Botrylloides leachii ( Savigny, 1816 )

Page, M. J., Willis, T. J. & Handley, S. J., 2014, The colonial ascidian fauna of Fiordland, New Zealand, with a description of two new species, Journal of Natural History (J. Nat. Hist.) 48 (27 - 28), pp. 1653-1688 : 1658-1659

Botrylloides leachii ( Savigny, 1816)

( Figures 4 , 3B, C )

Botryllus leachii Savigny, 1816: p. 199 –200, pl. 4, fig. 6.

Botryllus leachi: Michaelsen, 1922: p. 479 ; Brewin, 1946: p. 111 –112; Brunetti, 2009: p. 19 –21, pl. 1a–d. For synonymy see Brunetti, 2009: p. 19.

Material examined

New Records: Thompson Sound , Crayfish Heights (45° 13.182’S, 166° 58.656’E, 15 m, 30 January 2006, NIWA 49980 , eight colonies); Crooked Arm, Doubtful Sound (45° 25.121’S, 166° 56.00’E, 20 m, 2 February 2006, NIWA 49999 ) ; Breaksea Sound , First Cove (45° 34.74’S, 166° 44.43’E, 18 m, 2 February 2009, NIWA 49970 , NIWA 49971 ) ; Nine Fathom Passage , Dusky Sound (45° 44.237’S, 166° 53.199’E, 16 m, 1 February 2009, NIWA 49950 ) ; The Narrows , Long Sound (46° 02.335’S, 166° 44.16’E, 17 m, 28 January 2009, NIWA 49939 ) ; Long Sound , Only Island (45° 57.652’S, 166° 52.241’E, 16 m, 28 January 2009, NIWA 49937 ) ; Caswell Sound , Paua Bay (45° 01.01’S, 167° 08.4’E, 15 m, vertical rock wall, coll. M. Page, 3 February 2009, NIWA 49986 ) .

Previously recorded: (see Kott 1985): Australia; West Indian Ocean; Red Sea; South Africa; British Isles; North Sea; Mediterranean, Adriatic and Black Seas.

Description

Colonies are predominantly thin, encrusting dead black coral trees and rock walls, often overgrowing brachiopods and coralline algae. As is common in this genus, colony colour can vary greatly from red-purple (RP 4/4, NIWA 49999, Figure 3B ), mustard (Y 8/12, NIWA 49986, Figure 3C ) to white, almost transparent in colour (NIWA 49971). Zooids form branching meandering double row systems, and pear-shaped terminal ampullae are usually found at the growing edge of the colony. The zooids have a wide atrial opening with a large spatulate atrial languet, exposing much of the branchial sac ( Figure 4A ). The branchial sac has 11 rows of stigmata, the second row being incomplete. A distinctive flask-shaped stomach has eight continuous folds enlarged into lobes at the gastric end ( Figure 4B 1 ). There is a small inconspicuous gastric caecum, slightly lobed at its distal end, located halfway down the pyloric region of the stomach. The typhlosole lies in an open space between the first and eighth stomach folds and extends into the intestinal loop ( Figure 4B 2 ). The testis follicles have a ‘mulberry-like’ appearance (see Kott 1985) and are located ventral and adjacent to developing eggs that lie in a brood pouch extending from each side of the body wall ( Figure 4C ).

Remarks

The current species can be distinguished from other Botrylloides by the morphology of the gastric region and the location of the egg in a brood pouch at the posterior dorsal-lateral corner of the peribranchial cavity ( Brunetti 2009). Conspicuous lobes at the cardiac end of the stomach folds and a small caecum with a slightly swollen tip are common only to Botrylloides leachii and Botrylloides nigrum Herdman, 1886 . The present specimens of B. leachii however, can be separated from B. nigrum by eggs located in a brood pouch dorsal, and posterior to the testis follicles ( Figures 5A, B ), as figured for B. leachii by Brunetti (2009) from the Red Sea (p. 23, pl. 1a), a condition not described for B. nigrum from Guadaloupe ( Monniot 1983). Furthermore, B. nigrum is a tropical and subtropical species unlikely to be found in the cool water of Fiordland. The distribution of B. leachii throughout Fiordland, however, is consistent with the broad biogeographic range occupied by this species both in New Zealand and worldwide. It has been suggested that this species is opportunistic and possibly introduced ( Kott et al. 2009). Certainly, it is common in fouling communities on ship hulls and artificial substrata in ports and harbours, and may have been introduced into Fiordland by early whalers and sealers.

Figures

Figure 1. Map of Fiordland on the south-west coast of the South Island, New Zealand showing location of sampling stations.

Figure 2. Botryllus stewartensis (NIWA 49968): (A) part of a colony showing zooids arranged on sand-coated lobes; (B) zooid; (C) testis follicle; (D1, D2) parietal and mesial sides of the stomach. Scale bars: A, 10 mm; B, 1 mm; C, D 0.5 mm.

Figure 3. In situ images of: (A) Botryllus stewartensis (NIWA 49968); (B) Botrylloides leachii (NIWA 49998); (C) Botrylloides leachii (NIWA 49986); (D) Botrylloides sp. (NIWA 49967); (E) Botrylloides sp. (NIWA 68096); (F) Synoicum kuranui (NIWA 49977).

Figure 4. Botrylloides leachii (NIWA 4998): (A) Zooid; (B1, B2) parietal and mesial sides of the stomach; (C) ventral side of a zooid showing relative position of gonads. Scale bars: A, C 1 mm; B 0.5 mm.

Figure 5. Botrylloides sp. (NIWA 49967): (A) zooid with a wide atrial opening and spatulate upper and lower atrial lips; (B1, B2) parietal and mesial sides of the stomach. Scale bars: A, 1 mm; B 0.5 mm.