PhD thesis

58 Chapter III
Altenburger and Wanninger
Brachiopod neuromuscular development 21
Fig. 4. Development of the nervous system
in Novocrania anomala as revealed by
acetylated a-tubulin staining. (A–D)
Overlay of maximum projection micrograph
of a-tubulin staining and light micrograph.
(E and F) Three-dimensional
reconstructions of the dataset shown in
(D). Anterior faces upwards and scale
bars equal 50 mm. (A) First a-tubulin signal
in a juvenile 5 days after metamorphosis.
The former larval apical lobe
(AL) and posterior lobe (PL) are still
visible under the shell (s) of the juvenile.
Two ventral neurite bundles develop in
the anterior lobe (arrows). The juvenile
body is still covered by larval cilia (ci).
Some serially arranged neurites (sn) extend
inwards from the ventral neurite
bundles. (B) The ventral neurite bundles
(arrows) elongate further in posterior direction.
A median commissure (mco)
starts to form. From the anterior portion
of the ventral neurite bundles, serially arranged
mantle neurites (smn) extend distally
outwards, and serially arranged
neurites (sn) extend inwards. The cilia of
the juvenile gut (gu) are visible in the
median region of the juvenile. (C) Juvenile
with the same structures as in (B).
The median commissure (mco) is closed
and the ventral neurite bundles (arrows)
have fused anteriorly to form the anterior
commissure (aco). (D) Neural anatomy
of a juvenile 17 days after metamorphosis
with an anterior commissure (aco), a median
commissure (mco), and a posterior
commissure (pco) that interconnect the
ventral neural bundles (arrows). In addition,
the serially arranged mantle neurites
(smn), which extend toward the edge of
the juvenile mantle, are visible. (E) Threedimensional
reconstruction of the dataset
shown in (D), dorsal view. (F) Three-dimensional
reconstruction of the dataset
shown in (D). Postero-dorsal view demonstrating
that the ventral neurite bundles
(yellow) and the serially arranged
mantle neurites (green) bend ventrally.
(James et al. 1992). Rhynchonelliform larvae show a change
from positive to negative phototactism when reaching metamorphic
competence. In laboratory cultures, they swim in the
culture dish with the anterior lobe or the ventral side of the
body repeatedly forming contact with the bottom of the dish,
probably probing for a suitable place for settlement (Chuang
1996). We observed a similar behavior in Novocrania anomala
larvae before metamorphosis.
At the current state of knowledge, it remains difficult to
relate the differences in larval myoanatomy to aspects concerning
the ecology of the respective brachiopod larvae, because
the latter remains virtually unknown (James et al. 1992).
An earlier study showed that larvae of Novocrania anomala
are able to settle 4 days after fertilization (Nielsen 1991), although
we observed this behavior only in 7-day-old larvae.
Rhynchonelliform brachiopods are known to settle after 3