Paracyclops intermedius, Tang & Knott, 2009

Tang, Danny & Knott, Brenton, 2009, Freshwater cyclopoids and harpacticoids (Crustacea: Copepoda) from the Gnangara Mound region of Western Australia, Zootaxa 2029, pp. 1-70 : 17-26

Paracyclops intermedius sp. nov.

( Figs 7–12)

Type material. Holotype ♀ ( AM P.78718), allotype ♂ ( AM P.78719) and 3 paratypes (1 ♀ and 2 ♂ dissected and mounted on one slide each) ( AM P.78908–P.78910), Mrs. King’s tumulus spring, Bullsbrook, Western Australia (31°39'04''S, 115°57'11''E), 8 May , 1996.

Other material examined. Bevan Peters’ spring, Ellenbrook, Western Australia (31°35'14''S, 115°57'47''E): 9 ♀ (1 dissected and mounted on slide), 1 ♂ and 5 copepodids, 21 December , 1992 ; 13 ♀ (1 dissected and mounted on slide), 16 ♂ (1 dissected and mounted on slide) and 32 copepodids ( AM P.78911–P.78913), 28 August, 1995; Egerton spring, Ellenbrook, Western Australia (31°46'18''S, 115°58'51''E) : 1 ♂, 20 December, 1994; 1 ♀ dissected and mounted on slide, 9 October , 2006 ; 6 ♀, 9 October, 2007.

Description of female. Total body length (measured from anterior margin of cephalothorax to posterior margin of caudal rami) of holotype ( Fig. 7A) and specimen without telescoped somites (‘non-contracted’) from Bevan Peters’ spring August, 1995 collection, 730 and 740 µm, respectively; body width 315 and 240 µm, respectively. Mean body length and width of 5 specimens with telescoped somites from Bevan Peters’ spring December, 1992 collection, 536 and 218 µ m, respectively ( Fig. 7B). Prosome composed of cephalothorax and 3 free pedigerous somites; posterior margin of prosomites smooth. Urosome comprised of fifth pedigerous somite, genital double-somite and 3 free abdominal somites. Dorsal surface of fifth pedigerous somite with uneven posterior margin and setules along posterolateral corners. Urosomites 2–4 ( Fig. 7C) furnished with transverse surface ridges and serrate frill along posterior margin. Genital doublesomite slightly longer than wide (105 × 100 µm and 110 × 100 µm) in non-contracted specimens, but wider than long (mean 77.5 × 93 µm) in telescoped specimens. Seminal receptacle comprised of narrow anterior lobe and broad posterior lobe. Anal somite ( Figs 7C, 8A) with posteroventral spinular row extending around to dorsal surface; anal cleft with dense patch of spinules.

Caudal ramus ( Figs 7C, 8A) longer than wide (50 × 27.5 µm in both non-contracted specimens; mean 48.5 × 26 µm in contracted specimens); bears 6 setae (seta I absent). Base of seta II flanked by lateral transverse spinular row and medial oblique spinular row; lateral transverse spinular row extends along ventral surface beyond midline of ramus in paratype only. Spinular row at base of seta III extends ventromedially to seta V. Setae II and VII pinnate; other setae spinulate. Seta VI twice as long as seta III. Setae IV and V with proximal breaking plane .

Antennule ( Fig. 8B) 11-segmented, with armature and ancestral segmentation pattern in brackets as follows: 8 (I–V), 4 (VI–VII), 2 (VIII), 6 (IX–XI), 4 (XII–XIII), 1+spine (XIV), 2 (XV–XVI), 3 (XVII–XX), 4+ae (XXI–XXIV), 2+ae (XXV), and 7+ae (XXVI–XXVIII). First segment with 2 proximal groups of spinules; remaining segments unornamented.

