Habrobathynella adishankara, 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 : 157-165

Habrobathynella adishankara n. sp.

( Figs. 7–12 )

Type locality. The River Periyar at Kalady village (1010'60''N, 7613'0''E, elevation 10 m), Kerala State, southwestern India . This is the longest river (228 km) and one of the few perennial rivers in Kerala. Originating in the Western Ghats, one of the three biodiversity hotspots in India, at an elevation of 2438 m above sea level, the river has a total catchment area of over 5284 km 2. The influence of tectonism is evident from the stream pattern and presence of structural valleys . The river basin is ecologically sensitive owing to widespread erosion and mass movements. The average rainfall in the basin varies from 444 cm to 508 cm in the mountains to about 304 cm in the coastal fringes (Water Resources of Kerala, 1958). At the sampling site, the riverbed has a deposit of fine sand and detritus particles, but with little or no clay, and with patches of macrophytic vegetation.

Type material examined. Holotype Ƌ (ZSI-C5867/2/a–l), dissected on 12 slides; allotype ♀ (ZSI-C5868/2/a– l), dissected on 12 slides; 1 paratype ♀, mounted whole on 1 slide (ZSI-C5869/2); 1 paratype Ƌ (MNHN-IU-2013- 11983), dissected on 1 slide. 3 February 2005, Coll. Y. Ranga Reddy.

Diagnosis. Uropodal sympod with inhomonomous row of 6 spines, penultimate spine largest and ultimate spine similar to proximal spines. Pleotelson seta shorter than caudal furca. Male Th VIII small, subglobular, with protopod expanded distally in latero-external view; dentate lobe wide and with truncate distal margin; outer lobe conical and short, barely reaching midlength of balloon-shaped basipod. Antennule with 3 long and equal aesthetascs on fifth segment. Antennary proximal segment nearly as long as distal segment. Paragnaths with thumb-like smooth coupler and short triangular lateral lobes. Labrum with somewhat vaulted dentate margin. Maxilla with 1 seta on first segment as well as on mid-inner margin of second segment. Anal operculum deeply concave medially.

Description of adult male. Total body length of holotype 0.73 mm. Body elongate, 11 times longer than maximum width; cuticle thin and imperforate. In lateral view, pleomeres wider than thoracomeres ( Fig. 7 ); in dorsal view, body vermiform and uniformly narrow. Head 1.2 times as long as wide and about as long as first 2 thoracomeres combined.

Antennule ( Fig. 8 A): 6-segmented, measuring 41.3% longer than head, no sexual dimorphism. First segment with 3 plumose setae near outer margin, 1 plumose dorsal seta subdistally, and 1 small plumose seta on ventral surface subdistally. Second segment with 3 unequal plumose setae in a row on dorsal surface of subdistal outer margin, 1 ventral plumose seta and 1 dorsal simple seta at inner distal corner. Third segment with 1 plumose seta and 1 long simple seta at outer distal corner, 1 ventral simple seta near distal inner corner. Inner flagellum subquadrate, with 3 unequal setae. Fourth segment with apophysis, reaching about midlength of next segment and with 2 unequal plumose setae; 2 plumose setae on small protuberance on distal margin. Fifth segment with 3 equal aesthetascs, overreaching sixth segment, 3 unequal simple setae and 1 short modified seta at inner distal corner. Sixth segment with 3 relatively short equal aesthetascs and 4 slightly unequal setae.

Antenna ( Fig. 8 B): small, 2-segmented; proximal segment bare and 0.8 times as long as distal one; distal segment 1.3 times as long as wide, with 1 apical plumose seta, 2 subapical unequal simple setae and 1 simple seta on outer proximal margin.

Labrum ( Fig. 8 C): dentate margin somewhat vaulted on both sides, though not deeply, and bearing 12 main pointed teeth, and one smaller tooth on either side

Mandible ( Fig. 8 D): distal part of pars incisiva with 4 unequal teeth, proximal tooth smallest; distal tooth large, curved and pointed. Tooth of ventral edge lying close to the base of pars molaris. Pars molaris developed into pyriform outgrowth, carrying 2 isolated teeth on inner margin and 3 straight pointed unequal teeth in a group at proximal end; all teeth articulate and multicusped ( Fig. 8 E). Palp completely absent.

Paragnaths ( Fig. 8 F): coupler thumb-like, moderately developed and without ornamentation; lateral lobes small, triangular, disto-laterally directed and without ornamentation.

