Exechonella antillea ( Osburn, 1927 )

Cáceres-Chamizo, Julia P., Sanner, Joann, Tilbrook, Kevin J. & Ostrovsky, Andrew N., 2017, Revision of the Recent species of Exechonella Canu & Bassler in Duvergier, 1924 and Actisecos Canu & Bassler, 1927 (Bryozoa, Cheilostomata): systematics, biogeography and evolutionary trends in skeletal morphology, Zootaxa 4305 (1), pp. 1-79 : 21-25

Exechonella antillea ( Osburn, 1927)

( Figs 7–8 , Table 7)

Lepralia antillea: Osburn 1927 , p. 128–129, figs 6–7.

Exechonella antillea: Fransen 1986 , p. 87–90, fig. 29a–g.

? Exechonella antillea: Shier 1964 , p. 616; Hayward 1988, p. 293; Di Martino, Taylor & Portell 2017, p. 140, fig. 34.

Not Phylactella labrosa: Osburn 1914 , p. 213.

Not Exechonella antillea: Osburn 1940 , p. 366–367; Osburn 1950, p.95–96, pl.10, figs 9–10; Cook 1967, p. 337–339, pl.1, fig. e; Hayward 1974, p. 377, fig. 4c; Dumont 1981, p. 635; Cook 1985, 129–131, fig. 38, pl. 15, figs a, b; Winston 1986, p. 19, fig. 40; Vieira 2008, p. 82–83, pl. 19, figs a–c; Vieira et al. 2008, p. 24.

Not Exechonella antillea var spinosa: Osburn 1940 , p. 367–368, pl. 4, fig. 35.

Material examined. Lectotype: USNM 11960 , on a pottery shard. Caribbean Sea, Curaçao, Spanishwater, 19 April 1920, coll. by Dr C.J. van der Horst. Paralectotype: USNM 545920 , Caribbean Sea, Curaçao, Spanishwater, 18 April 1920, coll. by Dr C.J. van der Horst. Other material examined: NNHML Coll. N ° 2997, two slides, eight colony fragments embedded in Canada balsam, Sta. Cur82.093, Netherlands Antilles, Curaçao , St. Joris Bay, inner bay, eastern part, 4 October 1982, coll. by C.H.J.M. Fransen.

Description. Colony encrusting, unilaminar, multiserial. Autozooids pentagonal, hexagonal or oval in shape, separated by narrow grooves. Primary orifice wide pear-shaped, slightly longer than wide, poster (one-third) tending to be more quadrate (angular) than the anter (two-thirds) which has a rounded outline; anter wall underlain by an inner lamina which ends at well-defined triangular condyles, their tips directed to the orifice midline, extending beyond the edge a step-like curved area below. Operculum dark brown in non-cleaned material. Peristome low, collar-like, with relatively thin wall having 1–2 lateral blunt projections in some zooids. Peristome is often parallel-sided laterally or sometimes oval, its wall proximally lower and more narrow than distally with small medial blunt projection, areas either side of this projection wrinkled. Frontal shield smooth or slightly pustulose, perforated by 34–52 well-separated rounded or oval foramina, each with a wide smooth (often wrinkled) gymnocystal rim, raised slightly above the frontal shield and sloping towards the small central opening; fusions between the rims of 2–3, up to 5, foramina are not rare, sometimes common. Small marginal pores are predominantly oval. Lateral areas in some zooids are separated by a poorly developed narrow gymnocystal rim. Avicularia, when present, are placed on the outer raised wall of the two lateralmost foramina which are larger than the rest of the foramina and sometimes have a ‘double’ opening as a result of fusion of the opposite sides of foraminal gymnocystal rim. Each avicularium has a central nipple-like skeletal structure with a central pore through which the tendons of two muscles are passing towards a membranous mandible with a ring sclerite laying above the nipple-like structure. Mandible is thin, semi-round or semi-oval, closes the lumen of the foramen. Internal chamber of avicularium from where the muscles arise is filled with trilobate (?) granular tissue of unknown nature. There is also a central round body (presumed vestigial polypide with a ganglion) from which at least two bundles (presumably reduced retractor-muscles) go towards the bottom of the avicularian chamber. Adventitious kenozooids with 3–8 pores sometimes seen near autozooidal margins, these are often associated with the avicularia or may be alone. Vertical zooidal walls represented by multiporous mural septula with 1–2 rows of communication pores. Ancestrula not observed.

