MUD SHRIMPS (CRUSTACEA, DECAPODA, THALASSINIDEA) OF THE NORTHWESTERN GULF OF MEXICO ABSTRACT

BULLETIN OF MARINE SCIENCE, 31(1): 96-115, 1981 MUD SHRIMPS (CRUSTACEA, DECAPODA, THALASSINIDEA) OF THE NORTHWESTERN GULF OF MEXICO Nancy N. Rabalais, Scott A. Holt, and R. Warren Flint ABSTRACT Nine species of thalassinids representing three families (Upogebiidae, Axiidae, and Callianassidae) were collected on the south Texas continental shelf. Six were previously unrecorded from the northwestern Gulf of Mexico. Species accounts include taxonomic information, variations in adults, characteristics of juveniles, distribution records, and interspecific affinities. Discussion of three species known from the Texas and Louisiana coasts but not collected in the study were included to encompass all thalassinids known to occur in the northwestern Gulf of Mexico. A multivariate discriminant analysis of habitat variables accompanying thalassinid collections on the south Texas continental shelf provides information distinguishing the habitats of the species from one another. Callianassa acanthochirus, C. biformis and Upogebia affinis occur primarily in shallow depths (10 to 25 m) in sandy, poorly sorted sediments, Axiopsis oxypleura, C. latispina, C. atlantica, and C. sp. occur in deep water (65 to 134 m) in muddy, well-sorted sediments with distinctions in occurrences associated with sediment mean grain size. Callianassa marginata was taken from deep stations (65 to 85 m) but only in coarse sediments similar to those associated with the shallow water group. Ctenocheles leviceps was collected at mid-depth (30 to 50 m) in silty sediments. During a 3-year study of the south Texas continental shelf, numerous thalassinids were collected from a variety of habitats, expanding the list of recorded species and affording an opportunity to characterize their ecology. Biffar (1970; 1971a; 1971b) summarized literature and updated taxonomy for callianassids of the western Atlantic Ocean. Information on the thalassinids of the northwestern Gulf of Mexico has been confined mostly to estuarine and nearshore species and studies of sublittoral populations are nonexistent. Research involving callianassids has dealt primarily with geological aspects of sandy beach shorefaces (Hunter et ai., 1972), distribution of species in relation to sediment variables (Phillips, 1971), and osmotic and ionic regulation (Felder, 1978). Other discussions have been limited to distribution records in ecological surveys, checklists, or notes (Wi1lis, 1942; Hedgpeth, 1950; Leary, 1967; Felder, 1973; Harper, 1975). Species previously recorded from the northwestern Gulf are Upogebia affinis (Say), Callianassa latispina Dawson, Callianassa jamaicense Schmitt, Callianassa islagrande Schmitt, and Callianassa major Say. METHODS From 1975 through 1977, infaunal and epifaunal samples were taken in soft bottom sediments on the south Texas outer continental shelf (STOCS) at 25 stations along four transects (I-IV) situated perpendicular to shore (Fig. I). Other sampling sites included a rig monitoring station (RM), a replicate trawling transect (TL), and stations near hard bottom features at Hospital Rock (HR) and Southern Bank (S8). Water depths ranged from 10 to 134 m. Additional specimens from other studies on the Texas and Louisiana coasts were examined. Latitude and longitude for all stations are listed in the Appendix. In the STOCS study, replicate macroinfaunal (>0.5 mm) samples were taken with a O.I-m" Smith- McIntyre bottom grab which penetrated the sediment to a maximum depth of 17 cm. Epifaunal samples were taken with a 10.7-m otter trawl with 45-mm stretch mesh. Collections were made seasonally (winter, spring, and fall) along four transects during all 3 years; monthly collections (March, 96

RABALAIS ET AL.: MUD SHRIMPS OF THE NORTHWESTERN GULF OF MEXICO 97 o 10 20 30 -- -- TEXAS O'CONNOR GULF OF MEXICO U.S.A ME Figure I. STOCS study area in northwestern Gulf of Mexico with transects and stations indicated. (Exact locations and depths listed in Appendix.) (Scale indicated Nautical should be Nautical Miles) April, July, August, November, and December) were made on transect II, HR, and SB in 1976. Details of sampling schedules and methods are given in Holland et al. (1976; 1977; 1979),' Standards for measurement followed Biffar (\97\ a). Most measurements were made with an ocular micrometer on a Wild M-5 dissecting scope. Carapace length (ei) was measured from the tip of the rostrum to the posterior median margin of the carapace. Drawings were made with a camera lucida by the senior author. Representatives of all species from the STOCS study were placed in the United States National Museum (USNM). Others were retained at the University of Texas Marine Science Institute, Port Aransas, Texas (UTMSI). In addition to the many references consolidated by Biffar (197\ a), recent thalassinid literature used in the identification of species in this paper were de Saint Laurent (1972, \973), de Saint Laurent and Bozic (1976), Le Loeuff and Intes (1974), Kensley (1974), Rodrigues (1971), Thistle (1973), Boesch and Smalley (1972), and Williams (1974). I Reports to Bureau of Land Mgt" Wash. D.C.. Contract Nos. 08550-CT5 17, AA550 CT6-17. and AA55G-Cn-ll.

