Euryrhynchina puteola, Grave, Sammy De, Piscart, Christophe, Tuekam Kayo, Raoul P. & Anker, Arthur, 2017
Grave, Sammy De, Piscart, Christophe, Tuekam Kayo, Raoul P. & Anker, Arthur, 2017, A new groundwater-dwelling species of Euryrhynchina from Cameroon (Malacostraca, Decapoda, Euryrhynchidae), Zootaxa 4254 (1), pp. 120-126 : 121-126
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Material examined. Holotype. CAMEROON: 1♂ (cl 1.8), small well used for drinking water, behind the Gendarmerie, Quartier II of Mbanga city, Littoral Province, 04°29’50’’N 09°33’45’’E, 0.67 m wide, depth 9.5 m, water level (piezometric level) at 7.3 m with 2.2 m of water depth, leg. R.P. Tuekam Kayo, 20.i.2012 ( OUMNH.ZC.2016-05-001). Paratypes GoogleMaps . 4♂♂ (cl 2.7, 1.7, 2.8, 1.8), same data as for holotype ( OUMNH.ZC.2016- 05-002 to 2016-05-005) GoogleMaps ; 2 ♂♂ (cl 1.9, 2.1), 1 spec., sex unknown (cl 1.4) (MNHN-IU-2014-19519).
Description. Carapace smooth, without setae, branchiostegial groove barely visible; rostrum triangular in shape, falling short of distal margin of eyes ( Fig. 1 View FIGURE 1 A, B); suborbital angle poorly developed, antennal spine absent; pterygostomial angle protruding forward, triangular, overreaching rostrum ( Fig. 1 View FIGURE 1 B).
Pleon smooth, pleura 1–3 ventrally rounded, pleura 4–5 with postero-lateral angle somewhat quadrate.
Eyes ( Fig. 1 View FIGURE 1 A, B) reduced, pigmented cornea small, facets poorly if at all developed; anteromesial margin of peduncle not produced, without setae.
Antennular peduncle with stylocerite not laterally expanded ( Fig. 1 View FIGURE 1 D); anterolateral angle of basal article produced into sharp tooth, reaching to mid-length of second article; second article short, anterolateral and anteromesial angles bluntly produced; three antennular flagella present, entirely free throughout their lengths, middle flagellum consisting of five articles, ultimate twice as long as penultimate, aesthetascs only present on distal article.
Antennal scaphocerite broad, slightly longer than antennular peduncle ( Fig. 1 View FIGURE 1 A); lateral margin straight, ending in stout sharp distal tooth, latter shorter than distal margin of lamella ( Fig. 1 View FIGURE 1 E).
Mandible with incisor and molar processes widely separated ( Fig. 2 View FIGURE 2 A), palp absent; incisor process ending in four equally sized teeth; molar process weakly bilobed. Maxillule ( Fig. 2 View FIGURE 2 B) with two endites, palp distally bilobed. Maxilla ( Fig. 2 View FIGURE 2 C, D) with single endite, endopod short, proximally broadening; scaphognathite large. First maxilliped ( Fig. 2 View FIGURE 2 E) with broad caridean lobe, epipod present. Second maxilliped ( Fig. 2 View FIGURE 2 F) without podobranch. Third maxilliped ( Fig. 2 View FIGURE 2 G) without arthrobranch or pleurobranch.
First pereiopod ( Fig. 3 View FIGURE 3 A) slender, overreaching distal margin of scaphocerite by mero-carpal articulation; merus about twice as long as ischium; carpus equal to merus in length; fingers of chelae approximately as long as palm ( Fig. 3 View FIGURE 3 B). Second pereiopods equal in size, similar in shape ( Fig. 3 View FIGURE 3 C), overreaching distal margin of scaphocerite by mero-carpal articulation; merus slightly longer than ischium; carpus shorter than merus, cylindrical; chelae ( Fig. 3 View FIGURE 3 D) about 2.5 times as long as carpus; fingers straight, about 1.3 times as long as palm, cutting edges smooth, dactylus with three small blunt teeth proximally, pollex with two similar teeth proximally.
Third pereiopod ( Fig. 3 View FIGURE 3 E) with ischium, merus and carpus unarmed, merus about 1.6 times as long as ischium; carpus about 0.55 times as long as merus; propodus about 1.7 times as long as carpus, with 6–8 widely spaced spines along flexor margin; dactylus about 0.5 times as long as propodus, weakly biunguiculate. Fourth pereiopod ( Fig. 3 View FIGURE 3 F) generally similar to third. Fifth pereiopod ( Fig. 3 View FIGURE 3 G) with ischium, merus and carpus unarmed, merus about 1.8 times as long as ischium; carpus about 0.65 as long as merus; propodus about twice as long as carpus, with few widely spaced spines along flexor margin; grooming brush well-developed, consisting of four rows of 6– 8 serrulate setae.
