Discoconchoecia elegans (Sars, 1965)

Stępień, Anna, Błachowiak-Samołyk, Katarzyna & Angel, Martin V., 2015, A re-description of Discoconchoecia elegans (Sars, 1865) (Ostracoda: Halocyprididae) from high latitudes in the North Atlantic, Zootaxa 3995 (1) : -

Discoconchoecia elegans (Sars, 1965)

Conchoecia elegans Sars, 1865 ; Paraconnchoenia elegans Poulsen, 1973

Material examined. Lectotype— female, station N-2.

Allolectotype— (station N-2).

P aralectotype —nine female, stations N-1, N-2, N-3, N-9, ICE1, eight males, stations N-1, N-9, ( Table 2 ).

Description Female (collected in vicinity of Svalbard). Carapace ( Figs 2 A–B; 4A; Table 3 ). The carapace is 1.9–2.3 mm long, with a height of 0.82–0.98 mm (37.3% ± 2.3%) (N. B. all values have been standardized by expressing them as percentages of the carapace length (CL) of the individual) and breadth of 0.7 mm (31.5% ± 3.0%). There is a sculpture consisting of a few striae running parallel to ventral margin. The posterior dorsal corner of the right valve bears two spines ( Fig. 2 C), whereas on the left valve there is one small spine at the PDC. The maximum carapace height is at about mid-length. The rostra are similar in length (11.7% ± 0.4% CL), and similar in length to the incisures, which show some disparity in length - the left incisure is 11.3% ± 1.5% CL and the right incisure is 10.0% ± 0.5% CL. There is a shallow sulcus between the shoulder vaults. The left asymmetrical gland opens anterior to the posterior end of the hinge between the two carapace valves. The gland on the right valve is on the curve of posterior ventral corner.

Frontal organ ( Fig. 2 D; Table 3 ). The FO is straight, (37% CL) and extended just beyond the end of the limb of the first antenna. There is no clear division between stem and capitulum and the whole organ is bare without spines or setae and its tip is rounded. Its total length is 23.8% ± 2.2% CL.

First antenna ( Fig. 2 D; Table 3 ). The limb consists of five segments and its overall length is 17.8 ± 2.0% CL. Its segments are differentiated; the first being 35% of the total antennal length, and the second segment 50%. Both segments are bare. The fourth segment carries two sensory setae (a- and b-setae), and the fifth segment carries three, two of which are sensory (c- and d-setae) and one is long and distally carries fine spinules (e-seta). Sensory setae are all similar in length, about 13–14% CL, whereas the e-seta is twice their lengths (27.0 % CL).

Second antenna ( Fig. 2 E; Table 3 ). Protopodite length is 47.3% ± 2.3% CL and its length: height ratio is 1.5: 1.7. Close to the insertion of endopodite there is a patch of fine setules. The first exopodite segment is 12.9% ± 0.8% CL and bears a terminal seta on both left and right limbs. Segments 2–9 carry the swimming setae, which are similar in length to protopodite. The combined lengths of segments 2–9 is 6.6% ± 0.2% CL. The terminal ninth segment carries three setae; in addition to a swimming seta there are two bare shorter setae. The first endopodite segment ( Fig. 2 G) is 19.6% length of protopodite and its length: height ratio is 0.90: 1.26. It carries two plumose setae (a- and b-seta). The a-seta is about half the length of the b-seta (1.3% ± 0.1% and 2.4% ± 0.3% CL, respectively). The second segment carries five setae, three of which (h–j setae) are similar in length (16.6% ± 2.0% CL). The next two setae are a little longer, f-seta is 19% CL) and g-setae is 35% CL.

Mandible ( Fig. 2 H; Table 3 ). Both distal and proximal tooth edges consist of six sub-serrate teeth and two spines. Three setae are present on outer face of the basale, two are short, and the third is longer, and situated subdistally to the two former. On inner margin, sub-distal to toothed edge, there is a single seta. Typically for Conchoecinae there is a single, tiny seta located on a small process. Exopodite is represented by a long plumose seta situated on outer margin of the basale. The inner margin, opposite to the exopodite, is covered with a patch of fine setules. First endopodite segment carries a distal plumose seta on ventral margin, and dorsally two setae are present, one is bare and inserted medially, the second is plumose and inserted on the margin. The second segment has two ventral setae and three dorsal. One of the dorsal setae is plumose, but the rest are bare. The third segment possesses two spinose claw-like setae terminally and five shorter and thinner setae. Dorsal margin in distal part is covered by a patch of fine setules.

