Aggregate Form of Ritteriella picteti — Berner 
123 
Uj 1 
Fig. 3. Ritteriella picteti, aggregate from, oral mus- 
culature. IM, intermediate muscle; Li etc., oral sphincter 
muscles of the lower lip; OR, oral retractor; Ui etc., 
oral sphincter muscles of the upper lip. 
lower lip are made up of a narrow muscle, 
Li, a wider muscle, L2, and a wide muscle, L3. 
The oral retractor passes internally to the 
broad intermediate muscle which is discon- 
tinuous both dorsally and ventrally. The hor- 
izontal muscles are independent and run from 
the region just behind the last dorsal oral 
sphincter to about the region between the 
ends of the first body muscles. 
Internal Structure'. The gut forms a com- 
pact nucleus in which the course of the 
intestine cannot be clearly traced without dis- 
section. The oesophageal opening, at the base 
of the gill, is wide and slightly flared. The 
anal opening is situated on the anterior left 
side of the gut nucleus. The dorsal tubercle 
is of typical form, elongate and slightly curved 
in dorsal view. The dorsal ganglion is much 
like that figured by Metcalf (1918) for K. 
amboinensis. The endostyle is rather straight, 
sharply hooked at the anterior end and slightly 
hooked at the posterior end. It extends from 
a point below the lower lip to the area pos- 
terior to the bifurcation of muscle IV. There 
is one embryo placed laterally in the area 
between muscles V and VI. 
COMPARISON WITH OTHER SPECIES 
In comparing this species with R. amboinen- 
sis, the other member of the genus, one finds 
the two very similar. There are certain char- 
acteristics, however, that show striking 
differences; the body muscle bands in R. pic- 
teti are wider and composed of more fibers. 
Two typical individuals are compared in the 
table below. 
The large number of fibers in muscle VI of 
R. picteti before its division might indicate 
that there are in reality two muscles involved 
and that the posterior branch might be num- 
bered VII. It is felt however that, because of 
the long-established convention in numbering 
muscles, the normal order should be main- 
tained even though the muscle might be 
subdivided. Although the number 'of muscle 
fibers is not constant from specimen to spec- 
imen, the greater width of muscle bands and 
greater number of fibers in the specimens of 
R. picteti QxdLmmtd has been a constant feature. 
This variation in muscle-band width was also 
observed to a lesser extent in the solitary 
forms examined. The cross banding on the 
gill bars of I?. appears to be more closely 
spaced than that on the gill bars of R. am- 
boinensis. The oral musculature of the two 
species is quite different, having three 
oral sphincters on each lip whereas R. am- 
boinensis has only two. 
The greatest difficulty encountered has not 
been in the differentiation of the two Ritter- 
iella species but in the differentiation of R. 
picteti from the aggregate form of Salpa fusi- 
formis. If the muscle banding is distinct there 
TABLE 1 
Comparison of the Species of Ritteriella 
BODY 
MUSCLE 
R. picteti 
R. amboinensis 
Fibers 
Width in 
millimeters 
Fibers 
Width in 
millimeters 
I 
16 
0.75 
4 
0.1 
II 
16 
0.50 
5 
0.1 
III 
19 
0.50 
5 
0.1 
IV 
18 
0.50 
6 
0.1 
V 
17 
0.50 
6 
0.1 
VI 
24 
0.50 
6 
0.1 
Total length 
of animal.... 11mm. 9 mm. 
