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In the females, two of the six apical spines on the first maxilliped, in addition to being 
furnished with rows of very short spinules, have also a number of moderately long and con- 
spicuous spinules. The males of typical Auchaeta are easily separated from those of the next 
genus, by the exopodite of both the right and left fifth foot terminating in a long spiniform joint. 
Seven species of typical Euchaeta were obtained from the plankton collected by the 
‘Siboga’ in the Malay Archipelago. 
1. Luchaeta acuta Giesbrecht. Plate XX, figs. 1—g9. 
Euchaeta acuta Giesbrecht, 1893, p. 246, pls. 16 & 37. 
Euchaeta acuta Giesbrecht & Schmeil, 1898, p. 38. 
Euchaeta acuta \. C. Thompson, 1903, p. 18. 
Euchaeta acuta Thompson & Scott, 1903, p. 244. 
Euchaeta acuta Wolfenden, 1904, p. III. 
Euchaeta acuta Cleve, 1904, p. 190. 
Euchaeta acuta Sars, 1905 (a), p. 4. 
Euchaeta acuta Farran, 1905, p. 35. 
Euchaeta acuta Esterly, 1905, p. 157, fig. 23. 
Euchaeta acuta Pearson, 1906, p. 17. 
Euchaeta acuta Farran, 1908, p. 40. 
Euchaeta acuta van Breemen, 1908, p. 51, fig. 56. 
This species appeared to be very rare in the area traversed by the ‘Siboga’. Only one 
female and three males were obtained. The specimens were found in the plankton collected with 
the HENSEN vertical net at the following stations. 
Stat. 141 (1500 metres to surface). — Stat. 148 (1000 metres to surface). — Stat. 185 (1536 
metres to surface). — Stat. 203 (1500 metres to surface). 
The female of Luchaeta acuta resembles Euchaeta media very closely, but it can be 
distinguished from it by the peculiar shape of the genital segment, when viewed from above. 
The proximal margin of the left side is produced into a blunt process, which is distinctly notched 
on the anterior surface. The posterior margin of the last thoracic segment appears evenly rounded 
when seen from above, and from the side. The outer-edge spine on the second joint of the 
exopodite of the second pair of feet, scarcely extends to the base of the first outer-edge spine 
on the third joint. The second outer-edge spine on the third joint does not extend to the base 
of the third outer-edge spine. The appendicular seta on the furcal joints is longer than the 
others. Leneth, female 4,2 mm. 
According to the records, Euchaeta acuta has apparently a wide distribution in tropical 
and temperate seas. 
2. Luchaeta concinna Dana. Plate XIX, figs. 21—27. 
Euchaeta concinna Dana, 1849, p. 21. 
Euchaeta concinna Giesbrecht, 1893, p. 246, pls. 15, 16, 37- 
Euchaeta concinna Giesbrecht & Schmeil, 1898, p. 39. 
Euchaeta concinna Cleve, 1901, p. 7. 
Euchaeta concinna Thompson & Scott, 1903, p. 244. 
Euchaeta concinna Cleve, 1903, p. 363. 
Euchaeta conconna Wolfenden, 1905 (a), p. 1008, pl. C, fig. 1—6. 
SIBOGA-EXPEDITIE 
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XXIX a. 9 
