Cast netting new species: Integrative taxonomy of Distichodus notospilus (Characiformes: Distichodontidae) discovers new species and overlooked areas of endemism in Central Africa Author Schmidt, Ray C. Biology Department, Randolph-Macon College, Ashland, VA 23005, USA; & Smithsonian Research Associate, National Museum of Natural History, Division of Fishes, Washington, DC 20560, USA Author Knobloch, Elise C. Biology Department, Randolph-Macon College, Ashland, VA 23005, USA; Author Barrientos, Christian Wildlife Conservation Society, Equatorial Guinea. Edificio Candy Vista Mar Of. 208 Bata Litoral, Equatorial Guinea text Zootaxa 2021 2021-04-09 4952 2 291 313 journal article 7330 10.11646/zootaxa.4952.2.5 210b95ea-4596-487c-914d-03df0694d33e 1175-5326 4674078 B8276A74-838A-4B54-87C4-8589F81A58F2 Distichodus microps sp. nov. urn:lsid:zoobank.org:act: C350FA00-3277-4202-9998-46AF78E9E681 Figures 2 , 3 , 4 , 5 , 8 , 9 ; Table 4 Holotype . USNM 451325 , ALC, 98.0 mm SL, Equatorial Guinea , Litoral , Rio Mbia at Menzong , 32 m elev, 2.07529° N , 9.92378° E , 2017 Equatorial Guinea expedition team, 30 June 2017 . Paratypes . MRAC 2020,005 ,P,0004, 1 ALC, 86.5 mm SL, voucher EqGui2017_0282, collection information the same as the holotype .— MRAC 2020,005 ,P,0005-0008, 4 ALC, 80.1–98.1mm SL, collection information the same as the holotype .— USNM 451457 , ALC, 81.6 mm SL, voucher EqGui2017_0274, collection information the same as the holotype .— USNM 451458 , 5 ALC, 55.5–110.5 mm SL, collection information the same as the holotype . Diagnosis. Distichodus microps is readily distinguished from the larger-bodied, higher-scale count Distichodus spp. (group B in Arroyave et al. 2020 : D. antonii Schilthuis , D. atroventralis Boulenger , D. fasciolatus Boulenger , D. lusosso Schilthuis , D. mossambicus Peters , D. sexfasciatus Boulenger , D. langi Nichols & Griscom , D. rostratus Günther , D. engycephalus Günther , D. kasaiensis Vreven, Moelants, & Snoeks , D. ingae Moelants & Snoeks , D. polli Abwe, Snoeks, Manda, & Vreven , D. petersii Pfeffer , D. nefasch Bonnaterre , D. brevipinnis Günther , and D. schenga Peters ) in having fewer lateral line scales (40–41 versus>60) and in achieving a smaller maximum standard length (< 15 cm versus> 30 cm ). This new species is also distinguished from the smaller-bodied, lower-scale count Distichodus spp. (group A in Arroyave et al. 2020 ) in the following ways. Distichodus microps is distinguished from D. decemmaculatus Pellegrin , and D. teugelsi Mamonekene & Vreven , in having two rows of teeth on the lower jaw versus one. Distichodus microps can be readily distinguished from D. noboli Boulenger , D. hypostomatus Pellegrin , and D. maculatus in having fewer scales along the lateral line (40–41 versus 45, 53–60, and 75 respectively), and distinguished from D. rufigiensis Norman , in not having prominent vertical bars along the sides. Distichodus microps is distinguished from D. kolleri and D. altus Boulenger , in having fewer dorsal-fin rays (15–17 total rays versus 21–26 and 17–18 respectively), and further distinguished from D. altus and D. affinis Günther , in having fewer total anal-fin rays (12–13 versus 21–22). Distichodus microps is distinguished from D . notospilus in having more scales along the lateral line (41, rarely 40 versus 37–39, rarely 40; Tables 4 & 5 ), a nearly inferior mouth versus subterminal in D. notospilus , a curved posterolateral margin of the opercle versus straight in D. notospilus , a smaller eye (56.7–80.4 versus 70.1–104.3 % of snout length; Figs. 5 , 6 , & 8), and a less prominent elongated spot at the base of the caudal fin. Distichodus microps is distinguished from D. mbiniensis in having a shallower body (usually six scales from LL to the pelvic fin versus seven; 34.1–38.7 versus 33.6–42.4% SL), fewer anal-fin rays (usually 12 total rays versus 13 or 14), a longer anal fin (15.0–17.8 versus 13.4–17.3% SL), a more inferior mouth versus the subterminal mouth in D. mbiniensis , a deeper (12.4–14.2 versus 11.8–13.0% SL) and a longer caudal peduncle (11.9–14.8 versus 9.7–12.6% SL), a smaller eye (56.7–80.4 versus 58.6–88.0% of snout length; Figs. 4B , 5 , 7 , & 8), a more narrow and elongate subopercle ( Fig. 8 ), and a deeper infraorbital 1 with a more rectangular anterolateral margin versus a more shallow infraorbital 1 with a curved anterolateral margin in D. mbiniensis ( Fig. 8 ). TABLE 4. Morphometric measurements and meristics of Distichodus microps sp. nov. (n=12; holotype and 11 paratypes). Standard length expressed in mm. All other measurements expressed in percent SL unless noted. Meristic data from holotype are identified by an “*”.

