Brevicyclops viduus

Totakura, Venkateswara Rao & Reddy, Yenumula Ranga, 2015, Groundwater cyclopoid copepods of peninsular India, with description of eight new species, Zootaxa 3945 (1), pp. 1-93 : 55-61

Brevicyclops viduus n. g., n. sp.

( Figs. 34–37 )

Type locality. Farm bore at Araveetikota village (15o34.746′N, 78o55.561′E; elevation 263 m) in Prakasam District, Andhra Pradesh, South India ( Fig. 1 ).

Type material examined. Holotype male, dissected on 3 slides ( MNHN. Cp 2395); 3 paratype males wholemounted on 1 slide each ( MNHN. Cp 2392–2394); 0 1 April 2006; Coll. Y. Ranga Reddy.

Diagnosis. Small cyclopinae, total body length of males 228–300 µm; body cyclopiform, moderately strong; male genital somite 0.7 times as long as wide; anal operculum bowl-shaped, hardly reaching distal margin of anal somite; caudal rami 1.9 times as long as wide, with greatly reduced principal outer apical seta being shorter than innermost apical seta; antennule 16-segmented in male; mandibular palp lacking; maxilliped 4-segmented, setal formula 2.1.1.2; spine formula: 2.3.3.2; legs 1–4 with 2-segmented rami; setal formula of second exopodal segment of legs 1–4: 5.5.5.4; leg 1 basis without spine; coxal seta present on legs 2 and 3; intercoxal plates of legs 1–4 with rounded small prominences. Leg 5 reduced to 3 setae; leg 6 reduced to 2 distinctly unequal setae.

Description of adult male. Total body length, measured from base of rostrum to posterior margin of caudal rami (excluding caudal setae), 240 Μm. Naupliar eye absent. Body ( Fig. 34 a) moderately robust, with prosome/ urosome ratio 0.7 and greatest width (102 Μm) at posterior end of cephalothorax. Body length/width ratio 3. Rostral projection ( Fig. 36 a) well developed, broadly triangular, furnished with 2 short sensilla. Free pedigerous somites 2–4 with rounded lateral margins. Pseudosomite absent between prosome and urosome. Fifth pedigerous somite as wide as genital somite, and with oblique lateral margins. Cephalothorax ( Fig. 34 a) 2.1 times as wide as genital somite, 1.2 times as long as its greatest width and 40.5% of total body length; not produced postero-laterally. Hyaline fringes of prosomites smooth and narrow. Fifth pedigerous somite with smooth fringe dorsally, ornamented with 2 pairs of sensilla posteriorly. Genital somite 1.4 times as long as wide in dorsal view, about as long as wide in lateral view, ornamented with 2 pairs of sensilla dorsally, hyaline fringe smooth. Anal somite ( Figs. 34 a, b, 35a, b) 0.6 times as long as wide, ornamented with transverse row of latero-ventral spinules on posterior margin at base of caudal ramus ( Fig. 34 b) and ornamented with 2 small dorsal sensilla. Anal operculum ( Figs. 34 a, 35b) smooth, moderately developed, 71% of somite’s width, not reaching posterior margin of somite, distal margin straight. Anal sinus narrow, without apparent ornamentation.

Caudal rami ( Figs. 34 a, b, 35a, b) straight and close to each other and 15% longer than anal somite; each ramus 1.7 times as long as maximum width, with slightly concave outer edge and nearly straight inner edge ( Fig. 35 b); ornamented with 1 pore proximo-ventrally ( Fig. 35 a), 1 row of tiny spinules at base of outermost apical seta. Dorsal seta inserted at 4/5 of ramus length and uniarticulate at base; lateral seta arising from dorsal surface close to outer margin at 3/5 of ramus length, and about as long as maximum width of ramus; outermost apical seta spiniform, plumose, 0.7 times as long as ramus, unipinnate, inserted subapically; innermost apical seta much slender and 0.6 times as long as outermost apical seta; principal outer apical setae without breaking planes; outer seta greatly reduced and somewhat shorter than innermost apical seta; inner seta 8.4 times as long as caudal ramus and with heteronomous setulation; all caudal setae plumose.

