Patricia Rojas

Size shift in the Mexican earthworm species Balanteodrilus pearsei (Megascolecidae, Acanthodrilini): A possible case of character displacement

Abstract The earthworm genus Balanteodrilus includes three well-differentiated species. One of the species (B. pearsei) is common to eastern and south-eastern Mexico. All but one population of B. pearsei are medium-sized earthworms (6.4–11 cm in length). The smallest morph of B. pearsei was found sympatrically coexisting at La Mancha forest with another species of the genus. In this locality, resources are scarce, the two species present different vertical distributions and their abundances are relatively low. A change of size in this population was not the result of random variation. Three possible explanations are proposed: (1) character displacement resulting from past long-term competition; (2) response to poor soil nutrients; or (3) reproductive character displacement or reinforcement.

New Diplotrema and Lavellodrilus earthworm species from southern Mexico (Annelida, Crassiclitellata, Acanthodrilidae)

Two acanthodriline new species from the states of Tabasco and Chiapas in southern Mexico are described, Diplotrema chajulensis sp. nov. and Lavellodrilus sheylae sp.nov. Diplotrema chajulensis sp. nov. has spermathecae where the ampulla inserts at a right angle from the duct and the diverticulum continues the main axis; it is distinguished from other neotropical Diplotrema species that share this character by the pattern of genital marks and the type of penial setae. Lavellodrilus sheylae sp. nov. is unique in the genus Lavellodrilus by the unpaired condition of the mesial spermathecae; variation in the number of spermathecal diverticula (one or two) was considered a polymorphism. Finally we discuss reasons to maintain one of the new species in an austral genus (Diplotrema) in spite of some morphological differences observed among the Mexican-Cuban-Central American (MX-CA) worms and the austral species. A short esophagus in all the holoic and meroic acanthodriline earthworms from MX-CA and a mid-ventral position of spermathecal pores in Lavellodrilus are interpreted as ancestral characters that evolved and were fixed in the worms that inhabited an ancient Laurasian block, probably in response to the semi-aquatic conditions that prevailed in this region during millions of years.

Lavellodrilus notosetosus sp. nov. (Annelida, Crassiclitellata, Acanthodrilidae): a new Mexican earthworm with uncommon characters, revealed by a preliminary revision of subfamily Acanthodrilinae

A new acanthodriline earthworm species, Lavellodrilus notosetosus sp. nov., is described from tropical rain forests of southern Mexico. The new species is placed within the genus Lavellodrilus by the presence of mesial spermathecal pores. It is separated from other species of the genus by the dorsal location of setae cd in most of the body, last hearts in segment 13, first intestinal segment in 20 and genital setae in segment 12. A preliminary morphological revision of all genera and species of Acanthodrilinae was undertaken in order to: i) evaluate if the mesial spermathecal pores justify the status of Lavellodrilus, ii) determine how common (expressed as percentages of species having the character) the diagnostic characters of the new species are in the subfamily, iii) clarify if these characters exhibit a geographical pattern, and iv) contribute towards a comprehensive analysis of the Acanthodrilinae. In this revision, species were separated in nine geographical regions: USA, northern Mexico, southern Mexico, Caribbean Islands (northern hemisphere), and South America, South Africa, Madagascar, Australia, New Zealand, New Caledonia and Antarctic Islands (southern hemisphere). As a result of the revision it was found that among the 511 recognized species of Acanthodrilinae only 11 species have a mesial location of the spermathecal pores, in two cases probably representing monophyletic groups (Lavellodrilus and a group of South African Parachilota species). It was also found that the distinguishing characters in L. notosetosus sp. nov., notably the location of last hearts, genital setae and the first intestinal segment, are uncommon characters in the acanthodriline earthworm fauna of southern Mexico and Central America, but more frequent in North America, the Caribbean, and the southern hemisphere. We conclude that the acanthodrilines from the northern hemisphere are morphologically more similar to those from Australia, New Zealand, and New Caledonia than to those of South Africa and South America.

New species and records of the earthworm genus Ramiellona (Annelida, Oligochaeta, Acanthodrilidae) from southern Mexico and Guatemala.

Three new species from the Mexican states of Tabasco and Chiapas are added to the acanthodrilid earthworm genus Ramiellona, R. microscolecina sp. nov., R. tojolabala sp. nov. and R. teapaensis sp. nov. They belong to a group of species with penial setae and last pair of hearts in segment 12. All are holandric and the spermathecae have either a flat circular diverticle in a segment anterior to that of the ampulla (R. microscolecina sp. nov. and R. tojolabala sp. nov.) or two ovoidal and sessile diverticles on opposite sides in the same segment of the ampulla (R. teapaensis sp. nov.). Ramiellona americana (Gates) is re-described from a single specimen from central Guatemala, and the diagnosis of Ramiellona lasiura (Graff) from El Salvador is emended after reinvestigating a paratype specimen from the Senckenberg Naturmuseum Frankfurt. On the basis of several individuals from different populations of the Mexican states of Chiapas and Tabasco, the morphological variation of Ramiellona strigosa setosa Righi is described and its relationship with the Guatemalan Ramiellona strigosa strigosa Gates and Ramiellona eiseni (Michaelsen) is discussed. Finally, the position of Ramiellona within Acanthodrilidae and its relation to genera of the doubtful Octochaetidae is discussed.