Boroecia danae, 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 : 321-330

2.4. Boroecia danae new species

( Figures 10–12 )

Synonymy. 1973 Boroecia antipoda Poulsen : 170–171, Fig. 87 A–G.

Etymology. This species is named for the Swedish Research vessel Dana . Specimens were identified as Boroecia antipoda ( Müller, 1906) by Poulsen (1973), but our re-examination of his material showed that only one of his specimens (from Dana station 3642-3 46° 43’S, 176°09’E) belonged to Müller’s species and the remaining specimens can be attributed to this novel species. Unfortunately, all the Dana specimens were badly distorted after being compacted into small tubes, presumably to save storage space. Hence the description of this species has had to be based on material collected in Monterey Bay off California.

Type locality. The male holotype and the female paratype were collected by Dr P.R. Pugh during a cruise on the Western Flyer in Monterey Bay at 39° 39.5’N 124° 52’W at an estimated depth of 1600– 800 m on 29 May 2009 —Registration number NHMUK 2016-640.

Male. Carapace ( Figures 10 A,B,C ). The type specimen is slightly distorted but its overall length is 2.30 mm; both its width and height is 0.88 mm (38.3 % CL). The shoulder vaults are sharply edged with the posterior end square; this square end distinguishes this species from the other species with sharp edged shoulder vaults. Over the top of the rostrum is a longitudinal sculptural element, which becomes diamond shaped down across the shoulders. Under the incisure, the diamond surface pattern is distinct with the diamonds orientated vertically, but posteriorly the ornamentation becomes less distinct. Along the anterior half of the margin of the carapace is a line of small pegs, while the posterior half is smooth. The PDC is rounded and both valves are armed with three strong spines. On both valves is a line of pegs below the spines ( Figure 10 C )—there are nine on the right valve and at least 5 on the left (the left is slightly damaged). The LAG opens on a small prominence just anterior to the hind margin of the hinge between the carapace valves. Close to mid-height is a group of glands cells on the posterior margins of both valves with ~25 gland openings. The RAG opens at the PVC. Just dorsal to the RAG are four pairs of edge glands on both valves.

Frontal organ ( Figures 10 D,E ). The stem of the frontal organ (32.4% CL) is just shorter than limb of first antenna. The stem is sutured just proximal to where seta from antenna 1 is wrapped around it. The capitulum (10.6% CL) is bluntly pointed, slightly down-turned, and has longitudinal lines of fine setules on its basal half.

First antenna ( Figures 10 E,F ). The limb (33.6% CL) shows a clear segmentation and a group of black pigment cells within the first segment. The base of the a-seta (14.2% CL) is swollen and s-shaped, and distally the seta becomes slim and is aligned posteriorly. The b-seta is quite long (36.1% CL) and has a long, broadly ribbed subterminal pad. The c-seta, as in most of the other Boroecia species, is longer than the a-seta (15.4% CL). The d-seta (33.0% CL) is shorter than the b-seta, and only reaches just beyond the distal end of the armature on the e-seta; it carries numerous fine spines close to its end. The e-seta (44.3% CL) has an armature of about 56 pairs of straight spines and, immediately beyond them, 3 pairs of short spines that point distally; the seta is hinged distal to the armature and slightly flanged, and the flange is lined with fine spinules.

Second antenna ( Figures 10 G,H,I ). The protopodite (45.6% CL) is almost three times as long as the first segment of the exopodite (16.3% CL). The first exopodite segment is slightly curved and bare, and has a small terminal seta, which is wrapped around the articulation with second segment. The terminal segments, which carry the swimming setae, have a combined length of 7.2% CL, so the whole exopodite is shorter than the protopodite. The longest of the swimming setae is 38.4% CL. The endopodites have a- and b-setae that are bare and similar in length. The hook appendage on the right endopodite is large with a long basal shank and is then sharply angled back about 140°, the distal arm is slightly curved and extends back well beyond the base of the hook. Its tip is rounded and ribbed. The left hook forms a simple right angle and ends in a blunt point that is unridged. The base of the processus mamillaris on the first endopodite segment is parallel-sided and the end is bluntly pointed. The c- and d-setae are similar in length to the width of the second endopodite segment. The g-seta in long (49.7% CL) with a terminal flange that is lined with fine spinules. The f-seta (32.1% CL) is also slightly flanged. The base of the hseta is swollen and lined with spines; the i- and j- setae are simple and similar in length.

