Allometric growth pattern, sexual dimorphism and size at the onset of sexual maturity in Opusia indica (Brachyura: Ocypodoidea: Camptandriidae) from mangrove areas of Pakistan

Size at sexual maturity and patterns of somatic growth are important aspects of reproductive history of crab. The main purpose of this study is to provide an estimate for the onset of morphological sexual maturity in mangrove crab, Opusia indica from a population located in Korangi creek intertidal mud flat (Karachi, Pakistan) based on relative growth. The crabs were monthly collected through quadrat method from March 2001 to February 2002. A total of 1702 crabs was obtained, of which 764 were males, 939 were female. The morphometric measurement of carapace, abdomen, cheliped and male gonopod was related to carapace width. Based on carapace width males were significantly larger than female, indicating sexual dimorphism. The size at onset of sexual maturity in males was estimated as 5.51 mm carapace width and 5.3 mm carapace width in females. The positive allometric growth of female abdominal width were likely related to the incubation process

Morphological diversity of setae and chela in accordance to habitat within crabs of genus Macrophthalmus (Decapoda, Brachyura, Macrophthalmidae) from intertidal flats of Pakistan

Sentinel crabs of genus Macrophthalmus are deposit feeders inhabiting sandy muddy substrate. The diversity and distribution of these crabs depend upon physical, biological and environmental factors including tidal exposure, larval recruitment, salinity, pH, organic matters, air and water temperature, nutrient availability and sediment structure in which they survive. These species showed various morphological adaptations to cope with their environment and to extract food from their surroundings. Current study aimed to study structural variation in 2nd maxilliped and chela and correlate it with their habitat. The substrate structure appears as one of the most important controlling factor in the distribution of sentinel crabs. These crabs utilize their spatulate chela to gather the soft mud and sandy substrate for extraction of organic matter and specialized setae on their mouth appendages to manipulate sediment particles and to extract food from it. Current study describes the setae of the second maxillipeds within the five Macrophthalmid spp. known from the Pakistan coast by using scanning electron microscopy. In all the studied crab species plumose setae is present on meropodite, ischium and exopod flagellum, whereas spoon tipped setae are restricted to the palp region. Structural variations in these spoons tipped setae have also been reported during the present study. Comparatively, more spoon-tipped setae were present in M. sulcatus, a sand dwelling species than mud dwelling forms, provides evidence that the crabs from sandy habitats possess more spoon-tipped setae (an adaptation for processing sandy sediments) than those living in muddy habitats