Cymbasoma quintanarooense (Suárez-Morales, 1993)

Suárez-Morales, E. & Escamilla, J. B., 2001, Taxonomic report on some monstrilloids (Copepoda, Monstrilloida) from southeast Mexico with the description of a new species of M onstrilla, Journal of Natural History 35 (10), pp. 1433-1445 : 1987-1992

publication ID	https://doi.org/10.1080/002229301317067629
DOI	https://doi.org/10.5281/zenodo.15808228
persistent identifier	https://treatment.plazi.org/id/03EC9D1D-FF8B-6070-724C-FC4CFE44FEFB
treatment provided by	Carolina
scientific name	Cymbasoma quintanarooense (Suárez-Morales, 1993)
status

Treatment

Cymbasoma quintanarooense (Suárez-Morales, 1993) View in CoL

( figures 1 View Fig , 2 View Fig )

Material examined

One adult female, ethanol-preserved, undissected. Laguna de Chelem , Yucatan, Mexico (21°19.35' N; 89°49.10' W), 14 January 1991. Catalogue number: ECO-CH Z-00517 . GoogleMaps

Description

Female ( figures 1 View Fig , 2 View Fig ). Total body length 1.95 mm measured from anterior end of cephalic somite to posterior margin of anal somite. Cephalothorax (incorporating first pedigerous somite) accounting for 59% of total body length. Forehead slightly rounded in dorsal view. Anteriormost part of cephalothorax, just behind ocelli, with small dorsolateral patches of longitudinal striations ( figures 1A,B View Fig arrow 1); transverse striations on ventral surface between oral papilla and bases of the antennules ( figure 1B View Fig , arrow 2); additional transverse striations in wide band across dorsal surface, occupying second quarter of cephalothorax length ( figures 1A,B,D View Fig , arrow 3). Oral papilla lying midventrally 0.14 of length from anterior end of cephalothorax ( figure 1B View Fig ). Nauplius eye present, weakly developed, ocelli strongly pigmented with rounded shape in dorsal view.

Antennule representing 19.5% of total body length. Antennule four-segmented, segments clearly separated; armed with 0–I; 1– V; 2–I; 4–VIII setae (Roman numerals) and spines or spiniform setae (Arabic numerals), plus two aesthetascs ( figure 2B View Fig ). Two of these spines terminal, forming pincer-like structure. In terms of pattern described by Grygier and Ohtsuka (1995) for female monstrilloid antennular armature, setae and spines on first segment (1), second segment (2d,2v, IId), 1–3 1–2 and third segment (3,IIIv,d) all complete. Several elements absent (looked for, but not seen) on fourth segment (IVd, 4v, 4d, b). Setae b dichotomously 3 1–2 4 1–3 branched in distal one-third. Ratio of lengths of antennule segments: 16.7:25.3:14.5:43.5 (=100).

Incorpo rated first pedigerou s somite and three free succeeding pedigerou s somites each bearing a pair of biramous swimming legs. Pedigerous somites 2–4 accounting for 26% of total length in dorsal view. Legs 1–4 slightly decreasing in size posteriorly. Basis articulating with large, rectangular coxa along diagonal line. Basis with lateral hair-like seta on legs 1–4; on leg 3, this seta at least 2.5–3 times longer and noticeably thicker than on other legs. Endopodites and exopodites of legs 1–4, triarticulated. Ramus setae all biserially plumose except spiniform outer seta on exopod 1 and exopod 3 of each natatory leg. Outermost exopodal apical seta of legs 1–4 with inner margin lightly setulated, outer margin with small denticles ( figure 2C View Fig ). Armature of swimming legs as follows:

basis endopodite exopodite

leg 1 1–0 0–1;0–1;1,2,2 I–1;0–1;I,1,3 legs 2–4 1–0 0–1;0–1;1,2,2 I–1;0–1;I,1,2,2

Fifth leg a single large lobe, both arise from a common plate, slightly separated at base to its partner. Lobe about 2.5–3 times longer than thick, broadening distally, and armed with three relatively long setae, latter subequal in length and breadth ( figures 2D,E View Fig ).

Urosome consisting of fifth pedigerous somite, genital compound somite, and one free abdominal somite, the anal somite. Urosome, excluding caudal rami, accounting for 16% of total body length. Fifth pedigerous somite with anterior half wide with rounded margins, and abrupt transition to narrower posterior half with straight margins; dorsal patch of transverse striations on middle part of this somite. G enital compound somite globose in anterior two-thirds, with deep transverse cuticular striations covering about one- fifth of its dorsal surface. Somite with small, rounded ventral protuberance on anterior part, visible in lateral view ( figure 2D View Fig ). Compound somite representing slightly less than half (c. 48%) of length of urosome ( figure 2A View Fig ). Ratio of lengths of fifth pedigerous somite, genital compound somite, and anal somite: 34.7:47.8:19.1:17.4 (=100). G enital compound somite bearing long, basally separated ovigerous spines. Spines about 48.7% of total body length, tips not swollen but slender distally, terminal portion uneven, one slightly longer than the other ( figures 1C,E View Fig ). Caudal rami about as long as wide, moderately divergent, bearing three terminal setae subequal in length and breadth ( figure 2A View Fig ).

