Diacyclops brevifurcus Ishida, 2006

Karanovic, Tomislav, Grygier, Mark J. & Lee, Wonchoel, 2013, Endemism of subterranean Diacyclops in Korea and Japan, with descriptions of seven new species of the languidoides-group and redescriptions of D. brevifurcus Ishida, 2006 and D. suoensis Ito, 1954 (Crustacea, Copepoda, Cyclopoida), ZooKeys 267, pp. 1-76 : 13-18

Diacyclops brevifurcus Ishida, 2006 Figs 78

Diacyclops sp. B - Ishida 2006): p. 57, fig. 28 a–j.

Diacyclops brevifurcus sp. n. - Ishida 2006): p. 41, figs 1, 2.

Type locality.

Japan, Kyoto prefecture, Kyoto city, Kita ward, Mizoro-ga-ike pond, approximately 35°03.43'N, 135°46.11'E, floating bog bed.

Material examined.

Holotype female dissected on one slide (LBM 1430000887), 1 February 2005, leg. A. Ohtaka.

Other material: three females in ethanol (LBM 1430000888) and one female dissected on one slide (LBM 1430005384) from Japan, Shiga prefecture, Takashima city, Makinocho-Kaizu district, Lake Biwa on western side of Kaizu Ohsaki point, between near-shore boulders, 07 March 1994, leg. T. Ishida. Note: Consultation of original field data maintained at the Lake Biwa Museum showed that the the municipality (town) mentioned by Ishida (2006), viz., Nishiazai, was erroneous and that the collection site is actually in what was then the Kaizu district of Makino town.

Partial redescription.

Female (holotype). Cephalothoracic shield and pleurons of free prosomites missing from slide (only one piece of cephalothorax present), so pattern of cuticular pores and sensilla not observed. Preserved specimen yellowish. Integument relatively weakly sclerotised, smooth, without cuticular pits or cuticular windows.Urosome squashed and badly deformed, but similar to original drawing by Ishida (2006), with posterior ventral pair of pores observed on each of genital double-somite, third urosomite, and anal somite. Copulatory pore (Fig. 7B) small, oval, situated ventrally at about midlength of genital double-somite; copulatory duct narrow, siphon-shaped, well sclerotised, supported by pronounced transverse internal sclerotised ridge.

Anal somite (Fig. 7A) with short and broad anal operculum, ornamented with one pair of large dorsal sensilla (no. 104), one pair of small dorsal pores (no. 105), one pair of small ventral pores (no. 106), continous posterior row of small spinules, and two diagonal parallel rows of somewhat larger spinules on both sides of anal sinus. Anal operculum short, wide, slightly convex, reaching to midlength of anal somite, representing 50% of anal somite’s width.

Caudal rami (Fig. 7A) somewhat squashed on slide, but cylindrical in shape, parallel, inserted close to each other, with deep dorso-median anterior depression (as con tinuation of anal sinus), approximately twice as long as wide (ventral view) and twice as long as anal somite; ornamentation and armature as in Diacyclops ishidai sp. n., but innermost terminal seta much shorter and more slender (arrowed in Fig. 7A), only about 0.7 times as long as outermost terminal seta.

Antennula 11-segmented, generally as illustrated by Ishida (2006), but with additional seta on each of third, fourth, and sixth segments, giving same armature formula as in Diacyclops ishidai .

Antenna five-segmented, generally as illustrated by Ishida (2006), i.e. basis with strong exopodal seta, second endopodal segment with seven setae along inner margin, and third endopodal segment with seven terminal setae.

Labrum completely deformed on slide, impossible to illustrate.

Mandibula (Fig. 7C) composed of coxa and small palp. Cutting edge of coxal gnathobase without spinules on anterior surface, furnished with eight apical teeth and dorsalmost unipinnate seta; ventralmost tooth strongest and quadricuspidate, second and fourth teeth from ventral side bicuspidate, all other teeth unicuspidate; three dorsalmost simple teeth partly fused basally and progressively longer from ventral to dorsal. Palp about as wide as long, unornamented, armed with only two apical setae, one long and distally bipinnate, the other short and smooth; pinnate seta about 1.5 times as long as whole mandibula.

Maxillula (Fig. D) composed of praecoxa and palp (but palp broken off and missing from slide), unornamented. Praecoxal arthrite bearing four very strong distal spines (three of them smooth, blunt, and fused at base; one distinct at base, sharp and with two proximal spinules) and six medial elements (proximalmost one broken off, two most distal ones large and strong, three in between smaller and slender).

Maxilla (Fig. 7E) 5-segmented but praecoxa partly fused to coxa on anterior surface, unornamented. Proximal endite of praecoxa robust, armed with one sparsely bipinnate seta; distal endite very small, unarmed. Proximal endite of coxa with one bipinnate seta; distal endite highly mobile, elongated and armed apically with two pinnate setae, proximal one of which slightly longer but considerably stronger and basally fused to endite. Basis expanded into robust claw, and claw furnished with longitudinal row of spinules along concave (dorsal) margin, armed with two setae; strong seta slightly stronger than claw, unipinnate along convex (ventral) margin; small seta smooth and slender. Endopod two-segmented, with segmentation easily discernable; proximal segment armed with two robust, unipinnate setae; distal segment with one robust and two slender subapical setae, all smooth. Longest seta on distal endopodal segment 0.8 times as long as longer seta on proximal endopodal segment. All strong setae on basis and endopod, as well as basal claw, gently unguiculate.