MORPHOMETRICS	Holotype	Range	Mean±%SD
Standard Length (mm)	98.0	55.5–110.5
Predorsal length	51.7	49.5–55.4	52.4±1.6
Head length	23.0	21.2–25.2	23.7±1.1
Eye diameter	5.7	5.2–7.4	6.2±0.6
Snout length	8.1	8.1–11.0	9.0±0.8
Interorbital distance	9.3	8.9–9.9	9.4±0.3
Internasal distance	5.3	4.9–5.8	5.3±0.3
Prepectoral length	23.5	22.3–27.2	24.9±1.6
Prepelvic length	52.0	51.7–56.1	53.8±1.3
Preanal length	77.7	77.5–82.5	79.4±1.7
Dorsal-fin terminus to adipose fin	19.1	19.1–24.2	21.0±1.3
Body depth	36.5	34.1–38.7	36.1±1.5
Pectoral-fin length	19.1	17.8–19.5	18.8±.5
Pectoral-fin base length	5.8	4.4–5.8	5.3±0.5
Pelvic-fin length	19.4	17.4–20.2	19.2±0.8
Pelvic-fin base length	5.2	4.3–5.8	5.0±0.5
Dorsal-fin height	23.5	20.2–26.8	23.0±2.1
Dorsal-fin base length	19.8	15.6–19.8	18.1±1.3
Adipose-fin height	8.1	5.9–8.2	7.1±0.7
Adipose-fin base length	3.3	2.2–3.6	2.9±0.5
Anal-fin length	17.4	15–17.8	16.5±0.9
Anal-fin base length	13.8	10.3–13.9	12.3±1.2
Caudal peduncle depth	13.9	12.4–14.2	13.6±0.4
Caudal peduncle length	12.2	11.9–14.8	13.2±1.0
Eye diameter as % of snout length	70.9	56.7–80.4	68.5±6.5
Eye diameter as % of head length	24.9	23.9–29.3	26±1.9
Snout length as % of head length	35.1	35.1–43.9	38.2±2.5
MERISTICS

Scales in lateral line 40 (2), 41* (10) Scales LL to dorsal 6.5 (2), 7.5* (10) Scales LL to pelvic 6* (12) Scales around caudal peduncle 16* (12) Dorsal-fin count iii-12 (1), iii-13 (9), iii-14* (1) Anal-fin count iii-9* (10), iii-10 (2) TABLE 5. Morphometric measurements and meristics of topotypic Distichodus notospilus (n=26). Standard length expressed in mm. All other measurements expressed in percent SL unless noted.

MORPHOMETRICS	Range Mean±%SD
Standard Length (mm)	46.8–115.6
Predorsal length	51.7–55.5 53.9±1.0
Head length	21.3–28.4 25.8±1.4
Eye diameter	5.8–9.6 7.4±0.7
Snout length	7.7–10.3 9.0±0.6
Interorbital distance	9.0–10.9 10.1±.4
Internasal distance	4.7–5.9 5.3±0.3
Prepectoral length	24.7–29.9 27.0±1.2
Prepelvic length	53.0–56.5 54.3±0.8
Preanal length	75.2–82.3 79.3±1.7
Dorsal-fin terminus to adipose fin	19.9–22.9 21.4±0.8
Body depth	34.8–44.3 39.6±2.2
Pectoral-fin length	16.9–20.2 18.8±0.9
Pectoral-fin base length	3.8–5.7 4.9±0.4
Pelvic-fin length	17.6–22.4 20.4±1.1
Pelvic-fin base length	3.8–5.8 4.8±0.5
Dorsal-fin height	22.7–34.2 27.1±2.3
Dorsal-fin base length	16.4–20.3 18.2±1.0
Adipose-fin height	5.0–8.3 6.8±0.8
Adipose-fin base length	1.8–3.1 2.4±0.3
Anal-fin length	12.9–19.4 16.5±1.4
Anal-fin base length	11.2–14.8 12.5±0.8
Caudal peduncle depth	12.3–14.1 13.4±0.4
Caudal peduncle length	10.2–14.4 12.0±0.9
Eye diameter as % of Snout length	70.1–104.3 82.1±8.2
Eye diameter as % of Head length	26.5–33.8 28.6±1.7
Snout length as % of Head length	30.3–40.3 35.0±2.4
MERISTICS
Scales in lateral line	37 (2), 38 (9), 39 (14), 40 (1)
Scales LL to dorsal	6.5 (13), 7.5 (11)
Scales LL to pelvic	6 (7), 7 (19)
Scales around caudal peduncle	16 (26)
Dorsal-fin count	ii-14 (3), ii-15 (1), iii-13 (11), iii-14 (11)
Anal-fin count	iii-10 (12), iii-11 (14)

Description. Morphometrics and meristics for holotype and paratypes of Distichodus microps are summarized in table 4. Holotype shown in figure 5 and the live color of a paratype is shown in figure 9. Maximum observed size: 110.5 mm SL. Body laterally compressed and moderately elongate. Dorsal profile with convex curve from snout to anterior margins of head; weakly convex to dorsal-fin origin. Profile from origin of dorsal fin to adipose fin straight to slightly convex; concave from adipose to caudal fin. Ventral profile broadly convex from tip of snout to the terminus of the anal fin; slightly concave in area from anal-fin terminus to caudal fin. Body covered in relatively large ctenoid scales; extending