Larval Development in the Lutjanid Subfamily Apsilinae (Pisces): The Genus Paracaesio
Abstract:Larval development in the lutjanid subfamily Apsilinae is described and illustrated from specimens captured with plankton nets and midwater trawls in the Indian and Pacific Oceans. Series were assembled using body shape, fin-spine morphology, head spination, scale formation and counts, gill-raker counts, and pigment patterns. Identifications (mostly to the genus level) were confirmed from adult characters developed in the largest specimens and from the distributions of the adults. Larvae of the Apsilinae share with larvae of other lutjanids the presence of a spine on the dorsal postcleithrum, early forming, very elongate spines of dorsal and pelvic fins, and even longer pelvic-fin soft rays. They are further characterized by fin-ray counts (D X,10; A III,8), absence of external ornamentation on fin spines, early forming pigment on the midbrain posteriorly, and early formation of the third anal-fin spine and scales. Of the three Indo-Pacific apsiline genera, Lipocheilus, Paracaesio, and Parapristipomoides, we were able to identify only larvae of Paracaesio. However, within this nominal genus are two distinct larval morphologies (morphs), each with several larval types apparently corresponding to species. Due to incomplete understanding of adult taxonomy and distribution in Paracaesio, it was not possible to identify any of the larval types to species. Paracaesio larvae with about 70 lateral-line scales, a relatively slender body and very long, whip-like dorsal-fin spine 2 (to 96% body length) and equally long pelvic-fin ray 1 (to 370% P2 spine length), scales that formed between 8 and 11 mm, prominent pigment on the urostyle, and no melanophore at the cleithral symphysis are called Paracaesio morph-hi. These were identified as Paracaesio because, among apsilines, only this genus contains species with about 70 lateral-line scales. Five types of Paracaesio morph-hi larvae, distinguished primarily by pigment patterns and secondarily by minor differences in head spination, are described from larvae as large as 24 mm. For one larval type, apparently of the Paracaesio morph-hi group, the largest specimen (6.2 mm) was too small to have scales. Therefore, we could not establish that it was a Paracaesio species. We describe this very lightly pigmented larval type under the name Unidentified Apsilinae. Its South Pacific distribution nearly matches that of Parapristipomoides squamimaxillaris, so the possibility remains it is that species. Larvae considered to be Paracaesio because they have about 50 lateral-line scales, but too many gill-rakers to be Lipocheilus carnolabrum, are called Paracaesio morph-lo. These larvae have a relatively deep body, relatively short, robust dorsal-fin spine 2 (to 31% body length) and pelvic-fin ray 1 (to 125% P2 spine length), scales that form between 7 and 9 mm, a melanophore at the cleithral symphysis until 4-7 mm, and no pigment on the urostyle. Three types of larvae of this morph are described from larvae as large as 29 mm, and are distinguished by spination on supraorbital ridge, and lachrymal, and minor pigment characters. In one type, the largest larva was too small for us to be sure it had the adult complement of gill-rakers, and there is a possibility it is L. carnolabrum rather than a Paracaesio species. Another type was identified as either Paracaesio gonzalesi or P. kusakarii based on scalation and pigment. The presence of two, distinct morphs of Paracaesio larvae supports a suggestion made by W. D. Anderson, Jr., based on adult characteristics, that there are two monophyletic lines within this nominal genus. However, with the possible exception of one pigment character, larvae seem to provide no evidence that Paracaesio is monophyletic.
Document Type: Research Article
Publication date: 1997-11-01
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