Eurycercus (Bullatifrons) norandinus, Aranguren, Nelson, Monroy, Daniel & Gaviria, Santiago, 2010

Aranguren, Nelson, Monroy, Daniel & Gaviria, Santiago, 2010, Eurycercus (Bullatifrons) norandinus (Crustacea: Branchiopoda: Eurycercidae), a new species of Cladocera in the Neotropical Region, Zootaxa 2550, pp. 58-68 : 60-66

publication ID	https://doi.org/ 10.5281/zenodo.196797
DOI	https://doi.org/10.5281/zenodo.5619887
persistent identifier	https://treatment.plazi.org/id/91006912-EC7B-FFF0-FF28-60B3FADAF867
treatment provided by	Plazi
scientific name	Eurycercus (Bullatifrons) norandinus
status	sp. nov.

Treatment

Eurycercus (Bullatifrons) norandinus View in CoL sp.nov.

( Fig. 1–2 View FIGURE 1 View FIGURE 2 )

Type locality: Lago de Tota, State of Boyacá, Colombia (5°32’ N, 72°55’W) at 3015 m.a.s.l., littoral zone, mainly covered by the aquatic plant Egeria densa .

Material examined: all are parthenogenetic females. No males were found in the samples.

Holotype: female, collected the 14.02.2004, total length 1.93 mm, mounted in glycerol and deposited at the Museo de Historia Natural, Instituto de Ciencias Naturales, Universidad Nacional de Colombia (ICN- MHN-CR 2495).

Paratypes: 1 female, mounted in glycerol on slide (ICN-MHN-CR 2496) and 8 females, undissected, preserved in ethanol (ICN-MHN-CR 2497), collected the 14.03.2004; 8 females, mounted in slide with polyvinyl lactophenol, deposited at the Naturhistorisches Museum Wien ( NHMW 22987 to 22894), collected the 23.01.2004; 26 females undissected, preserved in ethanol, deposited at the Museo de Historia Natural, Universidad Pedagógica y Tecnológica de Colombia (UPTC-MHN-ART 0001).

Etymology: the name of the species refers to the geographical zone of the Cordillera de Los Andes where the material was collected.

Diagnosis. Eurycercus (Bullatifrons) norandinus show the lowest number of teeth of the dorsal margin of the postabdomen (mean 81.4 +/- 4.9 SD, range 73–92) and the lowest number of denticles at the postadominal claw (33.0 +/- 4.8 SD, range 20–40) despite of its bigger size compared with the other 4 species of the subgenus Bullatifrons . On the contrary, it show the highest number of denticles of setae (called also scrapping spines by Fryer 1963) 2 (mean 18.8 +/- 2.8 SD, range 12–23), 3 (19.8 +/- 2.8 SD, range 14–24) and 4 (20.8 +/ - 1.7 SD, range 18–24) of the corm of the trunk limb II, compared with the other 4 species.

Applying descriptive statistics to analyse morphological and meristical traits of individuals of the population, it is show that during ontogeny the rate of increase in teeth number of the dorsal margin of the postabdomen in relation to the postabdominal length is higher than in the other species. Eurycercus norandinus shows the lowest correlation coefficients between the length of postabdomen and the number of marginal and proximal spinules on the internal lobe of trunk limb I (Tab. 4). Likewise the increment of the number of these spinules in relation to the increment of the postabdominal length is the most regular ( Fig. 4 View FIGURE 4 C, D).

Description. Shape: in lateral view dorsal margin of carapace weakly arched, interrupted only by the bubble-like section of the head pore. Ventral margin anteriorly concave and its anteroventral margin weakly angled ( Fig. 1 View FIGURE 1 , A).

Size: total length 1.93 mm, maximal height of the carapace 1.19 mm.

Head: rostrum short, not surpassing in length the insertion point of the sensorial seta of the antennule, sharpen in lateral view, head as long as broad. Median head pore (main pore) projected as a bubble of 30 µm diameter. Distance between the lateral head pores (minor pores) 48 µm ( Fig. 1 View FIGURE 1 , A and C).

Antennule ( Fig. 1 View FIGURE 1 , B): with convex anterior margin, elongated, the lateral sensorial seta inserted in the median part, with 9 terminal sensorial setae.

Antenna: with characteristic morphology of Eurycercus , both articles 3-segmented. Exopodite with three, endopodite with five swimming setae.

Labrum: weakly developed, with gently rounded anterior border, without anterior and posterior marginal extensions ( Fig. 1 View FIGURE 1 , D).

Trunk limb I ( Fig. 1 View FIGURE 1 , E and F): internal distal lobe (IDL) with three 2-segmented clasping hooks, first and third hook longer than median one, with segments articulated allowing movement to one other, second hook with fused segments (limit between former segments can be noted); median hook more curved than the others; second segment of first and third hook with a row of hairs along the concave edge, median hook with row of hairs at the proximal section of the second segment. Basal segment with three clusters of spines: distal cluster and proximal clusters with 8 long spines each one, marginal cluster with 6 short spines; in addition, irregular clusters of very small spinules inserted near the proximal cluster, and a semicircular patch of grinding tubercles near the base of the lobe ( Fig. 1 View FIGURE 1 , F). Outer distal lobe (ODL) with 2-segmented setae, the outer one shorter than the first segment of the internal seta.

