Halocypretta parvirostrata Chavtur and Stovbun, 2008

Angel, Martin V., 2013, Planktonic ostracods (Myodocopa: Halocyprididae) from abyssopelagic depths in the Atlantic, North Pacific and Gulf of Oman: Chavturia abyssopelagica (n. gen., n. sp.), Halocypretta profunda (n. sp.), Halocypretta parvirostrata Chavtur and Stovbun, 2008 and Halocypretta striata (Müller, 1906), Zootaxa 3709 (5), pp. 401-431 : 415-421

Halocypretta parvirostrata Chavtur and Stovbun, 2008

( Figs 11 , 12 )

In their original description of the species Chavtur and Stovbun (2008) only had male specimens available. Amongst halocyprids material from the North Pacific sent to me by Dr Moira Galbraith of the Vancouver Sorting Centre have been three specimens, a male, a female and an A- 1 female. The A- 1 juvenile was in poor condition as it was in the process of moulting. The adult female has been used to supplement the original description. Generally, there is little sexual dimorphism, many of the characters are either identical, or very similar, to those described in Chavtur and Stovbun (2008). These specimens have been used to provide meristic data for comparison with Chavturia .

Supplementary description of the female.

The adult female was caught at a depth of 1000–2000 m at 48° 55.25’N 127° 13.3’W on 29th May 2010. Its length is 3.48 mm with a height of 2.16 mm (62.1 % CL) and a breadth of 1.60 mm (46.0 % CL).

Carapace ( Fig. 11 A, B). There is a faint sculpturing of longitudinal striae on the rostrum and under the incisure, but the rest of the carapace appears smooth. The rostrum is 12.1 % CL and the incisure is 3.5 % CL. There is a flange on the anterior margin on the ventral edge of the incisure. The opening of the right asymmetrical gland is at the posterior ventral corner, but details of the opening of the left gland could not be ascertained without mounting the carapace (note: The carapace of the A-1 moulting female specimen was mounted and shows that the gland opening is posterior to the rear end of the hinge between the carapace valves).

Frontal organ ( Fig. 11 D). The frontal organ is large and before dissection could be seen projecting out between the two rostra. The stem is very short stem (6.0 % CL). The capitulum (21.5 % CL) is slightly curved, parallelsided and has a rounded end armed with a few very fine spinules.

First antenna ( Fig. 11 C, D). The limb is five-segmented with an overall length of 14.3 % CL. There are numerous dark pigment granules within its first two segments ( Fig. 11 C). The first segment has a patch of long setules on its outer ventral surface. The second segment has a curved medial spinose seta (4.0 % CL) that arches anteriorly. Around the base of the seta and extending half way down the flanks on the outer surface is a covering of fine short spines; on the inner surface there is a similar distal patch of spines on the upper half of the segment. The penultimate segment carries a pair of subequal terminal setae (26.9 % CL). The terminal segment carries a long terminal seta (58.2 % CL) and a slightly shorter seta (46.2 % CL) and a third that is subequal to the two setae on the fourth segment. These shorter setae are probably homologous with the a-d setae in Conchoeciinae species, and the longest seta to the e-seta.

Second antenna ( Fig. 11 E). The protopodite is relatively short (26.4 % CL) and is a shorter than the first exopodite segment (30.0 % CL). At a quarter length along the first segment is a slight angle, which marks where the internal muscles to the terminal segments are inserted. It also carries a small terminal seta. The remaining segments that carry the swimming setae are quite short (8.3 % CL). The swimming setae are long (58.2 % CL). The first endopodite segment is broad and rounded. The a- and b- setae (4.5 and 7.0 % CL respectively) are broad at the base and taper to midlength: there they become slim, curved and finely spinose. The second endopodite segment is very short and squat: it carries the usual five terminal setae—the g-seta is very long (63.9 % CL), the f-seta is long (53.7 % CL) and h-, i- and j- setae are subequal and are not quite half the length of the g-seta (27.4 % CL). Mandible ( Fig. 11 F, G). The first segment of the endopodite has a subterminal dorsal seta that is bare and quite short. On flanks of this segment is a single long seta on its outer side and the three slightly shorter setae on the inner. The second segment has two subterminal ventral setae of moderate length and three dorsal terminal setae (only one shown in Fig. 11 F); a long one armed with very fine setules, and the other two are bare and somewhat shorter. The terminal segment has a patch of long setules dorsally and seven terminal setae. The longest of these setae is armed with short spines and is 22.4 % CL. One of the four ventral setae is longer than the two subequal setae that are dorsal to the longest seta.

The toothed edge of the basale has the typical halocypid structure of two spine teeth (one sharp the other blunt) and six cutting teeth. The two spine teeth are unarmed. The first of the cutting teeth is offset from the others, and none of them has any secondary teeth. There is a narrow rounded inner tooth and two outer setae which extend just beyond the tips of the cutting teeth and two long lateral setae. There is no subterminal seta near the insertion of the endopodite. The exopodite is represented by a broad, quite short, plumose seta.

