Bipinnaria asterigera (Echinoderma), from the Northumberland Plankton

Authors

  • Alexander Meek F.Z.S.


Summary.

The characters of the Bipinnaria asterigera of Nortliumberland waters are:-Colour transparent. Shape: long anterior lobe dividing into anterior and posterior median ocesses (the former pointed, the latter expanded distally and slightly bifide); the processes are long, and the anterior dorsal process consists of three branches. Size (two forms, a low and a high): preserved they measure ca. 2.8 mm. and 8 mm. respectively; the high form measures alive ca. 15 mm.

The characters of the young starfish to which it gives rise are:- Colour: disc or stomach brown, arms yellow. Slinps pentagonal, disc to ray as 8 t o 5; hydropore marginal. Spines, mostly simple, columnar, marginal, in several but mainly in 2 to 3 rows; adambulacral skeleton consists of an oral bearing two spines projecting towards the mouth and of rudimentary plstes external to the tube-feet, each bearing a ventral and an external spine. Tube-feet: one row on each side of arm, muscular and terminating in a rounded conical cap, adherent; terminal tube foot similar, and enclosed in a canal at tip of arm and protected by 1ateral spines. Internally each tube-foot is provided with an ampulla.

The original anterior interradius is that of the stone canal and hydropore. It also is the interradius of separation, which means the shedding of the larval structure anterior to the starfish, including the Oesophagus. It appears that, the oesophageal region of the stomach is rotated to the posterior of the new mouth, and the intestine is withdrawn at the p1ace of closure into the starfish.

Ancillary