Diacyclops parahanguk, Karanovic, Tomislav, Grygier, Mark J. & Lee, Wonchoel, 2013

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 : 48-53

Diacyclops parahanguk sp. n. Figs 2325

Type locality.

Japan, Shiga prefecture, Otsu city, Lake Biwa, Matsunoura Beach, lake beach next to inflow of small but fast-flowing irrigation runoff canal, 35°12.319'N, 135°55.768'E, interstitial water from medium to coarse sand.

Type material.

Holotype female dissected on one slide (LBM1430005391), collected at type locality, 4 October 2009, leg. T. Karanovic.

Etymology.

The species name is composed of the existing specific name hanguk proposed herein above (Korean for “Korea”) and the Greek prefix para (= near, beside), and refers to the close relationship between these two congeners.

Description.

Female (based on holotype). Total body length, measured from tip of rostrum to posterior margin of caudal rami (excluding caudal setae), 274 µm. Preserved specimen colourless; no live specimen observed. Integument weakly sclerotised, smooth, without cuticular pits or cuticular windows. Surface ornamentation of somites consisting of 44 pairs of sensilla and pores and four unpaired (mid-dorsal) pores as in Diacyclops hanguk ; no spinules except on anal somite, caudal rami, and appendages. Habitus (Fig. 23A, B) relatively robust (arrowed in Fig. 23A), strongly dorso-ventrally compressed, with all somites strongly telescopically contracted; prosome/urosome length ratio 1.5 and greatest width in dorsal view at posterior end of cephalothorax, not arched backwards between prosome and urosome. Body length/width ratio about 2.5 (dorsal view); cephalothorax 1.8 times as wide as genital double-somite. Free pedigerous somites without lateral or dorsal expansions, but with narrow and smooth hyaline fringes. Pleural areas of cephalothorax and free pedigerous somites better developed than in Diacyclops hanguk , covering insertions of cephalic appendages and praecoxae and partly coxae of swimming legs in lateral view.

Rostrum (Fig. 23B) well developed, membranous, not demarcated at base, broadly rounded and ornamented, as in Diacyclops hanguk , with one pair of frontal sensilla (no. 1).

Cephalothorax (Figs 23A, B, 25A) large, 1.15 times as long as its greatest width (dorsal view), widest at posterior end and oval; representing 47% of total body length (together with rostrum). Surface of cephalic shield ornamented as in Diacyclops hanguk , with one unpaired dorsal pore and 25 pairs of long sensilla; sensilla pair no. 39 not asymmetrical, and pair no. 21 more widely spaced than in Diacyclops hanguk ; sensilla and pores 39-58 belonging to first pedigerous somite, incorporated into cephalothorax.

Second pedigerous somite (Figs 23A, B) well developed, only slightly narrower than cephalothorax and tapering posteriorly, unornamented.

Third pedigerous somite (Fig. 23A, B) shorter and narrower than second in dorsal view, widest at anterior end and tapering posteriorly, ornamented as in Diacyclops hanguk , with one unpaired dorsal pore (no. I) and four pairs of large sensilla (nos. 63, 64, 72, 74).

Fourth pedigerous somite (Fig. 23A, B) significantly shorter and narrower than third, also tapering posteriorly, ornamented as in Diacyclops hanguk with one unpaired dorsal pore (no. II) and two pairs of large sensilla (nos. 75, 77).

Fifth pedigerous somite (Fig. 24A, B) significantly narrower than fourth pedigerous somite or genital double-somite in dorsal view, with flared latero-posterior corners, ornamented with two pairs of large dorsal sensilla (nos. 80, 81).

Genital double-somite (Figs 24A, B) even larger and wider (arrowed in Fig. 24A) than in Diacyclops hanguk , 0.75 times as long as its greatest width (dorsal view), but with same ornamentation an similarly shaped seminal receptacle, anterior expansion of seminal receptacle with median saddle and shorter lateral arms (arrowed in Fig. 24A) than in Diacyclops hanguk , hyaline fringe wavy.

Third and fourth urosomites (Fig. 24A, B) as in Diacyclops hanguk .