98 BULLETIN OF MARINE SCIENCE. VOL. 31. NO. I, 1981 At each collection site for the STOCS study, physical-chemical variables of the benthic habitat were measured at each station including bottom water temperature and salinity, water depth, and sediment texture properties. Correlations that existed between the occurrence of thalassinid species and environmental factors were studied with multiple discriminant analysis (Poole, 1974). Green (1971; 1974; 1977), Knight (1974), Bernstein et al. (1978), and Dueser and Shugart (1979) used this analysis in ecological studies with good success. A computerized program from the Statistical Package for Socia] Sciences (SPSS) using the Wilks stepwise method of analysis was employed (Nie et ai., 1975). Discriminant analysis provided a means of testing the goodness of fit of the different thalassinid species to environmental characteristics that may separate their distributions. The different species occurrences were assigned scores from the discriminant functions produced and the scores were projected in a multidimensiona] space defined by the environmental variables (Bernstein et ai., 1978). The axes defined by the discriminant functions were assumed to be independent and to correlate with the variables potentially important in discriminating between the species groups. RESULTS Over 200 thalassinids from approximately 2,000 benthic infaunal samples were collected from the STOCS area (Table I). An additional three were collected in epifaunal trawls. Specimens represented nine species among three families. Three species known from the Texas and Louisiana coasts but not collected in the STOCS area were included in the species descriptions in order to encompass all thalassinids known to occur in the northwestern Gulf. Species Descriptions Revisions proposed by de Saint Laurent (1973) partitioned Callianassa into six genera based (in part) on mouthparts and placed some American species in Callichirus. Le Loeuff and Intes (1974) more completely outlined these generic characters. The distinctions proposed, however, were not clear cut for Western Hemisphere callianassids and there has been a reluctance to subdivide a widely recognized genus (Callianassa) without a solid basis. The genus Callianassa is retained here until there is a more thorough review of American forms. The Thalassinidea were formerly divided into four families: Thalassinidae, Callianassidae, Axiidae, and Laomediidae. De Saint Laurent (1973) removed Upogebia from the Callianassidae to a separate family, Upogebiidae, based on opposing characters indicating a distant phylogenetic origin. Material examined is listed in abbreviated form for each species as follows: Date, station/stocs transect or study area as indicated in the Appendix, number, sex (if determinable) or condition (indicating imm.-immature, mutl.-mutilated or ov-ovigerous), size (c1 in mm), and USNM number (where appropriate). FAMILY AXIIDAE Axiopsis oxypleura (Williams, 1974) Calocaris (Calastacus) oxypleura Williams, 1974:451 Material Examined.-13 Sep ]975, 3/IV, ]; 16 Feb 1976, 5/1, 1 '? ov, 8.5; ]9 Feb ]976, 3/IlI, 2 0,6.0 and 7.8; 28 Mar 1976, I/SB, I '? ov, 9.0, USNM 172302; 10 Apr 1976, 3/HR, I '? ov, 8.5, ] 0,8.5; 14 Jun 1976,6/1, 1 imm., 3.6; 19 Sep ]976, 6/1V, 2 '? av, 6.0 and 6.8, 1 imm., 3.6; 19 Sep 1976, 3/1V, I imm. mutl.; 19 Nov 1976,5/11,1 mull.; 9 Dec 1976,3/11, I imm., 2.8; 10 Dec 1976, 4/SB, 1 '?, 6.8; 10 Dec 1976, 3/SB, 2 imm., 3.2 and 3.4; 14 Feb 1977,3/1, 1 '?, 5.5; 24 May ]977, 3/1V, imm., 1.0, 1 imm. 0,2.0; 1 Jun 1977,5/1, ] imm., 2.4; 1 Jun 1977,6/1, 1 imm., 3.6; I Jun 1977, 4/HR, 2 imm., 2.0 and 2.0; 6 Oct 1977, 2/HR, I 0, USNM 172303; 6 Oct 1977,3/1, I imm., 1.6; 7 Oct 1977,5/1, I imm., 2.0. De Saint Laurent (1972) amended the diagnosis of Calastacus. outlining the differences between it and Calocaris. In doing so, she relegated a few blind species to these genera, indicating that remaining species currently under the

RABALAIS ET AL.: MUD SHRIMPS OF THE NORTHWESTERN GULF OF MEXICO 99 Table I. Number of individuals of thalassinid species per STOCS station. (Station locations listed in Appendix and illustrated in Fig. I) Calli- Upo- Calli- elena- Cal/i- Axiop- Calli- Calli- Number anassa gebia anussa cheles anassa Calli- sis anussq anassa Tran- Sta- Depth of bi- a/- acantho- levi- marg;- anas~'a oxy- lati- atlansect lion (m) Samples formis finis chirus ceps nata sp. pleura spina tiea 4 ]0 36 2 3 5 I 18 48 2 42 48 5 82 36 3 6 100 36 2 ]0 3 134 48 2 2 5 II I 22 84 4 36 72 2 49 84 2 5 78 72 I 6 98 72 6 I 3 \31 84 8 6 III 4 ]5 1 25 36 48 30 5 40 36 2 65 48 I 3 106 48 2 8 2 6 125 36 2 IV 4 15 36 20 I 27 48 5 37 36 2 47 48 6 65 36 3 2 3 1 3 91 48 4 4 8 7 130 36 1 HR I 75 30 I 2 72 48 6 2 I 3 3 81 24 2 4 76 42 4 2 SB I 81 30 I 2 82 48 3 3 82 24 6 2 4 82 42 I 3 RM 34 6 1 TL 44 1 1 Total Number of Individuals 54 5 8 5 21 II 27 60 \3 % Occurrence 26.5 2.5 3.9 2.5 ]0.3 5.4 13.2 29.4 6.4 name Calastacus were distinct from both Calocaris and Calastacus in a number of characters and that their actual generic placement was impossible to determine owing to a need for general revision of the Family Axiidae. Williams (1974) was unaware of de Saint Laurent's paper when he published but now places Calocaris Jenneri and oxypleura in Axiopsis Borradaile, 1903 (personal communication). STOCS specimens of A. oxypleura lie within the range of variation given by Williams (1974) and have been verified by him. Some STOCS specimens, although sexually mature, are small in size compared to those in the type-series (cl 1.6 to 9.0 mm, as compared to 18.5 to 18.8 mm) and ornamentation (setae, tubercles, and spines) is less pronounced.

100 BULLETIN OF MARINE SCIENCE. VOL. 31, NO. J, \98\ Axiopsis oxypleura has been reported from the Straits of Florida at 365 m and from Quita Seno Bank off Nicaragua at 146 m (Williams, 1974), It was the third most abundant thalassinid in the STOCS study area and was widely distributed throughout the deeper stations, within a depth range of 65 to 134 m. Material Examined.-28 Juvenile Axiid Sep 1977, 4/IV, 1 imm. mutl. A single juvenile, unidentified axiid was collected. The pleura of the abdominal segments and the third maxilliped are similar to those of A. oxypleura, but the carapace is without spination; the rostrum is neither slender nor acute and is unarmed. The specimen was collected outside the range of occurrence of A. oxypleura from the STOCS area. FAMILY UPOGEBIIDAE Upogebia affinis (Say, 1818) Material Examined.-14 Feb ]976,4/1, I Cjl?, 6.5, ] imm., 4.8; 25 Jun 1976, 4/IV, 1 mutl., 3.]; 22 Sep 1976, 4/III, I imm., 1.8; ]] Oct 1976,4/1, ] imm., 4.5, USNM ]72304; 21 Aug 1978, 5/L, 1 imm., 3.2; 13 Jan 1979, 3/L, 3 0, all 6.5, I Cjl, 6.0. Specimens fit the description given by Williams (1965), all within the range of morphological variability outlined by Schmitt (l935a) and Thistle (1973). Most specimens are small (el, 1.4 to 6.5 mm), spination is reduced and other characters undeveloped. Fixed finger to dactylus length ratio ranges from 0.2 to 0.6. Thistle (1973) reported a ratio of 0.8 for U. affinis and 0.5 for U. omissa. Rostral spines are 1 where present, most are without; ocular spines are 1; cervical spines are 1 where present, most are absent; epistomal spines are absent; abdominal spines are absent; and dactylar teeth are 5. U. affinis is known to range from Massachusetts to southern Brazil (Williams, 1965; Thistle, 1973) and has been reported from the Texas coast at Rockport (Williams, 1965 and UTMSI IV-284). Felder (1973) reported U. affinis from muddy substrates of intertidal, estuarine mud flats and shallow bays in Texas and Louisiana. Dorges (1977) reported it as a characteristic and most important species in Georgia creek banks and in the muddy sediment of the marsh sides of tidal creek bars close to the ocean. STOCS specimens were infrequent, with only 5 individuals, all from the shallower, nearshore stations at depths of 10 to 15 m. Others have been collected off the Louisiana coast in 12 to 36 m. FAMILY CALLIANASSIDAE Ctenocheles leviceps Rabalais, 1979 Material Examined.-13 Jun 1976,4/1, 1 imm., 7.0, USNM 171580; 6 Aug ]976, 2/II, ] imm., 3.8, USNM 171578; 7 Oct 1976,2/11,1 imm., 4.4, USNM 171579; 2 Mar 1977, RM, I imm. 0,6.1, USNM ]71577; 5 Dec 1977, TL, I imm. 0,9.5, USNM ]7]576. Five specimens of this species were collected from an area southeast of Port Aransas and south of Port O'Connor in 10 to 49 m water depth. Callianassa marginata Rathbun, 1901 Material Examined.-28 Mar ]976, 1/HR, I 2, 2,8; 9 Apr 1976, 3/SB, 3 imm., 1.8, 1.2, and 0.6; 27 Aug 1976, 3/SB, 1 imm. 2,2.4; 20 Sep 1976, 4/IV, ] imm. mutl.; 9 Oct 1976, 2/HR, 2 0,2.0 and 1.8,

