Hippomenella mucronelliformis ( Waters, 1899 )

Berning, Björn, 2013, New and little-known Cheilostomata (Bryozoa, Gymnolaemata) from the NE Atlantic, European Journal of Taxonomy 44, pp. 1-25 : 10-13

Hippomenella mucronelliformis ( Waters, 1899)

Fig. 3 , Table 3

Lepralia mucronelliformis Waters, 1899: 11 , pl. 3, figs 15, 21.

Lepralia mucronelliformis – Norman 1909: 306.

Hippomenella mucronelliformis – Brown 1949: 513, figs 1, 2a,b,d,e.

Material examined

Lectotype

MM 3780 (here designated), Madeira (no further information provided as to the exact location or depth), on bivalve fragment, mounted on slide, Waters collection.

Paralectotype

MMF 42297 (here designated), Madeira (no further information provided as to the exact location or depth), on bivalve fragment, mounted on slide, J.Y. Johnson collection.

Other material

MM 3781, Madeira (no further information provided as to the exact location or depth), opercula, in Canada balsam on slide, Waters collection; NHMUK 1947.8.12.1, Madeira (no further information provided as to the exact location or depth), two colonies on bivalve shell fragments and several isolated zooids mounted on slide, from the Canon J. de G. Barreto collection.

Although Brown (1949) stated that the lectotype was chosen by Norman (1909: 306), this author simply mentioned that he had “seen the type”. This may not violate Article 74.5 of the ICZN Code ( ICZN 1999), and may represent a valid designation of the lectotype. However, it is unclear exactly what specimen Norman had seen: the colony now kept at Manchester Museum or that from the Funchal Museum. Both specimens carry identical labels and the handwriting of Waters, and are clearly syntypes. Moreover, the slide from the MMF, which was considered by Brown to contain the type specimen, originally comprised two colonies, judging from the remains of glue in the slide cavity, whereas neither Waters (1899) nor Norman (1909) explicitly mentioned how many specimens they were referring to. A small green label on MM 3780 indicates that this specimen was figured by Waters (a single autozooid; pl. 3, fig. 21), whereas a green and red label on MM 3781 denotes this specimen (supposedly containing opercula) as the figured type specimen (Pl. 3, Fig. 15). However, it is unclear from which colony the opercula were taken; more importantly, there is not a single operculum present on the slide today. They have either decayed or been lost, as one edge of the cover slide is shattered. This specimen must, therefore, not be regarded as a type.

To conclude, I disregard Brown’s (1949) statement that “the type” had been chosen by Norman (1909), and designate as lectotype of H. mucronelliformis the figured specimen MM 3780. The only remaining syntype specimen on the slide of sample MMF 42297 becomes the paralectotype.

Description

Colony encrusting, unilaminar, multiserial, forming small patches. Zooecia relatively large, subhexagonal, widest at about mid-distance, occasionally wider than long, separated by deep furrows ( Fig. 3 A-C); communication between zooids via up to 5 multiporous pore plates per neighbouring zooid ( Fig. 3G ). Frontal shield slightly convex proximally, somewhat raising distally towards orifice, secondary calcification forming a blunt prominent suboral mucro during ontogeny ( Fig. 3C, D ), surface rugose to nodular, central drop-shaped area imperforate, demarcated by a row of densely spaced areolar pores with radially aligned intervening ridges indicating the extent of the central umbonuloid part of the frontal shield ( Fig. 3C, E ), 1-3 additional rows of widely-spaced pores in the external area towards zooid margin, particularly abundant proximolateral of orifice with 1-2 rows extending between orifice and distal zooecial margin ( Fig. 3C ). Orifice elongate oval, longer than wide and usually widest in distal third, proximolateral edges rounded, the slightly concave proximal margin covered by the overarching and distally pointing mucro, blunt condyles formed by a continuation and slight inbending of lateral orifice margins, directed proximomedially and delimiting the proximal fourth or fifth of total orifice length ( Fig. 3D ); operculum strongly sclerotised with a pair of lateral ridges where muscles attach; usually 6 (range 4–7, in early astogenetic zooids up to 9) oral spines along distolateral orifice margin, the proximal pair slightly larger, two in ovicellate zooids ( Fig. 3A, B, F ).

