Bairdoppilata fithianae, Maddocks, 2025

The Bairdoppilata fithianae Species Group

The term species group is used here as an informal designation for a group of similar species inhabiting a geographic region. Unlike more precisely defined terms, such as species complex and superspecies, it carries no implications concerning monophyly, recency of divergence, allopatry, hybridization, or hierarchical level in a classification. Because there is no information concerning the soft-body anatomy, genetics, reproductive behavior, and stratigraphic record of these eight species of Bairdoppilata , the term species group should be understood as a descriptive generalization rather than a statement about evolutionary relationships.

Six of the eight species described here are quite similar. Of these, the most widely distributed and the most central morphologically is Ba. fithianae sp. nov. Ba. hypsiliformis sp. nov. and Ba. thyreoides sp. nov. have variable populations, which display some overlap in size, shape and patch patterns. It is suggestive that these two morphotypes have restricted distributions, Ba. thyreoides sp. nov. only in the Bahamas and Ba. hypsiliformis sp. nov. only on the Belize-Honduras coast. Ba. floreana sp. nov. is distinguished by its sinuous shape, Ba. fimbriata sp. nov. by the comb of blunt spines on the posteroventral flange of the LV, and Ba. sima sp. nov. by the recurved edges of both valves and the exaggerated flanges of the RV.

Ba. diatreta sp. nov. and Ba. collaevata sp. nov. stand somewhat aside from the group. Both are variable, and their plotted dimensions show partial overlap. They share a distinctive, filigree opaque patch pattern, which is sharply etched in Ba. diatreta sp. nov. but blurred in Ba collaevata sp. nov. Ba. diatreta sp. nov. is densely punctate, but Ba. collaevata sp. nov. tends to be more nearly smooth.

Two other species groups have been demonstrated for Bairdiidae in the northern Caribbean and Gulf of Mexico ( Maddocks 2021). One group includes Neonesidea longisetosa ( Brady, 1902) , N. gerda ( Benson & Coleman, 1963) , N. caraionae ( Maddocks, 2021) , and N. omnivaga Maddocks, 1986 in Maddocks & Iliffe (1986). Another group includes Neonesidea dinochelata ( Kornicker, 1961) , N. florea Maddocks, 2021 , and N. sp. aff. N. dinochelata of Maddocks (2021).

Coral reefs, lagoons, and carbonate platforms are discontinuously distributed along the mainland coasts of the Caribbean Sea and Gulf of Mexico, the islands of the Antilles and Bahamas, and far Bermuda. Over this distance (more than 960 nm, 1780 km), dispersal is facilitated by the Antilles Current, Caribbean Current, Loop Current, and the Gulf Stream. It is apparent that the geography of this archipelago provides both dispersion and sufficient isolation to encourage speciation in these swarms of bairdiids.

Other Tropical Atlantic Species of Bairdoppilata

Hartmann (1974) described five species of Bairdoppilata from the littoral zone of tropical West Africa. None have the caudate outline and crisply punctate exterior that are characteristic of the Ba. fithianae species group. Ba. angolaensis Hartmann, 1974 was collected on algae-encrusted rocks at Luanda and Lobito, Angola. The carapace is large (L= 0.91–0.94 mm), finely punctate, steeply arched, and not caudate, resembling Bairdoppilata sp. 2 of Morais & Coimbra (2017) (see also Maddocks 2022). The anterior and posterior opaque spots extend dorsally and ventrally in the RV, and in the LV they merge with a continuous band around the ventral margin. Ba. cytheraeformis Hartmann, 1974 was collected on a sandy beach south of Moçamedes, Angola. It shows affinities to the Caribbean species Ba. magnafasciata and Ba. parvafasciata Maddocks & Horne, 2024 . Ba. mocamedesensis Hartmann, 1974 was collected from algae on the rocky coast of Moçamedes, Angola. It is very small (L = 0.62–0.70 mm) and smooth, with a lateral outline resembling Bairdoppilata ? sp. 2 of Maddocks (1975) (L = 0.55 mm) from Ascension Island. Ba. sp. 32 of Hartmann (1974) is a large (L = 1.00 mm), weakly caudate species collected in a rock pool at Moçamedes, Angola. Ba. sp. 44 of Hartmann (1974) is a very large (L = 1.37 mm), non-caudate species, said to resemble Ba. angolaensis but more weakly sculptured. It has a central opaque spot connected to a dorsal spot, but no anterior and posterior spots. It was collected at Lüderitzbucht in Southwest Africa ( Namibia).

Maddocks (1975) identified two species of Bairdoppilata in open nomenclature from Ascension Island, neither of which is similar to the Ba. fithianae species group described here from the Caribbean.