Maxilliped (Fig. 7F) four-segmented, composed of syncoxa, basis, and two-segmented endopod. Ornamentation consisting of longitudinal rows of five large spinules on anterior surface of basis and first endopodal segment. Armature formula: 2.1.1.3. All inner setae pinnate, relatively strong but short and not unguiculate; inner seta on second endopodal segment basally fused to segment.

All swimming legs relatively small, composed of minute, triangular praecoxa, large, rectangular coxa, short basis, and slender exopod and endopod. Exopods and endopods approximately equally long on all legs, their segmentation formula (exopod/ endopod): 2/2.3/2.3/3.3/3. Ultimate exopodal segment spine formula 3.3.3.3 and setal formula 5.4.4.4. All setae on endopods and exopods slender and plumose, except apical seta of exopod of first leg pinnate along outer margin and plumose along inner; no modified setae observed. All spines strong and bipinnate. Intercoxal sclerite of all swimming legs with slightly concave distal margin and without any surface ornamentation on first and second leg, but with arc of spinules on posterior margin of third (Fig. 8A) and fourth (Fig. 4B) legs.

First and second swimming legs as in Diacyclops ishidai .

Third swimming leg (Fig. 8A) also generally similar to that of Diacyclops ishidai in shape, size and armature; apical spine on third endopodal segment proportionately much longer, about 1.5 times as long as segment and 0.9 times as long as apical seta; third endopodal segment about 1.2 times as long as wide and 1.4 times as long as second endopodal segment.

Fourth swimming leg (Fig. 8B) generally similar to that of Diacyclops ishidai in shape, but intercoxal sclerite with only one row of spinules (arrowed in Fig. 8B), and inner distal corner of basis with two spiniform processes separated by shallow notch (arrowed in Fig. 8B); proximal inner seta on second endopodal segment proportionally shorter than that of Diacyclops ishidai and apical spines longer and more robust; third endopodal segment about 1.4 times as long as wide, and 1.4 times as long as second endopodal segment; inner apical spine on third endopodal segment less than1.2 times as long as outer apical spine, 1.2 times as long as segment, and more than 0.7 times as long as distal inner seta.

Fifth leg (Fig. 8C) with much shorter protopod than in Diacyclops ishidai , but with longer and more robust exopod (arrowed in Fig. 8C) and subapical exopodal spine, and with shorter apical exopodal seta. Exopod cylindrical, 2.2 times as long as protopod and 2.9 times as long as wide; apical exopodal seta bipinnate distally, 0.85 times as long as basal seta, twice as long as exopod, and three times as long as subapical spine, but reaching beyond midlength of genital double-somite; subapical exopodal spine small but strong, bipinnate, 0.7 times as long as exopod and nearly twice as long as exopod’s greatest width.

Sixth leg completely deformed on slide, but generally similar to that of Diacyclops ishidai , consisting of a small, short, and broad semicircular cuticular plate armed with two short, smooth spines and one longer and distally unipinnate outermost seta; inner spine fused to plate, outer one articulated basally; outermost seta directed postero-dorsally.

Male. Unknown.

Variability.

The specimens from Lake Biwa show several features in the mouthparts that differ from those observed in the holotype. They have two long setae on the mandibular palp, two setae on the proximal endite of the maxilla, two setae on the basis of the maxilliped, and three setae on the syncoxa of the maxilliped. All other features agree well with those of the holotype, including the length of the innermost terminal caudal seta, armature of the antenna, shape of the notch on the fourth leg basis, and shape of the fifth leg exopod. The specimens from Lake Biwa have ten teeth and six or seven spinules on the labrum, and the same pattern of cuticular sensilla and pores on the somites as that in Diacyclops ishidai , but most of these characters cannot be compared with the holotype.

Remarks.

This is probably a surface-water species, but its morphological similarity to the newly described Diacyclops ishidai (see above) warranted its re-examination and inclusion in this paper. Ishida (2006) described it from a single female from Mizoro-ga-ike pond in Kyoto, and we redescribe it here based on an examination of the same holotype, mounted on one slide. In the same work, Ishida reported another three damaged females from Lake Biwa, but as other material examined, not as paratypes. We had a chance to examine this material as well and found four females in the vial, only one of which was in poor condition (with the posterior part of the usorome missing). We dissected one of them on one slide, while the others were examined undissected. All four specimens are indeed conspecific with Diacyclops brevifurcus Ishida, 2006, but with several differences in the mouth appendages (see variability above). It is hard to assess whether these differences are a result of geographical variation, or are just an abnormality in the holotype, because only one specimen from Mizoro-ga-ike pond was collected. Diacyclops brevifurcus is probably most closely related to Diacyclops ishidai , which we collected in the interstitial of two localities on the banks of the Daido River, which joins the Seta River, Lake Biwa’s outflow, several kilometers below the outflow point and is then part of the same water system as the lake. The morphological similarities and differences between these two species are outlined in the Remarks section for Diacyclops ishidai (see above).