RABALAIS ET AL.: MUD SHRIMPS OF THE NORTHWESTERN GULF OF MEXICO 101 I «,3.0, 1 mutt., 1 imm., 2.8; 10 Dec 1976, 3/SB, 1 imm. «,3.0, I imm. 1.6; 28 Jan 1977, 6/1V, 2 «,3.0 and 3.2, USNM 172305, I imm. «,3.4; 1 Jun 1977, 41HR, 4 imm., 2.2, 3.0, 2.0, and 2.4; 1 Jun 1977,2/HR, I imm., 2.0. STOCS specimens agree with the descriptions given by Rathbun (1901), Schmitt (\ 935a), and Biffar (\ 971a). The most distinctive characters separating C. marginata from other STOCS callianassids are the shape of the telson, which is as long as wide, and elongate uropods, the length of the outer being 4.4 times the width. Most of the specimens collected were juveniles (0.6 to 3.5 mm, cl). The reported size for C. marginata is 10.0 to 18.8 mm (total length, tl) (Biffar, 197Ia). Some sexually mature individuals, mostly female, were collected, but none were ovigerous. The reported range of C. marginata extends from southeastern Florida to points in the Caribbean in 55 to 640 m (Biffar, 197Ia). In the STOCS area, it was collected at stations 6 and 4 on Transect IV and at stations on HR and SB. The depth range for STOCS specimens was 15 to 85 m, with all but one collection from 65 to 85 m. Callianassa atlantica Rathbun, 1926 Material Examilled.-16 May 1975,3/11, 1 «OV,4.0, I 0,2.8, USNM 172306; ]9 Feb 1976, 3/III, 1 imm.,2.0, I 0,2.8; 27 Mar 1976,3/11, 1?, 3.0, 1 imm., 1.2; 27 Jun 1976, 6/III, 1 imm., 2.2; 19 Nov 1976,6/11, 1 «,4.8; 9 Dec 1976,3/11, 1 «OV,4.5, ] 0,2.8; 26 May 1977, 6/III, 1 imm., 2.2; 1Jun ]977, 3/1, I imm., 2.4; ] Jun 1977,6/1, I mutl., 2.8. Diagnostic characters are given here to distinguish this species from the similar C. hiformis: ischium and merus of third maxilliped wide, combined length 1.4 times greatest width; mesial surface of ischium of third maxilliped with crest of small, uniform spinous teeth; antennular peduncle extending beyond tip of antennal peduncle, more noticeably in larger specimens (4.8 mm, c1) than in small specimens (2.0 to 3.0 mm, c1); length of third segment of antennular peduncle five times length of second, in smaller specimens 2.0 to 3.5 times; tel son noticeably shorter than inner uropods; posterior margin of telson straight with slight median indentation and acute projection; rostral length 0.2 to 0.3 times that of eyestalks; eyesta1ks tapered, flattened; minor cheliped without small spine on midventral border of merus. The characters which are similar to and distinguish this species from C. biformis are illustrated in Figure 2. Previous descriptions of C. atlantica (de Man, 1928; Williams, 1965) failed to distinguish this species from the morphologically similar C. hiformis. Several specimens of C. atlantica in the U.S. National Museum collections, after close scrutiny, have been found to be C. hiformis (USNM 58294, USNM 42401, USNM 106465, USNM 107107). Specimens taken range in ci from 1.2 to 4.8 mm; maximum tl, 19.5 mm. Sexually mature females range in size from 15 to 17 mm, tl. Ovigerous females were collected in May and December. The reported range of C. atlantica is from Nova Scotia to Florida from shallow nearshore to 38 m (Williams, 1965). Frankenberg and Leiper (1977) reported it as a numerically dominant species from June to November in inshore, fine sand stations on the Georgia inner continental shelf. In the STOCS area C. atlantica was found exclusively at the deepest stations (98 to 134 m) on the northern three transects. Callianassa biformis Biffar, 1971 Material Examined.-20 Feb 1976, 4/III, I «,2.6,20,2.5 and 2.4; 23 Feb 1976, 4/1V, 1 0,2.1; 28 Feb 1976,3/[,2 imm., 1.6 and 1.6; 13 Jun 1976,4/1, 1 0,3.0; 26 Jun 1976, 4/III, 1 mutl., ] imm. 0,

