Protochordata is an entirely informal grouping of taxa with possible
affinities with possible chordate ancestors. It has no taxonomic
implication whatsoever. I don't know who first used the term. Conodonts
were also thought to be protochordates. I do not know who first used the
term - I'll keep looking. The term was used in the Traite de Zoologie
Concrete (Delage abd Herouard, 1898)-in other words, its use was
established long before Barrington (1965). I don't mind the term- unlike
Billie Swalla I don't think it means anything- it is a convenient way to
refer collectively to a group of organisms that, historically, were all
thought to have ancestors that may have been related to ancestors of
chordates. The origin of vertebrates has always been a compelling exercise.
Hemichordates always have been considered separate from Cephalochordates and
Tunicata, even though they appear to have similar pharyngeal perforations,
especially the cephalochordates. Hemichordates differ from the other two
groups in their ciliated larvae (like echinoderms), and in the absence of a
thyroid homologue- an endostyle. There are extensive references to these
matters in KOTT, P. 1998. Tunicata. Pp. 51-252, 259-261 (App. I-111),
265-292 (Index) and BURDON JONES Hemichordata,pp.1-50 in Wells, A. &
Houston, W. W. K. (eds) Zoological Catalogue of Australia. Vol. 34.
Hemichordata, Tunicata, Cephalochordata. CSIRO Publishing: Melbourne.
Berrill (1955) on the Origin of Vertebrates OUP) is a fun read, and Neilsen,
1995 The Evolution of Animals is an authoritative modern analysis. However
the list of references is formidable. Although these authors will givr you a
way into the literature- there are plenty of others
Although Billie Swalla has retrieved not very different numbers for use of
"Tunicata" and "Urochordata", I reiterate (from my initial message) my
(possibly subjective !) view - the word Tunicata is the one most often used
by the leading workers and in the major reviews.
Also, I find that Brien (1948) thinks that Ray Lankester first used the term
Urochordata-I have not been able to confirm this. Lankaster was using the
term Tunicata in 1913 (Science from an easy Chair, Adlard and Son; London so
I think Brien may be wrong. I'll chase this up too.
Happy Xmas , New year