Ooecium hyperstomial, depressed globular, slightly wider than long, endooecial surface fairly smooth, imperforate but distolaterally with numerous small round pits ( Fig. 3F ), proximal ooecial margin concave, shallowly arched, reaching towards lateral orifice rim, not closed by the operculum.

Avicularia adventitious, dimorphic, usually paired ( Fig. 3F ), occasionally single, rarely absent, situated lateral or proximolateral to orifice at zooid margin, directed laterally or proximolaterally except in early astogenetic zooids where the rostrum points proximally and the avicularia are more proximally positioned ( Fig. 3B ); small avicularium with a relatively short, proximally incurved rostrum, distally parallel-sided, downcurved and chute-like with open end, mandible thin and elongate, up to four times the length of rostrum ( Fig. 3A ); often one avicularium or sometimes both greatly enlarged, their width usually exceeding length of smaller avicularia ( Fig. 3C, F ), positioned on a slightly enlarged perforated cystid, rostrum proximally incurved, distally thin and parallel-sided with an acute downcurved tip, reaching over the lateral zooid’s frontal shield, mandible confined to rostrum; crossbar in both avicularium types complete without columella, proximal opesia semicircular.

Ancestrula not observed.

Remarks

Apart from its type location at Madeira, H. mucronelliformis has been reported from NW Morocco by Canu & Bassler (1925: 30) as well as from the Mediterranean Sea by Harmelin (1969: 1208, figs 6-9), Hayward (1974: 371), Zabala (1986: 407, text-fig. 134, pl. 6, figs B, C), and Zabala & Maluquer (1988: 117, text-fig. 244, pl. 8, fig. H), from depths down to 200 m. However, most of these works lack a thorough description and illustration, and because some of these records differ in a few aspects from the type, I have only included the records from Madeira in the synonymy list. For instance, in at least some of the specimens recorded by Zabala (1986) and Zabala & Maluquer (1988) from the Western Mediterranean, the suboral mucro is not developed or only very reduced, as can be seen in the provided SEM images. In turn, the orifice of the specimen from the Eastern Mediterranean Sea imaged by Harmelin (1969) has medially pointing condyles. Therefore, these records need to be checked for conspecifity based on SEM observations.

There are also several fossil specimens that have been recorded as H. mucronelliformis . Those from the Pliocene of Sicily ( Pouyet & Moissette 1992: 62, pl. 9, fig. 9) very much resemble the Recent type, whereas the Middle Miocene specimens from the Paratethys are similar but probably represent a distinct species, as they have a slightly different orifice shape and the proximal ooecial margin is rimmed ( Zágorsek 2010: 168, pl. 143, figs 1-4). These records show that the genus Hippomenella has a considerable fossil history in the Paratethys, and also that the Atlantic-Macaronesian region may have played an important role in acting as a refuge for Paratethyan-Mediterranean bryozoan taxa during the Messinian salinity crisis and/or the Pleistocene temperature minima (e.g., Berning 2006). Similar temporal and geographic distribution patterns were recently reported in species of the cheilostome genera Saevitella Bobies, 1956 and Calloporina Neviani, 1895 (see Berning 2012).

Figures

Fig. 3. Hippomenella mucronelliformis (Waters, 1899). A. Overview of autozooids in the lectotype (MM 3780); note the extremely long and slender mandibles of the small avicularia. B. Early astogenetic part of the paralectotype (MMF 42297), including the zooid interpreted by Brown (1949) to be the ancestrula (at lower left) but which is here considered as the first autozooid; note that the avicularia in early astogenetic zooids are proximally positioned and directed. C. Autozooids and an ovicellate zooid at the colony margin; note that the forming endooecium is not perforated by pseudopores and that the suboral mucro is absent in early ontogenetic zooids, forming only during later ontogeny (NHMUK 1947.8.12.1; photo: M.E. Spencer Jones). D. Close up of orifice (lectotype, MM 3780). E. Interior frontal shield with the umbonuloid ring-scar framed by areolar pores (NHMUK 1947.8.12.1; photo: M.E. Spencer Jones). F. Ovicellate zooid; note the superficial pits on the distolateral endooecium (NHMUK 1947.8.12.1; photo: M.E. Spencer Jones). G. Lateral view of a zooid (distal is to the right), showing five multiporous pore plates in the vertical wall (NHMUK 1947.8.12.1; photo: K.J. Tilbrook). Scale bars: A = 400 µm; B, C = 200 µm; D = 50 µm; E, F, G = 100 µm.