Diplosoma listerianum (Milne-Edwards, 1841)

Lambert, Gretchen, 2019, The Ascidiacea collected during the 2017 British Columbia Hakai MarineGEO BioBlitz, Zootaxa 4657 (3), pp. 401-436 : 407-409

Diplosoma listerianum (Milne-Edwards, 1841)

Figure 4 A–C

IHAK 17C BHAK 0639 UF 2490. South end of West Beach. On carapace and legs of spider crab Scyra acutifrons Dana, 1851 . IHAK 23 BHAK 1685 UF 2515. Kelpie Point , 15 m, Scuba. Tan colony on Scyra acutifrons . IHAK 31 BHAK 1693 Triquet Island Macro site, Scuba, 8 m. On Scyra acutifrons . IHAK 31 BHAK 1694 on spider crab Pugettia richii . IHAK 36 A BHAK 1704 West Beach Nero Site , shallow Scuba to 5 m. On red crab Pugettia foliata (Stimpson, 1860) . IHAK 43 Triquet , shallow Scuba, 5 m. On unidentified crab . IHAK 55 BHAK 1735 UF 2546. Kwakshua Petroglyph Cliff , Scuba, 17–20 m depth, vertical rock wall, high current . IHAK 60 BHAK 3242 UF 2561. Scuba , 17–20 m depth, on bryozoan. More white pigment granules in tunic than other samples .

Zooids with more black pigment. With two lamellariids Marsenina rhombica (Dall, 1871) , UF Mollusca 511737. IHAK 60 BHAK 3244 UF 2562. Scuba, 17–20 m depth. Large tan colony, growing on seaweed. XHAK 11 BHAK 3122 UF 2559. On ARMS plate, thin large tan colony.

Small colonies were collected on the legs and carapace of every spider crab Scyra acutifrons that was collected, an association also reported by Lamb & Hanby (2005), as well as on a Pugettia foliata (Stimpson, 1860) and a P. richii . One large tan colony occurred on an ARMS plate, and several were collected by Scuba from vertical rock walls and on various algal species. Two color morphs of D. listerianum were collected; in both types the tunic was colorless. One morph had zooids with varying amounts of black pigment on the thorax and abdomen; the other morph contained tan zooids with very sparse or no black pigment. No D. listerianum was collected on the laboratory floating dock; the only artificial substrate was the single colony on a settlement plate. No larvae were observed.

This species is actually a species complex, thus the worldwide distribution and possible native ranges are not well understood. It has been considered introduced or cryptogenic in most if not all of the locations where it has been collected ( Rocha & Kremer 2005). North American specimens occur from Alaska to southern California, Mexico, and Panama on the Pacific side, and from eastern Canada to Florida and Panama on the Atlantic side ( Van Name 1945 as D. macdonaldi Herdman, 1886 ; Lamb & Hanby 2005; Carman et al. 2011; Ma et al. 2018).

Figures

FIGURE 4. Aplousobranchia, Didemnidae. A–C: Diplosoma listerianum. A: colony on Scyra acutifrons; B, C: close-ups of zooids from two different color morphs. D–F: Trididemnum alexi. D: colony on living scallop; E: same colony closeup with amphipod Polycheria osborni burrowed into tunic surface; F: tunic spicules. Scale bars:A, 1 cm; B, 1.5 mm; C, 1.3 mm; D, 1.6 cm; E, 3.2 mm; F, 35 µm. Photos B and D by G. Paulay.