It seems like a polyp...

Definitely looks like some sort of Actinian. Could you provide more information on where the photo was taken (i.e. depth), or do you have more photos of the organism?

I am surprise to see what is your question is?

If this question is about just want to know what Cnidaria is then read this google definition

an aquatic invertebrate animal of the phylum Cnidaria, which comprises the coelenterates.

and if you really want to know seasonal variations, living habitat ect along coast of Karachi Pakistan , then try to download these papers and read what research on Cnidaria along karachi coast has been done.

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9125911&fileId=S1755267213001085

http://www.faunajournal.com/vol2Issue5/pdf/2-4-13.1.pdf

http://www.zsp.com.pk/pdf38/225-232%20_9_.pdf

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=4018476&fileId=S1755267207007294

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9579260&fileId=S175526721500007X

https://www.researchgate.net/profile/Shahnawaz_Gul/publication/282335015_OCCURRENCE_OF_ZOANTHID_COLONIES_(CNIDARIA_HEXACORALLIA_ZOANTHARIA)_AT_KARACHI_COAST_PAKISTAN_A_PRELIMINARY_REPORT/links/560d074108ae73e7a6a31a25.pdf

www.biotaxa.org/cl/article/download/11.1.1551/11557

http://zsp.com.pk/pdf38/225-232%20_9_.pdf

http://biotaxa.org/cl/article/view/11.2.1609

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9200283&fileId=S1755267214000189

Regards;

Muhammad Usman Saleem

Article OCCURRENCE OF ZOANTHID COLONIES (CNIDARIA: HEXACORALLIA: ZOA...

dear Salim 

thanks for sending me all the cnidarian links except those  which I authored.Incidentally i have all these papers but still I was unable ot identify the specimen in my photo.I have worked for 40 years on marine invertebrates of Pakistan mostly the crustaceans but when I come across other phyla I want expert opinion

then, please go to search tap available in researchgate( top right side of inbox), change the type " researchers" then type in it  "Cnidaria" , list of all researchers associated with this term will appear, contact them manually if you can

Hope this info will be fine for you.

Muhammad Usman Saleem