Thorny Armour, Soft Centre – Pencil Sea Urchins

Pencil urchins can be found in seagrass meadows, rocky shores and coral reefs

 Sea urchins are usually associated with sharp spines, but the pencil or thorny sea urchin (Prionocidaris baculosa) looks a little more dangerous because of its thorns. It is of course, painful to mistakenly step on it, but all of its spines and thorns are mere self-defence. These animals cannot jump up and attack a seagoer.

Unfortunately collected for the aquarium trade, this species is uncommon and rarely found in Peninsular Malaysia – but when in season, can be spotted in the seagrass meadows of Mukim Tanjung Kupang, Iskandar Puteri, Johor.

Thorny Armour, Soft Centre – Pencil Sea Urchins
An unwelcome bycatch, pencil urchins can wreck a fisherman’s net. They are always delicately extracted and tossed back to sea

While they look scary at first, a close examination will reveal the beauty of its armour, and the myriad colours hidden behind its thorns. Sea urchins fill an important ecological niche, eating detritus and generally cleaning up the seafloor. It is most active at night and also dines on sponges, bivalves, bryozoans and algae.

Thorny Armour, Soft Centre – Pencil Sea Urchins
Picking up and holding a pencil urchin requires skill; they are best left alone

It is actually possible to hold one as its tiny feet do not hurt when touched. Its spiky topside is there to ward off predators such as triggerfish or large wrasse. During the day, it often hides amongst rocks for safety, squeezing into crevices to get away from hunters. If in the process, it loses a spine or two, it can grow them back.

Thorny Armour, Soft Centre – Pencil Sea Urchins
Dr Serina Rahman is the co-founder of Kelab Alami and a Visiting Fellow at the ISEAS-Yusof Ishak Institute, Singapore. She is also a winner of the Iskandar Malaysia Social Hero Awards (IMSHA)

Kelab Alami conducts guided seagrass and island tours where you might be lucky enough to spot these critters. Log on to for more information (look out for our new membership plans and deals!).