THE CANADIAN FIELD-NATURALIST 



VOL. XXXV. 



OTTAWA, ONT., FEBRUARY, 1921 



No. 2. 



THE LARGER FRESHWATER CRUSTACEA FROM CANADA AND 



ALASKA. 



By Frits Johansen. 

 iCo)iti)iued from Vol. XXXIV, p. 148.) 



in. EUPHYLLOPODA (BrANCHIOPODA) ." 



The Crustacea belonging to this order 

 comprise the three super-families of the 

 "fair}' shrimps"' (Anostraca or Branchi- 

 pididae) the "tadpole-shrimps" (Noto.stra- 

 ca or Apodidae), and the "clam-shrimps" 

 (Conchostraca or Limnadidae (Estherii- 

 dae). Most of the species are of a fair size 

 and easily observed at the right time of the 

 year by any one interested in freshwater 

 life. 



They derive their name from the fact 

 that most of the appendages ("feet") 

 behind the mouth parts are peculiarly 

 formed so as to serve as respirator}- or lo- 

 comotory organs, being divided up into 

 many hairy leaves or flagella. When pre- 

 sent the tail has no appendages, with the 

 exception of its last joint, and the body is 

 composed of a great number of segments. 



From olden time, these interesting Crus- 

 tacea have attracted both laymen and 

 scientists, not only because of their pecu- 

 liar biology (seasonal occurrence, etc.), 

 but also because they have been considered 

 as representing a very ancient type of 

 Crustacea, if not the origin of that numer- 

 ous and widely distributed class. At any 

 rate, fossil remains of these Crustacea or 

 similar forms have been found in deposits 

 of great age; viz. Conchostraca from the 

 Devonian, Notostraca from the Trias, and 

 the Anostraca from the Oligocene (Ter- 

 tiary) on. 



The first important works on these Crus- 

 tacea were published bj' the Danish Zoo- 

 logist 0. F. Muller in the latter part of the 

 18th century ; since then a great number of 

 workers in different countries have studied 

 them very carefully, of whom G. 0. Sars 



in Norway, W. Baird in England, C. C. 

 Claus in Germany, E. Daday de Dees in 

 France, and A. S. Packard in the United 

 States, have probably contributed most 

 (see bibliography). 



A. Fairy-shrimps. 



The first sub-order (super-family) Anos- 

 traca is easily distinguished from the two 

 others by the lack of a shell (carapace) 

 and by the elongated shape of the body, in 

 which the head is distinctly marked off. 



The general form of these "fairy- 

 shrimps" has been often described and 

 may be assumed to be fairly well known, ^ 

 so that only the essential points need be 

 referred to here. The head carries two 

 pairs of feelers (antennas) of which the 

 first pair is short and slender, but the se- 

 cond pair much longer and stouter and is 

 in the males extraordinarily developed as 

 clasping organs (for use during copula- 

 tion), and of greatly varied form often 

 with accessory appendages, etc. On the 

 front end of the head is situated a simple 

 unpaired, median eye, remnant of the large 

 nauplius-eye of the larval stage. More 

 conspicuous, however, are the two large, 

 composite eyes on short peduncles which 

 are very movable and have brilliant, metal- 

 lic colours. The mouth (on the under side) 

 is supplied with various masticatory parts 

 (maxillae, mandibles, etc.), and behind 

 them follows a greater (11 or 17-19) num- 

 ber of ambulatory trunk-limbs, the foli- 

 aceous, hairy legs, of which the first and 

 last pairs are the shortest. They are admir- 



1 See Ottawa Naturalist, July. 1895 (A Hal- 

 kftt) and April, 1890 (E. E. Prince). 



