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

Figure 3. Terms used in descriptions for mouthparts;
maxilliped palp article numbered.
and Syscenus, this article is proportionally longer, about
twice as long as the preceding article; flagellum length
is variable, from longer than the body in Xenuraega to a
little longer than the peduncle in some species.
mouthparts
The mandible is simple, with a narrow, distally acute
uni- or bidentate incisor (occasionally weakly tridentate);
the molar process is usually present as a small
but distinct flat lobe, occasionally serrate (e.g. Aega
vigilans, see Bruce 1983) and when small it is difficult
to observe; the mandible palp is uniform throughout
the family, but unusually seems to have the basal article
arising from what appears to be a large articulated
(non-cuticularised) area giving rise to the appearance
of four distinct articles (as misinterpreted by Bruce
983, 988). This area is considered to be part of the
mandible.
The maxillule is remarkably uniform, and consists
of a short simple mesial lobe and the elongate lateral
lobe which is provided with 5– 0 robust setae. These
setae vary from broad-based triangular in shape to
slender, and may be hooked, hammer-head or falcate;
they are always terminally acute. The mesial lobe is
small and often lost in dissection, even from large
specimens; this lobe appears to be absent from Rocinela,
Syscenus, and Xenuraega, but present or absent in Aega,
Aegiochus, and related genera.
The maxilla is elongate and flattened, with a small
distomesial lobe (the basal endite of Brandt & Poore
2003). The distal margin is twisted and bent ventro-
laterally so that illustrations made from slide-mounted
preparations never show the true shape. Setation is
uniform with the lateral lobe having 3–5 hooked robust
setae, the mesial lobe with 2–4, one of which is
usually straight.
The maxilliped palp varies in the number of articles,
these differences being diagnostic for different genera.
The palp is not flat, being twisted and bent ventrally.
In Aega and Aegapheles, maxilliped palp article 5 is difficult
to observe by light microscopy (as evidenced by
frequent errors of interpretation in the literature) as it
is either largely or wholly concealed by article 4, or can
be viewed only from the side. A maxilliped endite is
present in most genera, and is usually small, usually
provided with small simple setae, occasionally larger
with long circumplumose setae (e.g. Aegiochus riwha
sp. nov.) similar to those of cirolanids. Critical differences
in the setation of maxilliped palp article 5 were
observed by Brusca ( 983), who used these differences
in support of his proposed subgenera Aega (Aega) and
Aega (Rhamphion). The subgenus Aega was defined as
having ‘stout recurved spines’ on maxilliped article 5
with Rhamphion having ‘long, stout, simple, setae, but
rarely recurved spines.’ However, these differences
have not been found to be sustained on closer examination.
Maxillipedal palp article 5 in some species of Aega
and Aegapheles appears partially fused to article 4; in
some species all the robust setae are elongate, in others
article 5 has both elongate and hooked robust setae.
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