Area

Area under Consideration

A little more than half of the Coastal Plain Province of the state is included in the area on which this report is based. It encompasses a small segment of the Fall Line Hills, the Vidalia Upland, Barrier Island Sequence, Bacon Terraces, Okefenokee Basin, and the eastern edge of the Tifton Upland districts (Clark and Zisa, 1976). The altitude ranges from approximately 150 meters to sea level, and within the area the tilted early Cenozoic sediments are largely overlain by Miocene and Pleistocene deposits including clay, limestone, marl, sand, and dolostone. A broad array of aquatic habitats is available to the ostracods and their crayfish hosts, ranging from spring-fed rivulets and rocky streams of the uplands to the large, sluggish, coffee-colored streams, ponds, and swamps of the Barrier Island Sequence and Okefenokee Basin districts. Ground water is also utilized along streams and in pitcher plant bogs of the Vidalia Upland District. Elsewhere, especially in the Okefenokee Basin and Barrier Island Sequence districts, the flatwoods offer burrowing crayfishes and their symbionts ready access to groundwater. Seasonal anastomosies of streams have left few low-lying areas lacking crayfish populations that support entocytherid communities. Swiftly flowing waters, except during flood stages, are virtually absent from the southeastern sector of the state. A discussion of the available crayfish (and hence entocytherid) habitats in Georgia is presented in Hobbs (1981:24). Despite this comparatively wide range of habitats in the area, apparently a similar entocytherid-host relationship obtains as that existing in northern Georgia (Hobbs and Peters, 1982:298):

Unlike entocytherid faunas in other areas in which unique species are symbionts of those crayfishes largely restricted to burrows, the ostracods infesting the burrowing crayfishes in northern Georgia are members of some of the same species that are found on the stream-dwelling crayfishes frequenting nearby epigean habitats.

Entocytherid Associates and Infestations

Frequently more than one species of entocytherid infests a single crayfish, and several crayfish species sharing a single locality may be infested with the same ostracod. Most of the latter available for this study were obtained from containers in which all of the crayfishes (one to four species) collected at a single locality were preserved together. Thus the ostracods could not be associated with a single host species. Only for those ostracods obtained from collections containing specimens of a single crayfish species can a specific host-commensal relationship be assumed to exist. In Table 2 the numbers refer to the number of times the corresponding crayfish was in collections from which the ostracod was taken, and the circles indicate that the ostracod was collected in at least one locality from a single host species, thus establishing a definite ostracodcrayfish association.

As in the northern Georgia entocytherids (Hobbs and Peters, 1982:298), “Whereas an obligate association with…crayfishes exists for all of the entocytherids in the area, evidence exists that none requires a specific host.” Every species in southeastern Georgia was found on two or more hosts except Dactylocythere striophylax, which could be associated unquestionably with only one host, Cambarus (D.) latimanus (LeConte, 1856). At least two other ostracods infested members of this host species, and there is no reason to believe that in the area C. (D.) latimanus is the only acceptable host of the ostracod, for it was found in “37 collections in [the] Broad River drainage” of South Carolina in which this crayfish was not one of the hosts in any of the localities (Hart and Hart, 1974:71).

The least discriminating entocytherid of the area, in terms of the hosts it infests, is An. ancyla, which is associated with 17 of the 28 species of crayfishes occurring in the southeastern part of Georgia.

Entocytherid Distribution in Southeastern Georgia

In most of the collections examined, more than one species of ostracod were present, and many, if not most, of those obtained from a single host species contained representatives of two or three species. The frequency of the occurrence of each with other entocytherids is listed in Table 3. For reasons presented below, it is not surprising that An. ancyla and E. elliptica were found together more frequently than any other combinations of species.

