Asteropterygion oculitristis (Darby 1965)

Asteropterygion oculitristis (Darby, 1965)

Asteropteron oculitristis Darby, 1965:29, pl. 15: figs. 3–7; pl. 16: figs. 1–8.—Kornicker, 1977a:791–796.

Asteropterygion oculitristis (Darby, 1965)

Asteropteron oculitristis Darby, 1965:29, pl. 15: figs 3–7, pl. 16: figs. 1–8.—Kornicker, 1977b:791, 796.

Asteropterygion oculitristis.—Kornicker, 1981a:290, figs. 9h, 135–141, pls. 121–137.

HOLOTYPE.—UMMP 48793, juvenile male, length 1.74 mm.

TYPE-LOCALITY.—Off Sapelo Island, Georgia, depth 59 ft (18.3 m).

MATERIAL.—See “Station Data with Specimens Examined.”

DISTRIBUTION.—Atlantic: South Carolina to Florida.Gulf of Mexico: Florida, Louisiana, Texas. Known depth range 1–28 m.

DIAGNOSIS.—Carapace rugose, with 3 posterior processes; rostrum overhanging fairly deep incisur (Figure 62).

Furca: Adult furca with 3 long stout claws followed by 5 or 6 short secondary claws.

Remarks Concerning Mandibular Basale

Skogsberg (1920:480, Fig. 7) illustrated a mandible of Asterope spinifera (Skogsberg, 1920:476) showing internal muscles. The illustration has a U-shaped process near the middle of the ventral margin of the basale. A muscle extends from the proximal side of the process back into the coxale, where it terminates near the ventral margin. Poulsen (1965:164) in a diagnosis for the family Asteropidae [= Cylindroleberididae] made the following observation concerning the mandibular basale.

On the ventral margin near the basis of the endite is in many species a groove with glandular openings; this groove is considered as the border between the endite and basale proper; in other species there is at this place only a slight indenture of the margin, in some species also the indenture is lacking and the actual border between basale and endite cannot be defined.

The following species were described by Poulsen (1965) as having on the ventral margin of the mandibular basale a hollow bearing glandular openings: Archasterope dentata Poulsen, 1965:343, Parasterope skogsbergi Poulson, 1965:381, P. jenseni Poulsen, 1965:389, Synasterope implumis Poulsen, 1965:424, S. serrata Poulsen, 1965:429, and Cylindroleberis minuta Poulsen, 1965:438. The ventral margin of the basale of Parasterope nana Poulsen, 1965 was described as having a “glandular furrow” (Poulsen, 1965:399). The presence of a hollow or furrow was indicated in illustrations by Poulsen (1965) of mandibles of additional species but was not mentioned in the text.

I have not examined the mandibles of specimens that Poulsen (1965) described as bearing hollows with glandular openings on the ventral margin of the basale, but after failing to find glandular openings in the hollows of specimens that I did examine, and after determining that the hollow is a topographic depression resulting from the shape of a U-shaped sclerotized boss serving as the anchor for a muscle (see illustration of Skogsberg, 1920:480, fig. 7), I have tentatively concluded that the hollow does not have a glandular function. Although the muscle that extends from near the middle of the ventral margin of the basale to the coxale is present in all members of the Cylindroleberididae that I examined, the boss is not developed equally in all of the species. The U-shaped depression in the mandibular basale of Empoulsenia pentathrix Kornicker, 1975:502, and Bathyleberis monothrix Kornicker, 1975:545, has been illustrated in SEM micrographs (Kornicker, 1975, figs. 312a, 313a,b,d, 338f).

As quoted above, Poulsen (1965:164) considered the hollow to be the border between the basale endite and basale proper. In practice, however, the hollow was not always used by Poulsen to demarcate the basale endite; for example, in describing the mandible of Parasterope jenseni, Poulsen (1965:389) stated: “On the ventral margin the basale is one triaenid bristle and distally of it a hollow for gland openings.” If the hollow separates the endite and basale proper, the bristle would have been described as being on the endite. The end of the muscle, which is marked in some species by a sclerotized boss under the hollow, attaches near the ventral margin of the basale proper rather than on the endite, but the position of the point of attachment varies. In some species the muscle is attached near the endite and in others it is attached near the middle of the basale; therefore, the position of the boss or hollow is of limited use in locating the border between the endite and basale proper.

Because the place of attachment of the muscle and also of the boss to which it is attached varies among species, its position may be useful in identifying species. The degree of development of the boss to which the muscle is attached may also be useful in identification.

