Amphilius crassus Thomson & Hilber

Thomson, Alfred W., Page, Lawrence M. & Hilber, Samantha A., 2015, Revision of the Amphilius jacksonii complex (Siluriformes: Amphiliidae), with the descriptions of five new species, Zootaxa 3986 (1), pp. 61-87 : 78-81

Amphilius crassus Thomson & Hilber , new species

( Fig. 8 , Table 6 )

Amphilius platychir (non Günther).— Bailey, 1969: 192 (in part), Kilombero (BMNH 1969.2.11.192–194) [Rufiji River basin].

Holotype. UF 184237, ex. UF 170743, Tanzania, Sonjo River at bridge in Man'gula on road from Mikumi to Ifakara, altitude 302 m, Rufiji River basin, 07° 48' 29.6”S, 36° 53' 47.6"E (86.3 mm SL).

Paratypes. Rufiji River basin: AMNH 258334, same data as holotype, ex. CU 93734 (10: 43.4–61.5); AUM 57571, same data as holotype, ex. CU 93734 (10: 40.7–66.8); BMNH 1969.2.11.192–194, Tanzania, Near Kiberege, trib of Kilombero River, ca. 07°57'S, 36°52'E (3: 30.8–31.7); CU 93731, Idete River at bridge in Idete on road from Ifakara to Taveta, altitude 310 m, 08°06'14”S, 36°29'17"E (7: 27.3–67.3); CU 93732, Tanzania, 12 Bridges River at overhead bridge for train on road from Mikumi to Ifakara, altitude 419 m, 07°27'53”S, 37°00'52"E (4: 49.7–72.4); CU 93734, same data as holotype, (40: 36.7–69.9); MRAC B3–06–P–7–16, same data as holotype, ex. UF 170743 (10: 43.3–60.5); SAIAB 187279, same data as holotype, ex. UF 170743 (10: 45.1–57.0); UF 170706, same data as CU 93732 (5: 47.6–80.3); UF 170729, same data as CU 93731 (8: 28.9–84.7); UF 170743, same data as holotype (40: 39.8–84.7).

Non-types. Wami River basin: CU 93730, Tanzania, Divue River above & below falls along road from Dumila to Turiani, altitude 374 m, 06°10'26.8”S, 37°34'59.8"E (10: 27.1–57.5); CU 93733, Tanzania, Wami River at bridge in Rudewa on road from Dumila to Kilosa, altitude 433 m, 06°40'45.2”S, 37°07'27.0"E (8: 27.1–41.2); UF 170707, same data as CU 93733 (10: 25.9–77.0); UF 170708, same data as CU 93730 (10: 40.0–59.4).

Diagnosis. Diagnostic characters are summarized in Table 2 . Amphilius n. sp.. Rufiji is diagnosed from A. jacksonii , A. ruziziensis , A. pedunculus , and A. lujani by its shorter caudal peduncle (caudal peduncle length 13.3– 15.5% SL vs. 16.0–20.9% SL), and from A. jacksonii , A. ruziziensis , and A. lujani by its deeper caudal peduncle (caudal peduncle depth 10.1–12.0% SL vs.4.8–9.5% SL). It is diagnosed from A. ruziziensis , A. n. sp. . Malagarasi, and A. frieli by its longer dorsal-fin insertion to adipose-fin insertion length (42.2–44.6% SL vs. 37.5–41.7% SL). Amphilius crassus is further diagnosed from A. jacksonii by its deeper body (body depth at anus 14.5–17.4% SL vs. 9.6–13.2% SL), and from A. ruziziensis by wider interorbital width (28.9–34.1% HL vs. 23.4–25.1% HL) and deeper body (body depth at anus 14.5–17.4% SL vs. 11.1–12.9% SL). It is further diagnosed from A. lujani by having fewer branched pectoral-fin rays (7–8, rarely 9 vs. 9), and from A. frieli by its fewer branchiostegal rays (6– 7, rarely 8 vs. 8–9), fewer branched pectoral-fin rays (7–8, rarely 9 vs. 9–10), fewer gill rakers on the first gill arch (6–8, rarely 9 vs. 10–11, rarely 9 or 12), and wider interorbital width (28.9–34.1% HL vs. 25.1–27.7% HL).

Description. Morphometric data are in Table 6 . Body elongate, ventral profile flattened ventrally to anal-fin base, then tapered dorsally to end of caudal peduncle. Dorsal profile rising steeply from tip of snout to dorsal-fin origin, then nearly horizontal to end of caudal peduncle. Greatest body depth at dorsal-fin origin. Caudal peduncle laterally compressed, with crenellated epidermal fold. Anus and urogenital openings located at midpoint of adpressed pelvic fin, closer to pelvic-fin insertion than to origin of anal fin. Skin smooth. Lateral line complete, extending from dorsal edge of opercular cavity to caudal-fin base.

Head and anterior part of body depressed and broad. Head wedge-shaped in lateral view. Snout broad, blunt when viewed from above. Head becoming wider from tip of snout to pectoral-fin base. Branchiostegal membranes moderately joined at isthmus forming a V -shaped connection.

Mouth broad, gently curved, subterminal. Lips moderately fleshy, slightly papillate. Rictal lobe large and slightly papillate. Anterior portion of premaxillary tooth band exposed with mouth closed. Premaxillary tooth patches joined, forming crescent shaped band. Premaxillary and dentary teeth short, conical. Dentary tooth patches forming U -shaped band, separated medially.