102 BULLETIN OF MARINE SCIENCEo VOL. 31. NO. I. 1981 Figure 20 a-ho Callianassa atlantica from STOCS (3/I1, 9 Dec 1976, Cjl ov) and USNM (51007, Cjl). a, third right maxilliped, mesial (STOCS); b, third left maxilliped, mesial (USNM); c, first left pereopod, lateral (USNM); d, first left pereopod, lateral (STOCS); e, anterior carapace and appendages, dorsal (USNM); f, first right pereopod, lateral (USNM); g, telson and uropods (STOCS); h, telson and left uropods (USNM)o i-m, Callianassa hi/armis, severa] individuals from STOCS 4/III: i, third left maxilliped, mesial; j, anterior carapace and appendages, dorsal; k, first right pereopod, lateral; I, first left pereopod, lateral; m, telson and right uropodso Scale = I mmo 200, 1 immo, 1.8, 1 Cjl, 2.2; 26 Jun 1976, 4/1V, I <;>,3.6, I 0,2.0, USNM 172308, I imm. 1.4; 20 Sep 1976, 4/1V, 1 imm. 0,200, I mutl. 2.2, 2 imm.; 22 Sep 1976, 4/11I, 1?, 3.4, 1 0,2.2, I immo, 2 imm., 1.2 and 1.4; II Oct 1976,4/1, I immo, 1.4; 30 Jan 1977, 4/IV, I immo, 1.8,30,206,3.0, and 200, I <;>,300,2 mutl., 200 and 2.2; I Feb 1977, 4/III, 2 0,2.4 and 2.0, I immo, 208, 2 mutl.; 25 May 1977, 4/1II, I immo, 1.2, 1<;>,].4, 1 <;>ov,3.4,2o,3.0and2.4, USNM 172307;25 May 1977,4/IV, I <;>,3.0, I.),2.6; 28 Sep 1977, 4fIII, 1 <;>,1.6, 1.), 1.6,3 immo, 1.4, 1.5, and 1.2,3 mutl. 2.2, 1.4, and 1.8;

RABALAIS ET AL: MUD SHRIMPS Of THE NORTHWESTERN GULf Of MEXICO 103 28 Sep 1977, 4/1V, 1 imm., 1.5, 1 <;>,1.7, 1 imm. 0,2.4; 19 Dec 1977, licc, 1?, 2.9; 27 May 1978, 3/L, 1 imm., muti. A full description was given by Biffar (197Ib), and STOCS specimens mostly agree, with a few differences. Diagnostic characters given by Biffar, with a few additional, are listed here to differentiate this species from C. atlantica, which is morphologically similar: ischium and merus of third maxilliped wide, combined length 1.1 to 1.4 times greatest width (STOCS specimens, 1.6 times greater); no teeth or spines on mesial surface of ischium of third maxilliped; antennular peduncle noticeably shorter than antennal peduncle; tel son approximately same length as uropods; posterior margin of telson slightly convex (STOCS specimens more nearly straight); with spinules at posterolateral corners of telson and no median projection; outer uropod bilobed, anterior lobe fringed with single row of setae, posterior lobe fringed with dense row of setae and series of strong simple setae next to indentation on posterior margin; rostral length 0.3 to 0.5 times length of eyestalk; front beyond lateral margins of eyestalks broadly rounded; minor cheliped with small spine on midventral margin of merus. The characters which are similar to and distinguish this species from C. atlantica are illustrated in Figure 2. Juvenile specimens consistently conform to characters as described by Biffar (197Ib). Most specimens are small, \.5 to 2.5 mm, cl; mature ones, 2.6 to 3.6 mm, c1, up to 10.5 mm, tl. An ovigerous female was collected in May, 1977. The range of C. hiformis, based on Biffar (1971b) and specimens in the U.S. National Museum (58294, 42401, 106465, 107107,99112) is from Bass River, Yarmouth, Massachusetts, to Bald Point, Franklin County, Florida. Biffar (I971b) reported C. hiformis as primarily intertidal from fine sands or mud estuaries, ranging in salinities of 12 to 300100, averaging 25%0. D6rges (1977) found it dominant in high salinity estuaries and the inner shelf outside the wave zone in Georgia. Callianassa hiformis is the second most abundant thalassinid from the STOCS area. The distribution is limited; all but two specimens were collected from the three most nearshore stations (10 to 15 m), the majority from 4/111. Considering these occurrences and their correlations with environmental variables, discussed later, the collection of two juveniles at 3/1 is considered anomalous. An additional specimen was collected from Corpus Christi Bay at a water depth of 2.9 m in sandy clay sediments with small shell debris (M. Poff, personal communication). Others have been collected off the coast of Louisiana in sandy sediments at 12 m. Callianassa acanthochirus (Stimpson, 1866) Material Examined.-14 Feb 1976,4/1, 1 <;>,3.6; 13 Jun 1976,4/1, IS?, 6.0, USNM 172310; 22 Sep 1976,4/I1I, I imm., 2.8; 11 Oct ]976,4/1,2 S?, 4.4 and 6.0,1?, 3.7; 4 May ]977, 3/1V, 1 0 muti.; 24 May 1977, 6/1V, 1 imm., 3.4; 17 Sep 1975, 3/G, 1 <;>,4.4; 24 Nov 1975, 2/G, I imm. 0, mutl., 21 Jan 1976, 5/G, 1 S?, 18.0; 21 Jan 1976, 4/G, I 0, 15.0; 22 Jan 1976, 3/G, 1 0, 29.0; 31 May 1978, lil, I <;>,5.0; 21 Sep 1978, 8/L, I mud., 8.5. The specimens generally agree with the descriptions by Biffar (1971a) and Schmitt (1935b) with one notable exception and several other variations, as illustrated in Figures 3A-F. The telson in all specimens is armed with an acute median posterior spine similar to that of C. marginata or C. atlantica. It was at first suspected that this spine was a characteristic of juvenile morphology; however, the telson of the largest (e1, 29 mm) specimen is also spined. STOCS specimens are armed with two reduced spines on the submedian mesial surface of the merus of the major cheliped rather than with three large spines on the dorsal margin as described. This may reflect the small size (21 mm, tl) and

104 BULLETIN OF MARINE SCIENCE. VOL. 31. NO. I. 1981 Figure 3. a-f. Callianassa acanthochirus. from several individuals (3/G, 17 Sep 1975, '?; 4/1, ] I Oct 1976, '?; IlL, 31 May ]978, '?; 4/G, 21 Jan 1976, 0). a, telson and uropods (3/G); b, third right maxi1liped, mesial (4/1); c, carapace, lateral (IlL); d, first right pereopod, lateral (4/G); e, first right pereopod, mesial (4/G); f, first right pereopod, lateral (4/1). g-k, Callianassa latispina. from STOCS (3/11I, 7 Sep ]975, I imm., and l/sb, 13 Feb 1976, I imm.); g, carapace, dorsal (3/I1l); h, first right pereopod, lateral (l/sb); i, telson and right uropods (l/sb); j, third left maxilliped, mesial (3/11I); k, carapace, lateral (l/sb). Scale = ] mm. sex (female) of most of the STOCS specimens. There are two or three pronounced subdorsal meral spines on specimens from Galveston. A Louisiana (IlL) specimen bears a single dorsal meral spine. Spines are present as described along the ventral margin of both the ischium and merus of the major cheliped of all C. acanthochirus examined. Three well-developed spines are present along the distal half of the dorsal margin of the palm of the major cheliped. A specimen from Galveston bears 4 spines in this region. The tel son is hexagonal, wider than long, rather than rounded as described. The rostrum of most is spinous, acute and deflected

