Mourellina, Reverter-Gil, Oscar, Souto, Javier & Fernández-Pulpeiro, Eugenio, 2011

Reverter-Gil, Oscar, Souto, Javier & Fernández-Pulpeiro, Eugenio, 2011, Revision of the genus Crepis Jullien (Bryozoa: Cheilostomata) with description of a new genus and family and notes on Chlidoniidae, Zootaxa 2993, pp. 1-22 : 18-19

Discussion of Mourellina n. gen.

Harmer (1926) described two forms of Crepis decussata : an erect, multiserial form, with avicularia, and a repent, uniserial form, without avicularia. Although it is not impossible that an encrusting uniserial network give rise to a multiserial erect part, as Harmer (1926) argued, in the absence of direct evidence that this is the case it appears unlikely that both forms belong to a single species. The erect form, here described as Mourellina decussata n. comb., forms quadriserial branches having a strict growth pattern, with the four-seried stems bifurcating into two biserial branches. Some autozooids are replaced by vicarious avicularia ( Figure 38 ), each provided with a polypide ( Figure 41 ). The repent form, here described as Mourellina gonzaloi n. sp., forms uniserial colonies in which new branches are produced by lateral budding from one side of the tubular caudal part of the autozooid and avicularia do not seem to exist. The projecting portion of the zooid is different in both species, being spoon-shaped and as wide as the tubular portion in M. decussata and boat-shaped and wider than the tubular portion in M. gonzaloi . Moreover, zooids are larger in M. decussata , especially the tubular portion, which is twice as long as in M. gonzaloi . Finally, the zooids of M. decussata have internal mural spinules, which are absent in the repent species. Overall, we consider both forms to be separate species, something that Harmer (1926: 320) himself suggested.

Nevertheless, the zooidal characters of both species are so similar that it is evident that a close relationship must exist. The zooids in both have the distal part angled outwards from the stem axis, with an adherent tubular proximal portion, the cryptocyst of the dilatation is reduced, and it has an upwardly curving distal lip. In M. gonzaloi the new branches are produced by lateral budding from the tubular section of the autozooid; in M. decussata a new series in a branch is also formed by lateral budding from the cauda, closely applied to the parent zooid. This arrrangement can be seen as a transformation of the lateral branching of the repent species, thus representing a homologous character. Therefore, we believe that the two species must be placed in the same genus. It cannot be Crepis , however, because, inter alia, the cryptocyst is much reduced to a small shelf under the frontal membrane; for the same reason it cannot be close to Chlidonia . We therefore propose here to erect a new genus for the two species, whose particular characteristics justify, in our opinion its placement in a new family.

As stated above, internal mural spinules are present only in M. decussata n. comb. These spinules are visible in the material preserved in alcohol (ZMA V.Br. 875/3) ( Fig. 42 ) but not in the slides (e.g. NHMUK 1928.3.6.121). Owing to the scarcity of material, and to its state of preservation after a century in alcohol, we were not able to determine if some of these structures are free internal spicules. We made histological cuts of a small portion of a branch, in which it was not possible to observe free spicules or internal spinules. Fresh material would be necessary to determine this one way or the other. If there are indeed free spicules, the genus would be one of only a few to exhibit them. The family Thalamoporellidae Levinsen, 1902 is apparently unique among Bryozoa in possessing such spicules (see e.g. Harmer 1926; Gordon & Parker 1991). The characters of this family, however, are very different from Mourellinidae n. fam.; moreover, thalamoporellid spicules have a very precise geometric form. On the other hand, simple or branching mural spinules have been reported in other cheilostome families that are taxonomically unrelated — in certain species of Electridae and Membraniporidae ( Gordon & Parker 1991) and Celleporidae ( Voigt & Cook 1983; Mawatari 1986) they project from the zooidal walls into the coelom. The presence or absence of internal mural spinules in Mourellina n. gen. may have no taxonomic significance at the genus level.

The proximal end of the colony is not present in any of the specimens of M. decussata , so it is not known if there is a basal encrusting part or rhizoids. In M. gonzaloi, Harmer (1926) described colony growth from a small basal disc that produces the first zooid. This pattern actually corresponds to the general branching pattern, quite abundant in the material examined (see Figs 43 and 48 ). It seems that the new branch is easily detached from the parent zooid, pulling off the cuticular rim of the basal pore, resembling a basal disc (see Harmer 1926, pl. 15, figs 9, 12 and Fig. 49 in the present paper).

The phylogenetic position of the Mourellinidae will not be clarified until more material is collected, with information about its reproduction, larvae, ancestrula and astogeny.

In the superfamily Calloporoidea, the family Quadricellariidae Gordon, 1984 also presents quadriserial stems and Nelliella Mawatari, 1974 has vicarious avicularia. However, the zooids in this family are essentially hexagonal to rectangular, flat-surfaced, and not divided in two different portions.

Within the Buguloidea, Mourellina may share some characters with the family Epistomiidae Gregory, 1893 and the genus Nordgaardia Kluge, 1962 . Both taxa present erect colonies and paired zooids with a long tubular portion and a distal dilatation with an extensive area of membranous frontal wall. Both also present strict patterns of branching (see detailed descriptions in e.g. Prenant & Bobin 1966; Hayward 1978; Cook 2001) that differ from what is found in Mourellina . Also, these taxa lack a cryptocyst and vicarious avicularia. The Epistomiidae presents branches with dorsal and frontal sides and Nordgaardia has ovicells.

From the appearance of the zooids, the lightness of calcification and the scarce development of the cryptocyst, this family might have affinities with the superfamily Buguloidea Gray, 1848.

Both M. decussata and M. gonzaloi have been collected from the Banda Sea, Indonesia, the former at 2081 m depth, and the latter between 1158 and 3112 m depth.

Figures

FIGURES 34 – 38. Mourellina decussata (Harmer, 1926) n. comb. (ZMA V. Bry. 1811, lectotype). 34, part of a colony; 35, a dichotomy; 36, 37, projecting portion of autozooids showing the cryptocyst; 38, a vicarious avicularium.

FIGURES 39 – 42. Mourellina decussata (Harmer, 1926) n. comb. 39, a dichotomy (ZMA Br. 1460, paralectotype); 40, same, lateral branching; 41, same, vicarious avicularia, showing the musculature; 42, internal mural spinules (ZMA V. Br. 875 / 3, paralectotype).

FIGURES 43 – 47. Mourellina gonzaloi n. sp. (ZMA V. Br. 875 / 5, holotype) 43, view of the colony; note the typical branching pattern (arrow up left); 44, 45, projecting portion of autozooids; 46, whole autozooids; 47, a new branch detached from the parent zooid.

FIGURES 48 – 49. Mourellina gonzaloi n. sp. (ZMA Br. 1450, paratype) 48, branching pattern (arrow: connection with the main axis); 49, a new branch detached from the parent zooid; note the basal disc.