Rybocyclops defayeae, Totakura, Venkateswara Rao & Reddy, Yenumula Ranga, 2015

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 : 30-33

Rybocyclops defayeae n. sp.

( Figs. 17–22 )

Type locality. Farm bore (water temperature 27ºC, pH 7.0) at Neerukonda village (16o32′19.8″N, 80o39′17.6″E; elevation 30 m) in Guntur District, Andhra Pradesh, South India ( Fig. 1 ).

Material examined. Holotype female (MNHN-IU-2013-11859) and allotype male (MNHN-IU-2013-11860), dissected on 3 slides; 9 paratypes: 1 female, dissected on 3 slides (MNHN-IU-2013-11861), 2 females (MNHN-IU- 2013-11862–11863), whole-mounted on 1 slide each, 6 females in alcohol in 1 vial (MNHN-IU-2013-11864). 12 July 2008, Coll. V. R. Totakura.

Diagnosis. Total body length of females 321–347 µm and of males 316–343 µm. Body slender; pseudosomite present between fifth pediger and genital double-somite; genital double-somite large; sixth legs located middorsolaterally; anal operculum extending up to somite’s limit, bowl-shaped, with smooth, straight distal margin, representing 65.3% of anal somite’s width; antennule 11-segmented in female; the same 15-segmented in male and digeniculate; mandibular palp absent; maxilliped 4-segmented, setal formula 2.1.1.2. Endopod only slightly shorter than exopod on legs 1–3, but distinctly so on leg 4; spine and setal formulae of second exopodal segment 2.2.2.2, and 5.5.5.4, respectively; caudal rami cylindrical, parallel, very close to each other and 1.7 times as long as wide; dorsal seta about 2.9 times as long as ramus, inserted at distal fifth of ramus length; lateral seta arising somewhat dorso-laterally at 3/5 of ramus length, 0.6 times as long as ramus’ width; outermost seta long as ramus; innermost apical seta small and slender, bipinnate, 0.4 times as long as outermost apical seta; principal apical setae without breaking planes; inner seta about 2.2 times as long as outer seta and 0.3 times as long as body; fifth legs alike in both sexes, represented by 3 reduced setae; sixth leg represented by 2 distinctly reduced spinous structures.

Description of adult female. Total body length, measured from tip of rostrum to posterior margin of caudal rami (excluding caudal setae), 338 µm; habitus ( Fig. 17 a) slender, dorso-ventrally compressed; prosome/urosome ratio 1.5; body length/width ratio about 3.4 (dorsal view). Free pedigerous somites 1–4 without particular expansions laterally; fifth pediger slightly producing obliquely. Naupliar eye not visible. Rostrum ( Fig. 19 a) well developed, linguiform and furnished with 2 large sensilla. Cephalothorax ( Fig. 17 a) almost 1.5 times as wide as genital double-somite, 1.7 times as long as wide; greatest width (108 µm) at middle of cephalothorax in dorsal view, 35.7% of total body length. Surface of cephalothoracic shield and pleurotergites of free pedigerous somites with small sensilla (no cuticular pores and pits), as illustrated. Hyaline fringes of prosomites narrow and smooth. Fifth pedigerous somite ( Figs. 17 a, 18a, b) ornamented with 4 small dorsal sensilla; hyaline fringe smooth, narrow and extending dorso-ventrally. Genital double-somite large, 0.9 times as long as wide; ornamented with 4 small dorsal sensilla; hyaline fringe smooth, narrow; median copulatory pore ( Fig. 18 b) small, ovoid, situated at the level of sixth legs; copulatory duct not discernible. Seminal receptacle with somewhat large anterior expansion, and small and narrow posterior expansion. Third urosomite slightly longer than fourth one and unornamented; fourth urosomite with 2 dorso-distal pores. Anal somite ornamented with 2 small sensilla dorsally ( Fig. 18 a), transverse row of minute spinules along posterior margin latero-ventrally. Anal operculum large, bowl-shaped, extending up to somite’s limit and representing 63.3% of anal somite’s width, smooth, with almost straight caudal margin. Anal sinus narrow.

