Arxius de Miscel·lània Zoològica. Volume 23 (2025) Pages: 103-107
New records of the freshwater oligochaetes (Annelida: Oligochaeta: Criodrilidae, Naididae) from Morocco
Taybi, A. F., van Haaren, T., Mabrouki, Y.
DOI: https://doi.org/10.32800/amz.2025.23.0103Download
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Taybi, A. F., van Haaren, T., Mabrouki, Y., 2025. New records of the freshwater oligochaetes (Annelida: Oligochaeta: Criodrilidae, Naididae) from Morocco. Arxius de Miscel·lània Zoològica, 23: 103-107, DOI: https://doi.org/10.32800/amz.2025.23.0103-
Reception date:
- 24/03/2025
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Acceptation date:
- 26/06/2025
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Publication date:
- 07/07/2025
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Abstract
New records of the freshwater oligochaetes (Annelida: Oligochaeta: Criodrilidae, Naididae) from Morocco
The freshwater oligochaete fauna of Morocco is still little known. Recent field surveys in northern Morocco have led to the discovery of Criodrilus lacuum Hoffmeister, 1845 and Ophidonais serpentina (Müller, 1774), providing the first evidence of their occurrences in freshwater ecosystems of the country. Further faunistic and hydrobiological studies could lead to the discovery of these species elsewhere in Morocco and North Africa.
Key words: Annelida, Freshwater, New records, Moulouya, Sebou, North Africa
Resumen
Nuevos registros de oligoquetos de agua dulce (Annelida: Oligochaeta: Criodrilidae, Naididae) en Marruecos
La fauna de oligoquetos de agua dulce de Marruecos es aún poco conocida. Recientes estudios de campo en el norte de Marruecos han permitido el descubrimiento de Criodrilus lacuum Hoffmeister, 1845 y Ophidonais serpentina (Müller, 1774), lo que proporciona la primera evidencia de su presencia en los ecosistemas de agua dulce del país. Estudios faunísticos e hidrobiológicos posteriores podrían llevar al descubrimiento de estas especies en otras partes de Marruecos y el norte de África.
Palabras clave: Anélidos, Agua dulce, Nuevos registros, Moulouya, Sebou, Norte de África
Resum
Nous registres d’oligoquets d’aigua dolça (Annelida: Oligochaeta: Criodrilidae, Naididae) del Marroc
La fauna d’oligoquets d’aigua dolça del Marroc encara és poc coneguda. Estudis de camp recents al nord del Marroc han donat lloc al descobriment de Criodrilus lacuum Hoffmeister, 1845 i Ophidonais serpentina (Müller, 1774), proporcionant la primera evidència de la seva presència en ecosistemes d'aigua dolça del país. Estudis faunístics i hidrobiològics posteriors podrien donar lloc al descobriment d'aquestes espècies en altres llocs del Marroc i del nord d'Àfrica.
Paraules clau: Annelida, Aigua dolça, Nous registres, Moulouya, Sebou, Nord d'Àfrica
Freshwater oligochaetes play a crucial role in freshwater ecosystems. They are essential for maintaining ecological balance, serving as an important food source for numerous macroinvertebrates and aquatic vertebrates. Additionally, they significantly contribute to ecosystem functioning through bioturbation of sediments in lakes and streams. Freshwater oligochaetes are also widely recognized as bioindicators of the trophic status and organic matter enrichment in aquatic environments (Timm and Martin 2015).
Globally, the diversity of freshwater oligochaetes is estimated at approximately 1,119 species (including hypogean species), classified into around 193 genera (Martin et al 2008). In Morocco, about 58 species belonging to 30 genera have been documented (Martin and Aït Boughrous 2012).
To enhance knowledge of freshwater oligochaetes in the region, several field expeditions have been conducted in northern Morocco, targeting major geographical barriers. These efforts have led to the discovery of two species recorded for the first time in the country, as reported in this study (fig. 1).
Fig. 1. Geographic distribution of Criodrilus lacuum (triangle) and Ophidonais serpentina (circles) in Morocco, within the Moulouya and Sebou River basins.
Fig. 1. Distribución geográfica de Criodrilus lacuum (triángulo) y Ophidonais serpentina (círculos) en Marruecos, dentro de las cuencas de los ríos Moulouya y Sebou.
As part of hydrobiological monitoring efforts, field surveys have been ongoing since 2014 in northern Morocco, particularly in protected areas and key geographical features such as the Middle Atlas Mountains and the Sebou and Moulouya River basins. To avoid the influence of flooding, sampling was conducted between March and August. Benthic fauna was collected using a Surber sampler (20 x 25 cm surface area, 0.4 mm mesh size). At each site, eight samples were taken to ensure coverage of microhabitat heterogeneity, primarily influenced by substrate type, macrophyte cover, and flow velocity. Samples were preserved in 75% ethanol.