The toothed edge of the coxale ( Fig. 11 G) consists of a broad tooth flowed by about eight rounded teeth that diminish in size. The distal tooth lists consists of two large teeth and seven flat ended teeth followed by a short ridged area that may represent another eight worn teeth. The inner list consists of about 15 uneven teeth, and the masticatory pad is made up of short spines and ridges.

Maxilla. There is a long basal seta. The first segment carries five anterior setae, a lateral seta, and three posterior setae. These setae are bare and quite long. There are also five short squat spines inserted in the middle of the outer face close to the articulation with the second segment. The second segment is elongate and bare. There are three long terminal claw-like setae, which are subtended by a pair of slim setae.

Fifth Limb ( Fig. 12 A). The basal segment of the limb has four proximal and two distal ventral setae, two pairs of lateral setae, a long dorsal seta which is the remnant of the exopodite and two long slightly laterally placed plumose setae, which extend to the end of the first segment. The first endopodite segment has a pair of ventral medial setae and a single dorsal medial seta; all three of these setae extend beyond the end of the terminal segment. The terminal segment has the usual three terminal seta; the dorsal one is just longer (10.1 % CL) than the middle seta, and the ventral seta is not much shorter.

Sixth limb ( Fig. 12 B). The basale has six ventral seta (2+ 2 + 2) that are finely pilose, a very short plumose dorsal seta, and the long seta that is a remnant of the exopodite only reached to the midpoint of the second segment. The first segment carries only a single ventral seta at 2/3s length. The second segment carries a dorsal and a ventral median seta, both of which are quite long and extend well beyond the end of the limb. The terminal segment carries the usual three terminal setae, of which the central seta is the longest and thickest (14.6 % CL), but the dorsal seta is only slightly shorter, and the ventral one is about 2/3s the length of the central one.

Caudal furca. The furca is badly damaged, but eight pairs of spines could be identified.

The moulting A-1 stage juvenile female was in a sample from a depth of 500– 100 m at 52° 29’W; 145° 44’W. It has a carapace length of 2.32 mm, a carapace height of 1.40 mm (60.3 % CL) and a width of 1.14 mm (49.1 % CL). It has some faint sculpturing on the surface of the carapace, which is horizontally on the rostrum and oblique on the anterior region of the flanks beneath the incisure. The anterior margin under the incisure is flanged; a characteristic which is typical of both this genus and Chavturia . The shape of the carapace is very similar to that shown in Chavtur and Stovbun (2008, fig. 1A). The left asymmetrical gland opens on a small tubercle located very close to the posterior dorsal corner, but posterior to the posterior end of the hinge between the two carapace valves ( Chavtur and Stovbun (2008) merely stated that it opens close to the hinge). The right asymmetrical gland opens on the smoothly curved posterior ventral corner slight above the lowest point of the ventral margin.

Other trivial discrepancies of this juvenile with Chavtur and Stovbun (2008) are:-

Second antenna. The protopodite is quite short (29.6 % CL), and is shorter than the first exopodite segment (34.5 % CL). In this immature female the first exopodite segment carries a terminal seta, but no such seta is evident in the adult male, nor is it mentioned or illustrated in Chavtur and Stovbun (2008). Hence this is a feature that is either a female or a juvenile characteristic. Many other halocyprid species have such a seta, but its presence has seldom been reported or illustrated by other authors.

Mandible. Two minor features seen in this specimen are missing from Chavtur and Stovbun (2008). They neither figure nor mention the narrow inner tooth on the toothed edge of the basale. They also illustrate the lateral margin of the second large tooth as being smooth, whereas in both the female and male specimens examined here, the margin is corrugated.

Maxilla. Chavtur and Stovbun (2008, fig. 2G) illustrates seven low teeth on the distal margin of the first segment. There were no teeth in the juvenile female but there were at least ten in the adult male examined.

Fifth and Sixth limbs. There were no obvious differences between the fifth and sixth limbs in both the adults and the juveniles and those in Chavtur and Stovbun (2008, fig. 3B, C), but in all the new specimens the limbs were badly contorted. The epipodial formulae for the fifth and sixth limbs (not recorded in Chavtur and Stovbun (2008)) were respectively 4 (+1 short) + 5 + 4, and 7 + 5 + 5.

Caudal furca. This was in good condition in the juvenile. The first pair of spines are the longest; they are sharply pointed and are relatively short (16.3 % CL). The spines diminished very gradually in length dorsally, rather less than in most other halocyprids. Also the arc of curvature of the smallest three pairs of spines reverses. A feature not noted in Chavtur and Stovbun (2008) was that the inner faces of the lamellae are covered with fine setules.

