Sunday, June 3, 2012

Development of the sea cucumber Cucumaria miniata

This series of images illustrates the development of a sea cucumber Cucumaria miniata. I collected adults of C. miniata from Lighthouse beach in Charleston, Oregon on April 24 2012 hoping to obtain gametes from natural spawning because this species is known to reproduce from mid-March to late April. I kept the adults in a sea table with flowing sea water at ambient temperature and crossed my fingers. On April 28 2012, two males and three females spawned. The adults were separated before spawning, so I collected the gametes and fertilized the eggs. Cucumaria miniata is considered a direct-developer. Even though it has a swimming larva, called doliolaria, this larva does not feed in the plankton. In contrast, some other sea cucumbers have a feeding auricularia larva, which eventually metamorphoses into a doliolaria stage. As is typical for direct developing sea cucumbers, C. miniata has large yolky eggs (500 µm in diameter and bright green in this species). A few hours after fertilization I observed early cleavage – a four cell stage is pictured here.

The second picture shows a 60-hour old early doliolaria larva of C. miniata – the preoral lobe (right) is more opaque compared to the posterior end of the larva (left). Although these do not feed they do have a vestige of a gut. Early on the larva is uniformly ciliated, but the advanced doliolaria larva of this species swims using three transvers ciliary bands (not shown).

By day seven of development one can see there are five-primary tentacles protruding ventrally toward the anterior end of the larva (about six o'clock on the image on the left). The five primary tentacles surround the mouth. At this stage the individual is referred to as a pentactula. The pentactula of this species also has two primary podia (one clearly visible on the image to the left) emerging from little pores (called podial pits) at the posterior end.  

The bottom image shows several of the many calcareous spicules in the pentactula. After two weeks of planktonic life the larvae (as pentactulae) settle on the undersides of rocks near conspecific adults.

Sewell, M. and McEuen, F. Phylum Echinodermata: Holothuroidea. In: Atlas of Marine Invertebrate Larvae. Edited by Craig M Young. Academic Press.

McEuen, F. Phylum Echinodermata, Class Holothuroidea. In: Reproduction and Development of Marine Invertebrates of the Northern Pacific Coast. Edited by Megumi F Strathmann. University of Washington Press.

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