Cerapus ryanadamsi, Drumm, 2018

Drumm, David T., 2018, Two new species of Cerapus (Crustacea: Amphipoda: Ischyroceridae) from the Northwest Atlantic and Gulf of Mexico, Zootaxa 4441 (3), pp. 495-510 : 503-509

Cerapus ryanadamsi n. sp.

( Figs 8–12)

? Cerapus sp. C sensu LeCroy, 2007: 557, fig. 482.

Material examined. Type material.— Holotype: male (♂), 2.5 mm, ( USNM 1488283 ), Manatee River (Florida), 27°30ʹ57.2034ʺN 82°36ʹ22.32ʺW, salinity: 36.4 ppt . Allotype: female (♀), 2.5 mm, ( USNM 1488284 ), same locality as holotype . Paratypes: 8 females (max 2.5 mm), 8 males (max 2.5 mm), 4 juveniles, ( USNM 1488285 ); all same locality as holotype . 6 males (1 adult, 5 subadults; max 2.5 mm), 10 females (max 2.5 mm), 3 juveniles ( USNM 1488286 ), Corpus Christie Bay , Texas, 27°49ʹ33.528ʺN 97°18ʹ18ʺW, salinity: 23.6 ppt.

Diagnosis. Rostrum short and apically acute. Male antenna 1, peduncle almost 4 × as long as flagellum, peduncular article 1 slightly longer than articles 2 and 3 which are slender and subequal in length. Male antenna 1 flagellum, 2 or 3-articulate; female flagellum 2-articulate. Male antenna 2 flagellum, 2 or 3-articulate; female antenna 2 flagellum 2-articulate. Male and female antenna 1 and antenna 2 peduncle with pigment bands. Male pereonite 1 without a lateral keel. Male gnathopod 2 “palmer” margin of carpus without process. Pereopod 7, posterior margin of basis with spinules extending more than three quarters distally and the carpus with posterodistal groups of long setae as well as anterodistally. Pleopod 2, inner ramus reduced, approximately 2.3 × as long as wide. Male uropod 1 peduncle with a large distoventral hook.

Description of male. Size, 2.5 mm ( Figs 8, 9A ). Rostrum short, apically acute, length 0.1 × head; lateral cephalic lobe with ventral corner rounded. Sternal keel absent on pereonites 1 and 2.

Antenna 1 ( Figs 9A, B ) slightly less than half body length; peduncle almost 4 × as long as flagellum, peduncular article 1 slightly longer than articles 2 and 3 which are slender and subequal in length; dorsal margin moderately convex; peduncular articles 2 and 3 with pigment bands; flagellum 2-articulate, article 1 with several aesthetascs and approximately 2.8 × as long as article 2, article 2 with one aesthetasc. Antenna 2 ( Fig. 9A ) slightly longer than antenna; peduncle approximately 2.8 × as long as flagellum, articles 4 and 5 with pigment bands; flagellum 2-articulate, article 1 approximately 3 × as long as article 2.

Mandibles ( Figs 9C, D ): left and right incisors with six teeth; left lacinia mobilis with five teeth, right with one large tooth and minutely denticulate margin; left mandible with two broad accessory spines and two intermediate plumose setae; molar seta present on left mandible; palp article 2, 1.5 × as long as article 3, with one small simple seta; article 3 with four setae. Lower lip ( Fig. 9E ) typical pointed mandibular projection. Maxilla 1 ( Fig. 9F ): inner plate small with one apical plumose seta reaching tip of outer plate; outer plate with ten spine-teeth; palp biarticulate with four subterminal setae and five terminal spines. Maxilla 2 ( Fig. 9G ): outer plate broader than inner plate, both plates apically setose; inner plate with setae along medial margin. Maxilliped ( Fig. 9H ): inner plate subquadrate with three stout nodular spines and ten plumose setae; outer plate with three stout apical setae and six stout nodular spines along medial margin; palp article 2 with one inner seta, article 3 with several long simple setae; article 4 with two long and robust and one short terminal seta.

Gnathopod 1 ( Fig. 10A ) subchelate; coxa small; carpus subequal in length to propodus; 1.4 × as long as deep with setose posterior lobe; propodus 1.6 × as long as deep with four rows of anteromedial setae, palm extremely oblique, setose; dactylus with posterior row of short spinules. Gnathopod 2 ( Fig. 10B ) carpochelate; coxa larger than coxa 1, broader than deep; basis with short, sparse setae along anterior margin and one posterodistal seta; carpus massive, 1.4 × as long as deep, palmer margin oblique with long posterior defining tooth and lacking palmer tooth; propodus approximately 2.9 × as long as broad, not recurved, with short setae on anterior and posterior margins; dactylus 0.8 × as long as propodus with short setae along posterior margin.

Pereopod 3 ( Fig. 10C ): coxa anteriorly produced, more than twice as broad as deep; basis 2 × as long as broad, with short setae on anterior margin and two longer setulate setae on anteroproximal corner; ischium 1.75 × as long as wide; merus as long as broad; carpus with three setulate setae along distal half of posterior margin; propodus with three setae on posterior margin. Pereopod 4 ( Fig. 10D ) nearly identical to pereopod 3, with fewer setae on anterior margin of basis and propodus with four setae on posterior margin. Pereopod 5 ( Fig. 10E ): coxa 1.6 × as broad as deep; basis about as long as broad; merus, posterior lobe with three plumose setae, smaller anterior lobe with one small seta; carpus, posterior lobe covered in denticles and bearing a seta; dactylus with one small accessory hook. Pereopod 6 ( Fig. 11A ): coxa 1.5 × as broad as deep; basis 1.7 × as long as broad, with short setae on anterior and posterior margins; ischium about as long as broad; merus 2 × as long as broad, with short distal setae; carpus slightly longer than broad with several long setulate setae on posterodistal corner and simple setae on anterodistal corner; propodus slightly shorter than merus with one long and several short simple setae; dactylus with two small accessory hooks. Pereopod 7 ( Fig. 11B ): coxa 2 × as long as deep; basis with spinules on most of posterior margin and several short simple setae, setae on anterior margin longer than setae on posterior margin; ischium with two short anterodistal setae; merus with posterodistal and anterodistal groups of long setae; carpus shorter than merus with posterodistal and anterodistal groups of long setulate and simple setae; propodus slightly longer than carpus with anterodistal group of long setulate setae; dactylus with two small accessory hooks.