Environmental parameters such as conductivity, pH, and dissolved oxygen were measured in situ using a multiparameter device (WTW, Multi–Line P4). Additional parameters, including nitrate concentrations and biological oxygen demand (BOD5), were analyzed in the laboratory following AFNOR (1997) and Rodier et al (1996) standards. Geographic coordinates were recorded using the WGS84 datum.
Criodrilus lacuum Hoffmeister, 1845 (Crassiclitellata, Criodrilidae) and Ophidonais serpentina (Müller, 1774) (Tubificida, Naididae, Naidinae) are recorded for the first time in Morocco. C. lacuum was discovered in a spring near Guercif, within the Moulouya River basin, while O. serpentina was found at several localities in the same basin (namely Ait Boulmane, Ait Oha Ohaki, Arbalou, and Sebra) as well as at Ain Chkef Spring in the Sebou River basin. In the surveyed areas, both species were typically associated with muddy substrates and aquatic vegetation in shallow, slow-flowing waters. Table 1 presents the number of individuals recorded at each site, along with the corresponding physico-chemical water parameters.
Tabla 1. Sitios de muestreo y sus parámetros hídricos: D, Fechas de muestreo; N, número de individuos encontrados; C, conductividad (µs/cm); DO, oxígeno disuelto (mg/l); DBO5 (mg/l); N, nitrato (mg/l). (Los sitios de muestreo se indican mediante sus coordenadas, datum WGS84).
Criodrilus lacuum exhibits an earthworm-like morphology. Although all Moroccan specimens were immature, the species was readily identified by its distinctive zygolobous prostomium and quadrangular tail with a concave dorsal margin (fig. 2A-2D). When sexually mature, C. lacuum develops a large, extensive clitellum, typically spanning segments 16-47, with spermatophores often present in the intersegmental furrow 13/14. However, no sexually mature individuals were found in this study.
Ophidonais serpentina is a relatively large naidine worm, characterized by a blunt snout and two to three purplish dorsal stripes on the anterior body. Dorsal setae generally begin at segment VI, although one or more needles may be absent (and in some cases, all are missing). When present, only a single needle is found per dorsal bundle. These needles are straight and thick, ending in a slightly bifid or blunt tip (fig. 2E-2G).
Fig. 2. Criodrilus lacuum (A-D) and Ophidonais serpentina (E-G) collected from Morocco: A, general appearance of C. lacuum; B, lateral view of tail showing concave dorsal margin; C-D, anterior dorsal and ventral views; E, general appearance of O. serpentina; F, anterior region of the body; G, dorsal needle from mid-body segment.
Fig. 2. Criodrilus lacuum (A-D) y Ophidonais serpentina (E-G) recolectadas en Marruecos: A, aspecto general de C. lacuum; B, vista lateral de la cola que muestra el margen dorsal cóncavo; C-D, vistas dorsal y ventral anterior; E, aspecto general de O. serpentina; F, región anterior del cuerpo; G, aguja dorsal del segmento medio del cuerpo.
This study adds two new species to the known freshwater oligochaete fauna of Morocco: C. lacuum and O. serpentina. Criodrilus lacuum is a West Palaearctic species widespread throughout Europe (Michalis 1993), where it typically inhabits mud and the root zones of aquatic plants in both fresh and brackish waters. During colder periods, it burrows deeper into sediments (Fischer and Dahm 2017). It has also been reported in North and South America, likely due to accidental introduction (Brown and James 2007). In North Africa, C. lacuum is the sole representative of the family Criodrilidae and was previously known only from Algeria and Tunisia (Martin and Aït Boughrous 2012).
In contrast, O. serpentina is a nearly cosmopolitan species. It usually inhabits freshwater environments rich in aquatic vegetation (Yu et al 2022) but can also adopt a parasitic lifestyle by residing in the mantle cavities of bivalves and crabs (Ardalan et al 2011). Prior to this study, the species had only been reported from Tunisia within North Africa (Martin and Aït Boughrous 2012).
Despite Morocco’s strategic geographic location and the ecological diversity of its freshwater habitats, its oligochaete fauna remains significantly understudied. Further hydrobiological investigations are urgently needed, as they may reveal additional new records and possibly species new to science. This need is heightened by the growing pressures of climate change and increasing aridity, alongside widespread anthropogenic impacts such as water abstraction, agricultural runoff, pollution, and habitat degradation (Yahya et al 2017, Mabrouki et al 2018, Marrone et al 2020, Taybi et al 2019).
Another major concern for Morocco’s freshwater biodiversity is the impact of non-native species. The Moulouya and Sebou River basins are among the principal hotspots of freshwater biological invasions in the country (Taybi et al 2023a), where numerous invasive vertebrate and invertebrate species have become established and are increasing in abundance (Mabrouki et al 2023a, 2023b, Taybi et al 2024, El Caidi et al 2025). Among them is the alien naidid worm Branchiura sowerbyi (Beddard, 1892), now present in both river basins (Taybi et al 2023b). These invasive species pose significant threats to native aquatic biodiversity, as they have the potential to alter existing biotic interactions within benthic communities.
