Habrobathynella muvattupuzha, Elia, Bandari, Shaik, Shabuddin & Reddy, Yenumula Ranga, 2016

Elia, Bandari, Shaik, Shabuddin & Reddy, Yenumula Ranga, 2016, Two new species of the genus Habrobathynella Schminke, 1973 (Syncarida, Parabathynellidae) from the southwestern peninsular India, Zootaxa 4150 (2), pp. 149-167 : 151-157

Habrobathynella muvattupuzha n. sp.

( Figs 2–6 )

Type locality. The River Muvattupuzha at Muvattupuzha town (958'0''N, 7634'59''E, elevation 15 m) in Kerala State, southwestern India . The landmass of the State is wedged between the Arabian Sea to the west and the Western Ghats , identified as one of the world’s biodiversity hotspots, to the east (Water Resources of Kerala, 1958). The river, formed by the concourse of three small rivers: Thodupuzha, Kaliar and Kothamangalam, near Muvattupuzha town, empties into Vembanad Lake, which is connected to the Arabian Sea. The maximum length of the river is about 120 km. The drainage basin area is about 1528 km 2 and rich in crystalline rocks of igneous and metamorphic origin. The soils are generally deficient in nitrogen, phosphorous and lime in the basin, but loamy with a great admixture of humus from the hills. Mean annual air temperatures range from 25.0 to 27.5°C, and the average rainfall in the basin varies from 254 cm in the coastal region to about 508 cm in the highlands. The riverbed at the sampling site has a deposit of fine sand and detritus particles, but with little or no clay, and is devoid of macrophytic vegetation.

Type material examined. Holotype Ƌ (ZSI-C5864/2/a–l), dissected on 11 slides; allotype ♀ (ZSI-C5865/2/a– k), dissected on 10 slides; one paratype ♀ (ZSI-C5866/2), mounted whole on 1 slide; one paratype Ƌ (MNHN-IU- 2013-11982), dissected on 4 slides. 29 October 2004, Coll. Y. Ranga Reddy.

Diagnosis. Parabathynellids of small size (0.7–0.8 mm in length). Uropodal sympod with inhomonomous row of 5 spines, with penultimate spine longer and thicker than others, and ultimate spine same as proximal spines. Pleotelson seta longer than caudal furca. Male Th VIII small, subglobular, with protopod being distinctly expanded distally (somewhat bowl-like in latero-external view); penile lobes only slightly extending beyond balloon-shaped basipod; outer lobe conical and short; inner lobe thumb-like in posterior view. Antennule with 2 long and equal aesthetascs on fifth segment. Paragnaths with minaret-like, smooth coupler and short lateral lobes. Labrum with almost straight dentate margin. Maxilla with 2 setae on first segment and 1 seta at midlength of inner margin of second segment. Anal operculum nearly flat.

Description of adult male. Total body length of holotype 0.73 mm. Body ( Fig. 2 ) elongate, slightly chitinised and 10 times as long as maximum width. In lateral view, pleomeres wider than thoracomeres. In dorsal view, body vermiform and uniformly narrow. Head 1.8 times as long as wide and about 1.3 times as long as first 2 thoracomeres combined.

Antennule (Fig. 3A): 6-segmented; no sexual dimorphism, measuring 37% as long as head. First segment with 1 plumose seta on outer margin, 2 plumose setae on dorsal surface and 1 long simple seta and 1 small ventral plumose seta near inner margin subdistally. Second segment with 3 plumose setae in a row on dorsal surface, 1 ventral plumose seta on outer margin, and 1 ventral simple seta on inner distal margin. Third segment with 1 long dorsal simple seta, 1 short ventral seta and 1 plumose seta near outer distal corner. Inner flagellum subquadrate, bearing 3 unequal simple setae. Fourth segment with apophysis, overreaching midlength of next segment and with 2 unequal plumose setae; 1 plumose seta occurring on small protuberance on distal margin. Fifth segment with 2 equal aesthetascs, overreaching sixth segment, 3 unequal simple setae and 1 short modified seta at inner distal corner. Sixth segment with 3 short equal aesthetascs and 4 slightly subequal setae.

Antenna (Fig. 3B): small, 2-segmented; proximal segment bare and 0.6 times as long as distal one; distal segment 2.3 times as long as wide, with 2 unequal apical setae; 1 small subapical seta on dorsal surface and 1 similar seta on outer proximal margin.

Labrum (Fig. 3C): dentate margin almost straight, bearing 10 main nearly uniform, pointed, incurved teeth, and 1 smaller tooth on either side. Also, fine spinules in a short row discernible on ventral surface, as illustrated.

Mandible (Fig. 3D, E): distal part of pars incisiva with 4 unequal teeth; proximal tooth smallest; distal tooth large curved and pointed. Tooth of ventral edge articulate at base and with smooth lateral margins. Pars molaris (‘lobe’) developed into pyriform outgrowth, carrying 2 isolated, curved claw-like setae on inner margin and 3 straight pointed, unequal claw-like setae in a group at proximal end (denticle not discernible); all teeth smooth, articulate and apparently without ornamentation. Palp completely absent.

