A new species of Diplotaxodon (Cichliformes: Cichlidae) from Lake Malaŵi Author Konings, Adrianus F. Cichlid Press, PO Box 13608, El Paso, TX 79913. text Zootaxa 2021 2021-01-07 4903 2 275 284 journal article 9052 10.11646/zootaxa.4903.2.7 a2718082-7cbb-4d25-850d-3dfb7d0ea8af 1175-5326 4423072 7F6F65B9-A5A2-498A-AD62-03F0CBDD85B5 Diplotaxodon dentatus , new species Figs. 2 , 3 , 4 ; Table 1 . Holotype . SAIAB 209443 (male), 108.7 mm SL, collected by trawl off Thumbi East Island , Monkey Bay , Malaŵi , Africa at 73 m depth , J. R . Stauffer , 27 March 1985 . Paratypes . SAIAB 209441 , 7 , 96.9–119.7 mm SL, data as for holotype . Diagnosis. The oblique mouth, a prognathic lower jaw, a small knob at the synthesis of the dentaries, the absence of distinct bars or stripes ( Eccles & Trewavas, 1989 ), the closely-spaced teeth, and lack of beak-like premaxillaries ( Trewavas, 1935 ; Turner, 1994 ) place this species in Diplotaxodon . Diplotaxodon dentatus has a smaller body depth (26.4–28.4 % SL) than D. altus (35.1–37.8% SL) ( Stauffer et al., 2018 ), D. greenwoodi (34.2–36.5% SL) ( Stauffer and McKaye, 1986 ), D. macrops (33.9–37.6 % SL), D. apogon (32.4–37.3 % SL), D. aeneus (34.3–37.1 % SL), and D. ecclesi (35.5 % SL) ( Turner and Stauffer, 1998 ). There are more gill rakers on the first ceratobranchial in D. dentatus than in D. longimaxilla (23–27 vs. 16–21). Diplotaxodon dentatus has fewer teeth in the outer row of the left lower jaw (17–25) that are exposed ( Fig. 3 ) when the mouth is closed and more widely spaced than those of D. limnothrissa (36–46), which are close together and embedded ( Turner, 1994 ). Diplotaxodon dentatus has a shorter snout length (26.6–29.2 % HL) than D. argenteus (31.7–34.2 % HL), a longer post-orbital head length (39.0–41.7 vs. 37.7–38.8 % HL), a narrower cheek depth (10.6–15.2 vs. 15.3–17.0 % HL), generally more gill-rakers on the first ceratobranchial (23–27 vs. 20–23), and a greater distance between the anterior origin of the dorsal fin to the posterior insertion of the anal fin (50.3–53.1 vs. 49.6–51.2 % SL). Description. Morphometric ratios and meristic data in Table 1 . Body fusiform, slender, and laterally compressed, deepest at origin of dorsal fin ( Figs. 2 & 3 ). Dorsal-fin origin posterior to operculum, above insertion of pectoral fin, dorsal-fin spines increasing to maximum length over 8-10 spines. Caudal peduncle relatively long, 4.8–5.6 times SL. Holotype with 16 abdominal and 18 caudal vertebrae (CT scan Fig. 3 ), typical of Diplotaxodon spp. Caudal fin emarginate. Anal-fin, below vertical through first dorsal-fin ray; anal-fin rayed section rounded not reaching to caudal-fin base. Pectoral-fin origin close behind gill slit; pectoral fin in mature males to anal-fin origin. Pelvic fin, short, and not to anal-fin origin. Ctenoid scales small, 32–38 in lateral line. Upper lateral line with slight upward curve anteriorly, to before posterior insertion dorsal fin; lower lateral line straight through mid-caudal peduncle; 0–1 pored scales posterior to hypural plate. FIGURE 2. Diplotaxodon dentatus , Holotype SAIAB 209443 (male), 108.7 mm SL, collected by trawl off Thumbi East Island, Monkey Bay, Malaŵi, Africa, 27 March 1985. FIGURE 3. CT scan of the lateral view of the holotype of Diplotaxodon dentatus SAIAB 209443 (male), 108.7 mm SL. FIGURE 4. The head of the holotype of Diplotaxodon dentatus SAIAB 209443 (male), 108.7 mm SL showing the exposed teeth (enlarged in inset) TABLE 1. Morphometric and meristic values of Diplotaxodon dentatus (n=8). The mean, standard deviation and range include holotype and paratypes.
