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Shore crab moult and mating sequence

The female shore crab (Carcinus maenas) is only receptive just after she moults her armour suit. The male guards her while she moults.

 
Photograph 1 of 6

Time zero. The split between the top and bottom half of the female crab's armour suit was spreading, with her new soft body visible behind.

 
Photograph 2 of 6

Time zero + 16 minutes. The split in the female's armour was now very wide and she was almost ready to emerge. The male was holding her carefully and appeared to be caressing her with his mouthparts.

 
Photograph 3 of 6

Time zero + 17 minutes. The female emerged completely from her old armour suit which dropped to the seabed.

 
 
Photograph 4 of 6

Time zero + 19 minutes. The male held the newly-emerged female right-way up, and the couple moved away from the discarded suit of armour.

 
 
Photograph 5 of 6

Time zero + 26 minutes. This part was a new observation for me. Before starting to mate, the male turned the female round and stroked the tip of her abdomen with his mouthparts for about a minute.

 
 
Photograph 6 of 6

Time zero + 28 to 75 minutes. The pair had now adopted the usual mating position (female upside-down and face forward, abdomens locked together). Eventually, the male would have turned the female back right-way up (as in their embrace before moulting and mating) and held her like that for the rest of the protective period while she hardened her new armour.