These arrows pierce my body like the young crabs do the mother crab and they are not of Shikhandin, but of Arjuna. The dictionary meaning is also justified and the other reading poses many problems grammatically.
Even if we take as माघमा it will be in singular and would not fit with the verb निकृन्तन्ति in the plural. For that some modification is needed माघमाः and it can go well with the verb. Then सेगव stands for the mother crab in the accusative. I am sorry that I could not get the correct reading on the net at that time. With this reading, there is no problem with the words.
The female crab is a figure of self-destruction. Thus, Draupadī remarks that Jayadratha attempting to kidnap her is digging his own grave like a female crab conceiving for her own destruction (ādāsyase karkaṭakī 'va garbham 3.252.9; vide the commentaries quoted on 6.114.60 to the effect that young crabs, being born, eat their way out of their mother's body).
The Mahabharata in Sanskrit
Book 4 Chapter 8 26
यथा कर्कटकी गर्भमाधत्ते मृत्युमात्मनः तथाविधमहं मन्ये वासं तव शुचिस्मिते॥ These words are spoken to Draupadi, when she sought the refuge of सुधेष्णा as her सैरन्ध्री expressing her fear that giving resort to her may result like the female conceive womb as her own death;