The early life history stages and metamorphosis in Dover
sole (Microstomus pacificus) are described from 201 larvae and
juveniles. Unlike other pleuronectids, with the possible exception
of the deep-sea sole (Embassichthvs bathvbius), initial migration of
the left eye is not associated with metamorphosis or transition from
plankton to benthos. The left eye exhibits a stasis during its
migration, so that premetamorphic larvae are optically asymmetrical
while planktonic. Seven characters are used to quantify the
progress of metamorphosis: completed eye migration, dorsal fin
position, dentition, pectoral fin development, condition of
posterior process of coracoid, pigmentation, and elongation of the
intestine into a secondary body cavity. Other characters associated
with metamorphosis are reduction in body depth associated with
reductions in lengths of neural and hemal spines and associated
dorsal- and anal- fin pterygiophores, decreasing interorbital
distance, increasing right eye diameter and right premaxilla length,
and development of body scales. Metamorphosis appears to require 9-
11 or 12 months to complete. The planktonic period of
premetamorphic and metamorphic larvae is about 18-24 months.
Metamorphic larvae appear to move inshore into shallower water as
metamorphosis progresses. Settlement occurs from about December to
April, primarily from January to March.
One of the earliest phylogenetic hypotheses about the
intergeneric relationships of the pleuronectid genera Microstomus,
Embassichthys, Glyotocephalus, and Tanakius was by Norman (1934),
who considered Microstomus plus Embassichthvs and Glyotocephalus
plus Tanakius to be sister groups. An alternative hypothesis by
Richardson (1981) suggested that Embassichthvs larvae resembled
larvae of Glyptoceohalus and Tanakius based on a "leptocephaluslike"
body shape, and that Microstomus was the primitive sister
group of these three genera because of its dorsoventrally deepened
body shape.
In order to evaluate Richardson's hypothesis of sister
group relationships based on body shape, I examined morphological
characters associated with eye migration and metamorphosis, and
changes in body shape during ontogeny from post-flexion larvae
through benthic juveniles. Richardson's-character of a moderate
"leptocephalus-like" body shape is an artifact of the paucity and
small size range of larvae available for her examination. The body
shape of larger Embassichthvs larvae is also dorsoventrally deepened
and the larvae appear to undergo changes in body shape during
metamorphosis similar to Microstomus. Three synapomorphies that
support Norman's hypothesis of an Embassichthys plus Microstomus
sister group relationship are dissociation of initial eye migration
with metamorphosis, a stasis during eye migration in premetamorphic
larvae, and a retention of a larval-like appearance to the eyes of
newly settled specimens. / Graduation date: 1993
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36387 |
| Date | 29 May 1992 |
| Creators | Harris, Phillip M. |
| Contributors | Markle, Douglas F. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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