Haikoucaris and allied

[Dieter Waloßek at Mizzou1.Missouri.edu]

Dear Ken and others,
Our paper appeared in 2004 and I have a PDF which I can send on demand. 
Don't know what happened to Taylor & Francis, but I am sure one has to 
pay for the PDF there anyway.

Actually, there is no need to re-write the arthropod evolutionary story 
because Anomalocarididae sensu Hou & bergström, 1997, in the strict 
sense do have appendages and are, therefore, Arthropoda, in our view 
even Euarthropoda. The problem was just the bad conservation of these 
often large and apparently soft forms, but Hou Xianguang, Bergström, 
Jan & Ahlberg, Per 1995 described the limbs of, at least, one of the 
taxa (Parapeytoia yunnanensis) quite well (though strangely placing the 
forms into the Nemathelminthes).  Accordingly, Anomalocarididae have a 
set of head limbs – the antennulae and 2-3 postoral biramous limbs – as 
well as trunk limbs with rigid basipodites bearing strong spines 
medially, an endopod and a soft exopod (I can send pictures on demand).

The other problem is that some authors have put clearly unrelated stem 
taxa and what-so-ever into the same basket anad named it 
"anomalocaridids". This resulted in an undue and confusing mixture of 
stem and euarthropod features (making them a paraphyletic assemblage). 
We referred only to those taxa, which have been named Anomalicarididae 
by Hou & Bergström in 1997. This excludes all stem arthopods like 
Pambdelurion, Kerygmachela and Opabinia.

In our paper – and this will be even strengthened in an upcoming paper 
on a new early representative of the Arthropoda s. str. in the journal 
Arthropod Structure & Development (possbily 34,2) soon – we identified 
the leg design of the antennula as plesiomorphic (and not a sensorial 
type, as found in trilobites and a few other arthropod taxa). As 
developed in Fuxianhuia protensa, Chengjiangocaris longiformis and the 
new taxon Shankouia zhenghei, all from the Maotianshan-Shale biota in 
China, Lower Cambrian, such an antennula is 15-segmented and (I use 
this term to avoid confusion between a1 and a2, both given the name 
antenna historically) seems to be modified into a grasping "organ" in 
the stem lineage of Chelicerata.
Forms like Anomalocaris saron (about a hand long, pictures on demand), 
exhibit this level – in our view. Amplectobelua symbrachiata has an 
antennula with the same segments (also about 15), but carries, instead 
of a regular series of spines, huge spines proximally and distally, 
while the middle regions has only short spines. The distal region 
bearing inwardly curved spines is virtually identical in both taxa 
(pictures on demand).
In Parapeytoia yunnanensis, there are only four huge spines (sawed 
marginally, picture on demand), and this holds true for all so-called 
"great-appendage" arthropods (= one segment per spine and not a bundle 
of spines as sometimes illustrated in papers).
Haikoucaris ercaiensis, newly described in our article, has an 
antennula of 3 spines, and Chelicerata s. str. 2 left forming the 
typical claw.

All these taxa share the two-divided peduncle portion, another 
characteristic of this grasping organ antennula. A two-segmented 
peduncle is even retained in a few pantopods.

Therefore, a characteristic of the cheliceratan lineage is the 
predatory habit using the antennulae, the first appendages of the head, 
as grasping devices. Hunting may have been different in the various 
stem taxa because some have large, some have smaller eyes and some have 
a long trunk with slim legs, while others have large exopods with long 
setae possibly for swimming.
In further consequence we confirm the developmental and neurobiological 
data that all antennulae whatever name and shape are homologous, i.e. 
the chelicerae are just modified antennulae (as are the "great 
appendages" or the first limbs of Anomalocarididae), even if one may 
disagree with our other interpretations. And it also confirms that 
Chelicerata are the sister group of the rest of Euarthropoda. A problem 
now is with the trilobites that have sensorial antennulae subdivided 
into many fine annuli. To us they cannot be regarded as closely related 
to Chelicerata or even in-group. Their has to be reconsidered in the 
future, not least since they have many more peculiarities not present 
in other euarthropod taxa.

A segmented uniramous antennula and biramous post-oral limbs 
(originally just a multi-annulated rod and a lateral flap) evolved only 
once, i.e. in the stem species of Arthropoda s. str. –  together with a 
set of more features (Maas et al. 2004 and Waloszek et al. 2005 in 
press).
No need to develop them many times independently.

That's about all we propose in our discussion. Take a look.

        Yours kindly, Dieter and Andreas

Chen Junyuan, Waloszek, D. & Maas, A. 2004:A new "great appendage" 
arthropod from the Lower Cambrian of China and the Phylogeny of 
Chelicerata. Lethaia37(1), 3-20.
Maas, A., Waloszek, D., Chen Junyuan, Braun, A.:, Wang Xiquiang & Huang 
Diying 2004.Research on Early Phylogeny of Arthropoda. Progress in 
Natural Science14(2), 158-166.
Waloszek, D., Chen J.-y., Maas, A. & Wang X.-g. in press 2005. Early 
Cambrian Arthropods – New Insights into Arthropod Head and Structural 
Evolution. Arthropod Structure & Development 34(2).


Dieter Waloszek and Andreas Maas
Section for Biosystematic Documentation
University of Ulm, Helmholtzstrasse 20, D-89081 Ulm, Germany
Tel. x49-(0)731-5031000, Fax x49-731-5031009
Biosystematic Information Service BIS: 
http://biosys-serv.biologie.uni-ulm.de/
Center of Orsten Research & Exploration C.O.R.E.:  
http://www.CORE-Orsten-Research.de
email: dieter.waloszek at biologie.uni-ulm.de