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Body elliptical, lacking rhinophores, with rounded lobes on either side of head; visible eyespots behind lobes. Groove separates body from foot, which tapers posteriorly; foot margin typically wider than body in most specimens, rarely covered by cerata. Anus a tube on dorsal side of body, opening above posterior end of tail on midline. Cerata cylindrical, with occasional white spots; each ceras contains one blood vessel and digestive diverticulum. No heart or pericardium present; circulation affected by rhythmic pulsing of cerata on alternating sides of body. Oviducal pore located on right side below cerata. Dorsum and cerata covered by extensive patches of brown pigment over a yellow base coloration. Dorsum raised into a hump down which runs a band of yellow background colour, splitting the otherwise solid patches of brown pigmentation down the midline (Fig. 1C). Recently-fed animals have a green colour due to Vaucheria chloroplasts retained in digestive diverticula, which ramify throughout body including cerata and foot. For 6 surveyed popu- lations, mean wet weight of adults ranged from 5.8 + 0.5 mg SE (San Francisco Bay) to 0.9 + 0.1 mg SE (south Tomales Bay), with an overall mean weight of 2.8 + 0.2 mg SE (n = 192, range = 0.3 – 15.5 mg). Penis ends in a stylet used in hypodermic insemination, with sperm transfer occurring anywhere on body of the recipient.