In terms of their occurrence in the region, An. ancyla was by far the most common of the eleven entocytherids present. It occurs in 62.2 percent of the localities from which specimens are available; that is more than twice as many as frequented by any other except E. elliptica, which was found in 44.0 percent of the localities. The other species were represented by the following percentages: An. hobbsi, 19.8%; E. prisma, 18.1%; U. equicurva, 14.1%; E. dorsorotunda, 7.3%; An. spargosis, 6.2%; An. tiphophila, 4.5%; An. freyi, 4.0%; Dt. striophylax, 2.3%; and U. simondsi, 1.7%.

The most widespread entocytherid in the region is Entocythere elliptica, which infests at least 10 of the crayfish species and has been found throughout the area in all seven of the drainage basins. Also widespread, more common, and infesting 17 crayfishes, but not known to occur in the Fall Line Hills District or in the St. Marys watershed, is An. ancyla. Ankylocythere hobbsi is rather common south of the Altamaha Basin but north of the river appears to be replaced largely by An. spargosis. Comparing their ranges with that of U. equicurva (Figure 9) in southeastern Georgia, we suggest the possibility that there they are vicariating for one another for we have no record of either An. hobbsi or An. spargosis occurring in the same locality with U. equicurva, yet populations of the latter almost surround their combined, slightly overlapping ranges. The range of Entocythere prisma lies almost within that of An. hobbsi and An. spargosis, with almost half of the known localities occurring in the Bacon Terraces District and the other in the Barrier Island Sequence District.

Similar to An. hobbsi, but with an even more restricted range, E. dorsorotunda appears to be confined to the Bacon Terraces and that part of the Barrier Island Sequence District that lies south of the Altamaha River.

Insofar as we are able to determine, the southern limit of the range of Dt. striophylax occurs within the area. Also the locality in Camden County for U. simondsi is the southeasternmost record for the species, and the localities for An. freyi in the Savannah Basin mark the easternmost reported for that species. Only the sparsity of localities for An. tiphophila in the area is noteworthy.

Ankylocythere freyi is probably the most restricted in its distribution of any of the entocytherids encountered in this study. In all of the localities cited for it by Hobbs III (1978), the hosts were dug from burrows, and except for the localities in Bleckley (based on a questionable determination) and Screven counties, the same is true for those recorded here. Uncertainty also surrounds the identity of a single specimen from Bryan County having strikingly different clasping apparatus (Figure 6g,h) and that from Coffee County (Figure 6i). It is puzzling, however, that there are so few records in this area, for in at least half of the localities from which our specimens came some or all of the crayfishes collected were from burrows. We have no explanation for the discontinuity in the range that seems apparent between the localities plotted in Figure 7. It is tempting to suppose that there is some connection between the fragmentary range and that plotted by Hobbs (1981, fig. 87) for the crayfish Cambarus (L.) diogenes (the most frequently cited host, in 6 of 10 localities, by Hobbs III). We have so few entocytherids that were gleaned from this crayfish (indeed few specimens of the crayfish!) in the area considered herein that we are not surprised that their association has not been encountered, and we suspect that not having done so reflects a lack of adequate sampling in the Savannah and Altamaha river basins.

With respect to the river basins, the Savannah watershed is populated by all of the entocytherids occurring in the area except E. dorsorotunda and U. simondsi; the Ogeechee Basin lacks the latter two and An. hobbsi; the Altamaha and Satilla basins are frequented by all of the species in the area except E. dorsorotunda, which is absent from the Altamaha, and An. freyi, which is not known to occur in the Satilla. The Suwannee, which perhaps has not been adequately surveyed, harbors only five of the eleven species, and, as one might anticipate, the river basins with the fewest species are the Newport (three species) and the St. Marys (two species). Their basins are much smaller than those of the other drainage systems and, correspondingly, are represented by fewer collections.