Maxilla ( Fig. 2 I; Table 3 ). Basal segment has three setae on inner margin, one of which is plumose, and the other two are bare. There are six setae on the outer margin. On the distal margin there is a single seta that extends to the end of the limb. The outer distal corner is covered by several small spines. Distal segment carries three terminal distal claw-like setae and two inner setae. Inner distal margin of the segment carries a clump of fine setules.

Svalbard Lofoten mean ± standard deviation

length from distal end of oval 12.01 ± 0.49 10.29 ± 1.09 plate to the tip of e-seta

Second antenna ...Continue on next page Svalbard Lofoten

mean ± standard deviation

Svalbard Lofoten

mean ± standard deviation

Fifth limb ( Fig. 2 J; Table 3 ). The epipodial setae are in a three groups of five, five and seven setae (proximal group with additional short, simple seta). Coxale - first endite has two setae, one bare, and one plumose. Second endite carries five setae, one is very short, spine-like and two are plumose. Third endite ventrally carries a group of six setae. The basale has six setae in proximal ventral group and three setae in distal ventral group. There is a long, bare seta on dorsal margin, which is the remnant of the exopodite, and laterally single plumose setae. Surface is covered proximally by fine setules. First endopodite segment has three bare setae, two ventrally and one dorsal. The second segment carries three unequal terminal setae.

Sixth limb ( Fig. 2 K; Table 3 ). Epipodial setae are arranged in three groups of five, five and seven setae (proximal group with additional short and simple seta). The coxale’s second endite has two plumose setae. The basale carries five ventral plumose setae, one lateral plumose seta and dorsally single bare seta, which extends almost to the mid-point of the first endopodite segment. First endopodite segment has a single ventral seta. Second segment carries single bare ventral seta, and single bare dorsal seta. Third segment has three unequal terminal plumose setae.

Seventh limb ( Fig. 2 L; Table 3 ). Terminal segment carries two long setae.

Caudal furca ( Fig. 2 M; Table 3 ). There are eight pairs of spine-like setae, which diminishing in size dorsally. Male (collected in vicinity of Svalbard). Carapace ( Figs 3 A–B; 4B; Table 3 ). On average the male carapace is slightly longer than female’s, 2.12– 2.28 mm long, with a height of 0.75–1.01 mm (38.1% ± 2.4% CL) and a breadth of 0.71–0.81 (36.9% ± 2.6% CL). The posterior dorsal corner of the right valve bears three spines ( Fig. 3 C).

Frontal organ ( Fig. 3 D; Table 3 ). The FO is relatively shorter than the female’s (18% CL), and shorter than the limb of the first antenna. The stem and capitulum are fused. The tip is rounded, and carries short setae along the dorsal and ventral margins. Its total length is 37.2% ± 3.3% CL.

First antenna ( Fig. 3 D; Table 3 ). The total limb length is 43.3% ± 0.5% CL, which is much longer than the female’s. First segment is 51% the length of total limb, and the second segment is 38%. Close to the midpoint of the second segment is a seta wraps around the stem of FO ( Fig. 5 A). The c-seta is shorter than in the female (6.7% ± 0.8% CL), whereas the a- and b-setae are similar in length, and only little shorter than the lengths of the d- and esetae. The e-seta carries the oval pad of hair-like setae which is one of the characteristic features of the genus ( Fig. 5 B). The distance of the distal margin end of the oval pad to end of the seta is 12.0% ± 0.4% CL. Proximal of the pad plate are inserted several short distally pointing spinules.

Second antenna ( Fig. 3 E; Table 3 ). The length of the protopodite is 49% ± 2.1% and its length: height ratio is 1.6: 1.8. First exopodite segment bears row of spines along its ventral margin and row of fine spinules along its dorsal margin. There is seta on the first exopodite segment of both left and right antenna. First endopodite segment ( Fig. 3 F) is about 31% length of protopodite, its length: height ratio is 1.5: 1.7. The c-, d- and e- setae are present on the second segment, but are very short. The f-seta and g-seta are 36.5% ± 10.9% CL and 79.6% ± 3.4% CL respectively and so much longer than in the female, while h-j setae are 18.2% ± 0.6% CL.