Supplementary observations of the male. There were very few differences between the male specimen and the description given in Chavtur and Stovbun (2008). The shape of the copulatory appendage is as illustrated in Chavtur and Stovbun (2008, fig. 3E), however, there are six oblique muscles compared with four or five described and illustrated in Chavtur and Stovbun (2008). The meristic characteristics of the new adult specimens are listed in Table 2 and compared with those of H. profunda and C. abyssopelagica . Generally measurements of the drawings in Chavtur and Stovbun (2008) have revealed no substantive discrepancies apart from my interpretation of parts of their figure 1. So there are no reasons to consider these new specimens from further east on the North Pacific to be different species. These records extend its known range well into the North-eastern Pacific where they were caught at shallower depths; this may have been because they were caught at higher latitudes than all but one of the Chavtur and Stovbun (2008) specimens.

The juvenile female may have been taken at an atypically shallow depth because it was moulting.

Figures

FIGURE 11. Halocypretta parvirostrata Chavtur and Stovbun, 2008. Female. A. Carapace, lateral view; B. Carapace, ventral view; C, First antenna, details; D, Frontal organ and first antenna; E. Second antenna; F. Mandible; G. Mandible toothlists. Scales in millimetres.

FIGURE 12. Halocypretta parvirostrata Chavtur and Stovbun, 2008. Female. A. Fifth limb; B. Sixth limb. Scales in millimetres.

Tables

TABLE 2. Comparison of meristic characters of male and female Chavturia abyssopelagica n. sp., Halocypris parvirostrata Chavtur & Stovbun, 2008, H. profunda n. sp. and H. striata (Müller, 1906). Characters that distinguish C. abyssopelagica from the Halocypretta species are italicised, and those that in combination distinguish between the three Halocypretta species are emboldened.

Character	C. abyssopelagica		H. parvirostrata		H. profunda		H. striata
	Female	Male	Female	Male	Female	Male	Female	Male
Carapace:
Length range (mm)	3.12– 3.72	3.16– 3.48	3.48	2.7–3.3	3.44	3.16	2.60–2.96	2.56–2.88
Height:length ratio (%)	58.4	57.5	60.3	69.8	66.3	60.8	58.9	58.8
Breadth:length ratio (%)	39.3	40.2	49.1	no data	67.4	no data	56.2	51.5
Rostrum (% CL)	11.7	10.2	12.1	14.0	no data	18.4	10.2	9.7
Incisure (% CL)	8.5	7.5	3.5	8.0	18.4	10.0	8.3	6.2
LAG	near PDC	near PDC	near PDC	near PDC	near PDC	near PDC	near PDC	near PDC
RAG	> PVC	> PVC	at PVC	at PVC	> PVC	no data	at PVC	at PVC
Frontal organ:
Stem (% CL)	15.5	13.8	6.0	4.3	6.3	6.5	6.0	5.0
Capitulum (% CL)	12.9	11.9	21.5	22.8	20.8	21.3	22.4	23.6
First antenna:
Limb (% CL)	16.2	14.9	14.3	no data	no data	no data	13.9	14.9
Dorsal seta (% CL)	6.3	4.9	4.0	3.4	3.9	3.9	4.0	3.8
a–d setae (% CL)	29.0	22.4	26.8	30.5*	29.6	32.9	27.5	33.0
e-seta (% CL)	46.3	47.8	58.2	60.9	64.9	67.4	58.3	66.0
Second antenna:
Protopodite (% CL)	25.1	28.6	25.9	32.6	27.5	30.2	-	32.9
Exopodite 1 (% CL)	26.9	26.6	29.9	33.2	33.3	31.6	28.5	32.6
Exopodite 2–9 (% CL)	7.9	6.8	6.9	7.4	12.2	10.2	9.5	9.2
Swimming seta (% CL)	54.2	49.3	58.2	67.3	58.6	64.4	64.0	42.5
f-seta (% CL)	44.2	39.4	53.7	47.1	52.9	55.2	>49.8	48.8
g-seta (% CL)	53.4	58.5	63.8	69.4	64.9	70.4	71.2	>63.9
h–j setae (% CL)	26.9	23.9	32.2	19.4	28.7	34.5	30.0	31.0
Mandible:
Long terminal seta (% CL)	21.6	19.4	22.4	16.1	22.6	no data	>22.4	no data
Fifth limb:
Long terminal seta (% CL)	11.5	11.3	10.1	13.3	10.3	10.3	11.7	10.5
Sixth limb:
Long terminal seta (% CL)	18.3	16.4	14.6	14.2	13.9	13.8	14.2	13.6
Caudal furca:
Long terminal seta (% CL)	19.4	19.4	no data	16.6	16.6	no data	14.9	no data
Copulatory organ:
Length (% CL)		20.9		29.4		25.3		21.4
Breadth:length ratio (%)		35.7		22.6		18.1		21.3
No. muscles		6		6		3		6

* Value estimated from Chavtur and Stovbun (2008) figure 1C.