Scottoecia arabica, Angel, 2012

Angel, Martin V., 2012, Scottoecia-a new genus of halocyprid ostracod, with the description of Scottoecia arabica nov. sp. and the redescription of Bathyconchoecia darcythompsoni (Scott, 1909), Zootaxa 3254 (1), pp. 32-54 : 34-41

Description of Scottoecia arabica new species

( Figures 1–4 )

Synonymy non 1908 Euconchoecia lacunosa Müller : 80–81, Pl. 10, figs 1–8.

1973 Bathyconchoecia lacunosa James : 436–440, figs 1a–n; 2a–f.

Male. Carapace The carapace length (CL) of the specimen from the Gulf of Oman is 3.44 mm ( Fig. 4A, B ) with a height of 1.60 mm (46.5 % CL), and a breadth of 1.32 mm (38.4 % CL).

There is overall a faint scaly pattern sculpture and two striae run parallel to the ventral margin. The posterior dorsal corner is rounded with the hinge between the valves ending very close to the posterior dorsal corner. The ventral margin curves smoothly, but maximum carapace height is towards the rear. The rostrum is well developed. From the anterior end of the hinge to tip of rostrum is 13.1 % CL, and is slightly shorter than the depth of the incisure (15.7 % CL). Below the incisure the anterior margin does not extend forward of the inner edge of the incisure, whereas James (1973) shows a slight anterior extension. The shoulder vaults are undeveloped, but between them on the hinge line at midlength is a shallow sulcus. The carapace glands open via keyhole shaped openings in the inner margin of the posterior margin. They are positioned symmetrically on each carapace valve 0.36 mm (10.5 % CL) below the hinge-line.

Frontal organ is absent.

First antenna ( Fig. 1C ). The limb’s overall length is 24.2 % CL, and it appears to consist of 6 segments. All the segments are bare, but the first segment has a clear swelling on its ventral side. Within the second and third segments is a large oval ganglionic mass, which enervates the pad setae, and is full of black pigment granules. The pad carrying these setae appears to be on the fourth segment (note: Poulsen (1969b) based on the musculature argues that the pad is carried on the fifth segment in Bathyconchoecia baskiae , which is fused with the fourth; since there is no suture delineating these two segments, it is referred to as the fourth segment herein). The setae are arranged in about 8 rows each of about 23 setae, but exact enumeration is impossible. These setae are about 25.7 % CL long, and are arched so as to model the inner contours of the body and carapace. The fifth segment carries a plumose seta (13.3 % CL), about half the lengths of the pad setae. There is a pair of terminal setae on each of the last two segments. The longest of these terminal setae is thick and 43.8 % CL, nearly double the lengths of the pad setae. The other three terminal setae are bare and 24.0, 17.0 and 16.0 % CL respectively.

Second Antenna ( Fig 1D ). Protopodite is ham-shaped and quite short (36.2 % CL), and is almost as broad as it is long. The basal half of the first exopodite segment (43.3 % CL) is slightly curved, but distally it is straight. It has a small terminal seta that curves around the suture between the first and second segments. Segments 2–9 carry the swimming setae and have a combined length of 6.6 % CL. The ninth terminal segment carries three short and slim setae (not shown) in addition to a long swimming seta. The shortest of these setae is bare, but the longer two carry numerous short spinules, a feature that seems to be unique. On the protopodite close to the insertion of the endopodite is a patch of fine setules.

The first endopodite segment is rectangular and ~38 % length of protopodite (13.7 % CL). There are two terminal setae of which the proximal a-seta is much the shorter and is finely spinose. The b-seta is 0.19 mm long and about a third the length of the first endopodite segment and x1.7 the a-seta. It is densely plumose along its whole length. The second endopodite segment is oval and is a little shorter (0.18 mm) than the b-seta. It has two tiny setae inserted at mid-length close to the bases of the hook segment and two terminal setae that are exceptionally long, 75.5 % CL and 34.7 % CL respectively. On the left antenna the hook segment ( Fig. 1F ) has a short hasp on the end which are inserted three sub-equal slim setae with lengths of 24.2, 13.6, and 9.1 % CL respectively. The distal part of the hook is rather flimsy and curves back to a rounded and smooth end. On the right antenna the distal part of the hook ( Fig. 1E ) is more robust. It is angles back about 120° from the hasp and then after being straight for much of its length, it re-curves towards its rounded end.