Curaçao, Caribbean Sea

m±sd r n AzL 793±82.3 650–927 14 AzW 580±42.4 530–650 15 OrL 210±12.1 190–238 19 OrW 198±13.7 169–220 19 FoN 43±5.5 34–52 15 FoD 52±6.8 36–60 33 OD 17±3.7 19–37 33 Remarks. Exechonella antillea ( Osburn, 1927) was originally described as Lepralia antillea from Curaçao, in the Caribbean Sea. It has subsequently been recorded by many authors from many tropical and subtropical areas: the Caribbean Sea and western Atlantic—Puerto Rico ( Osburn 1940), Florida ( Shier 1964; Winston 1982), Jamaica (Winston 1986), Curaçao ( Fransen 1986), Coast of Alagoas, Bahia and São Paulo, Brazil (Vieira 2008; Vieira et al. 2008), eastern Atlantic—Senegal and Ghana ( Cook 1967, 1985), Mediterranean Sea ( Hayward 1974), Red Sea ( Cook 1967; Dumont 1981; Winston 1986 [based on Dumont’s paper]), and the Pacific Ocean—California ( Osburn 1950).

In his 1927 paper Osburn mentioned nine colonies of what he described as E. antillea (“ April 19, one colony on an oyster shell, and May 18, 1920, eight colonies on a broken piece of pottery”, p. 128), but only two specimens were found in the USNM collection that were received by the USNM in 1968 after Osburn’s death. The information on his hand written labels differs, however, from what is in the 1927 paper. The USNM 11960 was indicated as ‘ type specimen’ on the label by Osburn , and we select it as a lectotype . The collecting date was written by him as Apr-19-21 that we interpret as between 19th and 21th of April since all the species described in the Osburn’s (1927) paper were collected during spring, 1920 (by C.J. van der Horst). This specimen, despite the date of collecting, grows on the pottery shard, not on oyster. The second existing colony USNM 545920 judging from the label was collected on 18 April, 1920. Osburn detached it from its substrate and glued it to a glass slide with Canada balsam. We selected it as paralectotype .

The above description is based on the lectotype, whereas the paralectotype has no avicularia, and some zooids have a peristome with flat pointed lateral processes. This specimen also shows the early developmental stages of the frontal shield with foramina being round elevated projections. In older zooids foraminal rims become wider and sometimes fuse.

Later Osburn (1940) reported without illustration as E. antillea a specimen from Puerto Rico. In addition, in this and also in 1927 paper he mentioned that the specimen that he briefly described as Phylactella labrosa ( Busk, 1854) from the Dry Tortugas, off Florida, in 1914 belongs to this species too. Examination of these two specimens showed that USNM 545921 ( Puerto Rico) belongs to E. vieirai n. sp., whereas USNM 545922 (Dry Tortugas) belongs to E. pumicosa (see also below).

Comparison of the specimen USNM 10741 , described as Exechonella antillea by Osburn (1950) from the Gulf of California, with the holotype from Curaçao, showed several important differences and resulted in the description of the new species E. californiensis n. sp. (see below).

Shier (1964) also reported E. antillea from northwest Florida. The description of his specimen is reminiscent of that of the holotype, but unfortunately there are no illustrations in the paper to make a more precise comparison possible.

Fransen (1986) redescribed Exechonella antillea based on specimens from the type locality ( Curaçao), and his description fits well to our observations. However, comparing his material (colony fragments mounted on slides embedded in Canadian balsam) with that described by Osburn (1927) we detected some differences that may reflect the variation mentioned by Fransen (1986). These differences are: (1) primary orifice shape was described as wide as long by Fransen, but it is slightly longer than wider in the holotype; (2) the frontal shield bears 40–86 foramina in the Fransen’s material, while the maximal number in the holotype is 52. Unfortunately, due to the preservation method there are no specimens for the SEM study among the Fransen’s material available. On the other hand, the semitransparent fragments in whole mounts make the investigation of internal structures possible; the internal brooding sacs containing an embryo each are clearly visible, as are the muscle ascending from the avicularium chamber and passing through the opening of the nipple structure (see below). Fransen also described and illustrated the tubular “attachment organs” situated on the basal side of zooids (see also Shier 1964).

Fossil specimens were recently described (as E. antillea ) from the early Miocene of Florida ( Di Martino et al. 2017). While general morphology and zooidal size are similar, the primary orifice is distinctly smaller in the fossil material that also shows no medial blunt process of the peristome as well as no lateral foramina with avicularia.

