Hippothoa muripinnata, Souto, Javier, Reverter-Gil, Oscar & Ostrovsky, Andrew N., 2014

Souto, Javier, Reverter-Gil, Oscar & Ostrovsky, Andrew N., 2014, New species of Bryozoa from Madeira associated with rhodoliths, Zootaxa 3795 (2), pp. 135-151 : 139-141

Hippothoa muripinnata n. sp.

( Figs 10–14 ; Table 2 )

Material examined. Holotype: MNCN –25.03/3858, 32º38’30.67’’ N, 16º49’47.49’’ W, 18 m, April 2011, on rhodolith. Paratypes: MNCN –25.03/3862, 3866, 3867, NHMUK 2014.1.16.2b: same data as holotype.

Etymology. From Latin muri pinna, merlon, alluding to the crenellate appearance of the basal walls.

Description. Colonies encrusting, delicate, uniserial. Branching pattern cruciform, frequent. Autozooids 0.20–1.00 mm long, 0.02–0.04 mm wide (depending on substratum), comprising a distal dilatation, oval to subrhomboidal, and slender cauda. Cauda often more than two thirds total zooidal length. Frontal shield smooth, with fine transverse striations visible by SEM; frequently with a median longitudinal keel, often poorly defined. Basal edges of dilatation and sometimes adjacent part of cauda with 20–30 small finger-like lobes, giving them a characteristic crenellate appearance (not obvious with a binocular microscope). Autozooidal orifice longer than wide, with slightly flared rim distally and laterally; orifice outline somewhat horseshoe-shaped, with distal edge rounded and lateral margins straight, nearly parallel; proximal edge almost entirely occupied by wide, shallow sinus. Condyles small, rounded or triangular (difficult to see using binocular microscope). Autozooids giving rise to two lateral buds from distal third of dilatation. Female zooids smaller than autozooids, with very short cauda, budding laterally from an autozooid. In turn, each female zooid buds flattened distal kenozooid producing globular ooecium. Ovicell cleithral, often larger than maternal zooid; ooecium separated from it by lateral sutures, longer than wide. Combined orifice transversely D-shaped, with wide, very shallow sinus. Ectooecium smooth, with fine concentric and radial striations visible by SEM. Low median keel connects proximal edge of ooecium with slightly raised, elongated central pseudopore. Both ooecium-producing kenozooid and female zooid have characteristic crenellate basal margin. Also, the ooecium-producing kenozooid forms a distal cauda of variable length, but no new zooid has been seen. Zooeciules and ancestrula not seen.

Remarks. Hippothoa muripinnata n. sp. differs from all other species of the genus in the characteristic crenellate border of the distal dilatation of the zooids, and in the single pseudopore of the ectoooecium.

Only two species of Hippothoa were previously reported from Madeira ( Norman 1909)— H. flagellum Manzoni, 1870 and H. divaricata Lamouroux, 1821 . The overall appearance of H. muripinnata (autozooids with long cauda, short female zooids, cruciform branching) is reminiscent of H. flagellum . However, there are differences, besides those reported above, in the shape of the autozooidal orifice (more quadrangular in H. muripinnata ), the development of a median longitudinal keel (though weakly manifestated) in both autozooids and ooecia, and the presence of a central pseudopore in the ectooecium. Hippothoa divaricata also has a median longitudinal keel in the autozooids, but has a different orifice, branching pattern and relatively larger female zooids. It is likely that H. muripinnata may have been reported previously as H. flagellum if specimens were studied at low magnification with a binocular microscope.

Only a few ancestrulae of Hippothoa are known. Ryland and Gordon (1977) described and figured the presence of finger-like lobes in the ancestrula of H. gigerium and H. trigemma (now Plesiothoa ). These kind of prolongations are especially well-developed in H. muripinnata . Zooeciules seem to be rather common in other species of the genus (e.g. Ryland & Gordon 1977; Hastings 1979; Hayward & Ryland 1999) but were not observed in the present species although the material was sufficient.

SD, Standard deviation; N, number of measurements.

Figures

FIGURES 10 – 14. Hippothoa muripinnata n. sp. 10, Part of a colony, with autozooids and female zooids (holotype); 11, autozooid showing the characteristic finger-like basal lobes (paratype 1); 12, autozooidal orifice (paratype 2); 13, 14, views of the ovicell and female zooid (holotype).

Tables

TABLE 2. Measurements (in mm) of Hippothoa muripinnata n. sp.

	Mean	SD	Minimum	Maximum	N
Autozooid length (distal dilatation)	0.303	0.0200	0.278	0.331	7
Autozooid width (distal dilatation)	0.162	0.0194	0.140	0.195	7
Orifice length	0.056	0.0072	0.043	0.061	8
Orifice width	0.049	0.0060	0.040	0.056	8
Female zooid+ovicell length	0.276	0.0060	0.270	0.282	3
Ovicell length	0.147	0.0185	0.126	0.159	3
Ovicell width	0.166	0.0085	0.157	0.174	3