Description of Phyllidiella rosans : Reunion island (Indian Ocean)

Phyllidiella rosans (Bergh, 1873)

This species has been observed on Reunion, Mayotte, Mauritius, Madagascar and Seychelles Islands

Order : Nudibranchia
Suborder : Euctenidiacea
Superfamily : Phyllidioidea
Family : Phyllidiidae
Distribution : Indo-West Pacific, Tahiti and Hawaii.
Maximal size : 35 mm
Abundance : Frequently on the fore reef zone

Species characteristics :

The colour of the ridges varies from pale blue, dark blue, purple, pink to grey

There are 6-9 rounded, longitudinal pink ridges which are relatively smooth

The stalk of the black rhinophores is pale pink.

Showing species characteristics...

Photo Florence Trentin
Reunion, "Les kiosques" at Saint Leu, 18 m,
18 mm, 09 January 2005.

Remarks :

There is in our region a group of nudibranchs that I will call Phyllidiella meandrina/rosans/zeylanica difficult to identify, for two reasons: on the one hand the existence of many intermediate forms and on the other hand the very marked differences of opinion between specialists about these species ... I finally decided to make a classification (very questionable) of these specimens
            - Group Phyllidiella rosans : There are 6-9 rounded, longitudinal pink ridges which are relatively smooth
            - Group Phyllidiella cf. rosans : Up to nine rounded, longitudinal pink ridges which are relatively smooth with with surnumerous pink tubercules
            - Group Phyllidiella meandrina : In the central part of the mantle there a characteristic pattern of pink to grey-blue rings
            - Group Phyllidiella cf. meandrina : The disposition of the tubercles looks like P. meandrina but there are transverse black area beetween the tubercles all over the notum
            - Group Phyllidiella zeylanica : In adult, up to nine longitudinal pink ridges (broken or interrupted) may occur and medially, presence of a more or less developed network of black band around the tubercles

Identification confirmed by Bill Rudman
    Synonymous (according worms) :
          - Phyllidia bourgini Risbec, 1928                                       - Phyllidia soria Er. Marcus & Ev. Marcus, 1970
          - Phyllidia rosans Bergh, 1873

Bibliographic data :

Material examined by David J.Brunckhorst ( see references/publications).

30 & 35 mm specimens, Reunion Island, 1-20 m depth, 1987, M.Jay
30, 25, 20, 19 & 16 mm specimens, Reunion Island, 5-20 m depth, 1989, M.Jay

Other external morphology characteristics

Live specimens ranged in length from 18-35 mm .
    There are 6-9 rounded, longitudinal pink to grey-blue ridges which are relatively smooth apart from some minute tubercular mounds on the lateral edges of the dorsum. These dorsal ridges may be interrupted in some individuals.
    The stalk of the black rhinophores is pale pink, and each rhinophoral clavus possesses 12 à 15 black lamellae (specimens greater than 30mm)
    Ventrally, the pale grey to white oral tentacles are long and possess rounded apices.
    The foot and gills are pale grey and the pale foot sole has numerous tiny, dark grey spots.

Similar species

Phyllidiella rosans is rather similar in colour and pattern to Phyllidiella zeylanica.

Phyllidiella rosans

Phyllidiella zeylanica

Live specimens ranged in length from 18-35 mm .

There are 6-9 longitudinal pink to grey-blue ridges.

The tubercules are rounded, which send a relatively smooth aspect to the pink to grey-blue ridge.

Only longitudinal black lines.

The rhinophores are black with the black pale pink and each rhinophoral clavus possesses 12 to 15 black lamellae (specimens greater than 30mm).

The gills and oral tentacles are pale grey.

The pale grey foot sole has numerous tiny, dark grey spots.

Live specimens ranged in length from 5-60 mm

Up to nine longitudinal pink to grey-blue ridges.

The ridges are formed from the coalesced bases of compound tubercles which send a very tuberculate, uneven and irregular aspect to the pink to grey-blue ridge.

Sometimes there is some cross-bars of black lines.

The rhinophores are black and each rhinophoral clavus possesses 20 to 23 lamellae (specimens greater than 30mm).

The gills and oral tentacles are dark grey.

The foot sole is white.

(Brunckhorst considered "smooth" non-tuberculate ridges characterised this species but from the various photos on the Bill Rudman Forum, it would seem some small tubercles, are part of the variability.)

References :

Bill Rudman Seaslug site : Sea Slug Forum : Phyllidiella rosans

Publications :

Brunckhorst, D.J. (1993) The systematics and phylogeny of Phyllidiid Nudibranchs (Doridoidea). Records of the Australian Museum, Supplement 16 : 1-107.

Other photos of Phyllidiella rosans :

Matthias Deuss

Mayotte, 31 December 2008