External Morphology


External traits can be used to help us organise and identify all animals. Digestive gland organisation in nudibranchs is one such trait. All nudibranchs either have a branched or unbranched digestive mass. Cladohepatic nudibrachs have a branched digestive mass, while holohepatic nudibranchs have an unbranched digestive mass. On this basis of this and some other external morphological traits, it is useful to divide the Nudibranchia order into two clusters (Rudman & Willan 1998). 

1.   Dendronotina, Arminina, and Aeolidina: all cladohepatic species

2.   Doridina: all holohepatic species

 J. funebris belongs to the Doridina suborder, and therefore resides in cluster 2. Other  characteristic traits of Doridina species include (Cimino et al. 1999):

1.   A pair of antero-dorsal chemosensory organs, named rhinophores

2.   Poster-lateral respiratory organ, the gills, usually arranged in a circle around the anus

3.   Lack cerata, and spicules arranged in ovoidal patterns on mantle.

Rhinophores:

Rhinophores allow dotted nudibranchs to respond to chemical cues from it’s environment. Such cues may be involved in intra or interspecific communication, or the location of food. For a nice example showing J. funebris ability to use their rhinophores to locate food, click on the Behaviour tab.

Respiratory organ:

The gills of dotted nudibranchs are retractable and can contract into a protective pouch (Todd 1983).

Spicules:

J. funebris is quite an easy animal to recognise thanks to their characteristic brown spicules arranged in ovoidal patterns on it’s mantle. The spicules and crystalline needles and provide another layer of protection from predation (Garcia-Gomez et al. 1990, Cimino et al. 1999). It is thought that the spicules are products of biosysnthesis, likely by using accumulated products from eating sponges. However there is currently little published evidence to support this theory.