Resurrection of the snailfish genus Allinectes (Teleostei: Cottiformes: Liparidae) for seven North Pacific species, including descriptions of three new species from Alaska Author Orr, James Wilder text Zootaxa 2025 2025-03-21 5609 3 301 334 https://doi.org/10.11646/zootaxa.5609.3.1 journal article 309346 10.11646/zootaxa.5609.3.1 f37a79d9-7d65-41ff-85b7-f9308890a3ba 1175-5326 15215135 4AA5686E-5B13-4CC2-9CD1-D73A5E68327F Allinectes ectenes ( Gilbert, 1896 ) Shovelhead Snailfish Figure 1 , Tables 1 and 2 Careproctus ectenes Gilbert, 1896: 442 (original description). Type locality:Aleutian Islands, north of Unalaska Island, Albatross station 3331, 350 fms.— Jordan & Evermann 1896: 452 (checklist).— Jordan & Evermann 1898: 2136 (description, subgenus Allurus , in key), 2866 (type species of new subgenus Allinectes ).— Gilbert & Burke 1912a: 80 (compared with C. attenuatus ).— Gilbert & Burke 1912b: 372–373 (compared with C. pycnosoma and C. curilanus ).— Burke 1930: 110 (description, designation of lectotype , in key).— Jordan et al. 1930: 403 (checklist, Aleutian Islands, subgenus Allinectes ).— Böhlke 1953: 136 (type catalog).— Kido 1985: 16 (compared with C. pycnosoma [in part = Allocareproctus tanix Orr & Busby, 2006 ]).— Kido 1988: 198 (compared with A. jordani ( Burke, 1930 )).— Orr & Busby 2001: 57 (comparison with Prognatholiparis ptychomandibularis Orr & Busby, 2001 ).— Orr & Busby 2006: 4 , 13 (comparison with Allocareproctus ).— Maslenikov et al. 2013: 14 (in part, Alaska).— Parin et al. 2014: 319 (checklist, expected in Commander Islands).— Murasaki et al. 2018: 241 (list of characters, compared with C. surugaensis Murasaki, Takami & Fukui, 2018 ).— Orr et al. 2019: 25 (subgenus). Careproctus (Allurus) ectenes Jordan & Evermann 1896: 452 (new subgenus, type by monotypy, objectively invalid); Jordan & Evermann 1898: 2136 [cited by Burke 1930 ]. Careproctus (Allinectes) ectenes Jordan & Evermann 1898: 2866 (new subgenus, type by monotypy, replacement name for Allurus ). Allinectes ectenes Burke 1930: 8 (new combination). Lectotype . USNM 48618 , ca. 67 mm , (“the largest 78 mm ” [TL?] in type lot of Gilbert 1896 ; specimen now in poor condition in two pieces), ripe female , Aleutian Islands , 3.5 km north of Unalaska Island , 54.0278°N , 166.8139°W , Albatross station 3331, 637 m (350 fms) depth, 21 August 1890 (designated by Burke 1930 ) . Paralectotypes . CAS-SU 3091 , ca. 62 mm , and USNM 53031 , ca. 60 mm ; both from the same locality as lectotype and in very poor condition, both now in three pieces . Additional Material Examined . USNM 64043 , 2 , ca. 58–60 mm (both in very poor condition, disintegrating, in more than three pieces), Aleutian Islands , Bowers Bank , north of Rat Islands , ca. 54.3°N , 178.3°W , Albatross station 3785, 494 m (270 fms) depth, 27 June 1900 . Diagnosis . Distinguished from all other species of Allinectes except A. curilanus and A. attenuatus by its higher counts of median-fin rays and vertebrae (dorsal-fin rays 48–51 vs. 42–47, anal-fin rays 44 vs. 37–41, vertebrae 54 vs. 47–51 in A. pycnosoma , A. istiophorus , new species , A. nanstanorum , new species , and A. busbyi , new species , combined), smaller pelvic disk (27.6–28.3% vs. 29.0–41.4% HL), and smaller gill slit (18.7% vs. 20.3–29.5% HL). Differing from A. curilanus in peritoneum pale (vs. dusky in A. curilanus ), narrower interorbital width (13.3–15.4% vs. 16.9–21.7% HL), longer anterior body (snout to pelvic