Summarized below are the numbers of species of entocytherids and crayfishes occurring in the Coastal Plain Province of the southeastern part of Georgia:

Districts Entocytherid

species Crayfish

species

Fall Line Hills 5 11

Vidalia Upland 9 21

Tifton Upland 5 8

Bacon Terraces 6 10

Okefenokee Basin 4 6

Barrier Island Sequence 11 23

Some of the differences noted in the distribution of the entocytherids in the river basins and districts might reflect inadequate sampling in those supporting fewer species; however, we are inclined to believe that most are realistic. The rarity of U. simondsi and the distances between the three known localities, however, suggest that it might have been overlooked in the Vidalia Upland and Bacon Terraces districts.

A comparison of the entocytherid and crayfish faunas of northern Georgia (as defined by Hobbs and Peters, 1982) and southeastern Georgia reveals little similarity. Of the 13 ostracods, representing six genera, found by them, only three (An. telmoecea (= U. equicurva), E. elliptica, and U. simondsi) were encountered in the present study. No representatives of the genera Ascetocythere, Cymocythere, and Donnaldsoncythere have been found in the Coastal Plain Province of Georgia, and the dominant genus Dactylocythere of northern Georgia, where six species were found, is sparsely represented by a single species in our collections from the Coastal Plain. The dominant genus of the latter province in Georgia is obviously Ankylocythere which there comprises five species, almost half of the entocytherids known from the region. Noteworthy perhaps is the observation that most Dactylocythere infest members of the crayfish genus Cambarus. (Of the 11 members of Dactylocythere occurring in North Carolina (Hobbs and Peters, 1977:6), only two were found to infest members of the genus Procambarus, and of the six occurring in northern Georgia, only one infests a member of Procambarus and another, a member of Orconectes). Conversely, members of the genus Ankylocythere are far more frequently associated with crayfishes belonging to the genus Procambarus, the dominant crayfish group occurring on the coastal plain from North Carolina to Middle America. Of the 27 crayfishes occurring in northern Georgia, 22 belong to the genus Cambarus, and only two, to Procambarus (see Hobbs and Peters, 1982:301). In contrast, of the 28 crayfishes in southeastern Georgia, 22 belong to the genus Procambarus, and only five to Cambarus; the latter are rare, or at least difficult to find. Only three crayfishes occur in both sections of the state. Thus, indeed, there are contrasting entocytherid and crayfish faunas in northern and southeastern Georgia.

The host crayfishes of southeastern Georgia are reviewed in Hobbs (1981). In that summary, synonymies, ranges, and notes on their biology are presented. The following species and subspecies are known to harbor one or more of the eleven entocytherids that have been found in this section of the state: Cambarus (Depressicambarus) latimanus (LeConte, 1856); C. (D.) reflexus Hobbs, 1981; C. (D.) striatus Hay, 1902; C. (D.) truncatus Hobbs, 1981; C. (Lacunicambarus) diogenes diogenes Girard, 1852; Faxonella clypeata (Hay, 1899); Procambarus (Hagenides) advena (LeConte, 1856); P. (H.) caritus Hobbs, 1981; P. (H.) pygmaeus Hobbs, 1942; P. (H.) talpoides Hobbs, 1981; P. (H.) truculentus Hobbs, 1954; P. (Leconticambarus) barbatus (Faxon, 1890); P. (L.) pubischelae deficiens Hobbs, 1981; P. (L.) pubischelae pubischelae Hobbs, 1942; P. (Ortmannicus) acutus acutus (Girard, 1852); P. (O.) enoplosternum Hobbs, 1947; P. (O.) epicyrtus Hobbs, 1958; P. (O.) fallax (Hagen, 1870); P. (O.) litosternum Hobbs, 1947; P. (O.) lunzi (Hobbs, 1940); P. (O.) pubescens (Faxon, 1884); P. (O.) seminolae Hobbs, 1942; P. (Pennides) petersi Hobbs, 1981; P. (Pe.) raneyi Hobbs, 1953; P. (Pe.) spiculifer (LeConte, 1856); P. (Scapulicambarus) howellae Hobbs, 1952; P. (S.) 1952; P. (S.) paeninsulanus (Faxon, 1914); P. (S.) troglodytes (LeConte, 1856).