208 
PACIFIC SCIENCE, Vol. XX, April 1966 
Arbacia dufresnei ( Blainville ) 
Fig. 1 
Arbacia dufresnei Mortensen, 1935:579 
(complete list of references); 1936: 215; 1952: 
8; Bernasconi, 1935:12, pi. V, pi. VI, figs. 8-10, 
pi. VII, fig. 4, pi. VIII, figs. 7-11. 
DIAGNOSIS: Denuded test green, radioles 
purple. 
MATERIAL EXAMINED: 11 specimens, from 
Stn. 22 (1); Stn. 27 (1); Stn. 39 (6); Stn. 
52 (3). 
REMARKS: These are typical representatives 
of this well known and attractive species. The 
largest specimen has a horizontal diameter of 
42 mm, and a height of 23 mm, while the 
smallest is 16 mm and 7 mm, respectively. Two 
specimens (both from station 52) carry repro- 
ductive products on the aboral side of the test. 
In one the products are eggs, and in the other, 
sperms. The presence of eggs and sperms on the 
test of A. dufresnei has also been observed by 
Studer ( 1880) and Mortensen ( 1936). A speci- 
men from station 39 is unusual in possessing 
seven anal valves (Fig. 1), while members of 
the family Arbaciidae characteristically have 
four or five. This single variant is apparently 
normal in all other respects. Jackson (1927) 
has reported considerable variation in the anal 
valves in Arbacia punctulata, at least 10% of 
the 10,000 specimens he examined having more 
or less than four anal valves. It is possible 
that a similar degree of variation exists in A. 
dufresnei. 
The characteristic green colour of the test is 
darker in smaller specimens. 
DISTRIBUTION: A. dufresnei is known from 
the southern part of South America, from Rio 
de la Plata in the east to Puerto Montt in the 
west, Antarctica (Booth Wandel Island), and 
the Falkland Islands, in depths ranging from the 
intertidal zone to 315 m. 
Family temnopleuridae Agassiz, 1872 
Pseudechinus Mortensen, 1903 
TYPE SPECIES: Pseudechinus albocinctus 
(Hutton). 
REMARKS: Genus Pseudechinus contains 
twelve species, all of which have a southern 
distribution. Six of the species are apparently 
restricted to the New Zealand region. 
Fell (1958, 1962) has discussed the system- 
atic position of this genus, consequent upon his 
discovery of weakly developed epi stroma in 
three of the New Zealand species, P. flemingi 
Fell, P. albocinctus (Hutton), and P. novaezea - 
landiae (Mortensen). As the presence of epis- 
troma is an important temnopleurid character, 
there is strong evidence for the retention of the 
genus in the Family Temnopleuridae. Morten- 
sen (1943) had supplied some independent evi- 
dence in favour of this systematic position. No 
larval stages are yet known for this genus, but 
they should prove to be of the characteristic 
temnopleurid type. 
Pseudechinus magellanicus ( Philippi ) 
Figs. 2,3 
Pseudechinus magellanicus Mortensen, 1943: 
232, figs. 125, 126a (complete list of refer- 
ences); 1952:9; Bernasconi, 1953:17, pi. VII, 
figs. 2-3, pi. VIII, figs. 1-6, pi. XVIII, figs. 3-4. 
DIAGNOSIS: Denuded test faintly red, radioles 
light red. Tubercles finely crenulate. Valves of 
globiferous pedicellariae each with one or two 
lateral teeth. Apical system with ocular I insert. 
Suranal plate large, naked. 
MATERIAL EXAMINED: 216 specimens, from 
Stn. 19 (8); Stn. 21 (5); Stn. 22 (8); Stn. 24 
(2); Stn. 27 (67); Stn. 29 (1); Stn. 33 (17); 
Stn. 37 (1); Stn. 39 (9); Stn. 40 (5); Stn. 
44 (7); Stn. 49 (1); Stn. 50 (1); Stn. 51 (6); 
Stn. 52 (17); Stn. 66 (7); Stn. 68 (34); Stn. 
73 (12); Stn. 74 (5); Stn. 75 (1); Stn. 77 (2). 
REMARKS: The smallest specimen has a hori- 
zontal diameter of 4 mm, while that of the 
largest is 29 mm. Two distinct size groups are 
represented, the first comprising those speci- 
mens with a diameter of 17-29 mm, and the 
second, those with a diameter of 4-10 mm. 
These probably represent two year-groups. Mor- 
tensen (1952) reported two size groups in a 
collection examined by him, but the groups 
comprised juveniles 2-5 mm in diameter and 