Zoogeography

It is convenient to relate the distribution of Myodocopa in the study area to biogeographical provinces previously defined by the distribution of other taxa. The history of province delimitation along the Atlantic coast of North America has been outlined by Hazel (1970:E5). The limits of provinces given by Hazel (1970, Fig. 4) have been accepted herein for the Arctic, Labrador, Nova Scotian, and Virginian Provinces. There is much disagreement among biogeographers concerning how a province should be defined (Yancey, Culver, Buzas, 1982). In the present paper “province” (Figure 63) is used in the traditional sense of being a geographical area encompassing a fauna! assemblage that may occupy the same or dissimilar environments. Biofacies is used to define assemblages within a province. Two biofacies are recognized in the study area: (1) lagoonal and estuarine biofacies and (2) shelf biofacies. The Nova Scotian, Virginia, Carolinian, and Gulf of Mexico Provinces have both biofacies, whereas the Arctic, Labrador, and Caribbean Provinces do not have a recognizeable lagoonal and estuarine biofacies. In the discussion of provinces below, the shelf biofacies is not separated as an entity because it supports essentially the same assemblage as the province of which it is a part.

Lagoons, estuaries, and the shores of shallow bays support a fauna characterized by either Eusarsiella zostericola or Parasterope pollex, or both species. Along the Atlantic coast, the northernmost known locality for this biofacies is Halifax, Nova Scotia, and the southernmost is the upper end of Lake Worth, near Palm Beach, Florida. In the Gulf of Mexico, the easternmost known locality is near Cape Romano, Florida, and its westernmost known locality is Port Isabel, Texas. The following species are considered to comprise this biofacies; Parasterope pollex, Eusarsiella zostericola, E. ozotothrix, E. texana, E. spinosa, E. cresseyi, E. disparalis. Other species sometimes occurring in this biofacies are Harbansus paucichelatus and Eusarsiella childi, as well as other shallow shelf species that enter when the environment approaches normal marine conditions. Most of the species are also collected on the shallow inner shelf. This biofacies may be similar, in part, to the Coastal Province of Buzas and Culver (1980), Culver and Buzas (1982), and differs from the Transhatteran Province of Watling (1979:277) in being based, in part, on taxa occurring only south of Cape Hatteras, and in not including shallow shelf species that do not also occur in lagoons, estuaries, and shallow bays. This biofacies also differs from the Transhatteran Province in being present in both the Atlantic Ocean and the Gulf of Mexico. Both the Transhatteran Province and the lagoonal and estuarine biofacies are based on a similar concept and observation, i.e., that the fauna is limited to very shallow water, and seems to have a wider range than fauna on the outer shelf. In a study of podocopid ostracodes, Garbett and Maddocks (1979) found appreciable commonality (15 of 39 species) in bays, estuaries, and lagoons of the northern Gulf of Mexico and Atlantic coast, which supports the concept of a single lagoonal and estuarine biofacies for both areas.

ARCTIC AND LABRADOR PROVINCES.—The boundary between these provinces, according to Hazel (1970:E7), is in the vicinity of Disk Bugt (70°N), western Greenland, and off southeastern Baffin Island (about 66°N); the southern boundary of the Labrador Province is off southern Newfoundland (Hazel, 1970:E9). Only a single species, Philomedes brenda, has been reported at shelf depths in the Arctic Province (Kornicker, 1982; Table 3). Philomedes brenda reaches its southern limit off Nova Scotia, and is amphiatlantic in distribution. The distribution of this species fits within the Arctic-Boreal faunal group of Franz and Merrill (1980a,b). Only 2 species are known from the Labrador Province, Philomedes brenda and P. albatross (Kornicker, 1982). The latter species, which also has its lower limit off Nova Scotia, fits within the Boreal faunal group of Franz and Merrill (1980a,b) although its range is more limited than that of most species they referred to that group. Both provinces are characterized by having few myodocopid species. Members of Philomedes are detritus feeders and perhaps this is an advantage in Arctic waters; detritus feeders were also found to be common in the Antarctic (Kornicker, 1975).

