Parastenocaris mahanadi, Ranga Reddy & Defaye, 2007

Reddy, Yenumula Ranga & Defaye, Danielle, 2007, Parastenocarididae (Crustacea, Copepoda, Harpacticoida) of India: description of Parastenocaris mahanadi n. sp., and redescription of P. curvispinus Enckell, 1970 from hyporheic habitats, Zootaxa 1580 (1), pp. 1-26 : 2-9

Parastenocaris mahanadi n. sp.

( Figs 1–4 )

Material examined. Holotype, adult male, dissected on one slide (MNHN-Cp2336); allotype, adult female, dissected on one slide (MNHN-Cp2337); paratypes: one male and three females, dissected on one slide each (MNHN-Cp2338, MNHN-Cp2340, MNHN-Cp2341, MNHN-Cp2359); one undissected female on slide (MNHN-Cp2339); five males and eleven females, ethanol-preserved (MNHN-Cp2342). Leg. Y. Ranga Reddy, 19 October 2005, water temperature: 29°C, pH 7.0.

Type locality. The River Mahanadi is one of the longest (ca 860 km) rivers in India and drains a substantial part of peninsular India. Originating from the Amarkantak plateau in the Eastern Ghats of central India, in the State of Chhatisgarh , the river flows eastward through a forest-clad gorge into the Bay of Bengal. It is one of the most active silt-depositing streams of the Indian subcontinent. The drainage basin area of this river is 141,464 km 2, with elevation ranging from 193 m. a.s.l. to 877 m. a.s.l., with an average of 426 m. a.s.l.. The interior coastal plain has a relatively low elevation and the relief is very low. In the region of the Mahanadi River , the climate is predominantly subtropical, with summer and winter temperatures being about 29°C and 21°C, respectively. Most rainfall (800–1200 mm) occurs from July to September .

The sampling site is located at Rajim, a small town (20°57'57" N, 81°52'51" E; altitude 281 m), 48 km southeast of Raipur city, the capital of Chhatisgarh State. Two other small rivers, the Pairi and the Sondu , join the River Mahanadi here and this confluence point is known as “Prayag of Chhatisgarh”. There the riverbed has a deposit of fine sand and detritus particles, but with little or no clay, and is completely devoid of macrophytic vegetation .

Diagnosis. Parastenocaridid of moderate size (mean female body length ca 450 µm). In male, seventh antennular segment without apophysis; aesthetasc on fifth segment extraordinarily long. Caudal rami somewhat divergent, as long as anal somite and over 4 as long as their maximum width; lateral setae inserted at about distal third of rami. Anal operculum with almost straight or slightly rounded posterior margin, without spinules. Leg 4 of male with 2 chitinized, claw-like spines at distal inner corner; endopodite small, 0.4 as long as first exopodite-segment and ornamented with 2 groups of long spinules. Leg 5 produced into a smooth, slender, acute spinous process at distal inner corner, and bearing only 3 setae. In female, caudal rami about 4 times as long as wide, each ramus with tiny spinules at distal inner corner.

Description of adult male (holotype). Total body length, measured from base of rostrum to posterior margin of caudal rami (excluding caudal setae): 455 µm (paratypes from 425 to 450 µm). Preserved specimens colourless. Naupliar eye absent. Body ( Fig. 1a ) nearly cylindrical, very slender, without demarcation between prosome and urosome; prosome/urosome ratio 0.7. Body length/width ratio 9.6. Integument weakly chitinized and without surface pits. Hyaline frills of all somites smooth. Cephalothorax subquadrate, 1.7 times as long as wide, 17.3% of body length, integumental window present but with vague contour, of circular shape. Urosomites 3–5 each with indistinct, rectangular integumental window dorsally; no window discernible on urosomite 2. All somites except preanal somite with small sensilla, as illustrated ( Fig. 1a–b ). Anal operculum ( Fig. 1b ) with almost straight posterior margin, smooth, not reaching posterior end of anal somite and representing about 70% of somite’s width. Anal sinus smooth.

Rostrum small, blunt, membranous, reaching middle of first antennular segment and not defined at base; with 2 small dorsolateral sensilla ( Fig. 1a ).

Caudal rami ( Fig. 1a–b ) symmetrical, divergent and as long as anal somite; each ramus 4.6 times as long as maximum width, gradually narrowing behind, posterior end about half as wide as proximal end and without ornamentation; armed with full complement of 7 setae (3 lateral, 1 dorsal and 3 apical). Dorsal seta relatively long, inserted close to inner margin at about ¾ of ramus length, 20% shorter than caudal ramus, with breaking surface at base and smooth. Lateral setae thin, unequal, shorter than ramus, inserted close to each other in a group, slightly anterior to dorsal seta. Inner apical seta about half as long as ramus. Middle apical seta strongest, without breaking plane, sparsely bipinnate, 2.6 times as long as outer apical seta, and one-third as long as whole body. Outer apical seta 35% longer than caudal ramus, without breaking plane, with pinnate outer margin.

