Maristella chicoi, 2019

MARISTELLA CHICOI REDA & GERRISH View in CoL , SP. NOV.

( FIGS 1–11)

urn:lsid:zoobank.org:act:AA86D432-0802-42D5-A854-79532ABE97EF

Genus H-group, sp. MSH (acronym = Massed Shallow Horizontals, also dubbed laterals) Gerrish & Morin, 2016: 190 (4–12), Torres & Cohen, 2005: 16.

Material examined – type: Observed in sand channels of patch reef and fore-reef habitats around Carrie Bow , South Water and Tobacco Cayes in Belize (+ 16.805830°N, − 88.083755°W) GoogleMaps .

Holotype: Adult male dissected (valves in alcohol, limbs on slide), LACM-MBC 15069 : Reda and Gerrish specimen BZ_MSH_3: South Water Caye, Belize (16.812N, 88.083W), G. Gerrish collection, in sweep net from horizontal displays in 3 m deep sand patches between patch reef corals, 16 June 2012 (≈18:20–19:00 h). GoogleMaps

in sweep net from horizontal displays in 3 m deep sand patches between patch reef corals, 6Jan2016 (≈ 18:20–19:00 h) – LACM-MBC 15068 and LACM-MBC 15072 : BZ_MSH_1f and 1f. 1, 1 female (valves in alcohol, limbs on slide). From Carrie Bow Caye, Belize in sweep net from horizontal displays in 3 m deep sand patches between patch reef corals, 13 January 2017 (≈18:20–19:00 h) – LACM-MBC 15073 : BZ_MSH_ 3f. 1, 1 female (limbs on slide) and LACM-MBC 15074 : BZ_MSH_ 3f. 2 (valves and copulatory limb) .

Morphological description and diagnosis: Important characters for distinguishing M. chicoi from congeners are italicized and in bold and noted with an asterisk (*); informative characters shared by M. chicoi and one or more species within the genus are noted with a theta sign (ϴ) and Maristella species sharing the characters are denoted with their initial in a superscript, also see Table 2.

Valve shape ( Fig. 1A, B): Oval, posterior D margin gently sloped; males with wide, somewhat rectangular keel and extends two-thirds height of the valve; ϴ caudal ridge with transparent spines (i,p) ( Figs 2C, 4B, C).

Paratypes: From South Water Caye , Belize collected in same sweep net as holotype – LACM-MBC 15067 : BZ_MSH_1, 1 male (limbs on slide) ; CASIZ 233394 and CASIZ 233393 : BZ_MSH_6, 1 male (valves in alcohol, limbs on slide) ; USNM 1550579 About USNM : BZ_MSH_4, 1 male (valves in alcohol, limbs on slide) ; USNM 1550580 About USNM : BZ_MSH_5, 1 male (valves in alcohol, limbs on slide) ; LACM-MBC 15071 : BZ_MSH_ batch.1, 5 whole males in alcohol ; CASIZ 233395 : BZ_MSH_batch.2, 5 whole males in alcohol ; USNM 1550578 About USNM : BZ_MSH_batch.3, 5 whole males in alcohol. From Carrie Bow Caye , Belize (16.806N, 88.083W) GoogleMaps collected in sweep net by G. Gerrish in 3 m deep sand patches between patch reef corals 20 November 2008 (≈ 18:20–19:00 h) – LACM – MBC 15094 View Materials : BZ_ MSH_12.1, 1 male (eye & valve on slide) and LACM-MBC 15065 : BZ_MSH_12.2 (valve, infold and upper lip on slide) ; LACM-MBC 15066 : BZ_MSH_9, 1 male (limbs on slide). From South Water Caye , Belize

Valve size ( Fig. 1A, B): Small size for genus; male ϴ L = 1.56–1.7 mm, mean = 1.618 ± 0.005 mm (i,p), ϴ Ht = 0.92–1.0 mm, mean = 0.954 ± 0.004 mm (i,p), ratio of L:Ht = 1.62–1.74 mm, mean = 1.695 ± 0.005 (N = 32).

Muscle scars ( Fig. 2B): About 15–16 with three larger scars dorsal to a tighter cluster of larger, joined and smaller more ventral scars.