Remarks

This species was originally assigned to the invalid ( Grygier, 1994a) genus Thaumaleus . It was described from fi ve females collected in Bahóa de la Ascensión on the eastern coast of the Yucatan Peninsula (Suárez-Morales, 1994). Like all species formerly asigned to Thaumaleus (except the latter’s type species), it has been reassigned to the genus Cymbasoma . Hence, the speci fi c epithet is here amended to quintanarooense corresponding to the gender (neuter) of the current genus name.

A fuller description and complementary illustrations are provided here for C. quintanarooense using the new material collected in Chelem, northern coast of Yucatan. Most of the information on body proportions and features found in the Chelem female of this species agrees with the descriptions and drawings of Suárez-Morales (1994). The total body length of the Chelem specimen (1.95 mm) falls within the range reported for the Ascension material (1.9–2.3 mm). H owever, several other features were not reported in the original description. The oral papilla was indicated by Suárez-Morales (1994) to be 0.28 of length posteriorly along the ventral surface of the cephalothorax, while the correct figure is in fact 0.14 in both groups of specimens. Suárez-Morales (1994) described two low cephalic protuberances, one ventral between the oral papilla and the antennule bases, and the other on the dorsal surface of the head. The former was probably a misinterpretation of striations like those found in the same position in the Chelem specimen; the latter dorsal protuberance was not found in the Chelem specimen. The well-de fi ned striation pattern on the dorsal surface of the cephalothorax that was noted here, as well as other cuticular ornamentation on the cephalothorax, fifth pedigerous somite, and genital compound somite, were not reported in the original description. The shape of the pigment cups in dorsal view is diVerent in the specimens from the two localities: subtriangular in Bahóa de la Ascensión, rounded in Laguna de Chelem.

The anal somite was depicted by Suárez-Morales (1994: figure 1A View Fig ) as being a large, partially divided somite; however, the anal somite is in fact short, and it is the genital somite that has a constriction and dorsal band of striations suggesting a partial intersegmental division near the base of the ovigerous spines (see figure 2E View Fig ). A suture on the anal somite is considered to be an important taxonomic character at the species level ( Isaac, 1975), and it is absent in C. quintanarooense . Although this species was compared originally only with other species possessing such a suture, its status as a distinct species is retained mainly due to its fifth leg structure (see below), and by the peculiar pattern of cuticular striations.

The antennular length of the Chelem specimen (0.4 mm) falls within the range reported for the Ascension material (0.2–0.4 mm). The antennular armature of this species was incompletely described by Suárez-Morales (1994). In the present work the antennular setation pattern of C. quintanarooense is analysed for the first time according to the nomenclature of monstrilloid setation pattern proposed by Grygier and Ohtsuka (1995) (see figure 2B View Fig ). N either the dichotomous branching of the three subterminal setae b ( figure 3E View Fig ), nor several elements of the armature of the distal 1–3 antennular segment were mentioned or depicted in the previous description. The length ratio of the antennular segments and the relative length of the antennules (20–22%) to the total body length are quite similar in specimens from both localities.

The fifth leg was described by Suárez-Morales (1994) as having one segment with two setae and an inner protuberance armed with a single seta; this interpretation takes into account the tendency of other species of this genus to have an inner lobe with various degrees of development ( Sars, 1921; Isaac, 1975; Suárez-Morales and Gasca, 1998). In some other species, such as C. reticulatum Giesbrecht, 1892a and C. claparedi Giesbrecht, 1892a , this inner protuberance is undistinguishable, the leg being represented by a single segment (see Giesbrecht, 1892a); this seems to be the correct interpretation of the fifth leg structure found in C. quintanarooense. The ovigerous spines have the same relative length in the Ascension and the Chelem specimens, in both cases representing 47–48% of total body length.

There are diVerences between the type specimens and those recorded in the Laguna de Chelem. M ost of them are related to the incomplete original description, and the others (sizes, proportions) are not strong enough as to propose a new taxon. Therefore, these diVerences should be considered only as an extended morphological range for C. quintanarooense.

Although its occurrence on the northern coast of the Yucatan Peninsula represents a modest latitudinal range extension, the distribution of this species is still restricted to the Yucatan area. The male of this species has been described by Suárez-Morales (in press) from material collected in the southern part of the eastern coast of the Yucatan Peninsula.