NOVA SCOTIAN PROVINCE (Figure 63).—This province extends south from the Labrador Province and has Cape Cod as its southern boundary. In addition to P. brenda and P. albatross, this province contains Harbansus bowenae, H. dayi, Synasterope cushmani, Heptonema latum, Eusarsiella vema, and 2 species that are also part of the lagoonal and estuarine biofacies, Parasterope pollex and Eusarsiella zostericola (Table 3). Synasterope cushmani and Eusarsiella vema have not been collected outside the Nova Scotian Province. Harbansus bowenae, H. dayi, and Heptonema latum were collected away from the shore, at depths of 36–292 m, and have their southern limits in the Carolinian Province. These three species appear to fit into a Transitional Group recognized by Williams (1984:4) for decapod species ranging from the Canadian maritime provinces for variable distances southward, and which are not species having either a northern or southern affinity.

VIRGINIAN PROVINCE (Figure 63).—This province with its northern limit at Cape Cod (42°N offshore) and its southern limit at Cape Hatteras is not recognized by some investigators who consider the fauna to represent an overlap with northern and southern affinities (Stephenson and Stephenson, 1954; Bousfield, 1960; Bowen et al., 1980:239; Culver and Buzas, 1980:9). Buzas and Culver (1980) concluded on the basis of the distribution of benthic Foraminifera that the Nova Scotian and Virginian Provinces should be grouped together. Other investigators, based on detailed faunal studies in the vicinity of Cape Hatteras and Cape Cod have concluded that a Virginian Province is justified (Hazel, 1970, 1975a,b; Valentine, 1971). Myodocopa in this province include the 3 species of the Transitional group that are present in the Nova Scotian and Carolinian Provinces, 2 endemic species (Bruuniella hazeli, Synasterope species 1), 5 species (Parasterope pollex, Eusarsiella zostericola, E. texana, E. spinosa, E. ozotothrix) that are also part of the lagoonal and estuarine biofacies, and 1 shelf species (Pseudophilomedes ferulanus) which is also present in more southern provinces (Table 3). The 3 additional species in the lagoonal and estuarine biofacies of this province have southern affinities. Thus of the 9 species in this province that have also been collected in other provinces, 4 have southern affinities and 5 have been collected in both the Nova Scotian and Carolinian Provinces. The myodocopid assemblage of the Virginian Province is characterized by a paucity of shelf species that are present south of Cape Hatteras. Bowen et al. (1979) stressed the complexity of the distributional patterns of the crustacean fauna of the Middle Atlantic Bight at different depths, and concluded that various taxa differ in their affinities, possibly related to dispersal abilities. Faunal resemblance (Simpson Index) of myodocopids in the Virignian Province is 56 when compared to the Nova Scotian Province and 73 when compared to the Carolinian Province (Table 4), reflecting the southern affinity of many species of the Virginian Province.

CAROLINIAN PROVINCE (Figure 63).—The northern boundary of this province is Cape Hatteras. The southern boundary has been set at different latitudes by investigators but generally between Palm Beach and Cape Canaveral, Florida. The southern limit on the basis of Myodocopa coincides with the southern limit of the lagoonal and estuarine biofacies, which is in the vicinity of Lake Worth (about 26°45′N). The boundary also coincides with a faunal break for octocorals according to Bayer (1961:328). Myodocopids in this province are diverse, comprising 36 species (Table 3): 7 endemic species (Philomedes keslingi, P. hirutai, Angulorostrum costatum, Synasterope psitticina, Eurypylus rousei, Eusarsiella nodimarginis, E. tubipora); 1 species (Parasterope hulingsi) described originally from the continental shelf of southern California (Baker, 1978:145); 3 species of the Transitional Group also present in the Nova Scotian and Virginia Provinces; 6 species of the lagoonal and estuarine biofaces (Eusarsiella disparalis plus the same 5 species of this biofacies present in the Virginian Province), and 19 species also in the Caribbean or Gulf of Mexico Provinces (2 of these also in the eastern Pacific). Herbst et al. (1979), on the basis of the northern range limits of the Carolinian decapod fauna represented by 291 species, concluded that the Cape Lookout-Cape Hatteras area is a barrier to 60.8% of the fauna. Of the myodocopids, 75% of species in the Carolinian Province are absent from the Virginian Province.

The area just north of Cape Hatteras has not been densely sampled for myodocopids; additional sampling may prove Cape Hatteras not to be so strong a barrier as presently perceived. Of possible significance is the absence of members of the Rutidermatidae, Asteropteroninae, and Cyclasteropinae north of Cape Hatteras. These taxa are present in the Caribbean and Gulf of Mexico Provinces, but have not been reported either in the Arctic (Kornicker, 1982) or Antarctic (Kornicker, 1975), suggesting that their distribution may be partly controlled by temperature.