Infold ( Figs 2A, 4A): Male * rostral row with 8–13 setae (2–5 along incisur) plus 0–3 anterior to row (N = 10) ϴ anteroventral row with 16–24 setae (i) (2–5 along incisur) plus 0–1 anterior and 0 posterior to row (N = 10); L posteroventral infold with 1–3 setae (N = 10). Female rostral row with 12 setae (4–5 along incisur) plus 3–9 anterior to row (N = 2); anteroventral row with 23–33 setae (1 along incisur) plus 0–14 anterior and 1–7 posterior to row (N = 2).

Eyes ( Figs 3A, 4E): Medial eye small (0.13–0.14 mm). Lateral eye larger (0.18–0.19 mm) with 16 ommatidia. Bellonci organ ( Fig. 3A): small (0.08 mm), attached to V cup of medial eye.

Male light organ ( Fig. 3B): L [lol] = 0.26–0.28 mm (0.28 ± 0.01, I = 6), W (low) 0.16–0.18 mm (0.17 ± 0.01, N = 6).

Upper lip ( Figs 3B, 4F–H): Male, central row of anterior field with total of 21–25 nozzles, raised lateral ridges and pegs with about 30–32 nozzles (N = 4). Ventral pair of long tusks with abundant, long hairs plus posterior and terminal nozzles. Dorsal lateral field near mouth with about 11–13 nozzles (N = 3).

Male first antenna ( Figs 5B, 6A, C): First article bare. Second article with medial spines near and on dorsal margins forming rows. Third article short with one dorsal ringed seta with short spines just proximal to middle and * One terminal longer ventral ringed seta with short spines. Fourth article with 1 terminal ringed dorsal seta with short spines and one shorter terminal ringed ventral seta with short spines. Sensory seta of fifth article with bifurcate tip; with 10 long bare proximal filaments forming two alternating rows of five and two distinctly more slender distal filaments. Sixth article with one terminal dorsal ringed seta with short spines. Seventh article: a-seta of equal length as seta of sixth article; ( Fig. 5B shows proximally broken a-seta); b-seta ringed with stout proximal filament with bulbous base followed by large sucker and small distal process with pointed tip, two distal slender filaments each bearing proximal tiny projection followed by ϴ 3–6 small suckers (n, p) (N = 16), distal filament extending to about tip of seta; c-seta similar to b-seta but slightly more than twice as long, with a slightly larger basal filament and sucker, with two more distal filaments each bearing proximal tiny projection followed by ϴ 3–6 small suckers (p, n) (N = 16), with six more distal bare filaments. Eighth article: d- and e-setae longer than b-seta, bare, filamentous, distally ringed; f- and g-setae long with slender filaments with dorsal spines (f- with nine, gwith 10) increasing in length distally; c-, f- and g-setae tapering and ringed, becoming bare and filamentous distally, longer than sensory seta (g-seta longest); each of these three setae with bifurcate tips.

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Second antenna ( Figs 5C, 6C): Protopod with short ringed seta. Endopod three-jointed: first article with five ringed setae (four proximal, one medial), one long proximal and about twice the length of three shorter proximal setae and one long medial seta; second article elongate with ϴ short (p) terminal ringed seta; third article about half length of second article, with long terminal ringed filament. Exopod: first article bare; second article with ringed terminal seta with tip reaching to about sixth or seventh article, with ϴ 6–10 ventral spines (p, i) (N = 18); articles 3–8 with basal spines becoming longer distally (basal spines often with thin distal spinelet) and with long ringed seta with natatory hairs (not shown); ninth article with four ringed setae (three long each decreasing in length with natatory hairs, one shorter with few short spines) and one short tapered terminal spine; Last spine of ninth article slightly smaller than spine of eighth article.

limb VLat view. CL = central lobe, OL = outer lobe, IL = inner lobe, Fb = finger branch, fs = finger sclerite, h = hood, ht = hood tip, pos = proximal setae of outer lobe, s = strut sclerite, sb = setal branch of outer lobe, TS = sclerotized external thumb of outer lobe, ts = thumb setae of outer lobe, ys = Y-sclerite. ∆ 15 = hood with rounded apex. B, LACM-MBC 15074 : BZ_MSH_ 3f. 2, female V view. lk = lateral knob of female genital lobe, sp = spermatophore .

