Porella biserialis, 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 : 428-431

Porella biserialis n. sp.

( Figs 66–73 , Table 13 )

Material examined. Holotype: MNCN 25.03/3951, locality V01. Paratypes: MNCN 25.03/3952, locality V01; MNCN 25.03/3953, locality DR05; MNCN 25.03/3954, locality DR08; MNHN IB- 2013-626, 627, locality DW117; OLL 2015/906, 907, 924 a,c, locality DW117; OLL 2015/908, locality DR05.

Etymology. Alluding to the biserial arrangement of zooids in the erect part of the colony.

Description. Colony erect, rigid, delicate, up to 2 cm in height, from a ribbon-like encrusting base. Branching angle usually between 70° and 90°. Encrusting part composed of elongate-rectangular zooids arranged in bi- to triserial ribbons that may bifurcate. Broad base around erect part composed of frontally thickened auto- and kenozooids. Autozooids separated by suture between slightly raised thin ridges; frontal shield umbonuloid, convex, imperforate except for single row of small but distinct and widely spaced areolar pores, its surface a meshwork of smoothed shallow ridges or nodules and pits; frontal shield distally rising to form peristome with suborbicular aperture. Narrow distalmost part of peristome formed by vertical extension of distal zooid’s frontal shield.

Encrusting zooids in early-astogenetic phase with 2 thin spines present distally on peristome during early ontogeny; four such spines in first zooid budded from ancestrula; lateral walls with 1–2 uniporous septula per wall.

Primary orifice suborbicular; proximal margin straight or slightly convex, occasionally forming extremely short, broad lyrula with straight edge; condyles short, triangular, pointing downwards, not seen in frontal view.

SD, standard deviation; N, number of measurements

Avicularia small, monomorphic, usually associated with peristome; a suboral avicularium positioned on inner surface of peristomial wall, 2 others on lateral or distolateral walls having slightly elevated position outside peristome, all 3 avicularia sloping towards and directed away from orifice; an additional avicularium occasionally budded on distal peristomial wall by distal autozooid; avicularia oval, rostrum semi-elliptical, serrated, avicularian frontal area oval, semicircular palatal foramen several times larger than semielliptical postmandibular opesia, crossbar complete, without columella; cryptocystal shelf slightly broader proximally than distally.

Erect part of colony consisting of narrow branches with zooids opening on one side only. Alternating zooids arranged in 2 parallel series, their peristomes projecting from branch surface thus giving thin distal branches a waisted appearance; proximal branches entirely cylindrical and considerably thicker owing to extensive secondary calcification; zooids slightly obliquely aligned to branch axis and orifices in both series facing away from branch midline. Zooidal series usually separated by suture between slightly raised ridges but this character occasionally not seen on frontal side. Abfrontal surface structure as in frontal shield, with distinct interzooecial sutures and marginal areolar pores.

Number and position of avicularia mostly identical to encrusting zooids though lateral pair often missing from zooids in erect part of colony. No lateral or distal avicularia observed in ovicelled zooids; additional avicularia may be formed anywhere on frontal and abfrontal zooidal walls during late ontogeny when many features and even orifices are disguised by secondary calcification.

Ovicells prominent. Ooecium produced by distal zooid, globular, slightly wider than long. Calcified ectooecium immediately covered and becoming somewhat immersed by secondary calcification of distal zooid during ontogeny, its surface as in autozooidal frontal shield, proximal margin concave and on same level as peristomial aperture, opening into peristome, not closed by operculum.

Ancestrula tatiform, slightly longer than wide, some nine spines evenly spaced around semicircular to oval opesia; lateral walls steeply sloping, smooth gymnocystal calcification particularly well developed proximally, usually budding single distal zooid.

Remarks. The new species is here assigned to the genus Porella Gray, 1848 , owing to its overall similarities in zooidal, orificial and ooecial characters. Porella is a speciose genus, comprising about 40 Recent species worldwide, 17 of which occur in European waters (Bock 2014). Porella biserialis n. sp. differs from all of the latter, and from the species of the closely related or synonymous genera Palmiskenea Bishop & Hayward, 1989 , Marguetta Jullien in Jullien & Calvet, 1903 and Bryocryptella Cossman, 1906 in the combined presence of an erect, biserial growth with zooids opening on one side only, and by the presence of three avicularia on the peristome.