RABALAIS ET AL.: MUD SHRIMPS OF THE NORTHWESTERN GULF OF MEXICO 105 distally. The description, with which one specimen from Galveston agrees, is spinous, triangular, elevated proximally, and lifted slightly upward. The ischium of the third maxilliped is more elongate than that described. With one exception, STOCS specimens were juvenile or female. The male is mutilated and first pleopods are not available for examination. The first pleopods of two sexually mature males from Galveston were examined; these match those described and illustrated by Biffar (\97Ia). Biffar (\97Ia) reported the range of C. acanthochirus as southeastern Florida, West Indies, and points in the Caribbean Sea, from shallow water mud flats and bays, coral heads, and reefs. Records from the STOCS area at 15 m and from 65 to 91 m, from off Galveston, Texas, in muddy sand sediments with shell hash at 12 to 15 m, from off Louisiana in muddy and sandy sediments at 13 and 18 m, respectively, and from Alabama (Heard and Reames, 1979) extend this range into the northern and northwestern Gulf of Mexico. Callianassa jamaicense Schmitt, 1935 This species is known from the Texas coast but was not collected in the STOCS area. It has been reported from Texas by Felder (\973), Leary (\967), and Hedgpeth (1950). Felder (\ 973 and 1975) listed its habitat as mud-sand substrates on beaches, mud flats, bottoms of bays and near river mouths with overlying waters of 3%0 to near-marine and summarized its distribution on the Louisiana coast. Specimens have been collected from Texas at Rockport (USNM 81904), Aransas National Wildlife Refuge (USNM 84354), Mullet Bay, Aransas County (UTMSI IV-281), and Galveston West Bay (UTMSI IY-282). An additional specimen, previously reported as C. atlantica by Holland et al. (\975),2 was taken at a depth of I m in Corpus Christi Bay (Station 2/CC). Callianassa islagrande Schmitt, 1935 This species is known from sand beaches especially on open barrier islands, including Padre and Mustang Islands on the south Texas coast (Felder, 1973), but was not collected in the STOCS area. Specimens in the USNM (72185, 102837, and 103527) are from Mustang Island. Felder summarized Louisiana distribution records. Callianassa major Say, 1818 This species is known from the northwestern Gulf but was not collected in the STOCS area. Felder (\973 and 1975) reported that C. major burrows in sandy beaches bordering marine and near-marine waters, intertidal to 2 m, and summarized its distribution on the Louisiana coast. Callianassa latispina Dawson, 1967 Material Examined.-16 May 1975, 3/II, 1 2 OV, 7.0; 7 Sep 1975, 3/III, I; 13 Sep 1975, 3/1V, I 2,4.2, 1 imm. 2,3.4; 13 Feb 1976, l/sb, I imm.; 14 Feb 1976, 3/Il, I 0,3.2; 16 Feb 1976, 3/1, 1 2 OV, 9.0, USNM 172311, 1 imm. 0,3.0; 16 Feb 1976,6/1,2 imm., 2.0 and 3.0; 19 Feb 1976, 3/III, I 0,5.2, I 2, 6.0, 2 imm., 2.0 and 2.0; 27 Mar 1976, 3/II, 1 mutl.; 27 Mar 1976, 6/II, 1 imm., 2.2; 9 Apr 1976, 2/SB, 1 0, 5.0; 14 Jun 1976, 6/1, I 2, 3.2, I imm. 2, 3.4; 25 Jun 1976, 6/1V, I 0,4.0; 27 Jun 1976,, Holland. J. S. et al. 1975. A benthos and plankton study of the Corpus Christi, Copano and Aransas Bay systems. Final Report 10 the Texas Water Developmenl Board, Univ. of Texas Mar. Sci. Inst., Port Aransas, 174 pp.