Telson ( Fig. 1 View FIGURE 1 C) broad, about 1.8 times as long as wide; dorsal surface with two pairs of spines all similar in shape and size, anterior pair at about 0.35 of telson length, posterior pair at about 0.55 of telson length; posterior margin conical in shape, laterally furnished with two pairs of spines, mesial 2.5 times as long as lateral, and additionally adorned with numerous long annulate plumose setae.
Uropod ( Fig. 1 View FIGURE 1 J) with lateral expansion on protopod; endopod and exopod subequal in length; diaeresis incomplete, with strong sharp spine laterally, adjacent to stout distolateral spine and short lateral tooth on lateral margin of exopod ( Fig. 1 View FIGURE 1 K).
Male first pleopod ( Fig. 1 View FIGURE 1 F) with reduced endopod; appendices internae lacking on all pleopods in males; second pleopod with well-developed appendix masculina ( Fig. 1 View FIGURE 1 G), equal in length to endopod, with terminal tuft of four stout setae ( Fig. 1 View FIGURE 1 H). Third to fifth pleopods similar in shape ( Fig. 1 View FIGURE 1 I).
Etymology. The species name puteola is derived from the Latin word puteolus, meaning a small well, in reference to the habitat of the new species; used as an adjective.
Distribution. The species is only known from a single phreatic well at the type locality. Monthly sampling in five neighbouring wells and other wells in the region, near the city of Penja (to the north of Mbanga), Yabassi (to the east) and Douala (in the south) did not recover any additional specimens.
Ecology. In addition to E. puteola sp. nov., the well fauna included the oligochaete families Naididae and Haplotaxidae , and not-yet identified cyclopoid copepods and stenasellid isopods. In respect to physico-chemical parameters of the groundwater in the area, the environment is characterised by a high and stable temperature (mean minimum from 27°C to mean maximum 28°C) and somewhat elevated acidity (mean pH values 6.32). Electrical conductivity, suspended matter, turbidity and the nutrient content of the well water were relatively low ( Table 1), but similar to those of other wells of this region ( Nana Nkemegni et al. 2015).
Mean values (min–max)
Water temperatures (°C) 27.2 (27–28)
Suspended matter (mg.L -1) 10.6 (3–18)
pH (UI) 6.32 (6.24–6.38) Electrical conductivity (µS.cm -1) 108.6 (88–122) Dissolved O2 (%) 73 (68–78.2)
HCO3 - (mg.L -1) 14.8 (10.6–15.8) Calcic Harshness (mg.L -1) 22 (10–35)
NH4 + (mg.L -1) 0.95 (0.7–1.2)
NO 2 - (mg.L -1) 0.009 (0.007–0.015) NO 3 - (mg.L -1) 1.9 (1.2–2.2)
PO4 2- (mg.L -1) 0.52 (0.47–0.55) Discussion. The new species can easily be distinguished from the only other species in the genus, E. edingtonae , by the absence of the setiferous lobe on the peduncle of the eyes, which is present in E. edingtonae and was considered to be of generic value by Powell (1976). Powell (1976) also considered the shape of the scaphocerite, the absence of gills on the third maxilliped, the presence of movable spines on the merus of the ambulatory pereiopods, the unspecialised second male pleopod, the modestly developed process of the uropodal protopod and the decreasing size of the spines on the diaeresis to be characteristic for the genus. Of these, the presence of meral spines can no longer be considered as a genus level character, given their absence in the new species.
Further differences between both species are the lower number of spines on the lateral portion of the uropodal diaeresis (one in E. puteola vs. 2–3 in E. edingtonae ); the lateral tooth of the scaphocerite falling short of the distal margin of the lamella (vs. far over reaching in E. edingtonae ); the absence of a spine on the merus of the ambulatory pereiopods (present in E. edingtonae ); the absence of a podobranch on the second maxilliped (present, albeit reduced in E. edingtonae ) and the absence of appendices internae on the male pleopods 2-5 (present in E. edingtonae ).
Although the species was discovered in a well, it is not clear whether it is a true stygobiont, as poorly developed facets seem to be present on the cornea of the eyes. The pigmented area of the eye appears to be very similar to that of the surface dwelling E. edingtonae , at least as illustrated by Powell (1976). Two South American species, viz. Euryrhynchus wrzesniowskii Miers, 1877 and E. burchelli Calman, 1907 , were described on the basis of animals collected in phreatic wells, but have since been found to be surface water species that aside from their initial record in wells have never been found again in subterranean waters ( Holthuis 1986). Thus it is possible that E. puteola is a stygophilous species rather than a true stygobiont.
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