disk 66.1–68.6% vs. 49.3–65.1% HL; snout to anus 114–116% vs. 96.6–115.3% HL), and absent, filamentous, or short pyloric caeca (14.2% vs. 15.1–29.0% HL). Differing from A. attenuatus in its longer anterior dorsal-fin rays, deeper body (depth at anal-fin origin 46.7–61.5% vs. 38.8% HL in A. attenuatus ), typically more dorsal-fin rays (48–51 vs. 48), fewer pectoral-fin rays (30–32 vs. 34), and peritoneum pale (vs. black). Further differing from A. istiophorus , new species , in peritoneum and stomach pale (vs. both dark in A. istiophorus , new species ), fewer pyloric caeca (0–6 vs. 7–11), more vertebrae and median-fin rays (54 vs. 48–51 vertebrae, 48–51 vs. 43–47 dorsal-fin rays, and 44 vs. 38–41 anal-fin rays), broader head (width 58.4–61.4% vs. 44.3–58.6% HL), and typically smaller pelvic disk (27.6–28.3% vs. 29.7–41.4% HL). Differing from A. nanstanorum , new species , in peritoneum pale (vs. black in A. nanstanorum , new species ), truncate caudal fin (vs. dorsalmost caudal-fin ray longer and thicker), more vertebrae and median-fin rays (54 vs. 47–49 vertebrae, 48–51 vs. 42–45 dorsal-fin rays, and 44 vs. 37–38 anal-fin rays), and deeper body at pelvic disk (61.6–69.2% vs. 44.2–52.8% HL). Further distinguished from A. pycnosoma by its strongly notched pectoral fin with long lower lobe (vs. shallow notch, with short lower lobe in A. pycnosoma ), protruding snout (vs. blunt, non-protruding), shorter head (20–25% vs. 26.9% SL), and anus nearer pelvic disk (15.8–22.4% vs. 25.7% HL). Description . Body extremely elongate, slightly tapered, rounded anteriorly, compressed posteriorly; depth at pelvic disk 61.6–69.2 (69.2)% HL; depth at anal-fin origin 46.7–61.5 (53.9)% HL. Head moderately small, 20–25 (20)% SL, width 58.4–61.4 (58.4)% HL, depressed, shovel shaped, with truncate or slightly protruding snout, nape not elevated. Snout depressed, rounded, snout tip projecting anterior to lower jaw for up to distance of about half ( lectotype [ Burke 1930 ]) or equal to pupil diameter. Snout shorter than orbit, 80.9–95.1 (95.1)% OL, 25.9–29.1 (29.1)% HL, snout tip slightly or strongly projecting, 24.4–42.5 (24.4)% OL, 7.4–13.4 (7.4)% HL. Mouth inferior; upper jaw 33.9–39.6 (39.6)% HL, maxilla extending to anterior part of orbit, oral cleft extending to anterior rim of orbit; mandible 41.1–48.8 (41.1)% HL. Premaxillary and mandibular teeth trilobed in 10 oblique rows of 8 teeth forming narrow bands. Orbit 30.6–32.0 (30.6)% HL, dorsal margin below dorsal contour of head, suborbital depth to upper jaw 7.9–9.7 (9.7)% HL, to lower jaw 18.1–24.6 (24.6)% HL; pupil round, about 30–40% OL. Interorbital space broad, bony distance 13.3–15.4 (14.7% HL, convex. Nostril single, with raised rim in lectotype , or in short tube, 1.6% HL. Free neuromasts not evident because of damage. Gill opening small, 18.7% HL in lectotype , upper margin at about level of dorsal rim of orbit, extending ventrally to above pectoral fin. Dorsal-fin rays 48–51 (48; Tables 1 , 2 ), anteriormost ray moderately elongate, 2.6–3.2 (3.2) in head, 31.3% HL, forming “distinct” notch, tip of anteriormost ray exserted ( Burke 1930 ). Anteriormost dorsal-fin pterygiophore inserted between neural spines 2 and 3. Pre-dorsal-fin length 25% SL. Anal-fin rays 44 ( Tables 1 , 2 ), two anal-fin pterygiophores anterior to first haemal spine, each bearing single ray, tips of anterior rays exserted ( Burke 1930 ). Anal-fin origin below vertebra 12 (caudal vertebra 