Diacyclops brevifurcus Ishida 2006

Diacyclops brevifurcus – gatunek widłonoga z rodziny Cyclopidae, nazwa naukowa gatunku została po raz pierwszy opublikowana w 2006 roku przez japońskiego biologa Toruo Ishidę.

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 continuation 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.

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