Antenna ( Figs 8C–D) 4-segmented, composed of coxobasis and 3-segmented endopod. Coxobasis with 2 distomedial setae, long distolateral exopodal seta and complex ornamentation on frontal and caudal surfaces as figured; spinular row present near bases of distomedial setae; all setae ornamented with spinules. Proximal endopodal segment armed with inner barbed seta and furnished with outer spinular row and inner oblique row of spinules on caudal surface. Middle endopodal segment bears 9 inner setae and spinular patch along outer margin. Terminal endopodal segment with proximal and distal spinular rows and 7 apical setae.

Labrum ( Fig. 8E) with 2 teeth on each lateral corner, 12 teeth along medial margin and long setules on anterior surface.

Mandible ( Fig. 8F) composed of coxa and reduced palp. Cutting edge of coxal gnathobase with quadridentate tooth, 2 bicuspidate teeth, 4 unicuspidate teeth, barbed seta and spinular row. Palp furnished with small and large spinular rows near its base and armed with 1 short and 2 long setae.

Maxillule ( Fig. 9A) composed of praecoxa, coxobasis and endopod. Praecoxal arthrite bears 7 medial elements, 3 distal unicuspidate teeth and distal spinulate seta; both proximalmost elements ornamented with spinules; distalmost element with large proximal spinule. Coxobasis with proximal seta and 3 terminal setae. Endopod 1-segmented, armed with 3 setae.

Maxilla ( Fig. 9B) 5-segmented, composed of praecoxa, coxa, basis and 2-segmented endopod. Praecoxa with outer spinular rows and 2 spinulate setae on endite. Coxa with spinules along outer margin and 1 and 2 spinulate setae, respectively, on proximal and distal endites. Basis drawn out into large claw furnished with large teeth along middle part of inner margin; accessory armature composed of strong spinulate spine and naked seta. Proximal endopodal segment with 2 spinulate setae; distal endopodal segment with 3 setae.

Maxilliped ( Fig. 9C) 4-segmented, comprising syncoxa, basis and 2-segmented endopod. Syncoxa unornamented; armed with 3 medial spinulate setae. Basis with 2 spinular patches along outer margin, proximomedial spinular row and 2 medial spinulate setae. Proximal endopodal segment with single spinule on anterior surface and inner spinulate seta. Terminal endopodal segment with 3 elements; innermost element fused to segment, furnished with long spinules and minute teeth.

Legs 1–4 biramous ( Figs 9D–E, 10A–D, 11A–B), with 3-segmented rami. Armature on rami of legs 1 to 4 as follows (Roman numerals = spines; Arabic numerals = setae):

Leg 1 ( Figs 9D–E) intercoxal sclerite with single spinular row on anterior surface and 2 spinular rows on posterior surface. Coxa ornamented with minute spinules on anterior surface and 2 well developed spinular rows on posterior surface; inner element semispinulose (proximolateral spinule present on right leg of paratype only— Fig. 9D). Basis with large mediodistal protrusion extending between insertion point of rami, inner row of setules and spinules on anterior surface. Outer seta setulate; inner spinulate spine extends to proximal ⅓ of terminal endopodal segment. Exopod with large spinules along outer margin of first segment and distal spinules on posterior surface and setules along inner margin of proximal and middle segments. Endopodal segments with distal spinular rows on anterior surface; outer margin setules on proximal and middle segments relatively stiffer than those on apical segment; middle segment with spinular row on posterior surface; terminal segment with large distolateral spiniform process. Outermost seta on terminal exopodal segment with lateral row of denticles and inner row of setules; all other setae on rami plumose. All spines denticulate; spinules present at insertion point of all spines.

Leg 2 ( Figs 10A–B) intercoxal sclerite with 2 spinular rows on anterior and posterior surfaces. Coxa ornamented as in leg 1, except with additional spinular row proximolaterally, 2 median spinular rows on anterior surface (position of missing spinules indicated by sockets (arrowed) in Fig. 10A; these spinules are intact in dissected non-type material) and lateral spinular row on posterior surface; inner spinulate spine bears single proximolateral spinule. Basis with lateral spinules, 2 middle spinular rows, minute spinules at insertion point of endopod and row of setules along inner margin. Rami ornamented as in leg 1, except for naked inner margin on middle exopodal segment and additional distal spinular row on anterior surface of proximal and middle exopodal segments and minute spinule at insertion point of most setae. All setae on rami plumose.

