Euconchoecia aculeata ( Scott, 1894 )

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 : 1951-1962

Euconchoecia aculeata ( Scott, 1894)

( Figures 7–10 , 21C, D )

Halocypris aculeata Scott, 1894 : S 142, Pl. XV, figs. 5, 6, 33, 38.

Euconchoecia aculeata Cleve, 1905: 131 . Müller, 1906: 129, Pl. XXXII, figs. 18–20, 22–26. Müller, 1912: 95. Poulsen, 1969: 41, fig. 15. Tseng, 1969: 18, fig 4. George, 1977: fig. 1–5.

Type material

Permanent preparations of the dissected specimens selected as lectotype and paralectotype and used in this detailed description of the species are deposited at the Natural History Museum, London registration number BMNH 2009.328 for the lectotype (female) and BMNH 2009.329 for the paralectotype (male). The remaining undissected paralectotypes retain the original registration numbers, 1893.4.22 . 14–17.

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 7A,B ). Material deposited in the Natural History Museum contained two females: one measured 1.18 mm. The other, selected as lectotype ( Table 2),

Notes: n = 1 for each species.

% CL, carapace length; n.d., no data.

has length 1.28 mm, height 0.64 mm and breadth 0.42 mm. Height: length ratio was 50.0%, breadth: length ratio was 32.8%. Carapace unsculptured. Lateral view elongate. Ventral margin curves smoothly into posterior margin. Posterior dorsal corner of both valves furnished with a small spine. Spine smaller on left valve. Dorsal margin straight and parallel to the ventral margin. Both rostra curve ventrally, with 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 7C ). Frontal organ fused into a slender structure with a rounded end that is slightly longer than A1 and 22.3% CL.

First antenna ( Table 3; Figure 7C ). With five segments, but suture between fourth and fifth segments ill-defined. Limb length ∼ 34% CL. Fourth segment with ∼ 24 thin

walled bundle setae all 17.0% CL. Fifth segment with four more unequal setae, the a-seta short 3.1% CL; b-seta 6.1% CL; c-seta 14.5% CL; d-seta 11.5% CL.

Second antenna ( Table 3; Figure 7D ). Protopodite 29.3% CL. Length of first exopodite segment approximately half protopodite. Most swimming setae are similar length to protopodite, all but the shortest terminal seta have long hairs distally. Endopodite ( Figure 7E ) with short, pointed, bare a- and b-setae. There are no c-, d- or e-setae. The f- and g-setae respectively 25.4% CL and 35.2% CL. The i-seta 23.0% CL, but the h- and j-setae are absent.

Mandible ( Table 4; Figure 8A ). 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 dagger-shaped tooth, a slightly smaller, rounded, tubular tooth and six subserrate triangular teeth. Two spinose setae are inserted laterally on the 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 8B ). 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 8C ). Ventrally basale with five (2+1+2) setae all with secondary spines, laterally two plumose setae, dorsally a single long dorsal spinose seta – the remnant of the exopodite. First segment with two ventral setae and one dorsal seta, all spinose. Second segment with three unequal curved terminal claw setae of unequal length; middle claw the longest 6.0% CL.

Sixth limb ( Table 5; Figure 8D ). Basale with one proximal, two medial ventral spinose setae and a distal plumose seta, laterally a plumose seta and dorsally a terminal spinose seta. 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 8.1% CL.

Caudal furca ( Table 5; Figure 8E ). Seven pairs of claw setae diminish in size dorsally; longest claw 14.1% CL. All have secondary spines along their trailing edges. Dorsal to the paired spines is a single seta with bilateral secondary spines. Between the first and second pair of claw setae is a verruciform process.