Mandible ( Figures 10 J , 11 A,B ). On the first segment, the sub-terminal dorsal seta is quite short and only has long setules on its basal half. On the outer face is a long ventral seta that extends well beyond the end of the limb. On the inner face are three shorter setae that extend just to the midpoint of the terminal segment. The second segment has the usual three unequal dorsal setae and two ventral setae. The terminal segment carries the characteristic seven terminal setae. Two of these terminal setae are long and claw-like; the longest is 17.6% CL. The coxale toothed edge consists of a single broad tooth followed by 11 smaller teeth ( Figure 11 A ). The distal tooth list consists of two spine teeth and 13 smaller ones, and the proximal list consists of about 20 teeth of varying sizes ( Figure 11 B ).

Labrum. With a smooth concave notch, flanked by about 17–24 filaments on each side.

Maxilla ( Figure 11 C ). The basal segment has 5 anterior setae, a single lateral seta and three posterior setae. There are three slim, short spines terminally on the outer surface. The terminal segment carries three terminal claw setae, of which the central one is subtended by two slimmer setae.

Fifth limb ( Figure 11 D ). With 5 + 4 + 5 epipodial setae. The basale has a group of five ventral setae, the most anterior of which is plumose, and a further pair of setae distally. Laterally the basale carries two pairs of setae and dorsally there is a long terminal seta that reaches well beyond the end of the limb and, just to one side, a plumose seta (not shown). The first endopodite segment has a pair of medial setae and a single dorsal medial seta; all these setae extend beyond the end of the segment. The terminal segment carries the usual three setae, of which the central one is the longest (8.0% CL). The dorsal terminal seta is only a little shorter than the central one, and the shortest ventral seta is around half the lengths of the other two.

Sixth limb ( Figure 11 E ). The epipodial setal formula is 6 + 5 + 5. The basale has a single plumose ventral seta and a single bare distal seta. Laterally it has a single plumose seta, and distally a short bare seta on its inner face and the same pair of setae on its outer face. Dorsally it has a short terminal seta and a somewhat longer plumose seta (not shown). The first endopodite segment carries a single ventral seta at two-thirds length, and the second segment a single ventral and a single dorsal seta. The terminal segment has three long subequal terminal setae (39.3% CL), all of which terminally have long setules.

Caudal furca ( Figure 11 F ). There are the eight pairs of spine setae, with a marked difference in lengths between the fourth and fifth pairs, that is a characteristic of the genus. The longest pair are 21.2% CL and have a slim curved sharply pointed tip. The first six pairs of these spine setae are armed with strong secondary spines, but the last two are slim and bare. The inner faces of the caudal lamellae are covered in fine setules and there is a long unpaired dorsal seta.

Copulatory appendage ( Figure 11 F ). The appendage is paddle-shaped with both sides slightly curved. The length is 20.8% CL and the width is about 26.4% of its length. The end is rounded and there are seven oblique muscles.

Female. The female paratype was caught in the same sample as the male holotype. Registration number NHMUK2016-631

Carapace ( Figures 12 A,B ). Carapace length is 2.60 mm, height 1.22 mm (50.8% CL) and width 1.04 mm (47.7% CL). Most of the carapace features resemble those of the male—notably the posterior ends of the sharpedged shoulder vaults are squared. The incisures are slightly shallower than the full length of the rostra (10.0% CL). There is a diamond pattern of sculpture over most of the carapace surface, but the vertical oblique striae are the clearest. The posterior dorsal corner is rounded and each valve carries five small spines. The LAG opens just anterior to the posterior end of the hinge between the carapace valves. The RAG opens at the posterior ventral margin, and just dorsal to it are the openings of four pairs of edge glands. Similar edge glands probably occur directly opposite on the other carapace valve, but the left valve is slightly damaged.

Frontal organ ( Figures 12 C,D ). The stem (20.0% CL) is longer than the first antenna, and is separated from the capitulum by a clear septum. The capitulum ( Figure 12 C ) (11.6% CL) is slightly down-turned and has a pointed end. For much of its length it is covered with fine spinules.

