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Comprehensive Description

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Description

Austrodecus macrum, new species Fig. 7

 

 

Material examined. Eltanin: 27-1929 (one speci­men (paratype, USNM 234599)), 27-1951 (one speci­men (paratype, USNM 234598)), 32-2110 (three specimens (one holotype, USNM 234596, two para­types, USNM 234597)).

 

 

Distribution. The type locality for this species is the Ross Sea (middle) in 2350 m. It is also found along the Ross Sea Ice Shelf in 2273-2284 m and off the Oates Coast of Victoria Land in 1442-1444 m.

 

 

Diagnosis. Of the A. glaciate section. Habitus ex­tremely slender, short lateral processes separated by slightly more than twice their diameters, dorsomedian line of trunk without tubercles, but with few papillae on low hump. Lateral processes with paired dorso­distal low bumps in place of tubercles. Ocular tubercle long, very slender. Palps and ovigers typical. Palps and proboscis moderately short in relation to extreme trunk length. Abdomen very long, with tiny dorso­distal tubercle. Legs very long, slender. Male cement glands not evident.

 

 

Description. Size typical of genus, leg span 5.7 mm. Trunk very slender with groups of papillae in place of dorsomedian trunk and lateral process tuber­cles. Lateral processes only slightly longer than their diameters but separated by slightly more than twice their diameters. Ocular tubercle very long, slender, distal eye area swollen, eyes large, without pigmenta­tion. Proboscis and palps short in relation to exces­sively long slender trunk. Abdomen a very long cylin­der with tiny dorsodistal tubercle flanked by pair of short setae.

 

 

Palps typical, armed with few distal setae and fewer dorsal bumps. Third segment only about 0.6 length of first, armed with 3 curved endal spines. Terminal two segments subequal in length, joined anaxially, armed with few ventral and distal short setae.

 

 

Ovigers typical, approximately the same size in both sexes, terminal segment the longest, armed with 6 short distal setae.

 

 

Legs extremely long, slender, major segments armed with very few setae and typical longer dorso­distal spine. First and fourth coxae 1 pairs with paired dorsodistal tubercles, but most distal tubercle reduced to rounded bump. Second and third coxae 1 pairs with paired slender tubercles of equal size. Second coxae long, almost 3 times length of first coxae. Major leg segments cylindrical, femora the longest segment, male cement glands not evident. Sex pores only evi­dent on fourth legs of any specimen (possibly all are females?). Second tibiae longer than slender propodi which are armed with very few setae, a well curved slender main claw and auxiliaries only about 0.3 length of main claw.

 

 

Measurements (holotype in millimeters). Trunk length (palp insertion to tip of fourth lateral process­es), 1.31; trunk width (across second lateral process­es), 0.48; ocular tubercle length, 0.53; proboscis length, 0.9; abdomen length, 0.41; fourth leg, coxa 1, 0.11; coxa 2, 0.3; coxa 3, 0.09; femur, 0.59; tibia 1, 0.48; tibia 2, 0.47; tarsus, 0.07; propodus, 0.36; claw, 0.13.

 

 

Etymology. The specific name (Latin: macrum, to be lean or thin) refers to the very slender habitus of the new species.

 

 

Remarks. This species appeared superficially at first to be a species of the genus Pantopipetta in its slenderness, but examination of the 6-segmented ovi­gers separated it from that genus, which bears much larger 10-segmented ovigers of an entirely different shape and invariably has much longer lateral process­es.

 

 

This is the most slender species of Austrodecus to be described thus far, and although in most other characters it is more or less typical of the genus, it is unfortunate to be unable at the moment to differentiate the sexes of this new species. They are probably all of one sex and, with no hint of cement gland in evidence, are possibly females. The sex pores on only the fourth leg pair can be discerned with any certainty, a fact which suggests males but which is inconclusive in itself.

 

 

Of the two previously known species in the Ross Sea, this species is more closely related to A. fagei, although both it and A. glaciale are slender species with long ocular tubercles. Neither species has the extreme slenderness of this new species, and both have dorsomedian trunk tubercles, although those of A. fagei are low and not as conspicuous as those of A. glaciale. It can be seen that the slenderness and low trunk tubercles of A. fagei tend to be closer to the extremely slender new species with its lack of orna­mentation and very long ocular tubercle, but there is no known species of such slender habitus and short lateral processes.” (Child 1994, p.68-69)

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© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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