Myopedicellina spinosa ( Robertson, 1900 ) Shaw & Proctor & Borisanova, 2024

Shaw, Scott R., Proctor, Heather C. & Borisanova, Anastasia O., 2024, Myopedicellina, a replacement name for Myosoma Robertson (Entoprocta: Pedicellinidae), Zootaxa 5555 (3), pp. 436-442 : 438-439

Myopedicellina spinosa ( Robertson, 1900) n. comb.

Type-species of the genus Myosoma Robertson, 1900

( Figs 1a , 2 )

Diagnosis. Body size: 0.64-3.6 mm.

Stolon pale, narrow (narrower than stalk). Sterile segments often short, making the colony resemble a dense mat. Stalk wide, tapering slightly from base to apex. Longitudinal musculature on oral side of stalk more strongly developed than on aboral side. Aboral side of stalk bearing spines ( Fig. 1a ). Calyx large, usually with 14 short tentacles (number of tentacles ranges from 10 to 18) ( Figs 1a , 2 ). Tentacular membrane wide. Aboral side of calyx usually with spines.

Distribution: Pacific coastal waters of southern California, United States, northwards to British Columbia, Canada.

Ecology. Natural enemies include the nudibranch sea slugs Ancula lentiginosa Farmer ( Fig. 3 ) and Ancula pacifica MacFarland , which can often be found on colonies of M. spinosa (J. Goddard, pers. comm.). Ancula pacifica is considered a specialized predator that feeds on entoprocts ( McDonald & Nybakken 1978; Nybakken & McDonald 1981; Picton & Morrow 1994; Behrens 2004).

Figures

FIGURE 1. Colony structure of the two described species of Myopedicellina new replacement name. Scale bar: 0.5 mm. 1a. Myopedicellina spinosa (Robertson, 1900) n. comb. based on Figs 1a, 2 in Wasson (1997). 1b. Myopedicellina hancocki (Soule, 1955) n. comb., based on Fig. 2 in Soule (1955).

FIGURE 2. Myopedicellina spinosa (Robertson, 1900) n. comb., collected 2 May 2010 from the underside of a boulder in a low-intertidal pool at Naples Point, 34.4337°, -119.9501°, Santa Barbara County, CA, USA, and photographed under a dissecting microscope in the lab. Photo courtesy of Jeff Goddard, Marine Science Institute, University of California, Santa Barbara. The largest calyx shown here was approximately 400 microns in diameter. Branching colonial ciliates are visible growing on the calyces of the entoproct, especially on zooids at upper left and upper right. The stolons connecting the zooids, and the spines on their calyces and stalks, are not visible. Two species of nudibranch sea slugs that specialize in feeding upon entoprocts, Ancula pacifica MacFarland, 1905 and A. lentiginosa Farmer, 1964, were found at Naples Point on the same date as this specimen of M. spinosa.

FIGURE 3. Dorid nudibranch sea slug Ancula lentiginosa Farmer 1964 and its white egg masses and entoproct prey, Myopedicellina spinosa, (Robertson, 1900) n. comb., in situ, low rocky intertidal, Tarantula Reef, Jalama Beach, 34.4949°, -120.4970°, Santa Barbara Co., CA, USA, photographed 7 July 2016. Photo courtesy of Jeff Goddard, Marine Science Institute, University of California, Santa Barbara. The nudibranch slug was only 4 mm long, but it looks like a giant in this “micro-forest” growing on the underside of a low intertidal cobble at Jalama. Myopedicellina spinosa are the translucent, wine-glass-shaped zooids bent over (probably in defensive posture) on their relatively thick and flexible stalks and visible underneath the slug and in the foreground. The skinny, semi-opaque white tubes at lower left appear to be zooids of a cyclostome bryozoan. The fuzzylooking stalks across the top and in front of the slug are colonial hydrozoans covered with translucent, branching colonial ciliates and a few brown benthic diatoms.