Witte (1993, p. 20, Pl. 1, Figs. 1–8 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 ) described Paranesidea multiforma from the coast of Gambia and Senegal. It is likely that two different species were represented among the illustrated specimens. The assignment to Paranesidea was based on “the muscle scar configuration and carapace morphology,” and bairdoppilatan supplemental dentition was not mentioned. The lateral outlines of the illustrated valves resemble those of the Ba. fithianae species group. Another illustrated form, Paranesidea sp. A (p. 21, Pl. 1, Figs. 22–25 View FIGURE 22 View FIGURE 23 View FIGURE 24 View FIGURE 25 ), has an exaggerated caudal process, which is a common feature in juveniles of Bairdoppilata .

From the equatorial shelf of Brazil, Coimbra & Carreno (2002) reported two species of Bairdoppilata . Both are smooth, high-arched, and non-caudate, unlike the Caribbean species described here. Coimbra et al. (2006) illustrated a RV of Bairdoppilata sp. from Imarui Lagoon, southern Brazil. Morais & Coimbra (2017) illustrated two species of Bairdoppilata in open nomenclature from algae of the rocky infralittoral in Santa Catarina State, southern Brazil, but neither can be identified with any of the Caribbean species described here. Machado et al. (2020, figs. 5G–J) illustrated two species of Bairdoppilata from the shelf of northeastern and eastern Brazil, neither of which resembles the Ba. fithianae species group of the Caribbean. Of 131 total species on the northeastern and eastern shelf of Brazil, they reported only 15 species in common with the Caribbean and Gulf of Mexico (2 Bairdiidae , no Bairdoppilata ).

Maddocks (2022) redescribed Ba.cushmani ( Tressler, 1949) from the Bahamas, Belize, Cozumel, Cuba, Florida, Grand Cayman Island, Honduras, and Jamaica, where it is usually the most abundant species of Bairdoppilata in these assemblages.

Maddocks & Horne (2024) described Ba. magnafasciata and Ba. parvafasciata from the central and northern Caribbean, Bahamas, and Florida. The former may have been identified as Bairdia fasciata Brady, 1870 A by Teeter (1975) from the Belize platform.

No species of Bairdoppilata have been reported from other volcanic islands of the Atlantic Ocean: Madeira, the Canary Islands, the Azores, the St. Peter and St. Paul Archipelago of Brazil, Rocas Atoll of Brazil, or Trindade Island of Brazil [see summary by Maddocks & Horne (2024)].

Subfossil Morphotypes and Diversity

Identifications based on subfossil assemblages have both deficiencies (no soft-anatomical information, no ecological parameters) and strengths (comparability to fossil assemblages). The taxa presented here are morphotypes, characterized by shared attributes of the carapace and interpreted as biological species. Figures 32 View FIGURE 32 and 33 View FIGURE 33 provide a visual summary of this swarm. Probable males, females, and juvenile instars have been recognized for each species and delineated on the Graphs 1–5. The geographic distributions ( Table 1, Appendix 1) demonstrate both allopatry and occasional sympatry, which support the interpretation as species. Some variability is observable for populations at different localities, but in the absence of ecological data, it is not possible to assess potential environmental influences.

There is no evidence of gross taphonomic distortion: Of the total 456 specimens for all species pooled ( Table 1), 77 (17%) are carapaces, 131 (29%) are LV, and 145 (32%) are RV (approximately equal). Juveniles are only 25% of the total, because of bias in picking and because they are less strongly calcified: Carj 11 (2%), LVj 62 (14%), RVj 41 (9%) .

In the subfossil assemblages from which these species are described, the most abundant bairdiid species is usually Neonesidea longisetosa ( Brady, 1902) . Other abundant bairdiids include Ba. cushmani ( Tressler, 1949) and several species of Paranesidea . Species with moderate frequencies include Ba. magnafasciata Maddocks & Horne, 2024 , Ba. parvafasciata Maddocks & Horne, 2024 , and several species of Neonesidea . By comparison, the species of Bairdoppilata described here are generally less abundant to uncommon ( Table 1, Appendix 1). Even so, it is puzzling that only three of these new species ( Ba. fithianae sp. nov., Ba. fimbriata sp. nov., Ba. floreana sp. nov.) are potentially recognizable in the illustrations from earlier faunal monographs.

It is noteworthy that Teeter (1975) did not report B. bradyi from the Belize platform, nor did he illustrate any species that can be identified with the two described here from Belize ( Ba. hypsiliformis sp. nov. and Ba. fimbriata sp. nov.). B. bradyi was not reported from the east and northeast coast of the Yucatan peninsula ( Palacios-Fest et al. 1983; Krutak & Gío-Argáez 1994). Krutak (1982) did not report B. bradyi or any species of Bairdoppilata from Vera Cruz. Neither B. bradyi nor any species of Bairdoppilata was listed from Bermuda by Keyser & Schöning (2000).

No faunal list is ever complete, and it has never been customary to list species that were expected but did not occur in the samples. Nevertheless, the deliberate notation of absences might have potential value: to evaluate collecting methods, to delineate species ranges, to detect environmental deterioration, and to evaluate the stochastic nature of species dispersion.