Choniomyzon libiniae

Santos, Cynthia & Björnberg, Tagea, 2004, Choniomyzon libiniae, sp. n. (Crustacea, Copepoda, Nicothoidae) from São Sebastião, SP, Brazil, Zootaxa 603, pp. 1-12 : 2-10

Choniomyzon libiniae , sp nov.

Material examined

Holotype: adult female ( MZUSP 15713), collected on Libinia spinosa H. Milne­ Edwards (Crustacea, Decapoda , Majidae ) from Anchovas Beach, São Sebastião Island, SP, Brazil, 15 December 2001.

Paratypes: eggs, nauplii, copepodid I, and copepodid II ( MZUSP 15714, 15715, 15716, 15717), collected on Libinia spinosa (Crustacea, Decapoda , Majidae ) from Anchovas Beach, São Sebastião Island, SP, Brazil, 15 December 2001; one male and one female (collection of Dr. Carlos F. Rocha), collected on Libinia spinosa (CCrustacea, Decapoda , Majidae ).

Description

Eggs: The female nicothoid ( Figs. 1 a, 1b) attaches her eggs (0.12 mm in diameter) to the eggs (0.59 mm in diameter) of the host. Two eggs (pink in color) were attached by a short cord to each host´s egg (Fig. 2). From the copepod eggs, nauplii emerge.

Nauplii (Figs. 3–7): Cyclopoid­like. Length 0.12–0.24 mm, ovoid in shape. Muscles parallel when seen laterally; V­shaped (Fig. 3) when observed dorsally, as in all cyclopoid nauplii. Antennule trimerous (Fig. 4) with s. f.: 1: 2: 3. Antenna (Figs. 5a, 5b) with coxa and basis unarmed, not articulated with 5–jointed exopod (s. f.: 1: 1: 1: 1: 2); endopod 2– jointed with last joint bearing 2 terminal setae and a small, lateral ovoid aesthetasc (Figs. 5a, 5b) which is very transparent, and hardly visible. Mandible (Fig. 6) with separate coxa and basis; exopod 3­jointed and not articulated to basis; exopod with thick aesthetasc­like setae (s. f. 1: 1: 1: 2); endopod articulated with basis, 2­jointed (s. f.: 0: 2). Caudal armature: 2 short thick setae. Inside mature nauplius, next stage (the copepodid) is visible (Fig. 7).

Copepodid I ( Figs. 8 –13): Cyclopiform, length 0.265–0.280 mm, well chitinized. Prosome oval: comprising cephalon fused with first thoracic segment, and one free segment. Urosome three­segmented. Caudal rami about as long as wide and bearing 5 setae each; 2 dorsal, 2 ventral plus very long internal seta ( Figs. 8a, 8 b). Antennule ( Fig. 8 b) 4– jointed: first joint indistinctly and incompletely subdivided; s. f. 2 + 1: 1: 4: 3 + 1 or 2 aesthetascs. Antenna (Fig. 9) 5–jointed (s. f. 0: I: 0: 2: 2); terminal pinnate setae, hook­like. Mandible (Fig. 10) blade­like, projecting into mouth, surrounded by sucker or cone­like projection with row of setules and transparent rim, the oral disc. Maxillule (Fig. 10 Mx1) very transparent, base with anterior and posterior branches or lobes and 4 thick setae.

Maxilla (Mx2) ( Fig. 8 b) trimerous, with hook­like terminal pinnate spine or seta. Maxilliped (Fig. 11) 6­jointed bearing hook­like terminal pinnate spine; fifth joint with one seta. First leg (Fig. 12): coxa and basis not ornamented, exopod with one joint (s. f.: III + I + 3); endopod one­jointed, with 6 setae. Second leg (Fig. 13): coxa and basis without ornamentation, endopod with 5 setae; exopod one­jointed (s. f.: III + I + 3). Posterior corners of first urosome segment each bearing two setae, one shorter than other ( Fig. 8a ).

– Antennule of male. – Antennule of copepodid III. 28 – Antenna of male. FIGURE 29 – Oral cone of male. FIGURE 30 – Male urosome. FIGURE 31 – Male: second leg. FIGURE 32 – Male: first leg. FIGURE 33 – Male: deformed first leg. FIGURE 34 – Male maxilliped. FIGURE 35 – Male maxilla. FIGURE 36 – Copepodid III: part of urosome and caudal ramus. FIGURE 37 – Copepodid III maxilliped. FIGURE 38 – Copepodid III first leg. FIGURE 39 – Copepodid III second leg. All scale bars equal to 0.10 mm.

