. pachychilus has a rather concave head, as in T. microstoma , T. placodon has a more distinct convex head. In both T. pachychilus and T. placodon , the smaller specimens have a straighter head profile. Coincidentally, in two large specimens of T. placodon , found at Jafua Bay, the head is slightly concave. The teeth of T. pachychilus are less broad, more densely spaced and slightly less numerous (36-47 vs. 41-57) than in T. placodon . Trematocranus pachychilus has more upper lateral line scales (22-24 vs. 19-22) and more dorsal fin rays (11-12 vs. 9-11) than T. placodon . The pharyngeal bones of T. pachychilus are less developed than in T. placodon . They are shallower (9.4-10.4% HL vs 13.8-16.8% HL), narrower (29.7-33.2% HL vs. 36.1-48.7% HL) and shorter (21.8-30.8% HL vs. 29.8-35.9% HL) than those of T. placodon .

The dentigerous area is also narrower than in T. placodon (21.9-24.4% HL vs. 24.2-27.5% HL). Both species have large, molariform pharyngeal teeth, although in T. pachychilus the lateral teeth are smaller and more numerous than in T. placodon . The number of teeth on the posterior pharyngeal row in T. pachychilus is higher than in T. placodon (23-27 vs.11-23).

In T. microstoma (Fig. 5B) the lips are intermediate except for some specimens of Mazinzi Bay (see discussion). The snout of T. pachychilus is shorter than that of T. microstoma (34.8-40.9% HL vs. 38.0-42.4% HL). Trematocranus pachychilus has bicuspid oral teeth on the outer rows while T. microstoma has slender unicuspid teeth. It has fewer inner teeth rows (3-5 vs. 6-8) on the lower jaw than T. microstoma . The lachrymal depth is clearly shorter than in T. microstoma (22.9-29.7% HL vs. 29.3-32.0% HL), while the eye diameter is larger (25.2-29.5% HL vs. 21.2-25.5% HL). The pharyngeal bones (Fig. 6) are more developed in T. pachychilus than in T. microstoma . The dentigerous area of T. pachychilus is wider than in T. microstoma (21.9-24.4% HL vs. 18.8-23.6% HL). The dentition of the lower pharyngeal bone is similar in both species, with the median teeth enlarged and the lateral teeth small and numerous.

Description.

Based on the holotype and six paratypes examined. See Figures 5A and 6A. Qualitative observations are made in the context of Lake Malawi haplochromine cichlids as was done by Snoeks (2004).

Body deep and laterally compressed. Head steep. Most specimens with a slight concavity at eye level; some, especially smaller specimens, with a merely straight head profile. Snout pointed. Mouth terminal. Lips very thick and equally developed in most specimens. Larger specimens with thicker lips than small specimens; smaller specimens often with a clear boundary between lower lip and chin. Maxilla does not extend to level of eye.

Teeth not readily observable, being to a large extent or fully covered by the fleshy gums. Outer row of teeth on upper and lower jaws with mainly unequally bicuspid and some unicuspid teeth in the postero-lateral parts; teeth slender, generally straight and slightly curved inwards; crown slightly wider than base. Anterior bicuspid teeth more pointed and sharp; lateral bicuspid teeth often rounded. Inner rows mostly with unicuspid teeth. Larger specimens with more bicuspid teeth anteriorly in inner rows. Inner teeth rows difficult to observe; 3-4 inner rows on upper jaw (counted in four specimens); 3-5 on lower jaw (six specimens).

Pectoral fins implanted slightly behind level of dorsal fin origin. Pelvic fin origin positioned slightly more backwards. Anal fin implanted anterior to level of first soft dorsal fin ray.

Lower pharyngeal bone triangular, large, wider than long, and deep. Teeth molariform; central teeth much larger than lateral teeth. Outermost teeth on the posterior rows very small and numerous.

Colour pattern in preservation.

Body generally brown; some specimens slightly more greyish. Dorsum darker than belly. Very dark-coloured on the dorsal parts of head and body contiguous with dorsal fin base in most specimens. Some large darker spots usually on operculum, supra-pectoral in front of dorsal fin origin, dorso-lateral above and on upper lateral line in middle of flank, supra-anal near end of upper lateral line, and caudal peduncle. Clear dark maculae on spiny part of dorsal fin; sometimes also on soft dorsal fin part and caudal fin. Pelvic and anal fins yellowish brown in females; fin base and distal part clearly darker in males. One specimen with a vague brown midlateral stripe along flank.

Etymology.

The specific name, pachychilus , means thick-lip and is derived from the Greek words παχυς (fat, adipose, plump) and χειλος (lip, edge) with reference to the diagnostic character, the thick lips.

Geographical distribution.

The specimens of T. pachychilus were only found at Jafua Bay, north of Cobue in Lake Malawi, Mozambique. All specimens were caught in a single haul of a bottom trawl at a depth of 10.8-12.8 m (12°07.13'S, 34°45.89'E).

Ecology.

Shell fragments of snails were observed in the stomachs of some specimens on X-rays. Stomach analyses were not performed so as to not damage the type series. Thick and fleshy lips are associated with rocky habitats in cichlids, since fish feeding between rocks use their lips as a seal to be able to suck out their prey from crevices and as a protection against sharp rocks ( Machado-Schiaffino et al. 2014). Since all specimens were found in bottom trawls over soft substrates, we are unsure about the association of the new species with rocky habitats.