Three pairs of simple, tapered circumoral barbels. Maxillary barbel large, fleshy and flattened with pointed tip; barbel extending posterolaterally from corner of mouth, to pectoral-fin base. Outer mandibular barbel thin with pointed tip, origin at posterior corner of lower jaw, extending to origin of pectoral-fin. Inner mandibular barbel originates anterolaterally of inner mandibular barbel, extending to edge of branchiostegal membrane. Branchiostegal membrane with 6 (22), 7 (123), or 8 (2) rays. Gill rakers on first epibranchial 1 (1), 2 (122) or 3 (24); rakers on first ceratobranchial 4 (19), 5 (95), or 6 (33); total gill rakers on first arch 6 (19), 7 (79) 8 (42) or 9 (7).

Eye small, positioned dorsolaterally approximately midway between tip of snout and posterior margin of operculum. Horizontal diameter of eye slightly wider than vertical diameter. Eye without free orbit; covered with skin confluent with dorsal surface of head. Anterior and posterior nares with prominent tubular rims; nares separate but relatively close to each other. Posterior nare located about midway between eye and tip of snout.

Dorsal-fin origin at point over tip of pectoral fin. Dorsal fin with i,6 (147) rays, and fin margin straight. Pectoral fin with i,7 (13), i,8 (130), or i,9 (4) rays; unbranched ray greatly thickened. Pectoral fin with four or five innermost rays progressively shorter making posterior fin margin rounded. Origin of pelvic fin posterior of dorsalfin insertion. Pelvic fin with i,5 (147) rays with first ray unbranched and greatly thickened. Pelvic fin with straight posterior margin.

Adipose-fin base longer than anal-fin base, origin anterior to origin of anal-fin base, fin extending past anal-fin insertion. Margin strongly convex with sharply rounded edge, deeply incised posteriorly. Caudal fin deeply forked with tips of lobes rounded; fin with i,5,5,i (4), i,5,6,i (141) or i,6,6,i (2) principal rays. Anal fin with short base, origin posterior to origin of adipose-fin base, with ii,6 (56), ii,7 (34), iii,5 (3), iii,6 (50), or iii,7 (5) rays. Anal-fin margin almost straight.

Coloration. Body variably mottled with dark saddles. First saddle posterior of head, second saddle at dorsal fin, third saddle between dorsal and adipose fins, fourth saddle under anterior part of adipose fin, and fifth saddle on caudal peduncle. All saddles connected laterally by broad stripe. Venter light brown with fourth and fifth saddles meeting those of opposite side. Dorsal, and anal fins light brown with dark medial band. Adipose fin dark brown to black, with anterior and posterior distal edges cream-colored. Pectoral and pelvic fins positioned horizontally with upper surfaces cream-colored with dark fin base and dark medial band. Lower surfaces light yellow. Caudal fin cream-colored with dark markings on upper and lower lobes. Caudal coloration variable but usually spotted and asymmetrical, with lower lobe more pigmented.

Distribution. Rufiji and Wami river basins, eastern Tanzania ( Fig. 6 ).

Etymology. From the Latin noun crassus (m), meaning fat or stout in reference to the deep, stout body.

Figures

FIGURE 6. Distributions of Amphilius pedunculus (diamonds), A. frieli (dots), A. crassus (crosses) and A. lujani (squares).

FIGURE 8. Amphilius crassus, UF 184237, 86.3 mm SL, holotype; lateral, dorsal and ventral views.

Tables

TABLE 6. Morphometric data for Amphilius crassus. Range and mean include the holotype.

	Holotype	Range (n=68)	Mean±SD
%SL
Head length	25.9	24.0–26.7	25.4±0.7
Head width	21.1	19.6–22.1	20.6±0.5
Head height	13.5	12.9–15.2	13.8±0.5
Body depth	17.3	15.6–19.3	17.0±0.8
Body depth at anus	17.0	14.5–17.4	15.7±0.7
Predorsal length	37.7	35.6–39.7	37.4±1.1
Prepectoral length	19.2	18.4–21.1	19.8±0.6
Preanal length	74.1	70.7–75.0	72.9±1.1
Dorsal-fin base length	12.2	10.1–12.3	11.1±0.6
Adipose-fin base length	22.7	19.3–24.2	21.2±1.2
Anal-fin base length	10.9	10.5–13.8	11.9±0.7
Pelvic-fin length	20.6	18.2–20.9	19.8±0.7
Pectoral-fin length	21.7	20.5–24.1	22.2±0.7
Anal-fin length	19.2	18.1–21.4	19.7±0.8
Caudal peduncle length	15.3	13.3–15.5	14.8±0.6
Caudal peduncle depth	10.5	10.1–12.0	10.9±0.4
Anus to anal fin length	14.9	12.4–16.6	14.2±0.9
Prepelvic length	49.8	46.7–51.6	49.2±1.1
Postpelvic length	50.7	49.3–54.6	51.4±1.1
Dorsal-fin insertion to adipose	43.3	42.2–44.6	43.1±0.6
Dorsal-fin origin to caudal	67.8	63.2–68.3	66.2±1.2
Preanus length	58.5	56.8–60.9	58.8±1.1
%HL
Snout length	50.5	45.3–50.7	48.2±1.2
Interorbital distance	28.9	28.9–34.1	31.0±1.3
Maxillary barbel length	76.1	65.5–91.4	75.0±5.6
Inner mandibular barbel length	34.3	33.7–50.7	39.8±3.7
Outer mandibular barbel length	60.4	51.1–82.2	64.1±6.0
Eye diameter	12.5	12.1–16.7	13.8±1.1