Metaconchoecia ampla

Chavtur, Vladimir Grygorjevich, 2003, Morphology and distribution of some new pelagic ostracods of genus Metaconchoecia (Halocyprida: Halocyprididae) from the North Pacific, Zootaxa 229, pp. 1-102 : 45-58

Metaconchoecia ampla nov. sp.

( Figs. 26­35 )

Metaconchoecia skogsbergi: Chavtur, 1977a: 145 ­146 (part); 1977b: 30 (part); 1977c: 20 (part). Metaconchoecia species nov. 4 Chavtur, 1991: 46 (part); 1992: 40, 49, table 2.

Etymology. The specific name “ ampla ”, from the Latin adjective for large refers to size of the carapace.

Holotype. IBM 2808 – adult female, length 1.75 mm, appendages mounted on slide and valves in alcohol, in collection of the Museum of Institute of Marine Biology, Vladivostok, Russia (together, with paratypes).

Type­locality. RV Vityaz 45th Cruise, station 6139, sample 243, lat. 53°11.5’­ 53°21.5’ N and long. 163°09’­ 162°56’ W, depth layer 1500­ 1000 m, June 12, 1969, using a Bogorov – Rass’s Net (S = 1.0 m²).

Paratypes. RV Vityaz 39th Cruise: IBM ­ 2809 – adult female (1.67 mm), station 5635, sample 264, lat. 44 °25’ N and long. 149°10’ E, depth 2500­ 2000 m, September 8, 1966; RV Vityaz 45th Cruise: IBM ­2810 – adult male, IBM 2803 – adult male, IBM 2806 – adult female, same station and sample as holotype; IBM 2804 – adult male (1.70 mm), station 6144,sample 275, lat. 51°42’ N and 167°55’ W, depth 7140­ 5065 m, June 17, 1969.

FEMALE

Carapace ( Fig. 26 A,B). The length of adult specimens range from 1.67­1,. 75 mm. Carapace is relatively elongated. Its maximum height is 47% of the carapace length (CL), and occurs posterior to the midline. Hence the posterior half of the shell is somewhat larger than the anterior half. The maximum width of the carapace is 40% CL and is positioned just posterior to midlength. The shoulder vault is undeveloped. The dorsal margin is broadly V­shaped with the apex just posterior to the insertion of the protopodite of the second antenna. The posterior dorsal corner is a rounded angle with a distinct apex. The posterior margin curves evenly, and the ventral margin is almost straight or slightly curved, curving smoothly into posterior end. The rostrum is minute and has a pointed tip. The rostral incisure is fairly shallow. In ventral view, the sides of the carapace are only gently curved. On the right carapace valve the asymmetric gland opens almost at the postero­dorsal corner, whereas the gland on the left valve is located at a position just posterior to the rostral incisure. There is no surface ornamentation.

Frontal organ ( Fig. 32 A,B). The shaft extends well beyond the end of the fist antenna and is about double the lengths of this limb. The capitulum is separated from the shaft by distinct suture. It is slightly expanded proximally and tapers to a pointed tip. Its dorsal surface is either straight or slightly concave near the middle. Its ventral surface is slightly concave distally. The end is downturned, and the surface of the capitulum is covered with minute spines.

A – lateral view of left valve of shell, B – ventral view of shell, C – frontal organ and 1st antenna, D – distal part of frontal organ and 1st antenna, E – left endopodite of 2nd antenna.

A – distal part of mandible, B – tooth edge of basal endite of mandible, C – toothrows and masticatory pad of coxa of mandible, D – maxilla.

A and B – 5th limb, C – distal part of copulatory appendage, D – furca and copulatory appendage.

First antenna ( Fig. 32 A). The boundary between second and third segments is indistinct. The dorsal surface of the first segment is bare. There is no minute dorsal seta on the second segment. The sensory a­, b­, c­, and d­setae are about 75% the length of the e­seta and are subequal or slightly longer in length than the limb. The sensory setae have thickened bases. The e­seta is about twice as long as the limb and bears short anterior and long posterior spines placed along its middle and distal sections. It tapers to a pointed tip, which is unflattened.

Second antenna ( Figs. 32 C, 33 A,B). The protopodite is without dark pigment spots. The exopodite is very long and about 80(82)% the length of the protopodite. The distoventral corner of the first endopodite segment has three triangular ridges and is covered with fine hairs. The a­seta is somewhat shorter than half the length of the b­seta. Neither a c­ nor a d­ setae are present. The f­, g­, h­, i and j­ setae are subequal, about 50% and 75% the length of the protopodite and exopodite, and about 2.5 as long as the first endopodite segment. They are parallel­sided and have pointed tips. The processus mamillaris on each endopodite is similar to the male..