Anal somite (Fig. 24A, B) also very similar to that of Diacyclops hanguk , but with wider and more posteriorly produced, convex anal operculum, this reaching posterior margin of anal somite and representing 70% of anal somite’s width.

Caudal rami (Fig. 24A, B) very short (arrowed in Fig. 24B), approximately 1.6 times as long as wide (ventral view) and 1.7 times as long as anal somite, almost cylindrical and parallel, inserted very close to each other (with hardly any space between), with deep dorso-median anterior depression (as continuation of anal sinus), with narrower base than rest of ramus in ventral view; armed and ornamented as in Diacyclops hanguk except for presence of arc of spinules at base of dorsal seta and proportionately longer dorsal seta (arrowed in Fig. 24A).

Antennula (Fig. 23C) with aesthetasc on eighth segment broad and reaching posterior margin of tenth segment (arrowed in Fig. 23C); other armature, as well as segmentation, ornamentation, and size proportions of segments as in Diacyclops hanguk .

Antenna (Fig. 23D) with segmentation and armature as in Diacyclops hanguk ; basis twice as long as wide and ornamanted with two additional rows of spinules (arrowed in Fig. 23D); setae on second endopodal segment proportionatelly somewhat longer than in Diacyclops hanguk .

Labrum (Fig. 23E) ornamented with two diagonal rows of 16 long and slender spinules each on anterior surface (arrowed in Fig. 23E), and with short central row of minute spinules in between; cutting edge almost straight, with 14 teeth between produced and rounded lateral corners.

Mandibula (Fig. 23F), maxillula, and maxilla (Fig. 23G) as in Diacyclops hanguk .

Maxilliped (Fig. 23H) with two setae on basis (arrowed in Fig. 23H) and with fewer spinules on first endopodal segment; armature formula: 2.2.1.2.

All swimming legs (Fig. 25B, C, D, E) with same segmentation, armature, and ornamentation as in Diacyclops hanguk , as well as proportions of most segments and armature elements; third endopodal segment of fourth leg about 0.9 times as long as wide, and 1.1 times as long as second endopodal segment; inner apical spine on third endopodal segment 1.6 times as long as outer apical spine (arrowed in Fig. 25E), about 1.3 times as long as segment, and 0.6 times as long as distal inner seta; apical spines diverging at approximately 20° angle.

Fifth leg (Fig. 24A) with slightly smaller protopod and longer exopod than in Diacyclops hanguk ; protopod rhomboidal in shape, about 0.65 times as long as greatest width and unornamented, but basal seta inserted on longer setophore; exopod 1.8 times as long as protopod and 2.5 times as long as wide; apical exopodal seta bipinnate distally, as long as basal seta, 3.2 times as long as exopod, and 4.2 times as long as subapical spine, reaching 2/3 length of genital double-somite; subapical exopodal spine strong, bipinnate, 0.8 times as long as exopod and twice as long as exopod’s greatest width.

Sixth leg (Fig. 24B) as in Diacyclops hanguk .

Male. Not collected.

Remarks.

As mentioned above, Diacyclops parahanguk sp. n. forms a sibling species pair with the Korean Diacyclops hanguk sp. n.The two species can be distinguished by their habitus (wider in Diacyclops parahanguk ), armature of the maxillipedal basis (one additional seta in Diacyclops parahanguk ), ornamentation of the labrum (more spinules in Diacyclops parahanguk ) and the basis of the antenna (more spinules in Diacyclops parahanguk ), relative length of the aesthetasc on the eighth antennular segment (longer in Diacyclops parahanguk ), and small differences in the shape of the seminal receptacle (shorter lateral arms in Diacyclops parahanguk ), genital double-somite (wider in Diacyclops parahanguk ), and caudal rami (shorter in Diacyclops parahanguk ), and the relative lengths of the dorsal caudal seta (longer in Diacyclops parahanguk ) and inner apical spine on the third endopo dal segment of the fourth leg (longer in Diacyclops parahanguk ). All these differences are marked with arrows in Figs 23-25. Also, sensilla pair no. 21 on the cephalothorax is more widely spaced in Diacyclops parahanguk .