Nitocrella knotti, Tang, Danny & Eberhard, Stefan M., 2016

Tang, Danny & Eberhard, Stefan M., 2016, Two new species of Nitocrella (Crustacea, Copepoda, Harpacticoida) from groundwaters of northwestern Australia expand the geographic range of the genus in a global hotspot of subterranean biodiversity, Subterranean Biology 20, pp. 51-76 : 53-56

Taxon classification Animalia Harpacticoida Ameiridae

Nitocrella knotti sp. n. Figs 2, 3, 4

Type locality.

Borehole HB54/4.1 (= Borehole HB405) (21°28'45"S; 121°46'45"E) on Telfer Road, 48 km NW of Telfer mine site and 350 km SE of Port Hedland, Western Australia, July 2008, J. Mifsud leg.

Type material.

Holotype female (WAM C51830) in absolute alcohol, 1 female paratype (WAM C51831) dissected and mounted on a slide, and 4 female paratypes (WAM C51832) in absolute alcohol.

Description.

Female. Body (Fig. 2A) subcylindrical, 610-635 µm (mean 620 µm; n = 3) long (measured from tip of rostrum to posterior margin of caudal rami) and 148-155 µm (mean 153 µm; n = 3) wide (at posterolateral margin of cephalothorax). Prosome composed of cephalothorax and 3 free pedigerous somites; tergite of first two pedigerous somites each with elliptical integumental window. Urosome comprised of fifth pedigerous somite, genital double-somite, and 3 free abdominal somites. Fifth pedigerous somite with short, dorsolateral row of spinules and numerous short rows of minute denticles (not drawn) and minute surface pits (not drawn) on dorsal and ventral surfaces. Components of genital double-somite (Fig. 2A, B) partially fused dorsally but completely fused ventrally, ornamented with short, anterolateral row of spinules on ventral surface, minute surface pits and numerous short rows of minute denticles on dorsal and ventral surfaces (only minute denticles on ventral surface are shown), and row of large spinules and serrated hyaline frill encircling posterior margin; genital field with large median copulatory pore, chitinized copulatory duct leading anteriorly to pair of bilobate seminal receptacles, and median genital pore covered by operculiform leg 6. First free abdominal somite with large integumental window on ventral surface, minute surface pits and numerous short rows of minute denticles on dorsal and ventral surfaces (only minute denticles on ventral surface are shown), and row of large spinules and serrated hyaline frill ringing posterior margin. Second free abdominal somite similar to preceding somite, but without integumental window. Anal somite (Fig. 2B, C) with minute surface pits (not drawn) and numerous short rows of minute denticles on dorsal and ventral surfaces and row of large spinules along posterior border and along posterior margin of anal operculum.

Caudal ramus (Fig. 2B, C) short, about 1.25 times longer than wide, bears minute surface pits (not drawn) and 7 setae. Insertion point of setae III, VI and VII flanked by spinules. Setae IV and V spinulate, with proximal breaking planes; other setae naked. Seta VII basally tri-articulate.

Rostrum (Fig. 2D) subtrianglar, not demarcated at base, with 2 dorsal sensilla.

Antennule (Fig. 2E) 8-segmented, with armature as follows: 1, 9, 8, 4 + ae, 2, 3, 4, and 8. Segment 1 proximally with additional spinular row and large tubular pore. Two (of 4) and 4 (of 8) setae basally biarticulate on segments 7 and 8, respectively. Two (of 4) anterodistal setae on segment 8 fused at base.

Antenna (Fig. 2F), comprising coxa, basis, exopod, and 2-segmented endopod. Coxa naked and unarmed. Basis with 2 small proximal spinules and 2 large inner distal spinules. Exopod 1-segmented, cylindrical, and armed with 2 pinnate setae. Proximal endopodal segment naked and unarmed. Distal endopodal segment as long as basis and proximal endopodal segment combined; ornamented with 2 distolateral hyaline frills, 3 proximomedial spinules, and 2 distomedial spinules; armed with 2 spines (1 spine with minute spinules along inner margin; other with subapical flagellum) plus 2 naked setae along inner subdistal margin and 1 pilose and 5 geniculate setae along apical margin (lateralmost geniculate seta with 2 spinules at mid-point and fused basally with pilose seta; shortest geniculate seta with subapical flagellum).