Pleopods 1 to 3 decreasing in size. Pleopod 1 ( Fig. 11C ): peduncle with two small distomedial hooks; rami subequal in length, outer ramus broader than inner. Pleopod 2 ( Fig. 11D ): peduncle with two small distomedial hooks and two plumose setae; inner ramus reduced, about 2.4 × as long as broad, with four setae and appearing to be biarticulate; outer ramus almost twice as long as inner ramus, appearing to be triarticulate. Pleopod 3 ( Fig. 11E ): peduncle with two small distomedial hooks and lacking setae; inner ramus reduced, about twice as long as broad, 1-articulate with two setae; outer ramus twice as long as inner ramus, 1-articulate.

Uropods ( Figs 11F,G ): Uropod 1 biramous; peduncle nearly 3 × as long as wide, with two simple outer distal setae and one large distoventral hook; outer ramus with outer row of spinules and five medial setae and one large apical spine; inner ramus 0.6 × as long as outer ramus, with large apical spine. Uropod 2 uniramous; peduncle 3.2 × as long as broad, 5 × as long as vestigial ramus; ramus with one hook and one subdistal seta. Uropod 3 uniramous; peduncle 2.3 × as long as broad, with two setae on inner margin; ramus vestigial with two hooks and one short robust seta. Telson ( Fig. 11F ) broader than long, each lobe with about 11 recurved hooks in two rows.

Description of female. Similar to male, including size at maturity, except for the following: Pereonite 1 shorter and pereonites 4 and 5 longer than in male. Antenna 1 first peduncle article strongly convex dorsally ( Fig. 12A ). Gnathopod 1 ( Fig. 12B ) carpus with long setae midway on anterior margin. Gnathopod 2 ( Fig. 12C ) subchelate, larger but similar to gnathopod 1, basis with spinules on anterior margin and carpus with posterodistal lobe. Pereopod 5 coxa larger. Uropod 1 peduncle without distoventral hook. Oostegites on gnathopod 2 to pereopod 5.

Intraspecific variation. Three males that were examined had three flagella articles in the antenna 1 and antenna 2. One male had the antenna 1 with two flagella articles and the antenna 2 with three flagella articles. The third article of the mandibular palp can have varying numbers of setae. For instance, one female had eight setae and another female had three setae. The second mandibular palp article seems to be consistent with one seta.

Etymology. Named after the author’s favorite singer/songwriter, Ryan Adams, whose music has enriched his life over the years.

Remarks. Three species of Cerapus have been recorded from the Gulf of Mexico ( LeCroy et al. 2009): C. benthophilus Thomas and Heard, 1979; C. cudjoe ; and the doubtful records for C. tubularis . The only one that has the distoventral hook on the uropod 1 peduncle is C. cudjoe but can be distinguished from C. ryanadamsi by the male having a lateral keel on the first pereonite, male and female flagellum of antenna 1 with four articles (two or three in male and two in female of C. ryanadamsi ), gnathopod 2 propodus 3.5 × as long as wide (2.9 × as long as wide in C. ryanadamsi ), and four setae on the second mandibular palp article (only one seta in C. ryanadamsi ). It is possible that this species is the partially described Cerapus sp. C sensu LeCroy (2007), occurring in the Gulf of Mexico including Tampa Bay and off Corpus Christie, Texas, the only major difference being that C. ryanadamsi has spinules on the posterior margin of the basis of pereopod 7.

Cerapus ryanadamsi n. sp. can be distinguished from C. slayeri n. sp. by the number of antennular flagella articles in the female, and by the smaller body size.

Geographic distribution. Known from the Manatee River near Tampa Bay in western Florida (type locality) and Corpus Christie Bay, Texas ( Fig. 13).

Figures

FIGURE 9. Cerapus ryanadamsi n. sp., adult male. A, holotype male, habitus (lateral view); B, head and antenna 1 (dorsal view); C, left mandible; D, right mandible incisor process and lacinia mobilis; E, lower lip; F, maxilla 1; G, maxilla 2; H, maxilliped. Scale bars: A = 0.5 mm; B = 0.2 mm; C, H = 0.1 mm; D,E,F,G = 0.05 mm.

FIGURE 10. Cerapus ryanadamsi n. sp., adult male. A, gnathopod 1; B, gnathopod 2; C, pereopod 3; D, pereopod 4; E, pereopod 5. Scale bars: A,C-E = 0.1 mm; B = 0.2 mm.

FIGURE 11. Cerapus ryanadamsi n. sp., adult male. A, pereopod 6; B, pereopod 7; C, pleopod 1; D, pleopod 2; E, pleopod 3; F, urosome and uropods; G, uropod 1 (ventral view). Scale bars: A-C, F = 0.1 mm; D,E = 0.05 mm.

FIGURE 12. Cerapus ryanadamsi n. sp., adult female. A, rostrum and antenna 1 (lateral view); B, gnathopod 1; C, gnathopod 2. Scale bars: A = 0.2 mm; B,C = 0.1 mm.