Mandible ( Fig. 3 G; Table 3 ), maxilla ( Fig. 3 H; Table 3 ), fifth limb ( Fig. 3 I; Table 3 ), seventh limb ( Fig. 3 K; Table 3 ), furca ( Fig. 3 M; Table. 3 ) are not sexually dimorphic and their structures and arrangement of setae are similar to those described for the female.

Sixth limb ( Fig. 3 J; Table 3 ). The sixth limb is very different. Its basale carries two proximal setae and one distal, very short on ventral margin. First and second endopodite segments are bare, third segment has three long terminal setae, all similar in length, 49.6% ± 3.4% CL, and carry long fine hairs terminally.

Copulatory appendage ( Fig. 3 L; Table 3 ). The appendage is characteristically shaped. Its length is 19.1% ± 1.6% CL and width 4.5% ± 0.8% CL. It has five oblique muscles and its tip is rounded.

Figures

FIGURE 2. Discoconchoecia elegans, female, station N- 2. A. Carapace lateral view; B, carapace ventral view; C, posterior dorsal corner; D, first antenna; E, second antenna; F, exopodite of second antenna; G, endopodite of second antenna; H, mandible; I, maxilla; J, fifth limb; K, sixth limb; L, caudal furca; M, seventh limb. Scale = 0.1 mm.

FIGURE 3. Discoconchoecia elegans, male, station N- 2. A, carapace lateral view; B, carapace ventral view; C, posterior dorsal corner; D, first antenna; E, second antenna; F, endopodite of second antenna; G, mandible; H, maxilla; I, fifth limb; J, sixth limb; K, seventh limb; L, copulatory appendage; M, caudal furca. Scale = 0.1 mm.

FIGURE 5. Discoconchoecia elegans, male, station N- 1. A, hook-like seta, B, oval ring on e-seta.

Tables

TABLE 3. Limb’s measurements of Lofoten and Svalbard individuals.

Character (% of carapace length)	Female (n=7)	Male (n=5)	Female (n=4)	Male (n=4)
Carapace
Length	2.12 ± 2.18	2.20 ± 0.78	2.09 ± 1.00	2.10 ± 0.79
Height (as % of length)	37.38 ± 2.35%	38.11 ± 2.46%	38.56 ± 0.46%	38.36 ± 0.38%
Breadth	31.53 ± 3.08	36.98 ± 2.67	31.44 ± 0.69	33.92 ± 0.33
Rostrum	11.78 ± 0.43	13.60 ± 0.61	12.74 ± 0.73	11.84 ± 0.50
incisure L	11.39 ± 1.50	13.71 ± 1.23	11.44 ± 0.37	13.56 ± 0.13
incisure R	10.07 ± 0.58	11.87 ± 1.53	10.19 ± 0.83	9.48 ± 2.09
LAG	2.05 ± 0.24	1.72	2.78 ± 0.57
RAG	33.07 ± 1.37	33.61 ± 1.68	34.00 ± 0.95
Frontal organ
Length	23.81 ± 2.21	37.25 ± 3.35	22.73 ± 1.06	34.61 ± 0.42
ratio FO: A1	137 ± 18.0	82.59 ± 6.12	129.96 ± 2.33	82.42 ± 0.06
First antenna
total limb length	17.81 ± 2.01	43.37 ± 0.50	17.98 ± 0.95	40.39 ± 2.61
segment 1 length	6.27 ± 1.58	22.57 ± 1.10	6.34 ± 0.57	21.04 ± 1.38
segment 2 length	8.95 ± 0.60	16.79 ± 0.56	9.13 ± 0.32	15.97 ± 0.48
a-seta	14.38 ± 0.89	31.53 ± 4.63	12.94 ± 1.30	31.41 ± 2.93
b-seta	13.00 ± 0.68	32.37 ± 8.90		32.99 ± 2.87
c-seta		6.76 ± 0.84		7.63 ± 1.43
d-seta	14.47 ± 0.37	35.41 ± 1.64		34.55 ± 0.65
e-seta	27.04 ± 1.64	36.86 ± 1.77	27.73 ± 2.93	34.20 ± 0.34
oval plate		3.70 ± 0.19		3.06 ± 0.31