106 BULLETIN OF MARINE SCIENCE, VOL. 31, NO, I, 1981 6/II, I imm., 2.8; 27 Jun 1976, 31m, I imm., 2.8; 17 Ju11976, 6/II, I 0,5,2; 17 Ju11976, 2/HR, I imm. 0,4.2; 27 Aug 1976, 4/SB, I imm., 2.4, I mutl., 3,6; 19 Sep 1976, 3/1V, 2,?, 8.0 and 7.0; 22 Sep 1976, 21m, 1,?, 4.0; 23 Sep 1976, 31m, I '?, 6,5, 1 0, 8,0; 9 Oct 1976, 5/II, I '?, 3,7; 9 Oct 1976, 2/SB, I imm" 2.0; 10 Oct 1976, 3/1, I 0,5.5; 10 Oct 1976,6/1, 2 0,4.0 and 5,5, I imm., 1.6; 19 Nov 1976, 3/II,2,?, 3.2 and 6.5, I imm., 2.8; 9 Dec 1976, 3/II, I '?, 4.4, I mud., 3.6; 28 Jan 1977, 3/1V, I 0, 6.0, I '? ov, 5,6; 28 Jan 1977, 7/1V, I 0,7.0, USNM 172312; 10 Feb 1977, 6/II, I,?, 6,5; 14 Feb 1977, 6/I, I imm" 3,3; 14 Feb 1977, 2/SB, I imm. mud.; 14 Feb 1977, 2/HR, I imm., 2.6; 14 Feb 1977,41 SB, 1 imm., 2.8; 31 May 1977,4/1, I 0, 12.0; 24 May 1977, 3/1V, I '? OV, 6.0; I Jun 1977,3/1, I,?, 7.0, USNM 172310, Imutl.; I Jun 1977, 6/I, I 0,4.4; 2 Jun 1977, 6/II, 2,?, 7,0 and 6,5; 27 Sep 1977,31 IV, 1,?, 4.0; 6 Oct 1977,6/1, 1 imm. '?, 4.0; 6 Oct 1977, 2/HR, I '?, 4.0; Oct 1973, 3/CC, I,?, 5.0; Aug 1973, 4/CC, I imm., 2.5; 4 Dec 1975, 3/G, 1 '?, 7.0; 21 Ju11975, 4/G, 1,?, 4.5; 1 Apr 1976, 1/G, 1 0, 11.5; 24 May 1978, 2/L, 1,?, 12.0; 20 Aug 1978, 6/L, 1 imm., 3.5; 20 Aug 1978, 7/L, 1 imm., 4.5; 21 Aug 1978, 6/L, I,?, 6.5, 1 imm" 2,8. The specimens fit the descriptions given by Dawson (1967) and Biffar (I97Ia), with a few variations for juveniles as noted below (Figs. 3G-K). The well developed keel on the sixth abdominal somite of adults is present on juveniles as a faint wing. The ischium of the large cheliped, sometimes dilated distoventrally, is not dilated in juveniles. The spine on the proximoventral margin of the merus is not as elongate in juveniles. Elevation on dorsal median edge near posterior margin of carapace is present on all specimens, juveniles included, although somewhat reduced on them. In STOCS specimens the rostrum is 0.5 to 0.7 the length of the eyestalks, as opposed to 0.4 to 0.7 as described. In juveniles the rostrum is 0.8 to 0.9 the length of the eyestalks. Sizes of individuals examined range from 2 to 12 mm (c1) with a maximum tl of 41 mm. Most individuals are small; ovigerous females were collected in January, February, and May. The male/female ratio is about I to 2. STOCS juveniles were at first confused with Callianassa minima Rathbun, 1901. The slender, acute rostrum in C. minima is slightly longer than the eyestalks; that of C. latispina is more broadly triangular towards the base and 0.8 to 0.9 the length of the eyestalks. The relative shape and length of the articles of the third maxilliped are similar; however, the spine on the distoventral corner of the merus of C. latispina is present, even in the smallest individuals. The chelipeds are likewise similar but the spine on the proximo ventral margin of the merus is always present on STOCS specimens although somewhat reduced in juveniles. The tel son of C. minima is elongate triangular with lateral spinules, that of C. latispina is elongate rectangular without lateral spinules. This is by far the most numerous and most widespread of all thalassinids collected. It was taken in both infaunal and epifaunal samples and from all transects. The depth range is 65 to 134 m, with the exception of one nearshore individual at station 4/1 in 13 m. Two specimens, previously reported as C. atlantica by Holland et al. (1975),3 were taken at depths of 3 and 4 m in Corpus Christi Bay (Stations 4/CC and 3/CC). Specimens from Galveston, Texas, (Stations I/G, 3/G and 4/G) are from 12 to 15 m. The type-locality of C. latispina is Louisiana (Dawson, 1967) and numerous additional specimens have been collected there in silty sediments at 20 to 90 m. Published records for the Gulf of Mexico are from Texas and Louisiana at depths of 7.5 to 15 m (Dawson, 1967; Harper, 1975). It is also reported from the Caribbean in 36 to 51 m (Biffar, 1971a). Callianassa sp. (unidentified) Material Examined.-13 Sep 1975, 3/1V, I imm., 2.8, I '?, 4.6; 6 Sep 1975, 3/II, I?, 6.5; 20 Feb 1976, 3/1V, I,?, 3.5; 25 Jun 1976, 6/1V, I imm" 3,0; 17 Ju11976, 2/HR, 1 imm" 3,0; 19 Sep 1976, 6/1V, I '?, 4.0; 9 Oct 1976, 2/SB, 1 '?, 3.0; 14 Feb 1977, 2/HR, 1 imm.; 24 May 1977, 3/1V, 1,?, 4.0; 1lun 1977, 4/SB, I '?, 5.5., See footnote 2,

RABALAIS ET AL.: MUD SHRIMPS OF THE NORTHWESTERN GULF OF MEXICO 107 Figure 4. Callianassa sp. (unidentified), from STOCS (2/SB, 9 Oct 1976, 1 S'; 6/IV, 25 Jun 1976, imm.; and 3/IV, 24 May 1977, 1 S'). a, first left pereopod, mesial (2/SB); b, telson and right uropods (2/SB); c, anterior carapace and appendages, lateral (6/TV); d, anterior carapace and appendages, dorsal (2/SB); e, third right maxilliped, mesial (3/IV). Scale = I mm. An unidentified callianassid collected in the STOCS area (Fig. 4) is superficially similar to C. latispina and C. marginata. Although specimens are small (el, 2.8 to 6.5 mm), they are not smaller in general than other species available for comparison (in particular, C. marginata, el, 0.6 to 3.4 mm; and juvenile C. latispina, cl, 2.0 to 3.4 mm). The rostrum is slender and spinous, 0.7 times the length of the eyestalks, and upturned distally. The rostral shape and length is similar to that in C. marginata (0.5 to 0.7 length of eyestalks) but that of C. marginata is not upturned distally. The antennular peduncles are longer than the antennal peduncles, similar to those in C. latispina and C. marginata. The third maxilliped is also similar to C. marginata in which there is a spinous crest composed of alternating sizes of sharply curved teeth on the mesial surface of the ischium. In C. marginata the crest is closer to the dorsal edge of the ischium. In C. latispina there is a similar mesial crest on the ischium but the teeth are more broadly triangular, subequal in size. There is no spinous projection on the distoventral comer of the merus as in C. latispina. The major cheliped is most similar in shape and relative length to those articles in C. marginata. The ventral margin of the ischium is toothed but not as strongly spinous as in C. marginata. The merus bears a small ventral spine, one-third the distance from the proximal end, similar to the cheliped of an immature C. latispina or the minor cheliped of C. biformis. The ventral margin of the merus of the major cheliped of C. marginata is not spined. There are no other spines or teeth on the chelipeds of this unidentified species. There is a dorsal projection on the posterior half of the carapace as in C. latispina but the protuberance is more anterior, halfway between the linea thalassinica and the posterior margin. The telson is most similar to that of C. atlantica in relative length and shape of its parts. The telson width is 0.8 its length, with an identation on the median posterior margin. On all but one specimen, there is a median acute tooth on the posterior margin. The length of the telson is noticeably shorter than the length of the uropods. The uropods are elongately oval, their length being 1.5 times the width. The outer uropod of C. marginata is 4.4 times longer than wide, bilobed and thick in the middle, with two conspicuous

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RABALAIS ET AL.: MUD SHRIMPS OF THE NORTHWESTERN GULF OF MEXICO 109 3 OF 2 A. 2 1 A. C. biformis o 2 3 OF I 8 OF 3 7 6 B. 5 4 3 :c~no 2 A. oxyp/eura -I~ C. atlan/ica -2 -I o 2 OFI Figure 5. Ninety-five percent confidence ellipses for species mean scores on discriminant axes defined by discriminant function I (OFI) and discriminant function 2 (OF2) (5A), and on discriminant axes defined by discriminant function) (OF)) and discriminant function 3 (OF3) (5B) (Sokal and Rohlf, 1969). longitudinal ridges, the anterior lobe being fringed with dense setae as in C. marginata and C. atlantica. Callianassa sp. was collected from deepwater stations on transects II and IV and from stations on HR and SB, within a depth range of 72 to 131 m. This unidentified Callianassa is probably an undescribed species. Because of time

