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Comprehensive Description

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Description

“LEIONYMPHON GLACIALE.

 

(Plate VII., fig. 3.)

 

 

Specific characters :‑

 

Body well built, with three very prominent transverse ridges produced to a point in the mid-dorsal line. Lateral processes rather widely separated, and with the stumps of spur-like processes distally.

 

Proboscis large, but shorter than the body, pyriform.

 

Palps 9-jointed, the five terminals being sub-equal in size.

 

Oviger 10-jointed (not mature).

 

 

This is a large and comparatively slender species.

 

 

The Body is well built with the lateral processes rather widely separated, and traversed by three very prominent pyramidal ridges which conceal the segmentation. These ridges are directed backwards to a very slight extent and excavated posteriorly; it is in the hollow thus formed that the segmental divisions may be seen. Three ridges are equally prominent ventrally, but they are not produced to a median point.

 

 

The Cephalon is not very much expanded, and a neck is not noticeable.

 

 

The Ocular tubercle is stout, not as tall as any of the three transverse ridges, and bears four well-developed eyes, above which it terminates in a short cone.

 

 

The Abdomen is rather long, directed obliquely upwards, not separated from the trunk by an articulation, and terminating in a blunt point. The cephalon bears a small blunt tubercle at its anterior margin on the outer side of the base of the chelifori, a pair of similar tubercles occur dorsally at the extremity of the lateral processes ; smaller ones also on the first coxae with traces of them on the second. The length of the body is 12 mm., its extreme width is 7 mm. The entire body is scabrous, a feature most distinctly noticeable on the transverse ridges and the abdomen.

 

 

The Proboscis is large, rather pyriform in shape, and measuring 10 mm. in length. It is movably articulated to the body on a large base, and widens slowly for one-third of its length where it is very slightly constricted ; it is then enlarged again, and tapering very slightly, ends in a rather broad round point, the triangular mouth being of moderate dimensions. The proboscis is smooth, and its distal .two-thirds are marked by three pairs of longitudinal bands, transversely divided near the tip.

 

 

The Chelifori are rudimentary and lie close together above the proboscis. The scape is short, slightly curved and enlarged distally ; the chef are well developed, as long as the scape, one half of their length is taken up by a bulbous palm ; the fingers are slender, quite smooth and much curved, but those of the two appendages are not exactly alike. With the exception of the fingers the entire appendage is scabrous.

 

 

The Palps arise laterally just outside the chelifori, and comprise nine joints (fig. 3a). The first is short and stout, the proportions of the second and fourth are as 8 to 11, the third being but little longer than the first ; the remaining five are short and sub-equal, the middle one and the last being a trifle the longest, together they scarcely equal the length of the fourth. The fourth joint possesses a prominent tubercle with a glandular opening at two-thirds of its length. The entire appendage

 

is more or less plentifully clothed with very minute spinous setae ; these however are only conspicuous on the ventral margin of the five terminal joints and at the end of the terminal one.

 

 

The Oviger is ten-jointed and rises ventrally immediately in front of the first lateral process, and appears to be that of a female (fig. 3b). It is not fully developed. The first joint is short and stout, the two following are twice as long and sub-equal, the third having the usual oblique termination. These three joints form a natural curve in one direction, and the three following curve in another. Measured in their extreme length the proportions of the various joints of the appendage are : 3 : 6 : 6 : 8 : 7.75 : 7 : 4 : 4 : 2.5 : 4. The third and following joints are all more or less covered with very short stout setae on the outer side of their curvature; these setae are most con­spicuous on the fourth, fifth, and sixth joints, on the last of which they are also lateral. The last four joints each bear a small number of stout but simple spines, 4 : 8 : 7 : 6, not arranged in a single row. The last joint tapers to a blunt point, and is without a terminal claw, a small group of these spines taking its place.

 

 

The Legs attain a length of about 55 mm. Of the three coxae the second is twice the length of the other two, the proportions of the remaining joints being 13.5 : 12 : 16 : 4, the last figure representing the tarsus and propodus together. The coxae are densely clothed with very minute setae, but on the femur they are much larger, though still small, and more conspicuous. They are arranged as a dorsal and a ventral band, separated laterally by a considerable interval, along the centre of which is a narrow band of similar set. This arrangement is continued along the tibiae but it is not so distinct on the second. The distal fringes are quite normal and inconspicuous. The tarsus is a very small cup-like joint, covered with spinous setae ventrally, with a few prominent ones distally. The propodus is uniformly covered with small spinous set, but ventrally there is a row of stout spines running the whole length of the joint. These spines are very irregular; beginning from the proximal end the first three or four rapidly increase to large dimensions, the rest are very irregular in size, but none are so large as the last of the proximal series. The joint terminates obliquely, the dorsal projection is not large; the terminal claw is stout, and its two auxiliaries are quite half as long, arising together from a process of the oblique termination.

