Bowerbankia pustulosa ( Ellis and Solander, 1786 )

Souto, J., Fernández-Pulpeiro, E. & Reverter-Gil, O., 2011, Presence of rhizoids in two species of the genus Bowerbankia (Bryozoa: Ctenostomata) and their systematic relevance, Journal of Natural History 45 (41 - 42), pp. 2543-2557 : 2544-2547

Bowerbankia pustulosa ( Ellis and Solander, 1786)

( Figures 1–4 , 7A )

Sertularia pustulosa Ellis and Solander 1786, p. 54 .

Bowerbankia pustulosa (Ellis and Solander) : Hincks 1880, p. 522, plate 76, figures 1–5; Brien and Huysmans 1937, pp. 13–40, figures 1–7; Prenant and Bobin 1956, p. 297, figures 122 (VI), 133, 134; d’Hondt 1983, p. 61, figure 34D; Hayward 1985, p. 150, figure 52; Zabala and Maluquer 1988, p. 74, figure 56.

Material examined

Ría de Ferrol : 43 ◦ 28 ′ 01 ′′ N, 08 ◦ 16 ′ 34 ′′ W, 8–10 m, 15 November 2009: two colonies and three fragments, on stone. MNCN-25.03 / 529: Ereaga , Bahía de Bilbao. 30 August 1994. J.A. Álvarez. MNHN-12250: Laguna de Santoña , Santander ( Spain). August 1972. Labelled as Bowerbankia imbricata (Adams) .

Description

Colony arborescent, branching, up to 8 cm high in the material examined, with a poorly defined main stem. Young portions light brown in colour, becoming darker with age due to chitinization; fixed material does not lose its colour. In fresh material both autozooids and kenozooids show numerous whitish bright spots that disappear quickly after fixation.

Erect branches formed by cylindrical kenozooids separated by transverse septa. Branching normally lateral; occasionally the in-line stolon may be deflected after ramification, giving the impression of a dichotomy.

Rhizoids produced near the proximal end of the kenozooids forming the main axis of the colony and its lateral branches. Rhizoids budded as tubular evaginations from an oval window ( Figure 3A ), curved towards the base of the colony, separated from the maternal kenozooid by a transverse septum ( Figure 3B ); buds developing as long tubes, formed by tubules separated by septa, that descend to the substratum joined to the axis of the colony ( Figure 3C ). Rhizoids may branch, especially near the basis of the colony, reaching the substratum and acting as supporting elements. They may also form new stolons that bud new autozooids ( Figures 3E , 4 ), probably forming basal portions of new erect branches.

Kenozooids each bearing in their distal parts a dense group of up to 30 autozooids occupying more than two-thirds of the length of the kenozooid. Groups form a long helix that undergoes slightly more than half a spiral turn around the stolon. Separation of the autozooids at the growing tips gives a characteristic feathery appearance to the group ( Figure 2A ). When the internode is formed by kenozooids without branching, the autozooidal groups may nearly overlap, seeming to form a long, continuous spiral ( Figure 2B ).

Autozooids budded at growing tips of the colony as small vesicles clearly arranged in two spiral series, causing slight torsion of the kenozooids bearing them ( Figure 1 ). Torsion is clear when the autozooid group is completely formed, but the spiral arrangement is less clear in later ontogeny. Autozooids deciduous, leaving a circular scar on stolon corresponding to their insertion point and the uniporous septula. Detachment of autozooids and production of new ones gives a denser appearance to the groups, masking the spiral arrangement.

Autozooids subcylindrical with quadrangular apertures; during evagination of the polypide, autozooids become bottle-shaped. Polypide with eight tentacles and a small gizzard, which is level with the basis of the tentacular sheath when the polypide is retracted. Setose collar conspicuous, with about 20 long, slender setae.

Zooids containing brown bodies are the same shape as functionally feeding autozooids, but slightly shorter.

Measurements

ZL: 0.581 ± 0.0883 (0.471 –0.731; 16) ; ZW: 0.180 ± 0.0242 (0.135 –0.221; 16) ; ZbL: 0.450 ± 0.0261 (0.416 –0.488; 12) ; ZbW: 0.153 ± 0.0194 (0.125 –0.185; 12) ; SL: 2.223 ±

0.2684 (1.762 –2.714; 11); SW: 0.203 ± 0.0222 (0.167 –0.238; 11) ; GL: 1.491 ± 0.2269 (1.095 –1.881; 11); G / S: 67.1 ± 7.07 (59.6–81.4; 11) .

Remarks

Whitish, bright spots in the cuticle of both autozooids and stolons ( Figure 2C ) apparent in fresh material but disappears quickly after fixation. This may explain why this feature has not been previously cited for this species, unless it corresponds to the spherical cells containing refractive crystals mentioned by Bobin and Prenant (1954).

Bowerbankia pustulosa seems to be distributed from the European Arctic to the European Atlantic coast, western Mediterranean and Adriatic seas. This species has been seldom reported from the Iberian peninsula, and all previous references should be considered uncertain or even wrong. Calvet (1927) reported B. pustulosa from the Balearics and Rosas (1944) from Portugal, but both are just nominal records that cannot be checked. Barroso (1912) reported this species from Santander, but his original material seems to be lost ( Álvarez 1991a). In addition, Barroso (1921) recorded B. pustulosa from the Gulf of Valencia, but the conserved material (MNCN-25.03 / 4) actually corresponds to Amathia pruvoti Calvet (see Álvarez 1991b; Souto et al. 2010). Finally, a sample from Cádiz held in the Museo Marítimo del Cantábrico (MMC-3 / M / 18), labelled as “ Bowerbankia pustulosa (Ellis et Sol.) ”, actually corresponds to Amathia lendigera (Linnaeus) ( Álvarez 1991b) .

In addition to the material collected in Ría de Ferrol, we have examined a colony from Bilbao Bay identified by Álvarez (MNCN-25.03 / 529), as well as another from Santander (MNHN-12250, labelled as B. imbricata ), which also corresponds to B. pustulosa . This species had not been previously recorded in the north-western Iberian peninsula ( Reverter-Gil and Fernández-Pulpeiro 2001), although a previous record given as Amathia distans Busk ( Fernández Pulpeiro and Reverter Gil 1995) might actually correspond to B. pustulosa (see Souto et al. 2010).

Figures

Figure 1. Growing tip of a branch in Bowerbankia pustulosa.

Figure 2. Bowerbankia pustulosa: (A) Feathery appearance of the tip of a branch; (B) internode formed by three kenozooids; (C) detail showing the bright, whitish spots.

Figure 3. Bowerbankia pustulosa: (A) Origin of a rhizoid; (B) development of the rhizoidal bud (detail in the inserted box); arrow marks the scars left by deciduous autozooids; (C) developed rhizoid, curved on the stolon; (D) rhizoidal septum; (E) rhizoid detached from the branch, forming new branches and autozooids (arrow).

Figure 4. Schematic representation of a rhizoid (in grey) forming a new stolon in Bowerbankia pustulosa (a: origin of the rhizoid; b: group of autozooids; c: septa).

Figure 7. Autozooids showing the retracted polypides (A) in B. pustulosa and (B) in B. citrina; (te: tentacles; gi: gizzard).