110 BULLETIN OF MARINE SCIENCE, VOL. 31, NO, I, 1981 limitations, a desire to get the present material into the literature, and a hope for further comparable material, the species is not detailed here. It will be dealt with later along with additional deeper Gulf material, the identifications of which have not yet been determined. Habitat Description Although data from this survey were insufficient for a comprehensive study of thalassinid ecology in the northwestern Gulf of Mexico, accompanying measures of physical variables provided adequate information to describe the habitats associated with each species. From the total list of physical measurements, a subset of variables was selected (Table 2) to provide maximum information (number of cases) and to minimize effects of colinearity (r < 0.80) such that all variables would be relatively independent (Mattson et ai., 1977). An initial univariate analysis of variance indicated that group means of all variables associated with the different species chosen showed a significant difference (P < 0.005). Multivariate discriminant analysis of these variables indicated that the first discriminant function (DFI) accounted for 80.0% ofthe discriminating information available (Table 2). DF2 and DF3 contributed an additional 10.0 and 5.3% of the predictor information, respectively. Chi-square tests for the remaining discriminant functions were not significant (P < 0.05). Plots of mean scores associated with the species (Figs. 5A and B) on the different discriminant functions with their 95% confidence ellipses (Sokal and Rohlf, 1969), showed separation of species according to an environmental model. Regression of the discriminant scores with the environmental variables, similar to an analysis by Dueser and Shugart (1979), produced linear correlations that could be interpreted for ecological meaning (Table 2). These linear correlations as well as results of the stepwise multiple regression were compared to the discriminant function standardized coefficients. As shown in Table 2, the ranking of variables by weight of the standardized coefficient was not always the same as ranking according to the regression results. Contrary to Green (1971), a more meaningful relationship between the discriminant axes and the parameters of the environmental model was drawn from interpreting the ecological significance of the linear correlations. Depth was the predominant variable in DFI (Table 2). Callianassa biformis, U. affinis and C. acanthochirus (shallow depth group) were separated from C. marginata, C. sp., A. oxypleura, C. latispina and C. atlantica (deep group). Ctenocheles leviceps was intermediate to these depth distributions and was the only species collected within the range of 30 to 50 m (Table I). Callianassa acanthochirus and C. marginata were collected at shallower and deeper stations than the intermediate depths of C. leviceps. The distribution of species according to depth is illustrated in Figure 6A. Sand/mud ratio and salinity were also important variables in DF! (Table 2) but were largely overshadowed by the effect of depth. Sand/mud ratio (Fig. 6E) distinguished occurrences of C. biformis from that of other shallow species (Figs. 5A and B). Salinities fluctuated widely around a mean of 34.<r!cc (range, 30.0 to 36.3%0) for stations yielding the shallow, nearshore species, but for all other stations from which thalassinids were collected the mean salinity was 36.0 to 36.2%0 with minimal variability (Fig. 6B). The effect of skewness (r = 0.898) in DFl was also overshadowed by depth (Table 2). The shallow habitat was characterized by poorly sorted sediments and the deeper, by well-sorted sediments. Sediment mean grain size (0 units) characterized DF2 (Table 2). Callianassa marginata was clearly distinguished from the other species of the deep group by

RABALAIS ET AL.: MUD SHRIMPS OF THE NORTHWESTERN GULF OF MEXICO III Callianassa /Jiformis -+- Upoge/Jia a(linis 0+- Callianassa acanthochirus I Ctenocheles leviceps -+- Callianassa marginata I Callianassa sp. 1 Axiopsis oxypleura -+- Callianassa lalispina ~ Callianassa atlantica -+- A. 0 zo 40 60 80 100 I~O 140 DEPTH (m) Callianassa /Jiformis I Upoge/Jla a"inis I Callianassa acanthochirus I Ctenocheles leviceps Collianassa marginata Callianassa sp. + Axiopsls oxypleura -+- Callianassa lalisplna + Callianassa atlantica ~, 6*' 30 3 1 1 8. 32-53 34 35 36 3'7 SALINITY (%0) Callianassa /Jlformis --4-- c. Upoge/Jia a(llnls I Callianasso acanthochirus I Ctenocheles leviceps I Callianassa marginata I Callianassa sp. I Axiopsis oxypleura I Callianassa lalispina I Callianassa atlantica ~' A 4 ~ 6..,, 8 MEAN GRAIN SIZE ( fi5 units) Callianassa /Jiformis ~ Upoge/Jia afflnis I Callianassa acanthochirus I Ctenocheles levlceps 0+- Callianassa marginata I Callionassa sp. I Axlopsis oxypleura I Callianassa Callianassa latispina atlantica I ~ ~' 2.0 2.5, 3.0 3.5 GRAIN SIZE DEVIATION 4~O 4.5 Callianassa /Jiformis I Upoge/Jla affinis I CallianassQ acanlhochirus I Ctenocheles leviceps -+- Callianassa marginata I Callianassa sp. ~ Axiopsis oxypleura -+- Callianassa latispina 0+- Callianassa atlantica +,,,,,. O' I 2 3 4 5 SAND/ MUD RATIO I 9 Ib Figure 6. Species group means and 95% confidence levels for selected environmental variables included in the multivariate discriminant analysis. D. E. association with a lower mean grain size (Figs. SA and 6C). Axiopsis oxypleura and C. sp. were further distinguished from C. atlantica by association with the same variable, with C. latispina intermediate. The variable of sediment grain size deviation characterized OF3 (Table 2). The