Caudal rami ( Figs. 17 a, 18a, b) cylindrical, parallel, 1.9 times as long as wide; ornamented with several spinules on distal ventral margin. Dorsal seta about 2.9 times as long as ramus, inserted at 4/5 of ramus length, uniarticulate. Lateral seta arising from dorsal surface, close to outer margin at 3/5 of ramus length, 0.6 times as long as ramus’ width. Outermost apical seta as long as ramus. Innermost apical seta small and slender, 0.4 times as long as outermost apical seta. Principal apical setae without breaking planes; inner seta 2.3 times as long as outer apical seta and about 0.4 times as long as body.

Antennule ( Fig. 17 a, b): 11-segmented, 63.6% as long as cephalothoracic shield, and ornamented with arched row of spinules proximally on first segment; armature formula as follows: 7.3.6.2.1.2.2.2+aes.2.2.7; segments 1, 3, 7, 8, 9 and 11 with 1, 3, 1, 1, 1, and 3 long bipinnate seta(e), respectively; all other setae smooth. Length ratios of antennular segments along medial axis 1.0: 0.3: 0.7: 0.3: 0.2: 0.3: 0.4: 0.4: 0.3: 0.4: 0.7. Probable segmental homology 1 (I–V), 2 (VI–VII), 3 (VIII–XI), 4 (XII–XIII), 5 (XIV), 6 (XV–XVI), 7 (XVII–XX), 8 (XXI–XXIII), 9 (XXIV), 10 (XXV), 11 (XXVI–XXVIII).

Antenna ( Fig. 19 b): 4-segmented, consisting of coxobasis and 3-segmented endopod. Coxobasis large, cylindrical, 1.6 times as long as wide, armed with 1 smooth seta at inner distal corner. Exopodal seta absent. First endopodal segment 1.3 times as long as wide, armed with 1 smooth seta on inner margin and ornamented with 1 row of spinules on outer margin. Second endopodal segment about 1.7 times as long as wide, with narrow concave sclerotized proximal outer corner, armed with 5 setae (2 at inner distal corner, 3 on inner subdistal margin), and ornamented with 1 row of spinules on outer subdistal margin. Third endopodal segment cylindrical, 2.1 times as long as wide, ornamented with 2 oblique rows of spinules near outer margin and armed with 6 smooth apical setae.

Labrum ( Fig. 19 c): trapezoidal, free margin nearly straight, with 16 small, equal teeth between slightly produced triangular corners and ornamented with some hair-like spinules.

Mandible ( Fig. 19 d): coxal gnathobase roughly divided into 3 groups of teeth; inner group of 3 large unequal teeth, innermost one being relatively large; middle group of 7 equal, small teeth and 1 subdistal spinular row; and 1 pinnate outermost seta on ventral surface. Palp completely absent.

Paragnath ( Fig. 19 e): conical and with serrulate lateral margins.

Maxillule ( Fig. 19 f): composed of praecoxa and 2-segmented palp. Praecoxal arthrite bearing 3 very strong, claw-like spinous processes and 1 stout pinnate seta and 6 medial elements (proximalmost one longest and pinnate). Palp composed of coxobasis and endopod. Coxobasis with smooth proximal (exopodal) seta and 3 medial setae (2 smooth and slender, 1 strong, pinnate and claw-like). Endopod with 2 equal, apical setae and 1 subapical seta.

Maxilla ( Fig. 19 g): 4-segmented; praecoxa fused to coxa. Proximal endite of praecoxa robust, armed with 2 pinnate setae; distal endite small, unarmed. Proximal endite of coxa with 1 plumose seta; distal endite fused at base, elongate and armed apically with 2 equal pinnate setae. Basis expanded into robust claw, which is ornamented with 2 longitudinal rows of spinules along inner margin, and armed with 2 dissimilar setae; strong seta longer than claw, finely serrulate on inner margin, and short seta occurring at base of claw. Endopod 2-segmented; proximal segment robust, armed with 2 unequal unipinnate setae; distal segment with 1 robust, unipinnate apical seta and 2 slender and smooth subapical setae.