2), pre-anal-fin length 34–36 (34)% SL. Pectoral fin deeply notched, with 30–32 (30) rays ( Tables 1 , 2 ). Upper lobe with 25 rays, extending well beyond anus to anal-fin origin, 71.6–81.1 (71.6)% HL, longer than lower lobe. Lower lobe elongate, 52.0–62.7 (62.7)% HL, with 7 rays, extending beyond anus short of anal-fin origin. Elongate rays of lower lobe mostly free of membrane ( Gilbert 1896 ). Notch strong. Uppermost pectoral-fin ray level with ventral rim of orbit. Insertion of lowermost pectoral-fin ray below mid-orbit. Pelvic disk small, length 30.8% HL, slightly wider than long, width 23.1–30.8 (30.8)% HL, anterior lobe weakly developed, flat, distance from tip of snout to pelvic disk 14% SL. Anus behind vertical from gill slit ( Burke 1930 ), closer to pelvic disk than to anal-fin origin, distance from disk to anus 15.8–22.4 (22.4)% HL, distance from anus to anal-fin origin 54.5–68.5 (54.5)% HL; distance from snout to anus 24% SL, 114.2–116.4 (116.4)% HL. TABLE 1. Proportional morphometric and meristic characters of species of Allinectes : A. ectenes , A. curilanus , A. attenuatus , and A. pycnosoma . Morphometric data are given in percent standard length and presented as the range, followed by the mean +/– standard deviation (SD). Data derived from previously published sources ( Gilbert and Burke 1912a ; Burke 1930 ; Kido 1985 ) are indicated with an asterisk. Data not available are indicated with an en dash.

A. ectenes			A. curilanus			A. attenuatus	A. pycnosoma
n	Range	Mean±SD	n	Range	Mean±SD	Value	Value
Standard length	3	60–64	62 ± 2.0	35	46.6–80	63.7 ± 7.7	37	39
%SL
Head length	3	20.4–25	22.1 ± 2.6	35	18.7–22.7	20.2 ± 1.1	23	27
Head width	2	12.5–13	12.8 ± 0.3	24	8.5–12.1	10.3 ± 0.9	13.6	15.4
Greatest body depth (at dorsal-fin origin)	1	14	24	7.7-17.3	10.8 ± 2.5	15.5	21.1
Body depth at pelvic fin	2	13–14.1	13.5 ± 0.9	24	7.6–14.7	10.5 ± 2.3	15.5	19.8
Body depth at anal-fin origin	3	11–13	11.9 ± 1.0	27	7.7–11.9	9.5 ± 1.0	9	16.7
Snout length	3	4.9–6.7	6 ± 1.0	24	4.4–7.2	5.5 ± 0.7	6.3	6.7
Snout tip length	3	1.6–3.4	2.8 ± 1.0	26	1.5–3.4	2.4 ± 0.5	0	0
Orbit length	3	6.3–8.4	7.1 ± 1.2	24	5.4–7.5	6.5 ± 0.6	7.3	8.8
Orbit depth	1	4.9	21	3.7–6.0	5.1 ± 0.6	5.4	6.5
Post-orbit length	3	7.9–10	8.7 ± 1.2	24	6.1–10.5	8.2 ± 1.1	9.5	11.6
Interorbital width (bony)	3	3.2–3.4	3.3 ± 0.2	23	3.3–4.4	3.8 ± 0.4	4.9	6.5
Interorbital width (fleshy)	24	3.7–8.6	5.6 ± 1.1	–	–
Suborbital depth to upper jaw	2	1.6–1.7	1.6 ± 0.1	24	1.5–2.8	2.2 ± 0.4	1.9	2.9
Suborbital depth to lower jaw	2	3.3–4.7	4 ± 1.1	24	3.7–5.6	4.5 ± 0.6	5.7	9.3
Mouth width	1	11.6	24	8–12	10 ± 1.1	10	12.6
Maxilla length	2	6.5–7.9	7.2 ± 1.0	28	6.9–10.8	8.2 ± 1.2	9.5	7.7
Mandible length	2	9.4–9.7	9.6 ± 0.3	24	7.9–11.5	9.1 ± 1	10.9	10.3
Gill slit length	1	3.9	29	3.0–5.9	4.5 ± 0.8	–	6.2
Pectoral-fin length	2	15.7–16.2	15.9 ± 0.4	26	13.1–17.4	15.1 ± 1.1	–	15.2
Lower lobe of pectoral fin length	2	11.3–12.5	11.9 ± 0.9	27	10.5–21.6	15.3 ± 3.0	–	9
Notch ray of pectoral fin length	2	4.7–4.9	4.8 ± 0.2	24	2.6–8.0	5.2 ± 1.1	–	7.2
Predorsal length	1	25.2	24	18.8–25.4	21.3 ± 1.7	25.5	27.2
Preanal length	2	34.4–35.5	35 ± 0.8	24	27.2–37.6	32.4 ± 2.5	32.5	39.5
Snout to pelvic disc length	2	13.0–14.1	13.5 ± 0.9	24	9.7–13.3	11.7 ± 1.0	15.7	15.4
Snout to anal fin length	2	24.2–25	24.6 ± 0.6	24	18.5–23.5	21.2 ± 1.3	26.3	27.7
Pelvic disc length	2	6.3–6.5	6.4 ± 0.2	31	4.0–8.4	5.8 ± 1.0	6.5	7.5
Pelvic disc width	2	4.7–6.5	5.6 ± 1.3	31	3.3–7.5	5.1 ± 1.0	5.7	7.5