Copepodid II ( Figs. 14 a, 14b): Body globular, reduced towards urosome, less sclerotized than first copepodid; length 0.273–0.298 mm. Articulations not or hardly visible. Widest part of urosome, provided with 2 thorn­like lateral protuberances. Antennule with ten joints (s. f.: 1: 0: 1: 1: 1: 1: 1: 1: 2 + 1: 4); boundaries between joints indistinct (Fig. 15). Antenna (Figs. 16a, 16b) 4 or 3–jointed; second joint with spine­like protuberance composed of two or three setae: last joint with cylindrical terminal protuberance and 2 lateral flanged spines. Mandibles ( Fig. 14 ) blade­like, well sclerotized, protruding into sucker or oral disc, lateral to labrum. Oral disc, circular, cup­like, with thin transparent rim. Maxillule (Fig. 20): very thin, transparent structure, similar to maxillule of adult, with coxobasis and 2 lobes, one bearing thick pointed seta, protuberance with thin seta and anterior lobe with 2 setae visible over border of sucker or oral disc. Maxilla (Fig. 17) 2 or 3–jointed, ending in 2 minute spines. Maxilliped ( Fig. 14 a) indistinctly 4–jointed, with 2 lateral spines on third joint and last joint in form of thick spine. First leg (Fig. 18): coxobasis with one seta; endopod 2–jointed (s. f.: 1 + I: III + 3); exopod 2–jointed (s. f.: 1: II + 3). Second leg (Fig. 19): coxobasis with one outer seta; endopod indistinctly 2–jointed (s. f.: 1 + I: 1 + 3 + I); exopod 2–jointed (s. f.: I: II + 3 + 1).

Female copepodid ( Figs. 21a, 21 b): Size 0.335 mm. General form of copepodid II with very conspicuous lateral transparent margins (wings), visible dorsally and ventrally. Segmentation of appendages distinct. Antennule (Fig. 27): 10 or 11 segments. Antenna, oral cone, mandible, maxillule and maxilla, maxillipeds (Fig. 37) similar to those of copepodid II. First and second legs with 2­jointed endopods and exopods (Figs. 38–39). First leg with spine on coxobasis; endopod with s. f.: 1: 6; exopod, s. f.: I: II + 5. Second leg (Fig. 39) with bare coxobasis and endopod with s. f.: 1: 5; exopod with spine on first segment and spine­like distal and external protuberance, 2 spine­like external distal protuberances on second segment, plus 5 setae. Urosome (Fig. 36) showing two lateral round protuberances, characteristic of female urosome.

Adult female ( Figs. 1 a, 1b): Length 0.62–0.83 mm (5 specimens); body oval­shaped, without divisions in prosome, rounded and wider in front. Lateral "wing­like" fold protuberant on both sides of head. Margin of fold ornamented by transparent rim conspicuous in young females (semi lateral view), in gravid females hardly or not visible. Urosome narrow, short and overlapped by posterior region of prosome; indistinctly divided into 2 segments. Antennule ( Fig. 40 ) 12–jointed (s. f.: 1: 1: 1: 2: 0: 1: 1: 1: 1: 3 + ae: 2: 4 + ae). Antenna (A2) (Figs. 41a, 41b) 3–jointed; first and second joints unarmed, third bearing 2 thick, finger­like structures one of which with 2 small pointed spines distally and a terminal denticulate or comb­like protuberance. Mandible: blade­like, tapering distally. Maxillule (Mx1) (Fig. 42b) situated lateral to oral cone with long pointed posterior lobe or seta, middle protuberance ending in pointed structure, and frontal lobe or joint indistinctly divided into two which projects over border of cone and is armed with 2 thick pointed setae and two thinner, smaller setae. In frontal view (Fig. 42a), it is possible to see mandibles (Md) protruding into the mouth of the specimen in form of two blades. Maxilla (Mx2) (Figs. 43a, 43b) 3–jointed: last joint with four short spiny protuberances – two of which longer. Maxilliped (Mxp) (Fig. 44) 5–jointed with first, second and third joints with seta or spine each, fourth joint with small lateral seta and spine, last joint with margin provided with row of thin setules and terminal comb­like structure ornamented with minute spines. First leg (P1) (Fig. 45): coxa unarmed, basis with external seta; exopod bimerous with s. f. = I + 0: I + I + 4; endopod bimerous, with s. f. = 0 + 1: 1 + 2 + 3. Second leg (Fig. 46): coxa unarmed; basis I + 0; exopod bimerous, with s. f. = I + 0: I + I + 3 + 1; endopod I + 1: 1 + 2 + 2. Third leg single­jointed with two longer and one very short small seta. Urosome marked off from body by two cup­like protuberances (genital openings). Urosome cylindrical, not terminal, placed posterior to genital cups, with 2 or 3 indistinct segments, last of which divided into two branches which end in the elongate caudal rami, about three times longer than wide. Caudal rami ornamented with two lateral fine setae, one on each side; a long blade­like bipinnate seta and two double as long setae coalesced at base and bipinnate.