Mandible ( Figs 5D–F, 6B, D, E): Coxal endite spinous with ringed seta near base. Basis: seven ringed setae on proximal two-thirds of ventral margin: one medium long spinous and one short bare (about a quarter length of longer seta) medial a-setae, one short bare lateral b-seta, one long spinous and one short bare c-setae and two d-setae (c-setae not close to d-setae; shortest a-, b- and c-setae all about same length; proximal d-seta medium long (smaller than distal c-seta), ϴ distal d-seta long and hirsute with short distal spines (m); dorsal margin with three long setae (one proximal and two longer, unequal, subterminal, medial setae distally ringed with short spines). Exopod: extending just short of end of first endopodial article, with medial wrinkled or hirsute distal process extending to pointed tip and two ventral setae (one longer ringed proximal seta with short spines and one shorter distal seta with short spines). Endopod: first endopodial article with four ringed ventral setae (one minute bare a-seta, one medium short b-seta with short spines, one long hirsute c-seta with short spines, and one longer d-seta). Second endopodial article: dorsal margin with about 16 setae: 1 a-, 1 b-, 1 c-, 3 d-setae (two long and one small ringed d-setae, longest does not extend to third article), nine dorsal medial whisk setae with fine hairs, one short stout unringed medial seta with medium spines, ϴ D d-setae do not extend to end article (p, i). Ventral margin with two short ringed ϴ non-overlapping (p, i) setae just distal from middle; finger long sclerotized slightly angled unringed with rounded tip and basal ringed finger seta. Dorsal and ventral margins with fine short spines. End (third) article with three moderately curved claws; all claws with tips curved and bearing few small proximal medial teeth. Dorsal claw thinner than ventral claws, with tip less curved, slightly longer but not extending beyond ventral claws; four ringed setae: one small, thin ventral medial a-seta, one long ventral medial c-seta (* ratio of c-seta: V claw small ), one longer ventral lateral b-seta with bulbous base and distal rings extending beyond claws and one dorsal lateral ringed d-seta extending to about half length of dorsal claw. End of d-seta with narrow tube tip similar to that of c-seta.

Fourth limb (first maxilla) ( Figs 7A, 8A, B): Endite: I = 3 long hirsute and unringed setae, one unringed with few proximal spines and thread-like tip, four distally ringed with few proximal spines and thread-like tip, three distally ringed with few proximal hairs and bifid or bare pointed tip; II = 2 distally ringed setae with few proximal hairs, three long hirsute and distally ringed; III = 3–4 long distally ringed with slight pectination. Coxa: hirsute lobe and stout hirsute D seta. Basis: with one long distally ringed bare lateral seta and 1 distal medial seta (one may be on first endopodial article). Exopod: hirsute, with 1 long hirsute distally ringed proximal seta and 2 long distally ringed terminal setae (outer seta hirsute and slightly longer than inner seta). Endopod: first article rectangular. Subterminal cutting tooth big squarish, proximally dented, ventrally projected. One long ringed alpha seta with short spines, one ringed beta-seta with row of about 40–45 teeth; first article with rows of medial hairs; second article narrower than first endopodial article with 3 ringed a-setae (a-1 with row of about 15–20 teeth, a-2 with row of about 20–30 teeth, a-3 with row of about 25–30 teeth); two stout b-setae, b-1 ringed, finely pectinate and with a row of about 35–40 teeth (distal teeth shorter), b-2, shorter, unringed, straight, claw-like, tapering with about 10 small teeth, b-2 seta L = about 50–65% b-1- seta (N = 9); ϴ 3 ringed c-setae (p,I, m, l), (c-2 and c-3 long finely pectinate with a row of about 40–50 teeth), c-1 short slender, (c1 L = about 40–54% b-2-seta); 3 d-setae, d-1 unringed, finely pectinate, claw-like with about 5–10 basal teeth, 5 dorsal spines; d-2 unringed, claw-like with about 5 teeth; d-3 distally ringed with about 40 teeth.

