(068/ANmar) Anurida maritima (Guérin, 1839)

*bisetosa Bagnall, 1949 [possibly a good species]
*megalops Bagnall, 1949

Anurida maritima is one of the most common intertidal invertebrates on rocky shores. The map confirms its widespread distribution around the coast of Britain and Ireland (apart from NE Scotland). The largest specimen Steven has seen was 3.4 mm in length although the maximum length of individuals in most populations is 3.0 mm. Anurida maritima is dark blue in colour, has eyes with 5+5 ocelli (Fig. 2), a circular post-antennal organ (PAO) with between 6 and 11 vesicles (Fig. 3) and does not possess a furca or empodium on the foot (Fig. 4).  In culture these animals can walk upside down on the lid of a petri dish, using the back/outside of their claw  (Fig. 6). How this is achieved remains unclear.

Bagnall thought that 'our' Anurida 'maritima' was not the same species as that originally described by Guérin (1839) from the south coast of France; he gave the new species the name bisetosa after the two long setae on the tibiotarsi of his specimens. However, bisetosa was sunk as a junior synonym of maritima by Goto and Delamare Deboutteville (1953) as they found this character to be variable in both French and British specimens. Recently, Arbea (2001) has examined many more characters and has concluded that Bagnall was correct and that bisetosa and maritima are good species. However there is considerable variability between specimens, and more work is required before a firm conclusion can be reached. 

 Michelle Davies used this question as the basis for her MSc thesis (MMU 2013) and found no evidence of cryptic speciation within Anurida maritima using specimens from Cheshire, Northumberland, Wales, the English south coast and one site in Brittany, France.  She did find a kelp (seaweed) sequence in one sample, which was not previously known to form part of its diet.

 

 

 

Map Anurida maritima updated 26Nov2012
Anurida maritima

Fig. 1: Anurida maritima (2.8 mm) collected in September 2001 from Crackington Haven, North Cornwall.

PAO and eye with five ocelli of Anurida maritima

Fig. 2: PAO and eye with five ocelli (1-5) of Anurida maritima collected from Torbay, Devon in July 1947 by E. Britton.

PAO with eight lobes of Anurida maritima

Fig. 3: PAO with eight lobes of Anurida maritima collected from 'Wales' in August 1967 by Balfour Browne.

Third leg of the same specimen of Anurida maritima

Fig. 4: Third leg of the same specimen of Anurida maritima shown in Fig. 3. There is only one long tenant seta on the tibiotarsus (*).

Mandibles of the same specimen of Anurida maritima

Fig. 5: Tips of the left (L) and right (R) mandibles of the same specimen of Anurida maritima shown in Fig. 2. Ant, anterior.

Anurida maritima walking upside down on the lid of a petri dish; note that it is using the back of its claws.

 
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