Mandible ( Figs. 32 D, 33 C, 34 A, 35 B). The coxale cutting edge has a straight anterior section followed by 14­15 teeth.The number of teeth on the distal and proximal list are obscure. The masticatory pad bears four narrow rounded flaps (covered with exceedingly fine, rather short and exceedingly dense spines), four stout teeth, numerous filaments (with bifurcated tip) and hairs. The cutting edge of the basale has two bare tube teeth, the posterior one pointed and the anterior one rounded;these are followed by six serrated teeth, of which the most posterior is rounded and lacks or almost lacks secondary cusps. The anterior inner tooth is also rounded and almost lacks serrations. The epipodite is triangular and developed. The exopodite is represented by stout and plumose seta. It is as long as the first endopodite segment. The dorsal seta on this segment is relatively rather thin, plumose and about half the length of the segment. The longest seta from the three dorsal setae on the second segment is stout and somewhat shorter than the main claw­like seta of this limb. On the dorsal surface of this segment are long hairs.

Maxilla ( Fig. 34 B). The basale has no seta. The length of the first endopodite segment is about 1.5 times the width. At about the middle of the anterior side there are three shorthaired setae. The posterior side bears four short­haired setae. The disto­medial seta extends just beyond tip of the limb. On the ventral surface of this segment there are some short spines. The terminal segment is comparatively short and wide. The anterior claw is about 1.5 times the length of the posterior claw. The structure of the precoxal and coxal endites is obscure.

Fifth limb ( Figs. 33 D, 35 C). The distal, middle and proximal groups of setae of the epipodial plate consist of four, four and three (four?) long and plumose setae respectively and the plate is not (?) covered with some short spines. The first endite of the protopodite bears one long plumose seta (one short short­haired seta is not found, probably, broken), and the second endite carries one long plumose and two short short­haired setae. On the endopodite there are nine setae, two of which are claw­like, three­long and plumose, and remainder are short with short­hairs. The first exopodite segment bears seven ventral, one dorsal short­haired setae, and one lateral seta is armed with long proximal and short distal hairs. The second segment has two ventral and one dorsal short­haired setae. The third segment has two fairly long claw­like setae and a shorter ventral seta.

A – upper lip, B – tooth edge and distal tooth row of coxa of mandible, C – 5th limb, D – 6th limb.

Sixth limb ( Figs. 34 C, 35 D).The distal, middle and proximal groups of setae of the epipodial plate consist of five, five and six (and one additional short) long and plumose setae respectively and the plate is not (?) covered with some short spines. The longer seta on the endopodite is plumose. On the first exopodite segment there are four medium length and one long (distal) ventral setae, one long lateral seta and one medium length dorsal seta (all plumose). The second segment has only one relatively long short­hairede ventral seta, and the third segment is with a short ventral seta and longer dorsal short­haired setae. The terminal segment is somewhat longer than the epipodial plate of this limb.

Seventh limb. This is deformed. The terminal segment bears two setae.

Caudal furca. There are eight pairs of claw­setae and an unpaired seta dorsal to the shortest pair of claw­seta. The inner surface is covered with fine hairs.

Upper lip ( Fig. 35 A). The posterior ventral edge is interrupted by a deep V­shaped notch. On each side of the notch there are some short flaccid spine­like processes, which decrease in strength medially.

MALE

Carapace. This is deformed. The length of adult specimen is 1.73 mm.

Frontal organ ( Fig. 26 C, D). The shaft only reachs the end of the second segment of the first antenna.The capitulum is relatively narrow. Its proximal half is slightly expanded, with a moderatelly convex ventral margin, whereas the distal part is relatively narrow, and either tapers slightly or is parallel­sided. The surface of the capitulum is partly covered with numerous minute spines.

First antenna ( Figs. 26 C, D; 28 A). The segmentation is fairly distinct. The a­seta extends back parallel to the limb (except proximally where it loops down and is slightly swollen) not quite reaching its proximal boundary. The b­seta is slightly longer than the dseta and bears 10 closely spaced various sized anterior spines and has 5 short spines and followed by 5 long closely spaced spines on its posterior margin. The c­seta is relatively thick and short, its length is about a half of the total length of the limb. The d­seta is armed with about 10 closely spaced various­sized anterior spines. The longest e­ seta is about one and a half the length of the limb. The e­seta armature comprises 11 pairs of spines, which lie at an acute angle to the seta. The first segment of the limb contains no dark pigment spots.