Fifth limb (second maxilla) ( Figs 7B, C, 8C, D): Epipod with 46 setae (N = 2). Protopod with long, rather straight anterior distal tooth with expanded round tip. Endites: I (E 1) = 3–6 stout, tapered, unequal setae with long stout hairs or spines (all distally ringed with bare pointed tip); 1–2 long setae with one distal and one proximal ring of concentric hairs; 1–2 medium setae with long medial hairs or spines; 1–2 short setae with 1 proximal ring of concentric hairs. II (E 2) = 6–8 seta; 3–5 stout unequal, distally ringed setae with proximal long hairs (some distally pectinate); one short unringed seta, 1–2 medium with about 10 teeth and proximal concentric ring of hair. III (E

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) = five setae (one stout, long ringed inner posterior seta with proximal hairs; two adjacent setae unringed, pointed, claw-like with about 10–20 distal small teeth and two adjacent seta ringed with about 10 teeth); one anterior setae ringed with about 15–20 teeth. Exopod with two prominent sclerites; first article sclerite rather ‘L’-shaped (shorter broader part of ‘L’ underlying anterior setal row); second article sclerite, large, irregular, occupying outer half of article. First exopodial article: posterior row of six progressively larger pectinate claw-like teeth ( Fig. 7B, C), one proximal smooth triangular peg (pl), and 1 large stout ringed peg-seta with about 15–20 teeth and proximal to peg; peg-seta shorter than longest tooth, peg shorter than shortest tooth; shortest tooth with ϴ 2–3 proximal bulges (p, i) and a * total of 5–10 cusps; anterior row of four ringed hirsute 1-a setae (two long distally ringed and pectinate setae, one anterior seta on proximal margin of article over sclerite or protopod, and one faint, medium ringed and hirsute). Second exopodial article with total of 14–15 setae: four anterior progressively longer a-claws (two stout ringed with teeth and ϴ two stout unringed with distal teeth (p, i) ), 8–9 ringed pectinate b-setae (anterior row of 4–5 b’seta, posterior row of 4 longer b’’-setae), one proximally hirsute posterior c-seta with distal rings and short spines, and one hirsute anterior d-seta with distal rings and short spines. Third exopodial article: inner lobe with two ringed setae (shorter subterminal one with long proximal hairs and distal short spines, terminal seta longest with long proximal hairs); outer lobe hirsute with two terminal medium-short distally ringed setae. Fourth and fifth exopodial article fused, hirsute with two long ringed setae.

Sixth limb ( Figs 7D, 8E): Epipod: 2–5 bare ringed epipodial setae (N = 17). Endites: separated from each other and rest of limb by grooves or sutures, with medial hairs. Endite setae: I = 3 (one long terminal seta with long spines or stout hairs and distally ringed, two short ringed proximal setae with long spines or stout hairs); II = 3–5 setae (two long terminal seta with long spines or stout hairs and ringed, one proximal short stout ringed setae with proximal hairs, 1–2 proximal medium stout ringed setae with few proximal hairs); III = 3–5 (2–3 long terminal setae with long spines or stout hairs and ringed, 1–2 short terminal ringed seta with few proximal stout spines); IV = 1–2 long terminal setae distally ringed with long mid spines or stout hairs. End article: basally separated by suture or groove from rest of limb not extending posteriorly, ϴ posterior margin rectangular (i) (rather than continuously curved), with long fine hairs on medial surface, lateral ventral surface with stouter long hairs, terminal ventral margin with slight irregularity in convex curve (slightly angled within region of anterior setae), and ϴ angled in the region of the posterior setae (i), with total of 6–10 ventral terminal setae: 3–7 anterior setae (1–3 proximal anterior setae with long hairs and ringed, 2–4 distal anterior stout setae with long proximal hairs and short distal spines and distally ringed), followed by space (gap = about 37% ventral length of end article; N = 17) between anterior and three posterior setae (shorter ventral of the posterior setae with long mid hairs and short distal spines and distally ringed, two more dorsal setae unequally longer and hirsute).

Male seventh limb ( Figs 8F, G, 9A): Limbs slightly expanded in distal setal area. Total of 8–12 setae (N = 9). Comb side with 0–1 proximal (each with 4–5 bells) and 3–5 terminal (each with 2–6 bells); peg side with 2–4 proximal (each with 4–5 bells) and 3–4 terminal (each with 3–6 bells). Comb is long, tapered, minutely fringed teeth with rounded tips and 5–6 short blunt teeth (2–3 each side), short teeth grooved or brush-like. Single sclerotized peg curved, thin, shorter than short comb teeth, with about 3–4 minute pointed terminal teeth; proximal to peg setae.