Leg 3 ( Figs 10C–D) similar to leg 2, except with relatively shorter outer seta on basis, additional inner seta on middle endopodal segment and setules along inner margin of last 2 endopodal segments, relatively finer spinules on outer margin of proximal and middle endopodal segments and relatively less developed distolateral spiniform process and shorter apical spine on terminal endopodal segment.

Leg 4 ( Figs 11A–B) intercoxal sclerite with few spinules on anterior surface, thin spinules along posterior margin and 2 spinular rows (1 row incomplete) on posterior surface. Coxa with more complex ornamentation pattern on posterior surface than observed for preceding legs. Outer seta on basis longer than that of leg 3. Rami ornamented as in leg 3, except with additional setules along inner margin of middle exopodal segment, naked medial margin on middle endopodal segment and relatively less developed distal spinules on anterior surface of proximal and middle endopodal segments. Terminal endopodal segment lacks distolateral spiniform process; inner apical spine 2 times longer than outer apical spine.

Leg 5 ( Fig. 11C) 1-segmented, armed with lateral and middle pinnate setae and inner spinulate spine; outer seta longer than other 2 elements. Base of outer seta produced, lacking spinular row; inner spine with spinules at base.

Leg 6 ( Fig. 11D) represented by spinulate seta and 2 short naked spines (only outermost spine articulates at base) on genital operculum.

Male. Total body length (measured from anterior margin of cephalothorax to posterior margin of caudal rami) of allotype ( Fig. 11E) and non-contracted specimen from Egerton spring, 610 and 670 µm, respectively; body width 185 µm in both specimens. Mean body length and width of 3 specimens with telescoped somites from Sawpit spring, 485 and 185 µm, respectively. Prosome composed of cephalothorax and 3 free pedigerous somites; posterior margin of prosomites smooth. Urosome comprised of fifth pedigerous somite, genital somite and 4 free abdominal somites. Fifth pedigerous somite lacks setules along posterolateral corners. Urosomites 2–5 furnished with transverse surface ridges (not figured) and serrate frill along posterior margin. Genital somite wider than long (55 × 85 µm and 60 × 85 µm in non-contracted specimens; mean 50 × 84 µm in contracted specimens). Caudal ramus longer than wide (35 × 25 µm in allotype, 40 × 25 µm in other noncontracted specimen, and mean 37 × 22.5 µm in contracted specimens), armed and ornamented as in female.

Antennule ( Fig. 12A) 16-segmented, digeniculate, with armature and ancestral segmentation pattern in brackets as follows: 8+ae (I–V), 4 (VI–VII), 2 (VIII), 2+ae (IX), 2 (X), 2 (XI), 2 (XII), 2 (XIII), 2+ae (XIV), 2 (XV), 2 (XVI), 2 (XVII), 2 (XVIII), 4 (XIX–XX), 4 (XXI-XXIII), and 11+ae (XXIV–XXVIII). Seta A on proximal segment simple, unmodified. Setae D and F on proximal segment with blunt, setulose apex; similar elements present on segments 2–5. One element on segment 10 modified into long, massive spine with recurved base and acuminate tip. One of two elements on segment 13 digitiform; similar element present on segment 14. Short, blunt element and modified ridged element(s) present on segments 14 and 15.

Leg 6 ( Fig. 12B) represented by 3 subequal elements on genital operculum; outer seta with sparse setules; middle seta spinulate; inner spine with spinules at base.

Etymology. The specific name alludes to the new species’ morphological similarity to P. affinis and P. canadensis .