Pelvic disc to anus length	2	3.3–4.7	4 ± 1.1	31	1.3–5.9	4.1 ± 1.2	5.7	7
Anus to anal fin length	2	11.0–14.6	12.8 ± 2.6	24	6.8–16	11.5 ± 2.5	6.8	10.8
Caudal fin length	–	24	7.5–10.5	8.8 ± 0.7	–	7.7
Dorsal fin attachment to caudal fin length	–	24	1.1–3.2	2.1 ± 0.7	–	–
Anal fin attachment to caudal fin length	–	24	1.3–3.9	2.7 ± 0.7	–	–
Caudal fin base depth	1	2.6	28	1.3–2.2	1.7 ± 0.3	–	3.9
Nasal tube length	1	0.4	21	0.2–1.1	0.6 ± 0.3	1.1	–

......continued on the next page TABLE 1. (Continued)

A. ectenes			A. curilanus			A. attenuatus	A. pycnosoma
n	Range	Mean±SD	n	Range	Mean±SD	Value	Value
Post anal-fin origin length	2	64.6–65.7	65.1 ± 0.8	24	62.5–72.9	67.7 ± 2.5	67.6	60.6
Pyloric caecum length	1	3	4	3.1–6.6	4.3 ± 1.7	–	–
Dorsal-fin ray 1 length	1	6.6*	31	5.6–11.8	8.0 ± 1.5	–	–
Dorsal-fin ray 2 length	25	3.6–8.1	5.3 ± 1.1	–	7.2
Dorsal-fin ray 3 length	1	6.4	22	2.4–6.8	4.4 ± 1.1	–	–
Dorsal-fin ray 4 length	1	6.2	20	3.2–6.1	4.5 ± 0.8	6.8	–
Dorsal-fin ray 5 length	17	3.5–7.1	5.4 ± 1.1	–	–
Dorsal-fin ray 6 length	11	5.0–7.7	6.0 ± 1.0	–	–
Dorsal-fin ray 7 length	5	5.0–6.3	5.5 ± 0.6	–	–
Meristics
Dorsal-fin rays	2	48–51	49.5 ± 2.2	26	48–54	50.9 ± 1.5	48	45
Anal-fin rays	2	44	26	42–49	44.9 ± 1.5	40	39
Pectoral-fin rays	2	31–32	31.5 ± 0.8	30	28–37	32.4 ± 2.2	34	39
Pectoral-fin lower lobe rays	2	7–8	7.5 ± 0.8	27	6–10	7.8 ± 1.0	–	9
Principal caudal-fin rays	–	19	10–11	10.5 ± 0.6	–	11
Precaudal vertebrae	2	10	28	9–10	9.8 ± 0.5	10	10
Caudal vertebrae	2	44	28	43–49	45.3 ± 1.4	>38	39
Total vertebrae	2	54	32	53–59	55.1 ± 1.4	>48	49
Pterygiophores anterior to haemal spine I	2	2	22	1–2	1.7 ± 0.5	–	1
Gill rakers	1	6	16	4–9	6.5 ± 1.5	–	–
Pyloric caeca	1	6	4	6–7	6.3 ± 0.5	10	17

Caudal fin slender, truncate, of about eight rays; dorsal- and anal-fin membranous connections to caudal apparently not greater than 30% caudal-fin length ( Burke 1930 ). Vertebrae 54, precaudal 10, caudal 44 ( Tables 1 , 2 ). Pleural ribs 3 (USNM 53031), anteriormost small, others long and slender, present on vertebrae 8–10. Skin thin. Pyloric caeca 0–6 (absent in lectotype ), if present “very short” (14.2% HL) or as “filaments” ( Burke 1930 ). Coloration . In life, nearly uniform dusky-brownish; lighter on snout, belly, and underside of head ( Gilbert 1896 ). Peritoneum, stomach, and intestines pale; orobranchial cavity dusky ( Gilbert 1896 ; Burke 1930 ). Body and fins dusky pale in preservation. Life history . The largest specimen known is 87 mm TL ( Burke 1930 ). The lectotype ( USNM 48618 ) is a ripe female, 64 mm SL with yolked eggs. Distribution . Allinectes ectenes is known from only five specimens taken in the Aleutian Islands at depths of 494 and 640 m ( Fig. 1 ). The three types were collected from north of Unalaska Island. Two additional non-type specimens of USNM 64043 identified by Burke (1930) were collected 150 miles north of the Rat Islands on Bowers Bank ( Townsend, 1901 ) ( Fig. 1 ). The stated locality of USNM 64043 for station 3785 from Townsend (1901) is “Rat Ids., Aleutian Chain, S. 150 m ,” in which “S” is presumed to mean “South,” is likely an error. The map of stations provided by Townsend (1901) shows the station listed with 3784 (“3784-5”) as being well north of the Aleutians and listed under the general heading “North of Aleutian Islands.” Stations 3784 and 3786 are both on Bowers Bank, about 250 km north of the Rat Islands, and both were occupied on the same day. To travel 500 km from north to south of the Rat Islands and back between the two stations within the same day would be impossible. In addition, depths 250 km south of the Aleutians are in the thousands of meters, far deeper than the stated depth. TABLE 2. Counts of dorsal-fin rays, anal-fin rays, pectoral-fin rays, and total vertebrae in species of Allinectes , including three new species: A. busbyi , A. istiophorus , and A. nanstanorum . * indicates a minimum count of vertebrae for A. attenuatus .

