Boroecia alaska, Stępień & Błachowiak-Samołyk & Krawczuk & Angel, 2018

Stępień, A., Błachowiak-Samołyk, K., Krawczuk, M. & Angel, M. V., 2018, A revision of the genus Boroecia Poulsen 1973 (Ostracoda, Halocypridae) with the descriptions of three new species, Zootaxa 4394 (3), pp. 301-346 : 330-331

2.5. Boroecia alaska new species

( Figures 13–15 )

Etymology. This species is named after the Gulf of Alaska, i.e. the locality where it was first identified.

Type locality. North-East Pacific at 52° 29’N 149° 0.1’W on 20 July 2002, in a haul from 1200–0m; the female paratype was collected in the same sample.

Holotype: A male 2.60 mm long, dissected, stained with lignin pink and mounted on slides, and deposited at the Natural History Museum London NHMUK2016-621

Paratype: A female 3.06 mm long, dissected, stained with lignin pink and mounted on slides. Also, collected at 52° 29’N 149° 0.1’W. Museum registration number NHMUK2016-622. The data for the other material examined, notably from Station GAK 13 at 58° 05.9’N, 147° 48.2’W (sounding 2000m) sampled during a yearround survey in the region ( Coyle & Pinchuk 2003, 2005), are listed in Table 6.

Male. Carapace ( Figures 13 A,B ). The length of the holotype is 2.68 mm (see Table 1). The carapace height is 41.8% CL and its width is 40.3% CL. There are weak oblique striae below the incisures. The rostrum (10.9% CL) is a little longer than the depth of the incisure (8.5% CL). The shoulder vaults are rounded. The PDC is rounded and carries no spines, although spines are present in the female. The LAG opens just anterior to the back of the hinge between the two carapace valves. Just below the PDC large male glands open on both valves. The RAG opens slightly above the PVC and on both valves.

Frontal organ ( Figure 13 C ). The stem (30.5% CL) ends level with the end of the limb of the first antenna. It is divided by a septum close to its midpoint. The capitulum (12.0% CL) is down-turned and bluntly pointed. It is covered with coarse spinules ventrally and laterally on its basal two-thirds.

First antenna ( Figures 13 C,D,E ). The limb (28.5% CL) is clearly segmented. The short a-seta (9.6% CL) lies back along the limb and has two basal lobes. The b-seta (31.1% CL) is longer than the d-seta and carries a longribbed sector ( Figure 13 D ) distal to which are fairly coarse spinules, about 16 on one side and about 13 on the other. The c-seta (8.4% CL) is relatively shorter than in any of the species in the genus other than B. hopcrofti . The d-seta (26.7% CL) is relatively shorter than all the other species and carries a long row of about 22 fine spinules ( Figure 13 D ). The e-seta (41,7% CL) is armed with 40 pairs of hooked spines ( Figures 13 D,E ). Distal to the armature, the seta is broadly flanged.

Second antenna ( Figures 13 F,G,H ). The protopodite (40.6% CL) is shorter than all the other species. The first exopodite segment (13.9% CL) has a terminal seta that is wrapped around the articulation with the second segment. The f-seta of the holotype is broken but the g-seta is 28.2% CL. The hook appendages on the endopodites ( Figures 13 F,G ) are similar to those of the other species. The h–j-setae are 25.0% CL and the h-seta has a slightly swollen base ( Figure 13 H ).

Mandible ( Figures 13 I,J ). The first exopodite segment has a densely plumose sub-terminal dorsal seta, and on its inner surface a long seta (not shown) and three other moderately long setae, of which the basal-most is plumose. The second segment has the usual three dorsal setae of different lengths and two ventral setae. The third segment has the usual seven terminal setae, two of which are claw-like; the longest is 14.6% CL. The toothed edge of the coxale has the characteristic structure for the genus ( Figure 13 J ) with an inner sharply pointed spine tooth, a rounded spine tooth, and six sub-serrate cutting teeth. The spine teeth and the first cutting tooth are offset from the others. There is also a very broad inner tooth.

Maxilla ( Figure 14 A ). The anatomy of this limb is like in the other species. The first endopodite segment has 6 anterior, 3 posterior and a single lateral seta. There are five terminal spines. The terminal segment has three terminal claw setae, subtended by a pair of slim setae.

Fifth limb ( Figure 14 B ). The setation of this limb is the same as in the female and similar to that of the other species. The longest terminal seta is 8.2% CL.

Sixth limb ( Figure 14 C ). All setae are short except the three terminal setae, which are 33.7% CL and terminally plumose.