Antennule ( Fig. 1c ) 8-segmented, elongate, prehensile, strongly geniculate between segments 6 and 7; spinules on segment 1 not discernible. Segment 2 longest, segment 4 very short, segments 3–5 enlarged. Segment 7 without apophysis. Setal formula: 0, 7 (1 unipinnate), 2, 0, 2, 0, 0, and 8. Aesthetasc on fifth segment 3 times as long as segments 6–8 combined, 92% of antennular length, curved, narrow, constricted at about midlength and distally tapering to blunt tip. Aesthetasc on segment 8 short, slender and straight.

Antenna ( Fig. 1d ): coxa unarmed. Allobasis 3.3 times as long as maximum width, with a single transverse spinule row on inner margin. Exopodite 1-segmented, cylindrical, well-defined at base, 4 times as long as wide, with 1 apical, bipinnate seta, more than twice as long as the segment. Endopodite 2.7 times as long as wide, 0.6 as long as allobasis, with 2 spines and 2 transverse spinule rows on inner margin; distal end with 5 spiniform setae, 2 of which geniculate; a row of spinules at distal outer corner.

Mandible ( Fig. 1e ): coxal gnathobase elongate, cutting edge with 3 coarse teeth ventrally, 1 smooth seta dorsally, and a row of smaller teeth in-between. Palp 1-segmented, cylindrical, about 5 times as long as wide, with 2 apical, unequal setae.

Maxillule ( Fig. 1f ): praecoxal arthrite well developed, rectangular, with 5 curved spines and 1 anteriorsurface seta. Coxal endite small, with 1 seta. Basis longer than coxal endite and armed with 2 terminal setae. Exo- and endopodite absent.

Maxilla ( Fig. 1g ) small; syncoxa with 2 unequal endites (distal 1 longer), each carrying 1 apical seta. Allobasis drawn out into long, strong claw. Endopodite small, spherical, with 2 apical setae.

Maxilliped ( Fig. 1h ): subchelate. Syncoxa 2.4 times as long as wide, bare. Basis 3.5 times as long as wide. Endopodite 1-segmented, small, rounded, carrying a unipinnate claw.

Leg 1 ( Fig. 2a ): coxa bare. Basis with 1 small, outer seta, with spinule row along outer margin and between exo- and endopodite. Exopodite shorter than endopodite, distal edge reaching proximal edge of second endopodite-segment. Exopodite: first segment with 1 short bipinnate outer spine and 3 transverse spinule rows on outer margin; second segment about half as long as first segment, unarmed, ornamentation represented by spinule row on outer margin; third segment only slightly longer than second, with 2 outer spines, 2 geniculate apical setae, and 2 outer spinule rows. Endopodite: first segment only slightly shorter than first 2 exopodite-segments combined, with 2 transverse spinule rows along outer margin, 1 spinule row at about midlength of inner margin, and a terminal row of fine spinules; second segment about half as long as first, with 1 apical spine and 1 geniculate seta, 1 outer and 1 inner spinule row. All armature elements of apical segments of exo- and endopodite unipinnate.

Leg 2 ( Fig. 2b ): coxa with transverse row of ventral spinules close to distal outer margin. Basis lacking outer seta, with spinule row on outer and inner margins. Exopodite: first segment as long as next 2 segments combined, with 1 elongate bipinnate outer spine, with 2 transverse spinule rows along outer margin, 1 spinule row distally; second segment unarmed, with 1 spinule row on outer margin and another spinule row apically; third segment only slightly shorter than second one, with 1 spiniform outer seta, and 2 subequal apical setae, and 1 spinule row on outer margin; all armature elements bipinnate. Endopodite 1-segmented, slender, subcylindrical, about 5 times as long as wide and half as long as first exopodite-segment; apex with 1 straight, elongate seta and 4 or 5 spinules.

Leg 3 ( Fig. 2c ): coxa bare. Basis robust with very long outer seta, 1 oblique row of large spinules at distal outer angle, 1 row of tiny spinules on inner margin; 1 short slender seta near distal inner corner, representing endopodite. Exopodite modified, apparently 2-segmented; ancestral first segment elongate, slender, slightly incurved, about 8 times longer than width at midlength, basal region somewhat expanded; with 2 spinule rows on distal outer margin; spinules of distal row very small; inner margin lined with narrow hyaline membrane and with small dentate structure subproximally. Ancestral second segment (apophysis) longer than outer spine, spatulate, with hyaline distal outer area; outer spine modified, smooth, incurved and acutely pointed, inserted close to the base of second segment.