Mandible ( Fig. 3E ). This limb is not sexually dimorphic. In the male specimen both the left and the right mandibles are damaged, so this description is mainly based on the female’s limb. The first endopodite segment terminally carries a dorsal seta that is finely spinose and extends to the end of the limb. The dorsal face is indented at two-thirds its length, and on the basal half are fine short setules, which point distally on the outer face and ventrally on the inner face. Ventrally, there is a pair of moderately long setae placed medially, one on either side, and distally there are two shorter bare setae on the inner face. The second segment has a median ventral seta, and three terminal setae on the dorsal side, one is long coarsely spinose and claw-like, the other two are shorter, slimmer and finely spinose. The terminal segment has the usual seven terminal setae. Dorsally there are two long, spinose and claw-like setae with an intermediate short, slim seta. The ventrally four setae are shorter and bare, but one of them is stouter and longer than the others.

The structure of the toothed edge of the basale ( Fig. 3F ) typifies the genus. There are two inner spine setae, one pointed, the other blunt. They are adjacent to a cutting tooth armed with secondary serrations and fine setules. These three are well offset from the other five elongate cutting teeth. The outermost of these cutting teeth is on the end of an isolated spur, which is covered with fine setules. At the midpoint of the spur a moderately long seta is inserted, and another is inserted near its base. There are another two short setae on the outer face of the basale. At its distal end close to the suture between the basale and the endopodite, there is a stout inner seta, and on the outer edge three plumose setae, one slightly offset from the other two. These three setae are located where there is a single seta often on a small process in Conchoeciinae , which is interpreted as being a vestigial exopodite.

The outer tooth list ( Fig. 4C ) on the coxale consists of two large and four smaller pointed teeth. The proximal list consists of two large teeth and about 4 smaller one. The masticatory pad is large, oval and covered with short, rather blunt, stubby spines, fringed by fine spiny setules around the inner margin.

Maxilla. This limb was too contorted to be drawn. On the anterior face of the basal segment are three basal plumose setae, and another plumose seta placed distally (note: in the female there are four basal setae, so in this specimen one seta may have been lost). There are a few setules between the basal group of setae and the distal one. On the posterior face there is a row of three bare setae, in the female there is another single seta inside the row, which was absent (probably lost) in the male. The terminal segment has a covering of fine short spines and carries two stout terminal claw setae which are flanked on each side by a pair of slim setae.

Fifth Limb ( Fig. 2A ). The epipodial setae are in three groups of 5, 4 and 4. The basale terminally carries a long bare dorsal seta (that is the remnant of the exopodite), and two moderately long plumose setae. On the inner face are two lateral setae that point basally. On the ventral margin there are two short setae. The first of the three endopodite segments carries a pair of ventral setae. The second segment has three ventral setae that are almost medial, and a short distal, subterminal seta. The third terminal segment carries the usual three terminal setae. The dorsal two are similar in length 10.3 % CL, and the shorter ventral seta is a third their lengths.

Sixth limb ( Fig. 2B ). The epipodial setae are arranged in three groups each of 5 setae. The basale has three plumose lateral setae on one side and one more on the other, and there is a short dorsal seta. The first segment has just two pairs of ventral setae. The second, penultimate segment is unusually long and slim (height is 11 % the length) with ventrally a pair of short medial setae, and a short slim, subterminal dorsal seta. The terminal segment carries three terminal setae. The two ventral setae are quite short (8.5 % CL), but the dorsal seta is exceptionally long (31.4 % CL and 150 % limb). It is arched terminally ( Fig. 2C ) and the distal half of its inner surface is uniquely lined with a double row of about 125 squarish spines ( Fig. 2D ).

Caudal furca ( Fig. 2G ). There are the usual eight pairs of caudal furca spines, which are only slightly curved. The longest first pair of spines (16.0 % CL) is offset from the others. Each of them has about four internal septa and is lined with short stout spines. The second pair project slightly beyond the ends of the first and lack the internal septa. Like all the other spines they are lined with short fine spines, and the spines decrease in length systematically. There is a dorsal unpaired seta some way from the last pair of spines.

Copulatory appendage ( Fig. 2E, F ). The appendage is rectangular in shape. It is 0.62 mm (18.1 % CL) long and 0.09 mm wide. The main shaft is free of musculature, but there are three oblique muscles in its base. The end piece, which curves around and protects the stylet, is rounded and toothed along its inner margin.

Female. Carapace ( Fig. 3A, B ). The carapace is shorter than the male’s. The length is 2.98 mm, the height is 1.58 mm (53.0 % CL) and the breadth is 1.30 mm (43.6 % CL). Unlike in the male, the anterior margin of the carapace does extend forward of the internal margin of the incisure. Otherwise, most of the carapace characters are very similar to those of the male.