Antennule ( Fig. 36 b): 16-segmented, digeniculate, unornamented. Armature formula as follows: 7+3aes.4.1.3+aes.1.2.1.1.0.3.2.1.1+aes. 1.3.10 +aes. All aesthetascs slender; most setae slender and smooth; short unipinnate setae present on segments 12 and 14. Segments 1, 4, 6, 15 and 16 with 2, 1, 1, 1, and 4 long pinnate setae, respectively. Length ratios of antennular segments along medial axis 1.0: 0.4: 0.2: 0.2: 0.1: 0.2: 0.3: 0.3: 0.1: 0.3: 0.2: 0.1: 0.2: 0.5: 0.5: 0.8.

Antenna ( Fig. 36 c): 4-segmented, consisting of coxobasis and 3-segmented endopod. Setal formula of endopod: 1.5.7. Coxobasis 1.9 times as long as wide, armed with 1 seta at inner distal corner; exopodal seta absent. First endopodal segment 1.6 times as long as wide, armed with 1 seta subterminally on inner margin, and ornamented with 1 crescentic row of minute spinules at outer distal corner; second segment 2.2 times as long as maximum width, armed with 5 unequal setae (1 mid-inner margin, 2 subterminal, 2 inner distal corner) and ornamented with 1 row of spinules on outer distal margin. Third segment 2.5 times as long as wide, armed with 7 unequal simple setae and ornamented with 2 rows of spinules on outer margin.

Labrum ( Fig. 36 d): relatively small, trapezoidal, no ornamentation discernible. Anterior cutting edge almost straight, with tiny, acute, equal teeth between slightly produced lateral corners.

Mandible ( Fig. 36 e), maxillule ( Fig. 36 f), maxilla ( Fig. 36 g): same as in type species.

Maxilliped ( Fig. 36 h): syncoxa 1.8 times as long as wide; other details same as in type species.

Legs 1–4 ( Fig. 37 a–d): relatively short, with 2-segmented exopod and endopod. Hairs present on rounded inner margin of basis, and lateral margins of exopod and endopod as illustrated. Endopod nearly equal in length to exopod on legs 1–3, but distinctly shorter on leg 4. Second exopodal segment spine formula: 2.3.3.2; setal formula: 5.5.5.4. Intercoxal plate with 2 lateral, rounded, unornamented prominences each on all legs. Outer seta on basis short and plumose on all legs. Coxa without seta on legs 1 and 4, but with 1 plumose seta each on legs 2 and 3. Legs 1–4 armature formulae as follows (legend: same as that of Paracyclopina orientalis ):

Coxa Basis Exopod Endopod

1 2 1 2

Leg 1 0-0 0-1 1- I 4 +1+I+ I 1 -0 1, 1+I, 1 Leg 2 1-0 0-1 0- I 4, 1+I, II 1 -0 1, 1+I, 1 Leg 3 1-0 0-1 0- I 4, 1+I, II 1 -0 1, 1+I, 1 Leg 4 0-0 0-1 0- I 3, 1+I, I 1 -0 1, 1+I, 1 Leg 5 ( Fig. 35 a, c, d): completely fused to somite and represented by 3 plumose setae. Basal seta on small protuberance; 2 other setae representing ancestral distal segment, located on short but somewhat broad prominence; latter 2 setae unequal, plumose and shorter than basal plumose seta.

Leg 6 ( Fig. 35 a): both legs partly fused medially; each leg large, cuticular plate, with medial septum, and armed with 2 distinctly unequal setae.

Etymology. The specific epithet, viduus , is derived from Latin adjective, vidua (= deprived of), alluding to the absence of females in the sample; gender masculine.

Female unknown.

Ecology. The taxa that co-occurred with the new species included a parabathynellacean ( Atopobathynella sp.) and a bogidiellid amphipod.

Remarks. As has already been pointed out, Brevicyclops n. g. is close to the Rybocyclops Dussart, 1982 , among the genera containing small cyclopoids. This is obvious from the following characters: cyclopiform body shape; 11-segemented antennule in female; 2-segmented exopod and endopod of legs 1–4; and details of maxilla and maxillule. However, Brevicyclops n. g. is distinct from the Rybocyclops in the antennal setal formula being 1.1.5.7 vs. 1.1.5.6; the spine formula of legs 1–4 either 2.2.2.2 or 2.3.3.2 vs. 2.2.2.2; and the principal outer apical caudal seta either extremely short, when present, or absent vs. always long. Clearly, the signal synapomorphy of the new genus is the greatly reduced ( B. brevisetosus n. sp. and B. viduus n. sp.) or non-existent ( B. asetosus n. sp.) principal outer apical seta on caudal rami. In fact, this character is a completely novel facet to the family Cyclopidae as a whole.