112 BULLETIN OF MARINE SCIENCE. VOL. 31. NO.1. 1981 habitats of C. biformis and C. acanthochirus were further differentiated according to this variable (Figs. 5B and D). C. biformis was found in sediments which were more homogeneous in the sorting of particle sizes than any other species. Because of the small data set (N = 3), C. leviceps was not clearly separated in the model based on habitat variables (Figs. 5A and B). The stations from which it was collected were characterized by sediments with high percent silt (x = 41.2%), whereas the shallow and the deep stations were characterized by 10.8 and 29.4% silt, respectively. DISCUSSION Thalassinids in the STOCS area were differentiated on the basis of habitat variables and the model derived from them. One group (C. acanthochirus, U. affinis, and C. biformis) occurred primarily in shallow depths (10 to 25 m) in sandy, poorly sorted sediments. The other group (A. oxypleura, C. sp., C. latispina and C. atlantica) occurred in deep water (65 to 134 m) in muddy, well-sorted sediments with distinctions among species occurrences associated with sediment mean grain size. Two species did not fall within these categories. Callianassa marginata was taken from deep stations (65 to 85 m) but only in coarse sediments similar to those from which the shallow depth group was collected. Ctenocheles leviceps was collected at mid-depth (30 to 50 m) in silty sediments. Other than four individuals of C. leviceps, no other thalassinids were collected between 25 and 65 m (Table I). It should be noted that no stations were situated at 50 to 65 m. Stations in the 25 to 50 m depth range were characterized by poorly sorted, silty-clay sediments where infaunal species assemblages comprised primarily of sedentary deposit feeders (Flint and Holland, 1980) were the least diverse of the STOCS area. This habitat may be restrictive to thalassinid populations. The shallow (10 to 25 m) and deep (65 to 134 m) areas of STOCS were characterized by actively burrowing deposit feeders. Sampling methods, however, may have also been selective against thalassinids in the 25 to 50 m depth sediments. In contrast, Le Loeuff and Intes (1974) identified a faunal change in the callianassids off the Ivory Coast at 60 to 70 m which corresponded to the limit at which the photic zone reached the bottom and which also was often the base of the thermocline. Similarly, the photic zone in the STOCS area seldom reached the bottom at greater than 60 m (D. Kamykowski, personal communication); however, the vertical position of the thermocline was highly variable and no typical depth limit could be established (N. P. Smith, personal communication). The need to reassess past references to C. biformis and C. atlantica was pointed out by the distinct environmental separation of these two morphologically similar congeners. Since the description of C. biformis (Biffar, 1971b), specimens of it and C. atlantica from the Atlantic coast of the United States, in particular Georgia, have been re-examined (R. W. Heard, personal communication). The C. atlantica reported by Frankenberg and Leiper (1977) was found to be C. biformis; the C. biformis listed by Dorges (1977) was verified. On the Georgia coast, C. atlantica is found primarily inshore in muddy sand intertidally and subtidally; C. biformis, in high salinity estuaries and the inner continental shelf from the beach to 3 miles offshore (R. W. Heard, personal communication). On the south Texas continental shelf, C. biformis is a shallow water, nearshore species and C. atlantica, a deep, offshore species. Callianassids typical of estuarine, intertidal or nearshore beach communities (C. jamaicense, C. islagrande, and C. major) were not collected. Shallowest

RABALAIS ET AL.: MUD SHRIMPS OF THE NORTHWESTERN GULF OF MEXICO 113 depths sampled were 10 to IS m. Previous records of C. latispina have been from estuarine or nearshore habitats. In the STOCS area, however, all but one of the C. latispina were collected from 65 m or greater. The diversity of thalassinids on the continental shelf of the south Texas coast is much higher than previously reported. Six species of thalassinids unreported from the northwestern Gulf of Mexico were collected. A sampling program aimed at collecting deep burrowing species from a greater diversity of habitats, taking account of diel activity, would significantly add to our present knowledge of thalassinid distributions. ACKNOWLEDGMENTS Samples were taken under Bureau of Land Management Contract Nos. AA-550-CT6-17, AA-550- CT7-11, and 08550-CT5-17 to the University of Texas Marine Science Institute, Port Aransas Marine Laboratory. Additional specimens were provided by D. E. Harper, Jr., Texas A&M Marine Lab, Galveston, Texas; J. S. Holland, Jr. and M. J. Poff, University of Texas Marine Science Institute, Port Aransas, Texas; N. Fotheringham, Dames & Moore, Houston, Texas; and Southwest Research Institute, Houston, Texas, under contract No. AA551-CT8-17 to BLM. Help in verifying identifications was given by D. L. Felder, A. B. Williams, and L. H. Pequegnat. The manuscript benefitted from the review of A. B. Williams, D. L. Felder, R. W. Heard, and A. H. Chaney. University of Texas Marine Science Institute Contribution No. 366. LITERATURE CITED Bernstein, B. B., R. R. Hessler, R. Smith, and P. A. Jumars. 1978. Spatial dispersion of benthic Foraminifera in the abyssal central North Pacific. Limnol. Oceanogr. 23: 401-416. Boesch, D. F., and A. E. Smalley. 1972. A new axiid (Decapoda, Thalassinidea) from the northern Gulf of Mexico and tropical Atlantic. Bull. Mar. Sci. 22: 45-52. Borradaile, L. A. 1903. On the classification of the Thalassinidea. Ann. Mag. nat. Hist., Ser. 7: 534-551. Biffar, T. A. 1970. Three new species of callianassid shrimp (Decapoda, Thalassinidea) from the western Atlantic. Proc. BioI. Soc. Wash. 83: 35-50. --. 1971a. The genus Callianassa (Crustacea, Decapoda, Thalassinidea) in South Florida, with keys to the western Atlantic species. Bull. Mar. Sci. 21: 637-715. --. 1971b. New species of Callianassa (Decapoda, Thalassinidea) from the western Atlantic. Crustaceana 21: 225-236. Dawson, C. E. 1967. Callianassa larispina (Decapoda, Thalassinidea), a new mud shrimp from the northern Gulf of Mexico. Crustaceana 13: 190-196. Diirges, J. 1977. Marine macrobenthic communities of the Sapelo Island, Georgia region. Pages 399-421 in B. Coull, ed. Ecology of marine benthos. Belle W. Baruch Library in Mar. Sci. No.6, Univ. of S. Carolina Press, Columbia, S. Car. 467 pp. Dueser, R. D., and H. H. Shugart, Jr. 1979. Niche pattern in a forest-floor small-mammal fauna. Ecology 60: 108-118. Felder, D. L. 1973. An annotated key to crabs and lobsters (Decapoda, Reptantia) from coastal waters of the northwestern Gulf of Mexico. Center for Wetland Resources, Louisiana State University, Pub!. No. LSU-SG-73-02, 103 pp. --. 1975. Physioecological Studies of Louisiana Callianassidae (Crustacea, Decapoda, Thalassinidae). Ph.D. dissertation, Louisiana State Univ., Baton Rouge, 117 pp. --. 1978. Osmotic and ionic regulation in several western Atlantic Callianassidae (Crustacea, Decapoda, Thalassinidea). BioI. Bull. 154: 409-429. Flint, R. W., and J. S. Holland. 1980. Benthic infaunal variability on a transect in the Gulf of Mexico. Estuar. Coast. Mar. Sci. 10: 1-14. Frankenberg, D., and A. S. Leiper. 1977. Seasonal cycles in benthic communities of the Georgia continental shelf. Pages 383-397 in B. Coull, ed. Ecology of Marine Benthos. Belle W. Baruch Library in Mar. Sci. No.6, Univ. of S. Carolina Press, Columbia, S. Car. 467 pp. Green, R. H. 1971. A multivariate statistical approach to the Hutchinsonian niche: bivalve molluscs of central Canada. Ecology 52: 543-556. --. 1974. Multivariate niche analysis with temporally varying environmental factors. Ecology 55: 73-83. --. 1977. Some methods for hypothesis testing and analysis with biological monitoring data. Pages 200-211 ill J. Cairns, K. L. Dickson, and G. F. Westlake, eds. Biological monitoring of water effluent data. Amer. Soc. Testing Materials.

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