over proximal half of adipose and caudal fins; extending beyond proximal half in lobes of caudal fin. Mouth inferior to nearly subterminal; two rows of bicuspid teeth in upper and lower jaws. Dorsal fin with straight to slightly concave distal margin; its origin anterior to vertical of pelvic-fin origin. Adipose fin origin nearly two thirds the distance from dorsal-fin terminus to caudal fin; anterior to vertical of anal-fin terminus and extends beyond vertical of anal-fin terminus. Caudal fin forked; tips of upper and lower lobe slightly rounded with moderate point. Anal fin with slightly concave margin; base about five-sixths the length of longest ray; not reaching caudal fin when flexed to body. Pelvic-fin origins at mid-length of snout to caudal fin distance; nearly as long as head length. Pectoral-fin origin posterior to vertical of posterior edge of subopercle; horizontal of pectoral-fin origin near or slightly inferior to mouth; nearly as long as pelvic fin. FIGURE 5. Distichodus microps , a new species, holotype, USNM 451325, ALC, 98.0 mm SL, Equatorial Guinea, Litoral, Rio Mbia at Menzong, 32 m elev, 2.07529° N, 9.92378° E; Photograph by S. Raredon. FIGURE 6. Topotypic Distichodus notospilus , OS 21266, Gabon, Province de la Ngounié, SINDARA C—Below the rapids of Sindara on the left bank, in a small inundation zone with a sandy bottom that is exposed in the dry season, 1.03492° S, 10.69116° E; Photograph by S. Raredon. Coloration. Live coloration: specimens silver with some red and gold flecks along head and sides anteriorly and becoming more diffuse posteriorly. Pectoral and anal fins red. Dorsal fin cream at based with black band beginning about one-third the length of the third ray stretching nearly to the distal tip and roughly to the base of the fourth ray through the base of the tenth ray ( Fig. 9 ). Diffuse ovoid black spot at base of caudal fin. Typical coloration of preserved specimens shown in figure 5. Specimens light grey to silver along sides. Scales darker gray on upper quarter of sides. Pores along the lateral line with melanophores forming a diffuse stripe. Faint black ovoid spot at base of caudal fin. Fins clear with black spot in dorsal fin as previously described. Etymology. The specific epithet is a combination of the Greek “micro” and “ops” and refers to the small eye relative to the snout and head length. Distribution. Distichodus microps is only known from the type locality in the Mbia River drainage in Equatorial Guinea . The type specimens were collected by cast net in ~ 2 m deep flowing water along the bank downstream from the older bridge crossing on the road from Bata to Rio Campo. Roman collected at two localities on the Mbia River in the 1960s but did not record any Distichodus species ( Roman 1971 ). Additional surveys are needed to determine the distribution of this species within the Mbia River drainage. Published sequences from populations in the lower Ntem River suggest that D. microps species may also be present in the Lower Ntem and potentially in other coastal rivers in southern Cameroon ( Fig. 2 ; see discussion for further comments). Conservation status. Distichodus microps is presently only known to occur in the Mbia River drainage in Equatorial Guinea . The extant of occurrence (EOO) is 3,467 km 2 and this species occurs in less than five threatbased locations. The ongoing threats to the habitats preferred by D. microps include habitat destruction and sedimentation resulting from road construction and logging activities in the region. Due to the restricted EOO and limited number of locations available to this species, this species is assessed in the IUCN Red List as Endangered ( Schmidt et al. 2020 a ).