Leg 4 ( Fig. 2d ): coxa without ornamentation. Basis with moderately long outer seta; 2 chitinized, slender, equal, pointed, overlapping claws at distal inner corner. Exopodite: first segment nearly as long as next 2 segments combined, with bipinnate outer spine, 2 transverse spinule rows on outer margin and 1 row distally; second segment unarmed; ornamentation consisting of 1 spinule row on distal outer margin and a terminal spinule row; third exopodite-segment as long as second one, with 1 bipinnate outer spine, 1 apical bipinnate seta and 1 spinule row on distal outer margin. Endopodite small, 1-segmented, 0.4 as long as first exopoditesegment, shape varying according to degree of flattening and angle of view, ornamented with 2 groups of spinules: spinules on proximal inner margin relatively short whereas those on distal region long and numerous, as illustrated ( Fig. 2d ); no special sclerotized structures at base of endopodite.

Leg 5 ( Fig. 2e, f ) small, subquadrate, distinct at base; distal inner corner produced into smooth, slender, acute spinous process; distal inner margin with about 6 spinules; distal margin uneven with 3 unequal setae; outermost seta longest and arising from a short papilla; fourth seta absent.

Leg 6 ( Fig. 2e ) bare, directed posteriorly, conical protrusion, with acute tip.

Description of adult female (allotype). Total body length, excluding caudal setae, of allotype 430 µm, of paratypes 420–445 µm, average 430 µm (n = 9). Habitus shape, ornamentation of prosomites and form of anal operculum similar to those of male. Dorsal integumental windows on cephalothorax and on anterior surface of genital double-somite, second and third abdominal somites indistinct. Genital double-somite as long as wide, without any trace of subdivision, ornamented with 6 sensilla. Genital field ( Fig. 3c ) located at proximal third of genital double-somite, anteroventrally; copulatory pore median with no operculum visible, internal structures not clearly discernible, seminal receptacles appearing as paired small lobes, another lobe of unknown function visible distally.

Caudal rami ( Fig. 3b ) about four times as long as wide, with tiny spinules at distal inner corner of each ramus; other details as in male.

Antennule ( Fig. 3d ) 7-segmented. Segment 2 as long as next 3 segments combined. Setal formula: 0, 4 (1 unipinnate), 4, 2, 1, 0, and 8. Segments 4 and 7 each with aesthetasc. Aesthetasc on segment 4 slender, nearly straight, constricted at about midlength and extending beyond antennular tip; that of segment 7 slender, straight, about 40% longer than the segment.

Other cephalic appendages and leg 1 ( Fig. 4a ) as in male.

Leg 2 ( Fig. 4b–c ): with same armature as in male; endopodite 0.6 as long as first exopodite-segment; apex appearing slightly bulbous in allotype (not bulbous in female paratypes).

Leg 3 ( Fig. 4d ): coxa without ornamentation. Basis with long outer seta, spinule row near distal outer corner and on distal inner margin. Exopodite: first segment 1.3 times as long as second, and with bipinnate outer spine; 2 spinule rows on outer margin and 1 row distally; second segment with 1 bipinnate outer spine and 1 apical seta; 1 spinule row along outer margin. Endopodite 1-segmented, a little shorter than first exopodal segment, curved outwards, lateral margins of distal half finely spinulose, tip acute.

Leg 4 ( Fig. 4e ): coxa without ornamentation. Basis with short outer seta, with spinule row along outer margin. Exopodite: first segment shorter than next 2 segments combined, with 1 bipinnate outer spine and 2 spinule rows on outer margin and 1 row distally; second segment unarmed, with 1 spinule row on distal outer margin and a terminal spinule row; third exopodite- segment longer than second, with 1 bipinnate outer spine and 1 apical seta, 1 spinule row on distal outer margin and fine spinules at base of outer spine. Endopodite lanceolate, curved outwards, longer than first exopodite-segment; lateral margins of distal half finely spinulose and with a circle of 4 or 5 somewhat long spinules at midlength.

Leg 5 ( Fig. 4f ): similar to male, except for somewhat shorter spinules on inner margin.

Etymology. The specific name, alluding to the River Mahanadi, the habitat of occurrence of the new species, is proposed as a noun in apposition to the generic name; the name is in singular masculine genitive.

Figures

FIGURE 1. Parastenocaris mahanadi n. sp., holotype, male, MNHN-Cp2336: a, habitus, dorsal; b, anal somite and caudal rami, dorsal; c, antennule; d, antenna; e, mandible; f, maxillule; g, maxilla; h, maxilliped. Scale i for a; scale j for b-h. Scales = 100 µm.

FIGURE 2. Parastenocaris mahanadi n. sp., holotype, male, MNHN-Cp2336: a, leg 1; b, leg 2; c, leg 3; d, leg 4; e, legs 5 and 6, lateral; f, leg, 5, ventral. Scale = 100 µm.

FIGURE 3. Parastenocaris mahanadi n. sp., allotype, female, MNHN-Cp2337: 1, habitus, dorsal; b, anal somite and caudal rami, dorsal; c, genital double-somite, ventral. Scale e for a; scale f for b–d; Scales = 100 µm.

FIGURE 4. Parastenocaris mahanadi n. sp., paratype females, MNHN-Cp2359: a, leg 1; b, leg 2; c, same, endopodite; d, leg 3; e, leg 4; f, leg 5. Scale = 100 µm.