Euconchoecia omanensis, Graves, 2011

Graves, Carol, 2011, Redescription of Euconchoecia chierchiae Müller, 1890 and Euconchoecia aculeata (Scott, 1894) (Halocyprididae: Ostracoda) from the Atlantic, and descriptions of two novel species of Euconchoecia Müller 1890, from the Gulf of Oman, Journal of Natural History 45 (31 - 32), pp. 1937-1981 : 1963-1970

Euconchoecia omanensis sp.nov.

( Figures 11– 15 , 21E,F )

Type material

Permanent preparations of the dissected holotype and allotype used in this description are deposited at the Natural History Museum, London registration number BMNH 2009.330 for the holotype (female) and BMNH 2009.331 for the allotype (male). Registration numbers BMNH 2009.332 – 341 are for the remaining female and male paratypes retained in 80% ethyl alcohol .

Etymology

The specific name refers to the type locality of the Gulf of Oman .

Description

The meristic characters of the carapaces of males and females, and the frontal organs, first and second antennae, mouthparts and limbs are listed in Tables 2 to 9 together with comparative data for the other species described here.

Female

Carapace ( Figure 11A,B ). Mean length measured 1.42 ± 0.06 mm (n = 100). Carapace of holotype ( Table 2) with a length of 1.42 mm, a height of 0.46 mm and a breadth of 0.40 mm. Height: length ratio 32.4%, breadth: length ratio 28.2%. Carapace is unsculptured. In lateral view elongate: maximum height is just anterior to mid-length. Ventral margin curves smoothly into posterior margin. Posterior dorsal corner of both valves furnished with a spine. Spine much smaller on left valve. Dorsal margin arcs anteriorly up towards dorsal end of hinge between carapace valves. Both rostra narrow and point forward, the left rostral process longer and more pointed. The ‘asymmetrical’ glands open at a similar height on posterior margin of each valve just below spine at posterior dorsal corner.

Frontal organ ( Table 2; Figure 11C ). Frontal organ fused into a slender structure with rounded end, that is significantly longer than A1 and 18.7% CL.

First antenna ( Table 3; Figure 11C ). With five segments, but the suture between fourth and fifth segments ill-defined. Limb length is ∼ 35% CL. Fourth segment with ∼ 24 thin walled bundle setae all 9.2% CL. Fifth segment with four more unequal setae, a-seta quite short 2.1% CL; b-seta 3.5% CL; c-seta 10.0% CL; d-seta 7.7% CL.

Second antenna ( Table 3; Figure 11D ). Protopodite is 24.6% CL. Length of first exopodite segment is approximately half protopodite. Most swimming setae are similar in length to protopodite, all but the shortest terminal seta have long hairs distally. Endopodite ( Figure 11E ) with short, pointed, bare a- and b-setae. There are no c-, d- or e-setae. The f- and g-setae, respectively, 17.8% CL and 23.2% CL. The i-seta is 7.2% CL, but h- and j-setae are absent.

Mandible ( Table 4; Figure 12A,B ). Coxale toothed edge of pars incisiva has two large and 10 small smooth teeth. Distal tooth list slightly narrower with two large tusk-like teeth and 10 small smooth teeth. Proximal tooth list very narrow, with two large and five small teeth. Outer margin of toothed edge of basal endite with a large daggershaped tooth, a slightly smaller, rounded, tubular tooth and six subserrate teeth. Two spinose setae are inserted laterally on basal endite. Exopodite represented by moderately long plumose seta inserted on outer margin of basis. First endopodite segment with one short, bare, subterminal dorsal seta and three finely spinose ventral setae. Second segment with one ventral and two dorsal setae all finely spinose. Third segment with seven spinose terminal setae, one very long and robust.

Maxilla ( Table 4; Figure 12C ). Basal segment with five anterior, one lateral and four posterior setae. Distal segment comparatively short and wide, with six terminal claw setae, the posteriormost is longest, anterior claw with secondary spines.

Fifth limb ( Table 5; Figure 12D ). Ventrally basale with five (2+1+2) setae all with secondary spines, laterally two plumose setae, dorsally a single long spinose seta. First segment with two ventral setae and one dorsal seta, all spinose. Second segment with three unequal curved terminal claw setae; middle claw the longest and is 4.1% CL.

Sixth limb ( Table 5; Figure 12E ). Basale with one proximal, two medial ventral spinose setae and a distal plumose seta, laterally a plumose seta and dorsally a terminal spinose exopodal seta. The first endopodite segment with two ventral setae. Second segment with a single spinose seta both ventrally and dorsally. Third segment with three unequal spinose terminal claw setae; longest middle claw is 7.1% CL.

Caudal furca ( Table 5; Figure 12F ). Seven pairs of claw setae diminish in size dorsally; longest claw 10.4% CL. All have secondary spines along their trailing edge. Dorsal to the paired spines is a single seta with bilateral secondary spines. Between first and second pair of claw setae is a verruciform process.