Labrum (Fig. 3A) subtriangular, with denticles along apical margin and large distolateral denticles plus 2 patches of minute denticles on posterior face.

Mandible (Fig. 3B) composed of coxa and 2-segmented palp. Coxa with inner subapical process, numerous unicuspidate teeth along distal margin, and unilaterally denticulate seta on inner distal angle. Proximal segment of palp unarmed, but furnished with 2 proximomedial spinules, 1 medial process, and row of apical spinules; distal segment armed with 5 apical naked setae.

Maxillule (Fig. 3C) composed of praecoxa and 3-segmented palp. Praecoxal arthrite bears proximal crescentic row of spinules, 2 chitinized naked setae on inner subapical margin, 2 long naked setae on anterior surface, and 8 apical elements (3 highly chitinized, of which 2 each furnished with minute apical teeth; 1 unipinnate; 1 with bristled tip; 3 naked). Coxal endite elongated, with subapical row of spinules and 1 geniculate and 2 naked setae at distal end. Basis as long as coxa, bears 5 apical naked setae. Endopod 1-segmented, vestigial, armed with 2 short naked setae. Exopod absent.

Maxilla (Fig. 3D) 3-segmented, composed of syncoxa, allobasis, and 1-segmented endopod. Syncoxa large, with 3 longitudinal rows of spinules on anterior surface and 1 pectinate and 2 naked apical setae on distal endite. Allobasis drawn out into long claw furnished with spinules along distal half of inner margin and bears 1 pectinate seta. Endopod 1-segmented, armed with 2 long apical setae.

Maxilliped (Fig. 3E) 3-segmented, comprising syncoxa, basis, and 1-segmented endopod. Syncoxa stout, with 2 rows of long spinules and 1 distal pinnate seta. Basis naked and unarmed, about 1.5 times as long as syncoxa. Endopod drawn out into long claw, with 1 proximal naked seta and denticles along distal half of inner margin.

Legs 1-4 biramous (Figs 3F, G, 4A, B); leg 1 with trimerous rami; legs 2-4 with trimerous exopod and bimerous endopod. Armature on rami of legs 1 to 4 as follows (Roman numerals = spines; Arabic numerals = setae):

Leg 1 (Fig. 3F) intercoxal sclerite naked and about twice as wide as long. Coxa with 2 rows of minute spinules and 1 row of large spinules on anterior surface; outer margin with 1 row of large spinules and 2 rows of fine spinules; inner distal corner with row of fine spinules. Basis with row of large spinules at insertion of each ramus and row of fine spinules along inner margin and on posterior surface; 1 additional large spinule present near base of inner spine; both spines with subapical flagellum. Outer spine on proximal exopodal segment with subapical flagellum. First two exopodal segments with large spinules along outer margin and on outer distal corner, as well as fine spinules along inner margin; distal segment with large spinules along outer margin and 1 spinule on apical margin. Both setae on terminal exopodal segment geniculate. Proximal endopodal segment long, extending almost to mid-point of distal exopodal segment, with fine spinules along inner margin; middle segment with fine spinules along outer and inner margins; distal segment with fine spinules along outer margin. Two (of 3) setae on distal endopodal segment geniculate. Both rami with minute surface pits (not drawn).

