Comprehensive Description

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Description

Ammothea adunca, new species, Fig. 2.

 

 

Material examined. Aurora Australis: sta. 2 (one male (holotype, SAM 11736)), sta. 25 (one male with eggs / larvae (paratype, SAM 11745)), sta. 57 (two juveniles (paratypes, SAM 11744)), sta. 61 (one juvenile (paratype, SAM 11757)), sta. 71 (one female (paratype, SAM 11746)), sta. 72 (one female (paratype, USNM 234619)), sta. 74 (one male (paratype, USNM 234620)).

 

 

Distribution. This species is from a rarely sampled area of the southern Indian Ocean: the Kerguelen Plateau in the vicinity of Heard Island. The type locality is about 90 km northeast of Heard Island in 380 m. It has also been taken in nearby localities to the northwest and northeast of Heard Island, in depths of 175-800m.

 

 

Diagnosis. Entire integument clothed in short scattered spines except proboscis, chelae fingers, and in areas where setae take their place. Trunk moderately compact, lateral processes narrowly separated, dorsomedian tubercles blunt, eye tubercle low, blunt. Proboscis proximally inflated, distally a slender downcurved cylinder. Chelifores massive, short, fully chelate in adults. Palps 9-segmented, slender, shorter than proboscis. Oviger major segments slightly to moderately curved, most ectal surfaces with fields of short setae, sometimes heavily setose. Legs moderately short, second tibiae longest. Propodus long, slender, without heel and heel spines. Claw about two fifths propodal length, auxiliaries about half main claw length.

 

 

Description. Size moderately large for genus, leg span 163 mm. Trunk moderately compact, lateral processes narrowly separated to as much as half their diameters distally, glabrous. Dorsomedian trunk tubercles prominent, blunt-tipped, not taller than ocular tubercle. Ocular tubercle blunt, eyes darkly pigmented, anterior pair twice size of posterior pair. Proboscis markedly downcurved along distal half, proximally inflated, more ventrally than laterally, distal part slender, tapering to small rounded oral surface. Abdomen large, erect, slightly inflated, without prominent setae.

 

 

Chelifores massive, much shorter than proboscis. Scapes short, inflated. Chelae broad, carried anaxially ventral to scapes, with short, fully formed, tong-shaped fingers.

 

 

Palps slender, 9-segmented, slightly shorter than proboscis. Terminal five segments each smaller and of lesser diameter than last segment, terminal segment spatulate, pointed in ventral view. All segments with groups of very short spines, without longer ventral setae on terminal segments.

 

 

Oviger longer segments moderately curved with fields of short spines or setae. Strigilis recurved on itself, each of terminal four segments shorter and of less diameter than next proximal segment, clothed in crowded ectal fields of short setae.

 

 

Legs moderately short, with no setae but tiny spines over entire leg. Second tibiae longest, with femora slightly longer than first tibia. Cement gland dorsodistal with small slightly raised pore exit. Propodus moderately long, slightly curved, without heel or heel spines. Sole with many tiny spines and few slightly longer spines along its length. All propodi and their spination similar. Claw about two fifths propodal length and auxiliary claws almost half main claw length.

 

 

Female differences: Size little larger in all dimensions and lateral processes more widely separated than those of male. Oviger also typical, but without recurved strigilis, segements linear, each shorter than corresponding male segment except for terminal segment, all with fields of tiny spinules.

 

 

Measurements of holotype (in millimeters). Trunk length (chelifore insertion to tip fourth lateral processes), 14.45; trunk width (across second lateral processes), 11.05; proboscis length, 10.87; abdomen length, 5.77; third leg, coxa 1, 3.5; coxa 2, 6.38; coxa 3, 4.66; femur, 17.35; tibia 1, 15.56; tibia 2, 19.82; tarsus, 1.29; propodus, 5.49; claw, 2.04.

 

 

Etymology. The species name (Latin: adunca, meaning bent inward or hooked) refers to the down-curved proboscis, a rare but not unique character in this genus.

 

 

Remarks. This new species superficially appeared to be a variation of Ammothea striata, but further detailed examination produced a number of specific differences which, when combined, were sufficient to place these specimens in the category of a new species. The principal differences are in the proboscis morphology and curvature. First, the proboscis of A. striata is banana-shaped and without bulges, while that of A. adunca is inflated proximally and quite slender over its distal half or two thirds. Second, the proboscis is only moderately curved from base to tip while that of A. striata is strongly curved downward at about 90° or even at a greater angle. These proboscis differences are consistent among the specimens of each species examined for this report. The proboscis of the new species appears much closer to that of A. profunda from the northern Pacific. Both have inflated proximal areas and tapering slender distal portions while the proboscis of A. profunda is less downcurved than that of A. adunca. These two species otherwise have more differences than the new species has with A. striata.

 

 

Other differences appear in the blunt ocular tubercle of A. adunca and the conical ocular tubercle of A. striata. The chelae are smaller in A. striata in relation to the massive scape in the new species, while they are larger in A. striata. There are few larger sole spines in the new species and a lack of them in A. striata, while the notably shorter second and fourth palp segments in the new species make the palp slightly shorter than the proboscis. The palp in Möbius’ species is longer than the proboscis.” (Child 1994, p.13-15)

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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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