Unravelling the Sticky Threads of Sea Cucumbers — A Comparative Study on Cuvierian Tubule Morphology and Histochemistry

Cuvierian tubules are peculiar organs found in several species of sea cucumbers, all belonging to the family Holothuriidae (order Aspidochirotida). Two main types of tubules can be differentiated on the basis of their gross external morphology, lobulated and smooth (

Fig. 6.1

;

Table 6.1

) (

Lawrence, 2001

). Lobulated tubules occur exclusively in the genus

Actinopyga

; they are never expelled and are not sticky (

VandenSpiegel and Jangoux, 1993

). On the other hand, smooth tubules are present in the genera

Bohadschia, Holothuria

, and

Pearsonothuria

, in which they generally appear as sticky white threads that function as a defence mechanism (

Hamel and Mercier, 2000

;

Flammang, 2006

). Indeed, once ejected, they can release a glue allowing instantaneous adhesion on any object, and can therefore entangle a predator in a matter of seconds (

Zahn et al., 1973

;

VandenSpiegel and Jangoux, 1987

). Smooth Cuvierian tubules will be the main focus of the present Chapter.

Fig. 6.1

General aspect in SEM of (A) a lobulated tubule from

Actinopyga echinites

and (B) of a smooth tubule of

Holothuria pervicax

(originals). Scale bars = 200 µm.

CR

Central rachis;

CL

connective tissue layer;

L

lumen;

LO

lobules;

M

mesothelium

Table 6.1:

Summary of the main morphological characteristics of Cuvierian tubules from various species of Holothuriidae (adapted from VandenSpiegel (1993); and Flammang and Plumet, unpubl. obs.)