Cook (1967, 1968) reported as Exechonella antillea several specimens from Senegal, Ghana, Guinea, Red Sea and Caribbean, mentioning the wide range of variation in many characters. Later on she admitted, however, that the east Atlantic material significantly differs from the specimens of Fransen from the Caribbean (pers. comm. in Fransen 1986). Also, the optical photo published by Cook (1967, pl. 1E) is of very poor quality. We believe that the specimens above mentioned (stored at the Natural History Museum, London, and Zoological Museum, University of Copenhagen) belong to different species and require careful re-examination.

Later Cook (1985) again reported E. antillea from Ghana, two specimens of which she illustrated using SEM. These both differ significantly from the holotype of E. antillea , in fact we believe that there are two different species included in her paper. The first specimen seen ( Cook 1985, pl. 15, fig. a) shows (in contrast with a holotype) the orifice wider proximally than distally and with fewer frontal foramina merged in short ‘chains’ (similar to E. pumicosa from the Caribbean, see below). The Figure 38 also demonstrates the spine-like processes on the peristome of the “typical” form that are reminiscent those in E. vierai from Brazil (see below). The second specimen shown, the so-called “cribrimorph form” ( Cook 1985, pl. 15, fig. b), has a characteristic radial series of foramina with fused rims (see Tilbrook 2006). Whilst neither of these specimens can be attributed to E. antillea sensu stricto both should be restudied and compared with those described by Cook (1967) from Ghana earlier.

Cook (1967), Dumont (1981) and Winston (1986) [based on Dumont’s paper] mentioned E. antillea in the Red Sea, but the analysis of the literature, illustrations and available specimens can not confirm this distribution (see discussions elsewhere in this paper). Hayward (1988) noted this species from Mauritian waters, but again this record devoid of the description and illustration, similar to the specimens described by Cook (1967, 1985), requires critical re-examination.

Finally, Exechonella ‘ antillea ’ was recorded by Vieira (2008) and Vieira et al. (2008) in Brazilian waters; we attribute this material to a new species (see below).

Distribution. Exechonella antillea has been attributed a wide distribution previously. However, our analyses have determined the presence of several morphologically distinct species, with geographically-limited distributions, within material formerly assigned to Osburn’s (1927) species. This species complex has been noted previously ( Cook & Bock 2004), and is similar to that found in other genera with supposedly “well-known, widelydistributed” species (e.g. Tilbrook 1999; Harmelin 2006; Harmelin et al. 2012). Therefore, E. antillea s. s. is restricted in its distribution to the Caribbean.

Figures

FIGURE 7. Exechonella antillea (Osburn, 1927). Caribbean Sea, Curaçao (A ‒ G: lectotype USNM 11960, non-cleaned colony). A, C, D, general view of lectotype from above. Some lateralmost foramina shown by arrows in D. B, close-up of autozooid with an operculum removed. E, close-up of autozooid with two lateralmost foramina bearing avicularia, each associated with kenozooid (k). Two more kenozooids (k) are seen proximally. F, avicularium with a mandible closing a foraminal lumen (arrowhead points to mandible edge). G, primary orifice with a peristome and condyles. Kenozooid (k) is seen in the upper left corner. Scale bars: A, B, F, G = 100 µm; C = 500 µm; D, E = 200 µm.

FIGURE 8. Exechonella antillea (Osburn, 1927). Caribbean Sea, Curaçao (A ‒ H: NNHML Coll. N ° 2997, total mounts). A, autozooid with forming polypide and ovary (ov). B, autozooid containing polypide and 2 - blastomers embryo (e) inside the internal brood sac (its wall shown by arrows). C ‒ D, autozooids with their frontal shield showing radiating sutures connecting foramina. Large lateralmost foramina bearing avicularia (not-recognizable in this magnification) are associated with kenozoidal (k) chamber. E, autozooid with polypide and lateral avicularium (arrowhead). F, avicularium showing semi-circular mandible (outline shown by arrowheads), rounded sclerite (s) and nipple-like structure with central opening (arrow). Granular tissue is visible. G, part of the frontal shield showing avicularium with semi-circular mandible (outline shown by arrowheads), rounded sclerite (s) and tendons of two muscles (arrow). Several foramina occluded by diatomeans are seen too. H, avicularian internal chamber with granular tissue and central body—presumed rudimentary polypide with retractor muscles below (arrows). Scale bars: A ‒ E = 100 µm; F = 50 µm; G, H = 20 µm.