Paragnaths (Fig. 3F): coupler minaret-like and without any ornamentation; lateral lobes short, occurring close to the base of coupler and without ornamentation.

Maxillule (Fig. 3G): with 2 endites; proximal endite small, oval, carrying 3 long, equal, claw-like serrulate spines and 1 very small, smooth spine. Distal endite subcylindrical, about 2.7 times as long as proximal endite, gradually bending inwards and armed with 4 apical claws, distalmost one largest, 2 unequal spines on inner margin, and 3 subapical setae on outer distal margin.

Maxilla (Fig. 3H): 3-segmented, nearly straight; basal segment 1.6 times as long as wide, with 2 strongly unequal setae on small protuberance at inner distal corner. Second segment somewhat cylindrical, 1.2 times as long as basal segment and armed with 13 simple setae. Third segment small but distinct, subquadrate, carrying only 1 stout claw.

Thoracopods (Th) I–VII ( Figs. 4 A–E, 5A–B): well-developed, Th I–III gradually increasing in size and Th IV– VII nearly similar in size; biarticulate, club-shaped epipod on Th II–VII, about 0.6 times as long as basis. Coxa of all thoracopods with distinct conical projection at inner distal border, and basis with 1 short simple seta overreaching midlength of first endopodal segment. Exopod 2-segmented, 0.7 times as long as endopod on Th I and about 0.8 times as long as endopod on Th II–VII; segment 1 slightly longer than segment 2, and with 2 unequal plumose setae, dorsal seta slightly overreaching midlength of exopodal segment 2 and ventral seta longer than exopodal segment 2. Ctenidia lying at base of ventral seta. Segment 2 with 2 apical unequal setae, outer seta plumose, inner one spiculated. Ctenidia at base of inner apical seta. Endopod 4-segmented, segment 4 smallest and ornamentation as illustrated. Setal formulae: Th I: 1+0/0+1/0+1/2(0); Th II–VII: 0+0/0+1/0+1/1(0).

Th VIII ( Fig. 5 C–F): small, subglobular, with distal region distinctly expanded in latero-external view. Dentate lobe somewhat large, overreaching inner lobe and with unequal denticles distally. Outer lobe conical, short and not extending up to posterior margin of basipod. Inner lobe thumb-like in posterior view and rectangular in posterior view. Basipod balloon-shaped with 1 seta. Exopod small plate-like, slightly curved inwards and with minute denticles distally. Endopod represented by a small simple seta.

Pleopod 1 absent

Uropod ( Fig. 6 A, C): sympod 4 times as long as wide, bearing inhomonomous row of 5 serrulate spines; proximal 3 spines of nearly equal length; penultimate spine largest; ultimate spine nearly as long as proximal spines; spine-row bearing inner margin of sympod moderately dilated. Exopod cylindrical, 3.7 times as long as wide, measuring 36% of sympod length and with 1 apical seta and 1 slightly subapical seta; both setae plumose; outer seta less than half as long as apical seta. Endopod falcate, about half as long as sympod and with 2 equal, short, plumose setae at proximal third of outer margin.

Pleotelson ( Fig. 6 A, B): rounded at posterolateral angle, with 1 seta on either side at base of caudal furca; seta bare and longer than caudal furca. Anal operculum nearly flat in ventral view ( Fig. 6 B).

Caudal furca ( Fig. 6 A, B): longer than maximum width; distal part with 2 apical, 2 inner pointed, serrulate spines, and 2 unequal plumose dorsal setae; apical spines longer than inner ones. Furcal organ small.

Description of adult female. Total body length 0.70 mm. Body and all appendages except Th VIII as in male.

Th VIII ( Fig. 6 D): small, crescentic lobe.

Etymology. The specific epithet alluding to the River Muvattupuzha , the type locality of the new species, is proposed here as a noun in apposition to the generic name.

Variation. Body size varies from 0.68–0.82 mm, mean 0.72 mm (n = 10). No variation was noticed in the number of spines borne by the uropodal sympod.

Distribution and ecology. H. muvattupuzha n. sp. has not yet been collected outside the type locality. The fauna that co-occurred with the new species included Parastenocaris curvispinus Enckell, 1970 , Parastenocaris muvattupuzha Ranga Reddy & Defaye, 2009 , nematodes, oligochaetes, and insect larvae.

Figures

FIGURE 2. Habrobathynella muvattupuzha n. sp., paratype female, habitus, lateral.

FIGURE 4. Habrobathynella muvattupuzha n. sp., holotype male: (A – E) Thoracopods I – V.

FIGURE 5. Habrobathynella muvattupuzha n. sp., holotype male (A – F): (A) Thoracopod VI; (B) Thoracopod VII; (C – F) Thoracopod VIII: (C) posterior; (D) ventral; (E) latero-external; (F) anterior. Abbreviations: bsp = basipod; dlb = dentate lobe; enp = endopod; exp = exopod; ilb = inner lobe; and olb = outer lobe.

FIGURE 6. Habrobathynella muvattupuzha n. sp., holotype male (A – C), allotype female (D): (A) pleotelson, lateral; (B) pleotelson (uropods omitted), ventral; (C) uropod, lateral; (D) Th VIII (arrow), lateral.