Distribution: Rare in the Solitary Islands Marine Park. Recorded from the Indo-Pacific region, from Tanzania in Africa to Kwalajein Atoll in the Central Pacific, north to Okinawa, south to Coffs Harbour in Australia. In Australia recorded from around Geraldton in Western Australia, northwards to the North West Shelf, the Great Barrier Reef in Queensland south to Coffs Harbour and Lord Howe Island in New South Wales.

Ecological Notes: Frequents rocky reef, depth to at least 28 m.

Additional Notes: Recognised by the network of bright or darker orange ridges on the mantle, the spaces between darker brown with closely spaced bright white spots. The mantle has a bright yellow or orange margin, the rhinophores are white with vertical black stripes up the back of the column and black edges to the lamellae. The gills are white with black tips. Grows to around 45 mm long.

References: Undersea Jewels, A colour guide to nudibranchs, Gary Cobb and Richard C Willan. Australian Biological Resources Study, Canberra, 2006. p.197.

Atlas of Living Australia at https://bie.ala.org.au/search?q=halgerda+tessellata. Accessed 13/01/2023.

Australian Museum, Sea Slug Forum. http://www.seaslugforum.net/showall/halgtess. Accessed 13/01/2023.

Reef Life Survey website at https://reeflifesurvey.com/species/halgerda-tessellata/. Accessed 13/01/2023