First antenna ( Figure 12 D ). The two sub equal segments are separated by a clear septum. The first segment contains black granules. The second has a patch of fine spines near it base on its ventral surface. At about twothirds the length of the segment is a long dorsal seta (14.0% CL) that extends to mid-length of the capitulum. The eseta is broken but is at least twice the lengths of the a–d-setae (14.0% CL). It is terminally flanged with fine spines along the rim. The sensory a–d-setae have short basal shafts.

Second antenna ( Figures 12 E,F ). The protopodite (39.2% CL) and the two exopodite segments are relatively shorter than the male’s. The longest setae on the endopodite are broken on both limbs. The processus mamillaris on both limbs has an ending that resembles a dolphin’s beak.

Mandible. There is no sexual dimorphism and the mandible has a structure and setation similar to that of the male. The longest terminal seta is 16.0% CL. The toothed edges are also the same as in the male.

Fifth limb. There is little sexual dimorphism and the limb resembles that of the male; the main difference being the smaller relative length of the longest terminal seta (7.2% CL), which reflects the female’s greater carapace length.

Sixth limb ( Figure 12 G ). The epipodial formula is 6 + 5 + 5. Usual sexual dimorphism present. The pattern of setation of the limb is much the same, but there are marked differences in the lengths of the setae. As is to be expected in the halocyprids, the most obvious difference is in the structure and lengths of the terminal setae. In these females, the terminal setae are unequal in length, bare, curved and slender. The middle terminal seta is the longest (12.4% CL).

Caudal furca. The structure of the furca is the same as in the male, although in the paratype the longest pair of claw setae is broken. The first six pairs all have coarse secondary spines, but the seventh and eighth pairs are bare and quite small. There is the marked difference in length between the fourth and fifth pairs of claw setae that is characteristic for the genus.

Poulsen material. Poulsen (1973) attributed specimens caught close to the Equator in the Indonesian Seas and in the Gulf of Panama to B. antipoda ( Müller, 1906) . However, re-examination of all his archived material showed that only the single female specimen taken at Dana station 3642-3 (46°43’S 176° 09’E) belonged to B. antipoda ( Müller, 1906) . All the other specimens are too small (the single male was reported to have a length of 2.1 mm, and mean length of 67 females was 2.4 mm; Poulsen 1973 p. 171). Comparison of Poulsen’s plot of the geographical range of B. antipoda (his Fig. 85) with that shown in Błachowiak-Samołyk & Angel (2003) (which includes all previously published records and large numbers of unpublished records from Discovery Investigations), shows there are only two other records of B. antipoda from north of 30°S (which are Tiefsee Station 54 in the Gulf of Guinea, and Station 175 in the eastern Indian Ocean Müller (1906)). Neither of these records can be verified and seem doubtful. We note that Poulsen (1969) did not report this species from his extensive sample set from the Gulf of Guinea, nor was it found during the Census of Marin Zooplankton (CMarZ) cruises in the Atlantic. We have examined in detail one of Poulsen’s female specimens ( Dana Station 3549 (07° 16’N 78° 30’W, 150–300mwo)), which we found to be in relatively good enough condition (all the other Dana specimens had been compressed into small tubes, presumably to save storage space) and found to be identical with the holotype of B. danae described herein. Poulsen also recorded a single male specimen from the Gulf of Panama, but it was not in the material loaned to us by the Copenhagen Museum.

Figures

FIGURE 10. Boroecia danae male, holotype. A. Carapace, lateral view; B. Carapace, ventral view; C. Detail of posterior dorsal corner; D. Frontal organ capitulum; E. Frontal organ and first antenna; F. First antenna, detail of setal armature; G. Second antenna; H. Second antenna hook appendage on left endopodite; I. Second antenna, left endopodite showing hook appendage. L. Mandible. Scalesin mm.

FIGURE 11. Boroecia danae male, Holotype.A. Mandible, toothed edge of basale; B. Mandible, toothed edge and tooth lists of coxale. C. Maxilla; D. Fifth limb; E. Sixth limb; F.Caudal furca and copulatory appendage. Scales in mm

FIGURE 12. Boroecia danae female, Paratype. A. Carapace lateral view; B. Carapace ventral view; C. Frontal organ capitulum; D. First antenna and frontal organ; E. Second antenna; F. Second antenna endopodite; G. Sixth limb.Scales in mm.