Male (Fig. 22): Size 0.320–0.350 mm. Characterized by transparency and by presence of wing­like protuberances on each side of body. Antennule (Fig. 26) has 10 segments. Antenna (Fig. 28) has long terminal finger­like protuberance, 4 times as long as wide. Maxilla of male (Fig. 35) with terminal segment 5 times as long as wide. Oral cone, maxillule, maxilliped (Fig. 34) similar to those of CII. First legs of male (Fig. 32) with spine or seta on the proximal segment of the endopod and exopod. Last exopod segment bearing 2 spines and 3 setae, and last endopod segment with 4 setae. Second legs (Fig. 31) with seta on first endopod segment and 4 setae on last. First segment of exopod with 2 spines; second segment with 4 setae and spine­like protuberance.

Legs of male (Fig. 33) frequently with deformed rami. Spine and protuberance with 2 minute setae representing third pair of legs on urosome (Fig. 30). Urosome unsegmented, containing 2 pear­shaped spermatophores. Caudal rami bearing 2 very fine lateral setae and 3 longer setae of which the 2 longest are coalesced at base.

In addition to the above mentioned forms of Choniomyzon , the following stages were also present in the samples and will be treated in more detail in a later paper: young female, ovigerous female and spent female (a female which has laid her eggs) (Figs. 23 to 25).

Diagnosis

The new species is characterized by the ovoid form and the indistinctly 3­segmented urosome, which is not terminal. The first and second legs do not show a button­like ornament as in C. panuliri Pillai. The antenna of the adult female bears finger­like projections, one or two of which have denticulate margins. The maxilla has four terminal spines and the maxillipeds have a terminal denticulate margin.

Etymology

The name of the species is a reference to its host, Libinia spinosa .

Figures

FIGURE 1 – Choniomyzon libiniae, n. sp.: a – Adult female, lateral view; b – Same, ventral view. FIGURE 2 – Egg of host Libinia spinosa with 2 eggs of C. libiniae attached. FIGURE 3 – Nauplius of C. libiniae, dorsal, yolk visible inside, muscles stippled. FIGURE 4 – Antennule of nauplius of C. libiniae. FIGURE. 5: a – Antenna of nauplius of C. libiniae, lateral; b – Same, frontal view. FIGURE 6 – Mandible of nauplius of C. libiniae. FIGURE 7 – Nauplius of C. libiniae about to metamorphose into copepodid I, visible inside outer skeleton. All scale bars equal to 0.10 mm.

FIGURE 14 – Copepodid II of C. libiniae: a – ventral view, second legs omitted and first legs outlined; last joint of maxilliped, detailed; b – partly lateral view of the same. FIGURE 15 – Antennule of copepodid II of C. libiniae, lateral. FIGURE 16 – Antenna of copepodid II of C. libiniae: a – ventral and b – lateral views of the same appendage. FIGURE 17 – Maxilla of copepodid II of C. libiniae. FIGURE 18 – First leg, right, of copepodid II of C. libiniae. FIGURE 19 – Second leg, right, of copepodid II of C. libiniae. FIGURE 20: a – Oral cone (oc), left mandible blade visible entering the cone laterally, maxillule right side, seen by transparency beyond the cone, left maxillule omitted, as well as right mandible­blade; b – Mandible blade; c – Maxillule. All scale bars equal to 0.10 mm.

FIGURE 21: a – Copepodid III (pupa); b – Same, lateral view. FIGURE 22 – Male. FIGURE 23 – Young female. FIGURE 24 – Ovigerous female. FIGURE 25 – Spent female. All scale bars equal to 0.10 mm.

FIGURE 40 – Antennule of adult female of C. libiniae. FIGURE 41 – Antenna of adult female of C. libiniae: a – ventral view; b – lateral view. FIGURE 42 – Oral cone (o. c.); maxillule (mx 1) and mandible (md): a – ventral view; b – lateral view of maxillule. FIGURE 43 – Maxilla of adult female of C. libiniae: a – dorsal view; b – lateral view. FIGURE 44 – Maxilliped of adult female of C. libiniae. FIGURE 45 – Posterior region of urosome (adult female) and third leg. FIGURE 46: a – First leg of adult female; b – Second leg of adult female. All scale bars equal to 0.10 mm.

FIGURE 8 – a – Copepodid I of C. libiniae, dorsal view; b – Same, ventral. FIGURE 9 – Antenna of C. libiniae. FIGURE 10 – Oral cone (o. c.), mandibles (Md), maxillules (Mx 1) and labrum (Lb) of copepodid I of C. libiniae. FIGURE 11 – Maxilliped of copepodid I of C. libiniae. FIGURE 12 – First leg of copepodid I of C. libiniae, right side, ventral. FIGURE 13 – Second leg of copepodid I of C. libiniae, left side, ventral. All scale bars equal to 0.10 mm.