Hippothoa longicauda, Souto, Javier, Berning, Björn & Ostrovsky, Andrew N., 2016

Souto, Javier, Berning, Björn & Ostrovsky, Andrew N., 2016, Systematics and diversity of deep-water Cheilostomata (Bryozoa) from Galicia Bank (NE Atlantic), Zootaxa 4067 (4), pp. 401-459 : 424-426

Hippothoa longicauda n. sp.

( Figs 52–59 , Table 11 )

Material examined. Holotype: MNCN 25.03/3944, locality DR09. Paratypes: MNCN 25.03/3945, locality DR09; MNCN 25.03/3946, locality V01; MNHN IB- 2013-623, locality DW117; OLL 2015/902, 903, locality DW117.

Etymology. Alluding to the extremely long zooidal cauda characteristic of this species.

Description. Colony encrusting, uniserial. Zooids elongate-oval, with long thin cauda several times longer than length of autozooid, with transition from zooidal dilatation to cauda fairly abrupt, similar to transition the cauda of distal zooid; frontal shield convex, smooth or with transverse wrinkles, rising towards zooidal orifice, distal wall obliquely or vertically descending immediately distal to it; in dilated part of zooid lateral walls have 1 pair of basal pore-chambers from which thread-like caudae are produced at angle of 70–90°, basal pore-chambers in lateral walls normally situated slightly distal to midlength of autozooid. Orifice surrounded by distinctly elevated rim, inclined frontalwards distally, longer than wide, anter horseshoe-shaped, poster wide and deep, U-shaped, delimited from anter by pair of small rounded condyles.

Female zooids approximately half size of infertile zooids and with shorter cauda. Ovicell terminal, prominent, cleithral. Ooecium formed by subjacent kenozooid not visible frontally, about same size as maternal zooid. Ectooecium smooth with a few faint longitudinal striations including a median suture visible only by SEM. No distal budding from ooecial kenozooid observed. Transversely oval orifice of ovicellate zooids dimorphic, as wide as long, with wide shallow sinus and fairly long, narrow condyles that extend along straight lateral shoulders.

Zooeciules not seen in the available material and may not be present in this species. Ancestrula not observed.

Remarks. Only two species of Hippothoa were previously thought to occur in this region— H. divaricata Lamouroux, 1821 and H. flagellum Manzoni, 1870 (e.g. Reverter-Gil & Fernández-Pulpeiro 2001). Both are considered to be shallow-water species and allegedly have a very extensive geographic distribution while their type localities are in the Mediterranean Sea. The types of both species are presumably lost and the taxa therefore illdefined. Even within Europe, however, there are morphological differences between populations, as evidenced by a comparison of orifice shape in H. flagellum from Great Britain (Hayward & Ryland 1999, fig. 17C) with that in an Adriatic population (Hayward & McKinney 2002, fig. 18H), suggesting either some variability between populations or that the genus is more speciose than previously acknowledged. A revision of the genus Hippothoa combining morphological and genetic analyses is urgently needed.

While Hippothoa longicauda n. sp. distinctly differs from the species generally considered to be H. divaricata in that it lacks the median keel on the autozooidal frontal shield and has dimorphic orifices in ovicellate and nonovicellate zooids, it is very closely related to H. flagellum . Orifice morphology in ovicellate and non-ovicellate zooids in our material are almost identical to specimens from Great Britain (Ryland & Gordon 1979, fig. 3; Hayward & Ryland 1999, fig. 17C), although the autozooidal orifices are slightly longer and more distally positioned in H. longicauda . More significant differences exist, however, in the position of the orifice, which is reported to be placed beyond the highest point of the autozooid, and is orientated parallel to the substratum or sloping downwards distad, in H. flagellum (Hayward & Ryland 1999) . In contrast, in H. longicauda the orifice is elevated, forming the highest point of the autozooid, and it is inclined upwards distad. Zooeciules were not observed in the available material of H. longicauda ; if these are truly absent it would mark another difference between the two species. As the name implies, H. longicauda is also characterised by developing caudae that are much longer than in any of the shallow-water species. If this character is genetically determined, however, or produced as a response to environmental conditions, is unclear at present. In a settlement panel experiment recently carried out in the Azores (Wisshak et al. 2015), the single Hippothoa species present developed longer caudae with increasing depth (B. Berning pers. observ.).

Hippothoa longicauda was exclusively found on coral skeletons in five Galicia Bank localities from 765 to 835 m depth.

SD, standard deviation; N, number of measurements

Figures

FIGURES 52 – 59. Hippothoa longicauda n. sp.: 52, general view of colony (MNHN IB- 2013 - 623); 53 – 55, general view of autozooids (OLL 2015 / 903, 902, MNCN 25.03 / 3946); 56, autozooidal orifice (OLL 2015 / 902); 57, basal view of autozooid as seen in transparency, showing the position of communication pore areas; 58, 59, female zooids with ovicells (MNHN IB- 2013 - 623,).

Tables

TABLE 11. Measurements (in mm) of Hippothoa longicauda n. sp.

	Mean	SD	Minimum	Maximum	N
Autozooid length	0.390	0.0311	0.340	0.433	9
Autozooid width	0.214	0.0151	0.183	0.229	9
Orifice length	0.073	0.0062	0.063	0.080	7
Orifice width	0.065	0.0049	0.056	0.072	7
Cauda width	0.018	0.0036	0.014	0.026	9
Distance between zooids	1.051	0.4398	0.566	1.893	8