Maxillule ( Fig. 8 G): consisting of 2 endites; proximal endite small, elongately oval, carrying 3 long unequal claw-like serrulate spines, 2 apical and 1 subapical setae and 1 simple setiform element at inner distal corner. Distal endite cylindrical, 2.6 times as long as proximal endite and with 2 apical claws and 1 subapical claw and 2 unequal claws on inner distal margin; 3 simple setae on subapical outer margin.

Maxilla ( Fig. 8 H): 3-segmented; basal segment 1.5 times as long as wide with 1 long simple seta at inner distal corner; second segment 1.3 times as long as basal segment and armed with 13 simple setae. Third segment small, somewhat squarish, carrying 1 stout claw.

Thoracopods (Th) I–VII ( Figs. 9 A–D, 10A–C): well-developed, Th I–III gradually increasing in size and Th IV–VII nearly similar in size, well-developed; epipod on Th II–VII biarticulate, club-shaped, slightly longer than basis. Coxa of Th I–VII with distinct conical projection at distal inner corner and basis with 1 simple seta slightly overreaching midlength of first endopodal segment. Exopod 2-segmented, 1.4 times as long as endopod on Th I and about as long as endopod on Th II–VII; segment 1 only slightly longer than segment 2, with 2 unequal plumose setae; dorsal seta as long as second segment on Th I, but ventral seta longer on Th II–VII. Segment 2 with 2 apical unequal setae, outer seta plumose, inner one spiculated. Ctenidia present at base of inner seta. Endopod 4- segmented, segment 4 smallest. Setal formulae of endopod: Th I 1 +0/0+1/0+1/2(0); Th II–VII 0+0/ 0+1/0+1/1(0).

Thoracopod VIII ( Fig. 11 A–D): small, sub-globular, with protopod expanded distally ( Fig. 11 A); dentate lobe wide and with truncate, finely denticulate distal margin. Outer lobe conical and short, barely reaching midlength of basipod. Inner lobe large and rectangular in latero-external view. Basipod balloon-like and 1.3 times as wide as long, carrying 1 simple seta at outer distal margin. Exopod small, somewhat hook-like, with minute denticles at distal margin. Endopod represented by a small seta.

Pleopod 1 absent

Uropod ( Fig. 12 A, C): sympod 3.3 times as long as wide, bearing inhomonomous row of 6 serrulate spines; penultimate spine longer and thicker than proximal spines; ultimate spine slightly shorter than proximal spines; exopod cylindrical, 3.5 times as long as wide and half as long as sympod length and with 1 apical seta and 1 subapical outer seta; both setae plumose; outer seta half as long as apical seta. Endopod falcate, 0.7 times as long as sympod, bearing 2 equal short, plumose setae at proximal fourth of outer margin.

Pleotelson ( Fig. 12 B, C): produced into small rounded lobe at postero-lateral angle ( Fig. 12 A); 1 seta on either side at base of caudal furca; seta bare, shorter than caudal furca. Anal operculum deeply concave medially in dorsal view ( Fig. 12 C).

Caudal furca ( Fig. 12 A, C) as in preceding new species.

Description of adult female. Total body length 1.03 mm. Body and all appendages except Th VIII as in male.

Thoracopod VIII ( Fig. 12 D): small, broadly triangular lobe.

Etymology. The specific epithet alludes to Adi Shankara, a renowned exponent of Advaita Vedanta philosophy (monism); used here as a noun in apposition to the generic name.

Variation. Body size varies from 0.85–1.07 mm, mean 1.01 mm (n = 7). Uropodal sympod with 6 or, rarely, 7 spines. No variation in the number of spines on caudal furca.

Ecology. H. adishankara n. sp. is so far known from the type locality, most probably endemic to Kerala State. The fauna that co-occurred with the new species included the following taxa: Serbanibathynella sp., unidentified harpacticoid and cyclopoid copepods, cladocerans, chironomid larvae, mayfly nymphs, oligochaetes, nematodes and rotifers.