Maxilliped ( Fig.19 h): 4-segmented, composed of syncoxa, basis and 2-segmented endopod. All segments distally expanded. Each of first 3 segments ornamented with 1 row each of very minute spinules on outer distal margin. Armature formula: 2.1.1.2. Apical setae on fourth segment prehensile. All setae bipinnate.

Swimming legs 1–4 ( Fig. 20 a–d): relatively short, with 2-segmented exopod and endopod. Endopod only slightly shorter than exopod on legs 1–3, but distinctly so on leg 4. Armature formulae of legs 1–4 (legend: same as that of Paracyclopina orientalis ):

Coxa Basis Exopod Endopod

1 2 1 2

Leg 1 0-0 0-1 0- I 4, 1+I, I 1 -0 1, 1+I, 1 Leg 2 1-0 0-1 0- I 4, 1+I, I 1 -0 1, 1+I, 1 Leg 3 1-0 0-1 0- I 4, 1+I, I 1 -0 1, 1+I, 1 Leg 4 0-0 0-1 0- I 3, 1+I, I 1 -0 1, 1+I, 1

Spine and setal formulae of second exopodal segment 2.2.2.2, and 5.5.5.4, respectively. All setae on exopod and endopod slender and plumose. Intercoxal sclerite of all legs with concave distal margin and without any ornamentation. Praecoxae on all legs short, smooth and narrow. Coxae on all legs unornamented. Basis with round inner distal corner, ornamented with long hairs. Inner spine on basis of first leg absent. Second endopodal segment of leg 4 about 1.2 times as long as wide; apical spine 0.8 times as long as segment and about half as long as apical seta.

Fifth leg ( Fig. 18 a–c): completely fused to somite and represented by 3 setae; basal plumose seta on small protuberance; 2 other setae representing ancestral distal segment and occurring on short but somewhat broad prominence; the latter 2 setae unequal, smooth and shorter than basal seta.

Sixth leg ( Fig. 19 i): small cuticular plate distinct at base, armed with 2 small spiniform elements.

Description of adult male. Total body length 318 µm. Habitus ( Fig. 21 a) slender, prosome/urosome ratio about 1.5 and greatest width (91 Μm) at posterior end of cephalothorax. Body length/width ratio 3.6; cephalothorax about 1.7 times as wide as genital somite, and 1.2 times as long as wide (dorsal view), representing 35.2% of total body length. Hyaline fringe of fifth pedigerous somite smooth, both dorsally and ventrally; somite ornamented with 4 dorsal sensilla, as in female. Genital somite almost 1.5 times as wide as long, with smooth hyaline fringe dorsally; ornamented with 4 dorsal sensilla; 2 relatively large, ovoid spermatophores visible from inside. Third urosomite larger than either of next 2 somites, ornamented with 1 mid-ventral pore; next 2 urosomites ornamented only with smooth, narrow hyaline fringes. Anal somite ornamented with 2 tiny dorsal sensilla and transverse row of spinules along caudal margin ventro-laterally. Anal operculum same as in female.

Antennule ( Fig. 21 b): 15-segmented, digeniculate, geniculation between segments 8 and 9, and 13 and 14; ornamented with 1 row of spinules only on segment 1. Armature formula as follows: 8.1.1.1.0.3.0.1.0.1.1.1.1.1.8. Short unipinnate seta present on segment 12; segments 1, 4, 6, 10, and 15 with 1, 1, 1, 1, and 4 long pinnate seta(e), respectively. Length ratios of antennular segments along medial axis 1.0: 0.3: 0.3: 0.2: 0.3: 0.2: 0.3: 0.6: 0.1: 0.2: 0.3: 0.2: 1.0: 0.7: 0.9.

