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Record: oai:ARNO:506238

AuthorA. Hazel McShine
TitleTaxonomic considerations on Branchiostoma caribaeum from Jamaica
JournalStudies on the Fauna of Curaçao and other Caribbean Islands
Volume46
Year1975
Issue1
Pages54-70
ISSN0166-5189
Abstract1. The original descriptions of Branchiostoma caribaeum are reviewed and the synonyms for the species mentioned. 2. A statistical analysis was carried out on twelve taxonomic characters of specimens of B. caribaeum from Kingston Harbour, Jamaica. The twelve characters were: total myotomes; preatriopore myotomes; postatriopore myotomes; myotomes between atriopore and anus; postanal myotomes; caudal fin length as a percentage of total body length; body depth as a percentage of total body length; dorsal fin ray chambers; ventral (preanal) fin ray chambers; gonads (on right side only); buccal cirri (on right side only). 3. The characters were ranked in order of increasing variation or decreasing taxonomic significance. The least variable and therefore the most important diagnostic character was found to be the number of preatriopore myotomes. This character cannot be used on its own to separate B. caribaeum from the other species of Branchiostoma of the Western Atlantic. 4. All the specimens of B. caribaeum found in Kingston Harbour show the origin of the upper lobe of the caudal fin considerably posterior to the lower lobe. The variability of the caudal fin shape within the species B. caribaeum is discussed. It is concluded that the shape of the caudal fin cannot be used as a diagnostic character to separate the species of Branchiostoma of the Western Atlantic. 5. The position of the anus in the majority (62 percent) of the specimens examined was behind the midpoint of the lower caudal lobe. The other 38 percent showed the anus at the midpoint of the lower caudal lobe. The variability of the position of the anus both within the species B. caribaeum and in the species of Branchiostoma of the Western Atlantic is discussed. It is also concluded that the position of the anus can no longer be used as a diagnostic character to separate the species of Branchiostoma of the Western Atlantic. This character does however, separate the Eastern Atlantic group of Branchiostoma species from those of the Western Atlantic, because in all the former groups the anus is located well in advance of the midpoint of the lower caudal lobe. 6. It is suggested here that B. platae may be a synonym for B. caribaeum. The main reason for this is that HUBBS (1922) stated that the two main characters by which B. platae differed from B. caribaeum were the shape of the caudal fin and the position of the anus behind the midpoint of the lower caudal lobe. It has been shown above that both these characters can no longer be used as distinguishing factors in determining whether a specimen is B. caribaeum or B. platae. 7. It is concluded that the species of Branchiostoma of the Western Atlantic are so similar that no one characteristic no matter how small the variation can be used to separate them unequivocally. Therefore statistical analysis of all populations of Branchiostoma are necessary for a complete diagnosis.
Document typearticle
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