Male

Carapace ( Figure 13A,B ). Mean length measured 1.15 ± 0.04 mm (n = 100). Carapace of allotype ( Table 6) with length of 1.20 mm, a height of 0.44 mm and breadth of 0.40 mm. Height: length ratio 36.7%, breadth: length ratio 33.3%. Carapace unsculptured. Maximum carapace height just anterior to mid-length. Ventral margin curves smoothly into posterior margin. Posterior dorsal corner of both valves furnished with a small spine. On the left valve the spine is smaller. The dorsal margin arcs anteriorly up towards dorsal end of hinge between carapace valves. Both rostra broad, curve ventrally, the left rostral process is longer. The “asymmetrical” glands open at a similar height on the posterior margin of each valve just below the spine at posterior dorsal corner.

Frontal organ ( Table 6; Figure 13C ). Frontal organ fused into a single slender structure with a rounded end that is significantly longer than A1 and 31.3% CL.

First antenna ( Table 7; Figure 13C ). With five well-defined segments. Limb length ∼ 35% CL. Fourth segment with ∼ 24 thin walled bundle setae all 14.4% CL. Fifth segment with five more unequal setae: a-seta 8.8% CL; b-seta 15.0% CL; c-seta 18.3% CL; d-seta 32.1% CL; e-seta 46.3% CL.

Second antenna ( Table 7; Figure 13D ). Protopodite 37.1% CL. Length of first exopodite segment approximately third of protopodite. Most swimming setae similar in length to protopodite, all but the shortest have long hairs distally. Endopodite with short, pointed, bare a- and b-setae. There are no c-, d- or e-setae. The f-seta, very long, g-seta, respectively, 39.2% CL and 60.0% CL. Right endopodite ( Figure 14A ) with elongated clasping organ in form of hook with a long proximal shank and very long curved end piece 5.4% CL. The h-seta is short and curved 2.9% CL; i-seta 19.2% CL; j-seta 9.6% CL. Left endopodite ( Figure 14B ) the hook reduced to just basal shank with three setae terminally.

Mandible, maxilla, fifth limb ( Tables 8, 9; Figure 14C–E , 15A ). Structure and arrangement of setae of mandible, maxilla and fifth limb are same as female.

Sixth limb ( Table 9; Figure 15B ). Basale with five spinose setae, one lateral spinose seta and one bare dorsal exopodal seta. First segment with two ventral setae. Second segment with a single bare seta both ventrally and dorsally. Third segment with three very long subequal terminal setae, with long hairs distally 30.4% CL.

Caudal furca ( Table 9; Figure 15C ). Structure and arrangement of claws same as female. Longest claw 12.5% CL.

Intromittent organ ( Table 9; Figure 15C ). Male copulatory appendage long 19.6% CL.

Remarks

Euconchoecia omanensis should be regarded as a separate species on the basis of the following combination of characters: both females and males are more elongate than E. chierchiae and E. aculeata ; the height: length ratio of E. omanensis was 32.4% and the breadth: length ratio was 28.2%; the spines on the posterior dorsal corner of the female were almost twice the length of the spines of E. chierchiae , and in the male the left spine on the posterior dorsal corner was 2% longer and the right spine was 3% longer. In both sexes the frontal organ reached well beyond the first antenna and on the second antenna the right clasper shank length was significantly smaller than in E. chierchiae , but longer than in E. aculeata .

Figures

Figure 11. Euconchoecia omanensis female: (A) lateral view, (B) carapace dissected and viewed dorsally – arrows indicate gland openings, (C) first antenna and frontal organ, (D) second antenna viewed from inside, (E) endopodite viewed from inside.

Figure 12. Euconchoecia omanensis female: (A) mandible, coxale not shown, (B) basal endite of mandible, (C) maxilla, (D) fifth limb, (E) sixth limb, (F) caudal furca.

Figure 13. Euconchoecia omanensis male: (A) lateral view, (B) carapace dissected and viewed dorsally – arrows indicate gland openings, (C) frontal organ and first antenna, (D) second antenna viewed from inside.

Figure 14. Euconchoecia omanensis male: (A) right endopodite viewed from inside, (B) left endopodite viewed from inside, (C) mandible, coxale not shown, (D) basal endite of mandible, (E) maxilla.

Figure 15. Euconchoecia omanensis male: (A) fifth limb, (B) sixth limb, (C) caudal furca and intromittent organ.

Figure 21. Euconchoecia. (A) E. chierchiae female, (B). E. chierchiae male, (C) E. aculeata female, (D) E. aculeata male, (E) E. omanensis female, (F) E. omanensis male, (G) E. hormuzensis female, (H) E. hormuzensis male, all viewed laterally.