Trunk limb II ( Fig. 1 View FIGURE 1 , G and H): consists of gnathobase and corm (fused body of the trunk limb), each with a variety of setae and scrapers. Gnathobase pyramidal, with 3 terminal appendages, anterior one with hairs along its axis, median shorter and with distal denticles, posterior longer and with lateral teeth up to its end. Distal edge of gnathobase with one robust spine and two series of spinules near its base ( Fig. 1 View FIGURE 1 , H). Filter plate with 7 feathered setae, the most proximal stronger than the others. Feathered setae 5 and 6 inserted more distal than feathered setae 1– 4 and 7. Corm with 8 robust scrapers, bearing denticles in the concave distal margin of each one. Scrapers 2 to 4 with 19, 22 and 23 denticles respectively.

Trunk limb III ( Fig. 2 View FIGURE 2 , A and B): exopodite with 8 setae, the disposition of the 5 distal setae typical of subgenus Bullatifrons , with exception of the third one, which is slightly bent ( Fig. 2 View FIGURE 2 , A). Gnathobase consisting of 3 apical setae of different length and structure, like in the other species of the subgenus, and bearing a filter, constituted by 9 setae ( Fig. 2 View FIGURE 2 , B).

Trunk limb IV ( Fig. 2 View FIGURE 2 , C): exopodite consisting of a big lamella with 8 setae, posterior seven setae feathered with filtering function, nearest seta to the gnathobase not feathered. Gnathobase with a group of 4 setae of variable length, the outer one more sclerotized than the others and without setules, with one strong spine inserted near the base of the inner seta, apical edge with a long geniculated sensilla and a bifurcated short and robust seta. Lateral surface of gnathobase with 3 clusters of spines, distal cluster and proximal clusters with 8 long spines each one.

Trunk limb V ( Fig. 2 View FIGURE 2 , D): exopodite consisting of a big, flattened lamella with 7 feathered setae in total separated in two groups, 3 being longer and “soft” and 4 shorter and “hard”. Gnathobase with a filter plate consisting of a group of 8 setae of similar size and structure, apically with a group of 3 feathered setae, the median being shorter than the others, with a sensilla between proximal and median setae.

Trunk limb VI: triangular flattened plate, rounded ventrally with dense fringe of long setae along anterior margin. As in E. macrocanthus it presents a finger-like process arising from de bract.

Postabdomen ( Fig. 2 View FIGURE 2 , E): total length 604 μm, dorsal margin slightly curved, with a row of 82 teeth, increasing proportionally their size until the posterior region. Lateral surface covered with clusters of small spinules increasing in size distally.

Postabdominal claw: length 158 μm, with two strong spines on its base, the distal one longer than the proximal, additionally with two rows of spines with 5 long and 8 short spines respectively; concave edge of claw with a proximal row of 20 small denticles and a distal row with 16 denticles of major size.

Variability in intra-specific morphology. Fourteen morphological variables within the studied population of Eurycercus norandinus are shown in table 2. The length of cephalic shield and body length presented the highest variation, with coefficients of 28.4 % and 28.0 % respectively. The number of denticles on the postabdominal margin and on the fourth seta of trunk limb II showed the lowest variation. The lengthfrequency distribution of the body size of the (44) individual studied is presented in Fig. 5 View FIGURE 5 . The minimal body length of a female with evidence of maturity (carrying eggs female) was estimated with 1.43 mm. Developing instars IV and V were differentiated, although instars I to III could not be separated between them. It was noted meristical variability in the clusters of the spines of the basal segment of the internal lobe of limb I: paratype NHMW 22888 carries 6 spines on the distal cluster, 9 in proximal cluster and 5 in marginal cluster, while paratype NHMW 89 carries 9, 10 and 6 spines and paratype NHMW carries 8, 10 and 4 spines, in contrast to holotype with 8, 8 and 6 spines respectively.

Differential diagnosis. Characters unique to the subgenus Bullatifrons and present in Eurycercus (Bullatifrons) norandinus are the morphology of the head pore which is projected like a bubble, the weakly expanded keel of the labrum lacking a prominent apex and the one-looped intestine.

Differential diagnosis of the species of Eurycercus (Bullatifrons) included the study of morphological and meristic traits of several animals of the population, compared with the other species of the subgenus ( Tab. 3 View TABLE 3 and 4, Fig. 3 View FIGURE 3 and 4 View FIGURE 4 ).

Eurycercus norandinus tend to have a bigger body size (mean value 1.37 mm, n = 44) than the other species of the subgenus ( longirostris 1.35 mm, n = 518; vernalis 1.32 mm, n = 526; pompholygodes 1.30 mm, n = 159; macrocanthus 1.26 mm, n = 117). See table 2 and 3.

