Aplidium californicum (Ritter & Forsyth, 1917)

Figure 2E

IHAK 20 BHAK 0657 UF 2506. Meay Channel, Scuba, 18 m, one colony, on algae.

IHAK 28 Second Beach, one colony 5 m, Scuba.

IHAK 31 BHAK 1698. Triquet Island Macro site, 8 m, Scuba, boulder field; one colony on Pugettia richii Dana, 1851 with Didemnum sp. 1 (undescribed species).

IHAK 37 Crazy Town surge channel 5 m, Scuba, rocky outcrop.

IHAK 60 Rattenbury Channel, 5–21m, Scuba. Large colony on rocky substrate.

RHAK 5 BHAK 0632 UF 2483. South wall, Seventh Beach, low intertidal. Three colonies, larvae in atrial chamber of zooids. Two other large colonies about 7 × 3 × 2 cm thick, not vouchered.

ZHAK 35 Sasquatch Commode tidepool rocky outcrop.

The colonies are very variable, making it a sometimes confusing species to identify. Ritter & Forsyth (1917) emphasized the variability in size, thickness and color even within a single colony. Colonies in the present collection are always flat and encrusting and may attain a large size 10 cm or more in diameter. Coloration is especially variable, though typically tan, grey or somewhat orangeish with a colorless tunic and a variable amount of embedded sand grains especially in the lower region. The zooids are usually arranged in irregularly circular systems but sometimes such an arrangement is not visible on the surface especially if the zooids are contracted. The zooids are exceptionally small, usually only 6 mm or so in length, and easily slip out of the colony when the tunic is gently squeezed. The thorax has 10–12 rows of stigmata. Ritter & Forsyth (1917) give a range of 8–14 rows but they apparently lumped more than one species. (Compare with descriptions, this study, of Aplidium kottae and Aplidium sp.) The stomach has a variable number of longitudinal ridges which may be undivided or divided. The embryos are incubated in the atrial chamber of the zooids and have a typical structure for this genus. See Van Name (1945) (as Amaroucium californicum) for a complete description of the colonies and zooids, mostly based on the original description by Ritter & Forsyth (1917).

This is a very common and widespread species from Alaska to southern California and Mexico, in shallow waters on rocky substrates and also in harbors on marina floats and pilings (Van Name 1945; Abbott & Newberry 1980; Lambert CC et al. 1996; Lamb & Hanby 2005).