Doliolaria | devbiopparvimensis

Doliolaria

       After the auricularia larval stage, the sea cucumbers metamorphose into their second larval stage, doliolaria. Sea cucumbers are doliolaria for a much shorter amount of time, a mere few days, than they are auricularia. Like auricularia, doliolaria swim in the water column by beating their cilia, however, there much fewer similarities than there are major differences between the larvae.
       Unlike auricularia, doliolaria are non-feeding, which perhaps explains why this larval stage is much shorter. Both the anus and mouth close.
       Additionally, the left hydrocoel, that up had grown 5 distinct bumps in the auricularia stage, begins to wrap around the esophagus in a doughnut like ring. These 5 bumps elongate and point towards the posterior end. This forms the oral vestibule. Eventually, this becomes the 5 buckle tentacles (Figure 1).
       Furthermore, the blastocoelic space shrinks down around the gut. As a result, doliolaria are smaller and more opaque than auricularia larvae (Figure 2)(Video 2).

Lastly, it seems that doliolaria larva swim much faster than auricularia. Haline bodies are retained (Figure 5).

In arguably the most dramatic change, the single convoluted ciliary band from the auricularia rearranges itself into five, separate, evenly spaced concentric bands around the doliolaria. What’s more, this striking rearrangement occurs in a matter of hours. Though there is no consistent way of labeling the ciliary bands, we have elected to label them 0-4, consistent with the paper, Lacalli (1993). Two major processes occur in transforming the ciliary band. Between horizontal sections of the ciliary band, there is a progressive disappearance of ciliary band. Between vertical sections of ciliary band, such as those labeled “unfused ciliary bands” in Figure 3, the ciliary bands fuse together and then separate horizontally (Lacalli & West, 2000). It is important to note that not all of the circumferential bands connect in a continuous ring (Figure 4).

Figure 1: Doliolaria - Buckle Tentacles surround the esophagus, pointing towards the anterior end

Figure 2: Side by side Auricularia and Doliolaria - Note the differences

Figure 3: Transitioining Ciliary Bands

Figure 4: Doliolaria Ciliary Bands - 5, separate, concentric bands; cilia clearly visible

Figure 5: Retained Haline Bodies in Doliolaria

Video 1: Early Doliolaria Swimming

Video 2: Auricularia and Doliolaria