Harris: The copepod genus Porcellidium 
81 
tightly rounded. Hyaline border, dorsal pits and ventral 
surface of cephalosome as for female, no ridges or wrinkles 
on ventral surface of rostrum. Caudal ramus sub-quadrate 
(1/w 0.75), medial edge straight, lateral edge convex, dorsal 
surface with feint ridges, |3 seta 14 way down ramus (Fig. 8E). 
First seta on antennule segment 2 more than twice length 
of second and third seta (Figs 7G), five plumulose setae 
on segment 2. Segment 3 with knob-like ventral process 
(no blade). Segment 4 with three conspicuous denticulate 
coupling denticles, (in some views they may appear as two 
denticulate pads, compare Figs 7 A and 8D). Aesthetasc 
short (more than twice length of segment 3+4). Segment 
5 of dactylus broad, 3 /4 length of segments 3+4, hooked 
terminally, segment 6 very small, fused to segment 5 (Fig. 
7F). Other limbs as for female except for the following: P2 
endopod with two plumose terminal setae (Fig. 6E), setae 
on segments 2 and 3 of P4 endopod all plumose (Fig. 6D), 
P5 rhomboid (almost rectangular, Figs 7B, C), first (lateral) 
seta longer than other setae, no setules at base of terminal 
setae, apical angle of P5 80°. Spermatophore l A body length. 
Remarks. Although Brady’s Porcellidium viride can be 
identified, the same does not apply to Philippi’s Thyone 
viridis. The reason Brady thought his animal was the same 
as Philippi’s Thyone viridis is the similarity of the P5 limbs. 
He says “There seems little reason to doubt the identity 
of this species [P. viride] with Philippi’s Thyone viridis ; 
the serration of the lower border of the fifth foot is very 
distinctive... ”, but this is a feature of nearly all male members 
of the Porcellidiidae. It may seem strange that Brady thought 
his animals the same as Philippi’s, but it is clear from his 
description and figure that he thought his own copepodid was 
an adult female. Brady had found P. tenuicauda (which he 
illustrates), and the adult female of P. viride which he identifies 
as P. fimbriatum , thus the only other animal he could compare 
with his (male) copepodid was Thyone viridis. It is important, 
therefore, to consider whether Brady’s synonymy is justified. 
Philippi gave a short (Latin) diagnosis of Thyone and 
then an extremely brief description of his T. viridis , “Almost 
3 /4 m long, common. Masticatory apparatus extremely 
complicated”. The only clue to the animal’s identity is a 
confusing sketch (Fig, 25A). It shows an animal with six 
segments to its antennule, but they are not transformed like 
an adult male members of the Porcellidiidae. This tells us 
that it is not an adult male or male copepodid: it must be an 
adult female. But the posterior end of the body clearly shows 
male P5 limbs with six terminal setae and quadrate caudal 
rami, therefore Philippi’s animal must be a sage IV or V male 
copepodid. Thus there is a conflict as to the sex of the animal. 
The shape of the body is even more confusing (see Fig. 
24A). It is egg-shaped and sharply truncated anteriorly with 
maximum width 14 down body. Adult animals of Claus’ P. 
tenuicauda are egg-shaped, but neither male nor female 
is truncated anteriorly. The males of both P. viride and P. 
fimbriatum are truncated anteriorly, but are not egg-shaped 
nor do they taper posteriorly. The females of these two 
species are oval and not truncated anteriorly. The copepodid 
of P. viride illustrated by Brady (1880) is not egg-shaped; the 
posterior half is broadly semicircular like other copepodids 
(Fig. 25B). It is clear that Philippi’s animal cannot be 
identified with any of the European species nor can Brady be 
justified in thinking it was the same as his animal. Philippi 
does not say whether he designated type specimens for his 
animal and no evidence has been found that suggests he 
did. Brady would not have provided a type specimen for 
his Porcellidium viride because he regarded it as a synonym 
for T. viridis. However, Brady (1880) illustrates the male 
antennules of P. viride which show the unique long first seta 
on segment 2. This feature is species specific and has not 
been found on any other member of the family. It allows the 
species to be identified with a high degree of certainty and is 
the basis on which the present redescription of Porcellidium 
viride rests. Sars (1904) also shows this long seta in his 
illustration of Porcellidium fimbriatum which proves that 
his animals were P. viride. 
Specimens from Wales and Scotland have a variable 
dorsal colour pattern of dark blue or purple on a pale yellow 
body colour (Figs 4A, 8F,G,H,I and Plate 1B,D, p. 67). The 
frequency of colour variability found in one sample is shown 
below (Table 1). Animals collected from Loch Hyne, Ireland, 
have a single pale pink dorsal patch (Fig. 4E). 
Collection data. Porcellidium viride has been collected 
from the following algae. Himanthalia elongata at Great 
Castle Rocks, Dale, Pembrokeshire Wales, (CB7.7/70, 209 
88 $$, 4 coupled + juvenile), V. A. Harris 1970, 
1974. Laminaria saccharina at Clachan, Seil Sound, Oban, 
Scotland ES12.9/74, 71 $$ (18 with eggs), 21 4 SS 
coupled to juveniles; ES14.9/74, 14 3 £_<$; ES17.9/74, 
85 (7 with eggs), 60 SS, 13 SS coupled to juveniles; 
ESI8.9/74 (holdfasts), 55 12 SS, 2 coupled to 
juveniles. Laminaria digitata at Clachan, Seil Sound, Oban, 
Scotland ESI9.10/74, 55 $9,12 S&, ES20.10/74, 58 
23 M; ES23.9/97, 41 $£, 9 S&, ES25.9/97, 55 $$ (25 
with eggs), 39 SS, 2 SS coupled to juveniles, V. A. Harris 
1970, 1974, 1987, 1997. Ulva lactuca at Loch Hyne, near 
Skibbereen, Co. Cork, Ireland LH3.9/97, 8 ?$, 6 SS, V. 
A. Harris, 1997. 
Samples collected from Laminaria digitata also contain 
populations of P. fimbriatum. 
Table 1. Frequency of colour patterns in a population of Porcellidium viride from Scotland. 
large purple 
area on all 
segments 
and posterior 
ofbody 
Fig. 8F 
large purple 
patches on 
cephalosome 
Figs 4A, 8G 
only posterior 
of body purple 
Fig. 8H 
rear of ceph¬ 
alosome purple, 
posterior of 
body not purple 
Fig. 8A, I 
animals pale 
yellow, no 
purple 
total 
female animals 
1 
43 
63 
33 
6 
146 
male animals 
0 
0 
0 
104 
2 
106 