Remarks. Paracyclops intermedius sp. nov. shares several features, such as urosomal surface ridges, 11- segmented antennule and one inner seta on the middle endopodal segment of leg 4, in common with the P. affinis -lineage, a natural group recognised formally by Karaytug (1998, 1999) that includes P. affinis (G. O. Sars, 1863) , P. canadensis (Willey, 1934) and P. uenoi Itô, 1962 . Paracyclops affinis is distributed in the Ethiopian and Palaearctic regions, whilst P. canadensis is restricted to North America and P. uenoi is endemic to the Ryukyu Islands ( Karaytug 1999). It is worth noting, however, that Ishida (2006) recently attributed four female cyclopoid specimens collected from Kyoto, Japan, to P. canadensis , which significantly extends the distribution of this species from the Nearctic to the Palaearctic. Although Ishida’s relatively detailed illustrations of his Japanese specimens clearly depict that the caudal rami, antennal coxobasis, natatory legs and leg 5 are structurally similar to those of P. canadensis , it is conceivable that Ishida’s specimens are not conspecific with P. canadensis , as they contain some disparate features, such as a naked anal cleft (highly spinulose in P. canadensis ), 10-segmented antennule (11-segmented in P. canadensis ) and different spinulation pattern on the posterior surface of leg 4 coxa. It is unfortunate that Ishida did not include the mouthparts in his description, as these appendages often contain species-specific characters (we currently must assume that these appendages are identical to those of P. canadensis ). A detailed examination of Ishida’s specimens is needed in order to resolve the taxonomic status of the Japanese P. canadensis .

Paracyclops uenoi differs from the other three related taxa by having two setae, as opposed to one seta, on the middle endopodal segments of legs 1 and 2. Paracyclops intermedius sp. nov. and P. canadensis differ from P. affinis by having caudal seta III shorter than seta VI, spinules along the outer margin of the maxillary coxa, one spinule on the anterior surface of the proximal endopodal segment of the maxilliped, two median spinular rows on the anterior surface of the coxae of legs 2–4, four spines on the terminal exopodal segment of leg 3, an unornamented base on the outer seta of leg 5, an aesthetasc on the male antennulary segment 1 and male leg 6 with the outer seta as long as the middle seta.

Paracyclops intermedius sp. nov. can be readily distinguished from P. canadensis by the: 1) absence of spinules on the lateral borders of the anal cleft; 2) presence of spinules near the insertion of the inner setae on the caudal surface of the antennal coxobasis (a characteristic of P. affinis ); 3) relatively more developed spinular rows on the frontal surface of the antennal coxobasis; 4) fused innermost element on the terminal endopodal segment of the maxilliped (a characteristic of P. affinis ); 5) large distolateral spiniform process on the terminal endopodal segment of leg 1; 6) presence of one spinule on the proximolateral margin of the inner coxal spines of legs 2–4 (a characteristic of P. affinis ); 7) relatively less developed spinules along the posterior margin of leg 4 intercoxal sclerite (a characteristic of P. affinis ); 8) different spinulation pattern on the posterior surface of leg 4 coxa; 9) relatively longer setae on leg 5 (the two setae are as long as the inner spine); and 10) presence of a modified element on male antennulary segment 10 (a characteristic of P. affinis ).

Paracyclops intermedius sp. nov. is not confined within the Gnangara Mound region, as we have collected one female and three male specimens of this species from a hole dug to the water table in Jandakot, Western Australia (ca. 20 km south of the Gnangara Mound region). This species may also occur in other Australian states, as Morton (1977) also described a species, named Paracyclops myallensis , from a swamp near Newcastle, New South Wales, that is similar to the material upon which our description is based. Morton’s record, however, must be confirmed as his description was based on only two female specimens and was not supported by a complete set of illustrations. Paracyclops intermedius sp. nov., together with P. chiltoni and P. affinis , are the only representatives of the genus recorded from Australia thus far. The last species was reported by G. O. Sars (1914) from New South Wales, Morton (1977) from one locality in New South Wales and Timms & Morton (1988) from Queensland’s Cape York area. Presently, there is no reason to doubt Morton’s (loc. cit.) unpublished record, as his relatively detailed description precisely matches Karaytug’s (1999) excellent redescription of P. affinis .