Antenna, labrum, mandible, maxillule, maxilla, maxilliped, legs 1–5, and caudal rami similar to those of female.

Leg 6 ( Fig. 22 b): almost held laterally, large cuticular plate, slightly fused at base, armed with 2 smooth, equal setae at outer distal corner.

Etymology. The new species is named in honour of Dr. D. Defaye, a well-known copepodologist in the world. The name is a noun in the genitive singular. Gender feminine.

Variation. In some specimens, proximal seta of leg 5 shorter than distal one (not figured).

Ecology. Rybocyclops defayeae n. sp. was accompanied by Nitocrella sp. and Paracyclops sp., and was found in the phreatic zone just like its sole Indian congener, Rybocyclopos dussarti Ranga Reddy & Defaye, 2008.

Remarks. Ranga Reddy & Defaye (2008) reviewed the background of the genus Rybocyclops Dussart, 1982 , discussed its affinities with the closely allied genera, and also amended its original diagnosis, as given by Dussart & Defaye (2001). Presently, this genus is known only by two species in the world, viz. the Madagascan Rybocyclops pauliani ( Lindberg, 1954) (type species), and the Indian Rybocyclops dussarti Ranga Reddy & Defaye, 2008 . The morphology of the former is still fragmentarily known.

Rybocyclops defayeae n. sp. fulfills almost all the criteria, as given in the amended generic diagnosis, and is rather closely related to R. dussarti by possessing the following salient features in the females: antennule 11- segmented, segment 5 having a modified conical seta; genital-double somite dilated proximally; dorsal caudal seta as long as or slightly longer than principal outer apical caudal seta; spine and setal formulae: 2.2.2.2 and 5.5.5.4; endopod of leg 4 shorter than exopod; coxal spine present only on legs 2 and 3; intercoxal plate without any ornamentation; and male leg 6 armed with two short setae.

Rybocyclops defayeae n. sp., however, is distinctly different from R. dussarti in that leg 4 endopod shows no sexual dimorphism, the setal armature being the same in both sexes. On the other hand, in R. dussarti , the second endopodal segment of the male leg 4 has one inner seta, which is absent in the female. R. defayeae n. sp. differs from R. dussarti in some other respects as well: body harpacticoidal vs. cyclopiform; caudal ramus length/width ratio 1.7 vs. 2.0; setal formula of the female antennule 4.3.6.2.1.2.2.2+aes.2.2.7 vs. 7.2.5.2.1.2.2.2+aes.2.2.7+aes (presently depicted version); anal operculum short vs. long; 15 male antennular segments vs. 16; rostrum elongate, linguiform vs. short, subtriangular; and female leg 6 dorso-lateral vs. completely dorsal.

The new species together with R. pauliani and R. dussarti forms a rather close-knit, Gondwanan, monophyletic lineage. The principal morphological differences between these species are as in Table 2 .

Figures

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

FIGURE 17. Rybocyclops defayeae n. sp. (a) paratype female, habitus, dorsal; (b) holotype female, antennule, lateral.

FIGURE 18. Rybocyclops defayeae n. sp., holotype female (a), paratype female (b, c). (a) urosome, dorsal; (b) same, ventral; (c) leg 5, latero-ventral.

FIGURE 19. Rybocyclops defayeae n. sp., holotype female. (a) rostrum, ventral; (b) antenna, lateral; (c) labrum, ventral; (d) mandible, lateral; (e) paragnath, ventral; (f) maxillule, lateral; (g) maxilla; lateral; (h) maxilliped, lateral.

FIGURE 20. Rybocyclops defayeae n. sp., holotype female. (a) leg 1, posterior; (b) leg 2, anterior; (c) leg 3, anterior; (d) leg 4, anterior.

FIGURE 21. Rybocyclops defayeae n. sp. (a) paratype male, habitus, dorsal; (b) allotype male, antennule, lateral.

FIGURE 22. Rybocyclops defayeae n. sp. (a) allotype male, urosome, dorsal; (b) paratype male, same, ventral.