Whereas most European species produce encrusting colonies, the supposedly widespread Porella laevis (Fleming, 1828) forms large erect colonies with robust branches that are composed of four or five zooidal series. Porella compressa (J. Sowerby, 1805) , which occurs from the Bay of Biscay northwards, develops thickly calcified, branching to massive colonies. In contrast, all species in the genus Palmiskenea produce bilaminar branching colonies. Marguetta pulchra Jullien in Jullien & Calvet, 1903 forms massive branches with zooids opening all around and has only a single suboral avicularium (J. Souto pers. observ.). The same applies to the type species of Bryocryptella , B. torquata (Jullien in Jullien & Calvet, 1903) (Reverter-Gil & Fernández-Pulpeiro 1999b). While it is clear that a revision of the species and genera mentioned above is urgently needed, none of these species can be unequivocally identified as a sister taxon of the new species from Galicia Bank.

One species that does appear to be very closely related to P. biserialis n. sp. is the erect biserial Palmicellaria tenuis Calvet, 1906 , although Palmicellaria Alder, 1864 is currently placed in the family Celleporidae Johnston, 1838 . Study of the type specimen (MNHN 419), however, suggests that this species is not a celleporid, and that, although ovicells are lacking, it is rather to be placed in the Bryocryptellidae (J. Souto pers. observ.). We therefore include Palmicellaria tenuis in the genus Porella (as Porella tenuis n. comb.). The two species can be distinguished by the different zooidal surface structure (shallow ridges or nodules and pits in P. biserialis , smooth in P. tenuis ), and by the morphology of the orifice and lyrula (orifice usually with a straight or convex proximal margin in P. biserialis , and almost straight lateral orificial margins and a short square lyrula in P. tenuis ).

Anatomical studies show that ovicells are acleithral in Porella smitti Kluge, 1907 (Ostrovsky 2013) and in two other Porella spp. (A. N. Ostrovsky unpubl.). We suggest that the same type of ovicell closure is present in P. biserialis .

Porella biserialis n. sp. is common on Galicia Bank, being recorded from more than 20 stations between 685 and 1697 m depth, mainly encrusting coral skeletons but also growing on shells and rocks.

Figures

FIGURES 66 – 73. Porella biserialis n. sp.: 66, frontal view of erect colony (MNCN 25.03 / 3952); 67, basal (abfrontal) side of erect colony (OLL 2015 / 906); 68, zooidal orifice in older part of a colony (MNCN 25.03 / 3954); 69, part of colony with several ovicellate zooids (MNCN 25.03 / 3954); 70, autozooid with ovicell (MNCN 25.03 / 3954); 71, zooidal orifice with proximal and lateral avicularia; 72, ancestrula and daughter autozooids in an adnate colony part (MNHN IB- 2013 - 626); 73, two ancestrulae (the tube-like do not belong to the colony) (MNHN IB- 2013 - 626).

Tables

TABLE 13. Measurements (in mm) of Porella biserialis n. sp.

	Mean	SD	Minimum	Maximum	N
Autozooid length (erect)	0.918	0.0894	0.728	1.057	12
Autozooid width (erect)	0.337	0.0435	0.270	0.426	12
Autozooid length (encrusting)	0.769	0.0750	0.640	0.888	14
Autozooid width (encrusting)	0.365	0.0561	0.276	0.479	14
Avicularium frontal area length	0.064	0.0040	0.058	0.069	7
Avicularium frontal area width	0.062	0.0067	0.052	0.069	7
Ooecium length	0.235	0.0131	0.226	0.250	3
Ooecium width	0.338	0.0265	0.319	0.368	3
Ancestrula length	0.506	0.0068	0.501	0.514	3
Ancestrula width	0.375	0.0258	0.346	0.396	3
Ancestrular opesia length	0.239	0.0132	0.229	0.254	3
Ancestrular opesia width	0.219	0.0209	0.195	0.233	3