Electra pilosa is a native encrusting Bryozoans found in the Gulf of Maine co-habitating with the cosmopolitan, MIS species Membranipora membranacea. Both of these encrusting colonies have a lacy appearance and are typically found on brown algae such as Laminaria sharing space on the same blade. Upon inspection, established colonies may look similar but they can be distinguished from each other by specific differential features.
Colony growth pattern is an important clue to differentiating Electra from Membranipora. Electra in its first stages of growth forms star-shaped colonies whereas Membranipora grows in a uniform, radial pattern (what Silén called "unitary multiserial", see LINK below). In contrast, the colony of Electra is separated into sectors divided by radial axes that extend beyond the margins of the colony forming a multi-pointed star (what Silén called "composite multiserial" growth). Each sector has a central growth axis composed of 2 or more parallel rows of rectangular zooids (approximately 0.33 by 0.5 mm in dimensions) flanked on each side by wings of oval or ovate zooids which fill in the area between the axes. The side walls of the calcified enclosure do not directly abut each other like in Membranipora (see February 12, 2012 post), but are separated by a translucent, calcareous surface membrane. Each enclosure is surrounded by several spines that vary in length. However, the median, proximal spine is larger than the rest and can be easily seen with a magnifing lens.
The bottom line when identifying encrusting Bryozoans in New England is to check for growth pattern (composite vs. uniform), boundary morphology (jagged vs. smooth), zooid skeletal structure (ovate vs. rectangular), arrangement of spines (larger pointed, proximal spine vs. 6 short, blunt spines, 4 at each corner of the rectangular enclosure) for Electra vs Membranipora, respectively.
Calcareous Enclosures of Electra pilosa