Male

Carapace ( Figure 9A,B ). Material deposited in the Natural History Museum contained two males. One measured 1.14 mm. The paralectotype ( Table 6) with a length of 1.06 mm, height of 0.60 mm and breadth of 0.46 mm. Height: length ratio 56.6%, breadth: length ratio 43.4%. Carapace unsculptured. In lateral view maximum carapace height is just anterior to mid-length. Ventral margin curves uniformly. Dorsal margin curves upwards towards the rostral processes. Posterior dorsal corner of both valves furnished with a small spine. On the left valve the spine is slightly the smaller. Both rostra curve ventrally, the left rostrum is slightly smaller. The specimen was damaged, so measurements are imprecise. The “asymmetrical” glands open at a

similar height on posterior margin of each valve just below spine at posterior dorsal corner.

Frontal organ ( Table 6; Figure 9C ). Frontal organ fused into a single slender structure with rounded end that is shorter than A1 and 22.2% CL.

First antenna ( Table 7; Figure 9C ). With five well-defined segments. Fourth segment with ∼ 24 thin walled bundle setae. All broken, so no measurements obtained. Fifth segment with five unequal setae. All broken, so no measurements obtained.

Second antenna ( Table 7; Figure 9D ). Protopodite 38.2% CL. Length of first exopodite segment approximately half prodopodite. Swimming setae shorter than the protopodite and 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 and gseta respectively 36.8% CL and 38.4% CL. Right endopodite ( Figure 9F ) with an elongated clasping organ in the form of a hook with long proximal shank and curved end piece 1.7% CL. The h-seta is short 1.9% CL with long i-seta 16.0% CL. Left endopodite ( Figure 9E ) “hook” is reduced to basal shank with three setae terminally.

Mandible, maxilla ( Table 8; Figure 10A,B ). The full detailed structure of these limbs cannot be described because of the poor state of preservation of the material. Structure and arrangement of setae on the endopodite and the structure of the maxilla are same as female.

Fifth limb. Missing.

Sixth limb ( Table 9; Figure 10C ). Basale with five spinose setae ventrally, one lateral spinose seta and one bare dorsal seta. First endopodite segment with two ventral setae. Second endopodite segment with a single seta both ventrally and dorsally. Terminal setae broken.

Caudal furca ( Table 9; Figure 10D ). Structure and arrangement of the furcal claws is same as female. Longest claw is 17.5% CL.

Intromittent organ ( Table 9; Figure 10E ). The male copulatory appendage is exceptionally long, 27.4% CL.

Remarks

A full and detailed description of the type material is given here because the original description is so incomplete that it has undoubtedly led to confusion in the subsequent literature. By unambiguously describing all its characters, even when very similar, if not identical, to those described above for E. chierchiae , confusion should be avoided in future.

Scott’s original description of this species as Halocypris aculeata ( Scott 1894) was vague and incomplete. Cleve (1905), with approval from Scott, transferred this species to the genus Euconchoecia , because Scott’s specimens were clearly not Halocypris , and Müller had described his new genus Euconchoecia . The description of E. aculeata by Müller (1912) records a length of 0.9–1.05 mm for females and 0.95 mm for males. This is smaller than the type specimens deposited by Scott at the Natural History Museum, London. Poulsen (1969) and Tseng (1969) both reported E. aculeata from various locations outside the Atlantic without re-examining Scott’s material. Given the inadequate quality of the original description, subsequent records of E. aculeata remote from the type locality require confirmation.

The species E. aculeata is very similar to E. chierchiae and both are of similar size. The female of E. aculeata is more elongate and the rostrum is narrower and more downward pointing in both sexes ( Figure 21 ). The frontal organ of female E. aculeata is marginally longer than the first antenna ( Table 2), and in the male the second antenna right clasper shank length is very much smaller than that of E. chierchiae ( Table 7). These characters readily distinguish these two species.

Figures

Figure 7. Euconchoecia aculeata 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 8. Euconchoecia aculeata female: (A) mandible, coxale not shown, (B) maxilla, (C) fifth limb, (D) sixth limb, (E) caudal furca.

Figure 9. Euconchoecia aculeata male: (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) left endopodite viewed from inside, (F) right endopodite viewed from inside.

Figure 10. Euconchoecia aculeata male: (A) mandible, coxale not shown, (B) maxilla, (C) sixth limb, (D) caudal furca, (E) 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.