Description This is a small cephalaspidean, commonly from 5mm to 15 mm in length, with a shell size up to 10mm. The body is coloured greenish-white with many patches of yellowish-white, and some yellow blotches sprinkled all over. Being a shelled animal, the body is somewhat elongated, too large to be fully retracted into the shell. The cephalic shield is deeply bifurcated on the read end, dividing it into a pair of well-developed flaps. The parapodial lobes are short, reflected over the anterior half of shell and not meeting dorsally. A large posterior infrapallial lobe encloses the rear end of the shell, and has a posterior extension, masquerading as the posterior end of the foot. All mantle margins and the fringes of the parapodia, the posterior pallial lobe and the part of the pallial lobe enclosing the shell are purple-blue coloured, contrasting strongly with the pale ground color of the animal. The purple blue line breaks up into a series of bluish spots in the anterior margin of the head. Some dark purplish blue spots are also visible beneath the shell. A large purplish spot separates the two eyes, however the presence of yellow and purple spots is variable among specimens (Rudman, 2003). The shell is bubble-shaped, coloured translucent whitish or yellowish, fragile, smooth, with no traces of ornamentation. The margins of the elongate aperture extends beyond the spire.
Biology Little is known about its biology. Like other species of this genus, probably feeds on diatoms and on filamentous algae. The spawn is a translucent ribbon with whitish capsules laid in a one and half turn spiral laid flat on the substrate (picture in Crocetta & Vazzana, 2008). A curious trailing behaviour among couples of individuals has been observed, where the leading individual is moving slowly on an almost straight pathway and the pursuing one hurries to catch the leader, moving on the exact trail of it, most probably by following the chemicals left behind, and when it catches, it tries to get under the leader and elevate it. Then the leader makes a quick turn on a vertical direction leaving its partner behind. After a few seconds of halt the pursuer follows the new route to catch the leader again (Yokeş in Sea Slug Forum, 2005). This has been observed both in open sea waters and in aquaria and probably corresponds to mating behaviour. Mollo et al. (2008) found toxic compounds with significant activity as feeding deterrents in this species. The conspicuous purple-blue margin of the animal distinguishes Haminoea cyanomarginata from all other Mediterranean species of this genus.
Cyanomarginata, from “Cyan”, from Latincyānus, from Greek κυανός (kýanos), ‘dark blue’ (and this from Hittite root kuwan–, ‘azurite’) + “Marginata”, from Latin “margo”, margin.
Distribution Described by Heller & Thompson (1983) from a single specimen 5.5mm long alive, found at Harvey Reef, off the Sudanese Red Sea coast between Port Sudan and Suakin (type locality), it was later found in the Mediterranean Sea where it has stablished viable populations in Greece (2001: Zenetos et al., 2009), Turkey (2002: Çinar et al., 2011), Malta (2006: Sciberras & Schembri, 2007) and Italy (2007: Crocetta, 2012) as this species seems to be quite common in these areas. A report of 100 specimens on rocks covered with algae between 4 and 17 meters deep at Kašuni, Split, Croatia on 26/12/2016 (J. Prkić pers. comm.) would be the first report for the whole Adriatic Sea. Despite the absence of records from the far eastern Mediterranean, it has presumably reached its new distributional area through the Suez Canal (Katsanevakis et al. 2004) however, as there are too few reports in the Red Sea, it is difficult to be sure whether it originated in the Indo-West Pacific or the Mediterranean (Rudman, 2003). We only know of a report for the Indian Ocean, based on a picture by Stewart Clarke shoot at Daymaniyat Islands, Oman in 2013. In the Red Sea this species is found in the coral rubble in shallow waters, while in the Mediterranean it is usually seen at night, between 5-30 m of depth, on rocky surfaces covered with algae.
Known georeferenced records of the species: Haminoea cyanomarginata
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