Brevicyclops brevisetosus n. sp. and B. asetosus n. sp., while sharing the synapomorphy of the genus, also show identical spine formula of 2.2.2.2 on second exopodal segment of legs 1–4. However, R. brevisetosus n. sp., R. asetosus n. sp. and R. viduus n. sp. differ from one another in subtle but important features as shown in the Table 3 .

Leg 5 is represented by only 3 setae, one of which is basal seta and the remaining two setae located on a small protuberance of the somite. This character state is shared by three genera, viz., Rybocyclops Dussart, 1982 , Bryocyclops Kiefer, 1927 , Palaeocyclops Monchenko, 1972 , all of which indeed constitute a distinct lineage within the subfamily Cyclopinae, now called Bryocyclops -group of genera, characterized, inter alia, by 11-segmented antennule, maxillule with distinct endopod bearing one inner and two or three apical setae and the overall armature details of maxilla, and 2-segmented exopod and endopod on legs 1–4, with leg 1 and 4 or at least leg 4 without coxal seta.

It is noteworthy that the genus Haplocyclops Kiefer, 1952 is also very close to the Bryocyclops -group in almost all the afore-mentioned characters. However, it differs from this group in the following characters: (i) legs 2–4 have one-segmented endopod and legs 3 and 4 with only one-segmented exopod (leg 1 segmentation is same as in Bryocyclops -group); (ii) the posterior location of the genital field on the double-somite of the female; and (iii) proximally located lateral seta on the caudal rami. Put differently, Haplocyclops is undoubtedly advanced over the Bryocyclops -group of genera. According to Karanovic & Ranga Reddy (2005), Haplocyclops (Kiefercyclops) fiersi Karanovic & Ranga Reddy, 2005 is the most reduced species in the whole of the family Cyclopidae .

Figures

FIGURE 1. Map showing the type localities of the cyclopoid species on the Indian peninsula.

FIGURE 34. Brevicyclops viduus n. g., n. sp., paratype male. (a) habitus, dorsal; (b) same, lateral.

FIGURE 35. Brevicyclops viduus n. g., n. sp., holotype male (a, b), paratype male (c, d). (a) urosome, ventral; (b) anal somite and caudal rami, dorsal (arrow pointing to reduced outer medial apical seta); (c) leg 5, latero-ventral; (d) same, ventral.

FIGURE 36. Brevicyclops viduus n. g., n. sp., holotype male. (a) rostrum, ventral; (b) antennule, lateral; (c) antenna, lateral; (d) labrum, ventral; (e) mandible, lateral; (f) maxillule, lateral; (g) maxilla, lateral; (h) maxilliped, lateral.

FIGURE 37. Brevicyclops viduus n. g., n. sp., holotype male. (a) leg 1, anterior; (b) leg 2, anterior; (c) leg 3, anterior; (d) leg 4, anterior.

Tables

TABLE 3. Principal morphological differences between Brevicyclops spp.

Characters	brevisetosa n. sp.	asetosa n. sp.	viduus n. sp.
Total body length (Μm) ♀ ♂	357 323–356	324–402?	? 228–300
Male antennule No. of segments No. aesthetascs on segment 1	17 2	??	16 3
Maxillule: length of claws	unequal	unequal	equal
Caudal rami L/W ratio Ornamentation on distal margin Outer medial apical seta	1.7 present reduced, setiform	1.6–1.8 absent absent	1.6 present reduced, spinule-like
Coxal spines present on legs	1–3	2 and 3	2 and 3
Legs 1–4 Ornamentation on coxa Exopod 2 spine formula	present 2.2.2.2	absent 2.2.2.2	absent 2.3.3.2
Leg 4: endopod 2 L/W ratio No. of armature elements Inner seta Outer seta	2.0 3 present absent	1.3 2 (female) absent absent	2.14 4 (male) present present