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Content Summary | External Morphology
Gills
Nudibrachs are belonging to class Gastropoda so they are member of snail group without shells. Their name, nudibranch, means "naked gills" (Debelius & Kuiter 2007). The gills work same as other marine species such as fish do (Coleman 2008). Gills extract oxygen from sea water so they are critical to nudibranchs' life (Debelius & Kuiter 2007).
Normally, their gills are placed on the back and the shape, structure and arrangement play an important role in nudibranch taxonomy (Coleman 2008). Yellow-daubed Gymnodoris has branched 7 or 8 gills on the back and they are arranged in circle shape around anus (Willan & Coleman 1984). Also, they cannot retract the gills into under the mantle pocket which is one of the characteristics of family Gymnodorididae (Marshall & Willan 1999; Debelius & Kuiter 2007).
Rhinophores
Most nudibranchs have a pair of rihnophore on their head which are known as chemosensory organs (Ruppert, Fox & Barnes 2004). The word, rhino, means "smell" so this organ function as "nose" which can detect odours in water (Coleman 2008). Most nudibranch has poor developed sight
compared to Cephalopoda because of the presence of rhinophores (Ruppert, Fox & Barnes 2004). Carnivorous nudibranch such as family Gymnodorididae use rhinophores to detect prey's mucus and track prey for foraging (Nakano & Hirose 2011).
Different structure of rhinophores play a key role in taxonomy as well (Coleman 2008). Family Gymnodorididae and family Nembrothinae are sharing similar features and the species of both family cannot retract their gills into the pocket but family Gymnodorididae has non-retractile rhinophores while family Nembrothinae have retractile rhinophores (Debelius & Kuiter 2007).
Pustula
Majority species of Gymnodoris have pustula on their body but yellow-daubed Gymnodoris has many creamy yellow pustula on their soft body. Gymnodoris aurita has similar pattern of pustula on its body but number is much fewer (Marshall & Willan 1999).
Genital aperture
Nudibranchs are hermaphrodites so they have both functional male and female reproductive organs usually on the right side of th
eir body around neck area (Coleman 2000). When 2 same species of nudibranchs meet each other and recognize that they are same species by chemoreception, they extended penis-like organ and enter into the female duct to and ejaculate sperm
into
the duct (Debelius 1998; Coleman 2008).
Other features
Yellow-daubed Gymnodoris has completely lost the mantle skirt (Marshall & Willan 1999). Also, velar appendage and the oral area are ambiguous (
Marshall & Willan 1999). The body is normally pale yellow but some individuals have reddish brown colour (Marshall & Willan 1999; Debelius & Kuiter 2007) .
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