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Description

“Leptoecia antarctica, n.sp.

 

St. 177. 5. iii. 27. 27 miles SW of Deception Island, South Shetlands. 63° 17' 30" S, 61° 17' 00" W. 1080 m. Gear DLH. Bottom: mud and stones. Sixty specimens.

 

DESCRIPTION. Ten specimens and about 50 tubes with an average length of 60 mm. and a diameter of 2 mm. The tubes have stout and very resistant walls of mud, from which it is difficult to extract the animal. The ten specimens free of their tubes must have been removed from them by the collector probably while the animal was alive. Most of the tubes contain a specimen.

 

The largest specimen examined has 56 chaetigers and measures 33 mm. by 2 mm. including the feet. The body is slender and flattened and in spirit there are no colour markings. There are two globular palps, two ovoid anterior tentacles and five occipital tentacles with short ringed ceratophores. The inner lateral tentacles reach back to the 6th chaetiger ; the median tentacle is about half their length and the outer laterals about one-third. I can find no trace of eyes. The buccal segment is longer than the pro­stomium and about equal in length to the following segment. It is not surpassed by the 1st foot. There are no tentacular cirri and no branchiae.

 

The first three chaetigers (Fig. 50, a) have a cirriform posterior lip to the pedal lobe and a tapering ventral cirrus, both of which decrease in size rapidly from before backwards. The dorsal cirrus also grows increasingly shorter till about the 7th foot, where it is a digitiform process reaching to the tips of the bristles. It retains this form through­out the rest of the body. Behind the 3rd foot the ventral cirrus is modified into a glandular pad.

 

The 1st foot has a few simple capillary bristles and a number of curved hooded bidentate crochets (Fig. 50, b) with a feeble pseudo-articulation. These are continued to the 4th chaetiger (Fig. 50, c) in which a single broadly bilimbate capillary bristle also occurs. The 5th foot has bilimbate capillary bristles only.

 

At the 10th foot there is a small dorsal group of comb chaetae (Fig. 50, d) with numerous short closely set teeth, a number of the usual twisted bilimbate capillaries (Fig. 50, e) with slender tips, and a pair of yellow hooded bidentate hooks (Fig. 50, f and g) . In the posterior feet the comb chaetae seem to be absent and the capillary bristles are narrower.

 

The dental formula is as follows : 7-7 : 9 + 5-8 (Fig. 50, h). The teeth and the junction of the carriers are dark brown, but the plates are pale yellow. The under jaws (Fig. 5o, i) are delicate translucent structures, except for a pair of dark chitinous pieces at the anterior end.

 

REMARKS. Chamberlin established the genus Leptoecia to include forms resembling Hyalinoecia but without gills.

 

The present species is near to Leptoecia abyssorum, Chamberlin (1919, p. 320), collected at a depth of 2005 fathoms between the Galapagos and Peru. It differs from Chamberlin's species in that the curved anterior crochets are continued to the 4th chaetiger and are feebly pseudo-compound : in L. abyssorum they are unjointed and confined to the 1st foot. Moreover, the number of teeth in the jaws is higher in Chamberlin's species. The only records of this genus are the present one and that of Chamberlin. It appears to be abyssal.”

 

(Monro, 1930)

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© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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