Remarks. Both H. muvattupuzha n. sp. and H. adishankara n. sp. perfectly fit the diagnosis of Habrobathynella Schminke, 1973 , as recently revised by Ranga Reddy & Totakura (2010) and “slightly modified by Schminke (2011). Going by the essential features of the complex penile appendage, i. e. the male Th VIII, which is crucially important in the systematics of Parabathynellidae ( Schminke 1973, 1976; Delamare Deboutteville & Serban 1974; Ranga Reddy & Totakura 2010), the two new species may be said to be more closely related to each other that than to their hitherto known 12 Indian and two Madagascan congeners. As for its size and shape, the said appendage in both taxa is small and the protopod is expanded distally, resulting in a somewhat cup- or bowl-like appearance, in latero-external view–reminiscent of the generality of Atopobathynella species besides some resemblance to the Indian Habrobathynella plenituda Ranga Reddy & Schminke, 2009 , and H. pseudoindica Totakura & Ranga Reddy, 2014 . Similarly, the penile lobes in both new species are only moderately produced and the outer lobe is short and conical. Further, the overall spine configuration on the uropodal sympod, as already described, is the same in both species except that the number of proximal spines is three in H. muvattupuzha n. sp. as against four or five in H. adishankara n. sp. The other points of similarity, inter alia, include: the poorly chitinised body; the equally long aesthetascs on fifth and sixth antennulary segments; the smooth couplers as well as small lateral lobes on the paragnaths; and the presence of a single seta on the mid-inner margin of the second maxillary segment. However, H. muvattupuzha n. sp. can be distinguished from H. adishankara n. sp., inter alia, by the following features: the uropodal sympod has three vs. four or five proximal spines; the pleotelson seta is long vs. short; the maxillule has six vs. five claws on the distal endite; the maxilla has two setae vs. one seta on the first segment, and the seta at the inner distal corner of the second segment strong vs. weak; the antennule has two vs. three aesthetascs on fifth segment; the antenna has short vs. long first segment; the paragnaths with minaret-like vs. thumb-like coupler; and the anal operculum flat vs. medially deeply concave. Both the new species stand out in the genus by their unique constellation of characters (see Diagnosis).

The salient morphological characters and their states among the then known species of Habrobathynella had been analysed by Ranga Reddy & Totakura (2010), Totakura & Ranga Reddy (2014), and Ranga Reddy et al. (2014). Now, we briefly mention the newly recognised and phylogenetically important character states in the present new species, and also refer to the parallel conditions in the allied lineages, wherever relevant.

Antennule. The fifth antennular segment in H. muvattupuzha n. sp. has two long aesthetascs, overreaching the sixth antennular segment. This character state is shared only with the Indian H. nagarjunai and both Madagascan species. All other species have three long or short aesthetascs on the said segment.

Antenna. In the Parabathynellidae as a whole, two-segmented antenna occurs only in three genera besides Habrobathynella : Kimberleybathynella Cho, Park & Humphreys, 2005 , Nipponbathynella Schminke, 1973 , and Nunubathynella Schminke, 1976 . The proximal segment tends to be reduced among various species of these genera, and this is particularly true of Habrobathynella species (see Ranga Reddy & Totakura 2010). On the other hand, the segment is nearly half as long as the next segment in H. muvattupuzha n. sp. much like what is seen in H. vidua , and it is almost as long as the next segment in H. adishankara n. sp., somewhat similar to the condition seen in certain species of Kimberleybathynella . The as-yet known most derived one-segmented condition is present only in Atopobathynella Schminke, 1973 .

Labrum. The vaulting is very vague in H. muvattupuzha n. sp. as in H. indica and H. ajraoi , whereas it is moderate in H. adishankara n. sp. as in H. pseudoindica . Among Habrobathynella species, the vaulting is most prominently developed in H. jeanneli , and the teeth are remarkably large and widely spaced in H. ajraoi . Interestingly, the vaulting is so deep that it has resulted almost in a bilobed condition of the labrum in the monotypic Haplophallonella Serban & Coineau, 1975 .

Mandible. Both H. muvattupuzha n. sp. and H. adishankara n. sp. conform to typical pattern of Habrobathynella in which the mandible is generally conservative. However, the unarticulated tooth on the ventral edge and the reduced and fork-like pars molaris with only four fused teeth (claws) in H. ajraoi are reminiscent of the closely allied, African Haplophallonella (Totakura & Ranga Reddy 2014) .

Paragnaths. The relative size, shape and ornamentation of the median coupler together with the size, shape, orientation and ornamentation of the lateral lobes constitute an important species-specific criterion (Ranga Reddy et al. 2014). While the coupler is ornamented in all species of Habrobathynella in which the paragnath morphology has been depicted, it is smooth in the two new species; the lateral lobes are also smooth and posteriorly directed in both new species. However, the form of the coupler is distinct in the two species being minaret-like in H. muvattupuzha n. sp. and thumb-like in H. adishankara n. sp.

Maxillule. In H. muvattupuzha n. sp., the proximalmost claw on inner margin of the distal endite is reduced to a spiniform structure, somewhat like in H. parakrishna , H. vaitarini , H. savitri and H. vidua (see Ranga Reddy & Totakura 2010). In H. adishankara n. sp., as also in H. ajraoi , the said claw is completely absent.

