Distichodus microps, Schmidt & Knobloch & Barrientos, 2021

Schmidt, Ray C., Knobloch, Elise C. & Barrientos, Christian, 2021, Cast netting new species: Integrative taxonomy of Distichodus notospilus (Characiformes: Distichodontidae) discovers new species and overlooked areas of endemism in Central Africa, Zootaxa 4952 (2), pp. 291-313 : 301-305

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 ).

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.

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).

Figures

FIGURE 2. Phylogeny of Distichodus spp. inferred from 996 bp of cytochrome b (A). Phylogeny inferred from concatenated dataset of 996 bp CYTB, 729 bp MYH6, and 627 bp of CO1(B). Posterior probabilities from Bayesian inference above major branches; above 0.95 not shown and branches with support values <70 were collapsed. Metadata and accession numbers for specimens included in the analyses shown in table 1 and average uncorrected p-distances among these different taxa shown in table 3.

FIGURE 3. Phylogeny of Distichodus spp. inferred from 627 bp of CO1. Posterior probabilities from Bayesian inference above major branches; above 0.95 not shown and branches with support values <70 were collapsed. Metadata and accession numbers for specimens included in the analyses shown in table 1 and average uncorrected p-distances among these different taxa shown in table 3.

FIGURE 4. Plot of PC2 and PC3 from principal component analysis of 24 log-transformed measurements from 51 specimens (A). Reduced-major axis regression of eye diameter as a percentage of snout length on log-transformed standard length (B). Trendlines are shown for each species; slopes for each species are not different (p-value = 0.7613), and the elevation among species are significantly different (p-value = 0.0002) with Distichodus microps being significantly different (p-value <0.01) from D. mbiniensis and topotypic D. notospilus. The holotype of Distichodus microps and D. mbiniensis are denoted by a filled triangle and star respectively. Component loadings and results of Mann-Whitney U tests shown in table 3.

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.

FIGURE 7. Distichodus mbiniensis, a new species, holotype, USNM 451317, ALC, 99.9 mm SL, voucher EqGui2017_0127, Equatorial Guinea, Wele-Nzas, Rio Ntoro at Aconibe—Acurenam Rd., 668 m elev, 1.29091° N, 10.9174° E; Photograph by S. Raredon.

FIGURE 8. Lateral views of head region in Distichodus microps sp. nov. (A), Distichodus mbiniensis sp. nov. (B), and topotypic Distichodus notospilus (C). Same specimens and locality information as previous figures. Photographs by S. Raredon.

FIGURE 9. Live coloration of Distichodus microps, USNM 451457, ALC 81.6 mm SL, voucher EqGui2017_0274, Equatorial Guinea, Litoral, Rio Mbia at Menzong, 32 m elev, 2.07529° N, 9.92378° E photograph by R.C. Schmidt (A); Distichodus mbiniensis, USNM 451319, ALC 61.3 mm SL, voucher EqGui2017_0130, Equatorial Guinea, Wele-Nzas, Rio Ntoro at Aconibe—Acurenam Rd., 668 m, 1.29091° N, 10.9174° E, photograph by R. C. Schmidt (B); Topotypic Distichodus notospilus, OS 19544, ALC, 104.1 mm SL, Gabon, Province de l’Ogooué-Lolo, Right bank of Ogooué River at Doumé village, 0.84245° S, 12.96249° E, Photograph by B. Sidlauskas, included with permission (C); Holotype of Distichodus mbiniensis, USNM 451317, ALC, 99.9 mm SL, voucher EqGui2017_0127, Equatorial Guinea, Wele-Nzas, Rio Ntoro at Aconibe—Acurenam Rd., 668 m elev, 1.29091° N, 10.9174° E; Photograph by R. C. Schmidt (D).