Distaplia occidentalis Bancroft, 1899

Lambert, Gretchen, 2019, The Ascidiacea collected during the 2017 British Columbia Hakai MarineGEO BioBlitz, Zootaxa 4657 (3), pp. 401-436 : 412-413

Distaplia occidentalis Bancroft, 1899 Type B: Flat encrusting colonies

Figure 6 B–G

DHAK 02 BHAK 1687 Rattenbury Island ARMS vicinity, Scuba, 5.2 m. One colony, red, in two pieces. With hatching tadpoles. Part of colony flat, part with very short protruding lobes.

DHAK 03 BHAK 1686 UF 2516. Mercury Islet ARMS vicinity, Scuba, 18 m. Light purple.

IHAK 9 BHAK 0539 UF 2458. Shatner Point, Fifth Beach, low intertidal, rock benches, mussel/barnacle/algal walls/tidepools. Low tide, fast current; big flat thick slab, zooids in systems; no larvae. Dark purple on surface, internal tunic is white and somewhat flocculent.

IHAK 12 Rocky intertidal across small bay from Hakai dock. One very small flat colony.

IHAK 18 BHAK 0655 UF 2504. Underside of lab dock. One colony with yellow tunic.

IHAK 18 BHAK 0659 UF 2508. Very large yellow rounded colony, about 9 cm in diameter.

IHAK 22 BHAK 0660 UF 2509. Mercury Islet, Scuba, 5–15 m. Flat white colony but with narrow base wrapped around rock .

IHAK 33 BHAK 1703 UF 2521. North Beach Nero Site , Scuba, 5 m. Orange-red encrusting .

IHAK 37 Crazy Town surge channel, Scuba, 5 m. Red .

IHAK 39 BHAK1708 UF 2524. NE Rattenbury Island , Scuba, 12 m. Bright orange, flat, 4 cm in longest dimension .

IHAK 42 BHAK 1710 UF 2510. Starfish Rocky Reef Site, Scuba, 18 m. Orange and purple mixed .

IHAK 43 Triquet, snorkel 5 m. Orange, purple and white .

IHAK 60 BHAK 1740 UF 2551. Rattenbury Pinnacle, Scuba, 17–20 m. Orange and black .

RHAK 6 BHAK 0628 UF 2479. Seventh Beach, North wall, low intertidal tide pool. Large white flat colony. Zooids only about 2 mm long.

XHAK 9 BHAK 2831 UF 2554. Kelpie Point ARMS, Scuba, 5 m. Very small; zooids very contracted but about 20 stigmata/ side.

The only morphological difference from Distaplia occidentalis type A is that these colonies are not mushroom shaped with a stalk; they are flat thick encrusting sheets in a wide variety of colors including many shades of purple, yellow, orange, red or white or even multiple colors, and may be up to 10 cm or more in diameter. Ritter & Forsyth (1917) comment on the two different growth forms: “colony varying from flat and encrusting to pedunculated or mushroom-shaped with all gradations between.” The zooids and tunic pigments are confined to the upper layer, the lower layer usually unpigmented, cream–colored and somewhat flocculent in texture.

Fertilization, the details of which are unknown, is internal and the embryos are incubated in a brood sac which extends into the tunic but is attached to the parent zooid at the base of the thorax. The oviduct is long and extends to the end of the brood sac, which means that the youngest embryos are at the posterior end of the brood sac. In all forms of D. occidentalis there are never more than four embryos in the brood sac ( Fig. 6F ), and the parent zooid dies after completing ovulation, thus later in the breeding season a colony may contain only or primarily brood sacs with maturing embryos, the adult zooids having died and been resorbed. The mature embryos are large (the body near to 1 mm in length, Fig. 6G ) and elongate, with three adhesive papillae in a triangular arrangement. Distribution and references same as for the mushroom-shaped colonies above.

Figures

FIGURE 6. Aplousobranchia, Holozoidae, various color morphs of Distaplia occidentalis. A: small mushroom-shaped colony. B–D: flat colonies. E: flat encrusting colony with protruding capitate heads. F: brood sac removed from tunic. Arrow indicates location of attachment to zooid. G: tadpole. Scale bars: A, 1 cm; B, 1 cm; C, 1.25 mm; D, 1.7 cm; E, 1 cm; F, 0.85 mm; G, 0.4 mm. D and E photos by G. Paulay.