The Marine Fauna of New Zealand: Isopoda, Aegidae (Crustacea)

pod 2.2 times as long as wide, distally subtruncate,
lateral margin strongly concave, with PMS on distal
one-third, mesial margin with PMS on distal half;
peduncle .6 times as wide as long, mesial margin
with 0 coupling hooks. Pleopod 2 appendix masculina
with straight margins, 0.73 times as long as endopod,
distally bluntly rounded. Exopods of pleopods –3
each with distolateral margin not digitate; endopods
of pleopods 3–5 each with distolateral point (minute);
pleopods 2–4 peduncle distolateral margin with prominent
acute RS.
Uropod peduncle ventrolateral margin with 2 RS,
posterior lobe about two-thirds as long as endopod.
Uropod rami not extending beyond pleotelson, marginal
setae dense, in several tiers, apices broadly rounded.
Endopod apically not bifid, lateral margin straight, without
prominent excision, proximal lateral margin with
0 RS, distal lateral margin with 2 RS, mesial margin
weakly convex, with 5 RS. Exopod extending beyond
end of endopod (slightly), 2.7 times as long as greatest
width, apically not bifid; lateral margin weakly convex,
with 2 RS; mesial margin straight or convex (distally
convex), with 7 RS.
femaLe: Pereopod 3 lacks the distal robust seta on
the propodus. Oostegites arising from the coxae of
pereonites –5. Eggs are large, 2.8–3.5 mm diameter.
Present data indicate that females may grow to a far
larger size than do the males.
size: Up to 75 mm for the largest female examined here
making it the largest aegid species. Males are smaller,
present material measuring from 27 to 38 mm.
Variation: The small number (five entire) of specimens,
the fact that the uropod apices are mostly damaged
with the robust setae rubbed off and the presence of
a dense fringe of plumose setae means that it is not
possible to precisely detail the variation present. The
robust setae on the merus of pereopods –3 present a
constant pattern of two rows, although the number
of robust setae varies: pereopod merus with +2 to
+3, pereopods 2 and 3 merus with 4+2 to 5+2, one
pereopod 3 with 3+2. Pereopod 3 has a large robust
seta adjacent to the base of the dactylus on males
NIWA23773, 23772 but this seta is absent or reduced
in females and absent in the male NMNZ Cr.9269. It is
not possible to say whether or not the absence of this
robust seta is due to damage, although the presence or
absence of such a prominent character would generally
be considered to be significant.
There is some variation in the shape of the uropod
endopod with some specimens having a distinctly oblique
mesial margin (Fig. 22E) in others it is subtruncate
(Fig. 22H). The robust setae vary: uropod exopod lateral
margin 0– 2, mesial margin 5–8; endopod lateral
margin 2–3, mesial margin 5–8.
49
The specimen from Juan Fernandez agrees well
with the description presented here with the exception
that the frontal lamina is shorter and wider, the
mesial margin of the uropodal exopod is slightly more
convex than illustrated and the RS on pereopod 2 form
a single row rather than two groups. The pleotelson
indentation is a little shallower but this may be due to
damage as it is clearly eroded and rubbed. Counts for
the RS on the merus of pereopods and 2: P : +3, +2;
P2: 5+2 (both). The uropod endopod mesial margins
both have 9 RS, slightly higher than for New Zealand
specimens.
remarks: Aega semicarinata, one of the largest species
of Aegidae, may be identified by the widely excavate
and crenulated posterior margin of the pleotelson, the
dorsal surface of which has two shallow submedian
depressions and one median posterior depression.
These depressions can give the impression of a weakly
defined longitudinal ridge, presumably after which
Miers named the species. The moderately expanded
antennule, large but separate eyes, coxae prominent in
dorsal view, simple propodus on pereopods –3 and
pereopod 3 propodus usually with a large club-like robust
seta all serve to further distinguish the species.
A number of names have been placed in synonymy
with this species — Aega bicavata Nordenstam, 930,
A. punctulata Miers, 88 and Aega urotoma Barnard,
9 4. Material from New Zealand provisionally identified
as Aega semicarinata proved to belong to two similar
but distinct species, here identified as Aega semicarinata
and Aega urotoma, the latter proving to be the same as
specimens of that species from South Africa.
The synonymy of Aega bicavata with A. semicarinata
was first proposed by Menzies (1962), and the figures
and description provided by Nordenstam agree well
with Miers’ ( 879) description as well with the specimens
examined here, and that species is retained as a
junior synonym.
Aega punctulata should never have been placed in
synonymy as Miers’ (1881) description and figures
more than adequately describe the critical points of
difference between the two species, including the
smaller eyes and evenly rounded pleotelson posterior
margin.
The similar Aega urotoma, first placed into synonymy
by Stebbing ( 920), has the antennule peduncle articles
and 2 far more widely expanded, antenna peduncle
article 5 flattened and expanded, smaller eyes, subtruncate
or shallowly indented pleotelson which also lacks
the prominent sub-lateral and posterior depressions
seen in A. semicarinata (Table ).
Another similar and very poorly characterised species
is Aega webbii (Guérin-Méneville, 836) which is
similar to A. semicarinata in eye size and in the emarginate
shape of the posterior margin of the pleotelson. It