Dorsal-fin rays
42	43	44	45	46	47	48	49	50	51	52	53	54	n
A. ectenes	1	1	2
A. attenuatus	1	1
A. busbyi	1	1
A. curilanus	1	4	6	6	6	2	1	26
A. istiophorus	4	13	20	12	4	53
A. nanstanorum	1	1	2
A. pycnosoma	1	1
Anal-fin rays
37	38	39	40	41	42	43	44	45	46	47	49	n
A. ectenes	2	2
A. attenuatus	1	1
A. busbyi	1	1
A. curilanus	2	1	7	10	4	1	1	26
A. istiophorus	19	20	10	5	54
A. nanstanorum	1	1	2
A. pycnosoma	1	1
Pectoral-fin rays
28	29	30	31	32	33	34	35	36	37	39	n
A. ectenes	1	1	2
A. attenuatus	1	1
A. busbyi	1	1
A. curilanus	1	2	2	2	11	6	2	1	1	2	30
A. istiophorus	5	8	10	10	7	3	43
A. nanstanorum	1	1
A. pycnosoma	1	1
Total vertebrae
47	48	49	50	51	53	54	55	56	57	58	59	n
A. ectenes	1	1
A. attenuatus	1*	1
A. busbyi	1	1
A. curilanus	3	8	11	6	2	1	1	32
A. istiophorus	17	26	9	4	56
A. nanstanorum	1	1	2
A. pycnosoma	1	1

Etymology . The specific epithet is derived from the Greek έχτευής, meaning “extended” or “drawn out” ( Jordan & Evermann 1898 ) in reference to its elongate body. Remarks . Although I obtained some new data from the types of A. ectenes , all are in very poor condition. Each is broken, two are in three pieces, and all are otherwise damaged. In addition, Gilbert (1896) and Burke (1930) based their explicit descriptions on the lectotype (the largest of the syntypes ), but it is unclear which specimens Burke (1930) used for his synopsis and remarks. They likely included a non-type lot of two specimens (USNM 64043), each now broken into three pieces and unidentifiable. No illustration is available of A. ectenes . The most significant character of the three new species described below is the length of the two anteriormost rays of the dorsal fin, which are longer than all succeeding rays and in two of the new species extend at least a third of head length (three in head length) to equal the head length (one in head length). The original condition of the anteriormost dorsal-fin ray in A. ectenes cannot be verified because it is damaged in all the types as well as in both specimens of USNM 64043, but apparently, the anterior dorsal-fin rays varied widely among these specimens. No illustration is available of the species and Gilbert (1896) makes no mention of the length of the rays of the dorsal fin in his original description of A. ectenes . However, in Burke’s (1930) redescription of the type of A. ectenes he noted the presence of a “dorsal notch” and the elongate first ray, “about 3.2 in head” and thus equal to orbit length. He also provided a synopsis and remarks with additional description that included the paralectotypes and two specimens of USNM 64043. He noted in his synopsis that the dorsal fin is more or less distinctly notched in the species, including in specimens of USNM 64043, giving proportional data for specimens in that lot—the anteriormost ray 3.4 in HL (29% HL) in the larger and 2.6 in HL (38% HL) in the smaller. In addition, Burke (1930) noted that the tip of the first dorsal-fin ray projects above the skin; in the new species nearly a third or more of the ray is exserted. Among species