Leg 2 (Fig. 3G) intercoxal sclerite posteriorly bilobate, with row of spinules on each lobe. Coxa with 4 rows of minute spinules on anterior surface; outer margin with 2 rows of fine spinules; inner distal corner with row of minute spinules. Basis ornamented as in leg 1, except lacks large spinule near inner margin and with additional row of minute spinules on anterior surface. Exopod ornamented as in leg 1, except with additional spinulated frill on inner distal corner of proximal and middle segments. First two exopodal segments protruded on outer distal corner. Proximal endopodal segment with spinules along outer and inner margins and short spinulated frill on inner distal corner. Distal endopodal segment about 1.5 times longer than proximal endopodal segment and furnished with spinules along outer and inner margins. Both rami with minute surface pits (not drawn) as in leg 1.

Leg 3 (Fig. 4A) similar to leg 2, except with naked intercoxal sclerite, outer seta (instead of spine) on basis, longer inner spine on middle exopodal segment, and inner distal seta (instead of spine) and longer inner proximal spine on distal endopodal segment.

Leg 4 (Fig. 4B) similar to leg 3, except with smaller intercoxal sclerite, row of spinules absent on posterior surface of basis, less protruded outer distal corner on first two exopodal segments, shorter inner spine on middle exopodal segment, 2 more elements on distal exopodal segment, shorter distal endopodal segment, and only 3 elements on distal endopodal segment.

Leg 5 (Fig. 4C) biramous. Basoendopod with long outer basal seta and 3 spinulated setae on endopodal lobe. Exopod 1-segmented, slightly longer than wide, with few spinules along inner margin and 4 unequal naked setae.

Leg 6 (Fig. 2B) represented by simple operculum covering genital pore, armed with 1 minute naked seta on outer distal corners.

Male. Unknown.

Variability.

One paratype with 5 elements on terminal exopodal segment of left leg 1 (Fig. 4D). Another paratype with 5 elements on terminal exopodal segment of right leg 2 (Fig. 4E).

Etymology.

This species is named in honour of the late Professor Brenton Knott (The University of Western Australia) who made significant contributions to research on groundwater fauna in Western Australia.

Differential diagnosis.

Among the three groups of Nitocrella proposed by Petkovski (1976), i.e. " chappuisi ", " hirta ", and " vasconica ", Nitocrella knotti sp. n. belongs to the " vasconica "-group as it also possesses the characteristic six armature elements on the distal exopodal segment of leg 4. With the addition of Nitocrella knotti sp. n. (including the second new species described below), this group currently contains 21 species reported from Eurasia, the Caribbean, and Australia (Table 2). Nitocrella knotti sp. n. shares with Nitocrella afghanica Štĕrba, 1973, Nitocrella jankowskajae Borutzky, 1972, Nitocrella kirgizica Borutzky, 1972, Nitocrella monchenkoi Borutzky, 1972, Nitocrella obesa Karanovic, 2004, and Nitocrella trajani Karanovic, 2004 an armature formula of I-0; I-I; II,2,0 on the exopod and 0-I; 0-0; 0,3,0 on the endopod of leg 1, II,2,0 on the distal exopodal segment of legs 2 and 3, and 0-I on the proximal endopodal segment of legs 2-4. However, Nitocrella knotti sp. n. can be easily distinguished from those taxa by having four armature elements (instead of two for Nitocrella jankowskaja , or three for Nitocrella afghanica , Nitocrella kirgizica , Nitocrella monchenkoi , Nitocrella obesa , and Nitocrella trajani ) on the distal endopodal segment of leg 2. Nitocrella knotti sp. n. differs further from the Australian Nitocrella obesa and Nitocrella trajani by having the genital and first abdominal somites fused ventrally (rather than completely separate), two setae (rather than three) on the antennal exopod, and three setae (rather than four) on the basoendopodal lobe of leg 5, among others; and from the Central Asian Nitocrella afghanica , Nitocrella jankowskajae , Nitocrella kirgizica , and Nitocrella monchenkoi by having four armature elements (instead of two) on the distal endopodal segment of leg 3 and three armature elements (instead of one for Nitocrella afghanica , or two for Nitocrella jankowskaja , Nitocrella kirgizica , and Nitocrella monchenkoi ) on the distal endopodal segment of leg 4.