Ratio of head size in relation to the body size smaller in comparison with Eurycercus macrocanthus , higher in respect to Eurycercus pompholygodes and almost similar to Eurycercus longirostris and Eurycercus vernalis .

The comparative study of 6 morphological traits (length of the body, headshield, postabdomen and postabdominal claw, diameter of median head pore, distance between lateral head pores) and 8 meristical traits (number of postabdominal teeth, number of denticles on postabdominal claw, number of spinules of proximal, distal and marginal clusters of trunk limb I, number of denticles of scrapers 2, 3 and 4 of trunk limb II) of the 4 known species and the new species, determines a strong morphological similarity between Eurycercus vernalis and Eurycercus longirostris .

The species Eurycercus pompholygodes associates to a minor degree with that group. Eurycercus norandinus and, in a higher degree, Eurycercus macrocanthus move away from the mentioned group. The differences to Eurycercus pompholygodes refer mainly to the shorter cephalic shield of Eurycercus norandinus , fewer denticles on the postabdominal claw, a larger diameter of the median cephalic pore and a greater distance between the lateral pores, likewise the new species presents a higher number of denticles on scrapers 2 to 4 of trunk limb II. Nevertheless, these two species present the major length of postabdomen (mean values: pompholygodes 556 µm, n = 34; norandinus 534 µm, n = 44) and of cephalic shield (mean values: pompholygodes 754 µm, n = 34; norandinus 674 µm, n = 44), compared to the other 3 species of the subgenus, which explains the slight association between them.

The regression statistics applied shows differences in the calculated slopes for each relation of variables (length of the cephalic shield, number of postabdominal teeth, number of proximal spinules of trunk limb I and number of marginal spinules of trunk limb I, all in relation to postabdominal length) of the species of Eurycercus (Bullatifrons) . The species Eurycercus longirostris and Eurycercus vernalis show a similar trend in the majority of relations. The rate of increment of the cephalic shield in relation to the length of postabdomen during ontogeny is higher in both species, followed by Eurycercus norandinus , Eurycercus pompholygodes and Eurycercus macrocanthus (Tab. 4).

The difference in the trends per species accentuates in the relation between postabdominal length and number of teeth on its edge. Eurycercus norandinus shows the lowest number of teeth despite of its relatively big size within the species of the sub-genus ( Tab. 3 View TABLE 3 ) and the highest rate of their increment in relation to the postabdominal length ( Fig. 4 View FIGURE 4 , B). That trend is also observed in the amount of denticles of the relatively big postabdominal claw.

Remarks. The discovery of a new species of Eurycercus in Lago de Tota suggests a long isolation of the lake and in general of high-andean lakes, which could have resulted in speciation. This has been observed in copepods like in Metacyclops leptopus totensis ( Reid et al. 1990) from the same lake, in Tropocyclops prasinus altoandinus ( Gaviria 1994) or in the genus Colombodiaptomus , which is distributed in a restricted area of the high-plane of the Cordillera Oriental ( Gaviria & Aranguren 2007).

It is recommended to study the populations of Eurycercus found in lakes of Cundinamarca state in Colombia (H. Dumont & S. Gaviria, pers. obs), that probably belong to the same species, and to determine their intra-specific variation.

With the discovery of Eurycercus (Bullatifrons) in Colombia, the distribution of the subgenus extends from the northern Palearctic ( E. macrocanthus and E. pompholygodes ) and eastern North America ( E. vernalis and E. longirostris ) to northern South America ( Eurycercus norandinus ). To date, the only evidence of the presence of the genus in South America were reports of Eurycercus lamellatus in Argentina ( Frey 1973) and in Brazil ( Elmoor-Loureiro 1997). It is strongly recommended to revise the taxa in both localities, as they will likely turn out to be different from Eurycercus lamellatus sensu stricto, as suggested by Frey (1986).

Variable	E. macrocanthus	E. pompholygodes	E. longirostris	E. vernalis	E. norandinus
Body length (µm)	1258	1302	1351	1321	1367
Length of postabdomen (µm)	501	556	437.7	427.2	539.6
Headshield length (µm)	499	74	656.6	646.7	673.7
Length of postabdominal claw (µm)	122	129.3	147.6	138.1	138.2
No. of denticles on postabdominal claw	38.4	44.7	37.4	34.8	33.0
No. of postabdominal teeth	84.5	90.4	93.3	95	81.4
Diameter of median head pore (µm)	-	21.6	24.5	24.8	25.0
Distance between lateral head pores (µm)	-	34.2	47.1	41.3	41.1
No. of proximal spinules of trunk limb I	-	7.6	6.9	7.1	7.2
No. of distal spinules of trunk limb I	-	5.6	6.3	6.9	6.9
No. of marginal spinules of trunk limb I	-	5.9	4.8	4.3	5.4
No. of denticles of scrapping spine 2 of trunk limb II	13	14.9	14.8	15	18.8
No. of denticles of scrapping spine 3 of trunk limb II	11	15.4	15.5	15.7	19.8
No. of denticles of scrapping spine 4 of trunk limb II	12.7	17.2	17.8	17.4	20.8