 

 

The single specimen of this species is immature, and was taken in Winter Quarters at a depth of 125 fathoms.” (Hodgson 1907, 50-52)

 

 

Ammothea glacialis (Hodgson).

 

 

Leionymphon glaciale, Hodgson, 1907, p. 50, Pl. vii, fig. 3.

 

Ammothea glacialis, Bouvier, 1913, p. 123.

 

 

Occurrence. – Station 194, off Oates Land, 180-200 fathoms; 1 young. Station 220, of Cape Adare, 45-50 fathoms, 1 immature, Station 314, McMurdo Sound, 222-241 fathoms; 5 immature. Station 318, McMurdo Sound, 130-180 metres; 1 young. Station 322, McMurdo Sound, 20 meters 1 female. Station 338, Entrance to McMurdo Sound, 207 fathoms. 2 female, 2 male (ovig.), 3 immature. Station 340, off Granite Harbour, 160 fathoms, 2 female, 1 male (ovig.), 2 immature, 1 young. Station 355, McMurdo Sound, 300 fathoms; 1 male (ovig.), 3 immature. Station 356, off Granite Harbour, 50 fathoms, 1 young.

 

 

Remarks. – This species has hitherto been known only by the immature holotype obtained by the “Discovery: and an adult female recently recorded by Hodgson from the “Gauss” collection. It is the most abundant species of the genus in the collections of the “Terra Nova.”

 

 

Adult specimens are little larger than the holotype, with which they agree except as regards the chelophores and, in the males, the ovigers. The form of the proboscis is better indicated by Hodgson’s description than by his figure. The ovigers of the male have the distal segments modified as in other species of the genus; the terminal segment is little longer than the preceding.

 

 

Measurements, in mm., of adults from Station 338. –

 

                                                                           
 

 
 

Female

 
 

Male

 
 

Length of proboscis

 
 

12

 
 

10.5

 
 

“ trunk

 
 

9

 
 

9.5

 
 

“ abdomen

 
 

4

 
 

3.5

 
 

Third right leg -

 
 

Coxae

 
 

11.5

 
 

11

 
 

Femur

 
 

17.25

 
 

15

 
 

First tibia

 
 

14.5

 
 

13.5

 
 

Second tibia

 
 

19

 
 

18.5

 
 

Tarsus and propodus

 
 

4.72

 
 

4.8

 
 

Main claw

 
 

2.32

 
 

2.4

 
 

Auxiliaries

 
 

1.24

 
 

0.92

 
 

Palp -

 
 

Second segment

 
 

4.8

 
 

4.4

 
 

Fourth segment

 
 

6.28

 
 

5.72

 
 

 

Young Stages. – Four very young specimens included in the list given above (Stations 194, 318, 340, and 356) are only referred to this species with some doubt. Their most conspicuous character is the presence on the legs of coarse short spines set in longitudinal rows; in the smaller specimens each spine is elevated on a conical prominence. The double dorsal tubercles of the lateral processes and first coxae are also beset with short spines. The proboscis is about as long as the trunk, conical in the smaller specimens, but becoming slightly pyriform in the larger, decurved, with a slight construction at one-third its length from the base. The transverse body-ridges have acute spine-like median processes as tall as the ocular tubercle. The fourth segment of the palp is not more than one third longer than the second. The ovigers are represented only by minute buds.

 

 

In their spiny armature, these specimens resemble those described by Bouvier (1906, p.20) as A. curculio, but afterwards (1913, p. 127) regarded by him as the young of A. gibbosa. They differ, however, in the form of the proboscis, which, in our specimens, is much stouter, and in the larger specimens shows a tendency towards a pyriform shape; further, in our largest specimens the second segment of the palp is three-quarters as long as the fourth, while in specimens of A. gibbosa, only a little larger, the proportion, in Prof. Bouvier’s figure, is less than one-half.” (Calman 1915, p. 50-51)

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Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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