of Allinectes , the anteriormost ray in A. istiophorus , new species , is much longer at 1.0 to 1.5 times in head length; in A. curilanus , the ray is shorter at 2.1 to 2.7 times in head length. In A. attenuatus , the first ray is “elongate, longer than the two or three succeeding rays” ( Burke 1930: 117 ). Thus, among the new species, the first dorsal-fin ray is significantly longer in both A. istiophorus , new species , and A. busbyi , new species ; in A. nanstanorum , new species , otherwise easily distinguished by its black peritoneum and lower vertebral and median-fin ray counts, the first ray is about equal in length to that of A. ectenes . Of the five specimens examined by Burke (1930: 110–112) , including the two non-types, pyloric caeca were absent in the lectotype and two other specimens; in the two remaining specimens they were “very short and small” or represented by “some filaments.” I found six short and small caeca in a paralectotype (CAS 3091) but was unable to find caeca in the other specimens. Finger-like pyloric caeca that are short but longer than in this paralectotype are present in A. curilanus , A. pycnosoma , and each of the three new species. In A. pycnosoma , 17 pyloric caeca are present ( Kido 1985 ); in the other species, 6–11 are present. In his original description, Gilbert (1896) described the color of the types as “dusky-brownish.” Because Gilbert in other reports specifically indicated when referring to the preserved coloration (e.g., “color in spirits”) of specimens, I accept this as his description of fresh specimens. Each of the new species described herein range in color from light to dark red, with some dark brown-black mottling in A. nanstanorum , new species . Snout-tip length is an important character used in distinguishing A. ectenes from A. curilanus , but appears to vary widely in A. ectenes . Both Gilbert (1896) and Burke (1930) described the snout of A. ectenes as overlapping the inferior mouth for a distance equal to ( Gilbert 1896 ) or half ( Burke 1930 ) the pupil diameter, and Burke described it as being similar to that of A. curilanus and C. simus Gilbert, 1896 , both of which have obviously produced snouts. The snouts of all the types of A. ectenes are compressed and damaged; however, in the lectotype , the snout is slightly protruding (although the pupil is damaged), and in one of the paralectotypes (CAS-SU 3091), the broad, rounded snout is clearly protruding and extends over the mouth for a distance about equal to the diameter of the pupil. Burke (1930) discussed the similarity of A. ectenes with A. curilanus , noting that they differed in the size of the gill slit and pelvic disk. Although both types of A. curilanus have larger gill slits and pelvic discs than evident in data available for two of the types of A. ectenes , the range of lengths among specimens of A. curilanus examined here fully encompasses the ranges in A. ectenes and are not useful to distinguish the species. Allinectes ectenes was described by both Gilbert (1896) and Burke (1930) as having a depressed head with a more or less pronounced snout, and a slender, strongly elongate body, and Burke (1930) described it as similar to Acantholiparis opercularis Gilbert and Burke, 1912a . However, species of Acantholiparis are easily distinguished from species of Allinectes by several characters, including most obviously by the lack of a pelvic disk as well as the diagnostic spiny opercle.