Hippoporidra dictyota, Ryland, 2001

Ryland, J. S., 2001, Convergent colonial organization and reproductive function in two bryozoan species epizoic on gastropod shells, Journal of Natural History 35 (7), pp. 1085-1101 : 1092-1095

Hippoporidra dictyota sp. n.

Hippoporidra Canu and Bassler, 1927 (family Hippoporidridae ).

Generic diagnosis. Colonies encrusting, multilaminar, mammillate or nodular, typically on pagurid-occupied gastropod shells. Autozooids dimorphic: a network of jumbled, standard-sized zooids surrounding mammillae of larger, more regular zooids (which have a smaller ori®ce). Frontal wall a cryptocyst with marginal pores. Ori®ce`cleithridiate’, the sub-oval outline constricted by prominent condyles into larger anter and smaller poster (®gure 3C, D); no oral spines. Ovicell prominent, imperforate, not closed by the zooidal operculum. Avicularia dimorphic: small adventitious or large vicarious. Type species Cellepora edax Busk, 1859 .

Background. The eastern Atlantic species of Hippoporidra have been revised by Taylor and Cook (1981). Hippoporidra edax is a fossil species from the Coralline Crag of SuOEolk, England, and is not known from Recent seas. It is not the marine species described, for example, by Hincks (1880: 311) or Hayward and Ryland (1979: 214) as H. edax Ðthat is H. lusitania Taylor and Cook, 1981 . From the western Atlantic oOE Florida, Smitt (1873) recorded three`forms’ referred to H. edax (f. typica, f. calcarea and f. janthina ), none associated with pagurids. Two species occur oOE North Carolina ( Maturo, 1968): H. calcarea (Smitt’s f. calcarea ) and an unnamed species, perhaps that from the`®shing banks’ identi®ed as H. edax by Osburn (in Pearse and Williams, 1951). If the latter is the present species it is quite unlike H. lusitania . The present species is accordingly described as new.

Type specimens. HOLOTYPE: BMNH 1999.12.17 .1 (®gure 1G, 1). Type locality: Black Rocks, ~ 10 nautical miles SSW of Cape Lookout , North Carolina, 34 ss 20 ¾ N, 76 ss 35 ¾ W, chart depth ~ 10 fathoms (5 18 m) at MLW; 4 August 1977 . Paratypes from type locality: BMNH 1999.12.17.2-3. Additional paratypes: Smithsonian Institution USNM 21601 collected by F. K. McKinney from approximately the same area, July 1983 .

Description. Colonies of massive form, ovoid or somewhat irregular, 18±30 mm long, originating on a pagurid-occupied shell; in some cases the distal part clearly overgrowing a small, whorled shell, suggesting later free growth as a carcinoecium; strongly patterned, mid to dark brown against oOE-white to pale buOE, with roundish or polygonal spots (maculae) of one colour separated by thin, intersecting stripes of the other (®gure 1G), as in netting (hence dictyota , from Greek dictyon, net); the pattern visible in sections as radiating stripes (®gure 1H); the centre of each macula raised, forming a mammilla; nearest neighbour distance of mammillae ~ 2.8 mm ( table 1). Zooids dimorphic, those of the mammillae larger than those of the surround (®gure 3). Mammilla zooids few, more or less elevated, directed up and partly comprising the mammilla, polygonal (commonly hexagonal), longer than wide (maximum ~ 0.60 Ö ~ 0.40 mm; table 1; ®gure 3B, C); the frontal wall raised as an imperforate suboral mucro, peripheral calci®cation thick, nodular and porous; ori®ce cleithridiate, ~ 80 Ö~ 65 m m, with prominent, narrowly triangular condyles separating the level, subcircular anter from the upward-slanting, almost semicircular poster (®gure 3C; operculum in ®gure 4B). Surrounding zooids smaller, ~ 0.40 Ö ~0.24 mm; away from the mammillae increasingly jumbled, close-packed, vertical in orientation; frontally budded so that a layer of functional zooids overlays the previous layer in which ori®ces appear more or less occluded (®gure 3A); the ori®ce surrounded by a convex collar of frontal wall ~ 200 m m diameter, cleithridiate, ~ 100 Ö~ 85 m m, the pointed condyles swept back towards the poster (®gure 3D); operculum in ®gure 4A. Ovicells only present away from the mammillae, prominent, smooth, imperforate, ~ 160 Ö~ 160 m m, with a less calci®ed triangle or crescent above the opening (®gure 3E). Large broad vicarious avicularia scattered abundantly among the autozooids, even close to the mammillae; mandibles broader than high, subtriangular, with the free sides distinctly sinuous (®gures 3C, E, 4E, F). Some zooids with a small adventitious avicularium in variable orientation near to the ori®ce; mandible in ®gure 4C, D. Lophophores dimorphic: in mammilla zooids (assumed male) each comprised two pairs of rigidly erect, unciliated tentacles, the dorsal pair being the longer, ~ 500 m m (®gure 5C); in surrounding zooids (assumed female) the lophophores comprised 12 normally ciliated tentacles in a symmetrical funnel, ~ 380 m m top diameter (®gure 5B); toward the mammillae the lophophores become bilaterally symmetrical, with the nearer (and morphologically dorsal) tentacles the longer (®gure 5A). The pagurid associated with the 1977 specimens was identi®ed as Paguriste s tortugae Schmitt , distributed from North Carolina to Surinam ( Williams, 1984).

Related species. The most similar congener is H. senegambiensis ( Carter, 1882) from West Africa. This has the same pattern of dark spots against a pale ground, or vice versa ( Cook, 1964). However, the colonies grow away from the shell as several (up to 10) long arms, producing an irregular, three-dimensional star. The large vicarious avicularia are highly variable, with the mandible spathulate, slenderly triangular, or shallowly triangular, almost semicircular. This last is somewhat like that of H. dictyota (®gure 5E, F), except that the free edges are convex rather than sinuous; other shapes have not been seen in H. dictyota .

Western Atlantic species have been reported from North Carolina ( Pearse and Williams, 1951; Maturo, 1968), around Florida ( Smitt, 1873; Osburn, 1914; Deichmann, 1954) and in the Gulf of Mexico ( Canu and Bassler, 1928). The large and distinctive` Texas Longhorns’ ( Deichmann, 1954), in which the Hippoporidra colony extends outwards from the shell as a pair of long (to 12 cm or more across), taperingÐand presumably balancedÐprojections, have been referred to H. edax , though such identi®cation clearly requires revision following Taylor and Cook’s (1981) clari®cation of that species. According to Williams (1984) the hermit crab associated with the` Texas Longhorns’ in Paguristes hummi Wass. Hippoporidra calcarea ( Smitt, 1873) may be nodular or have similar form but is smaller and uniformly pale; the mandibles of the vicarious avicularia are almost triradiate in shape. Neither of these species has spotted coloration, though such forms do occur in the Gulf (F. J. S. Maturo, personal communication in Ryland, 1979b). While Osburn (in Pearse and Williams, 1951) identi®ed specimens from the North Carolina ®shing banks as `H. edax ’ he had earlier ( Osburn, 1914) regarded H. calcarea as inseparable from `H. edax ’. Maturo (1968) recorded H. calcarea oOE North Carolina and as ranging southwards from Cape Hatteras. Smitt’s (1873) third species, H. janthina , has darkly pigmented violet or blue-black colonies.