Tropocyclops confinis (Kiefer, 1930)

Tang, Danny & Knott, Brenton, 2009, Freshwater cyclopoids and harpacticoids (Crustacea: Copepoda) from the Gnangara Mound region of Western Australia, Zootaxa 2029, pp. 1-70 : 26-32

Tropocyclops confinis (Kiefer, 1930)

( Figs 13–16)

Material examined. Lot 51 Cave ( YN555 ), Yanchep , Western Australia (31°34'31''S, 115°42'10''E): 2 ♀ dissected and mounted on one slide each ( AM P.78914–P.78915), 22 September, 2003 .

Redescription of female. Total body length (measured from anterior margin of cephalothorax to posterior margin of caudal rami) 660 µm, based on digital image of 1 specimen ( Fig. 13A). Prosome composed of cephalothorax and 3 free pedigerous somites. Urosome comprised of fifth pedigerous somite, genital doublesomite and 3 free abdominal somites. Genital double-somite ( Fig. 13B) longer (85–90 µm) than wide (60–70 µm); seminal receptacle not observed. Posterior margin of urosomites smooth. Anal somite ( Fig. 13C) with spinular row along posterior margin.

Caudal ramus ( Fig. 13C) more than two times longer (40 µm) than wide (17.5 µm), with 6 spinulate setae (seta I absent) and spinular row at base of seta III. Seta III 1.25 times as long as seta VI. Seta VII about 1.7 times as long as seta VI. Setae IV and V with proximal breaking plane.

Antennule ( Fig. 13D) 12-segmented; armature formula not recorded as many setae were missing or broken off. First segment with 2 ventral groups of spinules; finely serrate hyaline membrane present on segments 10–12.

Antenna ( Figs 13E–F) 4-segmented, comprising coxobasis and 3-segmented endopod. Coxobasis with 2 distomedial naked setae, long distolateral exopodal seta, proximal spinular row on frontal surface and 2 lateral and 2 median groups of spinules on caudal surface. Proximal endopodal segment with inner naked seta and small patch of spinules along lateral margin. Middle endopodal segment with 8 inner setae (position of 1 missing seta indicated by arrow in Fig. 13E) and spinules along outer margin. Terminal endopodal segment armed with 7 setae.

Labrum ( Fig. 13G) with 15 teeth between lateral corners and long setules on anterior surface.

Mandible ( Fig. 14A) composed of coxa and reduced palp. Gnathobase with 6 unicuspidate teeth, bifurcate tooth (each branch with rounded tip), barbed seta and fine spinular row. Palp with few spinules near base and usual 3 setae (1 short and 2 long).

Maxillule ( Fig. 14B) comprising praecoxa and 2-segmented palp. Praecoxal arthrite bears 7 medial elements (3 spinulate, 4 naked), 3 distal chitinized teeth and distal spinulate seta. Coxobasis with proximal seta and 3 terminal setae. Endopod 1-segmented, armed with 3 setae.

Maxilla ( Fig. 14C) 5-segmented, comprising praecoxa, coxa, basis and 2-segmented endopod. Praecoxa with outer patch of fine spinules and endite armed with 2 spinulate setae. Proximal and distal coxal endites with 1 and 2 spinulate setae, respectively. Basis drawn out into powerful claw furnished with large spinules along middle part of both margins; accessory armature composed of large spinulate spine and naked seta. Proximal endopodal segment with 2 strong setae; frontal seta with large teeth along upper margin. Distal endopodal segment with 3 setae.

Maxilliped ( Fig. 14D) 4-segmented, comprising syncoxa, basis and 2-segmented endopod. Syncoxa bears 3 spinulate setae. Basis with 2 large patches of spinules along outer margin, large patch of spinules on anteromedial surface and 2 medial setae. Proximal endopodal segment bears long spinules on antero-medial surface and inner spinulate seta. Terminal endopodal segment with 3 elements; longest element with fine spinules scattered along both margins and row of teeth along distal half of upper margin.

Legs 1–4 biramous ( Figs 14E, 15A–E, 16A–B), with 3-segmented rami. Armature on rami of legs 1 to 4 as follows (Roman numerals = spines; Arabic numerals = setae):

*Position of missing seta indicated by socket (arrowed in Figs 14E, 15B, 16A)

Leg 1 ( Figs 14E, 15A) intercoxal sclerite unornamented and bilobed distally. Coxa unornamented on anterior surface; posterior surface with 2 groups of spinules laterally. Basis with spinules at insertion point of endopod. First 2 segments of each ramus with distal spinular row on anterior and posterior surfaces; outer margin of endopodal segments with fine setules. Outermost seta on terminal exopodal segment with denticles along outer margin and setules along inner margin; all other setae plumose. All spines denticulate; spine on terminal endopodal segment long and slim, about 1.8 times longer than segment.