Female seventh limb ( Fig. 9B): Total of 18–20 setae (N = 4). Comb side with 2–5 proximal and 6–7 terminal; peg side with 3–5 proximal and 4–5 terminal. Single sclerotized peg thin, long and hooked (N = 2).

Male eighth limb (copulatory) ( Figs 10A, 11A–D): The basal part of the first article with a prominent Y-sclerite with a strut so that the sclerite forms a rectangular loop with a medial distal inner extension (finger) terminating near the distal tip of the finger branch of the inner lobe; loop slightly broader distally. Inner lobe: with two branches, finger branch and setal branch, separated by terminal cleft. Finger branch: tip with numerous minute denticles, some serrated and few large triangular denticles. Setal branch: external surface with 3–6 ringed bare non-terminal setae with tapered bases and 2–3 long ringed bare terminal setae with tapered bases (N = 5); tip with some minute denticles. Outer lobe: with thumb sclerite articulating with distal corner of strut ofY-sclerite of first article extending from the articulation curving toward the anterior midline to form the thumb; three ringed bare thumb setae are grouped dorsal and below end of thumb; two outer posterior ringed, bare setae. Hood: With pronounced distal sclerite (hood sclerite) articulating near base of thumb; with rounded apex and an extended, triangular, tapered flap (usually folded over the distal inner lobe in preserved specimens); tip of hood is thin, rounded and bears minute scales, pores or cusps. Central lobe: lies ventral to inner and outer lobes; with 2–3 stout ringed, hairy setae with tapered bases.

Female eighth copulatory limb ( Fig. 10B): Smaller than male and unjointed. Low irregularly tubular medial ridge terminating laterally in more prominent round knob; medial ridge with attached irregularly rounded spermatophore. Setose openings ( Cohen & Morin, 1997) not observed (but not examined with SEM or confocal microscopy).

Furca ( Fig. 2D): each lamella with nine claws; only claw 2 fused to lamella; claw 3 more slender than and longer than claw 4; all claws with two rows of posterior teeth (one medial row, one lateral row) and larger claws with row of smaller thin spines. Anterior of lamella with few tiny spines; margin posterior to claws with spines. Claw L ratios: first:second = 1.4–1.6, second:third = 1.5–1.7, third:fourth = 1.2–1.3 (N = 4), fourth:fifth = 1.2–1.4 (N = 2).

Geographical distribution ( Table 2): Maristella chicoi occurs in shallow patch reefs and deeper spur and groove formations on the Mesoamerican barrier reef near South Water Caye, Belize (+ 16.811782°N, - 88.082533°W). It has been observed on the fore-reef as far north as Tobacco Caye, as far south as Carrie Bow Caye and on multiple shallow back-reef regions near Blue Ground Range, Belize. It is likely that the range of M. chicoi extends throughout a large region of the Mesoamerican reef. Marisella chicoi displays over sand channels between corals (bottom depths 2–18 m).

Bioluminescent displays ( Table 3; see Supporting Information, Video S3): Maristella chicoi is one of the few species known to produce a strictly horizontal display. While displaying, males travel up to 2–3 m producing a tightly spaced string of lights. The species show high entrainment in a unique way, where new males will intercept a displaying male and start displaying parallel to, but at a slight angle from, the initiating male. The resulting impression is lines of light pulses that repeatedly bifurcate as they extend horizontally through the water column. Waves of entraining males can often be observed simultaneously displaying at multiple depths but overlapping when observed from above with multiple rows and layers of light pulses being placed in the same direction. The first 3–5 pulses of each display are slightly longer in duration (2.0– 2.5 s) and pulses decrease in duration as the display continues (0.5– 1.5 s). Trains can contain >>30 pulses and extend 1.5–2.5 m horizontally in the water column. The beginning pulses of the display occur 2–3 cm apart but final pulses often are <1 cm apart. Individual displays last up to one minute but the bifurcating waves produced by multiple entraining individuals can last 2–3 min.

Colour of living ostracodes: The carapace and limbs of M. chicoi are transparent and without pigmentation. The compound eyes are large (compared to body size) and appear black with 16 apparent ommatidia. The abdomen is generally dark brown but can range to tan in some cases. The light organ is apparent and appears as a bright yellow rectangular at the anterior of the body.

Etymology: Named in honour of Victor Orlando ‘Chico’ Escobar (1976–2013), a dedicated Belizean field assistant and close friend.