Copulatory appendage ( Figure 14 E ). The length of the appendage is 30.0% CL and it contains six oblique muscles.

Caudal furca ( Figure 14 D ). The caudal furca has eight pairs of hook setae. There is the sharp disparity in the lengths of the fourth and fifth seta pairs that is typical of the genus. The longest hook seta is 20.5% CL.

Female. The female paratype came from the same sample as the holotype.

Carapace (Figre 15 A,B). The length of the carapace of the paratype is 3.06 mm; its height is 49.7% CL and its width is 35.3% CL (see Table 1). The carapace has a more pronounced anterior taper than the male. The shoulder vaults are rounded. The posterior dorsal corner is rounded and there are three spines on both valves. The LAG opens just anterior to the posterior margin of the hinge between the valves, and the RAG opens at the PVC. Just dorsal of the RAG on both valves are the openings of four pairs of edge glands. The rostrum (10.2% CL) is a little longer than the depth of the incisure (8.1% CL). There are some rather obscure longitudinal striae paralleling the ventral margin.

Frontal organ ( Figures 15 C,D ). The stem (19.4% CL) projects well beyond the end of the limb of the first antenna. The capitulum ( Figure 15 C ) (10.5% CL) is angled down about 30°, and arches at two thirds length to a pointed tip. The proximal half of its dorsal surface is coarsely spinose, whereas most of its ventral surface is finely spinose.

First antenna ( Figure 15 D ). The limb (15.6% CL) is clearly segmented and shorter than the stem of the capitulum. Both basal segments have patches of short spines on the ventral surface. The dorsal seta (16.3% CL) is inserted medially on the second segment and reaches to two-thirds the length of the capitulum. The a–d setae (12.2% CL) have slightly inflated bases and are less than half the length of the e-seta (31.6% CL). The end of the eseta is slightly flanged and lined with fine spinules.

Second antenna ( Figures 15 E,G,F ). The protopodite (39.0% CL) is over two and a half times the length of the first endopodite segment (14.9% CL), which carries a terminal seta that is wrapped around the articulation with the second segment ( Figure 15 G ). The combined lengths of the distal exopodite segments is 6.5% CL, and the longest swimming seta is 37.3% CL. The first endopodite segment ( Figure 15 F ) has a pointed processus mamillaris and the a- and b-setae are bare, with the a-seta being the slightly one. The g-seta (37.3% CL) is flanged distally to the end of the f-seta (23.8% CL) and the flange is lined with fine spinules.

Labrum ( Figure 15 H ). The labrum has a smooth, shallow notch and is flanked by 17–24 filaments.

Mandible, maxilla and fifth limb are very similar to those of the male.

Sixth limb ( Figure 15 I ). The basale carries seven setae on its ventral surface, all of which are finely spinose. On its dorsal surface, the bare terminal seta, which is considered to be a remnant of the exopodite (Boxshall 1998) is shorter than the sub-terminal plumose seta. The first endopodite segment carries a single seta ventrally that is inserted at about two-thirds its length. The second segment has a single medial seta both ventrally and dorsally, both of which extend just beyond the end of the segment. There are three terminal setae on last endopodite segment, with the central one (11.6% CL) being the longest.

Caudal furca ( Figure 15 J,K ). The furca is typical for the genus with eight pairs of claw setae; the longest of which is 23.8% CL. There is a marked difference between the length of the fourth and fifth pairs, and the terminal two pairs carry very fine spinules ( Figure 15 K ). The inner surface of the furca’s lamellae are covered in fine setules.

Figures

FIGURE 13. Boroecia alaska male 2.68 mm, Holotype.A. Carapace, lateral view; B. Carapace, ventral view; C. First antenna and frontalorgan;D. Armaturesof first antennalsetae;E.Detailof armature of e-seta ofthe first antenna;F.Second antenna;G. Hook appendage of endopodite of the left second antenna; H. Endopodite of the right second antenna; I. Mandible; J. Toothed edge of basale of mandible.Scales in mm.

FIGURE 14. Boroecia alaska male, 2.68 mm, Holotype. A. Maxilla (distorted); B. Fifth limb; C. Sixth limb; D. Caudal furca; E. Copulatory appendage.Scales in mm

FIGURE 15. Boroecia alaska female 3.04 mm, Paratype. A. Carapace, lateral view; B. Carapace, ventral view; C. Capitulum of frontal organ; D. First antenna and frontal organ; E. Second antenna; F. Endopodite of second antenna; G. Detail of end of first segment of second antenna endopodite showing the terminal seta; H. Labrum; I. Sixth limb; J. Caudal furca; K. Detail of 6–8th caudal furca spines.Scales in mm.