Second antenna ( Figs. 26 E, 27 A­D, 28 B). The protopodite has no dark pigment spots. The exopodite is about 80% (83%) the length of the protopodite.The first endopodite segment bears three triangular ridges. The distoventral surface of this segment is covered with fine hairs. The processus mamillaris is bulbous with a beak­like extension pointing slightly forwards. The b­seta is about twice the length of the a­seta and 1.5 the length of the 2nd endopodite segment. The c­ and d­setae are relatively long. The e­seta is large, stout and claw­like. The hook appendage on the right limb is strongly developed with a long curved distal section and a number of subterminal ridges. On the left limb the hook appendage is smaller, with a relatively short straight distal section and no subterminal ridges and terminal verruca. The sensory h­, j­ and i­setae are about 35% the length of the g­seta. The g­seta is subequal to the protopodite, about 1.5 the length of the exopodite and 2.5 of the first endopodite segment. The f­ and g­setae are somewhat flattened distally.

Mandible ( Figs. 28 C­E, 29 A­C). The limb is similar to that of the male, but differs in following respects: the ventral setae on the first endopodite segment and main claw­like seta are somewhat longer. The disto­dorsal seta of this segment is stout and long. The surface of the second endopodite segment is bare.

Maxilla ( Fig. 29 D).The basale and endopodite are similar to the female’s. The most anterior seta on the endite of the precoxale is relatively short and bears very thick secondary setae distally. Its main claw­like seta is bare. There are four posterior bare tube setae. On the posterior process of the coxal endite all teeth are bare.

Fifth limb ( Fig. 30 A, B). Similar to the female’s.

Sixth limb ( Fig. 31 A).The distal, middle and proximal groups of setae of the epipodial plate consist of five, five and six (and one additional short) long and plumose setae respectively and the plate is not (?) covered with some short spines. The longer seta on the endopodite is plumose. On the first exopodite segment there are three short ventral and one plumose long lateral setae. The second segment has a minute ventral seta, and the third segment is with a minute ventral seta and longer dorsal seta lying parallel to the limb. The terminal setae and the limb of the exopodite are subequal.

Seventh limb ( Fig. 31 B). The terminal segment bears two setae. The longest seta is about four times as long as the limb.

Caudal furca (30 D, 31 C) and Upper lip are similar to those of the female.

Copulatory appendage ( Figs. 30 D, 31 D). The limb is straight, relatively narrow and 29% the length of the carapace. Its end is obliquely truncated. The anterior side is distinct concave near the end. There are four oblique muscle bands.

Remarks. This species is closely related to M. skogsbergi ( Iles, 1953) , but Table 10 lists some of the characters that can be used to distinguish between the two species.

Distribution. This is known from the regions of the Kurile­Kamchatka and Aleutian Trenchs at the depth range 1000­7140 m.

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Figures

FIGURE 26. Metaconchoecia ampla nov. sp. (Female: A and B – holotype; Male: C­E ­ IBM 2810)

FIGURE 27. Metaconchoecia ampla nov. sp. (Male ­ IBM 2810) A ­ 2 nd antenna, B and C – distal part of right endopodite of 2 nd antenna, D – distal part of left endopodite of 2 nd antenna.

FIGURE 28. Metaconchoecia ampla nov. sp. (Male ­ IBM 2810) A – seta “ a ” of 1 st antenna, B – a­ and b­setae of endopodite of 2 nd antenna, C and D – mandible, E – tooth edge of coxa of mandible.

FIGURE 29. Metaconchoecia ampla nov. sp. (Male – IBM 2810)

FIGURE 30. Metaconchoecia ampla nov. sp. (Male – IBM 2810)

FIGURE 31. Metaconchoecia ampla nov. sp. (Male – IBM 2810) A – 6 th limb, B – 7 th limb, C – furca, D – copulatory appendage.

FIGURE 32. Metaconchoecia ampla nov. sp. (Female ­ holotype) A – frontal organ and 1 st antenna, B – frontal organ, C – distal part of endopodite of 2 nd antenna, D – mandible.

FIGURE 33. Metaconchoecia ampla nov. sp. (Female ­ holotype) A – 2 nd antenna, B – a­ and b­setae of endopodite of 2 nd antenna, C – tooth edge of basal endite of mandible, D – 5 th limb.

FIGURE 34. Metaconchoecia ampla nov. sp. (Female ­ holotype) A – toothrow and masticatory pad of coxa of mandible, B – endites of maxilla, C – 6 th limb.

FIGURE 35. Metaconchoecia ampla nov. sp. (Female ­ holotype)

Tables

TABLE 10. The comparison of characteristics among M. skogsbergi and M. ampla nov. sp.

Characteristic	M. skogsbergi	M. ampla nov. sp.
Carapace (both sexes): right	opens above posterodorsal corner	opens at (or almost) posterodorsal corner
asymmetrical gland (RAG)
dorsal margin	straight	broadly V­shaped