File:The Canadian field-naturalist (1924) (20331218918).jpg

Title: The Canadian field-naturalist
Identifier: canadianfieldnat1924otta (find matches)
Year: 1924 (1920s)
Authors: Ottawa Field-Naturalists' Club
Subjects:
Publisher: Ottawa, Ottawa Field-Naturalists' Club
Contributing Library: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library
Digitizing Sponsor: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library

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January, 1924) The Canadian Field-Naturalist These 2 mm. long metanauplii of Eubranchipus thus correspond almost exactly to the stage of Branchinecta mentioned and figured by Sars (1896, p. 55, Tab. VIII, Fig. 17); but the Eubran- chipus larvae are readily distinguished from the Branchinecta metanauplii by the much longer and thicker first pair of antennae (A); by the more spatulate than oval-shaped labrum (L), and by the different number and shape of the spines (N) in which the tail (T) ends (see above). Although Sars (1896) does not include the body and tail in his Fig. 17, it is clear from the little younger
Text Appearing After Image:
/7^3 stage (Fig. 16) of Branchinecta, that the cercopods (paired process) (C), in which the tail ends, develop much earliei in Branchinecta than in Eubranchipus (where they are first found at a length of 3 mm.), and carry at least 3 spines, as compared to the two spines (N) protruding directly from the tail- end of Eubranchipus larvae 2 mm. long. The colouration of these 2 mm. long metanauplii of Eubranchipus, when alive, was more vivid orange than in the 1; mm. stage, but less so than in the ones 3-4 mm. long. It need hardly be added that the position, when swimming, is partly vertical, partly horizontal, and that the movements are ef- fected both by the second pair of antennae and by the foliaceous legs, the tail not yet being suffi- ciently long and movable to be of much assistance. To illustrate the appearance of v^Vb Eubranchipus gelidus at the stage where it is 3 mm. long, I repro- duce a rough sketch of the young- est specimen collected by Dr. A. G. Huntsman in a pond near Bond Lake, at Toronto, Ontario, on April 10, 1920 (see The Cana- dian Field-Naturalist for February, 1921, p. 28). The same stage was collected by myself at Billings' Bridge, Ottawa, Ontario, on April 13, 1922 (see the same publication for January, 1923, p. 1), and, as mentioned, on April 21, 1923, near Wrightville (Hull), Quebec, (see below). It will be seen from my sketch (Fig. 3), about lOOx, that the two pairs of antennae (A and A A) are still fairly large (1 mm. long), and' the paired eyes (EE) still better set off on peduncles and de- veloped; but that the mandibular palps (Mp) and labrum (L) are now much smaller, and the latter more oval in shape than formerly. On the other hand, the mouth- parts (maxillae and mandibulse) and particularly the foliaceous legs (P) are better developed, all eleven of the latter ones now being free of the abdomen-tail (T) and practically as in the adults, except the last 1-2 pairs. The head and body occupy exactly two-thirds of the total length, and the genital region is better indicated than in the younger stages. Apart from

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