Leg 2 ( Figs 15B–C) ornamented as in leg 1, except for additional spinular rows on posterior surface of intercoxal sclerite and medial spinular row on posterior surface of coxa. Inner coxal spine with long spinules proximally and minute spinules distally. All setae on rami plumose.

Leg 3 ( Figs 15D–E) identical to leg 2, except proximal exopodal segment with longer outer spine that is adpressed against outer margin of middle exopodal segment and terminal exopodal segment bears only 3 spines.

Leg 4 ( Figs 16A–B) intercoxal sclerite and coxa ornamented as those of leg 3, except posterior surface of coxa with additional spinular rows along midline. Rami ornamented as those of leg 1. Terminal endopodal segment with inner spine 2.5 times as long as outer spine.

Leg 5 ( Fig. 16C) 1-segmented, armed with spine and 2 setae; middle seta about 2.2 times longer than inner spine; unilaterally spinulate spine with spinular row at insertion point.

Leg 6 not observed.

Remarks. Our material agrees favourably with the illustrations of Tropocyclops confinis (Kiefer, 1930) provided in Dumont (1981), Yeatman (1983) and Boxshall & Braide (1991). Moreover, careful comparisons between our material and two female T. confinis specimens from Madagascar, which were kindly provided by Professor Henri Dumont (Ghent University), revealed that we are almost certainly dealing with the same species. Several morphological differences were detected between our samples and those from Madagascar as follows (features of our material given first followed by Dumont’s specimens): 1) the second endopodal segment of the antenna bears eight rather than nine inner setae; 2) the anterior surface of the intercoxal sclerites of legs 1 to 4 are naked instead of ornamented with an incomplete spinular row; 3) the posterior surface of leg 1 intercoxal sclerite is naked rather than furnished with two spinular rows; 4) the inner margin of leg 1 basis is naked rather than ornamented with setules; and 5) the inner margin of leg 5 is naked as opposed to furnished with spinules. Due to the lack of material from the Yanchep Caves, we are uncertain at this time whether these subtle differences represent either geographical or interspecific variation. Examination of additional material from Western Australia is required to resolve this issue. Nevertheless, we believe it is appropriate to treat our specimens as T. confinis until there is evidence to the contrary.

With a spine formula of 3.4.3.3 on the terminal exopodal segment of legs 1 to 4, T. confinis , along with T. prasinus (Fischer, 1860) , T. tenellus (G. O. Sars, 1909) , T. brevispinus Shen & Tai, 1962 , T. longiabdominalis Shen & Tai, 1962 , T. polkianus Einsle, 1971 , T. brevis Dussart, 1972 , T. rarus Dussart, 1983 , T. nananae Reid, 1991 , T. jamaicensis Reid & Janetzky, 1996 and T. bopingi Dumont, 2006 , belong to the “ terni ”-group (sensu Kiefer 1931). Among this group, T. confinis shares an unusual configuration with respect to the outer spine on the proximal exopodal segment of leg 3 (i.e., this spine is held parallel to the segment— Fig. 15D) with T. bopingi . The former taxon can be readily distinguished from the latter by the larger body size (660 µm vs. 380–420 µm), presence of spinules on the antennal coxobasis, absence of an inner seta on leg 1 basis, absence of a mediodistal triangular process on the basis of legs 2 to 4 and considerably shorter outer seta on leg 5.

Tropocyclops confinis has been reported previously in the Ethiopian, Palaearctic, Oriental, Neotropical and South Pacific Regions ( Dussart & Defaye 2006). The discovery of T. confinis from Lot 51 Cave in Western Australia, therefore, constitutes the first record of this species from the Australian continent. In fact, this species may be widespread in Australia, as Morton (1977) described a species, designated Tropocyclops sp. A , from surface waters in Victoria, Tasmania, New South Wales and Queensland that resembles the material upon which our description is based. This would not be unexpected considering T. confinis has a relatively broad distribution pattern as discussed above. Nonetheless, Morton’s record must be verified, as his taxonomic account was brief and lacked illustrations. It must be noted that Timms & Morton (1988) recorded two Tropocyclops species (listed as Tropocyclops sp. 1 and 2) from several freshwater sites in tropical Australia, but the specific identity of both taxa remains unknown.

The occurrence of T. confinis in ground water (Lot 51 Cave) southeast of the Yanchep National Park Caves raises an intriguing issue of their source, as this species typically inhabits rivers, lakes and ponds ( Defaye 1988). The cave is, at present time, quite isolated from other wetlands, and is the only cave in the general area known to have harboured the phreatoicid isopod Paramphisopus palustris (Glauert, 1924) , a freshwater species found typically in wetlands of the Swan Coastal Plain of Western Australia ( Gouws & Stewart 2007). Extensive sampling of surface waters within Australia is needed to determine the distribution pattern and preferred habitat(s) of this species on this continent.