Frontal Organ. There is no frontal organ.

First antenna ( Fig. 3C ). Its overall length is shorter (16.1 % CL) than in the male. The setation is similar, but the longest terminal seta is not as long. There are numerous black pigment cells extending to bases of pad setae. The pad setae are 25.8 % CL, the dorsal seta is 16.7 % CL and the four terminal setae are 36.5, 21.1, 21.2, and 19.5 % CL respectively

Second antenna ( Fig. 3D ). As in the male the protopodite is drop-shaped (35.2 % CL). First endopodite segment is rectangular (and a third the length of the protopodite), and its two terminal setae are very different in length. The a-seta, which carries short spinules, is only a third the length of the b seta, which is 3.9 % CL and has long setules on its basal quarter and fine spinules along most of the rest of its length. The second endopodite segment is a little shorter than the b-seta and has a short spine at its midpoint. Terminally it carries five setae - the h-, i-, and j-setae are slim, finely spinose, and quite short 23.8, 9.4, and 9.1 % CL, respectively. The longer, thicker g-seta and f-seta are both bare with lengths of 64.4 % and 38.9 % CL, respectively. The first exopodite segment (17.8 % CL) is slightly curved and has a short terminal seta adjacent to the suture with the second exopodite segment. The remaining eight exopodite segments (8.4 % CL) each carry a swimming seta. The last segment also has three additional short setae with are all finely spinose.

Labrum. As in the male the labrum is almost flat with about 14 fringing straight spinules.

Mandible ( Figs 3E, F and 4C ). This limb was better preserved than the male’s and appears to have the same structure. The longest of the setae on the terminal segment is 23.2 % CL, and is almost the same length as the limb.

Maxilla (not illustrated). Anterior margin of first segment has five (3 basal + 1 + 1) setae – the two single setae are plumose. Posteriorly there is a single bare seta and a row of three plumose setae. The terminal seta is covered with short fine bristles and ends in two broad hook setae subtended on either side by a pair of slim setae.

Fifth limb ( Fig. 4A ). The epipodial setae are in three groups of 5, 4 and 4 respectively. The basale has two ventral setae, two bare lateral setae on one side and a plumose seta on the other. The plumose seta is inserted near the distal end of the segment and close to the base of the long dorsal seta. The first segment has a pair of medial ventral setae and a subterminal lateral seta. The second segment has three medial setae, two of which are ventral and one is lateral. The third segment has three terminal setae. The central seta is thicker than the others but very similar in length (11.1 % CL) to the dorsal and a little longer than the ventral one.

Sixth limb ( Fig. 4B ). The basale has three lateral setae, dorsally a plumose seta, and a very long bare seta that extends to the end of the limb. The first segment has a line of three ventral setae and two lateral setae, but no dorsal seta. The second segment is very long and thin; it has two medial ventral setae, and subterminally a dorsal seta. The last segment has three terminal setae of which the central one is the longest (13.8 % CL).

Seventh limb. The limb is quite short and the suture between the two segments is indistinct. However, the terminal segment is densely covered with short bristles, and its two setae are not very different in length.

Caudal Furca. As in the male there are eight pairs of spines all with secondary spines. The first pair is the longest (17.1 % CL), and are quite curved and have four internal septa. The remaining seven pairs are almost straight and lack septa. There is a long unpaired seta.

Figures

FIGURE 1. Scottoecia arabica n. sp. Male (Holotype Charles Darwin Station 54002#1 200–250 m). A. Carapace lateral view; B. Carapace ventral view; C. First antenna; D. Right second antenna; E. Detail of hook appendage on the endopodite of the right second antenna; G. Detail of the left hook appendage. Scales in mm.

FIGURE 2. Scottoecia arabica n. sp. Male (Holotype Charles Darwin Station 54002#1 200–250 m). A. Fifth limb; B. Sixth limb; C. Sixth limb dorsal terminal seta enlarged; D. Detail of armature on sixth limb dorsal terminal seta; E. Copulatory appendage; F. Detail of end of copulatory appendage; G. Caudal furca. Scales in mm.

FIGURE 3. Scottoecia arabica n. sp. Female (Paratype Charles Darwin Station 54002#1 200–250 m). A. Carapace lateral view; B. Carapace ventral view; C. First antenna; D. Second antenna; E. Mandible; F. Toothed edge of the basale of the mandible. Scales in mm.

FIGURE 4. Scottoecia arabica n. sp. Female (Paratype Charles Darwin Station 54002#1 200–250 m). A. Fifth limb; B. Sixth limb; C. Mandible tooth lists and masticatory pad. Scales in mm.