Maxilla. The number of armature elements at the inner distal corner of the first segment varies between one and three among the congeners (Ranga Reddy et al. 2014). H. muvattupuzha n. sp. has two strongly unequal setae as in H. schminkei , H. krishna and H. pseudoindica , but only a single seta in H. adishankara n. sp., H. milloti , H. jeanneli , H. savitri , H. vidua , H. borraensis , and H. parakrishna . The most plesiomorphic state of three setae occurs in H. nagarjunai , H. indica , H. plenituda , H. vaitarini and H. ajraoi . Similarly, the mid-inner margin of the second segment in the two new species has only one seta, as in H. parakrishna , H. pseudoindica , H. schminkei , H.

savitri and H. borraensis . A maximum of three setae occurs in same position in H. indica and H. plenituda . The apical seta at the inner distal corner of the second segment shows several character states (see Totakura & Ranga Reddy 2014). In H. muvattupuzha n. sp., the seta is spiniform and about 80% as long as the apical claw whereas it is relatively slender, 55% as long as apical seta, and bulbous at the base in H. adishankara n. sp. In the two new species, the third segment is distinct from the apical claw as in the case of H. jeanneli , H. nagarjunai , H. schminkei , and H. plenituda whereas it is fused with the apical claw in all other species.

Thoracopod I. The two new species are no different from most of the Habrobathynella species in having a seta at the inner distal corner of the first endopodal segment. It is only in H. ajraoi and H. pseudoindica that this seta is missing –a novel apomorphic feature in Habrobathynella (Totakura & Ranga Reddy 2014) . The seta, when present, shows different character states in its length. It is short, being less than half as long as the second endopodal segment in H. nagarjunai and H. parakrishna , whereas in all the remaining species including the new species, it is at least half as long as, or slightly longer (e. g. H. plenituda ) than the second segment. So, the presence or absence of the afore-mentioned seta, and when present, its length relative to second endopodal segment merit attention at species-level decisions.

Thoracopod VIII male. The length of the basipodal seta generally varies between species (Totakura & Ranga Reddy 2014). It is moderately developed in the two new species whereas it is longest in H. ajraoi . The basipod is without ornamentation in the two new species whereas it is ornamented in H. schminkei , H. plenituda and H. krishna . Totakura & Ranga Reddy (2014) mentioned the ascending order of the length of penile region in Habrobathynella species. With the addition of the two new species, its ascending order is as follows: jeanneli ˂ vaitarini ˂ nagarjunai < borraensis < plenituda < muvattupuzha n. sp. ˂ adishankara n. sp. ˂ pseudoindica ˂ krishna < parakrishna ˂ savitri ˂ schminkei ˂ milloti ˂ ajraoi ˂ vidua < indica . The inner lobe in the two new species is shorter than the dentate lobe, as is the case in most species of Habrobathynella . However, it is longer in H. milloti , H. indica and H. krishna and as long as the dentate lobe in H. schminkei and H. ajraoi .

Uropod. Both H. muvattupuzha n. sp. and H. adishankara n. sp. have a similar configuration of a inhomonomous spine row, except that they have, respectively, three and four (rarely five) proximal spines, closely resembling the condition of H. krishna and H. vidua (see Totakura & Ranga Reddy 2014). The relative lengthwidth ratios of the uropodal exopod and endopod and also the relative lengths of their setae vary between certain species (Totakura & Ranga Reddy 2014; Ranga Reddy et al. 2014).

Figures

FIGURE 7. Habrobathynella adishankara n. sp., paratype female, habitus, lateral.

FIGURE 8. Habrobathynella adishankara n. sp., holotype male (A – H): (A) antennule, dorsal; (B) antenna; (C) labrum, ventral; (D) mandible, lateral; (E) mandible, ventral; (F) paragnaths, ventral; (G) maxillule, lateral; (H) maxilla, lateral.

FIGURE 9. Habrobathynella adishankara n. sp., holotype male: (A – D) Thoracopods I – IV.

FIGURE 10. Habrobathynella adishankara n. sp., holotype male: (A – C) Thoracopods V – VII.

FIGURE 11. Habrobathynella adishankara n. sp., holotype male, Thoracopod VIII (A – D): (A, D) latero-external; (B) laterointernal; (C) ventral. Abbreviations: bsp = basipod; dlb = dentate lobe; enp = endopod; exp = exopod; ilb = inner lobe; and olb = outer lobe.

FIGURE 12. Habrobathynella adishankara n. sp., holotype male (A – C), allotype female (D): (A, C) pleotelson, lateral; (B) pleotelson, furcal ramus, dorsal (uropods omitted); (D) Th VIII (arrow).