Variable Holotype Mean SD Range
Standard length, mm 108.7 105.5 7.0 96.9–119.7
Head length, mm 37.6 36.6 2.2 34.1–40.4
Percent of standard length
Head length 34.6 34.7 0.75 33.8–36.0
Body depth 27.0 27.5 0.77 26.4–28.4
Snout to dorsal-fin origin 35.5 36.0 1.5 34.5–39.2
Snout to pelvic-fin origin 38.7 39.8 1.8 37.7–43.4
Dorsal fin base length 46.6 47.5 1.0 46.2–49.3
Anterior dorsal to anterior anal 41.2 41.8 1.4 39.6–44.2
Anterior dorsal to posterior anal 51.1 51.4 1.1 50.3–53.1
Posterior dorsal to anterior anal 27.1 26.0 1.2 24.2–27.9
Posterior dorsal to posterior anal 15.0 14.1 0.9 12.4–15.2
Posterior dorsal ventral caudal 21.6 22.0 1.3 20.1–24.0
Posterior anal to dorsal caudal 25.5 23.5 1.4 21.5–25.5
Anterior dorsal to pelvic-fin origin 27.8 27.8 0.7 26.8–29.2
Posterior dorsal to pelvic-fin origin 46.8 48.3 1.4 46.4–50.1
Caudal peduncle length 20.4 19.3 1.0 17.7–20.7
Least caudal peduncle depth 12.0 11.2 0.6 10.1–12.0
Percent of head length
Snout length 27.9 27.9 0.7 26.6–29.2
Postorbital head length 40.8 40.1 0.9 39.0–41.7
Horizontal eye diameter 31.9 32.0 1.3 29.9–33.9
Vertical eye diameter 30.1 31.0 1.8 28.4–33.6
Pre-orbital depth 18.2 18.3 1.5 15.7–20.0
Cheek depth 13.3 12.9 1.4 10.6–15.2
Lower jaw length 41.2 3q9.8 1.2 38.0–41.2
Head depth 71.6 67.8 3.9 62.8–73.1
Counts Mode Freq Range
Dorsal-fin spines 16 15 50 14–16
Dorsal-fin rays 13 13 50 11–13
Anal-fin spines 3 3 100
Anal-fin rays 10 11 50 10–12
Pelvic-fin rays 5 5 100
Pectoral-fin rays 14 13 87.5 13–14
Lateral line scales 35 35 37.5 32–38
Pored scales posterior to LL 1 0/1 50 0–1
Cheek Scales 2 3 75 2–3
Gill-rakers on first epibranchial 6 7 62.5 6–8
Gill-rakers on first ceratobranchial 24 25 37.5 23–27
Teeth outer row of left lower jaw 22 22/26 25 17–25
Tooth rows on upper jaw 2 2 100
Tooth rows on lower jaw 2 2 100
Head elongate (33.8–36.0 % SL), length greater than body depth, with lower jaw at oblique angle ( Fig. 2 & 4 ). Eye large (horizontal eye diameter 29.9–33.9 % HL, vertical eye diameter 28.4–33.6 % HL), greater than pre-orbital depth (15.7–20.0 % HL). Snout smaller than orbit diameter, 26.6–29.2 % HL, with premaxillary pedicel to vertical through anterior orbit. Cheek shallow (10.6–15.2 % HL) with 2–3 scale rows. Mouth large and superior, lower jaw 38.0–41.2 % HL; teeth on lower and upper jaw caniniform, with space between them about width of tooth ( 17–25 in outer row of left lower jaw) and exposed ( Fig. 4 ). Teeth on pharyngeal jaws unicuspid ( Fig. 5 ). First ceratobranchial with 23–27 gill-rakers and first epibranchial with 6–8 rakers. FIGURE 5. CT scan of the upper and lower pharyngeal bones of the holotype of Diplotaxodon dentatus, SAIAB 209443 (male), 108.7 mm SL. Coloration. Preserved males with dark snout. Flank dark dorsally, fading lighter ventrally. Dorsal fin with black lappets; caudal fin with 5–6 central rays black; anal fin with distal portion of membranes dark gray to black and without egg spots; pelvic fins black and pectoral fins clear. Head with black gular region. Coloration of preserved females similar to males, but lighter overall. Live coloration not recorded.
Remarks. In general appearance Diplotaxodon dentatus is most similar to D. argenteus and also shares the character of exposed teeth when the mouth is closed. When the morphometric and meristic data for D. dentatus were compared to that of the lectotype and paralectotypes of D. argenteus the first principal component (size variable) of the morphometric data explained 94.6% of the observed variance and the sheared second principal component explained 39.4% of the remaining 5.4%. Variables that had the highest loadings on the sheared second principal components of the morphometric data were distance between the posterior insertion of the dorsal fin and origin of the pelvic fin (0.55), distance between the anterior insertion of the dorsal fin and origin of the pelvic fin (-0.39), and caudal peduncle depth (0.33). The first principal component of the meristic data explained 45.8% of the variance. Variables with the highest loadings on the first principal components of the meristic data were number of gill-rakers on the ceratobranchial of the first arch (-0.56), pored scales posterior to the hypural plate (0.55), and number of gill-rakers on the epibranchial (-0.41). A plot of the second sheared principal component of the morphometric data versus the first principal component of the meristic data shows that D. dentatus is clearly separated from D. argenteus ( Fig. 6 ). FIGURE 6. First principal components (meristic data) plotted against the sheared second principal components (morphometric data) of Diplotaxodon dentatus (x) and Diplotaxodon argenteus (*). Ct scans revealed that the stomachs of the type series were empty, however, based on the exposed teeth in the oral jaws and the unicuspid teeth of the pharyngeal jaws ( Fig. 5 ) it is suggested that D. dentatus is a piscivore. Etymology. Dentatus from Latin meaning toothed or having teeth alluding to the caniniform teeth on the outer margin of the dentary and premaxilla which are exposed when the mouth is closed.