NORTHERN GULF OF MEXICO PROVINCE (Figure 63).—None of the collections considered herein are from the southern Gulf of Mexico. The continental shelf of the northern Gulf has been generally interpreted as an extension of the Carolinian Province (Briggs, 1974:214). Mainly because of a large number of endemic myodocopid species (35%, 17 of 48 species) in the northern Gulf, I have interpreted the northern Gulf to be a separate province. The southern boundary of the Northern Gulf Province excludes the Florida Keys and has its eastern continental boundary at about Cape Romano, Florida, and its western boundary, provisionally, in the vicinity of Tampico, Mexico. Consideration of the Gulf as a separate province is not without precedent (Puri, 1966:477); also, Bold (1974:215) recognized a Gulfian Province for Neogene podocopid and platycopid ostracodes; and Antoine (1972, fig. 1), based on geological characteristics, delimited 2 provinces in the northeastern Gulf and 1 in the northwestern Gulf; and Culver and Buzas (1982, 1983) recognized three provinces in the Gulf based on depth zonation of Foraminifera on the shelf, and a fourth province on the continental slope and abyssal plain. Nevertheless, the Gulf myodocopid assemblage is closely related to the Carolinian assemblage: 46% (22 of 48 species) of Gulf myodocopids live also in the Carolinian Province, and the faunal relationship (Simpson Index) between the two provinces is high (58) (Table 4).

In addition to the 17 endemic species, this province supports 6 species of the lagoonal and estuarine biofacies that are also present in the Carolinian Province, and 25 species that are also present in either the Caribbean or Carolinian Provinces, or in both provinces (Table 3). One of the species (Pseudophilomedes ferulanus) is present in the Virginian Province as well as in the Caribbean and Carolinian provinces. None of the species of the transitional group are in the Gulf of Mexico.

Morkhoven (1972:241) observed from a cursory examination of mostly podocopid ostracodes that assemblages from the northwestern Gulf differed markedly from assemblages from the northeastern Gulf. Considerable differences also are apparent in comparisons of myodocopids from each quadrant; 41% of the species in the NE quadrant were not collected in the NW quadrant. Myodocopa in the northeast quadrant comprise 14 genera with 34 species (6 endemic) (Table 3). Faunal resemblence of species (Simpson Index) is 59 when compared with the northwest quadrant, and also when compared with the Carolinian Province. The northwest quadrant includes 16 genera with 34 species (10 endemic) (Table 3). Faunal resemblance (Simpson Index) is 47 when compared with the Carolinian Province (Table 4). Species living in both the NE and NW quadrants of the Gulf are more likely to also live in the Carolinian Province than species living in only 1 quadrant, and species living only in the NE quadrant are much more likely to also live in the Carolinian Province than species living in only the NW quadrant (43% compared to 14%). The high percentage of species in the Carolinian Province that live in both the NE and NW quadrants of the Gulf (70%) suggests that species able to traverse the Mississippian fan are also able to traverse the southern tip of Florida, or were able to in the past when the sea level differed.

CARIBBEAN PROVINCE (Figure 63).—This province includes the southern tip of Florida and the Florida Keys, the continental coast of the Caribbean Sea, Bermuda, and the West Indies, which includes the Bahama Islands and the Antilles. Briggs (1974:72) recognized a West Indian Province, separate from the Caribbean Province, which included the Bahamas, Antilles, and Bermuda as an outpost. This is not justified on the basis of the Myodocopa because the faunal relationship between the Bahamas and the Southern tip of Florida is 89 (Simpson Index), and only 25 when comparing the Bahamas and Antilles (mostly Lesser Antilles) (Table 4). A close relationship between podocopids of the shallow carbonate platforms of Yucatan, Florida, and the Bahamas was noted by Bold (1977). The Myodocopa of the Antilles and of the continental Caribbean are not well known, and faunal relationships are not yet clear. The zoogeography of the Caribbean fauna is especially difficult to interpret because of fragmentation of the region as a result of plate movements (Hedges, 1982).

Only 4 Myodocopa have been described from Bermuda (Kornicker, 1981b); 2 additional species are reported herein (Table 3). The Myodocopa in Bermuda are not as closely related to West Indian fauna as are other crustacean groups. Southern affinity of the Bermudan fauna is suggested by the presence of Rutiderma sterreri, which is closely related to, and possibly conspecific with R. dinochelatum, a Bahaman species.